Urethanes. II. The effect of amine bases on the thermal degradation of carbanilates

Abstract

AbstractThe amine‐catalyzed, low‐temperature (< 200°C) thermal degradation of aromatic urethanes, specifically carbanilates, was studied to determine the primary reactions responsible for the loss of starting material and the resultant products. The primary degradation reactions are (1) the reversible dissociation of the urethane to isocyanate and alcohol and (2) the nonreversible nucleophilic attack by a basic species on the carbon attached to the carbamate oxygen to yield amine, carbon dioxide, and an alkylated base. Secondary products fall into two categories, neutral and basic species. The neutral components consist of carbanilide, dialkyl carbonate, isocyanurate, and N‐alkylated carbamates. The basic components, derived from starting materials, are pseudoureas and guanidines. Their formation depends solely on the presence of carbanilide in the reaction mixture. When the amine catalyst is 1,4‐diaza[2.2.2]bicyclooctane, novel piperazine compounds are formed. In general, quarternized triethylenediamine species undergo nucleophilic displacement reactions to form N‐alkyl‐N′‐ethylpiperazine derivatives.