Affiliation:
1. Department of Chemistry, Dalhousie University, Halifax, NS B3H 4J3, Canada.
Abstract
The generation of diarylmethyl carbocations within non-protic zeolites (LiY, NaY, KY, RbY, CsY, and NaX) was carried out via laser excitation (266 nm or 266 nm / 308 nm) of diarylacetic acids. Rapid loss of CO2, followed by photochemical oxidation of the diarylmethyl radicals resulted in the formation of the diarylmethyl carbocations. The reactivity of the diarylmethyl carbocations was found to be highly dependent on the alkali metal counterion and the Si/Al ratio of the zeolite framework. Furthermore, the effect of various para-electron donating substituents (4-H, 3-CH3, 4-CH3, 4,4′-CH3, and 4-OCH3) on the diarylmethyl carbocation reactivity was investigated. Comparison of the Hammett plots constructed for the reactivity of the diarylmethyl carbocations in zeolites with those in solution (CH3CN–H2O (1:2) and TFE) showed decreased sensitivity of the electrophilic species towards para-electron donating substituents in the heterogeneous media. The leveling effect observed in the zeolite Hammett plots has been attributed to the presence of an isokinetic relationship, specifically, a low isokinetic temperature for the reaction of diarylmethyl carbocations with the aluminosilicate zeolite framework.
Publisher
Canadian Science Publishing
Subject
Organic Chemistry,General Chemistry,Catalysis
Cited by
3 articles.
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