Studies on the Elimination Reaction of 2-Arylethylammonium Salts

Abstract

<p>The mechanism of the elimination reaction of 2-phenylethyltrimethylammonium ion with ethoxide ion in ethanol has been examined using tracer and kinetic isotope effect methods. The absence of exchange of the β-hydrogen with solvent and the observation of a nitrogen-15 isotope effect of 1.4 per cent have eliminated a two step process involving a carbanion intermediate. Tracer studies using α- and β-deuterium labelled compounds have also excluded the less probable reaction pathways involving ylide and carbene intermediates. It is concluded, therefore, that the reaction is a concerted E2 process.</p> <p>Information concerning the extent of C-H and C-N bond weakening at the transition state has been obtained by determining the influence of base strength on the nitrogen isotope effect in the reaction of ethyltrimethylammonium ion and the influence of parasubstitution on both hydrogen and nitrogen isotope effects in the reaction of a series of 2-arylethyltrimethylammonium salts. The results have been interpreted in terms of a hypothesis that any structural change which causes one bond to be weakened more at the transition state will have a corresponding effect on the other bond.</p>