A systematic chemistry of organic reactions on solid acids /
The reactions of a number of organic molecules on a variety
| Main Author: | |
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| Format: | Thesis Book |
| Language: | English |
| Published: |
[Place of publication not identified] :
[publisher not identified] ;
1996.
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| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=743274431&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | The reactions of a number of organic molecules on a variety of solid, acids including zeolite solid acids and metal halide solid superacids have been systematically studied using in situ solid state 13C and 15N NMR. The overall results of this investigation suggest the emergence of a systematic chemistry of organic reactions on solid acids. The reactions of ketones with or without ammonia as co- adsorbate were investigated on a variety of zeolites with different acidities and pore sizes. The overall reaction sequence for ketones was acid catalyzed aldol condensations followed by secondary reactions such as double bond rm'gration, hydrogen transfer and cracking. The ketones and their aldol condensation products form adsorption complexes with Bronsted acid sites of the zeolites. The strength of complex formation was reflected in the 13C isotropic chemical shift changes. These are interpreted quantitatively as a measure of the effective acidity of the zeolitic environment under actual reaction conditions. The tetrahedral gem-amino hydroxy intermediates formed from the nucleophilic addition of ammonia to benzaldehyde were thoroughly characterized on acidic zeolites at low temperature. Two classes of carbenium ions, cyclopentenyl ions and indanyl ions, were observed and characterized on zeolite solid acids by 13C NMR. These cations formed from the oligomerization reactions of hydrocarbons in acidic zeolites. The claim for the observation of a persistent allyl cation on HZSM-5 was disproved. These in situ results suggest that zeolites are only strong acids but not superacids. A general method for the preparation of carbenium ions in the solid state was developed in this dissertation, based on the use of solid Lewis superacids, such as AlBr3 and frozen SbF5, and the in situ NMR techniques previously developed in this laboratory. This method allows the measurement of the principal components of 13C chemical shift tensors of carbenium ions at temperatures as low as 77 K. The general utility of this method was demonstrated through the syntheses of several classes of carbenium ions, such as simple alkyl cations, acylium ions and arenium ions, and the subsequent NMR measurement of the principal component data. |
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| Item Description: | Vita. "Major Subject: Chemistry". |
| Physical Description: | xiii, 214 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references. |