Organic reactions in melts and solids. Part 10. Reactions of carboxylic acids and anhydrides with carbamates

Transacylation reactions have been carried out in melts between carboxylic acids and ethyl carbamate, mono-N-substituted carbamates. and di-N-substituted derivatives at 150-180 °C. Phthalic acid, pyromellitic acid, and phthalic anhydride reacted with ethyl carbamate and N-substituted ethyl carbamates to give the corresponding amides and imides. carbon dioxide, and ethanol in high yields. Benzoic acid. 4-methoxy- and 4-nitro-benzoic acid, and acetic acid gave with ethyl carbamate mono-N-substituted ethyl carbamates and phenyl N-phenylcarbamate gave amides in low yields. Ethyl NN-diethyl- and NN-diphenyl-carbamate did not react with either phthalic acid or the monocarboxylic acids mentioned. In the case of phthalic acid the rates of reactions and overall kinetic order are similar to those found for transacylations with amides. Two examples of the preparation of thermally stable polyimide oligomers are given.