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A study of the reaction of tetramethyldiborane with sodium in liquid ammonia and the products derived from this reaction

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A study of the reaction of tetramethyldiborane with sodium in liquid ammonia and the products derived from this reaction

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Content A STUDY OF THE REACTION OF TETRAMETHYLDIBORANE WITH SODIUM IN LIQUID AMMONIA AND THE PRODUCTS DERIVED FROM THiS REACTION A D is s e r ta tio n P re s e n te d to th e F a c u lty o f th e D epartm ent o f C hem istry The U n iv e rs ity o f S outhern C a lif o r n i a In P a r t i a l F u lf illm e n t o f th e R equirem ents f o r th e Degree D octor o f P h ilo so p h y by G-eorge W . Cam pbell, J r . Ja n u a ry 1951 UMI Number: DP21748 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI DP21748 Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106 -1346 Ph.D. C '51 Cl 87 This dissertation, written by George W...„CaapbellA „ Jr.,....................... under the guidance of h.%.3.. Faculty Committee on Studies, and approved by all its members, has been presented to and accepted by the Council on Graduate Study and Research, in partial ful fillment of requirements for the degree of D O C TO R OF P H IL O S O P H Y Dean .......... Committee oil Studies Chairman TABLE O P CONTENTS CHAPTER PAGE I . HISTORICAL INTRODUCTION 7 I I . THE BEHAVIOR OF TETRAMETHILDIBORANE TO W A RD SODIUM IN LIQUID AM M ONIA 11 The H ydrogen!c R e a c tio n 12 A pparatus 13 The R e a c tio n o f th e Diammoniate of T etrarae th y ld ib o ra n e w ith Sodium 16 R ate Study A pparatus 16 R e s u lts 18 D isc u ssio n 19 The Non-Hydrogenic R e a c tio n 23 The Non-Hydrogenic R e a c tio n w ith E xcess Sodium 23 A pparatus Zk The Thermal R e a c tio n of th e Non-Hydrogenic R e ac tio n P ro d u c ts 28 Form ula and A n a ly s is 29 The A ttem pts t o P re p a re Na2HB(CH^)2 w ith o u t th e T rim ethylam ine D isplacem ent 31 The Non-Hydrogenic R e ac tio n w ith T etram eth y ld ib o ra n e In Excess 32 An A ttem pt to P re p a re an A d d itio n Compound o f Sodium and T rim eth y lb o ro n . 3 ^ 11 CHAPTER I I I . THE PROPERTIES AND PROBABLE STRUCTURE OF Na2HB(CH3 ) 2 The T reatm ent of N agH B ^H ^^ w ith S ila n e The R e a c tio n of Na2HB(CH^ )2 w ith G h lo ro slla n e A ttem pts to Show th e E x is te n c e of NaB(CH^ )2 The R e a c tio n o f C h lo ro s ila n e w ith th e A lk a li H ydrides The R e ac tio n o f Na2HB(CH^ )2 w ith D iborane The Q u estio n of Sodium B orohydride as a P ro d u ct of th e R e ac tio n of Na2HBlCH^ )2 and Diborane A pparatus The T est of th e A pparatus E x p erim en tal S tu d ie s The B ehavior of Na2HB(CH«j)2 Toward Ammonia The R e a c tio n s of NagHBCCH^Jg w ith T rim ethyiboron The R e a c tio n o f Na2HB(CH^ ) 2 w ith T rira e th y l- boron in M ethyl E th e r The B ehavior o f T rim eth y ib o ro n Toward th e A lk a li H ydrides The R e a c tio n o f Na2HB(CH-j)2 w ith T rim e th y i boron in L iq u id Ammonia PAGE 36 37 37 38 ; 39 40 43 43 46 46 * * 7 48 49 50 51 H i CHAPTER PAGE , ! The R e a c tio n w ith T rim ethyiboron During th e P re p a r a tio n P ro c e ss 52 D isc u ssio n 54 IV. THE NATURE OF THE NON-HYDROGENIC REACTION W H EN SODIUM IS IN EXCESS 62 The M agnetic Study of th e P ro d u c t o f th e Non-Hydrogenic R e ac tio n 62 A p p aratu s 63 Sample P r e p a r a tio n and E x p erim en tal R e s u lts 68 : D isc u ssio n 71 A R e ac tio n S e r ie s A ccounting f o r th e F orm ation o f Na2HB(CH^)2 72 S p e c u la tio n on th e Mechanism o f th e Non-Hydrogenic R e ac tio n 76 The Mechanism o f Ammoniation o f T e tra m e th y ld lb o ra n e 79 V. FUTURE STUDIES CONCERNING NagHBtCH^Jg 83 The P re p a r a tio n o f Na2HB(CH3 ) 2 83 The Non-Hydrogenic R eactio n when T e tra m e th y l- d ib o ra n e i s in Excess 84 The Base P r o p e r ti e s of Na2HB(CH3 )2 85 The H ydride P o t e n t i a l o f Na2HB(CH3 )2 87 The H y p o th e tic a l S ubstance NaBtCH^^ 88 lv CHAPTER PACE The Non-Hydrogenic R e ac tio n of Sodium w ith th e A nalogs of T e tra m e th y ld ib o ra n e 88 VI. SU M M A RY AND CONCLUSIONS 90 BIBLIOGRAPHY 9^ TABLES TABLE X. I I . I I I . IV. V. VI. V II. V III. IX. X. XI. X II. X III. The R e ac tio n o f w ith Sodium in L iq u id Ammonia The R e a c tio n o f an Ammonia S o lu tio n o f T e tra m e th y ld ib o ra n e w ith Sodium Amraonolysis o f th e R e ac tio n P ro d u ct o f and Sodium, F ollow ing th e Trlm ethylam ine D isplacem ent A n a ly sis of Na2HB(0H-^)2 An A ttem pt to P re p a re Ka2HB(GH^ )2 w ith o u t Trim ethylam lne D isplacem ent An A ttem pt to P re p a re Na2HB(GH^)2 usin g E xcess (GRj) The R e a c tio n o f NagHBCCH^^ w ith C h lo ro s lla n e The R e a c tio n o f Na2HB(CH^)2 w ith D iborane The F orm ation o f an Ammoniate o f Na2HB(GH-^)2 The R e a c tio n o f T rim eth y ib o ro n w ith Na2HB(GH^)2 in M ethyl E th e r The R e a c tio n o f Na2HB(GH^)2 w ith T rim ethyiboron In L iq u id Ammonia The A n a ly sis o f th e N o n -V o la tile P roduct o f th e R e a c tio n of T e tra m e th y ld ib o ra n e and T rim e th y l boron w ith Sodium The M agnetic Study o f th e P ro d u c t of th e Non- H ydrogenic R e a c tio n FIG-URES i FIGURE PAGE1 i 1 . A p p aratu s f o r th e Study o f Sodium R e a c tio n s in L iq u id Ammonia Ik 2. R ate Study A pparatus 17 3. The R e a c tio n o f an Ammonia S o lu tio n o f | T etram eth y ld ib o ra n e w ith Sodium 22 ■ A pparatus f o r th e P re p a r a tio n o f 26 ! 5. A pparatus f o r th e A d d itio n o f A ^ G l^ to th e Na2HB( CH^)2-B2H^ R e a c tio n P ro d u c t 6 . A pparatus f o r th e P r e p a r a tio n o f th e Non-Hydrogenic R e ac tio n P ro d u c t f o r M agnetic M easurements 6^ 7. A pparatus f o r M agnetic Measurements 67 CHAPTER I HISTORICAL INTRODUCTION The developm ent o f th e ch em istry o f th e boron h y d rid e s i s r e l a t i v e l y r e c e n t. The f i r s t r e a l c o n tr ib u tio n r e s u lt e d from th e work o f S tock and h is co -w o rk e rs, 1 which began o n ly about fo u r decades ago. Hence, a lth o u g h much has been accom plished in t h i s p e r i o d ,'' th e re a re s t i l l many p h ases o f t h i s ch e m istry which have n o t been e x p lo re d . T his d i s s e r t a t i o n i s dev o ted to th e very i n t e r e s t i n g b e h a v io r of te tra m e th y ld ib o ra n e w ith sodium i n l i q u i d ammonia. No stu d y of t h i s p a r t i c u l a r system has been re p o r te d in th e l i t e r a t u r e , a lth o u g h th e r e a c tio n s o f sodium w ith o th e r boron h y d rid e compounds have been p u b lis h e d and th u s a b a s i s f o r com parison has been e s ta b li s h e d . The r e a c tio n o f th e diam m oniate o f d ib o ran e w ith sodium i n l i q u i d ammonia was s tu d ie d by S c h le s in g e r and B u rg ,3 and found to produce one e q u iv a le n t o f hydrogen r a p i d l y . A slow secondary r e a c tio n produced a sm a ll a d d i t i o n a l amount o f hydrogen. On th e b a s i s o f t h i s and o th e r 1 A. S to c k , H ydrides o f Boron and S ilic o n ( I th a c a , New York: C o rn e ll U n iv e rs ity P re s s , 1933)* 2 H. I . S c h le s in g e r and A. B. Burg, Chem. Rev. 21» 1 (1 9 ^ 2 ). 3 H. I . S c h le s in g e r and A. B. Burg, J . Am. Chem. Soc. 6 0 , 290 (1 9 3 8 ). 8 c o n firm a to ry evidence th e diammoniate wae a s sig n e d th e fo rm u la JbH^NH^H^ j . The p rim ary r e a c t i o n w ith sodium wae th e n a t t r i b u t e d to th e ammonium io n , w h ile th e secon d ary r e a c tio n was p o s tu la te d to be due t o an e q u ilib riu m Involving) BH^NH^ o r i t s a c id - r e a c t in g form NH^ JbH ^ N ^ ]. By an alo g y , th e form ula of th e diam m oniate o f te tr a m e th y l d ib o ra n e m ight be ex p ected to be NH^ {(GH^^BHIfl^BHCCH^^], w ith s im ila r p r o p e r t i e s tow ard an ammonia s o lu tio n o f sodium. I n c o n t r a s t t o th e r e a c tio n o f th e diam m oniate of d ib o ra n e w ith sodium, I t was observed by Dr. A. B. Burg^ t h a t when d ib o ra n e i s b ubbled th ro u g h a s o lu tio n o f sodium in ammonia, l e s s th an one e q u iv a le n t o f hydrogen I s p ro duced. T his su g g e ste d t h a t th e re m ight be a com peting non- h y d ro g en ic r e a c t i o n betw een sodium and d ib o ra n e . S tock and Pohland-5 r e p o r te d e a r l i e r t h a t a sodium amalgam a b so r bed d ib o ra n e , and proposed t h a t th e p ro d u c t have th e fo rm u la Na2B2H^, where th e an io n Jb2H ^ w o u ld be i e o e l e c t - r o n ic to e th a n e . More r e c e n t l y , how ever, i t has been shown t h a t t h i s r e a c t i o n produced sodium b o ro h y d rid e I n s te a d o f Na2B2H ^.^ Hence th e e x is te n c e o f a compound h aving t h i s ^ A. B. Burg, P r iv a te Communication. 5 A. S tock and E. P ohland, Ber 59B. 2210 (1923). 6 J . H. K asper, L. V. McCarty, and A. S. Newkirk, J . Am. Chem. Soc. 2±> 2588 (19^9). 9 fo rm u la has n o t been d e m o n stra te d . However, th e e x is te n c e ! o f some o f th e m ethyl d e r i v a t i v e s o f ap p e a rs to be J » l i k e l y on th e b a s i s o f th e s tu d ie s r e p o r te d in t h i s i d i s s e r t a t i o n . ! F u rth e r s tu d ie s which a r e r e l a t e d to t h i s work have been r e p o r te d by K rause and G ro sse .? These w orkers r e p o r t | i t h a t trip h e n y lb o ro n , and o th e r t r l a r y l boron compounds j form a d d itio n compounds w ith sodium which may be g iv e n th e j g e n e ra liz e d fo rm u la NaB(Ar)^. These compounds a re s o lu b le ■ i in d i e t h y l e t h e r , and a re h ig h ly c o lo re d . A ccording to th e ; i i a s s ig n e d fo rm u la s, th e compounds sh o u ld c o n ta in an odd number o f e l e c t r o n s and hence sh o u ld show param agnetism . S tu d ie s in p ro g re s s in t h i s la b o r a to r y under th e d i r e c t i o n o f Dr. W . K. W ilm arth have v e r i f i e d th e s to ic h io m e try of th e s e compounds, b u t th e m agnetic p r o p e r t i e s a re s t i l l u n c e r ta in . The r e a c t i o n o f trip h e n y lb o ro n w ith sodium has a ls o Q been r e p o r te d by Bent and Dorfman, who r e p o r te d th e sodium r s a l t NaBtGfcH^)^ to be d e c id e d ly y ello w . These w orkers a ls o ' r e p o r te d t h a t tr i- a lp h a - n a p h th y lb o r o n added two m oles of sodium to form th e compound which was l i g h t 7 E. K rause and A. v. G roese, Die Ohemle d e r M e ta ll- O rganlschen V erblndungen. Gbr. B o rn tra e g e r, B e r lin , 1937» ! p. 210. 8 H. E. Bent and M. Dorfman, J . Am. Chem. Soc. 57, 1259 ( 1935)• 10 y ello w In c o lo r . T rim eth y ib o ro n i s found to r e a c t only slo w ly w ith sodium in l i q u i d ammonia, w ith th e p ro d u c tio n o f h y d ro g en .^ No a d d itio n compound o f sodium and trim e th y ib o ro n has been r e p o r te d . I t i s r e a d i l y seen from th e l i t e r a t u r e t h a t th e s tu d i e s o f th e r e a c tio n s o f sodium w ith th e v a rio u s r e l a t e d boron compounds a re n o t com plete, and t h a t th e r o l e o f sodium in th e s e r e a c tio n s i s n o t y e t c l e a r . I t i s hoped t h a t th e r e s u l t s o f th e r e s e a r c h r e p o r te d in t h i s p ap e r w i l l a id in u n d e rsta n d in g th e s e r e a c tio n s and in c l a r i f y i n g th e t o t a l p i c t u r e . 9' a. B . Burg, P r iv a te Communication CHAPTER I I THE BEHAVIOR OF TETRAMETHYLDIBORANE TOW ARD SODIUM IN LIQUID AM M ONIA T e tra m e th y ld ib o ra n e r e a c t s w ith sodium In l i q u i d ammonia in a t l e a s t two e n t i r e l y d i f f e r e n t ways. One o f th e r e a c tio n s w i l l be term ed "h y d ro g e n ic w, s in c e th e r e a c t i o n r a p id ly pro d u ces hydrogen, w h ile th e o th e r r e a c tio n w i l l be d e s ig n a te d sim ply a s w n o n -h y d ro g e n icH. I f te trs m e th y ld ib o r a n e and ammonia a re b ro u g h t t o g e th e r a t a te m p e ra tu re n e a r th e f r e e z in g p o in t o f ammonia (-77-7°) allow ed to r e a c t f o r ab o u t two h o u rs o r lo n g e r, th e am m oniation p ro d u c t i s c l e a r l y p r o to n lc in i t s a c tio n tow ard sodium, f o r th e a d d itio n o f sodium to th e l i q u i d ammonia s o lu t io n r a p id ly pro d u ces one e q u iv a le n t of hydrogen. On th e o th e r hand, I f te tra m e th y ld ib o ra n e I s added to a s o lu tio n o f sodium in l i q u i d ammonia, n ea r to i t s f r e e z ing p o in t, no hydrogen i s produced even on extended sta n d in g . A c o lo r change a ls o accom panies t h i s l a t t e r r e a c t i o n , f o r i f sodium i s i n excess th e s o lu t io n a c q u ire s an In te n s e b lu e -g re e n c o lo r which tu r n s y ello w as th e system i s slo w ly fro z e n (rem oving th e sodium from th e s o l u t i o n ) . I f t e t r a m e th y ld ib o ran e i s in ex cess th e l i q u i d s o lu t io n becomes y ello w a t -77°C . The s to ic h io m e try o f t h i s r e a c t i o n in v o lv e s one mole of te tra m e th y ld ib o ra n e and two m oles of 12 i — - - -- - — ............ - ~ - - - - - ;sodium. The age o f th e s o lu tio n a p p a re n tly does n o t a f f e c t th e c o lo r when sodium i s i n e x c e ss , b u t when te tr a m e th y l- ' d ib o ra n e i s in ex cess th e y ello w c o lo r fa d e s to c o l o r le s s a t a r a t e ro u g h ly in p r o p o r tio n to th e ex cess of r e a c t a n t , i The n a tu re o f th e n o n -hydrogenic r e a c t i o n h as been f u r t h e r ex p lo re d by rem oving th e s o lv e n t ammonia a s com- , ’p l e t e l y as p o s s i b le , to a v o id am m onolysis, and e x t r a c tin g th e r e s id u e in vacuo u sin g m ethyl e th e r as a s o lv e n t. The e x tr a c te d p ro d u c t was th e n warmed to room te m p e ra tu re w ith i •th e rem oval o f a l l v o l a t i l e com ponents. The r e s id u e th u s : i !o b ta in e d had th e r e p ro d u c ib le e m p iric a l form ula NagHBtCH^Jg, p ro v id e d sodium was in ex c ess in th e i n i t i a l r e a c t i o n m ix tu re . When te tra m e th y ld ib o ra n e was in excess in th e i n i t i a l r e a c tio n m ix tu re , th e a n a ly s is o f th e ex t r a c t e d p ro d u c t was n o t re p ro d u c ib le in s u c c e s s iv e e x p e ri m ents, in d ic a t in g an i n t e r f e r i n g s id e r e a c t i o n . The Hydrogenlc Reaction The r e p o r t by S c h le s in g e r and Burg,^- t h a t th e diammo n ia te o f d ib o ra n e r e a c te d w ith sodium i n l i q u i d ammonia w ith th e r a p id p ro d u c tio n o f one e q u iv a le n t o f hydrogen, fo llo w e d by a slow seco n d ary r e a c t i o n w hich p ro d u ces a osm all a d d i tio n a l amount o f hydrogen, was v e r i f i e d i n t h i s x H. I . S c h le s in g e r and A. B. Burg, J . Am. Chem. Soc. 60, 290 (1938). 13 la b o r a to r y . The new d a ta a re given in Table I . T able I The R e a c tio n of B2H^*2 KH^ w ith Sodium in L iq u id Ammonia E x p 't 1 E x p 't 2 V ol. o f B2H6* 9.6 1 cc 9-73cc Equiv. Vol. o f Na l*K3cc 22.?cc R e a c tio n tim e 30 20 h r s k> 5 min 2 .5 b r s Vol. o f H2 ev o lv ed 5*55 ec 5»92cc 5*10cc 5 * ^lcc E qulve. Hg/mole BgH^ 1 .1 5 1 .2 3 1.05 l . l l c c * A ll G ases a re e x p re sse d in term s o f volume a t s ta n d a rd c o n d itio n s . ~ n The sodium i s e x p re s se d i n term s o f th e volume i t would occupy as a gas a t s ta n d a rd c o n d itio n s . A p p a ra tu s. The a p p a ra tu s used in t h i s work was d e sig n e d a f t e r t h a t used by S c h le s in g e r and Burg^ and i s shown in F ig u re s 1 A to 1 0. The te c h n iq u e in v o lv e d was to m elt sodium in a vacuum (F ig u re 1 B) by h e a tin g in an o i l b a th , and th e n to f o rc e th e l i q u i d m e tal (B) th ro u g h a c a p i l l a r y in to a sm a ll b u lb C. Then, by s e a lin g o f f th e b u lb and d e te rm in in g th e In c re a s e in w eig h t o f th e tu b e and b u lb a f t e r d is s o lv in g away th e e x c e ss sodium , th e w eight of sodium w ith in th e b u lb c o u ld be d eterm in ed q u ite a c c u r a te ly , 2 I b i d . . 60. 290. ■APPARATUS F O R T H E STU D Y O F SODIUM R E A C T IO N S IN LIQUID AMMONIA / \ FIGURE 1A B f B’ D FIGURE IB FIGURE 1C 15 The sodium was th e n in tro d u c e d i n t o th e system ( p r e - , i v io u s ly baked out in vacuo) th ro u g h th e opened tu b e A ; (F ig u re 1 A ), by means o f th e b u lb c ru s h e r (F ig u re 1 G) as a stream o f dry hydrogen was p a s se d th ro u g h th e system and o u t th ro u g h tube A. S ince i t was u n lik e ly t h a t m oist • a i r would d i f f u s e upward a g a in s t a stream o f hydrogen, th e I sodium b u lb would be cru sh ed w ith o u t a c c e s s o f m o is tu re or oxygen and dropped th ro u g h th e tu b e G in to th e r e a c tio n chamber B (F ig u re 1 A). Then, in o r d e r to r e e s t a b l i s h a vacuum, th e rem ain d er of tu b e A was drawn out to a f in e c a p i l l a r y w h ile hydrogen was p a s s in g th ro u g h , and th e n s e a le d im m ediately on s h u ttin g o f f th e hydrogen. The b u lb c ru s h e r (F ig u re 1 C) c o n s is te d of a sm all iro n a n v il p l a t e G, w hich was ta p p e d to re c e iv e a th re a d e d 1 /8 in c h w elding rod A. In th e c e n te r o f p l a t e G was a h o le a p p ro x im a tely 2mm in d ia m e te r. There were two copper g u id e s (B and B1) s o ld e re d to th e ro d A, th ro u g h which a 1 /8 in c h rod (D) c o u ld p a s s . By w rapping a ru b b e r band about th e h a n d le o f th e b u lb c r u s h e r , th e rod D co u ld be h e ld in p la c e . The s e a le d c a p i l l a r y neck o f a sodium b u lb (D, F ig u re I B ) was th e n i n s e r t e d in th e h o le in th e end p l a t e C, and h e ld in p la c e by moving th e rod D in to p o s i t i o n . T his a p p a ra tu s was th e n i n s e r t e d in to tu b e A (F ig u re 1 A) and by ta p p in g on th e end of rod D (F ig u re 1 C) th e sodium b u lb was c ru sh e d . As th e ro d D was p u lle d o u t, 16 th e sodium b u lb r e a d i l y f e l l o u t of p la c e in to th e r e a c tio n t f l a s k . The R e a c tio n o f th e Diammoniate of ‘ T etram eth y ld ib o ran e w ith Sodium. A p r e lim in a ry stu d y o f th e r e a c t i o n o f t e t r a m e th y ld ib o ran e w ith sodium was made u sin g th e te c h n iq u e d e s c rib e d above. The r e s u l t s o b ta in e d in d ic a te d t h a t th e r e a c tio n p ro ceed ed in a manner s im i l a r to th e d ib o ra n e r e a c t i o n , b u t a t a slow er r a t e . ^ In o rd e r to e x p lo re th e .p o s s i b i l i t y o f a m easurably slow r e a c t i o n , an a p p a ra tu s was developed whereby th e te m p e ra tu re , i n i t i a l c o n c e n tra t i o n s , r e a c tio n tim e and evolved hydrogen co u ld be m easured w ith good a c c u ra c y . R ate Study A p p a ra tu s. The a p p a ra tu s d e sig n e d to m easure th e r a t e o f th e r e a c tio n o f sodium w ith te tr a m e th y l d ib o ra n e i s shown i n F ig u re 2. An a c c u r a te ly w eighed sample o f sodium was in tro d u c e d in to chamber B, by th e b u lb c r u s h e r method; th e n th e system was e v a c u a te d and th e l i q u i d ammonia s o lu t io n o f te tra m e th y ld ib o ra n e was formed in D a t - 77°C by d i s t i l l a t i o n o f th e m a te r ia l s from th e vacuum l i n e th ro u g h sto p c o ck F. A ll o f th e ammonia used in th e ex perim ent came from th e m easured sample In th e c a l i b r a t e d tu b e 0. Next a s u i t a b l e p o r tio n o f th e rem ain in g ammonia was d i s t i l l e d o ver in to B to d is s o lv e th e J See E xperim ent 1, T able I I , p . 2 0 . RATE STUDY APPARATUS put"? ■ -to Topler Pump \ i FIGURE 2 18 sodium. D uring t h i s p r o c e s s , th e c a p i l l a r y tu b e was cooled a t G > by l i q u i d n itr o g e n , In o rd e r to av o id prem atu re de l i v e r y o f sodium in to D. F in a lly t h i s b a r r i e r was allow ed to m e lt, and ex c e ss p r e s s u r e o f ammonia was a p p lie d from S to fo rc e th e sodium s o lu t io n in to th e r e a c tio n chamber D. T his f i n a l p o r tio n o f th e ammonia se rv e d a ls o to wash th e l a s t o f th e sodium th ro u g h th e c a p i l l a r y system . As soon as th e sodium and th e l a s t o f th e ammonia had been d e liv e r e d in to D (z e ro tim e ) , th e c a p i l l a r y tu b e was s e a le d o f f a t E. P ro p e r m ixing was ac h iev e d by a sh o rt-sw e e p sh a k in g . The e x te n t o f a r e a c t i o n a t s u c c e s s iv e tim e i n t e r v a l s was th e n d eterm in ed by m easuring th e hydrogen d e l iv e r e d in to th e Tflpler pump system by m om entarily opening sto p c o ck F. A l i t t l e ammonia, which swept a l l th e hydrogen th ro u g h F, was tra p p e d b e f o re th e pump and r e tu r n e d soon a fte rw a rd to th e r e a c tio n chamber. R e s u l t s . The r e s u l t s o b ta in e d by means o f th e r a t e m easurem ents d em o n strate d t h a t th e r e were two com peting r e a c tio n s w hich occur when th e s o lu tio n of sodium i s added to th e ammonia s o lu tio n o f te tra m e th y ld ib o r a n e . I f th e te tra m e th y ld ib o r a n e s o l u t i o n was allo w ed to s ta n d f o r two h o u rs o r lo n g e r a t - 7? °0 » th e r e a c t i o n w ith sodium proceeded i w ith th e e x p e c te d e v o lu tio n o f hydrogen, b u t a t a r a t e w hich was to o f a s t to be m easured by th e a p p a ra tu s d e s c rib e d above. I f , however, th e te tra m e th y ld ib o ra n e s o lu t io n was 19 n o t more th a n f i f t e e n m in u tes o ld , th e hydrogen was slow ly and only p a r t i a l l y r e le a s e d , w h ile an Im portant s id e - r e a c t i o n to o k p la c e betw een th e sodium and th e te tr a m e th y l- ; , i d ib o ra n e . The d e t a i l e d r e s u l t s a re shown in T able I I , p ag es' 20 and 21, and F ig u re 3, page 22. E xperim ent 1 was made u sin g th e a p p a ra tu s o f F ig u re 1, w h ile th e o th e r s u t i l i z e d th e a p p a ra tu s o f F ig u re 2. D is c u s s io n . In view o f ex p erim en ts 1 and 5 of T able I I , i t a p p e ars th a t th e h y d ro g en -p ro d u cin g r e a c tio n in v o lv e s th e diam m oniate o f te tra m e th y ld ib o r a n e , which would be f o r - : m u lated as th e ammonium s a l t , analogous to th e diam m oniate o f d ib o r a n e .^ The r e a c t i o n w ith sodium would th e n be w r i tte n as fo llo w s: 2NH4 [(GH^HBNHgBmOH^)^] * 2Na — » 2Na [(CH3 ) 2HBHH2BH( CH3 ) 2NH3 + Hg . The r e s u l t s of Table I I a ls o in d ic a te t h a t th e fo rm a tio n of th e ammonium s a l t i s slow and t h a t s u f f i c i e n t tim e must be p e r m itte d f o r th iB r e a c t i o n to ta k e p la c e . O th erw ise , th e non -h y d ro g en ic r e a c tio n o c c u rs between th e sodium and th e t e tra m e th y ld lb o ra n e . ^ S c h le s in g e r and B urg, l o c . c i t . 20 T able I I The R e ac tio n o f an Ammonia S o lu tio n o f T e tra m e th y ld ib o ra n e w ith Sodium Experim ent 1 V ol. o f (GH3 )4 B2H2 1 1 . 0?ec E qulv. Vol. o f Na 3 4 .3cc Age o f (CH3 )^B2H2 S o l. 90 mln a t -78°C Time (mln) 10 20 35 78 138 1260 2460 Vol. o f H2 ev o lv ed ( c c ) 2 .2 2 3 -0 1 3-41 4 .2 8 4 .6 6 5 .5 0 6.23 E q u lv s . H„/mole (c h 3 )4b2h 2 o.4o 0 .5 4 0 .6 2 0 .7 7 0 .8 4 0.99 1 .13 E xperim ent 2 Vol. o f (0H3 )^B2H2 1 2. 5 8 c c E qulv. Vol. o f Na I ? . l e e Age o f (CH3 )j^B2H2 S o l. 10 mln a t -77°G Time (m ln) 3 5 45 V ol. o f H2 ev o lv ed (c e ) 1 .1 0 1 .2 4 1 .2 4 S o lu tio n E q u lv s. H2/m ole (CH^)^B2fi2 Vol. o f (OH^J^BgHg E qulv. Vol. o f Na Age o f (CH^)^B2H2 Sol Time (m ln) 3^ 0.1 8 0 .2 0 0.20 E xperim ent 3 lG .21 cc became c o l o r le s s 8 1 8 .3cc 10 mln a t - 77°C 15 25 70 Vol. o f H2 ev o lv ed (c c ) 0 .5 0 0 .5 8 0 .6 8 0.75 0.89 S o lu tio n became c o l o r le s s 21 ,Equlvs.BL>/mole (c h 3 )^b2h2 0 .1 0 0 .1 1 0.13 0 .1 5 0.17 Experim ent 4 Vol. o f {GE^)^B2E2 8. 94cc E qulv. Vol. of Na 3 6 . 2cc Age o f (GE3 )^B2E2 S o l. 15 mln a t; -77°G Time (mln) 9 16 31 93 168 1530 Vol. o f H2 ev o lv ed (e c ) 1 .9 1 2 .0 1 2.25 2 .3 0 2.45 2 .5 1 E q u lv s. H«/mole ( 0H^) lf^2. 2 ® 0 .4 5 0.50 0.51 0.55 0 .5 6 E xperim ent 5 Vol. o f (GH3 )/j32H2 1 0 .5 8 ec E qulv. Vol. o f Na 2 1 . 3 ec Age o f (CH3 ) ^ 2 H2 So1* 2 h r s a t -770c Time (mln) 1 3/k 6 3 /4 12 86 101 V ol. o f H2 ev o lv ed (cc) **.68 4 .8 5 4.85 5 .0 1 5.03 E q u lv s. H2/m ole (GEj )^B2E2 0.89 0 .9 2 0.92 0.95 0.95 EQUIVALENTS O F H PRODUCED PE R M O L E O F (C H ,),B 7H THE REACTION OF AN AMMONIA SOLUTION OF T ETRAM ETH YLDIBO RANE WITH SODIUM © c» o C \ © 4 * . © to TIME (MINUTES) FIGURE 3 23 ! The Non-Hvdrogenlc R e a c tio n The non-hydrogenIc r e a c tio n r e q u ir e s more th a n 1 .8 m oles o f sodium p e r mole o f te tra m e th y ld ib o ra n e , a c c o rd in g to E xperim ent 3 , T able I I . F u rth e r stu d y has shown t h a t when th e r a t i o : o f sodium to te tra m e th y ld ib o ra n e i s l e s s th a n two m oles to one, th e s o lu t io n becomes y ello w , i n d i c a tin g t h a t th e sodium h as r e a c te d c o m p le te ly . I f , however, sodium i s p r e s e n t in ex c ess o f th e tw o -to -o n e r a t i o , th e 'b lu e c o lo r o f sodium i n ammonia i s r e t a i n e d , and hence th e s o l u t i o n a p p e a rs to be b lu e -g re e n to g re e n , depending upon th e amount o f ex c ess sodium . When th e s e g reen s o lu t io n s a re slo w ly fro z e n th e c o lo r becomes y e llo w , as th e sodium s e p a r a te s from th e s o lv e n t. The age o f th e s o l u t i o n , when sodium i s in e x c e ss , a p p a re n tly does n o t a f f e c t th e c o lo r o f th e s o l u t i o n , w hile i f te tra m e th y ld ib o ra n e i s in ex cess th e y ello w c o lo r fa d e s to c o l o r le s s a t a r a t e depending upon th e amount o f th e e x c e s s . Due to th e a p p a re n t secondary r e a c tio n in th e l a t t e r c a s e , most o f th e s tu d i e s have been made w ith s o lu t i o n s c o n ta in in g an ex cess o f sodium. The Non-Hydrogenlc R e a c tio n w ith E xcess Sodium. I n i t i a l l y th e n o n -h y d ro g en ic r e a c tio n was th o u g h t to be a sim p le a d d itio n r e a c tio n o f sodium to te tra m e th y ld ib o ra n e . Due to th e in te n s e y e llo w c o lo r o f th e r e a c tio n p ro d u c t, i t wae th o u g h t t h a t i t m ight w e ll be a s a l t w ith th e fo rm u la NaBH(0H^)2 » th e an io n o f which would c o n ta in an odd e l e c t ro n and would hence be a f r e e r a d i c a l io n . T his would be analogous to th e s a l t s r e p o r te d by K rause and G rossed and by Bent and Dorfman^ who worked w ith th e sodium a d d itio n compounds o f th e t r i a r y l b o r o n compounds. The s a l t NaBtC^H^}^ i s y e llo w , and In d i e t h y l e t h e r s o lu tio n r e sem bles th e y ello w ammonia s o lu tio n o f th e r e a c t i o n p ro d u ct o f sodium and te tra m e th y ld ib o r a n e . S in ce th e sodlum - t r i a r y l boron compounds a r e s o lu b le i n d i e t h y l e t h e r , i t was b e lie v e d t h a t such a s o lv e n t would be u s e f u l i n sep a r a t i n g th e r e a c t i o n p ro d u c t o f sodium and te tr a m e th y l d ib o ra n e from th e e x c ess sodium . D im ethyl e t h e r was used a s a s o lv e n t in s te a d o f d i e t h y l e t h e r , fcuwever, due to i t s g r e a t e r s o lv e n t e f f e c t . A p p a ra tu s. The s e p a r a tio n p ro c e s s u s in g d im e th y l e th e r as th e s o lv e n t was accom plished by means o f th e a p p a ra tu s shown in F ig u re T his a p p a ra tu s p e rm its th e s o lv e n t to be condensed i n th e r e a c t i o n tu b e , th e s o lu tio n th u s form ed to be f i l t e r e d , and th e s o lv e n t th e n t o be d i s t i l l e d b ack to th e r e a c t i o n tu b e f o r re p e a te d e x t r a c t i o n In u sin g th e a p p a ra tu s o f F ig u re ty, th e system was 5 K rause and G ro sse, l o c . c i t . 6 H. E. Bent and M. Dorfman, J . Am. Chem. Soc. 57. 1259 (1935). 25 vacuum flam ed and f i l l e d w ith dry hydrogen. An a c c u r a te ly i ' w eighed sample o f p ure sodium was In tro d u c e d In to A by th e ! 'm ethod o f S c h le s in g e r and B u rg .7 The system was e v a c u a te d 1 a g a in , and d ry ammonia was condensed i n A to form a sodium ! s o lu t io n . The s o lu tio n was fro z e n by l i q u i d n itr o g e n , and ja m easured q u a n tity o f te tra m e th y ld ib o ra n e was condensed above I t . On warming to -77°C , th e s o lu t io n m e lte d , and tw ith shaking th e r e a c tio n o c c u rre d w ith o u t th e e v o lu tio n o f 1 hydrogen. The ammonia was th e n e v a p o ra te d away. The r e s id u e was next t r e a t e d w ith trim e th y la m in e , ■ w hich was condensed in sm a ll p o r tio n s i n A by means o f a d ry i c e - e t h e r b a th ( t o a v o id th e co n d e n sa tio n o f m ercury a t low er te m p e r a tu re ) . The te m p e ra tu re of t h i s f i r s t p o r tio n was m a in ta in e d a t -78°C f o r a minimum o f one h o u r, and th e trim e th y la m in e was th e n e v a p o ra te d away. T his p ro c e s s was re p e a te d w ith f r e s h p o r tio n s o f trim e th y la m in e a t s u c c e s s iv e ly h ig h e r te m p e ra tu re s , f i n a l l y re a c h in g -50°C w ith th e f o u r th p o r tio n . The p ro c e s s was th e n r e p e a te d a t t h i s te m p e ra tu re u n t i l a v ap o r te n s io n m easure ment showed th e re c o v e re d amine to be f r e e o f ammonia. The p ro d u c t co u ld th e n be d is s o lv e d i n d im e th y l e th e r and th e s o lu t io n f i l t e r e d th ro u g h th e s i n t e r e d g la s s f i l t e r C, le a v in g th e ex cess sodium b e h in d . I t has been found 7 Supra. ♦ p. 13. A P P A R A T U S FO R T H E P R E P A R A T I O N OF Na2itTB(CH3)2 FIGURE 4 27 d e s i r a b l e , how ever, t o warm th e r e s id u e from th e tr i m e t h y l - , amine d isp la c e m e n t p ro c e s s t o room te m p e ra tu re , removing th e hydrogen and o th e r v o l a t i l e p ro d u c ts p r i o r to th e e x t r a c t i o n . The s ta b le n o n - v o la ti le r e s id u e was th e n d is s o lv e d in a p p ro x im a te ly 3 cc o f l i q u i d d im e th y l e t h e r and th e s o lu t io n was p o u red th ro u g h th e f i l t e r . The e th e r was now d i s t i l l e d back in t o A and th e e x t r a c t i o n was r e p e a te d as many tim es a s seemed u s e f u l. F in a ll y th e e t h e r s o lu t io n was c o l l e c t e d i n th e tu b e B w hich was r e moved from th e f i l t e r system by s e a lin g o f f a t D. T his i tu b e B was th e n a tta c h e d to th e vacuum a p p a ra tu s a t E f o r f u r t h e r tr e a tm e n t of th e e x t r a c t . In g e n e r a l, t h i s a p p a ra tu s has proved to be v ery s a t i s f a c t o r y in p r a c t i c e . However, th e e x t r a c t i o n p ro c e s s has been a r e p e a te d cause o f d i f f i c u l t y due to th e n a tu re o f th e s o lu t io n . The s o lv a te d p ro d u c t in t h i s p ro c e s s was g e l a ti n o u s , re se m b lin g aluminum h y d ro x id e , and hence ten d ed t o c lo g th e f i l t e r . The f i l t r a t i o n was somewhat more r a p id when a r e l a t i v e l y la r g e volume of d im e th y l e t h e r was u sed , b u t th e a p p a ra tu s l i m i t s th e volume o f s o lv e n t to a maxi mum o f ap p ro x im a tely 3 ce. Thus th e e x t r a c t i o n m ight be q u ite s u c c e s s f u l In one e x p e rim e n t, w h ile in th e n e x t th e f i l t r a t i o n p ro c e s s m ight prove im p o s s ib le . In t h i s r e s p e c t, th e method o f c o n d e n sa tio n of th e s o lv e n t was a ls o im p o rta n t, f o r i f th e e t h e r was condensed by means o f l i q u i d n itr o g e n , 28 f i n e l y d iv id e d m ercury from th e vacuum l i n e condensed as 'w e ll. The m ercury th e n clogged th e f i l t e r q u ite th o ro u g h ly , p r e v e n tin g th e e x t r a c tio n . The Thermal R e a c tio n .o f th e Non-Hydrogenlc R e ac tio n P ro d u c ts . U sing th e a p p a ra tu s and p ro c e d u re d e s c r ib e d above, th e n o n -h y d ro g en ic r e a c tio n of te tra m e th y ld ib o ra n e ;and sodium was s tu d ie d . A lthough th e trim e th y la m in e d i s placem ent p a r t i a l l y s t a b i l i z e s th e r e a c t i o n p ro d u c t a g a in s t ;ammonolysis up to - 50°G, one mole o f ammonia p e r mole o f •te tra m e th y ld ib o ra n e i s s t i l l r e t a i n e d . On warming th e r e s id u e from th e d isp la c e m e n t p ro c e s s to room te m p e ra tu re , one mole o f hydrogen, one mole o f am ln o -d im eth y l-b o ro n (GH^)^BNHg and one mole o f trim e th y la m in e a re ev o lv ed p e r mole o f te tra m e th y ld ib o r a n e . The n o n - v o l a t i l e s o l i d p ro d u c t rem ains in th e r e a c t i o n tu b e . The d e t a i l e d r e s u l t s a r e g iv e n in T able I I I . 29 T able I I I Ammonolysls o f th e R e a c tio n P ro d u c t o f (CH3 )^B2H2 and Sodium, fo llo w in g T rim ethylam ine D isplacem ent E xperim ent 1 2 3 ^ W eight of Na 2*Klmg 36.3mg 4-0.9mg 6 6 . 3mg V ol. o f 6 .5 0 c c 8 .5 8 cc 8 .1 5 cc l*k 06cc V ol. o f H2 evolved in N H -j S o l. O.Occ O.Occ O.Occ O.Occ A f te r (CHo )^N D isplacem ent V ol. o f H2 evolved 6 .5 0 c c 8 .0 5 cc 7*57cc 1 2 .6 lc c ;v o i. o f ( ch3 )2bnh2 e v o lv ed 6 .2 3 c c not d eterm in ed Vol. o f (CH^JoN ev o lv ed a t room temp. b u t r e ta in e d a t - 50 oC 5»92ce not d eterm in ed Form ula and A n a ly s is . The f i n a l p ro d u c t o b ta in e d from th e r e a c tio n o f te tra m e th y ld ib o ra n e and sodium, fo llo w e d by th e d isp la c e m e n t p r o c e s s , th e ammonolysls a t room tem pera t u r e and th e e x t r a c t i o n p r o c e s s , i s a m a te r ia l h av in g th e e m p iric a l fo rm u la Na2HB(CH^)2 . T his su b sta n c e i s s ta b le and n o n - v o l a t i l e , up to 90°C in vacuo. The fo rm u la was d eterm in ed by h y d r o ly tic a n a l y s i s , p ro d u cin g hydrogen and d im e th y l b o r ic a c id , w hich were m easured a s g a s e s . The sodium was d eterm in ed g r a v im e tr ic a lly a s sodium s u l f a t e . The a c id h y d r o ly s is o f Na2HB(CH3 )2 fo llo w s th e e q u a tio n Na2 HB(CH3 ) 2 * H2 0 + 2HC1 » 2NaGl + (C ^ g B O H * 2H2 . The r e s u l t s o f s e v e r a l such a n a ly s e s a r e g iv e n i n T able IV. 30 E xperim ent E qulv. Vol. o f Na (c c ) 1 6 .0 T able IV A n a ly sis o f Na2HB(CH3 )2 1 2 3 ^ * Obsd Calcd Obsd C alcd Obed Oalcd Obsd C alcd , 12.1 - 6.6 8.3 21.8 V ol. o f ( CHL )pB0H : ( o o ? 2 V ol. o f H2 (c c ) E xperim ent ? .5 8 .0 6 .2 6 .1 4 .0 4 .2 1 6 .2 1 6 .0 1 4 .2 1 2 .1 8 .3 *« 9 .8 1 0 .9 2 3 .7 2 1 .8 81 Obsd C alcd Obsd Calcd Obed C alcd Obsd C alcd Equlv. Vol. o f Na (c c ) 1 4 .4 1 9 .4 1 6 .7 1 3 .4 1 5 .7 Vol. o f (C H ^ )9B0H (c c ? 2 V ol. o f Ho (c c ) 2 5 .0 7 .2 9 .9 9 .7 8 .7 8 .4 7 .2 7 .8 1 3 .1 1 4 .4 2 1 .0 1 9 .4 1 8 .2 1 6 .7 15-7 - The c a lc u la te d v a lu e s a re b a se d upon th e sodium a n a l y s i s , u n le s s i t ap p e a rs t o be o b v io u sly low. I t i s then b a se d upon th e hydrogen ev o lv ed . E xperim ents 7 and 8 were done w ith th e t r im e th y l amine d isp la c e m e n t p r o c e s s . The stu d y of th e new compound N ag H B ^H ^^, i s o l a t e d In t h i s work f o r th e f i r s t tim e , i s o f c o n s id e ra b le i n t e r e s t from a s t r u c t u r a l s ta n d p o in t, and a l s o because of i t s ch em ical p r o p e r t i e s . I t w i l l be d is c u s s e d more f u l l y in th e fo llo w in g c h a p te r s . 31 The A ttem pts to P re p a re Na2HB(CH^) 2 w ith o u t th e T r i m ethylam ine D isp la ce m en t. In o rd e r to red u ce th e tim e r e q u ir e d f o r th e p r e p a r a tio n o f Na2HB(GH^)2 , a stu d y o f t h i s p ro c e s s was made In w hich th e le n g th y trim e th y la m in e d isp la c e m e n t was o m itte d . In t h i s p r o c e s s , te tr a m e th y l d ib o ra n e was added to an ammonia s o l u t i o n c o n ta in in g an e x c ess o f sodium . A fte r r e a c t i o n had ta k e n p la c e a t -78°G, as was in d ic a te d by th e fo rm a tio n o f a g reen s o l u t i o n , th e ammonia was removed a s co m p letely a s p o s s ib le a t t h i s te m p e ra tu re in vacuo. The r e s id u e was th e n warmed slow ly to room te m p e ra tu re i n vacuo. The p ro d u c t was th e n ex t r a c t e d from th e e x c e ss sodium by means o f d im eth y l e t h e r . The a n a ly s is o f th e e x t r a c t gave th e r i g h t p r o p o r tio n s of Na, (CH^)2B, and H2 f o r Na2HB(CH^)2 , b u t in a d d itio n some trlm e th y lb o ro n was o b ta in e d i n th e h y d r o ly s is p r o c e s s . T his o b s e rv a tio n i n d ic a t e s th a t some d is p r o p o r tio n a tio n ta k e e p la c e in t h i s c a s e , w hich i s av o id ed when th e t r i m ethylam ine d isp lace m en t p ro e e s s i s u se d . The d e t a i l e d r e s u l t s o f t h i s stu d y a r e g iv e n i n T able V. 32 T able V The A ttem pt to P re p a re NaoHB(CI-h)o w ith o u t T rim ethylam ine D isplacem ent E xperim ent 1 2 3 Obed C alcd Obed C alcd Obed Calcd E qulv. Vol. o f ,Na In th e P ro d u c t l6 .7 e e - l? .6 c c - 13.^00 V ol. o f (CH3 )2B0H Produced by H y d ro ly eie (c c ) 8 .7 B.k 8 .2 8 .8 7*2 6 .7 Vol. o f Hp Produced by H y d ro ly sis (c c ) 1 8 .2 1 6 .7 2 2 .2 17-6 15-7 1 3 -^ Vol. o f B(CHo)o O b tain ed by J H y d ro ly sis (c c ) k.7 0 .0 1 .2 0 .0 2 .9 0 .0 # The hydrogen a n a ly s is was h ig h i n E xperim ent 2 due to c h a rrin g of th e sam ple i n h y d r o ly s is . The Non-Hydrogenlc R e a c tio n w ith T e tra m e th y ld ib o ra n e In E x cees. The non-hydrogen1c r e a c t i o n , when te tr a m e th y l d ib o ra n e i s i n e x c e s s , p ro c e e d s in much th e same manner as when sodium i s in e x c e s s , b u t l e s s c le a n ly . The t e t r a m e th y ld ib o ran e I s added to th e fro z e n s o lu t io n o f sodium in ammonia and th e m ix tu re i s warmed t o -?8°C f o r th e r e a c t i o n . The s o lu t io n becomes y ello w v ery s h o r t l y , i n d i c a tin g t h a t a l l o f th e sodium has been lised in th e r e a c tio n . The ex cess o f te tra m e th y ld ib o r a n e , how ever, a p p e ars to c a ta ly z e f u r t h e r r e a c t i o n o f th e f i r s t p ro d u c t, f o r th e c o lo r o f th e s o lu t io n fa d e s a t a r a t e ro u g h ly in p r o p o rtio n 33 to th e e x c ess r e a g e n t, b u t only a s l i g h t excess i s n e c e ssa ry f o r com plete d e c o lo r I z a tI o n . i F u r th e r ev id en ce t h a t an im p o rta n t s id e r e a c t i o n i s o c c u rrin g in t h i s ca se i s shown by th e r e s u l t s o f s e v e r a l a tte m p ts to p re p a re th e compound NagHBtGH^^ by th e method e x p la in e d e a r l i e r ,® b u t w ith an ex c ess o f te tr a m e th y l d ib o ra n e . The r e s u l t s o f t h i s stu d y a r e g iv e n in T able VI. T able VI The A ttem pt to P re p a re Na?HB(CH3 ) 2 u sin g Excess (CH^hj.BgHo Experim ent 1 2 3 Obsd C alcd Obsd C alcd Obsd C alcd E quiv. Vol. o f Na added 2 6 .8 .«• 2 6 .0 2 3 .8 V ol. o f (CHo)4B2H2 added 1 9.5 1 3 .4 1 5 .4 13.0 1 4 .3 1 1 .9 Vol. o f H2 P roduced in Ammonolysls 1 6 .9 19.5 1 6 .4 1 5 .4 2 0 .8 14.3 E quiv. Vol. o f Na in E x tr a c t 2 2.2 — 2 6 .0 — 1 9 .8 — V ol. o f (CH3 )2BOH on H y d ro ly sis 1 1 .4 1 1.1 9 .5 1 3.0 7 .9 9 .9 Vol. o f H2 on H y d ro ly s is 3 0 .4 22.2 3 6 .1 26.0 27-3 1 9 .8 V ol. o f (CHo)oB O btained on Hydro l y s i s of E x tr a c t n o t d eterm in ed n o t d e term in ed 3-3 0 8 S u p ra . . pp. 24-28. 3^ I t i s a p p a re n t th a t th e r e s u l t s of th e s e ex p e rim en ts are not c o n s i s t e n t , ex cep t t h a t a g re a t d e a l more hydrogen i s alw ays produced by th e h y d r o ly s is p ro c e s s th a n would be j o b ta in e d i f p u re Na2HB(GH^)2 were p r e s e n t . I n th e t h i r d experim ent trim e th y lb o ro n was found in th e h y d r o ly s is p ro - ! d u c ts , a lth o u g h th e system had rem ained a t room te m p e ra tu re | in vacuo f o r tw e n ty -fo u r h o u rs p r i o r to th e h y d r o ly s is . Hence i t i s in d ic a te d t h a t some d is p r o p o r tio n a t io n had j o c c u rre d in t h i s p ro c e d u re , which may, i n p a r t , e x p la in | th e anom alously h ig h p ro d u c tio n of hydrogen. In view o f th e f a c t t h a t Na2HB(GH^)2 co u ld n o t be • produced in a p u re s t a t e from a r e a c t i o n i n w hich t e t r a m e th y ld ib o ran e was p r e s e n t in e x c e s s , no f u r t h e r e x p e r i- m ents were t r i e d under such c o n d itio n s . I An A ttem pt t o P re p a re an A d d itio n Compound o f Sodium and T rim eth y lb o ro n An a tte m p t was made t o p re p a re an a d d itio n compound o f sodium and trim e th y lb o r o n i n l i q u i d ammonia. Under th e c o n d itio n s o f th e e x p e rim e n t, how ever, no a d d itio n r e a c tio n „ was o b se rv e d . T rim eth y lb o ro n was added to an ammonia t s o lu t io n which c o n ta in e d an excess of sodium. The system was th e n allo w ed t o s ta n d f o r f o r t y - e i g h t h o u rs a t -78°G. ■ N e ith e r th e i n t e n s i t y n o r th e shade o f th e b lu e c o lo r o f th e sodium s o lu t io n a p p e a re d to be a f f e c t e d in any way by 35 j t h e p re se n c e of th e trim e th y lb o ro n . A f te r rem oving th e 1 ammonia by s u b lim a tio n , a l l o f th e trim e th y lb o ro n was sub lim ed from th e system a t room te m p e ra tu re as th e ammonia com plex. I t must be re c o g n iz e d , how ever, t h a t th e am m onlation o f trim e th y lb o ro n i s a v e ry r a p id r e a c t i o n and t h a t i n t i - m ate c o n ta c t of trim e th y lb o ro n w ith th e sodium c o u ld not be accom plished w ith o u t th e p r i o r fo rm a tio n of th e am moniate. . T h e re fo re th e o b s e rv a tio n m ight be due to one o f two p o s s i b i l i t i e s . I t may be t h a t trim e th y lb o ro n i s to o weak as an e l e c t r o n r e c e p to r to form th e a d d i tio n compound. Gn th e o th e r hand, I t i s p o s s i b le th a t th e b r i d g e - s t r u c t u r e o f d ib o ra n e and I t s d e r i v a t i v e s i s a n e c e s s a ry f a c t o r in th e fo rm a tio n o f Na2HB( > and t h a t t h e r e i s no mechanism a v a ila b le f o r th e fo rm a tio n o f th e an alo g o u s s a l t N a g B tC H ^ . CHAPTER I I I THE PROPERTIES AND THE PROBABLE STRUCTURE OP Na2HB(CH3 )2 A stu d y o f th e ch em ical p r o p e r t i e s and th e s t r u c t u r e o f Na2HB(CH3 ) 2 i s o f c o n s id e ra b le im p o rta n ce. I f th e e m p iric a l fo rm u la Na2HB(CH3 >2 i s a t r u e r e p r e s e n t a t i o n o f th e s t r u c t u r e o f t h i s m a t e r i a l , th e n th e a n io n i s ex p ected to have an u n sh ared e l e c t r o n p a i r . T his s i t u a t i o n should g iv e r i s e to b ase p r o p e r t i e s , ac c o rd in g to th e Lewis-*- th e o ry o f a c id s and b a s e s . In a d d itio n t o th e ex p ected b a se p r o p e r t i e s o f Na2HB(CH3 )2 » th e r e a c t i o n s I n d ic a te t h a t th e h y d rid e p o te n t i a l o f t h i s new su b sta n c e i s q u ite h ig h , p o s s ib ly even ex ceeding t h a t o f th e a l k a l i h y d rid e s . The h ig h re d u c in g i s t r e n g t h , which t h i s h y d rid e p o t e n t i a l would i n d i c a t e , g r e a t l y l i m i t s th e stu d y o f th e b ase p r o p e r t i e s o f Na2HB(CH3 )2 . The e x p e rim e n ta l s tu d i e s of th e s e two Im p o rta n t c h a r a c t e r i s t i c s o f th e new su b sta n c e Na2HB(CH3 ) 2 a r e d i s c u ssed in th e fo llo w in g p a ra g ra p h s . J- G. N. L ew is, J . F r a n k lin I n s t i t u t e (3 ) 2 2 6 . 293-313 (1 9 3 8 ). 37 The T reatm ent o f NagHBCOH^)^ w ith S lla n e S ila n e was s e l e c t e d as a; p o t e n t i a l L ew is-ty p e a c id f o r t e s t i n g th e b a s e - a c tio n o f f^HBCCH^^* I t i s w e ll known t h a t th e ”o c t e t - r u l e B i s n o t e x c lu s iv e ly fo llo w ed by s i l i c o n in i t s compounds. Hence a s u f f i c i e n t l y s tro n g b a se could c o n c e iv a b ly add to s l l a n e expanding th e v a le n c e s h e l l o f s i l i c o n to te n e l e c t r o n s . A p r o to n lc a c tio n of s i l a n e a ls o c o u ld be e n v isa g e d . In accordance w ith th e s e c o n s id e ra t i o n s , a m ethyl e t h e r s o lu t io n o f Na2HB(CH^)2 was t r e a t e d w ith s i l a n e a t -?8°C . However, o ver a p e r io d o f tw enty h o u r s , no m easu rab le r e a c t i o n o c c u rre d . T his in d ic a te d t h a t i n m ethyl e t h e r Na2HB(GH3 )2 i s n o t s u f f i c i e n t l y s tr o n g , as a b a s e , t o d e m o n stra te th e a c id p r o p e r t i e s o f s i l a n e . The R e a c tio n o f NagHB(QH^),-, w ith C h lo ro s lla n e I t seemed l i k e l y t h a t c h lo r o s lla n e m ight be somewhat'; s tr o n g e r as a L e w is-ty p e a c id th a n s i l a n e . Hence a m ethyl e t h e r s o lu tio n o f Na2HB(GH3 )2 was t r e a t e d w ith c h l o r o s l la n e in th e hope t h a t a r e a c t i o n m ight be in d u ced . In t h i s c a s e , J u s t as w ith s i l a n e , th e Lewis a c id -b a s e r e a c t i o n was n o t o b se rv e d . However, an Im p o rtan t r e a c t i o n d id occur w ith th e p ro d u c tio n o f an eq u im o lal amount of s i l a n e . As a w orking h y p o th e s is , th e fo llo w in g e q u a tio n was c o n s id e re d : Na2HB(GH^)2 f SiH3Cl — » SiHjj. + NaGl + NaB(CH3 )2 . 38 The d e t a i l e d r e s u l t s o f t h i s stu d y a r e g iv en in T able V II. T able VII A ttem pts to Show th e E x iste n c e o f NaBtCH^o . An a tte m p t # as made to show th e p re se n c e o f th e p o s tu l a te d su b sta n c e NaB(CH3 ) 2 by t r e a t i n g th e p ro d u c t of th e r e a c tio n o f Na2HB(GH^)2 and c h l o r o s l la n e w ith m ethyl e t h e r , and f i l t e r i n g th e s o lu t io n th u s form ed. However, th e p ro d u c t o f th e r e a c tio n was n o t s o lu b le , and hence th e e x t r a c tio n p ro c e s s was n o t e f f e c t i v e . The h y d r o ly s is o f th e r e s id u e produced hydrogen In th e ex p ected am ount, b u t o n ly a sm a ll, n o n - s to ie h io m e tric amount o f d lm e th y lb o ric a c id was ob t a in e d . A f u r t h e r a tte m p t t o d is s o lv e th e p ro d u c t o f th e Na2HB(GH^)2- c h l o r o s l l a n e r e a c tio n was made u sin g l i q u i d ammonia as th e s o lv e n t. I n t h i s ca se a ls o e x t r a c t i o n was n o t p o s s i b le , f o r a r e a c t i o n o c c u rre d , p ro d u cin g a volum i nous w h ite p r e c i p i t a t e . A sm all volume o f ( G ^ ^ B N ^ was s e p a ra te d from th e ammonia s o lv e n t. H y d ro ly sis o f th e r e s id u e produced hydrogen i n th e ex p e cte d am ount, b u t no The R e a c tio n o f Na«HB(CH0 ) 0 w ith C h lo ro s lla n e E xperim ent E quiv. Vol. of I^HBCGH-jj^ Vol. o f SiH3Gl added Vol. o f SiH^ produced 1 0 .2 cc 1 0 .4 cc 1 3 .4cc 1 1 ? . 9cc 1 1 .6ce 1 1 .9 cc 2 39 d im e th y lb o rlc a c id was o b ta in e d . The p ro d u c tio n o f in l i q u i d ammonia, fo llo w ed by th e p ro d u c tio n o f hydrogen by h y d r o ly s is , w ith o u t th e e v o lu tio n o f d i m e th y lb o rlc a c id , su g g e sts th a t th e r e a c t i o n o f ammonia w ith HaB(CH3 )2 m ight in v o lv e a t r a n s i t i o n o f hydrogen from p r o to n ic c h a r a c te r in ammonia to th e h y d rid e io n . This r e a c t i o n would be r e p r e s e n te d by th e fo llo w in g e q u a tio n . NaBCOH^Jg + — » NaH + (GH3 )2BNH2 I I I ) . T h is e q u a tio n h as not been co n firm ed , how ever, s in c e th e p ro d u c tio n o f (GH3 )2BNH2 was h o t s to i c h io m e tr ic . A f u r t h e r a tte m p t to show th e p re se n c e o f NaB(03^)2 was made by t r e a t i n g th e r e s id u e of th e r e a c t i o n o f Na2HB(GH3 )2 and c h lo r o s ila n e w ith d im eth y lb o ro n brom ide in m ethyl e t h e r . The p ro d u c ts of t h i s r e a c t i o n , how ever, co u ld n o t be s e p a ra te d f o r i d e n t i f i c a t i o n . In view o f th e r e s u l t s of t h i s s tu d y , th e e x i s te n c e o f a compound w ith th e fo rm u la NaB(CH3 )2 has n o t been p ro v e d , a lth o u g h th e p ro d u c tio n o f s l l a n e by th e r e a c tio n o f Na2HB(CH3 ) 2 w ith c h lo r o s ila n e i s good ev id en ce t h a t m a te r ia l h av in g such a co m p o sitio n i s pro d u ced . The R e a c tio n o f C h lo ro s lla n e w ith th e A lk a li H y d rid e s. The r e a c t i o n o f c h lo r o s ila n e w ith th e a l k a l i h y d rid e s was s tu d ie d i n o rd e r to compare th e r e l a t i v e h y d rid e a v a i l a b i l i t i e s o f th e s e s a l t s w ith Na2HB(CH3 )2 * C h lo ro s ila n e was added to m ethyl e th e r s l u r r i e s o f th e f i n e l y ground h y d r id e s , and th e m ix tu re s were allo w e d to s ta n d f o r seventy- two h o u rs o r lo n g e r a t -7 8 °G. The r e a c t i o n w ith sodium h y d rid e gave a n in e p e r c e n t c o n v e rsio n o f c h l o r o s ila n e to s l l a n e . The s i m i l a r r e a c t i o n w ith lith iu m h y d rid e gave a somewhat h ig h e r y i e l d of s l l a n e , b u t t h i s system was warmed to ap p ro x im a tely - 30°0 f o r s e v e r a l h o u rs b e fo re th e r e a c tio n was sto p p e d . • On th e b a s i s o f th e s e r e s u l t s , i t ap p e a rs t h a t th e h y d rid e r e a c t i v i t y o f th e a l k a l i h y d rid e s in m ethyl e th e r i s n o t as h ig h a s th a t o f NagHBlCH^^. However, th e slow r a t e o f r e a c t i o n co u ld w e ll be due t o th e i n s o l u b i l i t y of th e a l k a l i h y d rid e s i n m ethyl e t h e r , o r th e fo rm a tio n o f an in s o lu b le c o a tin g of sodium c h lo rid e on th e s u r f a c e o f th e h y d rid e s a l t . The R e a c tio n o f NagBBtOH^g w ith D lborane D iborane h a s d em o n strate d p r o p e r t i e s w hich in d ic a t e t h a t i t may be c l a s s i f i e d a s a good L ew is-ty p e a c id . For exam ple, d lb o ra n e r e a c t s w ith carbon monoxide t o form b o rin e c a rb o n y l, BH^GO. 2 S im ila r ly th e r e a c t i o n o f d ib o ra n e w ith trim e th y la m in e p ro d u c e s th e b o rin e -trlm e th y la ra in e com plex, BH3 • CM^)3 , and th e r e a c t i o n w ith d im e th y l e t h e r ~ ^ A. B. Burg and H. I . S c h le e in g e r, J . Am. Ghem. Soc. i i , 780 (1 9 3 7 ). 41 ■produces th e h o r in e e t h e r a t e Hence i t was 1 a n t i c i p a t e d t h a t d ib o ra n e w ould b e c a p a b le o f d e m o n stra tin g th e b ase a c t i v i t y o f NagHBtGH^g by th e fo rm a tio n o f an a d d i tio n compound. T h e re fo re m ethyl e t h e r s o lu t io n s of Na-gHBCCH^)*) were t r e a t e d w ith e x c e ss amounts o f d ib o ra n e . The r e s u l t s in d ic a t e t h a t w h ile an a d d i tio n r e a c t i o n does ta k e p la c e , th e mole r a t i o r o f b o rin e (BH3 ) to Na2HB(CH3 ) 2 in th e p ro d u c ts i s c o n s id e ra b ly g r e a t e r th a n o n e -to -o n e . The p ro d u c ts of t h i s r e a c t i o n d id n o t r e le a s e any d ib o ra n e a t 25°C in vacuo o ver a p e r io d o f se v e n ty -tw o h o u rs . The 1 r e s u l t s o f t h i s stu d y a re g iv en i n T able V III. T ab le V III The R e a c tio n o f NagHBiCH^^ w ith D lborane Experim ent 1 2 Equiv. Vol. o f NagHBtGH^Jg 9*3cc ? .3 c e to 13.5cc* Vol. o f B2H^ added 7 .8 cc 1 3 .7 cc Vol. o f B2H£ r e t a i n e d 6 . 6 cc 8 .5 c c * I n E xperim ent 2, th e maximum e q u iv a le n t volume o f Na2HB(CH3)2 was 1 3 »5 c c , on th e b a s i s o f th e volume o f (CH3)4B2®2 u se d . The sodium a n a ly s is in d ic a t e d a volume o f 7 . 3 cc, b u t i t was low due t o th e n e c e s s a ry s e p a r a tio n o f th e sodium from a r e l a t i v e l y la r g e am ount o f aluminum. The a d d i tio n of d ib o ra n e to Na2HB(CH3 ) 2 m ight be e x p e c te d to fo llo w th e e q u a tio n 3 H. I . S c h le s in g e r and A. B. B urg, J . Am. Ghem. Soc. 60, 296 (1 9 3 8 ). 42 2Na2HB(CH3 ) 2 + B2H6 ----» 2Na2HB(CH3 )2 «BH3 . ( I l l ) The s to ic h io m e tr y o f t h i s e q u a tio n , how ever, does n o t s a t i s f y th e r e s u l t s o f T ab le V III. Gn th e o th e r hand, th e H h y d r id e w n a tu re o f Na2HB(CH3 )2 , w hich was d e m o n stra te d by I t s r e a c t i o n w ith c h lo r o s lla n e ^ may w e ll le a d to an e x p la n a tio n o f i t s r e a c t i o n w ith d ib o ra n e . I t seems p o s s ib le t h a t th e r e t e n t i o n o f d ib o ra n e by Na2HB(CH3 )2 i n an amount g r e a t e r th a n was ex p e cte d m ight be due to th e fo rm a tio n o f sodium b o ro h y d rid e and a b o rin e complex o f th e h y p o th e t i c a l s a l t NaB(GH3 )2 . The s a l t MaB(GH3 )2 would have an u n sh a re d e l e c t r o n p a i r and a t th e same tim e i t would be e l e c t r o n d e f i c i e n t , s in c e only s i x e l e c t r o n s would occupy th e a v a i l a b l e bond o r b i t a l s of th e b o ro n atom. T his would be ex p e cte d t o le a d t o p o ly m e riz a tio n o f th e an io n However, each p olym eric group o f JjBtGHj)^ u n i t s would have an u n sh a re d e l e c t r o n p a i r , which sh o u ld g iv e r i s e t o b a se p r o p e r t i e s . Hence th e r e t e n t i o n of d ib o ra n e in amounts ex c ee d in g t h a t p r e d ic te d by e q u a tio n I I I seems re a s o n a b le . The fo llo w in g e q u a tio n s would be in a c c o rd w ith t h i s new p o s t u l a t e . Na2HB(CH3 )2 + iB 2E6 — > NaB% + NaB(CH3 )2 (IV) xNaB(CH3 )2 + #B2H6 — > Nax B(CH3 ) 2 x *BH3 (V) ^ Suora.T~p. 38. 43 The Q u e stio n o f Sodium B orohydride as a P ro d u c t o f i , ! th e R e a c tio n o f Na2HB(CH^?2 and D lb o ra n e . I f NagHBCGH^Jr, ' r e a c t s w ith d lb o ra n e w ith th e p ro d u c tio n o f sodium b o ro - h y d rld e , a s h as been s u g g e ste d , i t sh o u ld be p o s s ib le to d e m o n strate th e p re se n c e of th e b o ro h y d rid e by chem ical means. One o f th e methods whereby t h i s m ight be accomp- < l l s h e d ap p e a rs to o f f e r a re a s o n a b le p r o b a b i l i t y o f su c cess,' and a t t h e same tim e i t i s s p e c i f i c f o r th e p re se n c e of b o ro h y d rid e . Sodium b o ro h y d rid e r e a c t s w ith aluminum ; c h lo r id e w ith th e p r o d u c tio n o f aluminum b o ro h y d rid e ^ a c c o rd in g to th e fo llo w in g e q u a tio n : AlgClg + 6NaBI% ---- » 6HaCl + 2A1(BHj ^)3 . (VI) Hence th e tre a tm e n t o f th e r e a c t i o n p ro d u c ts o f Na2HB(OH3 )2 and d ib o ra n e w ith aluminum c h lo rid e w ould o f f e r a means o f p ro v in g th e p re se n c e o f sodium b o ro h y d rid e . An a p p a ra tu s f o r t h i s ex perim ent h a s b e e n d ev e lo p ed , and i t i s d e s c r ib e d below . A p p a ra tu s. The a p p a ra tu s f o r th e tr e a tm e n t of th e r e a c t i o n p ro d u c t o f Na2HB(CH3 )2 and d ib o ra n e w ith aluminum c h lo r id e i s shown in F ig u re fy. The sam ple o f Na2HB(CH3 )2 i s p re p a re d in tu b e B by th e method d e s c r ib e d e a r l i e r . 6 A m ethyl e th e r s o lu t io n of th e p ro d u c t i s f i l t e r e d th ro u g h 3 H. I . S c h le s in g e r,iF U T. S anderson and A. B. Burg, J . Am. Ghem. S oc. 62 3421 (1940). ^ S u p ra . , pp. 2 4 -2 8 . A P P A R A T U S FO R T H E ADDITION OF A 1 2C I 6 TO T H E N a 2H B ( C H 3| 2 b 2h 6 R E A C T IO N P R O D U C T t FIGURE 5 *±5 , th e s i n t e r e d g la s s f i l t e r C and c o l l e c t e d in tu b e D. The ; a p p a ra tu s i s th e n s e p a r a te d by s e a lin g o f f a t E. The m ethyl e t h e r s o l u t i o n i s n ex t t r e a t e d w ith an e x c ess o f d ib o ra n e . A f te r s u f f i c i e n t tim e a t -78°C h as b een p e r m itte d f o r th e r e a c t i o n , th e ex cess d ib o ra n e and th e m ethyl « e t h e r s o lv e n t a r e d i s t i l l e d away. The a p p a ra tu s i s th e n f i l l e d w ith d ry hydrogen and aluminum c h lo r id e i s i n t r o duced th ro u g h th e ground J o in t (J in t o tu b e F. Then, w ith a c u r r e n t o f hydrogen flo w in g th ro u g h th e a p p a ra tu s end o u t th ro u g h Q, th e aluminum c h lo rid e i s h e a te d u n t i l some su b lim es th ro u g h G -. T his removes any hydrogen c h lo rid e which m ight be produced by th e h y d r o ly s is o f aluminum c h lo rid e by a tm o sp h e ric m o is tu re . Then, a s hydrogen s t i l l flow s th ro u g h th e sy stem , th e tu b e c o n ta in in g th e aluminum c h lo r id e i s drawn out to a c a p i l l a r y a t H. The tu b e i s th e n s e a le d im m ediately when th e flo w o f hydrogen i s stopped. The a p p a ra tu s i s n ex t e v a c u a te d and th e aluminum c h lo rid e i s sublim ed th ro u g h tu b e I in to th e r e a c t i o n tu b e D, which c o n ta in s th e a d d itio n p ro d u c t o f Na2HB(GH^)2 and d ib o ra n e . Tube I i s th e n s e a le d , s e p a r a tin g th e r e a c t i o n m ix tu re . from th e ex c ess aluminum c h lo r id e . The r e a c t a n t s a re mixed th o ro u g h ly by sh a k in g . The m ixing p ro c e s s i s more e f f e c t i v e i f one o r two g la s s beads a re p la c e d in tu b e D. The r e a c t i o n m ix tu re i s th e n warmed g e n tly t o r e a c t i o n . The p ro d u c ts o f th e r e a c t i o n a re s e p a r a te d by f r a c t i o n a l c o n d e n sa tio n in th e vacuum l i n e . The T e st o f th e A p p a ra tu s . T his method h as been t e s t e d by t r e a t i n g a sam ple o f sodium b o ro h y d rid e w ith aluminum c h l o r id e , In th e manner d e s c rib e d above. The r e a c t i o n produced aluminum b o ro h y d rid e , which was i d e n t i f i e d by vapor p r e s s u r e m easurem ents and h y d r o ly tic a n a ly s is . However, th e y i e l d was l e s s th a n t e n p e r c e n t of t h a t e x p e c te d on th e b a s i s o f th e sodium b o ro h y d rid e p r e s e n t. D e s p ite th e poor y i e l d , th e method i s y e t c a p ab le o f p ro v - | in g th e p re s e n c e o f sodium b o ro h y d rid e In th e r e a c t i o n p ro d u c ts of Na2HB(CH^)2 and d ib o ra n e f o r as l i t t l e as one- h a l f m i l l i l i t e r o f gaseous aluminum b o ro h y d rid e may be p o s i t i v e l y i d e n t i f i e d . E x p e rim e n ta l S tu d ie s . A sample o f th e NagHBtCH^).^- d ib o ra n e r e a c t i o n p ro d u c t was t r e a t e d tirlth aluminum c h lo rid e u s in g th e a p p a ra tu s d e s c r ib e d above, b u t th e p ro d u c tio n o f aluminum b o ro h y d rid e co u ld not be d e t e c t e d . However, th e sample s iz e was q u ite sm a ll ( l e s s th a n 1 3 . 5 cc e q u iv a le n t volume o f Na-^HBtCH^^ was u s e d ), and hence any aluminum b o ro h y d rid e produced m ight w e ll have escap e d d e t e c t i o n . I t i s p ro p o sed to r e p e a t t h i s ex p erim en t in th e f u tu r e u sin g a l a r g e r a p p a ra tu s , and a ls o a l a r g e r sample o f Na2HB(CH^)2. 47 The B ehavior o f NaoHB(CH^)g Toward Ammonia i In stu d y in g th e p r o p e r t i e s o f N a^B C C H ^^, i t was d e s i r a b l e to use a s o lv e n t o th e r th a n m eth y l e t h e r i n some of th e e x p e rim e n ts. For t h i s p u rp o se th e b e h a v io r o f Na2HB(CH^)2 tow ard ammonia was s tu d ie d . Ka2HB(CH^ ) 2 i s s o lu b le in l i q u i d ammonia, and i t form s a y ello w s o lu t io n w hich i s i d e n t i c a l in appearance to t h a t form ed by th e non- h y d ro g en !c r e a c t i o n o f te tra m e th y ld ib o ra n e and sodium , when te tra m e th y ld ib o ra n e i s in s l i g h t e x c e ss . The Na2HB(CH^)2 i s n o t m easu rab ly ammonolysed a f t e r many h o u rs a t -78°C . I f th e ammonia i s c a r e f u l l y sublim ed from t h i s system , and th e r e s id u e i s slow ly \irarmed in v acu o , i t may be warmed to 90°G w ith o u t a p p re c ia b le am m onolysls. I f th e ammonia i s n o t removed c o m p le te ly , and i f th e system i s n o t th o ro u g h ly e v a c u a te d , how ever, slow ammonolysls i s o b se rv e d a t room te m p e ra tu re . The s u b s ta n c e Na2HB(GH^ )2 forms an ammoniate i n w hich th e mole r a t i o o f ammonia t o s a l t i s g r e a t e r th a n one to one. T his r e s u l t was o b ta in e d by t r e a t i n g a sample of Na2HB(GH«^)2 w ith ammonia a t -77°C . The ammonia was th e n removed by s u b lim a tio n a t -SO0^ } ^ a nd th e system was warmed slo w ly to 25°C in vacuo. To a n a ly se th e r e s i d u e , i t was th e n t r e a t e d w ith an excess of w a te r, p ro d u cin g hydrogen, d im e th y l b o r i c a c id , sodium h y d ro x id e and ammonia. A fte r 48 th e rem oval o f th e hy d ro g en , th e v o l a t i l e p ro d u c ts w ere : condensed i n a w eighed b u lb , to g e th e r w ith an e x c e ss o f ' hydrogen c h l o r id e . The n o n - v o la ti le ammonium c h lo r id e th u s o b ta in e d was d e te rm in e d g r a v lm e tr lc a lly a f t e r th e rem oval o f th e v o l a t i l e components o f th e m ix tu re . The d e t a i l e d r e s u l t s o f t h i s experim ent a re g iv e n In T able IX. Table IX The Form ation o f an Aramoniate o f Na2HB(CH3 )2 E qulv. Vol. of Na2HB(GH3 )2 (b a se d upon th e sodium c o n te n t) 9 *7 cc V ol. o f Ammonia In th e Ammonie,te 1 2 .7 c c Mole R a tio o f Ammonia to Na2HB(0H^ ) 2 1 .3 1 S im ila r s tu d i e s u sin g trim e th y la m ln e in s te a d o f ammonia, showed t h a t th e r e was no m easu rab le r e t e n t i o n o f trim e th y la m ln e by Na2HB(CH3 )2 a t room te m p e ra tu re In vacuo. The R e a c tio n s o f Na2HB(CH3 )2 w ith T rim eth y lb o ro n T rim eth y lb o ro n i s a m o d e ra tely good L e w is-ty p e a c id . Ekwever, th e b e h a v io r o f Na^HBtCH^Jg tow ard tr im e th y lb o r o n has been found to depend upon th e s o lv e n t. I f t r im e th y l boron i s added t o a m ethyl e t h e r s o l u t i o n o f Na2HB(CH^)2 , a d d i tio n o c c u rs and th e p ro d u c t i s s t a b l e in vacuo a t - 78°C, b u t decomposes w ith th e l o s s o f th e trim e th y lb o ro n a t room te m p e ra tu re . I f ammonia i s the s o lv e n t, how ever, 49 th e r e a c t i o n p ro d u c t i s n o t decomposed in vacuo a t tem pera t u r e s up to 50°C. When te tra m e th y ld ib o r a n e and t r lm e th y l- ;bo ro n a re added s im u lta n e o u s ly to sodium In l i q u i d ammonia, th e f i n a l p ro d u c t ap p e ars to be i d e n t i c a l to th e a d d itio n compound o f NagHBCCH^Jg and trim e th y lb o ro n w hich i s formed in t h i s s o lv e n t. i The R e a c tio n o f MaoHBCQH^)^ w ith T rim e th y lb o ro n In M ethyl E th e r . I n t h i s stu d y was d is s o lv e d in m ethyl e t h e r , and a m easured sample o f trim e th y lb o ro n , l a r g e r th a n needed f o r th e r e a c t i o n , was condensed i n th e r e a c t i o n tu b e by means o f l i q u i d n itr o g e n . T his m ix tu re was allo w ed t o s ta n d a t - 78 °G f o r tw e n ty -fo u r h o u rs o r lo n g e r , in each c a s e , f o r com plete r e a c t i o n . D uring t h i s tim e a f lo c c u l e n t w h ite p r e c i p i t a t e form ed. The m ethyl e t h e r and th e ex c e ss trim e th y lb o r o n w ere removed by d i s t i l l a t i o n a t -78°G. The r e s id u e was th e n warmed to room te m p e ra tu re , i n vacuo, w ith th e r e s u l t i n g e v o lu tio n o f tr im e th y lb o ro n . The t o t a l volume of trim e th y lb o ro n added to th e system was acco u n te d f o r by th e e x c e ss tr im e th y l b o ro n re c o v e re d a t - 78°0 and t h a t p ro d u ced by th e th e rm a l d ec o m p o sitio n . These r e s u l t s in d ic a t e t h a t an equim olar a d d itio n p ro d u c t o f Na2HB(0H<j)2 and trim e th y lb o ro n i s form ed a t - 78°G and t h a t i t i s n o t s t a b l e in vacuo a t room te m p e ra tu re . The d e t a i l e d r e s u l t s o f t h i s s tu d y a r e given in T able X. 50 Table X The R e a c tio n o f T rim eth y lb o ro n w ith Na^HBtCH^Jg in M ethyl E th e r? E xperim ent 1 2 E quiv. V ol. of Na2HB(CH^ >3 k. 5 cc 1 0 . 9 cc V ol. o f B(CH^)<^ added 1 5 . 6 cc 1 5 . ^cc V ol. o f BCCHoK r e t a i n e d a t - ? 8°C, b u t ev o lv ed a t 25°C 6 .5 cc l l . l e c The B eh av io r o f T rim eth y lb o ro n tow ard th e A lk a l i H y d rid e s. The compound Na2HB(CH2 ) 2 h as been shown by i t s r e a c t i o n w ith c h lo r o s ila n e to be a p o te n t so u rce o f h y d rid e. Hence i t was c o n s id e re d d e s i r a b l e to d e te rm in e w h e th e r th e a c t i v i t y o f Na2HB(0H^ ) 2 tow ard trim e th y lb o ro n in m ethyl e t h e r co u ld be a t t r i b u t e d t o t h i s h y d rid e a v a i l a b i l i t y . T h e re fo re m ethyl e t h e r s l u r r i e s o f f i n e l y ground sodium h y d r id e , and o f lith iu m h y d rid e , were t r e a t e d w ith t r i m ethylboron a t -78°G . T here was no ev id en ce t h a t any r e a c t i o n o c c u rre d betw een th e sodium h y d rid e and t r i m e t h y l b o ro n . In th e c a se o f lit h iu m h y d r id e , a sm all amount o f 7 T his stu d y r e q u ir e d a method o f i s o l a t i n g tr im e th y l boron from m ethyl e t h e r . D i s t i l l a t i o n methods were o u t o f th e q u e s tio n b ecause th e b o i l i n g p o in ts a r e n e a r ly th e same. An e f f e c t i v e ch e m ic al m ethod was to add ammonia to th e mix t u r e , th e n f r a c t i o n a l l y condense th e trim e th y lb o ro n ammo- n i a t e from th e e t h e r and ex c e ss ammonia a t - 78°C, The t r i m ethylboron was th en r e c o v e re d from i t s aramoniate by t r e a t ment w ith aqueous h y d ro c h lo r ic a c i d . T his method h as c o n s i s t e n t l y g iv e n q u a n t i t a t i v e re c o v e ry o f trim e th y lb o ro n from known m ix tu re s , w hereas th e use of calcium c h lo r id e to remove ammonia from th e ammonlate gave o n ly 57$ and phos p h o r ic , a c id a n h y d rid e o n ly 27$ re c o v e ry . 51 trim e th y lb o ro n was r e t a i n e d a t -78°C , b u t th e r e was th e p o s s i b i l i t y t h a t t h i s co u ld have been due to a sm a ll amount o f oxide o r h y d ro x id e im p u rity . In view o f th e s e r e s u l t s , th e n , t h e r e i s no c o n c re te ev id en ce to i n d i c a t e t h a t trim e th y lb o ro n can form th e t r i ms th y lb o ro h y d rid e s a l t a t - 78°G. On th e o th e r hand, th e a p p a re n t f a i l u r e to r e a c t co u ld w e ll be due to th e form a t i o n o f an in s o lu b le c o a tin g o f th e tr im e th y lb o ro h y d rld e s a l t on th e s u r f a c e o f th e a l k a l i h y d rid e . T h e re fo re , th e s e r e s u l t s must be c o n s id e re d in c o n c lu s iv e . The R e a c tio n o f Ha^HB(GH^)o w ith T rim eth y lb o ro n in L iq u id Ammonia. Ammonia i s a good io n iz in g s o lv e n t. Hence i t was d e s i r a b l e to compare th e e f f e c t o f t h i s s o lv e n t w ith t h a t o f d im e th y l e t h e r i n th e r e a c t i o n betw een l^H B C C H ^^ and trim e th y lb o ro n . T h e re fo re an ammonia s o lu t io n o f Na£HB(GH^)2 was t r e a t e d w ith more th a n th e c a lc u l a te d q u a n tity o f trim e th y lb o r o n . A f te r tw e n ty - f o u r h o u rs a t - ? 8°C, th e ammonia was su b lim ed from t h e system and th e r e s id u e was slo w ly warmed to 50QC i n vacuo. In t h i s p ro c e s s th e ex cess trim e th y lb o ro n was sublim ed from th e r e a c t i o n p ro d u c t as th e ammonia complex The a d d i t i o n p ro d u c t r e t a i n e d 0 . 8^ m oles of tr im e th y lb o ro n p e r mole of Na2HB(GH-j)2 , a t 50°C, The d e t a i l e d r e s u l t s o f t h i s stu d y a r e g iv en in T ab le X I. 52 T able XI The R e a c tio n o f w ith T rim eth y lb o ro n in L iq u id Ammonia E quiv. Vol. o f Na£HB(CH^)2 V ol. o f T rim eth y lb o ro n added V ol. o f T rim eth y lb o ro n r e t a i n e d a t 50°G 7 . 25 cc I 8 . 5 cc 6 . lc c R a tio o f B(CH^)-j to Na2HB(CH^ )2 i n P ro d u c t 0 .8 ^ The R e a c tio n w ith T rim eth y lb o ro n d u rin g th e P re p a ra t i o n P r o c e s s . I t has been o bserved e a r l i e r t h a t when d is p r o p o r tio n a t io n o f th e d im e th y lb o rin e group o c c u rs , i s r e ta in e d v ery firm ly by th e p r o d u c t, even a t e le v a te d ro u g h ly , te tra m e th y ld ib o r a n e was allo w ed t o r e a c t w ith sodium ( i n e x c e ss) in l i q u i d ammonia by th e method des- trim e th y lb o ro n was a ls o added to th e o r i g i n a l m ix tu re . T here was no v i s i b l e d if f e r e n c e a t any p o in t i n t h i s p r e p a r a t i o n , from th e s i m i l a r p ro c e s s w ith o u t tr im e th y lb o ro n . The p ro d u c ts p r i o r to th e m ethyl e t h e r e x t r a c t i o n were warmed to 100°C i n vacuo f o r a s h o r t p e r io d o f tim e . The s o l i d p ro d u c t was th e n e x t r a c t e d w ith m ethyl e t h e r , an d th e ® S u p ra. . Table V, p . 32. 9 S u p ra , pp. 2^-27. d u rin g th e p r e p a r a t io n o f Na2HB(CH^)2 , th e tr im e th y lb o ro n te m p e ra tu re s .® In o rd e r t o s tu d y t h i s e f f e c t more tho c r lb e d e a rlie r,^ e x c ep t t h a t more th a n a m olar r a t i o o f 53 e x t r a c t was a n a ly s e d by h y d r o ly s is ; th e sodium was d e t e r mined g r a v l m e t r i c a l l y . The a n a ly s is a g ree d w ith t h a t of !Na2HB(GH^)2 , e x c e p t t h a t an e q u iv a le n t volume o f t r i m e t h y l bo ro n was o b ta in e d , I n d ic a tin g th e fo rm a tio n of a su b s ta n c e h av in g th e form ula NagHBfGH^g'BCCH^)^. The d e t a i l e d r e s u l t s o f t h i s s tu d y a r e g iv en In T able X II. T ab le X II l The A n a ly s is o f th e N o n -V o la tile P ro d u c t of th e R e a c tio n o f T e tra m e th y ld lb o ra n e and T rim eth y lb o ro n w ith Sodium Obed. G alcd. E qulv. Vol. o f Sodium 8 .7 e c V ol. o f (CH3 ) 2BOH 4 .2 c e 4 .4 c c Vol. o f H2 lO.kcc 8 . 7 ce V ol. o f B(GH^)^ 4 .7 c c (4 .4 c c ) (V ol. o f B(CH3 ) o added 9 -^ c c ) i * These c a lc u l a te d v a lu e s a r e b a s e d upon th e c o r r e s ponding a n a ly s is o f Na2HB(GH3 ) 2 . These r e s u l t s would seem to i n d i c a t e t h a t th e r e a c tio n p ro d u c t o b ta in e d by t h i s p ro c e s s c o rre sp o n d s t o t h a t o b ta in e d by t r e a t i n g an ammonia s o lu t io n of NagHBtGH^^ w ith tr im e th y lb o r o n ,■L0 s in c e th e c o m p o sitio n o f th e p ro d u c ts and th e o b s e rv a tio n s e>f s t a b i l i t y a r e a p p a r e n tly th e same. T tr S u o ra . . p . 5 1 . 5b ; D isc u ssio n ; A r e c o g n itio n o f th e s t r u c t u r e of Na2HB(GH^ )2 i s im p o rta n t f o r a f u l l u n d e rs ta n d in g o f th e p r o p e r t i e s o f t h i s new m a t e r i a l . A d e te r m in a tio n of th e s t r u c t u r e o f t h i s su b sta n c e by means of X -ray d i f f r a c t i o n s tu d i e s does n o t seem f e a s i b l e s in c e th e e x t r a c te d p ro d u c t i s n o t a p p r e c ia b ly c r y s t a l l i n e . Hence th e s t r u c t u r e must be . c o n s id e re d on th e b a s i s o f th e ch em ical e v id en ce t h a t i s ' a v a i l a b l e . The fo llo w in g e x p e rim e n ta l o b s e rv a tio n s con- ' c e rn in g t h i s m a te r ia l a re s i g n i f i c a n t . 1 . Na2HB(CH^)2 in m eth y l e t h e r form s a o n e -to -o n e a d d i tio n compound w ith trim e th y lb o ro n a t - ? 8°G. At room te m p e ra tu re in vacuo, how ever, t h i s p ro d u c t d i s s o c i a t e s w ith th e e v o lu tio n of th e tr im e th y lb o r o n , 2 . Na2HB(GH^)2 in l i q u i d ammonia form s a o n e -to -o n e a d d itio n compound w ith tr im e th y lb o r o n . At te m p e ra tu re s up to 50°C in vacuo t h i s p ro d u c t does not lo s e trim e th y lb o ro n . 3 . NagHBtCH^Jg l i q u i d m ethyl e t h e r form s an a d d i t i o n p ro d u c t w ith d ib o ra n e w hich c o n ta in s more th a n one e q u iv a le n t of d ib o ra n e p e r mole of Na2HB(CH^)2 . T h is p ro d u c t does n o t lo s e dibors.ne a t 25 ° i n vacuo. 4. One mole o f Na2HB(CH^)2 in m ethyl e t h e r r e a c t s q u a n t i t a t i v e l y w ith c h l o r o s i la n e a t - 78 °C to p ro d u ce one mole o f s i l a n e . 55 5 . Na2HB( d is s o lv e s in m ethyl e th e r to form a w a te r - c l e a r s o lu t io n a t low c o n c e n tr a tio n s . I f th e concen t r a t i o n i s g r e a t e r th a n a p p ro x im a te ly 0 .3 m o lar, th e s o lu t i o n a p p e a rs to be g e l a t i n o u s . 6 . Na2HB(CH^ )2 i s co m p letely s o lu b le in l i q u i d ammonia, form ing a y e llo w s o lu t io n . 7 . R epeated e x t r a c t i o n o f Na2HB(CH^)2 > f i r s t w ith m ethyl e t h e r and th e n w ith l i q u i d ammonia does n o t a f f e c t th e a n a ly s is o f t h i s m a te r ia l . In view o f th e b e h a v io r of Ka2HB(0H^ )2 in m ethyl e th e r s o lu t io n s (o b s e r v a tio n s 1 , 3 * ^ end 5 ) i t was b e lie v e d f o r a tim e t h a t t h i s su b sta n c e m ight c o n s i s t o f a v e ry I n tim a te m ix tu re of sodium h y d rid e and a p o ly m eric su b sta n c e w ith th e sim p le fo rm u la NaB(CH^)2 . The a s s o c ia t i o n o f sodium h y d rid e w ith th e p o ly m e ric m a te r ia l m ight be co n ceiv ed a s a s o r t o f double s a l t i n which th e h y d rid e i s not s p e c i f i c a l l y bonded t o th e b o ro n atom , b u t f irm ly h e ld by l a t t i c e f o r c e s . Hence th e m ix tu re m ight w e ll be p e p tiz e d in m ethyl e t h e r , t o form a c o l l o i d a l s u sp e n sio n , w ith o u t a p p r e c ia b ly changing th e a s s o c i a t i o n of sodium h y d rid e and th e NaBiGH^^ polym er. A ccording to t h i s h y p o th e s is th e r e a c t i o n o f c h lo ro - s il a n e w ith Ka2HB(CH^)2 ( o b s e r v a tio n 4 ) , would be a t t r i b u t e d to th e sodium h y d rid e , i n term s o f th e e q u a tio n SIH3CI + NaH — * NaCl + SlH^. (V II) 56 iA c tu a lly , i t h as been o b se rv e d t h a t c h l o r o s ila n e r e a c t s v e ry slow ly w ith th e a l k a l i h y d rid e s to produce s i l a n e . 11 A ccording t o t h i s p o s t u l a t e co n cern in g th e n a tu re o f Na2HB(CH^)2 , th e ease w ith w hich c h l o r o s i la n e r e a c t s w ith Na2HB(CH-^)2 , to g iv e a q u a n t i t a t i v e y i e l d o f s l l a n e co u ld w e ll be a t t r i b u t e d to an e x c e p ti o n a ll y f i n e l y d iv id e d s t a t e j o f th e h y d rid e . I f Na2HB(0H^ )2 were a m ix tu re o f sodium h y d rid e and p o ly m e ric NaJBCCH^^, th e r e a c t i o n w ith d ib o ra n e w ould a c t u a l l y be two r e a c t i o n s . One would be th e a d d i t i o n of b o r in e (BH^) t o sodium h y d rid e to form sodium b o ro h y d rid e , w h ile th e o th e r would be th e a d d i tio n o f b o rin e to th e p o ly m e rized a n io n jB(CH^)2J . The mole r a t i o o f b o rin e (BH^) to Ha2HB(CH^)2 in one experim ent was 1 .4 4 , 12 w hich would in d ic a t e t h a t th e e x te n t of p o ly m e riz a tio n o f NaB(GH^)2 in t h i s c a s e , av e ra g e d betw een two and th r e e u n i t s . The r e a c t i o n of trim e th y lb o ro n w ith t h i s p o s tu l a te d m ix tu re o f sodium h y d rid e and NaB(0H^)2 In m eth y l e th e r s o l u t i o n (o b s e r v a tio n l ) w ould seem to be due to th e f o r m a tio n o f a trim e th y lb o ro h y d rld e s a l t , NaHB(GH^)^. T his b o ro h y d rid e i s not known, and p ro b a b ly w ould be u n s ta b le S u p ra . . pp. 39-4-0. 12 S u p ra . . E xperim ent 1, Table V II I , p. 4-1. 57 a t room te m p e ra tu re . A ttem p ts to p re p a re a l k a l i t r i m e t h y l - b o ro h y d rid e s a l t s by t r e a t i n g m ethyl e t h e r s l u r r i e s o f f i n e l y ground a l k a l i h y d rid e s gave no e v id e n c e o f such s a l t s . ^*3 T h is a p p a re n t la c k o f r e a c t i o n , how ever, m ight be due to a s u r f a c e c o a tin g on th e v e ry in s o lu b le a l k a l i h y d rid e s . F i n a l l y , th e g e la tin o u s n a tu re o f th e c o n c e n tra te d s o lu t io n s o f Na2HB(CH^)2 i n m ethyl e t h e r ( o b s e r v a tio n 5 ) m ight be i n t e r p r e t e d t o i n d i c a t e p o ly m e riz a tio n o f th e s o l u t e , which w ould c o rre sp o n d to th e a n t i c i p a t e d p o ly m eric n a tu re of NaB(OH^)£* The o b se rv e d p r o p e r t i e s o f NagHBfCH^^* how ever, a re n o t e x p la in e d u n iq u e ly in te rm s o f t h i s h y p o th e s is w hich assum es a n e a r ly eq u im o lar m ix tu re of sodium h y d rid e and NaB(CH^)2 , so I n tim a te t h a t m ethyl e t h e r w i l l n o t e x t r a c t one from th e o th e r . A c tu a lly th e l a r g e r number of th e e x p e rim e n ta l o b s e rv a tio n s a r e h a rd to r e c o n c i l e w ith t h i s i n t e r p r e t a t i o n , w hich in any ca se i s h a rd t o d e fin e from a s t r u c t u r a l v ie w p o in t. NagHBtGH^^ i s s o lu b le in m ethyl e t h e r ( o b s e r v a tio n 5 ) and i n l i q u i d ammonia ( o b s e r v a tio n 6 ), w h ile sodium h y d rid e i s h ig h ly in s o lu b le in b o th o f th e s e s o lv e n ts . I t h as a l s o b e e n d e m o n stra te d t h a t th e e x t r a c tio n o f Na2HB(CH^)2 by means of th e s e s o lv e n ts does n o t v a ry th e S u p ra . . pp. 50-51* 58 | co m p o sitio n ( o b s e rv a tio n 7 ) as would be e x p e c te d i f i t were ; a m ix tu re o f tw o d i f f e r e n t compounds. i T h e re fo re i t rem ains t o c o n s id e r t h e s a lt- f o r m u la j ; N a^B tG H ^Jg, w hieh a p p e a rs t o b e in a c c o r d w ith a l l f a c t s so f a r d is c o v e re d . The a n io n p o r tio n of t h i s compound r s 1 >2 would have th e e l e c t r o n i c s t r u c t u r e jCHyB'CH^J . In i view o f th e u n sh a re d e le c tr o n s on b o ro n , t h i s s t r u c t u r e w ould be e x p e c te d to g iv e r i s e t o b a s e p r o p e r t i e s in jNagHBCGH^Jg. A ccording to th e l s o e l e c t r o n i c s e r i e s o f jb a s e s OH^, NH^, CH^, BH3” 2 , th e h y p o t h e t i c a l b ase (BH^)“ 2 sh o u ld be e x tre m e ly s tr o n g . S in ce [CCH^^BhJ"2 i s a m e th y la te d d e r i v a t i v e of t h i s h y p o th e tic a l io n , th e n Na2H B ( m i g h t w e ll be e x p e c te d t o show r a t h e r excep- ■ t i o n a l b ase s t r e n g t h , e s p e c i a l l y s in c e m ethyl g ro u p s u s u a lly s tr e n g th e n a b a se more th a n hydrogen d o e s . On f u r t h e r e x a m in a tio n o f th e su g g e ste d e l e c t r o n i c fo rm u la f o r th e a n io n p a r t o f Na2HB(GH^)2 , i t a p p e a rs t h a t t h i s su b sta n c e sh o u ld be a re a d y s o u rc e of h y d rid e io n . F o r com parison, th e h y d rid e io n i s e a s i l y removed from sodium b o ro h y d rid e , NaBH^. The e l e c t r o n - d e n e i t y about th e b o ro n atom i n Na2HB(GH^ )2 would be g r e a t e r th a n in sodium b o ro h y d rid e b ec au se o f th e u n sh a re d e l e c t r o n p a i r . A lso , a f t e r th e rem oval o f th e h y d rid e io n , t h e p re se n c e of m eth y l groups would te n d to s t a b i l i z e th e p ro d u c t by h y p e r- c o n ju g a tlo n . F i n a l l y , th e lo s s o f h y d rid e io n by th e 59 . [(CH^JgBH]-^ io n would b e fa v o re d by th e m utual r e p u ls io n o f th e p r o d u c ts , ea ch o f w hich would b e n e g a tiv e ly ch arg ed . ; Hence, I f t h i s p o s t u l a t e d s t r u c t u r e f o r NagHBCCH^^ i s ’c o r r e c t , i t a p p e a rs t h a t I t m ight w e ll be a more p o te n t so u rc e o f h y d rid e io n th a n sodium b o ro h y d rid e . The r e a c t i o n of Na2HB(CH^)2 w ith c h l o r o s i l a n e i s r e a d i l y e x p la in e d in term s o f th e h y d rid e io n a v a i l a b i l i t y of th e an io n [1 cH3 )2BhJ~2 ( o b s e r v a tio n k ) . The r e a c t i o n o f d ib o ra n e w ith Na2HB(CH3 )2 i s a ls o in a c c o rd w ith t h i s i n t e r p r e t a t i o n ( o b s e rv a tio n 3 ). In t h i s c a se th e f i r s t s t e p i n th e r e a c t i o n would be th e f o r m ation o f sodium b o ro h y d rid e ; th e seco n d would be th e non- s to i c h lo m e tr ic a d d itio n o f b o rin e (BH^) t o th e p ro b a b ly p o ly m e ric s u b s ta n c e NaB(GH3 )2 * These r e a c t i o n s a re r e p r e s e n te d by th e fo llo w in g e q u a tio n s . Na2HB(GH^ )2 + iBgH$ ---- > NaBH^ + NaB(CH3 )2 (V III) xNaB(CH3 ) 2 t £B2H6 ----> Nax B(GH3 )2 *;*BH3 (IX) I t h as been s t a t e d t h a t trim e th y lb o r o n r e a c t s w ith Na2HB(CH3 )2 , i n m ethyl e t h e r , t o produce an a d d i tio n p ro d u c t w hich i s n o t s t a b l e a t room te m p e ra tu re ( o b s e r v a tio n 1 ), w h ile i f ammonia i s used a s th e s o lv e n t, th e a d d i tio n p ro d u c t i s s t a b l e in vacuo a t te m p e ra tu re s a s h ig h as 50°C ( o b s e r v a tio n 2 ) . The d if f e r e n c e in s t a b i l i t y betw een th e two forms o f Na2HB(CH3 )2 *B(GH3 seems to r e q u i r e two d i f f e r e n t means o f a tta c h m e n t of th e tr im e th y lb o r o n . T his 60 o b s e rv a tio n i s n o t i n t e l l i g i b l e in te rm s of th e form er i p o s t u l a t e which i n t e r p r e t e d th e s t r u c t u r e o f Na2HB(CH^)2 to be an I n tim a te m ix tu re o f sodium h y d rid e and th e hypo t h e t i c a l su b s ta n c e NaB(0H^)2 . In te rm s of th e s i n g l e - s a l t fo rm u la , how ever, i t seems l i k e l y t h a t th e r e a c t i o n in one s o lv e n t can be a t t r i b u t e d t o th e h y d rid e a c t i v i t y o f Na2HB(CH^)2 » w h ile in th e o th e r s o lv e n t th e b ase a c t i v i t y o f t h i s s a l t - l i k e su b s ta n c e i s d e m o n stra te d . D im ethyl e t h e r i s n o t a good io n iz in g s o lv e n t. Hence i t i s q u ite u n lik e ly t h a t Na2HB(GH^)2 c o u ld d is s o lv e in t h i s s o lv e n t w ith com plete i o n i z a t i o n . I t seems re a s o n a b le t h a t in t h i s ca se one o f th e sodium io n s m ight w e ll be h e ld q u ite c l o s e ly by th e io n in a s t r u c t u r e ap p ro x im a tin g a t e t r a h e d r a l c o n f ig u r a tio n a b o u t t h e bo ro n atom . Hence th e r e a c t i o n o f Na2HB(CH-j)2 as a b ase in m ethyl e t h e r m ight be s e r i o u s l y h in d e re d s t e r i c a l l y , th u s empha s iz in g th e " h y d r id e - p o te n tia l" o f t h i s s a l t . The h y d r ld e - a c t i v i t y o f Na2HB(CH^ )2 tow ard c h l o r o s i l a n e in m ethyl e t h e r seems to s u p p o rt t h i s i n t e r p r e t a t i o n . Gn th e o th e r hand, in a good io n iz in g s o lv e n t such a s ammonia, t h i s c o n fig u r a t i o n would be more r e a d i l y d is tu r b e d , p e r m ittin g th e i n t e r a c t i o n o f Na2HB(CH^)2 w ith a L e w is-ty p e a c id such as tr im e th y lb o ro n . T h e re fo re i t seems l i k e l y t h a t i n l i q u i d ammonia th e r e a c tio n o f tr im e th y lb o r o n w ith I^H B C C H ^^ i s a d e m o n s tra tio n o f th e a n t i c i p a t e d b ase p r o p e r t i e s o f 61 t h i s new s u b s ta n c e . The e q u a tio n f o r t h i s r e a c tio n would ; ' » be w r i t t e n a s fo llo tirs: Na2HB(CH3 )2 + B(CH3 )3 — » Na2HB2 ( 0^ 3 )5 . (X) 1 Hence in term s o f t h i s p o s t u l a t e , th e r e a c tio n o f tr im e th y l b o ro n w ith Na2HB(GH^ )2 in m ethyl e th e r would produce sodium trim e th y lb o ro h y d rid e a c c o rd in g to th e fo llo w in g e q u a tio n : Na2HB(CH3 )2 + B(CH3 )3 — > NaB(0H3 )2 + NaHB(GH3 ) 3 . (X I) ■ I n view o f th e s e c o n s id e r a tio n s i t a p p e a rs t h a t th e s i n g l e - s a l t fo rm u la Ha2HB(CH3 )2 i s i n f u l l a c c o rd w ith a l l o f th e e x p e rim e n ta l o b s e rv a tio n s c o n c e rn in g t h i s s u b s ta n c e . The v e ry i n t e r e s t i n g p r o p e r t i e s w hich have b ee n d em o n strate d by th e r e a c tio n s o f t h i s new s a l t , w hich m ight be g iv e n th e name disodiura d im e th y lb o r in id e , sh o u ld s ti m u la te con s id e r a b le f u r t h e r stu d y . I CHAPTER IV THE NATURE OF THE NON-HYDROGENIC REACTION W HEN SODIUM IS IN EXCESS The p ro c e s s whereby th e new compound i s p re p a re d h as been d e s c r ib e d e a r l i e r . ^ T his p r e p a r a t io n in v o lv e s th e n o n -h y d ro g e n ic r e a c t i o n o f sodium and t e t r a - m e th y ld lb o ra n e , when sodium i s in e x c e s s . At f i r s t i t seemed l i k e l y t h a t t h i s r e a c t i o n in v o lv e d th e a d d i t i o n o f sodium to te tra m e th y l'd lb o ra n e to form a compound w ith th e fo rm u la N a ^ C G H ^ O n th e o th e r hand, th e d i s s o c i a t i o n o f t h i s h y p o th e tic a l compound to th e odd e le c t r o n s a l t NaHBCGH^Jg a ls o was c o n c e iv a b le , in view of th e in te n s e y e llo w c o lo r . Such an o d d - e le c tr o n compound a s NaHBCCH^^ would be d e te c te d by m agnetic m easurem ents, f o r th e p re se n c e o f an u n p a ire d e l e c t r o n c a u ses param agnetism . The r e s u l t s o f th e m agnetic s tu d y , how ever, I n d ic a te t h a t th e p ro d u c ts o f th e n o n -h y d ro g en ic r e a c t i o n a c t u a l l y a r e d ia m a g n e tic . The M agnetic Study o f th e P ro d u c t o f th e Non-Hydrogenlc R e a c tio n A stu d y o f th e m ag n etic p r o p e r t i e s of th e p ro d u c t o f th e n o h -h y d ro g en lc r e a c t i o n was r e s t r i c t e d by s e v e r a l 1 S u p ra . , pp. 2 ^ -2 ? . 63 f a c t o r s . The sam ple had to be p re p a re d In th e same tu b e In which th e m agnetic m easurem ents were to be made, s in c ^ a t r a n s f e r o f th e s o lu t io n would p ro b a b ly r e s u l t in decom p o s i t i o n and am m onolysis. I t was im p e ra tiv e t h a t th e s o lu t io n be m a in ta in e d a t a te m p e ra tu re below - 75° C to a v o id am m onolysis. For f r e e su sp e n sio n in th e magnet th e maximum p e rm is s a b le o u te r d ia m e te r o f th e tu b e c o n ta in in g « th e sam ple was 8mm, g r e a t l y ham pering th e th o ro u g h m ixing o f th e s o l u t i o n . I t was im p o rta n t t h a t no w a te r be p e r m itte d t o condense on th e sample tu b e , s in c e i t would a f f e c t th e o b se rv e d m ag n etic p r o p e r t i e s . An a p p a ra tu s was d e sig n e d to s a t i s f y a l l o f th e s e re q u ire m e n ts . A p p a ra tu s . The a p p a ra tu s d e sig n e d f o r th e m agnetic m easurem ents i s shown in F ig u re s i?A t o 6C. The sam ple of th e p ro d u c t o f th e n o n -h y d ro g en ic r e a c t i o n was p re p a re d by means o f th e a p p a ra tu s o f 6a . An a c c u r a te ly w eighed amount o f m e t a l l i c sodium was in tro d u c e d i n t o A, in a d ry hydrogen atm o sp h ere, th ro u g h tu b e B, a c c o rd in g t o th e method o f S c h le s in g e r and B u rg .2 The a p p a ra tu s was th e n e v a cu a ted and a sm a ll volume o f ammonia was condensed in to A form ing a c o n c e n tr a te d s o lu tio n o f sodium i n l i q u i d ammonia. A m easured e x c e ss o f te tra m e th y ld ib o ra n e was th e n condensed above i t by means o f l i q u i d n itr o g e n . At t h i s p o in t th e m a g n e tic a lly o p e ra te d s t i r r e r C was low ered t o th e s o l i d ^ 3upra. p . 13. - ........ A P P A R A T U S FOR THE P R E P A R A T I O N OF T H E N O N -H Y D R O G EN IC R EACTION P R O D U C T FOR MAGNETIC M EASUREMENTS. FIGURE 6A FIGURE 6B FIGURE 6C 65 ammonia, and th e system was p la c e d in an e t h e r b a th main t a in e d betvreen -75 a nd -77°G . As th e ammonia m e lte d th e s t i r r e r dropped t o th e b o tto m o f tu b e A, and by r a p id ly moving i t up and down th e s o lu t io n was e f f e c t i v e l y s t i r r e d . The s t i r r e r was th e n r a i s e d from th e s o l u t i o n , w hich had become y ello w i n c o l o r , and i t was f a s te n e d i n t o p la c e by means o f th e p lu n g e r E. The s o l u t i o n was th e n f ro z e n by means o f l i q u i d n itr o g e n , and th e sam ple tu b e A was sep a r a t e d from th e r e s t o f th e a p p a ra tu s by s e a lin g a t H. To p e rm it s u sp e n sio n o f th e tu b e in th e m ag n etic f i e l d a lo o p was s e a le d a t th e p o in t o f s e p a r a tio n , as i s Shown in F ig u re $G. The upper end o f th e s t i r r e r G, F ig u re 6>A , had a b u lb D c o n ta in in g a m ag n etic a ln ic o - m e ta l c o r e . Hence th e s t i r r e r was r e a d i l y r a i s e d and lo w ered by means o f p o w e rfu l, b u t s m a ll, perm anent m agnets. The lo w er end o f th e b u lb D was fla n g e d i n such a way t h a t th e m a g n e tic a lly o p e ra te d p lu n g e r E w ould f a s t e n i t i n p la c e s e c u r e ly . To im prove th e e f f i c i e n c y o f th e s t i r r e r , sm a ll g lo b u le s of g la s s were s e a le d along th e low er end t o s e rv e a s f i n s . Throughout th e p r e p a r a t io n o f th e sam ple i t was n e c e ss a ry to p r o t e c t th e sam ple tu b e from th e c o n d e n sa tio n o f atm o sp h e ric m o is tu re . T h is was acco m p lish ed by means o f th e a p p a ra tu s shown in F ig u re £B. T his g la s s ja c k e t f i t o v er tu b e A t o a p o in t J u s t below H, F ig u re $A. The 66 1 u p p er cup J , F ig u re 6B, was packed lo o s e ly w ith g la s s w ool, ; ■ and a stream o f d ry n itr o g e n was p a s se d upx^ards th ro u g h t h i s p a c k in g , p re v e n tin g th e d i f f u s i o n o f m o is tu re in s id e th e J a c k e t. T his Ja c k e t was q u ite e f f e c t i v e in p re v e n tin g th e c o n d e n s a tio n o f m o is tu re , b u t i t was th e so u rc e of c o n s id e r a b le d i f f i c u l t y , f o r th e in n e r tu b e was v e ry slow ' to re a c h th e te m p e ra tu re o f th e s u rro u n d in g s . Hence con d e n s a tio n s w ith l i q u i d n itr o g e n were slow , and th e p ro c e s s ■ o f warming th e system to - 77 °C, t o i n i t i a t e th e r e a c t i o n , i was a ls o v ery slow . ! The m ag n etic m easurem ents^ were made by means o f th e magnet and th e c o o lin g system s c h e m a tic a lly shown i n F ig u re 7 ;A. A s p e c ia l Dewar f l a s k was so c o n s tr u c te d t h a t th e upper p a r t o f th e f l a s k c o n ta in e d a m e ta l b lo c k A, w hich was w rapped w ith c o o lin g c o l l s B. The low er s e c tio n o f th e Dewar was sm a ll i n d ia m e te r, p e r m ittin g I t t o f i t b etw een th e p o le s of th e magnet C. The to p o f th e Dewar was f a s te n e d to th e cap D. There was a h o le down th ro u g h th e e n t i r e a p p a ra tu s w hich p e rm itte d a sample tu b e w ith a d ia m e te r o f 8m m to hang f r e e l y . The rem ovable cap E a t th e bottom o f th e Dewar p e r m itte d th e sam ple t o be drawn 5 The o p e r a tio n o f th e magnet was perform ed by Dr. S. S. D h a rm a tti, w ith th e k in d c o o p e ra tio n o f Dr. W . K. W ilm arth. APPARATUS FOR MAGNETIC STUDIES To Micrpbalance F IG U R E 7A C » FIGURE 7B 68 ; i n t o th e m agnet w ith th e Dewar in p la c e . The u p p er end ! . o f th e a p p a ra tu s was p r o te c te d a g a in s t th e d i f f u s i o n o f ' m o is tu re down in to th e Dewar f l a s k by a stre a m o f d ry ; n itr o g e n and a p p r o p r ia te condensing b a f f l e s . A window in th e Dewar f l a s k p e r m itte d o b s e rv a tio n o f th e sam ple, and p ro p e r a d ju stm e n t o f th e sample tu b e . The sam ple to be s tu d ie d was suspended from a m ic ro b a la n c e lo c a te d d i r e c t l y above th e m agnet. The m agnet was m a in ta in e d a t low te m p e ra tu re s by c i r c u l a t i n g l i q u i d n itr o g e n th ro u g h th e c o o lin g c o i l s B under th e r m o s ta tic c o n t r o l. The sam ple tube was in tro d u c e d i n t o th e magnet a t low te m p e ra tu re s by means o f th e a p p a ra tu s shown in F ig u re $B. A la r g e d ia m e te r g la s s tu b e B was a tta c h e d to th e low er end o f th e magnet Dewar A by means o f a ru b b e r c o n n e c tio n , A stream o f d ry n itr o g e n was th e n p a s se d th ro u g h t h i s tu b e to p re v e n t th e upward d i f f u s i o n o f m ois t u r e in t o th e Dewar f l a s k . Then th e g la s s Ja c k e t C ( a ls o see F ig u re 0 ) c o n ta in in g th e sam ple was p la c e d i n th e p o s i t i o n shown and th e sam ple was drawn i n to th e magnet Dewar. Then, as dry n itr o g e n was s t i l l flo w in g down th ro u g h th e J a c k e t B, th e cap (E o f F ig u re 0A) was p la c e d o v er th e end o f th e Dewar. The J a c k e t B was th e n removed and th e m ag n etic m easurem ents c o u ld be made. Samole P r e p a r a tio n and E x p e rim e n ta l R e s u l t s . The 69 p r e p a r a t io n o f a sam ple o f th e p ro d u c t o f th e n o n -h y d ro g en ic , r e a c t i o n o f sodium and te tra m e th y ld lb o r a n e f o r m ag n etic m easurem ents i s governed by two im p o rta n t re q u ire m e n ts . The te tra m e th y ld lb o ra n e must be in s l i g h t e x c e s s , such t h a t any param agnetism o b se rv e d m ight be a t t r i b u t e d to th e r e a c t i o n p ro d u c t and n o t t o ex cess f r e e sodium. S eco n d ly , th e p ro d u c t must be y e llo w in c o lo r s in c e i t i s t h i s c o lo re d m a te r ia l w hich i s th e o b je c t o f t h i s s tu d y . T his second re q u ire m e n t p r e s e n te d c o n s id e r a b le d i f f i c u l t y , f o r : when ex c ess te tra m e th y ld lb o r a n e i s p r e s e n t th e y ello w c o lo r fa d e s slo w ly to c o lo rle ss.* * T his d i f f i c u l t y was overcome by f r e e z in g th e s o l u t i o n w ith l i q u i d n itr o g e n as soon as th e c o lo r change from b lu e to y e llo w was co m plete. The sam ple was th e n p la c e d in th e magnet a t -138°G and th e magnet was warmed slo w ly to -79°G* The m agnetic su sc e p t i b i l i t y was m easured a t th r e e d i f f e r e n t te m p e ra tu re s . The d e t a i l e d r e s u l t s o f t h i s stu d y a re g iv e n i n T able X II I . * ♦ * Supra. . p. 32 70 Table XIII The M agnetic Study o f th e P ro d u c t o f th e Non-Hydrogenic R e a c tio n C o n c e n tra tio n o f th e Na-CCH-aJ^BgEUj R e a c tio n P ro d u c t C r o s s - s e c tio n a l A rea of th e Sample Tube M agnetic F i e l d S tre n g th M agnetic S u s c e p t i b i l i t y M easurem ents. Temp. -138°C -99°C -7900 Change in sample w eight in m ag n etic f i e l d - 6 . 05mg - 5 . 90mg -5.90m g - 6 . 02mg 0 .8 9 m /l 0 . 28cm^ 8917 G-auss C olor o f Sample y ello w y ello w c o l o r l e s s c o l o r l e s s M agnetic S u s c e p t i b i l i t y Measurement on P ure Ammonia ( i n th e same tube)* Temp. -77°C Change in sample w eight in m ag n etic f i e l d -8.*f0mg M olar S u s c e p t i b i l i t y o f th e Sample Xia - 238 x 10“ ^ cgs E le c tro m a g n e tic u n its X jjj (c a lc 'd )-* f o r one u n p a ire d e l e c t r o n a t -7 9 °0 - 1918 x 10“ ° cgs E le c tro m a g n e tic u n i t s 5 P. W . Selwood, M agnetochem lstry (New York: I n t e r - s c ie n c e P u b l i s h e r s , I n c . , 1 9 ^ 3 ), p . 116. 71 D is c u s s io n . The r e s u l t s o f th e m ag n etic m easurem ents show no te m p e ra tu re dependence, as would be e x p e c te d i f th e sam ple were p a ra m a g n e tic . On th e b a s i s o f th e m agnetic p r o p e r t i e s o f th e ammonia sam ple, th e r e s u l t s a p p e a r to in d ic a t e a param agnetism c o rre sp o n d in g to a p p ro x im a te ly 1 2 .5 p e r c e n t o f one u n p a ire d e l e c t r o n p e r mole o f r e a c t i o n p ro d u c t. However, t h i s amount o f m agnetism i s q u i t e sm a ll and m ight w e ll be a t t r i b u t e d to th e e f f e c t o f a d ia m a g n e tic s o lu t e on a d ia m a g n e tic s o lv e n t. The sam ple tu b e c o n ta in in g th e r e a c t i o n p ro d u c t a ls o c o n ta in e d b i t s of b ro k en g l a s s , from th e sodium b u lb , w hich would a f f e c t th e r e s u l t s t o a s m a ll, though u n d eterm in ed , am ount. Hence th e s e r e s u l t s a lo n e a r e n o t s u f f i c i e n t to show th e s o lu t e t o be p a ra m a g n e tic . The e f f e c t o f th e l o s s o f c o lo r by th e sam ple on th e m ag n etic p r o p e r t i e s , how ever, i s more c o n c lu s iv e . The r e s u l t s i n d i c a t e t h a t t h e m agnetic s u s c e p t i b i l i t y o f th e sam ple does n o t change a s th e y ello w s o lu t io n fa d e s t o c o l o r l e s s . T his f a c t , to g e th e r w ith th e o b se rv e d tem pera t u r e independence would i n d i c a t e t h a t th e sample i s d i a m a g n e tic . T h is c o n c lu s io n , th e n , w ould e lim in a te th e th e o ry t h a t th e n o n -h y d ro g en ic r e a c t i o n o f te tr& m e th y l- d ib o ra n e and sodium p ro d u c e s th e odd e l e c t r o n s a l t NaHBiCH^^* On th e b a s i s o f th e s e r e s u l t s , how ever, i t i s s t i l l p o s s i b le t h a t th e r e a c t i o n p ro d u c t i s th e dim er 72 o f th e o d d - e le c tr o n s a l t , which m ight w e ll he i n e q u i l i brium w ith a v e ry sm a ll amount o f th e monomer. A R e a c tio n S e r ie s A ccounting f o r th e F o rm atio n o f NaoHBCCH^)^ An u n d e rs ta n d in g o f th e n a tu re o f th e n o n -h y d ro g en ic r e a c t i o n o f te tr a m e th y ld lb o r a n e i s o f c o n s id e r a b le impor ta n c e . The e x p e rim e n ta l o b s e r v a tio n s , form ing th e b a s is o f a r e a s o n a b le i n t e r p r e t a t i o n o f th e r e a c t i o n a s a s e r i e s o f s t e p s , a r e summ arized a s f o llo w s . 1 1 . I n th e i n i t i a l r e a c t i o n , w hich o c c u rs a t - 7 ,^) C» no m easu rab le volume of hydrogen i s p ro d u ced o v er a p e r io d o f s e v e r a l h o u rs . 2. The trim e th y la m ln e d isp la c e m e n t p ro c e s s rem oves a l l b u t one mole o f ammonia p e r mole o f te tra m e th y ld lb o ra n e ; t h i s rem ain in g ammonia e v id e n tly i s f ir m ly bonded. 3. The s to ic h io m e tr y o f th e i n i t i a l r e a c t i o n a t -77°C in v o lv e s one mole o f te tra m e th y ld lb o r a n e and two m oles o f sodium . The o v e r - a l l s to ic h io m e tr y p e rm its o n ly o n e - h a lf o f th e te tra m e th y ld lb o r a n e t o be used i n th e fo rm a tio n o f Na2HB( th e r e s t form s (CH^^BNHg s im u lta n e o u s ly w ith th e p r o d u c tio n o f one mole o f hydrogen a t 25°C. k. The r e a c t i o n p ro d u c ts a t -77°0 a r e d ia m a g n e tic . 5. A ll o f th e f i n a l p r o d u c ts a r e v o l a t i l e a t room te m p e ra tu re e x c e p t Na2HB(GH^)2 « 73 6. The f i n a l p r o d u c t, Na2HB(GH^)2 » can be o b ta in e d , b u t o n ly In an impure c o n d itio n , when th e trim e th y la m in e d isp la c e m e n t p ro c e s s i s o m itte d . 7. When th e trim e th y la m in e d isp la c e m e n t p r o c e s s i s u se d , th e p ro d u c ts r e t a i n one to th r e e m oles o f t r i m e t h y l amine a t - 50°G, p r i o r to th e th e rm a l d e c o m p o sitio n , b u t none i s r e t a i n e d a t 25°C. 8. Pure Na2HB(GH-j)2 form s an am m oniate, s t a b l e in .vacuo a t room te m p e ra tu re , b u t c o n ta in in g a l i t t l e more ammonia th a n a o n e -to -o n e r a t i o would demand. 9 . The l a s t t r a c e o f d im e th y l e t h e r , u sed a s a s o lv e n t f o r Na2HB(GH^)2 » i s n o t r e a d i l y removed from th e p r o d u c t, even a t room te m p e ra tu re ; m ethyl e t h e r p a r t i a l l y d is p l a c e s th e ammonia from th e p ro d u c t when th e trim e th y la m in e d i s p la cem en t p r o c e s s i s o m itte d . 10. At no tim e i n t h i s p ro c e s s i s any m ethane produced. 11. The c o lo r o f th e ammonia s o l u t i o n o f th e p ro d u c ts o f th e i n i t i a l r e a c t i o n i s y e llo w , i d e n t i c a l i n ap p earan ce to an ammonia s o lu t io n o f Na2HB(GH^)2 ; th e ammonia s o lu t io n o f Na2HB(GH^)2 i s s ta b le to w ard am monolysis a t - 7 5 ° C. 12. When a sm a ll e x c e ss of te tra m e th y ld ib o r a n e i s added to a sodium s o lu t io n i n l i q u i d ammonia, th e s o lu t io n becomes y ello w — th e n fa d e s to c o l o r l e s s . A lso , when a known s o lu t io n o f Na2HB(CH^)2 in l i q u i d ammonia i s t r e a t e d w ith te tr a m e th y ld ib o r a n e , th e y ello w c o l o r fa d e s o u t. ?k 13. When trlm e th y lb o r o n i s added s im u lta n e o u s ly w ith th e te tr a m e th y ld ib o r a n e to sodium in l i q u i d ammonia, th e f i n a l p ro d u c t o f th e n o n -h y d ro g en ic r e a c t i o n has th e fo rm u la Na2HB(CH3 )2 *B(CH^)^, and i s s t a b l e a t room tem pera t u r e ; t h i s c o rre sp o n d s to th e p ro d u c t o f th e r e a c t i o n o f Na2HB(0H^)2 w ith trlm e th y lb o ro n i n ammonia s o l u t i o n . l*f. T rlm eth y lb o ro n does n o t r e a c t w ith sodium in l i q u i d ammonia to form t h e h y p o th e tic a l compound Na2B(GH^)^, an alogous to Na2HB(CH3 )2 « The i n i t i a l , r e a c t i o n o f te tra m e th y ld ib o r a n e w ith sodium does n o t produce hydrogen ( o b s e r v a tio n l ) . S ince te tr a m e th y ld ib o r a n e i s e l e c t r o n d e f i c i e n t , t h i s r e a c t i o n m ight be e x p e c te d to be one o f a d d i t i o n . The s to ic h io m e try o f th e r e a c t i o n ( o b s e r v a tio n 3) would a p p e a r to su p p o rt t h i s h y p o th e s is , f o r th e a n io n p a r t o f th e h y p o th e tic a l a d d itio n p r o d u c t, Na2( w e l l have a s t a b i l i t y s i m i l a r to t h a t o f i t s l s o e l e c t r o n i c analogue 2 , 3 -d lm e th y l- b u ta n e . The in te n s e y e llo w c o lo r o f t h i s s o l u t i o n m ight be i n t e r p r e t e d to i n d i c a t e th e d i s s o c i a t i o n o f t h i s p o s tu l a t e d a d d i tio n compound to form th e f r e e - r a d i c a l io n ([(CH^BHj. M agnetic m easurem ents, how ever, i n d i c a t e t h a t t h i s o d d - e le c tr o n compound i s not p ro d u ced i n s u f f i c i e n t q u a n tity t o be d e te c te d ( o b s e r v a tio n k ) . On th e o th e r hand, th e su b se q u en t o b s e r v a tio n s , p a r t i c u l a r l y item s 11, 12 and 13 seem to I n d ic a te c l e a r l y t h a t i s 75 one o f th e p ro d u c ts o f th e n o n -h y d ro g e n ic r e a c t i o n a t i - 77°G. Hence i t ap p e a rs t h a t t h i s r e a c t i o n cannot be : i n t e r p r e t e d a s th e sim p le a d d itio n o f sodium to te tr a m e th y l d ib o ra n e . S in ce only o n e - h a lf o f th e te tra m e th y ld ib o r a n e i s p r e s e n t i n th e r e a c t i o n p ro d u c ts a s NagHBtGH3 Jg, th e rem a in d er f i n a l l y a p p e a rin g as (GH3 )2BNH2 ( o b s e r v a tio n 3 ), i t seems l i k e l y t h a t th e n o n -h y d ro g e n ic r e a c tio n p ro d u ces eq u im o la l am ounts of NagHBCCH^Jg and th e d im e th y Ib o rin e , ammonlate (CH^JgHBNH^. T h is ammine com plex, th e n , a p p a re n tly i u ndergoes th e rm a l d e c o m p o sitio n , o r am m onolysis, a t room te m p e ra tu re . The fo llo w in g e q u a tio n s would r e p r e s e n t th e s e r e a c t i o n s . -770<3 2Na + • (CH3 )^B2Hg + NH3 ------- » Na2HB(GH3 )2 + (G H j^H B N ^ ( I ) ( CH3 ) 2HBNH3 (CH3 )2BNH2 + h2 ( I I ) I t a p p e a rs t h a t th e s e e q u a tio n s b e s t e x p la in th e e x p e rim e n ta l e v id e n c e , s in c e th e a l t e r n a t i v e s in v o lv e s t r a i n e d assu m p tio n s. The fo rm a tio n o f an ammonia s o lv a te o f Na2HB(CH3 ) 2 m ight w e ll be a t t r i b u t e d to weak hydrogen bonding t o boron th ro u g h th e u n sh ared e l e c t r o n p a i r , a s w e ll a s i n d e f i n i t e and r e l a t i v e l y weak am m onlation o f th e sodium io n s . T his p o s tu l a te d hydrogen-bonded s o lv a te w ould have th e fo llo w - r og3 h n -2 in g e l e c t r o n i c c o n f ig u r a tio n : ^CH3 : | : H:N:Hj . T h is p o s t u l a t e i s su p p o rte d by th e o b s e rv a tio n t h a t tr i m e t h y l amine d isp la c e m e n t removes th e ammonia o f s o lv a tio n , y e t 76 no trim e th y la m in e i s r e t a i n e d by th e s a l t a t room te m p era- I i 1 t u r e ( o b s e r v a tio n 8 ). I t i s n o t p o s s i b le f o r trim e th y la m in e to form a hydrogen bond t o th e b o ro n , and hence th e r e l a t i v e s t a b i l i t y o f th e two s o lv a te s i s u n d e ra ta n d a b le in term s o f t h i s h y p o th e s is . The ease by w hich trim e th y la m in e i s a b le to remove th e ammonia from th e ammonlate i s o f i n t e r e s t . I n th e d isp la c e m e n t p r o c e s s , a la r g e ex c e ss o f trim e th y la m in e i s alw ays p r e s e n t. The system i s allo w ed to s ta n d f o r s e v e r a l h o u rs f o r an e q u ilib r iu m d i s t r i b u t i o n o f ammonia betw een th e s a l t and th e trim e th y la m in e . S in ce trim e th y la m in e h a s no s tr o n g a tta c h m e n t to Na2HB(CH^)2 , th e d r iv in g f o r c e f o r th e d isp la c e m e n t would ap p e ar t o be due to th e a b i l i t y o f trim e th y la m in e to hydrogen-bond th e ammonia i n c o m p e titio n w ith th e NagHBCCH^^. S in ce Na2HB(0H^)2 i s n o t s o lu b le in trim e th y la m in e and th e amrao- n i a t e i s s u f f i c i e n t l y s o lu b le to Im p art a v ery p a le y ello w c o lo r to th e trim e th y la m in e , th e a c tio n o f trim e th y la m in e would p ro b a b ly d is p la c e th e b a la n c e o f l a t t i c e f o r c e s in f a v o r o f th e s o l i d Na2HB(GH^)2 * S p e c u la tio n oh th e Mechanism o f th e Non-H ydrogenic R e ac tio n I t w ould be d e s i r a b l e to know more ab o u t th e mechanism o f t h i s n o n -h y d ro g e n ic r e a c t i o n . K in e tic s tu d ie s do n o t a p p e a r to be f e a s i b l e a t p r e s e n t , due t o th e c o n d itio n s u n d er which th e r e a c t i o n ta k e s p la c e . S p e c tro s c o p ic 77 s t u d i e s m ight he u s e f u l in t h i s r e s p e c t , h u t s p e c i a l a p p a ra tu s would be n e c e s s a r y , and an I n t e r p r e t a t i o n o f th e r e s u l t s o f such a stu d y would he v ery d i f f i c u l t . I n th e ab sen ce o f such In fo rm a tio n , s e v e r a l mechanisms a p p e a r to he r e a s o n a b le i n view o f su ch d a ta a s a r e a v a i l a b l e . In th e s e c o n s id e r a ti o n s , th e s t r u c t u r e s o f th e r e a c t a n t s must be c o n s id e re d . I t h as been d e m o n stra te d by m ag n etic s t u d i e s t h a t i n s o lu t io n s o f a l k a l i m e ta ls in l i q u i d ammonia, th e e l e c t r o n s a r e l a r g e l y p a i r e d , e x c e p t . a t v e ry low c o n c e n tr a t io n s .^ T e tra m e th y ld ib o ra n e i s e l e c t r o n d e f i c i e n t , and i t i s ex p e cte d to be s t r u c t u r a l l y s i m i l a r to d lb o ra n e . Hence th e s t r u c t u r e o f te tr a m e t h y l d ib o ra n e i s p ro b a b ly b e s t r e p r e s e n te d by th e f o llo w in g gh3n ,-H'. / h3 g r a p h ic fo rm u la : /B . B . I n t h i s fo rm u la th e gh3 '-H'' ch3 d o tte d l i n e s r e p r e s e n t w h a lf - b o n d s M , ' where a s i n g l e p a i r o f e l e c t r o n s o c c u p ie s bond o r b i t a l s o f th r e e d i f f e r e n t atom s. In view o f th e s e c o n s id e r a tio n s i t seems t h a t th e r e a c t i o n o f sodium w ith te tr a m e th y ld ib o r a n e can ta k e one o f two g e n e ra l p a th s . I n th e f i r s t , th e e l e c t r o n s from th e s o lu t io n would add d i r e c t l y t o te tr a m e th y ld ib o r a n e , b S. F re ed and N. Sugarman, J . Ghem. Phys. 11, 3 5 ^ 6 0 ( 1 9 W . 7 R. E. R undle, J . Am. Ghem. Soc. 6£, 1327 (19^-7)• 78 p ro d u c in g an a n io n which w ould be i s o e l e c t r o n i c w ith 2,3-<iiin® thylbutane. T his an io n m ight th e n r e a c t w ith th e s o l v e n t , th ro u g h un sy m m etrical d i s s o c i a t i o n , p ro d u cin g (OH^JgHBNH-^ and th e new s a l t Na2HB(CH^)2 * The second g e n e ra l p a th t h a t t h i s r e a c t i o n c o u ld ta k e would c o r r e l a t e th e e l e c t r o n a d d i tio n by means o f th e b ase a c t i o n o f th e s o lv e n t ammonia, and th e a d d itio n o f th e e l e c t r o n s s u p p lie d by th e sodium m e ta l. I t i s not p o s s i b l e , I n t h i s c a s e , t o re a c h a d e c is io n a s t o w h eth er th e i n i t i a l r e a c t i o n would be due t o th e a d d i tio n o f ammonia, o r th e e l e c t r o n s from th e s o l u t i o n . I t may w e ll be t h a t th e s o lv a te d e l e c t r o n s , c o n ta in in g b o th th e s o lv e n t ammonia and th e e l e c t r o n s from th e sodium m e ta l, r e a c t s im u lta n e o u s ly , c le a v in g te tra m e th y ld ib o r a n e i n t o th e f i n a l p r o d u c ts , (GH3 )2HBNH3 jHB( CH3 )2J . However, in o r d e r to v i s u a l i z e th e s e p a r a te a s p e c ts o f such a r e a c t i o n , th e fo llo w in g e q u a tio n s a r e w r i t t e n , a r b i t r a r i l y s e l e c t i n g th e a d d i tio n o f th e s o l u t e e l e c t r o n s a s th e f i r s t s te p . 2 - e 2 *xNH3 t* CHq. ,'H'. GH? 3> ' B. 3 G H - ■H'' CH' 0H3v . Hs GH3 jGHj ''H ''' NCH3 j t XNH3 ( I I I ) C H / G H - + nh3 CH- G H * J - h v / jh, B HoN ' XCH, (IV) In th e ab sen ce o f s u p p o rtin g ev id en ce t h i s s p e c u la tio n can n o t have m eaning o th e r th a n to show t h a t a r e l a t i v e l y 79 ‘ sim p le r e a c t i o n mechanism can be found f o r th e non- h y d ro g e n ic r e a c t i o n , e x p la in in g th e c le a v a g e o f (CH^J^BgHg i n t o eq u lm o la r p r o p o rtio n s o f d i f f e r e n t p r o d u c ts . The Mechanism o f Ammoniatlon o f T e tra m e th y ld ib o ra n e A stu d y o f th e r e a c t i o n o f sodium w ith te tr a r a e th y l - d lb o ra n e in l i q u i d ammonia a ls o in v o lv e s th e s o lv e n t ammonia and am m oniatlon r e a c t i o n s . The dlam m oniate o f te tr a m e th y l d ib o ra n e h as b een shown to e x i s t a s th e ammonium s a l t mechanism o f fo rm a tio n o f t h i s s a l t i s n o t known, and k i n e t i c s t u d i e s o f t h i s r e a c t i o n do n o t a p p e a r to be f e a s i b l e a t p r e s e n t . A knowledge o f th e e x p e c te d In te r m e d ia te compounds, how ever, can se rv e to show w h eth er a p o s tu l a te d mechanism m ight re a s o n a b ly e x p la in th e o b serv ed am m oniatlon r e a c t i o n . The am m oniatlon o f te tra m e th y ld ib o ra n e i s a slow p r o c e s s , r e q u i r i n g an opening o r c le a v in g o f th e h y d ro g en - b rid g e bon d s. There a re two g e n e ra l p a th s t h i s r e a c t i o n can ta k e . One would In v o lv e th e c le a v a g e of te tr a m e th y l d ib o ra n e i n t o two s e p a r a te p a r t s , w hich would th e r e f o r e p ro d u ce ( CH^) gHBNH^ a s an in te r m e d ia te . The o th e r p a th would in v o lv e th e cleav a g e of th e h y d ro g e n -b rid g e bonds o f te tr a m e th y ld ib o r a n e , w ith o u t co m plete s e p a r a tio n of 8 Supra. . p . 19. 80 th e d im e th y lb o rin e g ro u p s. ; A ccording to th e r e s u l t s o f th e stu d y of th e non- ' h y d ro g e n ic r e a c t i o n o f te tr a m e th y ld ib o r a n e and sodium in l i q u i d ammonia, th e ammlne complex (CH^^HBNH^ i s produced a t -77°0«^ T h is com plex, how ever, does not r e a c t w ith th e sodium w hich i s p r e s e n t i n e x c e s s , even o v er a p e r io d o f s e v e r a l h o u rs . I f t h i s complex were an in te rm e d ia te in th e am m oniatlon o f te tr a m e th y ld ib o r a n e , i n ac co rd an c e w ith one o f th e s u g g e s tio n s above, th e n th e ammonium io n would be produced i n t h i s sy ste m , and th e h y d ro g e n ic r e a c t i o n w ith sodium would be o b s e r v e d . H e n c e I f e q u a tio n I Is a v a l i d r e p r e s e n t a t i o n o f th e n o n -h y d ro g e n ic r e a c t i o n of te tr a m e th y ld ib o r a n e and sodium , th e ammine complex ( C H <5) cannot be an in te r m e d ia te i n th e am m oniatlon r e a c t i o n o f te tra m e th y ld ib o r a n e . A c o n s id e r a tio n o f th e p o s s ib le mechanism o f am m oniatlon w hich does n o t in v o lv e th e fo rm a tio n o f th e - d im e th y lb o rin e ammlne complex i s o f i n t e r e s t , a lth o u g h i t m ust b e b a s e d e n t i r e l y upon s p e c u la tio n . The i n i t i a l s te p in t h i s p ro c e s s would p ro b a b ly in v o lv e th e c le a v a g e o f one o f th e h y d ro g e n -b rld g e bonds o f te tra m e th y ld ib o r a n e by th e 9 S u p ra . . p . 75» e q u a tio n I . S u p ra . . p . 19* 81 b a se a c tio n of th e ammonia. In t h i s p r o c e s s , th e a s s o c ia tio n o f th e s o lv e n t a p p e ars to b e q u ite im p o rta n t. The a d d i tio n o f ammonia as an a s s o c ia te d g ro u p o f ammonia m o le c u le s, fo llo w e d by th e d i s s o c i a t i o n o f t h i s i n t e r m e d iate p ro d u c in g th e ammonium io n w ould a p p e ar to be q u ite re a s o n a b le . T h is s u g g e s te d p ro c e s s i s in d ic a t e d i n th e fo llo w in g e q u a tio n s . GH« -H \ CHo 3;B fe' 3 + (NH,) OH3 N CH^ H H CHo\ M H:N:H : NsH 3 e r •• h G H , ' H — B — CHr I GH 3 (V) H H: fi: CHov H CH3 h - - - b - g h 3 I CH3 H H :N:H fi CHo .H 3X GHo H :N:H I • ' H — B — G H < I CHo (VI) The p ro d u c t o f e q u a tio n V I, above, w ould be e x p e c te d to r e a r r a n g e r e a d i l y in to th e f i n a l form o f th e am monlated te tra m e th y ld ib o r a n e , due t o th e b a s i c i t y o f th e amine group o f th e a n io n . T his re a rra n g e m e n t i s r e p r e s e n te d by th e fo llo w in g e q u a tio n . NH/* CH3 ^ H H “ * " H — B —CH. I CH 3 NH^ H ) H G H G H 3 -B I 1 N-B k 1 1 CH 3 H H 3 - •CHo (V II) The mechanism s u g g e s te d by e q u a tio n s V, VI and VII 82 a p p e a rs to be re a s o n a b le In view of a l l o f th e a v a i l a b l e ;in fo rm a tio n co n c ern in g t h i s system . However, i t i s b ased upon s p e c u la tio n , and th e r e a r e , w ith o u t d o u b t, o th e r mechanisms in agreem ent w ith th e e x i s t i n g d a t a , which c o u ld be s u g g e ste d e q u a lly w e ll. N e v e rth e le s s th e s e con s i d e r a t i o n s show t h a t th e am m oniatlon p ro c e s s can o cc u r by a sim ple mechanism w hich does n o t in v o lv e th e ammlne com plex, ( CH3 )gHBNH^, as an in te r m e d ia te . CHAPTER V FUTURE STUDIES CONCERNING Na2HB(CH3 >2 The s tu d y o f th e b e h a v io r o f te tr a m e th y ld ib o r a n e tow ard sodium i n l i q u i d ammonia i s a p io n e e r r e s e a r c h program , and th e r e s u l t s d e s c r ib e d i n t h i s d i s s e r t a t i o n r e p r e s e n t o n ly th e f i r s t s ta g e s . T his r e s e a r c h h as been co n cern ed w ith th e n o n -h y d ro g e n ic r e a c t i o n of te tr a m e t h y l d ib o ra n e w ith sodium , when sodium i s i n e x c e s s , and w ith th e new compound Na2HB(CH3 ) 2 , which i s a p ro d u c t of t h i s r e a c t i o n . T here a r e y e t many problem s in t h i s f i e l d w hich w a rra n t f u r t h e r s tu d y . Due to th e u n u su al b e h a v io r o f th e bo ro n compounds, w hich a re th e o b je c t of t h i s stu d y , i t i s n o t p o s s i b l e t o a n t i c i p a t e many o f th e s p e c i f i c problem s in advance. However, on th e b a s i s o f th e r e s u l t s w hich have been o b ta in e d , a number o f e x p e rim e n ta l s tu d i e s a p p e a r to be q u i t e im p o rta n t. The P r e p a r a tio n o f Na?HB(0H3 ) 2 . The p r e p a r a tio n p ro c e s s f o r sm a ll sam ples o f Na2HB(CH3 ) 2 i s r a t h e r te d io u s , b u t q u ite p r a c t i c a l . However, due to th e n e c e s s a ry low te m p e ra tu re e x t r a c t i o n p r o c e s s , i t i s n o t y e t p r a c t i c a l to p r e p a r e la r g e sam ples in t h i s m anner. I t i s p o s s i b le t h a t much may be le a r n e d ab o u t Na2HB(CH3 )2 by p r e p a r in g la r g e sam ples w ith o u t th e e x t r a c t i o n p r o c e s s , b u t th e p re se n c e o f th e e x c e ss amount o f sodium would alw ays in tr o d u c e a v a r i a b l e o f unknown e f f e c t . Much tim e h as a lre a d y been d e v o te d to t h e p r e p a r a t io n p r o c e s s , b u t th e need o f an im proved p ro c e s s i s o f s u f f i c i e n t Im portance to w a rra n t even more a t t e n t i o n i n th e f u t u r e . The N on-H ydrogenlc R e a c tio n when T e tra m e th y ld ib o ra n e i s in E x c e ss. The n o n -h y d ro g e n ic r e a c t i o n o f te tr a m e t h y l d ib o ra n e w ith sodium , when te tra m e th y ld ib o r a n e i s i n e x c e ss h a s n o t b een s tu d ie d f u l l y b ecau se when a tte m p ts w ere made to p re p a r e HagHBCCH^)^ u n d er th e s e c o n d itio n s , t h e a n a ly s e s o f th e f i n a l p ro d u c ts d id n o t ag ree w ith t h a t o f t h i s new compound. However, i t now a p p e ars t h a t th e o r i g i n a l r e a c t i o n o f te tr a m e th y ld ib o r a n e w ith sodium a t - ? 7°C p ro duces NagHBCCH^^ (y e llo w i n l i q u i d ammonia). T h is p ro d u c t, th e n , a p p a re n tly r e a c t s w ith th e e x c e ss te tra m e th y ld ib o r a n e , d is c h a r g in g th e y e llo w c o l o r o f th e s o l u t i o n , in a manner w hich h as n o t been d e te rm in e d .^ T h e re fo re , t h i s a s p e c t o f th e problem seems to co n cern th e p r o p e r t i e s o f Na2HB(CH^)2 r a t h e r th a n th e n o n -h y d ro g e n ic r e a c t i o n o f te t r a m e t h y l d ib o ra n e w ith sodium . I t i s n o t y e t p o s s i b le to d e te rm in e w h eth e r th e r e a c t i o n in v o lv e s th e b a se a c t i v i t y of Na2HB(CH^)2 , o r th e h y d rid e p o t e n t i a l o f t h i s s a l t , a lth o u g h i t would a p p e ar t h a t i t sh o u ld I l l u s t r a t e th e b a se p r o p e r t i e s o f Na2HB(0H^)2 , s in c e i t ta k e s p la c e in 1 Supra. . o . 73, Item 12. 85 l i q u i d ammonia. 2 I f so , i t m ight be p o s t u l a t e d t h a t th e p ro d u c t o f t h i s r e a c t i o n would have t h i s fo rm u la Na£{HB(0H^)2 ] 2 * a n a l y s i s of th e p ro d u c t o f t h i s r e a c t i o n , how ever, i n d i c a t e s t h a t t h i s p o s t u l a t e i s n o t c o r r e c t , f o r th e p r o d u c tio n o f d lm e th y lb o ric a c id in h y d r o ly s is does n o t exceed one mole f o r each two m oles o f sodium .^ T h e re fo re i t seems t h a t a th o ro u g h stu d y of t h i s system i s needed. The Base P r o p e r t i e s o f NagHEKOH^g . The b a se a c t i v i t y o f Wa2HB(0H^)2 h as been d e m o n stra te d by i t s r e a c t i o n w ith tr lm e th y lb o ro n i n l i q u i d ammonia.^ I t would be o f con s i d e r a b l e v a lu e to e x te n d t h i s stu d y t o o th e r L e w is-ty p e a c id s . The s e l e c t i o n o f such a c id s i s r e s t r i c t e d by th e g r e a t re d u c in g s t r e n g t h o f There a r e r e l a t i v e l y few compounds w hich a re p o t e n t i a l a c id s , y e t can n o t be re d u c e d o r H h y d rld iz e d " by t h i s new compound. Some such compounds have b een chosen f o r c o n s id e r a ti o n i n t h i s r e s p e c t . 1 . P hosphorus h a s d e m o n stra te d t h a t i t s o c t e t can be exceeded in compound fo rm a tio n . Hence i t a p p e ars t h a t p h o sp h in e (PH^) m ight d is p la y a c id ic p r o p e r t i e s to w ard 2 S u p ra . . p p . 60- 6 1 . 3 S u p ra . , T able V I, p . 33• ^ S u p ra . . pp. 60- 6l . 86 Ma2HB(CH^)2 . However p h o sp h ln e i s more p r o to n ic th a n ammonia and p ro b a b ly would r e a c t w ith Na2HB(CH^)2 to p r o duce hydrogen. T h e re fo re m e th y l-p h o sp h ln e (C H ^P ^) would a p p e a r to be more d e s ir a b le f o r t h i s s tu d y . S in ce m e th y l- p h o sp h in e i s more b a s i c th a n p h o sp h ln e , how ever, i t would n o t be a s good an e l e c t r o n a c c e p to r . On th e o th e r hand, i f th e b a se s tr e n g t h o f Na2 HB(0H^ )2 i s as g r e a t a s h as been a n t i c i p a t e d , th e a c c e p to r p r o p e r t i e s o f m ethyl p h o sp h ln e m ight w e ll be d e m o n stra te d . T h e re fo re th e stu d y o f th e b e h a v io r o f Na2HB(CH^)2 tow ard each o f th e s e p o t e n t i a l L e w is-ty p e a c id s ap p e a rs t o be o f c o n s id e r a b le i n t e r e s t . 2. T rim e th y l aluminum Al(OH^)^ w hich e x i s t s as th e d im e r,5 sh o u ld show good a c i d p r o p e r t i e s . Hence i t would be ex p ected to r e a c t w ith Na2HB(CH^)2 i n much th e same manner a s trlm e th y lb o r o n . 3 . Aluminum b o ro h y d rld e Al(BH^)3 m ight c o n c e iv a b ly d e m o n stra te a c i d p r o p e r t i e s to w ard th e b a se Na2HB(CH^)2 . Ammonia adds to aluminum b o ro h y d rld e to form th e s t a b l e £ com plex Al(BHij,)3 *NH^. As t h i s complex i s warmed, i t decomposes i n a complex m anner. Hence th e r e a c t i o n o f Na2HB( C H ^^ w ith th e ammonlate o f aluminum b o ro h y d rld e m ight w e ll in v o lv e b o ro h y d rld e d is p la c e m e n t. N e v e rth e le s s K. S. P i t z e r and H. S. Gutowsky, J . Am. Chem. Soc. 6 8, 220^ (19^6). ^ H. I . S c h le s in g e r . R. T. S anderson and A. B. Burg, J . Am. Chem. Soc. 62, 3^2 (1 9 ^ 0 ). 8? 'the r e s u l t s of t h i s s tu d y sh o u ld be o f I n t e r e s t . The H ydride P o t e n t i a l o f Na^HBtCH^) o • The ^ h y d r id ie '1 n a tu r e o f NagHBtCJL^ may u lti m a t e ly p ro v e to b e t h e most ' Im p o rta n t p r o p e r ty o f t h i s new s u b s ta n c e . I t h a s b een d e m o n stra te d t h a t NagHBtCH^^ i s a more p o te n t so u rc e o f h y d rid e th a n th e a l k a l i h y d rid e s in m eth y l e t h e r , a lth o u g h th e i n s o l u b i l i t y o f th e h y d rid e s a l t s i s c e r t a i n l y a f a c t o r h e r e . I t i s c o n c e iv a b le t h a t some h y d r i d i z a t i o n r e a c t i o n s m ight be a c c o m p lish ed by means of N a^B CQ H ^^ w hich a re n o t p r a c t i c a l w ith o th e r so u rc e s o f h y d rid e such a s th e a l k a l i h y d r id e s , th e a l k a l i aluminum h y d r id e s , o r th e b o ro h y d rid e s . The developm ent o f t h i s phase o f th e c h e m istry o f how ever, w i l l depend upon th e a v a i l a b i l i t y o f t h i s s u b s ta n c e in q u a n t i t i e s much g r e a t e r th a n can be had a t p r e s e n t . The p ro p o sed e x p e rim e n t, in w hich th e r e a c t i o n p ro d u c t o f Na2HB(CH-j)2 and d ib o ra n e i s to be t r e a t e d w ith aluminum c h l o r i d e , 1 ? i s co n cern ed w ith t h i s a s p e c t o f th e c h e m istry o f Na2HB(CH<^)2 . I f t h i s ex p e rim en t p ro d u ces aluminum b o ro - h y d rid e , i t w i l l d e m o n stra te t h a t th e r e a c t i o n o f d ib o ra n e w ith Na2HB(GH^ ) 2 p ro d u ces sodium b o ro h y d rld e . T h e re fo re I t c o u ld f u r n is h good ev id en ce t h a t th e r e a c t i o n o f d ib o ra n e w ith Na2HB(GH^ ) 2 in v o lv e s th e h y d rid e a c t i v i t y o f t h i s new 7 Supra. . p p . 88 s a l t . O th er compounds w hich m ight r e a c t w ith Na2HB(CH^ ) 2 b ec a u se o f t h i s h y d r id lc p r o p e r ty would In c lu d e t h e o rg a n ic h a l i d e s , b o ro n t r i f l u o r i d e , t i n t e t r a c h l o r i d e , and many o t h e r s . Hence t h i s p r o p e r ty o f Na2HB(CH^ ) 2 m ight w e ll le a d t o good a v a i l a b i l i t y o f some q u ite r a r e hydrogen compounds. The H y p o th e tic a l S u b stan c e NaB( CHo )„. The " h y d r id ic 1 1 r e a c t i o n o f Na2HB(CH<^)2 im p lie s th e p ro d u c tio n o f th e h y p o th e tic a l s u b sta n c e NaB(CH^)2 . S e v e ra l u n s u c c e s s fu l a tte m p ts have been made t o d e m o n stra te th e e x i s te n c e of 8 t h i s compounds However, b e f o re th e h y d r id ic r e a c t i o n o f Na2HB(CH3 ) 2 w ith c h l o r o s i la n e can be c o m p letely d e f in e d , t h i s a s p e c t o f th e r e a c t i o n m ust be c l a r i f i e d . Hence i t a p p e a rs t h a t t h i s stu d y i s q u i t e Im p o rta n t. The N on-H ydrogenic R e a c tio n o f Sodium w ith th e A nalogs o f T e tra m e th y ld ib o ra n e . I t h a s been o b se rv e d by Dr. A. B. Burg^ t h a t , when d ib o ra n e was b u b b le d th ro u g h a s o l u t i o n o f sodium in l i q u i d ammonia, l e s s hydrogen was p ro d u ced th a n was e x p e c te d on th e b a s i s of th e h y d ro g e n ic r e a c t i o n o f sodium w ith t h e diam m onlate o f d ib o ra n e . T his o b s e rv a tio n I n d ic a te s t h a t i t may be p o s s i b le to p r e p a re th e h y p o t h e t i c a l su b sta n c e Na2BH-j. Hence i t seems to be Q S u p ra . . pp. 38-39. 9 A. B. B urg, P r i v a t e Communication. 89 : v ery im p o rta n t to i n v e s t i g a t e t h i s system more th o ro u g h ly . A stu d y of th e r e a c t i o n o f sy m m etrical d im e th y ld ib o ra n e i would a ls o h e o f v a lu e i n t h i s r e s p e c t . CHAPTER VI SU M M A RY AND CONCLUSIONS This stu d y of th e r e a c t i o n o f te tr a m e th y ld ib o r a n e w ith sodium in l i q u i d ammonia and th e p ro d u c ts d e riv e d from t h i s r e a c t i o n , h as e f f e c t i v e l y opened a new and i n t e n s e l y i n t e r e s t i n g f i e l d o f bo ro n c h e m is try . On th e b a s i s o f th e e x p e rim e n ta l work acco m p lish ed i n t h i s i n v e s t i g a t i o n , th e fo llo w in g c o n c lu s io n s have b een drawn. 1. The dlam m onlate o f te tra m e th y ld ib o r a n e r e a c t s w ith sodium , in l i q u i d ammonia in acco rd an ce w ith th e fo llo w in g e q u a tio n . ch3 ) 2hbnh2bh ( gh3 ) Na jT CH3 ) 2HBNH2BH ( CH3 ) J * NH3 + |-H2 2. I f te tr a m e th y ld ib o r a n e i s added to a s o lu t io n o f sodium in l i q u i d ammonia, a r e a c t i o n t a k e s p la c e a t - 77°C w hich does n o t produce hy d ro g en . On th e b a s i s o f much c o n firm a to ry e v id e n c e , i t h as been d e te rm in e d t h a t t h i s r e a c t i o n i s b e s t r e p r e s e n te d by th e fo llo w in g e q u a tio n . -77°G (CH3 )^B2H2 t 2Na t NH3 Na2HB(CH3 )2 * (CH3 )2HBNH3 When th e ammonia i s removed from th e s e r e a c t i o n p r o d u c ts , and th e r e s id u e i s warmed, th e d im e th y lb o rin e ammoniate decomposes a c c o rd in g to t h e fo llo w in g e q u a tio n . 25°C (gh3 ) 2hbnh3 ------» (ch3 ) 2bnh2 + h2 Hence th e o n ly p ro d u c t of th e n o n -h y d ro g e n ic r e a c t i o n o f 3 t Na te tr a m e th y ld ib o r a n e and sodium , n o n - v o l a t i l e a t 25°C» i s th e new compound NagHBtGH^)^. 3 . S p e c u la tio n on th e mechanism o f th e n o n -h y d ro g e n ic r e a c t i o n o f te tra m e th y ld ib o r a n e w ith sodium h a s s u g g e ste d t h a t t h i s r e a c t i o n may ta k e p la c e by a r e l a t i v e l y sim ple r e a c t i o n mechanism. if-. The a n io n p o r t i o n o f th e new s a l t - l i k e compound, NagHBCCH^Jg* w e ll have th e f o llo w in g e l e c t r o n i c s t r u c t u r e r G H -a H:B:GH 5 . I t h as been d e m o n stra te d t h a t ^ 2^ ( 0^ ) 3 i s a v e ry p o te n t so u rc e o f h y d r id e . Thus c h l o r o s i la n e r e a c t s w ith Na2HB(GH^)2 to p ro d u ce an e q u iv a le n t amount of s i l a n e . 6 . I f Na2HB(CH^)2 » in m ethyl e t h e r , i s t r e a t e d w ith d ib o ra n e , an a d d i t i o n r e a c t i o n o c c u rs w hich In v o lv e s more th a n one mole o f b o r in e (BH^) p e r mole o f Na2HB(CH^)2 . T h is r e a c t i o n h as been t e n t a t i v e l y a t t r i b u t e d to th e h y d rid e a c t i v i t y o f HagHBCCH^^i an<i hence th e p ro d u c tio n o f sodium b o ro h y d rld e h as been p o s t u l a t e d . F u r th e r i n v e s t i g a t i o n o f t h i s r e a c t i o n h as b e e n s u g g e ste d t o co n firm t h i s p o s t u l a t e . 7 . The r e a c t i o n o f trlm e th y lb o ro n w ith Ha2HB(0H ^)2 » in l i q u i d m ethyl e t h e r a t -78°C , p ro d u ces an a d d i tio n compound which i s not s t a b l e a t room te m p e r a tu r e . I t h as 92 b een s u g g e ste d t h a t t h i s r e a c tio n i s a n o th e r exam ple o f th e h y d r ld ic n a tu r e o f Na2HB(CH^)2 > and t h a t sodium t r i - m e th y lb o ro h y d rid e , NaHB(GH^)^, I s th e r e l a t i v e l y u n s ta b le p ro d u c t. 8. The r e a c t i o n o f tr lm e th y lb o r o n w ith Na2HB(GH^)2 In l i q u i d ammonia p ro d u ces an a d d i tio n p ro d u c t w hich does n o t d i s s o c i a t e a t 50°0 i n vacuo. T his p ro d u c t, which h as th e fo rm u la Na2HB(0H^)2 , B(CH^)^, p resum ably I l l u s t r a t e s th e b a se c h a r a c te r o f Na2HB(GH^)2 * Hence th e a n io n p o r tio n of t h i s r e a c t i o n p ro d u c t i s p o s tu l a te d to be i s o e l e c t r o n i c w ith 2 ,2 ,3 - tr i m e t h y lb u ta n e . 9. The h y d r id ic r e a c t i o n of Ha2HB(GH^)2 w ith c h lo ro - s i l a n e s u g g e s ts th e p r o d u c tio n o f th e h y p o th e tic a l sub s ta n c e NaBCCH^)^. A ll a tte m p ts t o d e m o n stra te th e e x is te n c e o f t h i s compound have been u n s u c c e s s f u l, b u t th e f u r t h e r i n v e s t i g a t i o n o f t h i s r e a c t i o n h as been p ro po sed . 10. I t h as been d e m o n stra te d t h a t th e n o n -h y d ro g e n ic r e a c t i o n o f te tra m e th y ld ib o r a n e i^ ith sodium , when t e t r a m e th y ld ib o ra n e i s in e x c e s s , p ro d u ces Ha2HB(GH^)2 ; t h i s a p p a re n tly r e a c t s w ith th e e x c e ss te tr a m e th y ld ib o r a n e in a manner w hich h as n o t been d e te rm in e d . The f u r t h e r i n v e s t i g a t i o n o f t h i s r e a c t i o n h as been s u g g e s te d . 11. On th e b a s i s o f th e r e s u l t s o f t h i s i n v e s t i g a t i o n i t a p p e a rs t h a t th e am m oniatlon r e a c t i o n o f 93 te tra m e th y ld ib o r a n e does n o t In v o lv e th e fo rm a tio n o f th e d im e th y lb o rin e amraonlate ae an in te r m e d ia te . :A r e a s o n a b le mechanism h as been s u g g e s te d f o r t h i s r e a c t i o n in o rd e r t o show t h a t such an in te r m e d ia te i s n o t n e c e s s a r y . BIBLIOGRAPHY BOOKS K ra u se , E . , and A. v. G ro sse , Die Chemle d e r M e ta ll- O rgan lsch en V erblndungen. B e r lin : Gbr. B o rn tra e g e r, 1937. Selwood, P. W., M ag n eto ch em lstry . New York: I n t e r s c i e n c e P u b l i s h e r s , 19^3. S to c k , A. . H y d rid es o f Boron and S i l i c o n , I t h a c a , New York: C o rn e ll U n iv e r s ity P r e s s , 1933* ARTICLES B e n t, H. E . , and M. Dorfman, J . Am. Chem. Soc. £2., 1259 (1 9 3 5 ). B urg, A. B ., and H. I . S c h le s in g e r , J . Am. Chem. Soc. 59. 780 (1 9 3 7 ). F re e d , S . , and N. Sugarman, J . Ghem. P hys. 3 5 ^ 6 0 (19^3) K a sp e r, J . H ., L. V. M cCarty, and A. S. Newkirk, J . Am. Chem. Soc. 2 1 , 2588 ( 1 9 % ) . L ew is, G. N ., J . F r a n k lin I n s t i t u t e ( 3 ) 2 2 6 . 293-313 (1 9 3 8 ). P l t z e r , K. S ., and H. S. Gutowsky, J . Am. Chem. Soc. 68, 2204 ( 1946). 1 R undle, R. E . , J . Am. Chem. Soc. 6£, 1327 (1 9 ^ 7 ). S c h le s in g e r , H. I . , and A. B. Burg, J . Am. Chem. Soc. 6 0 . 290 (1 9 3 8 ). S c h le s in g e r , H. I . , and A. B. Burg, Chem. Rev. 2 1 , 1 (19*1-2). S c h le s in g e r , H. I . , R. T. S anderson, and A. B. B urg, J . Am. Chem. Soc. 62, 3^21 (19^+0). S to c k , A ., and E. P o h lan d , B er. i^ B , 2210 (1 9 2 3 ).

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Creator Campbell, George W (author)

Core Title A study of the reaction of tetramethyldiborane with sodium in liquid ammonia and the products derived from this reaction

Degree Doctor of Philosophy

Degree Program Chemistry

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag chemistry, organic,OAI-PMH Harvest

Language English

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Advisor Burg, Anton B. (committee chair), [illegible] (committee member), Copeland, C.S. (committee member), White, Paul A. (committee member), Wilmarth, W.K. (committee member)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c17-617798

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