Synthesis of Amides and Amidines by Reaction of Carboxylic Acids and Amines in the Presence of Polyphophoric Acid Trimethylsilyl Ester (PPSSE)

Article abstract of DOI:10.1246/bcsj.59.2171

The reaction between amines and carboxylic acids in the presence of poliphosphoric acid trimethylsilylester (PPSE) has been investigated from the view point of the synthesis of amides and amidines.Benzanilide was selectively prepared from benzoic acid and aniline in the presence of PPSE and pyridine at 100 degC, whereas a mixture of benzanilide and N,N'-diphenylbenzamidine was obtained without the use of pyridine.The reaction at 160 degC almost exclusively gave N,N'-diphenylbenzamidine.Various simmetrical amidines were obtained from combinations of carboxylic acids and aromatic amines in high yields by simply heating at 160 degC with four molar amounts of PPSE.The reactions of aliphatic and aromatic amines with N-monosubstituted and N,N-disubstituted amides also afforded corresponding unsymmetrical amidines under the same conditions.The reaction mechanism is discussed in some detail.