The synthesis and properties of some carboxy-substituted analogs of butter yellow

Abstract

A seven step synthesis of 3,3′-bis(carbomethoxy)-4,4′-bis-(dimethylamino)-azobenzene from anthranilic acid is described. It has been found that the carbomethoxy groups affect the required oxidative azo coupling and methylation steps. Perborate coupling of 2-carbomethoxy- N-acetyl- p-phenylenediamine gives the corresponding azo compound in good yield, but the reaction also produces variable amounts of an azoxy compound. Tetramethylation of 3,3′-bis(carbomethoxy)-4,4′-diaminoazobenzene requires forcing conditions [(CH 3O) 2SO 2 at 160 °C]. Protonation of 3,3′-bis(carbomethoxy)-4,4′-bis-(dimethylamino)azobenzene gives the ammonium ion tautomer because the carbomethoxy groups force the adjacent dimethylamino groups out-of-plane. In contrast, protonation of 3,3′-bis(carbomethoxy)-4,4′-diamino-azobenzene and 4,4′-bis(dimethylamino)azobenzene-3,3′-dicarboxylic acid gives the azonium ion tautomer.