Solid-state dehydrochlorination and decarboxylation reactions. Part 1. Reactions of p-aminosalicylic acid hydrochloride and p-aminosalicylic acid, and revised crystal structure of p-aminosalicylic acid

Abstract

The decomposition of p-aminosalicylic acid hydrochloride involves initial dehydrochlorination followed by decarboxylation to give m-aminophenol hydrochloride. The solid-state decarboxylation of p-aminosalicylic acid (I) presumably follows the same mechanism as the solution reaction (proton electrophilic substitution) since no decarboxylation of several meta-substituted salicylic acids was found. In addition, analyses of the crystal packing of (I) revealed several carboxy-protons within 5 Å of the nucleophilic ring carbon atom. A solid-state electrophilic substitution involving one of these protons would be consistent with available data concerning the solid-state reaction of (I).

The crystal structure of (I)[a= 7.209(2), b= 3.786(1), c= 25.109(9)Å, β= 103.22°, space group P2₁/c] is reported and the published structure corrected. The structure was solved by direct methods and refined to an R 0.044 for 1 044 observed reflections.