Effects of N-alkyl substitution on the formation and rate-limiting deprotonation of the spiro-Meisenheimer intermediate of Smiles rearrangement of 2-(p-nitrophenoxy)ethylamine, in aqueous solution

Abstract

For intramolecular rearrangement of 2-(p-nitrophenoxy)ethylamines to the corresponding 2-(p-nitroanilino)ethanols the kinetic effects of N-alkyl substitution have been interpreted in terms of a mechanism whereby base-independent formation of a spiro-Meisenheimer intermediate is rate determined at high base concentrations but general-base-catalysed deprotonation of the intermediate (β 0.18–0.35) becomes rate determining at low base concentration. Reactions of the N-ethyl and N-isopropyl substrates are further complicated by a change to a specific-base-catalysed mechanism in ethanolamine buffers of high concentration; this observation requires that formation of the product by ring opening of the anionic spiro-Meisenheimer intermediate is not sensitive to general-acid catalysis.