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90
the isomerization of epoxides to aldehydes and ketones,16 sulfonation17 and
aroylation18 of aromatics using NafionÒ-H.
Unlike conventional resinsulfonic acids (polystyrenesulfonic acids) such as
DowexÒ-50, AmberlystÒ IR-112 and PermutitÒ-Q, NafionÒ-H and related
perfluroalkanesulfonic acids are not only much stronger acids but are also stable at
temperatures up to 200 °C. Mechanistic studies of various transformations show
that the acidity of NafionÒ-H is comparable to that of 100% sulfuric acid (Ho » -
12)19 and is considered to be a superacid. It is interesting to note that, NafionÒ-H
does not affect the bulk acidity of the solvent in which it is present but rather only
the surface acidity where the solvent is in direct contact with the acidic sites.
While it is difficult to determine the molecular weight of NafionÒ resins due
to the differences in preparation and morphology, it is more useful to talk about
equivalent weight.20 Equivalent weight is defined as the number of grams of dry
NafionÒ per mole of sulfonic acid groups when it is in the acid form.21 This can be
determined by acid-base titrations, analysis of atomic sulfur as well as by FT-IR
spectroscopy. Commercially available resins usually have sulfonic acid groups in
the range of 0.01 to 5 mequi/gram catalyst. NafionÒ resins with equivalent weight
of 1200 usually contain tetrafluoroethylene and perfluorovinyl units in a ratio of
7:1.
The reactions using NafionÒ-H conveniently eliminate the use of volatile or
noxious reagents. NafionÒ-H catalyst can be easily recovered and recycled after
Object Description
| Title | Synthesis of organofluorine compounds via Lewis/Bronsted acid and base catalysed reactions and related chemistry |
| Author | Vaghoo, Habiba Ebrahim |
| Author email | vaghoo@usc.edu; vaghoo@usc.edu |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program |
Chemistry vinyl fluorides |
| School | College of Letters, Arts and Sciences |
| Date defended/completed | 2008-06-24 |
| Date submitted | 2008 |
| Restricted until | Unrestricted |
| Date published | 2008-10-31 |
| Advisor (committee member) |
Olah, George A. Shing, Katherine S. |
| Abstract | This dissertation describes the development of new and practical methodologies for the synthesis of a broad variety of fluorinated heterocycles and vinyl fluorides via acid and base catalysis, respectively. It also describes efficient cyanosilylation of carbonyl compounds using a variety of nucleophilic catalysts.; Chapter 1 explores the rich history of fluorine and its compounds. Important milestones that have made a significant contribution to the field of chemistry are highlighted with emphasis on fluorine's role in medicinal chemistry. Methods to introduce fluorine are also included in this chapter.; Chapter 2 deals with the use of gallium (III) triflate as a versatile Lewis acid for the synthesis of different fluorinated heterocycles and α-aminonitriles. The condensation-cyclization reactions of various aromatic amino derivatives with fluorinated ketones to afford the corresponding fluorinated benzimidazolines, benzothiazolines, benzoxazolines, and dihydrobenzoxazinones, as well as fluorinated 1, 5 benzodiazepines and quinoxaline derivatives is described. Also included in this chapter are the syntheses of α-aminonitriles and their fluorinated analogs via the multicomponent Strecker reaction using gallium (III) triflate. Monofluoro-, difluoro-, or trifluoromethyl groups have been incorporated into both heterocycles and the α-aminonitrile products by varying the nature of the fluorinated ketones.; In Chapter 3, Nafion^®-H, a perfluoroalkanesulfonic acid resin, is shown to be a suitable solid acid catalyst with high selectivity and catalytic activity for the one-pot synthesis of fluorinated heterocycles. The Nafion-H mediated reactions are easily achieved under mild conditions in high yields and purity. Monofluoro, difluoro and trifluoromethylated derivatives can be prepared and its advantage as a solid superacid is highlighted by the recyclability studies.; Chapter 4 describes a new approach for the stereoselective synthesis of vinyl fluorides using α-substituted fluoro(phenylsulfonyl)methane derivatives under mildly basic reaction conditions. A variety of fluorovinyl sulfones as well as α-fluoro-α,β-unsaturated carbonyls can be synthesized to afford the E-isomer.; Finally, in Chapter 5, cyanosilylation of aldehydes and ketones using various nucleophilic catalysts under mild conditions is portrayed. Use of dimethylformamide (DMF) as solvent, afforded the trimethylsilylated cyanohydrins in good to excellent yields. K2CO3 and (MeO)2P(O)(O^-)(N^+Bu4)3 have been employed as the nucleophilic catalysts for the cyanosilylation using trimethylsilyl cyanide (TMSCN). |
| Keyword | fluorine chemistry; fluorinated heterocycles; fluorinated aminonitriles; cyanosilylation |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m1729 |
| Contributing entity | University of Southern California |
| Rights | Vaghoo, Habiba Ebrahim |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | cisadmin@lib.usc.edu |
| Filename | etd-Vaghoo-2053 |
| Archival file | uscthesesreloadpub_Volume44/etd-Vaghoo-2053.pdf |
Description
| Title | Page 104 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 90 the isomerization of epoxides to aldehydes and ketones,16 sulfonation17 and aroylation18 of aromatics using NafionÒ-H. Unlike conventional resinsulfonic acids (polystyrenesulfonic acids) such as DowexÒ-50, AmberlystÒ IR-112 and PermutitÒ-Q, NafionÒ-H and related perfluroalkanesulfonic acids are not only much stronger acids but are also stable at temperatures up to 200 °C. Mechanistic studies of various transformations show that the acidity of NafionÒ-H is comparable to that of 100% sulfuric acid (Ho » - 12)19 and is considered to be a superacid. It is interesting to note that, NafionÒ-H does not affect the bulk acidity of the solvent in which it is present but rather only the surface acidity where the solvent is in direct contact with the acidic sites. While it is difficult to determine the molecular weight of NafionÒ resins due to the differences in preparation and morphology, it is more useful to talk about equivalent weight.20 Equivalent weight is defined as the number of grams of dry NafionÒ per mole of sulfonic acid groups when it is in the acid form.21 This can be determined by acid-base titrations, analysis of atomic sulfur as well as by FT-IR spectroscopy. Commercially available resins usually have sulfonic acid groups in the range of 0.01 to 5 mequi/gram catalyst. NafionÒ resins with equivalent weight of 1200 usually contain tetrafluoroethylene and perfluorovinyl units in a ratio of 7:1. The reactions using NafionÒ-H conveniently eliminate the use of volatile or noxious reagents. NafionÒ-H catalyst can be easily recovered and recycled after |
