Mechanism of an intramolecular addition–elimination between amino and amide groups; a biphasic Brønsted plot for acid catalysis as evidence for rate-limiting proton transfer to the addition intermediate

Abstract

Formation of 2-trifluoromethylperimidine from 1-amino-8-trifluoroacetylaminonaphthalene involves intramolecular nucleophilic addition of the amino group to the amide carbonyl followed by elimination to form the cyclic imine; a biphasic Brønsted plot with slopes αca.O and 1.0 respectively for catalysis by acids (HA) with pK_HA values below and above a break point at pK_HA 8.5 is compatible with rate-limiting protonation of the zwitterionic addition intermediate by general acids and with a proton switch mechanism for reaction with water.