A study of the activation of hydrogen by cuprous salts in quinoline / by Max K. Barsh

PDF

Download

Open document

Flip pages

Download a page range

Download transcript

Copy asset link

Request this asset

Transcript (if available)

Content A.STUDY OP THE ACTIVATION OP HYDROGEN BY CUPROUS SALTS IN QUINOLINE by Max K. Barsh A Dissertation Presented to the FACULTY OP THE GRADUATE SCHOOL UNIVERSITY OP SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OP PHILOSOPHY (Chemistry) June 1955: UMI Number: DP21771 All rights reserved INFO RM ATIO N 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 DP21771 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 4 8 1 0 6 -1 3 4 6 "Ph. D C . '55 BASS. This dissertation, written by ......,..:...MA£..Ki...BARSH„;....■ ...... ......... . under the direction of.Wz&.Guidance Committee, and approved by all its members, has been pre sented to and accepted by the Faculty of the Graduate School, in partial fulfillment of re quirements for the degree of D O C T O R O F P H I L O S O P H Y Dean yh^XJ /9 sy Date.................... ,..... Guidance CorAmittee Chairm an .. ACKNOWLEDGMENTS The author wishes to dedicate this work to his wife, Carol, whose inspiration encouraged him to strive for the degree of Doctor of Philosophy. For the assistance received, the author wishes to express his appreciation to his research director, Dr. Wayne K. Wilmarth, and wishes to thank the faculty and many students of the University of Southern California. The author would like to express his gratitude to the Office of Naval Research under which a large part of this work was done. M.K.B TABLE OP CONTENTS CHAPTER PAGE I. GENERAL INTRODUCTION............................. 1 II. AN INVESTIGATION OP THE HYDROGENATION PRODUCTS OP CUPRIC ACETATE IN QUINOLINE . . . 3 Introduction and statement of the^problem . . 3 Historical background .................. 1| Experimental............. 5 A. Cuprous acetate solutions.........: . . 6 B. Hydrogenation of cupric disalicyl- aldehyde................. . 8 C. Oxidation of the cuprous solutions. . . 11 D. Hydrogenation of nickel disalicyl- aldehyde in pyridine...................11 E. Reaction of nickel metal and nickel disalicylaldehyde ...................... 13 P. Oxidation of the ' ‘reduced" nickel solutions ................. 13 G. Analysis for nickel . . . . . . . . . .13 Results and conclusions . . ................. 1I 4 . Summary ............................. . 19 III. ORTHO-PARAHYDROGEN CONVERSION BY SOLUTIONS OP CUPROUS ACETATE IN QUINOLINE........... 20 Introduction and statement of the problem . . 20 CHAPTER j Theoretical considerations.................... i i | Experimental procedures ...................... A. Materials used......................... . B. Preparation of cuprous acetate solutions ............... ....... C. Preparation and analysis of para-rich hydrogen. ...................... D. Ortho-parahydrogen conversion . . . . . E. Minimum stirring speed determination. . •F. Ortho-parahydrogen conversion by a solution of cuprous and cupric acetates in quinoline............................. G, Deuterium exchange with cuprous acetate in quinoline. ........... H. Solubility of hydrogen and/or deuterium in quinoline. ........ Results and conclusions . . . ................ Summary . ................................... IV. HYDROGENATION OF CUPRIC ACETATE IN QUINOLINE IN THE TEMPERATURE RANGE 0-60°C.............. Introduction. .................... ........... Experimental procedures ...................... A. Materials used .. .............. .. PAGE 22 25 25 27 28 30 30 31 33 33 3k 51 53 53 5 1+ 51+ vi CHAPTER PAGE B. Hydrogenation apparatus. . ...■.......... 55 C. Hydrogenation or deuteration procedure . 57 Results and discussion................. 59 Summary................. 85 V. MISCELLANEOUS SUBJECTS........................... 87 A. Copper-I salts...........................87 B. Copper-I conversion.............. 88 C. High temperature o-p hydrogen conversion . 92 D. Calculation of hydrogenation rate from conversion data......................... 93 E. Copper-I carbon monoxide interaction In quinoline......................... • . 95 P. Acetic acid effect ........ 97 VI. GENERAL SUMMARY. . ............................105 BIBLIOGRAPHY . . . . . . . ............................109 LIST OP TABLES TABLE PAGE I. Magnetic Data on Copper Compounds............. 15 II. Magnetic Data on Stability of the Nickel Solutions in Pyridine to Oxyg;en................ 17 III. Magnetic Susceptibility of Nickel Solutions in Pyridine. ..... ..................... 18 IV. Ortho-Parahydrogen Conversion by Cuprous Acetate in Quinoline ........... ...... 35 V. Solubility of Hydrogen and Deuterium in Quinoline Calculated to 25«0°C. . ......... 36 VI. Temperature Coefficients of the Conversion Rate Constants................. 1+1 VII. Ortho-Parahydrogen Conversion During and After Hydrogenation of Cupric Acetate in Quinoline t s 100°C........... 1^5 VIII. Hydrogenation Data— 6 o °C . Observed ...... 6l IX. Hydrogenation Data— 6o°C. (and Conversion Data) Corrected for Acetic Acid. ...... 62 X. Hydrogenation Data— J>0°, I 4 .O0, 25°, and 0°C. . 63 XI. Hydrogenation Data— 100°C.--Corrected for HOAc................................... 66 XII. Conversion Data Calculated to Hydrogenation at 100°C. 73 viii TABLE XIII. XIV. XV. XVI. XVII, XVIII, Deuteration Data............................... Hydrogenation and Deuteration Rate Constants. Formation of Copper-I Quinoline Solutions . . Parahydrogen Conversion by Cuprous Sulfate in Quinoline................. . Equilibrium Data— Acetic Acid Effect--6o°C. . Equilibrium Data— Acetic Acid Effect--100°C. . PAGE j ! 80 | I 82 | 89 i f 1 1 i 91 i 99 105 LIST OP FIGURES FIGURE PAGE ! 1« Apparatus for Preparation of Cuprous Acetate j 5 ! for Magnetic Measurements 7 \ 2, Modified Apparatus for Preparation of I f Cuprous Acetate for Magnetic Measurements. . . 9 i 3. Apparatus for Preparation of Nickel Solutions for Magnetic Measurements......................... 12 L | . • Reaction Vessel for Parahydrogen Reactions . . . 29 Limiting Stirring Speed Determination. ..... 32 \ j 6, Solubility of Deuterium and Hydrogen in j Quinoline...........................................37: 7a Effect of Concentration on Conversion Rate j . ! Constants at 100°C. . .................... . 38 8. Effect of Concentration on Conversion Rate Constants at 80.0°C...................... 39 9a Effect of Concentration on Conversion Rate Constants at 60a0°C................................I 4 .O 10. Temperature Coefficient of Conversion Rate Constants................................. i j . 2 11. Ortho-Parahydrogen Conversion During and After Hydrogenation of Cupric Acetate at 100°C.............. i|6 12. Constant Pressure Hydrogenation Apparatus .... 56 .0 . 13. Hydrogenation at 60.0 C.--Extrapolated to O-HOAc. 67 X FIGURE PAGE 11+. Hydrogenation at 6o.O°C.--vs. HOAc . . . . . . .68 15.' Hydrogenation at £0.0°C.................... . . .69 16. Hydrogenation at i+0.0°G................. . 17. Hydrogenation at 25.0°C. . . ............. 18 • Hydrogenation at 0.0°C..................... . . .72 19. Hydrogenation at 100°C..................... • 0 CO Deuteration Rate Data...................... 21. Total Arrhenius Curve, D2 and H2, Hydrogenation and Conversion ........... . . .83 22. Evaluation of ’ ’n^-^O0 Equilibrium Data. . . . J00 23. Evaluation of 1 1 n“ ........................ 2l+. Evaluation of um1 t — 6o° Equilibrium Data. . 25. Evaluation of 1 1 mM ........................ ! { j CHAPTER I GENERAL INTRODUCTION Aside from the pleasure one receives in doing chem istry research, a detailed study of any chemical system is of importance because it can lead to greater understand ing of all chemical systems. In this dissertation a de tailed physical chemical study is made of the homogeneous system cupric acetate, cuprous acetate, quinoline, para- enriched and normal hydrogen and/or deuterium. The minutiae, of course, involve many more species than are stated above but the system considered is essentially as described. As a consequence of this study the kinetic behavior and chemical properties of solutions of cuprous and cupric acetates in quinoline when treated with hydrogen or deuterium were elucidated. The use of para-enriched hydrogen offered the opportunity to investigate the most intimate details of the chemical kinetics and thus correct ly to formulate the gross behavior of the hydrogenation of the cupric acetate solutions. This of course was pos sible only after the correct valency of the species in solution was determined. Interpretation of the results of these investigations possibly gives one insight into the processes involved in the activation of the hydrogen i molecule for reaction. ; i It is pertinent here to indicate the method of or ganization of this dissertation as it simplifies the read ing and resultant interpretation. With the exception of | the terminal chapter which considers a general summary of all of the work presented and suggestions for further work and Chapter V, having to do with miscellaneous topics, the other chapters are integral units concerned with the different phases of the problem and are essentially in chronological order. These other chapters have each an introduction and/or theoretical section, an experimental section, a results and conclusion section and a summary. Each may be read independently of the others. The mis cellaneous chapter is concerned with subjects *ahich, al though pertinent to the general problem, do not lend them- | selves without undue confusion or encumberance to location within the other chapters. It is hoped that the material presented in the fol- i lowing chapters will contribute to the understanding of hydrogenation processes in general. i CHAPTER II AN INVESTIGATION OP THE HYDROGENATION PRODUCTS OF CUPRIC ACETATE IN QUINOLINE ' I. INTRODUCTION AND STATEMENT OP THE PROBLEM i An exploratory investigation of the homogeneous cat alytic hydrogenation of cupric acetate and cupric disalicyl- aldehyde dissolved in quinoline was reported by Calvin.^- Subsequent study by Calvin and Wilmarth^ confirmed the fact that cupric acetate was quantitatively reduced to cuprous acetate, a thermodynamically stable valence state in quino line solution. The hydrogenation of the cupric acetate was readily studied by minimissing the normally large induction ■ period of the autocatalytic reaction through introduction of a known amount of the catalytically active pure cuprous acetate. Since cuprous salicylaldehyde was not available, the hydrogenation of the cupric disalicylaldehyde was ini tiated by a partial reduction of the cupric salt with hydra zine. The color change and general characteristics of the , reaction indicated that cuprous salicylaldehyde was the ! hydrogenation product, but the product here was not directly confirmed. The following account is concerned with the magnetic properties of the hydrogenation products as a means of elucidating their structure and valence state. ^M. Calvin, Trans. Faraday Soc., 1181 (1938). ^W. K. Wilmarth, "Catalytic Homogeneous Hydrogena tion,1 1 (unpublished doctoral dissertation, University of California, Berkeley, 19ij.2). _____________________ ____________ I II. HISTORICAL BACKGROUND i I j | An investigation of the magnetic properties of the | hydrogenated products of pyridine solutions of cupric and I o j nickelous disalicylaldehyde was made by Tyson and Vivtan^ | and Fobes and Tyson.^ Their measurements of the cupric j solutions on a Gouy balance showed the presence of one un- | paired electron both before and after hydrogenation. From / this it was concluded that the hydrogenation of the cupric compound in pyridine solution did not involve reduction to j a cuprous species, but instead involved the reduction of | I the salicylaldehyde to salicyl alcohol. j I I | A comparison of the similarities of the reaction, j ! \ j such as color change during hydrogenation and chemical j i • | | nature of the solvent, leads one to believe that the reduc-i I I j tion of the copper compounds in quinoline, as reported by J Calvin and Wilmarth^ and in pyridine, as reported by Tyson and Vivian, probably involves the same mechanism and re action products. It would appear, then, that either these cuprous compounds must be paramagnetic, a phenomenon which could be achieved by metal to metal bonding in a dimer, or the measurements of Tyson and Vivian must be in error. The i latter possibility seemed likely, since the cuprous solu- I tions are rapidly oxidized in air and Tyson and Vivian j ff* Tyson, Jr., and R. E. Vivian, J. Am. Chem. j I Soc., 6 a , 1^03 U 9 W . i | bli. A. Fobes and G. N. Tyson, Jr., J. Am. Chem. Soc.j i6 a, 3530 (19^1). I 5 Wilmarth, loc. cit. j report no special precautions in their handling of the solu- | tions. On the other hand, the hydrogenation catalyst was j ! believed to be a dimer, and metal to metal bonding was a j | - ! j possibility. In view of the above contradictions the in- i | terpretation of the results of the hydrogenation of nickel j i : k ! disalicylaldehyde as presented by Pobes and Tyson was alsoj | ; open to question. In order to clarify the above situations! a magnetic study of copper and nickel solutions in pyridinel \ and quinoline was undertaken. III. EXPERIMENTAL I j Solutions of cuprous acetate were prepared in both j f S t j ] quinoline and pyridine, with care being taken to exclude ! ■ | oxidants. In addition, solutions of cupric disalicylalde- j i ■ I hyde in each of the solvents were hydrogenated and the stoichiometry was determined by following the uptake of thej hydrogen manometrically. The magnetic susceptibility of j T the solutions in the reduced state was measured by the Gouyj method; these solutions were then allowed to become oxi dized to the cupric species by exposure to air and/or \ \ oxygen, and were remeasured. ■ The hydrogenation of nickel salicylaldehyde was ft jreported to occur under conditions somewhat similar to i those reported above, but since this reaction occurred very; ' k ’ 1 °Pobes and Tyson, loc. cit. i ^Selwood, Magnetochemistry, Interscience Publishers j ;Inc., New York, pp. k-o. i L „..§Fobes_..and...Tyson,., loc . -cit- —---- J much more slowly, it was possible that an entirely differ- j j i ent process was taking place. These experiments were re- j j peated with the hope of demonstrating the presence of a I i | monovalent species. However, in preliminary attempts, the J ‘ hydrogenation yielded some metallic nickel (highly ferro- j i ' i \ magnetic) before an appreciable color change had occurred j in the bulk of the solution. This situation was remedied i by anaerobically filtering off the nickel metal and making I i magnetic measurements on the remaining solution. An ef- * 5 fort was also made to obtain monovalent nickel by reduc- j } } j tion of the solutions of nickel disalicylaldehyde with { j ! i nickel metal under conditions similar to those of the j I i hydrogenation experiments. j ! ' j j i j A. Cuprous acetate solutions. A solution of cuprous ! i | acetate in quinoline was prepared by introducing a rapidly i ! i weighed sample of the analytically pure dry cuprous acetate! i into a jacketed all-glass reaction vessel equipped with a magnetic stirrer. The system was evacuated and a known j ! I quantity of purified quinoline, contained in the magnet i ! cell which was sealed to the neck of the reaction vessel i 5 i ! i I I was added to the solid by tilting the apparatus. (See ; ! ^ ! Figure 1.) The solution was hydrogenated (negligible ! ; Hr I i Supplied by W. K. Wilmarth. i 7 Magnet ce Reaction vesse FIGURE 1 APPARATUS FOR PREPARATION OF CUPROUS ACETATE FOR MAGNETIC MEASUREMENTS 8 ! i ■ ‘ 5 * O ' ! j amount of hydrogen absorbed) at 100 C. to insure the removal i ' i j of any traces of cupric salts produced by air oxidation • • | \ which may have occurred during the introduction of the ; ; solid cuprous acetate into the flask. When the color of ! ; the solution became the clear1 ruby red that is associated ■ 1 : ■ i i with the completely hydrogenated solution, the vessel was immediately cooled and the hydrogen pumped off. The magnet cell in which the magnetic susceptibility of the solution was to be measured (see above) was filled with the solu- j I i j tion by properly tilting the apparatus, the cell was J 1 { | sealed off from the reaction vessel while still under j ! j vacuum, and the magnetic measurements were made. | ) The solutions of cuprous acetate in pyridine were handled in exactly the same manner as described above. B. Hydrogenati on of cupric disalicylaldehyde. A weigbed sample of the salt was diluted to the desired volume in a volumetric flask with purified solvent. Five ml. of this i | solution were introduced into the reaction vessel of the j j apparatus shown in Figure 2 (see description, above sec- tion). Fifteen ml. of this solution were placed in a j i small storage flask attached to the apparatus through a ground glass joint and stopcock in such a manner that by | turning the flask through 180° its contents would be de- j livered into the reaction vessel ifthe stopcock was open. Small reaction flask Magnet ce Reaction vesse FIGURE 2 MODIFIED APPARATUS FOR PREPARATION OF CUPROUS ACETATE FOR MAGNETIC MEASUREMENTS ! io j i The system was evacuated and the flask and contents were j isolated from the remaining apparatus by closing the con- j necting stopcock* The 5*0 ml* portion was cooled by cir- j i « | culating ice water through the outer jacket and was ex- j I . j | • posed to the vapors of hydrazine for several seconds to i I j reduce a fraction of the cupric disalicylaldehyde to the i cuprous state* The vessel was immediately evacuated* This solution was then hydrogenated at 100°C.-until the i reduction was completed (as determined by following the rate of absorption of hydrogen at constant pressure). The vessel was then immediately cooled and evacuated. The flask was turned and the lf> ml, portion of the cupric solu- i i tion was added to the reduced material* The solution was j ^ o 1 then hydrogenated at 100 C. with careful observation of ] j the volume and rate of absorption of the hydrogen at ap proximately one atmosphere until the reduction was com plete* The volume of hydrogen absorbed, as measured by a gas buret in the system, agreed well with the calculated amount for reduction of cupric to cuprous species. The vessel and contents were immediately cooled and evacuated. The reduced solution was then transferred under vacuum to it ! the magnet cell as described above for measurements in the j | Gouy balance. This procedure was fbllowed for both the ! I I i j pyridine and the quinoline solutions. | £. Oxidation of the cuprous solutions. In all cases i ; ' the reduced red colored solutions were exposed to air or i ! j to a stream of oxygen and magnetic measurements were re- 1 peated. The oxidation, even at room temperature, pro- j ! | | ceeded as rapidly as the oxygen was able to diffuse into | ; 1 t ! | the solutions and they again became characteristically I i j green colored as they were before hydrogenation. j ! i ! D. Hydrogenation of nickel disalicylaldehyde in j j pyridine. In order to be able to remove the metallic ! | nickel before measuring the magnetic susceptibility of the j j j j reduced solution, hydrogenation was accomplished in a j \ 5 i ; j flask separated from the magnetic cell by a sintered glass j j filter. (See Figure 3.) A known amount of solution was i i placed in the flask, evacuated, and cooled to 0°C. Hydro- j i I gen gas was admitted at one atmosphere pressure. The j j system was sealed off and allowed to warm up slowly to 100°C. After eight days at this temperature the system ! i i | was cooled to room temperature and the contents of the j ; flask were filtered into the magnetic cell by appropriatelyj i • 1 : tilting the apparatus and applying the proper temperature j I differentials to the flask and cell. The magnetic cell j i S 1 i :and contents were then cooled in a dry-iee-acetone bath ! | and were sealed off from the flask and its residue (some j 12 Magnet cell > Sintered glass " ’ filter Reaction flask FIGURE 3 APPARATUS FOR PREPARATION OF NICKEL SOLUTIONS FOR MAGNETIC MEASUREMENTS 13 I solution end metallic nickel)* The reduced solution was I | then measured on a G-ouy balance. • 2. Reaction of nickel metal and nickel disalicylalde- * - j I i j hyde. In order to determine whether nickel metal was j r! j ! capable of causing the reduction of the nickel solution, j ) - ' . i an experiment was performed using the apparatus described | I above but with slight modification. The nickel solution j i i and the nickel pellets (in excess) were placed in a flask, j I The system was evacuated and sealed off under vacuum. I i ‘ • ; I s The remainder of the procedure, except for the cooling i \ | techniques, was followed as described above. I ! I i This and the hydrogenation procedure were repeated J < j ! • \ I without the sintered glass filter; in this case the j ! j filtration was carried out after the flask was opened. j P. Oxidation of the “reduced” nickel solutions. In all cases the solutions were exposed to a small stream of oxygen for several hours and the magnetic measurements were repeated. The results were essentially the same as !before oxidation. G. Analysis for nickel. The dimethylglyoxime precipi- I ■" station procedure was followed. Five ml. aliquots of the .pyridine solutions were allowed to evaporate to dryness. | The residues were digested with a mixture of concentrated j | nitric and perchloric acids. The resulting solutions were I ; neutralized with a slight excess of ammonium hydroxide and | : precipitated with an alcoholic solution of dimethylglyoximei ! ! | The precipitates were collected on sintered glass filters, j i o i l washed thoroughly, and finally dried at 110 C. j i i i IV. BESULTS AND CONCLUSIONS j The results of the experiments with the cupric and cuprous solutions are summarized in Table I. It is immed- | lately apparent that (1) in all cases the reduced state wasj ' , 1 I clearly diamagnetic, (2) the stoichiometry of hydrogenationj I i | corresponded to a change from the cupric to the cuprous j ! . I ! valence state, and (3) the oxidation of the reduced state I i i j produced solutions which had essentially the same magnetic I ! ■ ® j susceptibility as the cupric state. Therefore it can be j 1 I concluded that the hydrogenation products, were the soluble cuprous compounds. This conclusion is in agreements with the results of Calvin^ and Wilmarth.^® in view of the re latively small color changes accompanying the reactions of » I copper disalicylaldehyde in pyridine, it is entirely pos- j < sible that Tyson and Vivian^ would not have observed the ; oxidation to the cupric state while handling their solutions, | 9Calvin, loc. cit. j -^Wilmarth, loc. cit. ! i l l ! J xxTyson and Vivian, loc. cit. ! TABLE I MAGNETIC DATA ON COPPER COMPOUNDS Compound3 Molarity of solution Solvent Hydrogen absorbed (ml. at S.T.P.) Experimental Calculated * 1°6 (2U°0.) Number of unpaired electrons A Cu(OAc) 0.073 Quinoline — — Diamagnetic — B Cu(0Ac)2 0.073 Quinoline — — u5o one C Cu(OAc) o.oSU Pyridine — Diamagnetic — D CuCOAc)^ 0.05k Pyridine — 783b one E Hydrog.Cu(salicyl.) 0.079 Quinoline 13.7° 13.3 Diamagnetic — F Cu(salicyl.)2 0.079 Quinoline — — 1310 one G Hydrog.Cu(salicyl.) 0.080 Pyridine 13.2d 13.5 Diamagnetic — H Cu(salicyl.)g 0.080 Pyridine — — 1279 one D, F, and H are results of cuprous solutions exposed to oxygen or air. Precipitation of small amount of solid occurred during the oxygenation so that the suscepti bility value has only semi-quantitative significance. C p The initial solution was 1$.0 ml. of 7*9 x 10 M. Cu(salicyl.)?. cl The initial solution was 1$.0 ml, of 8.0 x 10“^ M. 0u(salicyl.)o. I 16 I The initial results of the magnetic measurements ! j of the variously treated pyridine solutions of nickel dis- ; i ! alicylaldehyde are shown in Table II* Since the above dataj I indicated that the nickel solutions were stable in air, j ; the experiments were repeated without the anaerobic pre- ' i ; j cautions, but with chemical analysis of the solutions for i 1 ’ nickel content after filtration. The results are shown in ! - I Table III. j r 1 ! The constancy of the magnetic susceptibility when ! ; calculated on the basis of the analytically determined I j nickelous concentrations indicates that either no univalent! I ' I i nickel was formed or that, if formed, it must have had the j t | same susceptibility as the original divalent nickel and, | in addition, did not react at an appreciable rate with ! I > j oxygen of the air* However, it seems unlikely that the J I univalent state is thermodynamically stable under these ! conditions, as attempted reduction with nickel metal pro- I I O \ I duced no observable change even after ten days at 100 C. ! 12 i I While Pobes and TysonA^also concluded that the nickelous I ! I ' I | ion was not reduced to the univalent state, they apparently] ‘ } } did not observe the unmistakable presence of nickel metal I ] as a hydrogenation product. ; :__________ j i 12 ' ■ Pobes and Tyson, loc. cit. j 17* TABLE II MAGNETIC DATA ON STABILITY OF THE NICKEL SOLUTIONS IN PYRIDINE TO OXYGEN Solution Change in -weight by magnetic field (gm.)' Before exposure to After exposure to oxygen oxygenc Hydrog. Ni( salicyl.), 0.0065 0.0060 Ni(salicyl.) after treatment ■with nickel metal 0.0121 0.0121 Reported magnetic data in grams because process of anaerobic filtering caused changes in concentration of solutions by partial dis tillation of solvent, b Corrected for solubility of oxygen in pyridine. 18 TABLE III MAGNETIC SUSCEPTIBILITY OF NICKEL SOLUTIONS IN PYRIDINE ' Molarity of Number of solution X x 106 m unpaired Solution (Experimental) electrons . 'NiCsalicylOg 5.9 x lO* * 2 3960 2 *Ni(salicyl.)g after ! treatment with nickel metal 5.2 x 10“2 UllO 2 Hydrog. Ni(salicyl.)2 3.3 x 10“^# UlUO 2 ; * The remainder of .the nickel in the hydrogenated solution was ipresent as a nickel mirror and fine nickel metal precipitate. 19 | V. SUMMARY I i The magnetic susceptibilities of hydrogenated pyridine and quinoline solutions of cupric and nickelous | acetate and salicylaldehyde were measured before and after | j j reaction with oxygen. The results confirmed other evidence! . \ i that the cupric salts were reduced to the cuprous valence state. Mo evidence for a stable univalent nickel compound was obtained. It is suggested that the discrepancy between the magnetic susceptibilities reported here and others pre viously reported was due to oxygenation by air in the earlier studies. CHAPTER III ORTHO - PARAHYDROGEN CONVERSION BY SOLUTIONS OP CUPROUS ACETATE IN QUINOLINE I. INTRODUCTION AND STATEMENT OP THE PROBLEM It was shown by Calvin1 and subsequently by Wilmarth^ that homogeneous catalytic hydrogenation of solutions of cupric acetate occurred at 100°C. and 38 cm* Hg pressure, and that the autocatalytic reaction was catalyzed by one of the reduction products, the cuprous species* Other investigations by Tyson and Vivian^ and Pobes and Tyson^J- on the magnetic properties of hydrogenated pyridine solu tions of cupric and nickelous disalicylaldehyde, seemed to indicate that the hydrogenation of the cupric compound in pyridine solution did not involve reduction to a cuprous species, but instead involved the reduction of the salicylaldehyde to salicyl alcohol. A comparison, however, ^M* Galvin, Trans. Paraday Soc., 3h» 1181 (1938). 2 , , W. K. Wilmarth, "Catalytic Homogeneous Hydrogena tion," (unpublished doctoral dissertation, University of California, Berkeley, 19i|2). 3 G. N. Tyson, Jr., and R. E. Vivian, J. Am. Chem. Soc., 6|, 11^03 (19^1). M. A. Pobes and G. N. Tyson, Jr., ibid., 63, 3^30 (1914-1) . 21 of the similarities of the copper solution reactions in pyridine and quinoline, such as color change during hydro- ! genation and chemical nature of the solvent, led one to suspect that the reactions described by Calvin, Wilmarth, and Tyson and Vivian probably involved the same mechanism and reaction products. The possibilities that either the i cuprous compounds were paramagnetic, or that the measure- t ments of Tyson and Vivian^ were in error, were investigated ! by Wilmarth, Barsh and Dharmatti.® Magnetic susceptibility measurements demonstrated that the cupric species was paramagnetic but that both the pure cuprous species and the direct hydrogenation products of the cupric species were diamagnetic. This was in contra-; diction to the results of Tyson and Vivian and of Fobes and ' Tyson,’ ? but was in substantial agreement with the conclu sions of Calvin® and of Wilmarth. 9 Calvin also reported that ortho-parahydrogen conver- , sion was not observed during hydrogenation with para-rich hydrogen, but that when the reduced solution was allowed to J I stand overnight, conversion did occur. : ^Tyson and Vivian, loc. cit. ! ^W. K. Wilmarth, M. K. Barsh and S. S. Dharmatti, j J. Am. Chem. Soc., Jki 5035 (1952). 7 Fobes and Tyson, loc. cit. 8 Calvin, loc. cit. 1 9 W. K. Wilmarth, Ph.D. Dissertation, loc. cit. The main purpose of the investigation was to study the. rates of conversion of,qrtho-parahydrogen by solutions of cuprous acetate in quinoline and, if possible, to relate the conversion process to the hydrogenation process* The latter was achieved through a study of the rate of ortho-parahydro- gen conversion during and after hydrogenation, with para-rich hydrogen, of a solution of cuprous and cupric acetates in quinoline* of deuterium gas with a solution of cuprous acetate in quinoline. II. THEORETICAL CONSIDERATIONS. In the presence of a suitable catalyst (C) in a homogeneous system, ortho- and parahydrogen reach equilib rium as follows: At equilibrium the ratio of to k2 at room temperatures is known to be 3* The rate at which the P-H2 is converted Replacing hydrogen concentration by percentage of hydrogen Also, an exploratory study was made of the exchange (1) to o-H ' , e , v ' expressed as 3*---= =*i<C><Cp-H2> - k2(C)(C0_H2) (2) and evaluating k2 in terms of k^ at room temperatures, the | « above equation becomes Substituting k° * k-j_ + k2 (I4. ) into equation (3) gives ~ d (P P - H2 ) = k ° C (P I,,.H , - 2 5 ) 'p-Hp "OJ (5) dt Upon integration this becomes i | i , (pt - 2 n (Pt - Pco) .Q-. i ln (p0 - 25) = ln (p0 - p«) B _k ct (6) I ! where Pt, Po» and represent per cent P-H2 at time t, 0 j • j and infinity. Farkas^O has shown that the measured resistance of a Pirani gauge containing para-rich hydrogen can be sub stituted directly for the percentage values in equation 6, giving (Rt - R*,) In --------- s -k°(C)t (7) | \ nQ - %) 1 i | where R^., RQ, and R^ are the resistance values of the gauge | j corresponding to the percentages of the parahydrogen at 10A. Parkas, Z. Physik, Chem., BIO, I 4 .I9 (1930). ! 2k j j time t, 0, and infinity, and kQ has the previously defined I value. When the ortho-parahydrogen conversion occurs in j a liquid phase, such as in a solution of cuprous acetate I in quinoline, and the rate is followed by Pirani gauge ■ analysis of small samples extracted from the gaseous phase, i a rate constant k can be determined according to the fol- 1 | lowing equation: i ( R t - *co) In --------r « -kt (8) j ( H 0 ~ i - ' . ■ ■ | It is clear that the rate constant for conversion occur- j ring in the solution, k°, is related to the rate constant, i Ik, as follows:. I k • / k°(C) f ksJ f n7l J (9) | Vg f aV]_ J v 7' ! i i i where k_ is the rate constant in solution for the pure I S t I | solvent, a is the solubility of the hydrogen in the solvent in ml./ml., V-^ is the volume of the liquid phase, and Vg is the volume of the gas phase. Equations 8 and 9 are true I j only if the stirring is sufficiently violent that diffusion j is not rate-determining. i j The rate of exchange of deuterium with an exchange- ! J able substrate in solution can also be followed by Pirani ! ; gauge analysis of small samples extracted from the gaseous 25 phase, if the experimental conditions are so chosen that the resistance reading for hydrogen deuteride is approxi mately the same as for normal hydrogen. Under these condi tions equation 8 becomes, (Rt ~ rH) • % ln (Rq - Rh) = ”kDt t where R0 and R^. are the Pirani gauge resistance values at times 0 and t, R j j ; is the resistance value for normal hydrogen, and kj) is the rate constant for the exchange process corresponding to k, for the conversion process. III. EXPERIMENTAL.PROCEDURES A. Materials used. The quinoline for all the experi ments was the end product of several vacuum distillations of Eastman synthetic quinoline, over KOH, BaO and anhydrous Cu(0Ac)2 respectively, through an all-glass 15-plate Oldershaw perforated plate fractionating column and multi- I ratio take-off head. The resultant product boiled between ! ! 137.5 and 138.5°C. at 1*8 to 50 ram. Hg pressure, and was ] I collected at a ten to one reflux ratio after the first ' fraction had been discarded. The clear colorless liquid was stored in a brown, glass-stoppered bottle under nitro gen gas. I I j The anhydrous cupric acetate was prepared according ! to the directions of H. Spath.The preparation consisted ! | of gently heating appropriate quantities of Cu(N0o)2 i ^ i I with acetic anhydride under a reflux condenser until the i ; evolution of gases ceased. The crystals which precipitated ! on cooling were filtered and washed several times with : acetic anhydride and finally with dry ether. The solid i I was dried in a vacuum desiccator over and NaOH. i The solid was a light blue powder which did not change ! weight in air during an average weighing time. i j Anal.:: Calcd: C, 26.1*8; H, 3.31; Cu, 35.00. | Found: C, 26.21*; H, 3.25; Cu (residue), 31*.18. j j The anhydrous cuprous acetate had been prepared by i TO j Wilmarth by the reduction in inert atmosphere of an am- | moniacal solution of cupric acetate monohydrate with the | j acetate salt of hydroxylamine. The products of the reduc- J tion were precipitated out of glacial acetic acid, washed I I ; repeatedly with dry acetic acid and dry ether until only I the pure cuprous salt remained. The product was dried | : under vacuum and was sealed into evacuated tubes which | were to be opened just before use. i I .................... — — ■■ -■ — ■ I- H I Spath, Monatshefte fiir Chemie, 237 (1912). j "^Wilmarth, loc. cit. 27 Anal.: Calcd; C, 19.57; H, 2.5^; Cu, 51.9 Pound: C, 19.78; H, 2.1*5; Cu (residue), 50.03, 1*9.71*. All other chemicals used were of the usual C.P. quality. i • i i | B. Preparation of cuprous acetate solutions. The i ' first attempts at preparing solutions of CuOAc in quinoline j I j by dissolving weighed amounts of anhydrous CuOAc in quino- 1 . . . . | line were abandoned; first, because of the difficulty in j j making the anhydrous solid salt, and second, because of i the difficulty in preparing and transferring the air- | sensitive solution to the reaction vessel. An alternative j method was developed which avoided the necessity of pre- i | paring the cuprous salt directly. This involved the re action of the anhydrous GuCOAc^ with Cu metal as follows: A weighed sample of anhydrous Cu(0Ac)2» & thoroughly cleaned coil of No. 2l* copper wire, and the necessary amount of quinoline were added to a small narrow neck flask having a ground joint at the neck. This flask was then attached by the joint to a side arm of an all-glass l jacketed reaction vessel equipped with magnetic stirrer | (see Wilmarth)13 in such a manner that the contents of the I | flask would be delivered to the vessel by rotation of the | 1 | ; ^Wilmarth, loc. cit. 28 ! i I flask through 180 . (See Figure ! ( . • ) The contents of the ! I flask were then degassed thoroughly under vacuum, and were heated under vacuum to about 130°C. by immersing and oc- \ casionally shaking the flask and contents alone in a hot j 1 i . I oil bath for several hours or -until the reduction, as evi- ' i 3 f i * j | denced by striking color change from green to clear ruby j | red, had occurred. In order to prevent distillation of \ 5 I | | ! the quinoline into the reaction vessel during heating, a j . 1 ! I ! | stream of cold air was directed at the neck of the flask. j ! I | After the flask and contents had cooled somewhat, the flaskj | was rotated through 180° and the solution was delivered j ! \ I into the reaction vessel, the copper coil being held back j I i I by the narrow neck of the flask. The flask was then sealed! i I | off from the reaction vessel. The copper coil was removed, j i * i washed several times in methanol, and weighed. Prom the j I ... ; i I difference in weight of the copper, the weight of the j I cupric salt, and the volume of quinoline added, the con- j centration of the solution in the reaction vessel was cal culated. The concentrations were checked against analysis i by electrodeposition. i i ! i | —• Preparation and analysis of para-rich hydrogen. |The preparation and analysis of para-rich hydrogen was 29 Go s sampling bulb narrow necked flask R eaction vesse FIGURE k REACTION VESSEL FOR PARAHYDROGEN CONVERSION 30 j done according to the methods of Wilmarth and Baes. Ik | j ! D, Ortho-parahydrogen conversion. The solution in the jacketed vessel (see Section B) was first agitated withj * ; ^ o * | normal hydrogen at 100 C. (hot circulating oil in outer j \ i ! jacket) for several minutes to insure the presence of only j I ' ! ; the cuprous species. The vessel and contents were cooled ; ; i ; and evacuated, Para-rich hydrogen was then introduced at j [ $0 cm, Hg pressure above the solution. The vessel was | I heated at 100.0°G, - O.Oij. for about twenty minutes, at j ; ' • 1 5 ! | which time temperature equilibrium was established. The j { stirrer was then started and brought immediately to 1000 j ! . . . | | R.P.M. Small samples of gas were removed periodically* j I . | | The time of removal was noted. This same procedure was j j ' j followed for conversion runs at 80 and 6o°C. Zero time > is thus the time of removal of the first sample. j i I - • i I E. Minimum stirring speed determination. The con version, of ortho-parahydrogen occurs in the liquid phase I J but the conversion rate is followed by extraction of ; samples of the gas phase. Therefore it is necessary that j ! ! j the stirring be rapid enough so that it is not the rate ! ■ ^W. K. Wilmarth and C. P. Baes, Jr., J. Chem. Phys.i j 20, 116 (1952). I determining factor in the conversion process. The minimum | | stirring speed was determined by measuring the rate of con-j I i | version of a solution of cuprous acetate at various stirringj < 1 i speeds. The results shown in Figure 5 indicate that for ! | an observed rate constant of 0.032 (corresponding to a i i | ihalf life of about 21 minutes) a stirring speed of 800 i ! - ’ ; i ! R.P.M. was adequate. Accordingly all the conversion runs ■ were stirred at 1000 R.P.M. ; i ’ i ! F. Ortho-parahydrogen conversion by a solution of j 1 Cuprous and cupric acetates in quinoline. A 0.0997 gram I | acetate and 15.0 ml. of quinoline were added to the reac- S 2 tion vessel. A small copper coil, £.0 ml. of quinoline, and 0.0118 gram of cupric acetate were added to the small nar row necked flask attached to the reaction vessel (see description of preparation of cuprous acetate on previous page). The reduction in the flask proceeded as previously described. The contents of the flask were added to the main reaction vessel and the flask was then sealed off I from the system under vacuum. The vessel and contents were | heated with stirring until the cupric acetate had dissolved,, j The resulting solution containing known amounts of cupric | and cuprous acetate was cooled to 22°C. and para-rich ! • . " , j hydrogen was introduced at 60 mm. Hg pressure. The system Observed rate constant 32 O.OU <D--- 0.03 0.02 0. 011- iiOO 1600 800 1200 RPM FIGURE ^ LIMITING STIRRING SPEED DETERMINATION 100°C. ! was preheated at 100° (without stirring) for 1$ minutes j ! and then the solution was stirred at 1000 R.P.M. Small ! ; ! ? i s gas samples were removed periodically and the time of re- | ■ | ! moval and color of the solution was noted. The samples ■ i I were analyzed for their parahydrogen content and the data j * ! | tabulated. \ [ \ . | G. Deuterium exchange with cuprous acetate in quino- j ' —2 i ! line. A 6.06 x 10** M solution of cuprous acetate in j i ; | quinoline was treated as described in section D above, I I except that deuterium was used ins tead of parahydrogen. | I H* Solubility of hydrogen and/or deuterium in quino- | S j i line. A 3^*0 gm. quantity of pure quinoline was weighed j I ^ j | into a jacketed all-glass reaction vessel (see Figure 1|) j \ I I attached to a 10 ml. buret and leveling bulb* The quino- I line was degassed by boiling under vacuum and was then heated with stirring until temperature equilibrium was ; I i established. Then the stirring was stopped and the desired i gas was quickly introduced at one atmosphere pressure above ■ the solution and into the buret. There was no indication j ! . ! |of lack of saturation at initial introduction of the gas. j Volume readings were taken as soon as possible and an j i initial value was obtained by extrapolation to zero time. ! The system was then stirred until solubility equilibrium was achieved. The stirring was stopped and final volume : readings were taken. The solubilities were measured at 0°, 21}.,66, J 4O.I0, 60.8°, 80.8° and 100.8°C. IV. RESULTS AND CONCLUSIONS | j The rates of conversion of ortho-parahydrogen by i ! ! solutions of cuprous acetate in quinoline were measured i , i | at 6o°, 80°, and 100°C. and are summarized in Table IV. t | The values of k°C in column 7 were calculated according to ; equation 9 from the rate constants, k, the values of Vi/Vg, the measured rate constant for pure quinoline,* ks as shown in the first line of Table IV, and the hydrogen ! solubility data^ in Table V, and Figure 6. The values I j of k°C were plotted against the square of the corresponding i cuprous acetate concentrations in column I 4 . of Table V I as shown in Figures 7,» 8, and 9» The values of k° in Table VI were obtained from the slopes of these curves, A plot of In k° vs l/T as shown ' in Figure 10 was then used to estimate a value, of E, the j activation energy of the conversion process and A, the i tk * The constant was determined at 100.0 C.; its temp erature coefficient was assumed to be negligibly small. j The solubility of hydrogen in cuprous acetate j solutions and in pure quinoline was assumed to be the same. 3$ TABLE IV ORTHO-PARAHYDROGEN CONVERSION BY CUPROUS ACETATE IN QUINOLINE Run number Tempera ture °C. (CuI)a x 102 (Cu1)2 x 10^ k min.~l Ti Vg k°C. min,~l ! 0 100.0 0 0 0.000359 2.U6 0.00288 ' 1 100.0 1.02 1.0U 0.00263 0.826 0.051a I 2 100.0 2.03 k.12 0.00516 0.826 0.109 ; 3 100.0 2.99 8.96 0.0100 0.826 0.215 : ub 100.0 3.25 10.5 0.00663 0.1|02 0.285 i 5 100.0 3.8? 15.0 0.0176 0.826 0.379 i 6 100.0 U.22 17.9 0.0219 0.826 0.1 4 - 7 2 7 • 100.0 It.77 22.8 0.0280 0.826 0.606 1 8 i 100.0 5.18 26.9 0.032 0.826 0.69- ^ 9 80.0 3.00 9.00 0.00335 0.808 0.083 10 80.00 h.27 18.3 0.00601; 0.808 0.153 - 11 80.00 $.25 27.6 0.00877 0.808 0.223 : 12 i 80.00 5.81 33.8 0.0110 0.808 0.281 1 13 60.0 3.03 9.18 0.000715 0.786 0.0205 ; 11; 60.0 U.3U 18.8 o.ooi5U 0.786 0.0151; : 19 i 60.0 5.91 3U.9 0.00286 0.786 0.087 Corrected for volume expansion of solvent. to From final slope of Fig. 11. 36 SOLUBILITY OF TABLE V HYDROGEN AND DEUTERIUM IN CALCULATED TO 25.0°C. QUINOLINE t°C. Solubility in ml.gas/ml.solvent Hydrogen Deuterium 100.8 0.01*67 0.01*80 80.8 0 .01*22 0.01*36 60.8 0.0376 0.0386 50.0 0.0355 — - 1*0.1 0.0333 0.031*5 2l*.6 0.0300 0.0311* 0.0 0,0253 0.0270 . Hg/ml. Quinoline (Calculated to 25.0°C. 37 0.0i| 0.02 ' 2 0 00 FIGURE 6 SOLUBILITY OF DEUTERIUM AND HYDROGEN IN QUINOLINE min 38 0.6 0. 1* o o X 0.2 10 20 (Cu1)^ x 10^4- (moles/liter)^ FIGURE 7 EFFECT OF CONCENTRATION ON CONVERSTION RATE CONSTANTS AT 100°C. rain 39 0.3 0.2 o 0.1 20 (Cu^)^ x 10^- (moles/liter) ^ FIGURE 8 EFFECT (OF CONCENTRATION ON C ON VERST ION_R AT E _C0NSTANTS_AT_.80.0oC., k°C. min. i*0 0.08 O.Oi* 1*0 20 J x 10^ (moles/liter)2 FIGURE 9 EFFECT OF CONCENTRATION ON CONVERSION RATE CONSTANTS AT 60.0°C ia TABLE VI TEMPERATURE COEFFICIENTS OF THE CONVERSION RATE CONSTANTS 1 -,^3 t°C. k® log k° T°A x 10 100.0 2£8 2. 1*11 80.0 83.1 1.919 60.0 .2U.9 1.398 2.68 2.83 3.00 log(k 3+2 2.0 _ • o I—I K o 1.0 2.6 2.8 3.0 l/T x 103 FIGURE 10 TEMPERATURE COEFFICIENT OF CONVERSION RATE CONSTANTS pre-exponetial term in the rate constant expression k° = A ;e/rt (id These are as follows: E « li|«i+ kcal./mole A = 1.2 x 1C)9 1.2 moles'”^ sec."-*- I 1 The results clearly indicate a second order depen- ;dence of the conversion rate on the total concentration of the cuprous acetate. Further, while several possible 'mechanisms are consistent with the concentration dependence ;in the rate expression, the pre-exponential term favors . the simple termolecular expression 2CuI + p-H2 = 2CuxH (12) This is especially interesting since Calvin has postulated . the following mechanism to explain the homogeneous auto- catalytic hydrogenation of cupric acetate in quinoline: a slow rate-determining activation of the hydrogen mole cules by some form of the cuprous species followed by a rapid reaction between the activated hydrogen and the cupric acetate. The above is most* simply expressed by the follow- & ' * ing equation: 'Since cuprous and,cupric acetates are probably neg ligibly ionized but appreciably solvated in quinoline any reference to either only indicates its existing valence state in solution. I nCu1 f H2 kl , (CuI)n.H2 (13) | (Cu^.Hg 4 - 2CU11 3 „ (n + 2)CuI 4 - 2H“ (llf) where » k^ » k^ . The above implies that the rate-determining step in I s the hydrogenation of cupric acetate in the presence of the j cuprous acetate is the same as that in the ortho-parahydro-j 9 < gen conversion. If this is true then cuprous acetate ; should cause no conversion during the hydrogenation of cupric i acetate with para-rich hydrogen. However, a slow rate of ; i conversion’ ' * would be produced by the paramagnetic cupric ! I i acetate (all paramagnetic substances catalyze the conver- j j sion). j An experiment to verify the above prediction (see ! i I experimental section P) was performed and the results are shown in Table VII. The data plotted in Figure 11 are shown in columns one and three. The rate constants k, as defined in equation 8, which were determined from the initial and ! Exploratory experiments indicated that the rate of conversion by cupric acetate would be approximately l/lO the rate of that by the cuprous acetate under comparable conditions. h$ TABLE VII ORTHO-PARAHYDROGEN CONVERSION DURING AND AFTER HYDROGENATION OF CUPRIC ACETATE IN' QUINOLINE t = 100°C. ^t “ ^00' ^ R^ — Rqq Time in minutes ? ^0 ~ ^00 In XO n * p 0 00 Color of solution 0.0 1.00 2.30 green 2U.5 .968 2.27 yellow green U5.6 .939 2.2 1* muddy green 61.7 .923 2.22 orange red 7iw8 i .901* 2.20 red : 10I 4 . . 7 .735 1.99 red , 150.0 .536 1.68 red 2.3 2.0 - 8 8 « K i l -p o K o rH G rH 1.5 - time in min. FIGURE 11 ORTHO-PARAHYDR0GEN CONVERSION DURING AND AFTER HYDROGENATION OF CUPRIC ACETATE AT 100°C, - p r * O' | final slopes of the curve, are 0.0011+ and 0.00663 respect- | ively. It should be pointed out that a new zero time I should have been chosen for the evaluation of the final | slope. However, when this was done it gave a slope not I j significantly different from the one plotted. The results j j clearly establish the identity of the rate-determining stepij I of the conversion and the hydrogenation processes. 1 i I | Since the hydrogenation and the conversion processes ! | occur through a common mechanism one should also be able to I | calculate the rate of hydrogenation from the known conver- i sion rate at the same concentration and temperature. The ! rate of absorption of hydrogen in terms of the rate con stant, k, can be shown to be = v' k(l f ! L ) a (15) min. 1 aV]_ where is the volume of the solution phase in the hydro genation reaction and the other terms have their previously designated meanings. Since, under the experimental condi - |tions used, the following was true S »1, (16) aVi equation 15 simplifies to 1+8 ! j = V' k v s (17) i min. X y“- i ! i The above equation was evaluated at a cuprous concentra- j tion of 3.9 x lCT^M at V^/Vg equal to 0.826 with the aid j i of the data of Table IV, columns 5 and 6, and was compared with observed hydrogenation data. The results are as fol lows : Calcd. rate of absorption of 1.06 ml./min. Obs. rate of absorption of H2 1.05 ml./raih* | While the agreement is well within the experimental error ! | of the data at this concentration range (0 to 0• 0I 4 . M in j i j I i j CuOAc), comparisons at higher concentrations are not as j i i satisfactory. This will be discussed in more detail m j Chapter IV. Mills and Weller^ have reported on a study of the catalytic homogeneous hydrogenation of cupric acetate in quinoline. It was concluded that the rates of absorption I of hydrogen was between first and second order with respect i I j to the cuprous acetate concentration. This conclusion can-j j | i not be considered valid because the measurements were made j ! I without cognizance of the acetic acid inhibition effects i 15 S. Weller and G. A. Mills, J. Am. Chem. Soc., I£, 769 (1953). j 1+9 ; and in a cuprous acetate concentration range where it is now' established that the rates are stirring speed dependent. In his discussion of the hydrogen activation, Calving assumed a cuprous acetate hydrogen-active dimer and sug gested that this dimer has a ring structure similar to that formed by acetic acid in non-polar solvents and in the gas phase. However, the results here do not indicate the neces sity of considering such a dimer. Rather the activation can be visualized as an interaction of two copper atoms and a molecule of hydrogen with subsequent cleavage of the hydrogen molecule. Complete cleavage would formally require copper-hydrogen bonds of 1+1+.5 Kcal./mole.^ Actually this calculation is somewhat uncertain since electron promotion would presumably be required to open the full d shell of electrons in the cuprous ion, but some energy might be regained through some metal-metal interaction across the ring. In support of this mechanism it should ; i be noted that the nickel atom, which is isolectronic with the cuprous ion, forms a gaseous hydride NiH, with a dis sociation energy of approximately 60 Kcal./mole.-*-? • i ’ “ 'This value is l/2 the difference between the dis sociation energy of the hydrogen molecule and the measured ■ activation energy for the conversion process. > "^Calvin, loc. cit. 17 A. G. Gaydon, ’ ’Dissociation Energies," (New York: j Dover Pub., 191+5), p. 212. If one accepts the copper-hydrogen bond mechanism involving! I the cleavage of the hydrogen molecule, it is evident that j | a reversal of this process would result in ortho-parahydro-j I ' j gen conversion. In addition, the copper-hydrogen bonds i I ’ ! might be chemically reactive enough to account fbr reduc- i i i | tion of cupric acetate. j ! " 1 Q ' \ In a recent publication, Wender ° has reported \ another example of a homogeneous catalytic hydrogenation, j I I He concluded that f Co(CO)^J ^ acted as such a catalyst in | the hydrogenation of butyraldehyde• A chain mechanism | involving Co(CO)^H and hydrogen atom was postulated^-9 al- i s i though no evidence was presented. Such a mechanism would j | not be entirely ruled out in our case although, in the j ) " , i | hydrogenation experiments, the usual tests for a chain j j reaction were negative. In addition, such a mechanism | * j . requires a metal-hydrogen bond twice as strong as the. one which has been postulated in the rate-determining step. Copper-hydrogen bonds such as has been postulated j might be expected to be quite reactive chemically and per- j haps it is not too' surprising to find that when deuterium j i " I j was substituted for hydrogen, exchange was found to occur . . . _ l \ !8l. Wender, J. Am Chem. Soc., 72, I 4 . 8I 4 . 2 (1950). | ! 19l. Wender, R. Levine and M. Orchin, J. Am. Chem. I I Soc., ]2, 4375 (1950). | i I-with, either the acetate groups or the quinoline solvent, j j ; " ! |The rate of exchange appears to be of the same order of i • ■ . i !magnitude as the parahydrogen conversion and hence the pos- ! i |sibility exists that it is an integral part of the conver- \ sion mechanism* As an alternate to the previous mechanism one might assume that the hydrogen molecule adds to the double bond in the quinoline ring. Since the cuprous atoms are probably solvated by the basic nitrogen atoms of the quinoline, a catalytic addition might occur although the exact mechanism is somewhat difficult to visualize* i | Such a partially hydrogenated quinoline would be expected | to be thermodynamically unstable and a reversal of the formation would account for both the parahydrogen conver- i \ sion and the deuterium exchange. ! I V. SUMMARY j j The rate of conversion of ortho-parahydrogen by . solutions of cuprous acetate in quinoline has been measured, The second order dependence of the conversion process on i the concentration of the cuprous species has been establish! I | | ed at three different temperatures. Prom the temperature j i ! j coefficient, a value for the energy of activation of the j ! ! ^ ! j conversion process has been estimated. It has been experi-j > . ! j mentally verified that the rate determining step for the j 52 hydrogenation of cupric acetate in quinoline and for the ortho-parahydrogen conversion by cuprous acetate in quino line are identical at 100°C. This observation has been substantiated by a calculation of the rate of hydrogenation from the rate constant for the conversion process. The exchange of deuterium with a solution of cuprous acetate in quinoline has been measured but no definite conclusions concerning the mechanism of exchange and its relationship to the conversion process have been reached. CHAPTER IV HYDROGENATION OP CUPRIC ACETATE IN QUINOLINE IN THE TEMPERATURE RANGE 0-60°C. I. INTRODUCTION The kinetics of the autocatalytic hydrogenation of cupric acetate in quinoline were studied by Calvin^ and Wilmarth^ and were subsequently correlated^ with the kinet ics of conversion of para- to orthohydrogen by cuprous acetate in quinoline. It was concluded that the rate- determining step for the conversion process was the same as for the hydrogenation process at 100°C. and for cuprous concentrations below O.OI4 . molar, and that both processes were first order with respect to hydrogen, second order with respect to the cuprous acetate, and zero order with respect to the cupric acetate. However, the hydrogenation rates for concentrations above 0.0i ( . molar, in cuprous acetate were less than the rates predicted from the lower concentrations. This inconsistency was believed caused at "Si. Calvin, Trans. Farad. Sec., 3k» 1181 (1938). p W. K. Wilmarth, "Catalytic Homogeneous Hydrogena tion," (unpublished doctoral dissertation, University of California, Berkeley, 19l(.2). 3 W. K. Wilmarth and Max K. Barsh, J. Am. Chem. Soc. 7£, 2237 (1953). 5k least in part by the limited rate of solution of the hydrogen gas in the liquid phase by virtue of stirring speed limitations during reaction. Investigation on the hydrogenation process at a lower temperature was indicated where presumably the hydrogenation rate would be sufficiently slow compared to the rate of solution of the gas, so that the stirring speed would not be rate influencing even at relatively high cuprous acetate concentrations. Thus the rates of hydro genation of cupric acetate in quinoline were studied in the range 0 - 60°C. and up to a cuprous acetate concentra tion of 0.085 molar. The 6o°C, hydrogenation results were compared with the parahydrogen conversion data for further substantiation of the identity of the rate determining steps for the two processes. The lower temperature hydro genation data on.the average appeared to have anomalously low rates at the higher cuprous acetate concentrations. Subsequent investigations were made with deuterium in the effort to resolve these anomalies and to probe for the pos sibility of nonclassical tunneling as suggested by Bell.^ II. EXPERIMENTAL PROCEDURES A. Materials used. The quinoline was prepared, P* Bell, Acid-Base Catalysis (Oxford; The Clar endon Press, 19^1)* PP« 192, 20lj^ handled and stored as described by Wilmarth and Barsh. j The cuprous acetate solutions were prepared by the reac- ; ; ■ tion of copper wire with anhydrous cupric acetate in quino- ; line solution. The cupric acetate solutions were prepared I i i . | j by the addition of weighed amounts of the anhydrous salt | I ! ] into pipetted amounts of quinoline. The hydrogen and deuterium used were of electrolytic purity and were dried j by passing first through two 15 mm# x 50 cm. tubes packed j with glass beads and phosphorous pentoxide and then through i ' I : a liquid nitrogen trap, ! | 1 B. Hydrogenation apparatus. The apparatus used for ! : the hydrogenation and deuteration rate studies was designed. i ’ to maintain constant pressure and temperature throughout .the gas absorption process. Its general characteristics : are shown in Pigure 12. The pressure is sensed by the I mercurial manometer through which the relay is fired. ! ; i | The relay controls both valves (on-off type) to the surge ! i f - | tank simultaneously but opposite in phase. The needle ! | valves regulate the pressure control capacity. The surge I » - • • tank in conjunction with the capillary section of the I j tubing leading to the mercury reservoir serves to filter j i — — - j i d I i ^Wilmarth and Barsh, loc. cit. j i « o Topler pump Reaction vessel To valves Relay Manometer level control To relay Vacuum Surge tank Pressure Valve Needle valves To relay FIGURE 12 CONSTANT PRESSURE HYDROGENATION APPARATUS 57 out the surges caused by the opening and closing of the valves and thereby minimizes "hunting effects*" The buret j I I temperature was maintained at 25°C. by water pumped from a I 1 2 constant temperature bath. The temperature in the re actionj A i - ■ } vessel was maintained at the desired value from correspond-j ing constant temperature baths. _ j i C. Hydrogenation or deuteration procedure. The hydro genation procedures at 6o°C. were handled in the manner de- | scribed by Wilmarth for 100°C., i.e., runs were made with j ! • I I various initial amounts of acetic acid so that it Was ! i j i * | possible to eliminate the small inhibitory effect of the J ! ! I acetic acid produced by extrapolating to zero concentrations \ ! i ■ ; ! of the acid. The measured slopes at various points of the I 1 ' 2 • ! plot of the volume of hydrogen absorbed against time gave ! \ | ! • 1 i the rate of absorption of hydrogen at cuprous acetate i ! i ! concentrations determined from the stoichiometry of the j I reaction. j Below 6o°C. an alternative procedure was used since j the time necessary for a complete hydrogenation run was prohibitively long. The hydrogenation for a given cuprous acetate concentration was precisely followed a sufficiently long time so that the best straight line through a plot of the volume of hydrogen absorbed against the time would be ' L O * J equivalent in accuracy to the measured slopes at oO C. i i Different cuprous acetate concentrations were established j j i ! by absorbing the necessary hydrogen at a higher tempera- | ( j ture where the rate of absorption was rapid, and then j ( j j quenching to the desired temperature for further measure- j | ^ I ments. An approximate acetic acid correction was made j ! i where indicated by interpolation from the 60 C. data since . j | it was observed that the inhibition effect was temperature j independent at 60, 100°G. and presumably also for the lower] i ' i i temperatures. ; j The method of preparation of quinoline solutions J i i ; for hydrogenation containing both cuprous and cupric species] 6 i ; was identical to that described by Wilmarth and Barsh, ] j i i The thermostating liquid was pumned through the outer walls! i * ! ! of the reaction vessel until the vessel and its contents ] | j ; under vacuum reached thermal equilibrium. Thermocouple | : i ! measurements both within the cell and its outer jacket in- : i ; i dicated that (1) the temperature difference between outer j i i | | jacket and cell proper was less than 0.1°C,, and (2) the j I i i ] equilibrium was always reached in less than twenty minutes.! | , j j The appropriate buret and manometer was filled with the j 5 i desired gas and the manometer was adjusted to the necessary Wilmarth and Barsh, loc. cit. pressure with the. aid of the manometer level control. The automatic pressure control was activated, the initial reading of the buret was macte and then the stopcock to the reaction vessel was opened. Simultaneously the magnetic stirrer and an electric timer were started. An intervals j s the buret reading and corresponding time was ^recorded. j When the reaction had proceeded sufficiently, the thermo- j i stating liquid was withdrawn, the stirrer was stopped and j t . i the pressure control device was deactivated. The gas was j ' I | pumped out of the reaction vessel and back into the buret j [ ! by cycling the topler pump. Then a final buret reading ! I was taken. I j I i i III. RESULTS AND DISCUSSION j i • ■ I ■ ! S The experimental evidence in a paper by Wilmarth and! i 7 P i I | Barsh and the work of Calvin and Wilmarth indicate that I ; j I the hydrogenation process can be simply expressed by the i ! j i jfollowing equations: j ! 2(0^) + (H,) jdfe 2 (CuI)H (18) ! I ki ! 7 Wilmarth and Barsh, loc. cit. 8 Wilmarth, loc. cit. 60 (CiA) + (Cu11) — 2(0^) + (H+) (19) where ^2 » k-^ >> k°. If k° (Cu-^O^H^) is rate determining then the rate of disappearance of hydrogen in the solution is expressed by tion of the hydrogen gas at constant pressure by the solu tion where the rate of diffusion (and therefore stirring ‘ I rate) of the gas into the solution is not rate influencing.; Thus a plot of the rate of absorption of hydrogen at con- : stant pressure against the square of the formal cuprous species concentration yields a straight line passing through the origin and having a slope, k, which when expressed in the proper units gives the rate constant k°. tions of cupric acetate in quinoline at 60°, f>0°, I 4 .O0, 25°, and 0° were measured, corrected for acetic acid ef fects where such correction was necessary, and tabulated in Tables VIII, IX and X. The hydrogenation measurements of Calvin^ and Wilmarth^ at 100°C. were experimentally = k° (H2)(Cu1)2 (20) This of course is a direct function of the rate of absorp- The rates of hydrogenation and deuteration of solu- 9 Galvin, loc. cit. 10 Yifilmarth, loc. cit. TABLE VIII 60° HXDROGENATION DATA (OBSERVED) Observed slope**" rate units in Stirring speed Ou.1 x 10 (Cu*)^ x 10^- ml./min. (HOAc) x 10*+ Pressure in cm. RPM 3.00 9.00 0.0517 17 36.1 1000 5.13 26.U 0.123 106 36.1 1000 5.13 26. k 0.102 600 36.1 1000 ,5.89 3U.7 0.1U7 181 36.1 1000 5.89 3U.7 0.150 310 36.1 1000 5.89 , 3U.7 0.12$ 677 36.1 1000 7.16 51.2 0.21U 318 36.1 1000 7.16 51.2 0.210 U39 36.1 1000 7.16 51.2 0.173 811 36.1 1000 8.U7 71.8 0.27l| 161 36.1 1000 8.U7 71.8 0.278 568 36.1 1000 8. I4 . 7 71.8 0.222 9h0 36.1 1000 9.31 86.9 0.302 537 36.1 1000 9.31 86.9 0.316 651 36.1 1000 9.31 86.9 0.2$3 1027 36.1 1000 • S f - Measured for $0 ml. solution at 2$°C. TABLE IX 60° H Y D R O G E N A TIO N D A T A (AND CO N VE R SIO N DATA) CORRECTED FOR HOAc (Cu1) x 102 (Cu1)2 x 10^ Rate at 0 (HOAc)* in ml./min. Notes 3.00 9.00 0.517 See curve - / < * 5.13 26. k 0.13U See curve , < 5.89 3U.7 0.175 See curve „ 7.16 51.2 0.262 See curve 8.U7 71.8 0.360 See curve 9.31 86.9 — ■ See curve « 3.03 9.18 0.01*61 Calculated from p-Hg conv. k»3k 18.8 0.0951 Calculated from p-H2 conv. 5.91 3U.9 0.179 Calculated from p-H2 conv. Measured for £0 ml* solution at 25°C. TABLE X HYDROGENATION DATA - $0°, 1* 0 ° , 2$°, AND 0°G. (Cul) (CuX)2 Observed slope,* (HOAc) Initial Stirring 102 X , ioU rate in ml./min. 10^ f i n i * Pressure speed t°c. Uncorrected Corrected"”1 ' Cu(0Ac)2 (#) in cm. RPM Notes 52 . O- 2.92 8.53 0.0259 -------- 8.3 0.57 36.1 85o Solid Cu(0Ac)9 1*.03 16.3 0 .01* 1 * 6 0,01*61* 117 0.57 ‘ f t 36.1 85o it 5.63 31.6 0,0886 0.101* 279 0.57 ! * ■ 36.1 850 tt 6.55 1*2.9 0.107 0.133 368 0,57 u ■ 36.1 85o ? 5.23 27.3 0.070 0.0815 2 1 *0 1.61 6 36.1 85o Solid Cu(0Ac)2 Uo " 2.01 1*.06 0.001*78 -- 5.1* none 0 72.7 300 No solid visible 2.80 7.88 0.00936 — 86 i t u 72.7 300 tt 3.10 9.61 0.00515 0.0051*0 110 i t It 72.7 300 n U.31 18.6 0.0270 -- 39 0.27 9 36.1 600 Solid Cu(0Ac)o U.U2 19.1 0.0290 0.0297 51 0.27 tt 36.1 600 « d 5.61 31.5 0.0373 0.01*21 170 0.27 1 1 36.1 1*00 5.93 35.1 0.01*00 0.0l*6l 200 0.27 It 36.1 1*00 No solid visible 2.89 8.37 0.0122 - — 2.6 0,57 0 36.1 85o Solid Cu(OAc)9 3.20 10.3 0.011*1* ---- 31* 0.57 1 1 36.1 85o tt * 3.99 16.0 0.0231* 0.0252 110 0.57 I* 36.1 85o tt 5.60 31.1* 0.01*30 0.0510 280 0.57 It 36.1 300-850 it 6.50 1*2.3 0.0525 0 .061*6 361* 0.57 It t 36.1 850 1 Solid Cu(0Ac)o 5.20 27.0 0.0373 0.01*35 237 1.61 6 36.1 850 25 Lm lt.01 16.1 0.00629 — — 1*.3 0.27 9 36.1 300 Solid Cia(OAc) 0 U.95 2U.5 0.00970 0,0101* 97.6 0.27 36.1 1000 it 5.02 25.3 0.00991 0.0106 105 0.27 n 36.1 300 tt 5^6 3UJ* 0.0121* 0.011*1 189 0.27 it 36.1 300 No solid visible 6.61 1*3.9 0.0130 0.0152 263 0.27 it 36.1 300 tt 1*.06+ 16.5 0.00666 — ~ 9.2 0.27 it 36.1 300 Solid Cu(0Ac)p 6.12 37.5 0.0125 0.011*1* 216 0.27 H 36.1 300 t t 6.21 38.6 0.0116 0.0133 225 0.27 it 13.6 300 t t 6.28 39.1* 0.0120 0.0139 230 0.27 it 72.7 300 * 6.33 1*0.0 0.0122 0.011*1 236 0.27 it 13.6 300-850 tt 0 TABLE X (Continued) HYDROGEMATION DATA - $0°, Ij O 0, 25°, AND 0°C. (Cul) t°C. 102 (Cu- * - ) 2 10^ Observed slope,* rate in ml./min. (HOAc) 10^ Initial CufoAc)2 3 (#) Pressure in cm. Stirring speed RPM Notes Uncorrected Corrected 25 6,1 4 . 0 I 4 I.O 0.0136 0.0157 2U3 0.27 9 13.6 85o No solid visible 6.59 I 43. l l 0.0133 0.0156 259 • 0.27 it 13.6 85o it 6.61 U3.8 0.0136 0.0159 26U 0.27 It 13.6 850 tt 1 4 .00++ 16.0 0.006I 4 . 5 -- U.o 0.27 -0 36,1 856 Powdered glass 3.16 10.0 0.0050 -- _ 26.2 0.57 0 - 36.1. 85o Solid Cu(OAc)? $.63 31.6 O.Olli-O 0.0153 133 0.57 lt 36.1 85o tt 6.U0 la.o 0.0179 0.02014 210 0.57 it 36.1 85o tt 3.07 9.U2 0.00383 22.6 1.61 6 36.1 85o tt 5.19 26.9 0.0105 0.0120 217 1.61 tt 36.1 850 tt 8.02 61i.3 0.0190 0.0223 U98 1.61 tt 36.1 85o tt 8.09 65.5 0.0219' 0.0258 506 1.61 tt 36.1 85o tt 8.15 n 66.5 0.0208 0 » 0 2l j.6 511 1.61 tt 36.1 85o tt u l i . O l j . 16.3 0.000U81 0.0 0.27 9 36.1 I 400 Solid Cu(0Ac)o 5.3U 28.6 0.000956 O.OOlOii 137 0.27 tt 36.1 I 4 OO tt c 6.57 143.2 0.00129 0.00150 250 0.27 n 36.1 270 tt 6.59 U3.8 0.00131 0.00150 25o 0.27 tt 36.1 300-850 tt 6.61 11.1 0,000627 — UO.9 0.57 0 36.1 600 tt 3 . 3 1 4 - 17.5 0.00127 0.00H41 128 0.57 « 36.1 600 it li.18 31.8 0.00312 0.003147 131 0.57 tt 36.1 85o u 5.65 U3.U 0.00307 0.00362 222 0.57 1 1 36.1 900 tt 6.57 U3.U 0.00235 0.00271 222 0.57 « 36.1 U5o » Measured for 50 ml, of solution. ''Corrected for HOAc where necessary, +Test for actinic activity. ++Test for surface effect. # Curve legend. confirmed and are included in Table XI. The data were plotted as described and are shown in Figures 13, li|, l5> ; l6, 17 and 18. The dotted lines represent the data un- i corrected for acetic acid. The 60° and 100°G. parahydro- gen conversion data in Tables IX and XII as described by 1 Wilmarth and Barsh*^ along with some previously unreported 1 i . 0 ' 100 C. conversion data (expressed in the proper units) has / o o 'been plotted along with the 60 and 100 G. hydrogenation data in Figure 13 and 19 respectively. The 60°C. data in Figure 13 indicates that the rate of hydrogenation is second order with respect to the cuprous. ; acetate concentration in the range of 0 to 0.08£ molar and further that the rate determining step of the hydrogenation process is the same as for the conversion process. These 12 data substantiate the conclusions of Wilmarth and Wil marth and Barslr^ for the 100°C. data in the 0 to 0.1). molar cuprous acetate concentration range as shown in Figure 19* Although the stirring speed limit for the 6o°C. was not determined it appears that the observed hydrogena tion rate was not stirring speed influenced. f ■^Wilmarth and Barsh, loc. cit. 1 2 Wilmarth, loc. cit. -*-3wilmarth and Barsh, loc. cit. 66 TABLE XI 100°C. HYDROGENATION DATA (CORRECTED TO 0 CONCENTRATION HOAc) Cu1 x 102 (Cu1)2 x 10^ Rate* of hydrogenation ml./min. Stirring speed RPM 0.9U6 .898 0.10 1000 1.69 2.86 0.35 1000 2.U5 6.00 0.59 1000 3.28 10.7 0.88 1000 3.79 1U.U l.Oli 1000 U*73 22.3 1.33 1000 5. 1 4 - 8 30.0 1.73 1000 6.23 38.8 2.10 1000 6.99 U8.8 2.53 1000 9.6** 92.0 3.2 1000 • S f r n Measured for 50 ml. solution at 25 c. M. K. Barsh, Unpublished data* Rate of absorption of H£/50 ml. soln. 0. 1+ 0.2 LEGEND G Rates extrapolated to 0-conc. HOAc. A See Figure li+. O Conversion calculated to hydrogenation. 20 FIGURE 13 HYDROGENATION AT 60.0°C.~EXTRAPOLATED TO O-HOAc Rate of absorption of H2/5>0 ml. soln, o o * ro o Co 3 0 » i o > M O S 2i > M ^3 O ! Ch 1 O' to \ O f e r j O o 0 • 1 I • a o > o -p" 99 a o > X H O . ro CD 3 o H C D C O H* ct C D Hg/min./^O ml. soln. 69 0.16 0 - 0.08 LEGEND See Table X £0 1 + 0 20 30 10 (Cu^)^ x 10^ (moles/liter) 2 FIGURE 1$ HYDROGENATION AT 90 .0°C . 70 0.08 O.Oii 07 C N J LEGEND See Table X ■O- (Cu-*-) ^ x 10^ (moles/litesr)^ FIGURE 16 HYDROGENATION AT U 0.0°C . • ^/miru/fjO ml. soln. 0.03 Oy 0.02 0.01 LEGEND See Table X 20 30 CO ; (Cu-^)^ x 10^ (moles/liter FIGURE 17 HYDROGENATION AT 2$.0°C. . ^/min./^O ml. soln. 72 o.oU o- o- CK LEGEND O- See Table X 20 10 (Cu-'-) ^ x lcA (moles/liter) ^ FIGURE 18 HYDROGENATION AT 0 .0 °C . 73 TABLE XII 100°C. CONVERSION DATA CALCULATED TO HYDROGENATION Cu^ x 102 (Cu*)2 x 10^ Rate5 4 - of hydrogenation ml./xnin. Stirring speed RPM 1,02 1.0U 0.168 1000 2.03 1+.12 0.330 1000 2.99 8.96 0.639 1000 3.25 10.5 0.870 1000 3.17 15.0 1.12 1000 U.22 17.9 1.U0 1000 U.77 22.8 1.79 1000 5.18 26.9 2.06 1000 5.99** 35.9 2.36 ^ 1000 9.6 92.0 3.9 1000 ^Measured for 50 ml* solution at 25°C. ■ M ' c M. K. Barsh, Unpublished data. . H^/min./fjO ml. soln LEGEND _0 W.K. Wilmarth original hydrogen-i i ation data corrected to ! 0 conc. HOAc. o-p H2 conversion by M.K. Barsh ; calculated to hydrogenation. -A Hydrogenation data by M.K. Barsh. 20 10 (Cu1)^ x 10^ (moles/liter)2 FIGURE 19 —j HYDROGENATION AT 100°C. ^ o ■ At 50 C. the rates of hydrogenation as indicated in ! I Figure 15 were second order with respect to the cuorous I i . | j acetate concentration and behaved in general like the 60 j and 100°C. rates. ! I r I . o ! j At low concentrations of cuprous acetate the 1 4 .O C. j | rates of hydrogenation as shown in Figure l6 were also | ! i second order with respect to the cuprous acetate concen trations. However at the high cuprous concentrations the~ rate increased with addition of excess solid cupric acetate, ! I This might be explained by assuming that the addition of j 1 the excess salt alleviated the situation where the reverse j ; i rate of the Cu^- H2 interaction competes measurably with j • the rate of solution of the cupric acetate. | j j The 25°C. hydrogenation rates as shown in Figure 17, j i although apparently second order with respect to cuprous i i \ ! ' ! I acetate concentration for most of the cuprous concentration! f • i jrange, appear to be dependent upon the presence of excess j I ■ ■ j cupric acetate. This behavior may be explained in part by j ! | j the above i^.0°C. explanation. . However, the rate behavior at j (the.highest cuprous concentrations, where the solid cupric j salt is still present in large excess, is at present lack ing a satisfactory explanation. i | Although the 0°C. reaction behavior as shown in j • j ! Figure 18 may be explained in terms of the rate of i 76 i solubility of the cupric salt, this behavior is most likely1 additionally complicated by the ease with which cupric acetate supersaturates in quinoline and thus may account for the high irreproducibility of the rate data# The 100°C. data in Figure 19 can be most convenient-■ ly considered in three ranges of concentration, i#e#, O-O.Oij. molar, O.Olj. - 0.05 molar, and 0.0£ - 0.09 molar. As previously stated, below O.Olj. molar the hydrogenation 1 rates and "conversion”* rates are the same and are second order with respect to the cuprous acetate concentration. Between 0.0l| and 0.0^ molar the hydrogenation rate is less than the corresponding predicted and observed "conversion" rate. Above 0.05 molar the observed hydrogenation rate is less than the "conversion" rate which in turn is less than the expected rate. In the intermediate concentration range, where presumably the hydrogenation process but not the con-, I version process may be stirring speed influenced, one is led to believe that perhaps the methods of measurement of the processes could explain the observations. However the data, is not adequate to draw any final conclusions. At the higher concentrations, where the stirring speed becomes in- ; creasingly rate influencing, it is clear that the decrease I ____________________ I ^"Conversion" rate refers to hydrogenation rate ! calculated from conversion data. in the observed rates from the expected rates is inter- ; pretable in terms of a limited or non-equilibrium solu- , / t bility of the hydrogen gas in the solution. The question ' of the relative magnitudes of this decrease with respect to the hydrogenation and conversion processes has not been • , resolved but it probably does not affect the interpretation. For all temperatures at relatively high cuprous ace-' tate concentrations and where cupric acetate concentration approaches zero, the step of equation 19 must become rate determining. A possible alternate hydrogen absorption path from cuprous to copper may then occur concurrently. Just such a situation is stpposed to exist for the observed : slow formation of copper (colloidal or very finely divided) during the 100°G. conversion process at approximately 0.1 molar in cuprous acetate where presumably the following equilibrium must exist: 2CU1 Cu° j k3 «1 . (21) kJ+ The visible manifestation of Cu° is probably dependent on nucleation conditions in solution. The general second order behavior with respect to the cuprous acetate and the first order behavior with respect to hydrogen of the conversion and hydrogenation 78 rates indicates that the transition state contains one ! . - ' ! molecule of hydrogen for two molecules of the cuprous I I species. This has been interpreted as a simple terraolecular; ! collision of two atoms of cuprous species with a molecule j of hydrogen. Calvin-^ however suggested the following ring! i ! structure for a CU2 ^2 intermediate from cuprous acetate j and hydrogen, but it is now known that other cuprous -H R- \ H- I ■Cu •0 \ Cu- ■0 ■R (22) salts such as the sulfate and disalicylaldehyde are also capable of para-hydrogen conversion. Thus it is clear that the activation of the hydrogen by the cuprous species ; is not sensitive to the nature of the anion or to a specific! | geometry of the hydrogen carrying intermediate. Further | it is sufficient to interpret the observed kinetics in terms of the following equation o 2Cu H k 2CuIH (23) 1 i^-M. Calvin,. J. Am, Chem. Soc., 6l, 2230 (1939). ■^M. K. Barsh, Unpublished work. as this interpretation is generally compatible with the explanation for all of the conversion and hydrogenation behavior and in addition is consistent with a one electron oxidation-reduction hydrogenation step Cu1! ! + Cu11 - k. 2 — >- 2CU1 + H+. {2k) After a few preliminary experiments had established that deuterium would behave in a manner analogous to hydro gen, the rate measurements were repeated with deuterium* The data were handled in the same manner as the hydrogena tion data and are summarized, in Table XIII and in Figure 20 These data substantiate the second order dependence of the reaction rate on the cuprous concentration but offer no additional clues to the high cuprous acetate concentra tion behavior at the low temperatures. The deuteration and hydrogenation rate constants are summarized in Table XIV and in Figure 21 their logs are plotted versus the reciprocal of the absolute temperature along with the cor responding conversion rate constants as determined in Chapter III. It can be seen from the parallelism of these plots that non-classical tunneling, if present, is not here measurable. The resultant plots show some curvature for which the limiting slope above 60°C. yields an 80 TABLE XIII DEUTERATION BATA t°c. (Cu1) x 102 (Cu-*-)2 x 10^ Observed slope,* rate in ml./min. Uncorrected Corrected** Pressure in cm. 0 2*.2l* 18.0 0.0001*7 0.00052 36.1 6.60 2*3.9 0.00058 0.00062* 36.1 25 3.02 9.19 0.00252* 0.00326 36.1 2*.l6 17.2* 0.001*19 0.002*65 36.1 1*.19 17.6 0.00390 0.001*33 36.1 i£ 2.96 8.78 0.00911* 0.00991* 36.1 l*.ll 17.0 0.012*9 0.0163 36.1 2*.17 17.5 0.0153 0.0166 13.6 5o 2.87 8.28 0.0175 0.0199 36.1 2*.il* 17.2 0.0332 0.0371 36.1 60 2.79 7.79 0.0337 --- 36.1 l*.l 9 17.6 0.0661 13.6 'Measured for 50 ml. of solution at 850 RPM stirring speed. "'Corrected for HOAc where necessary. D2/min./!? 0 ml, soln 81 0.08 60 C . S 0°c. o.oU 25 C 10 A (moles /lit er) ^ ,I\2 FIGURE 20 DEUTERATION RATE DATA TABLE XIV HYDROGENATION AND DEUTERATION RATE CONSTANTS Process t°C. 1 T°A x 103 k,a Gas solubility St ml./ml. Vol. solution Vs ml. k° log k9 Hydrogenation 0 25 3.67 3.36 U.69 0.0300 5o.o 3.1U O.U98 Uo 3.20 15.5 0.0350 50.7 8.76 0.9UU 50 3.10 31.3 0.0385 50.9 16.0 1.205 60 3.00 50.7. 0.0U20 51.U 23.6 1.373 100 2.68 777 D 0.0585 52.9 252.0 2.U02 Deuteration 0 25 3.67 3.35 2.75 0. 031U 5o.o 1.75 0.2UU uo 3.20 9.28 0.0362 50.7 5.06 0.70U 50 3.10 22.2 0.0399 50.9 1 0 4 1.03 60 3.00 37.5 , 0.0U31 5i.U 16.9 1.228 100 2.68 0.0601 . . . 191 c 2.280 aCorrected for HOAc effect. Measured from initial slope of hydrogenation curve, eg, (HOAc) = 0. cEstimated from Calvin* s data on hydrogenation and deuteration. C O to log k LEGEND O Hydrogenation and deuteration & o-p hydrogen conversion. 0.0 o - 1.0 -2.0 L _______________J________________ 1__ 2.60 2.80 (l/T) xleP 3*00 FIGURE 21 TOTAL. ARRHENIUS CURVE, Da AND H2, HYDROGENATION AND CONVERSION-, 3.20 CD w I Qk activation energy of kcal and below 6o°C. an activa tion energy of 12.0 kcal. However, the limits of the ex perimental error justify drawing one line through all of the points. This gives an activation energy of 13 kcal and a pre-exponential factor of 10^ 1? moles”^ sec."^ These values are consistent with the proposed termolecular mechanism and with the viewpoint expressed in the work by Wilmarth and Barsh, ° namely that in the absence of metal- metal bonding the cleavage of the hydrogen bond would formally require copper hydrogen bonds of about 1|5 kcal/molew An attempt was made to estimate the nature of the inhibitory effect of the acetic acid from the 6o°C. hydro genation data assuming that this effect occurred because of the interaction of the acetic acid with the cuprous acetate. mCu1 + nA * Cu^% , A = HOAc. (25) For equal concentrations of Cu1 but different concentra tions of A, it can be shown that n log - log (CUmA^,) i . (26) ^ ) 2 (Cu’ ^Ajj) 2 Wilmarth and Barsh, loc. cit. 85 For equal concentrations of A but with varying concentra tions of Cu*' a similar equation involving m can be derived. Thus—to and n can be evaluated from the slopes of the plots of the appropriate functions. The values of m and n which were found to be 1 and l/2 respectively imply the presence of a dimeric acetic acid in the quinoline solution. Per haps this might not be too surprising since acetic acid is known to be a dimer in the vapor state and in low dielectric organic solvents. The basic strength of the quinoline however raises a question as to this possibility. Resolution of these alternates resides possibly in cry- oscopic measurements in quinoline. With a knowledge of m and n it was possible to estimate the equilibrium constant for the Cu^ - HOAc interaction. The K was found to be unity for both 6o° and 100°C. It must be realized, however that the above results are based on relatively few ex perimental measurements. Thus the conclusions derived therefrom must be considered only as indicative, not definitive. IV. SUMMARY The rates of hydrogenation and deuteration of quino line solutions of cupric acetate in the presence of cuprous 86 species has been measured at 0, 25, 4o, and 6o°C . The i second order dependence of the hydrogenation process as I j established at 100°C. was also valid for the hydrogenation and deuteration processes at the lower temperatures. Pur- \ I ther experimental verification of the same rate determining I [ step for the hydrogenation and the ortho- parahydrogen i ! conversion process was found in the 6o°C . data where the j hydrogenation and conversion data were plotted on the same curve. The Arrhenius curves for the hydrogenation, deuter- | ation and conversion processes for the temperature range I 25 to 100°G. were plotted and activation energies were j j ■ | j estimated. An attempt was made to determine the nature j ! ! ! of the inhibitory acetic acid effect. ) CHAPTER V MISCELLANEOUS SUBJECTS A, Copper--! salts, . It was found that the air sensitive solutions of cuprous acetate in quinoline were almostr impossible to prepare pure from the solid salt and quinoline. Since! all attempts to transfer weighed amounts j of solid into the quinoline resulted in some aerobic oxida-j tion, an alternate method of preparing the solutions was > i i devised. This consisted of shaking and gently heating the I ! ! j cupric acetate with a copper wire (No. 28) spiral in the j I ! j quinoline in an evacuated system until reduction to the j s - \ • ' i cuprous species was complete. Analysis of the resultant I ! solution agreed exactly with the stoichiometry indicated j I \ by the weight difference of the copper spiral. The appear- j ance, chemical behavior and specifically the behavior of j these solutions in the previously described kinetic studies confirmed the identity of these solutions with those pre pared by weighing the dry copper-I salt into the quinoline. Encouraged by the above described preparation of 1 the copper-I acetate from the copper-II acetate in quino- j line, a series of qualitative experiments were performed j | with other copper-II salts, and copper wire in both quino line and pyridine. Accordingly, a small amount of a j copper-II salt and a long spiral of copper wire (No. 28) | were sealed under vacuum into a tube with quinoline or pyridine. The tube was then shaken in a hot water bath ! i until no further color change occurred from the normally j green colored cupric species to the characteristic red or \ | orange colored cuprous species. The salts and solvents j used are shown in Table XV'. It is clear that in general ! the copper-I specie is stable with respect to copper metal | i I and copper-II specie in quinoline or pyridine. However, j i : it is interesting to note that the more soluble hydrated 1 t [ | j cupric salts reacted more rapidly than the anhydrous salts 1 ! i ; in spite of the ease of disproportionation of the cuprous species in water into copper metal and copper-II species. The effect of water on the reduction of copper-II to copper-I species in quinoline or pyridine was not further studied. B. Copper-I conversion. Because of the similarity of the appearance and behavior of the other cuprous salts to cuprous acetate in quinoline, an attempt was made to investigate the p-hydrogen conversion rate with one of the other salts. The sulfate salt was chosen for the experi ment because of its availability and because of the ease of preparing the anhydrous species by simply heating the hydrated salt. 89 TABLE XV FORMATION OF COPPER-I SOLUTIONS Cu^-^ salts used Solvent Color Nitrate »3H20 quinoline Red Sulfate*5h20 quinoline Ruby red Chloride«2H20 quinoline Yellow Disalicylaldehyde anhyd. quinoline Dark ruby red Nitrate«3H20 pyridine Orange-red Sulfate*SH20 pyridine Red Sulfate anhyd. pyridine Light red Chloride ^HgO pyridine Yellow Dis alicylaldehyde anhyd. pyridine Ruby red Dis alicylaldehyde anil. pyridine Red The cuprous sulfate salt was prepared by the method described for cuprous acetate in Chapter III except that i i ' i i ! | since the anhydrous copper-II salt was very insoluble in | ! ' i 1 quinoline it was only possible to prepare a relatively i ' ' \ dilute solution. This solution was pre-treated with normal! i ' ' I | hydrogen and subsequently stirred with p-rich hydrogen at ! _ j 100 and 90 C. according to the conversion procedure pre- ; | 1 | viously described in Chapter III. Samples of the hydrogen ! I j ; gas which were removed periodically from the reaction were I : analyzed on a Pirani gage by the usual methods and the : 5 i ! | final solution was analyzed by electrodeposition. The re- j ; " ! suits are shown in Table XVI• It can be seen that the rate constants for the sul- « 1 » j fate salt are of the same magnitude as that of the acetate j | i j salt (assuming second order copper-I® dependence). The j ! i estimated value of activation energy is based upon one j I value each at 100 and t)0°G. and is therefore only of semi- quantitative significance. It is clear, however, that the | ; \ j behavior of this salt is comparable to that of the acetate i t • ! t ' j ; salt with respect to its conversion properties. Therefore ! I one might venture to predict the hydrogenation rate for ! ' i I quinoline solutions of cupric sulfate in the presence of j j copper-I species if the solubility properties of the ! | anhydrous cupric salt were not the limiting factor. ! 91 TABLE XVI PARA-HYBROGEN CONVERSION BY CUPROUS SULFATE IN QUINOLINE t° c . Concentration moles/liter Rate constant k° Calculated Act. E 100° 90° 0.0138 0.0138 3.39 x lO"3 1.75 x 10“3 17.8 kcal. 92 However, since tbs solubility is very small and observably slow, the kinetic behavior of the! hydrogenation, if it oc curred at a reasonable rate, would probably be difficult to interpret. Although it has been possible to prepare the red quinoline solution from cupric salicylaldehyde anil (con centration of 0.0076 m/l) by reaction with copper wire, there was no measurable p-hydrogen conversion at 100°C» Thus, merely the presence of the red colored solution, which has been associated with the copper-I species in quinoline, does not guarantee hydrogen activity either with respect to conversion or hydrogenation. C. High temperature 0-0 hydrogen conversion. Several attempts were made to study the rate of conversion of p-hydrogen by solutions of copper-I acetate in quinoline at temperatures of 120°C. It was found that the rates of conversion were not reproducible, and that a given solution would show a decrease in rate with time. It was also ob served that metallic copper, partially in colloidal state, was formed. Further tests indicated that the rate of formation of the copper metal was greatly accelerated at the higher temperatures. It is probably true that even at 100°C. there may be some of this process occurring, but it was not experimentally observable and did not appear to | i have any effect on the measured rate, even after several ; 1 ! repeated conversion runs on a given solution. j ; D. Calculation of hydrogenation rate from conver- j I sion data. It has been indicated that the unanimity of thej t, rate determining mechanism for the hydrogenation and con- j version processes establishes a basis for the calculation | of the rates of hydrogenation from rates of conversion, at the same conditions. A brief consideration of the postulate ed rate mechanisms and these equations show how this was done. The rates of p-hydrogen conversion and hydrogena tion by cuprous species in quinoline may be expressed respectively by -d(p-Hg) a s k (Cc)(p-H2) - k2 (Cc)(o-H2) (27) dt -d(H2) = kh (Ch)(H2) (28) dt where (p-H2), (b-H2) and (H2) are the concentrations of para, ortho, and normal hydrogen respectively, (Cc) * * concentration of the conversion catalyst, and = • con centration of the hydrogenation catalyst. If, in equation 27, one lets ki + k2 = k° (29) | | then it follows from the equilibrium statistics of ortho | and parahydrogen that j ki = 3 / k k°. (30) j Since it is clear from Chapter III that the following re- ; f lationships are valid: i k°Cc » k* = k Rv (31) I where R,r - total volume of H2 - ,r V --------------------------- £=_ V c ie H2 dis solution volume H2 dis sol. in o One may write for the conversion reaction from equation 30 and 31 kx = 3 / k kRv (32) Cc ! r Now, if it is assumed that the utilization of the i ! hydrogen by the hydrogenation and conversion processes in [ i the rate-determining step occur by the same mechanism, then! i k/3 = kh. (33) | t Equation 32 can be rewritten in terms of a, the ratio of j ml hydrogen gas dissolved per ml solution } i i | ki = 3/1n b * ^ 4 ? — ■ uu) ! c a V ] _ i where Vg and are the volume of the gas above the solu- i i I tion and the volume of the solution respectively. Solving ! ! ! j for equation 27 in terms of the ml. of hydrogen gas ab- . \ i I sorbed per minute, expressing the hydrogen concentration in terms of the solubility a, and substituting equations 28, 33* and 3k> results in ml H gas absorbed/min = (^Z_i)(l 4 * (aC*.) (35! 2 alV-L),. 11 I t i - I i where - volume of the solution in the hydrogenation pro-j ! ! j cess and the other: terms have their previously defined j I j ; meanings. Since experimentally j ! i 1 « (36)! j | | and since a comparison of the conversion and hydrogenation ; | processes would be made at Cc = C^, equation (a) simplifies! to I (ml)g = kV*! jvg)c (37)1 min ( ) c E. Copper-I carbonmonoxide interaction in quinoline. It had been suggested by Dr. Wilmarth that perhaps other substances than the cupric species would be hydrogenated in the presence of the cuprous species in quinoline. The possibility that a mixture of hydrogen and carbon monoxide 96 j i would be absorbed by a solution of cuprous acetate in quino- line was considered, but a preliminary experiment indicated that only carbon monoxide was absorbed at room temperature. The stoichiometry of the absorption was studied by observ ing pressure differences in a volume calibrated system. -2 A 3.12 x 10 M. quinoline solution of cuprous ace tate was prepared in the usual way and was connected to a volume calibrated mercury manometer. The solution was stirred at room temperature with pure dry carbon monoxide \ . ' j gas until no further pressure changes were observed. The j j - j j solution changed color from the usual characteristic ruby j [ j red through light yellow, finally resulting in a nearly ! | . { | colorless quinoline solution and a light yellow precipitate^ * It was possible completely to reverse the absorption process by stirring and heating while the carbon monoxide was being pumped off. The whole cycle was repeated with identical results. The stoichiometry was determined from the volume pressure relationships was as follows: 0.99 m moles Cu-I 0*52 m moles CO This corresponds to approximately 2 m moles of copper-I for each m mole of carbon monoxide and implies the formation of j a CU2CO type of compound. The nature of the carbon monoxidej bonding is interesting, since the compound does not have ; 97 i the structure usually assigned to copper carbonyl, eg*, ; : Cu(C0)2Cl* Perhaps this Indicates a significant parallel- ' ' ism with the postulated CU2H2 type of structure as sug- j | gested by Calvin"*" for the parahydrogen conversion mechanism ; 1 F, Acetic acid effect * The inhibitory effect of 1 i acetic acid on the rates of hydrogenation of cupric acetate' ; in quinoline has been noted in the previous chapters. In all cases where it was appreciable, it was eliminated by 1 extrapolation to zero concentration of the acid either by j direct experimental techniques or by calculation from the available data. However, there has been little considera- ; tion of the mechanism of the inhibition outside of hypo thetical conjecture. Although the available data is limit ed, an attempt is made here to determine some of the more salient features of this effect. If it is assumed that the inhibition occurs because of the interaction of the acetic acid with the cuprous species present mainly as the monomer mCu1 4 * nA - Cu^^ . Where A = HOAc (38) then for solutions containing different amounts of acetic " Hi . Calvin, J. Am. Chem. Soc., 6l, 2230 (1939) acid, the following relationship may be written KfCu1)(A^)1 < C 5 ; V ° 9 ) (CujjjAn) 2 n Where K = K(CuX) (A»)2 (Cu )m(A)n I\m# fl\n For equal concentrations of Cu^ this simplifies to n log ^ 1 (A)2 log ^CumAn)l <Cui5iV2 C14.0) Thus n may be evaluated if the necessary concentrations can ■ to an evaluation of m. I . 0 From the 60 C« hydrogenation data of Chapter IV as summarized in Figure II4 . the necessary concentrations were ■ obtained with the aid of the calculated rate constant and the observed rate at chosen (A) concentrations. (See Table XVII.) For calculation of n these were then handled ■in the following way: From plots of the (Cu^) versus (A) T X and tbs (Cu^An) (see Figure 22) values of A and Cu^n were T obtained at the same values of Cu . The logs of the ap propriate ratios were then plotted as shown in Figure 23. A complimentary treatment for the evaluation of m gave corresponding curves as shown in Figures 2I 4 . and 25» The measured slopes resulted in n = 0.5 - 0.15m * 1 * 0.I4. be estimated. The same set of equations can obviously lead TABLE XVII EQUILIBRIUM DATA FOR CALCULATION OF m, n, AND K IN HOAc EFFECT AT 60°C. t ° c . (Cu1) observed x lO2^ Rate observed ml./min. Rate constant k* ml. ; 1 Calculated (Cul) x 101 * Calculated (Cu1) x 102 Calculated (CuAl x 102 Observed concen tration (A) x 102 Net con centra tion (A) x 102 min. mole 60 £.13 0.103 50.7 20.3 l * . 5 o 0.63 5.69 5.06 60 5.89 0.128 50.7 ' 25.2 5.02 0.87 6.38 5.51 60 7.16 0.176 50.7 3U.7 5.89 1.27 7.72 6.1*5 60 8.1*7 0.226 50.7 1 * 5 . 1 * 6.66 1.81 9.H* 7.33 60 5.13 0.117 50.7 23.1 i*.80 0.33 1.77 1 . 1 * 1 * 60 5.89 0.11*8 50.7 29.2 5.39 0.50 2,1*5 1.95 60 7.16 0.211 50.7 1*1.6 6.1*5 0.71 3.85 3 . H * 60 8.1*7 0.273 50.7 53.8 7.33 1.11* 5.27 U.13 VO VO 100 CuA A x 10 A O ' 0. 200.10 0 .1 6 0.08 0.06 0.12 0,0k— 0.0 (Cu^) x 10^ qioles/liter FIGURE 22 EVALUATION OF , , nu~6o° EQUILIBRIUM DATA log (CuA)g/(CuA)1 0. 1+ 0.3 Slope = 0.2 0.1 0.8 0.2 log Ao/A FIGURE 23 EVALUATION OF ! , nf t 102 CuA x 10 Cu r0.08 0.18 -0.0? 0. 11+ 0.10 . 0. 0% 0.06 0.02 6 8 10 (Cu^) x 10^ moles/liter FIGURE 2i+ EVALUATION OF "m"— 60° EQUILIBRIUM DATA log Cui/Cu2 103 0.35 0.30 Slope s 1.0 0.25 0.20 0.15 0.6 0.8 0.2 0.4 log (CuA)i/(CuA)£ FIGURE 25 EVALUATION OF "mu 101+; The calculation of the equilibrium constant for the j Cu"^-H0Ac interaction using the 6o°C. data of Table XVII j and the 100°C. data of Table XVIII (data obtained from j 1 2 * | original hydrogenation data of Wilraarth) resulted in j s j | values of 1 £ 0.3 for both temperatures. However, since ! i ■ " i j there was insufficient precise original data with which to ! 1 ' ! make these calculations the above conclusions can only have! limited significance as indicated by the magnitude of error] for the evaluated terms. I 2 Wilmarth, loc. cit. i_ TABLE mil EQUILIBRIUM DATA FOR CALCULATION OF K IN HOAc EFFECT AT 100°C. O o • (Cu1) observed x 102 Rate observed ml./min. Rate constant k* ml. 1. Calculated (Gu1)2 x 10^ Calculated Cu1 x 102 Calculated (CuA) x 102 Observed concen tration (A) x 102 Net con centra tion (A) x 102 min. mole 100 1.70 0.165 777 2.12 1.1*6 0.21* ll*.8 l!*.5 100 2.1*5 0.286 777 3.68 1.92 0.53 15*6 15.1 100 3.19 0.1*10 777 5.27 2.30 0.89 16.1* 15.5 100 1.70 0.250 777 3.22 1.80 — 7.8 — 100 2.1*5 0.381 777 U.91 2.22 0.23 8.6 8.1* 100 3.19 0.529 777 6.75 2.60 0.59 9.1* 8.8 s UT CHAPTER V I GENERAL SUMMARY | The kinetics and general properties of various mod ifications of hydrogen with cuprous and cupric acetate in quinoline and pyridine were studied. The valence states ■ of the copper species involved were confirmed by the stoich iometry of the reactions and by magnetic measurements. Prom a consideration of the detailed mechanisms it was con cluded and subsequently experimentally verified that the rate determining step for the parahydrogen conversion by solutions of cuprous acetate in quinoline was identical with the rate determining step for the autocatalytic hydrogena- tive reduction of cupric acetate in quinoline. The ob served second order behavior of the cuprous species in the hydrogenation and conversion reactions was interpreted in terms of a termolecular collision but this interpretation did not permit an unambiguous choice as to the nature of the hydrogen carrying intermediate for the processes. It was demonstrated that some cuprous salts other than the acetate were capable of parahydrogen conversion but that not all soluble cuprous salts are active. The temperature coefficients for the conversion and hydrogenation reactions were evaluated and the activation energies and correspond ing pre-exponential factors were calculated. The i parallelism of the deuteration and hydrogenation Arrhenius j ! curves suggest that non-classical ’ ’tunneling'* is not occur-j j ring and that within experimental limits, the zero point I I i energy difference between hydrogen and deuterium in the j i ground state is the same as in the transition state* j An attempt was made to evaluate the inhibitory acetic acid effect with respect to the hydrogenation pro cess. On the assumption that this effect was due to an equilibrium between the -acetic acid and the active cuprous ; species it was possible to estimate the numerical coeffic- i ! ' i ; ients of the species involved and to calculate the equili- j | j ! brium constants for 60 and 100°C. I 1 . j j As a result of the problems investigated there i j arises, of course, many others of equal interest and im- j portance. A more detailed study of the hydrogenation and j | \ ■ conversion processes at high cuprous concentrations is in- j i dicated to clarify the behavior observed. A complete in- j j ; vestigation of the kinetics of the parahydrogen conversion j ! by quinoline solutions of a variety of cuprous compounds and i * • ' j an investigation of the extent of solvation by the salts in: \ j |solution might give a clearer insight into the detailed na-j ; I ture of the cuprous-hydrogen intermediate assumed necessary I |for the conversion. The detailed effects of acetic acid an^ I * • ; I or some soluble acetate salts on possible inhibitory on the conversion rates of cuprous acetate in quinoline should prove interesting since they might aid in the more complete resolution of these inhibitory effects observed in the hydrogenation of cupric acetate. A further study of the deuterium exchange with cuprous acetate in quinoline is indicated since this phenomena is far from being well understood. The strange behavior of the apparent solu bility properties of cupric acetate in quinoline certainly could stand additional scrutiny. A study of the properties of the solid and perhaps isolatable addition product of carbon monoxide and cuprous acetate in quinoline should prove interesting and perhaps fruitful in terms of a new series of metal carbonyls. BIBLIOGRAPHY BIBLIOGRAPHY 110 ;Bell, R. P., Acid-Base Catalysis* Oxford: The Clarendon Press, 19ljd.. |Calvin, M., Trans. Faraday Soc., 34* H 8l (1938)* j , J. Am. Chem. Soc., 6l, 2230 (1939)* i Parkas, A., Z. Physik. Chem., BIO, 1|19 (1930) • i _____, Light and Heavy Hydrogen. Cambridge: Cambridge j University Press, 1935* ! ■Fobes, M. A., and G. N. Tyson, J. Am. Chem. Soc., 63, 3530 (1941). iFrost, A. A., and G. Pearson, Kinetics and Mechanism. New York: John Wiley and Sons, Inc., 1953* 1Gaydon, A. G., Dissociation Efaergies. New York: Dover Publications Inc., 191+5* Glasstone, S., Textbook of Physical Chemistry. New York: D. Van Nostrand Company, Inc., 1946. :Hildebrand, J. H. and R. L. Scott, The Solubility of Non-Polar Electrolytes. Third edition; New York: Reinhold Publishing Corporation, 1950. Hinshelwood, C. N., The Kinetics of Chemical Change. Oxford: The Clarendon Press, 1947* Selwood, P. W., Magnetochemistry. New York: Interscience Publishers Inc., 1937* Spath, H., Monatshefte filr Chemie, 33, 237 (1912). Tyson, G. N., and R. E. Vivian, J. Am. Chem. Soc., 63* 1403 (I94I). “ ~ ' Weller, S., and G. A. Mills, J. Am. Chem. Soc., 75. 769 (1953). “ ~~ Wells, A. P., Structural Inorganic Chemistry. Oxford: The Clarendon Press, I9I+7. Wender, I., J. Am. Chem. Soc., J2t i j . 81^.2 (1950). Wender, I., R. Levine, and M. Oechin, J. Am. Chem. Soc., 22, 1+375 (1950). Wilmarth, W. K., "Catalytic Homogeneous Hydrogenation." Unpublished doctoral dissertation, University of California, Berkeley, I9I+2. Wilmarth, W. K., and C. P. Baes, Jr., J. Chem. Phys., 20, 116 (1952) . Wilmarth, W. K., H. K. Barsh, and S. S. Dharmatti, J. Am. Chem. Soc., 7^* 5°35 (1952). Wilmarth, W. K., and M. K. Barsh, J. Am. Chem. Soc., 75* 2237 (1953). UfHversrty of S o u m *™ Llbmrv

Asset Metadata

Creator Barsh, Max K (author)

Core Title A study of the activation of hydrogen by cuprous salts in quinoline / by Max K. Barsh

Contributor Digitized by ProQuest (provenance)

Degree Doctor of Philosophy

Degree Program Chemistry

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

Tag chemistry, inorganic,OAI-PMH Harvest

Language English

Advisor Wilmarth, W.K. (committee chair), Brown, Ronald J. (committee member), Copeland, C.S. (committee member), Vollrath, Richard E. (committee member), Warf, James C. (committee member)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c17-619785

Unique identifier UC11353975

Identifier DP21771.pdf (filename),usctheses-c17-619785 (legacy record id)

Legacy Identifier DP21771.pdf

Dmrecord 619785

Document Type Dissertation

Rights Barsh, Max K.

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA