Charge-transfer and Proton-transfer in the Formation of Molecular Complexes. IV. Picric Acid Complexes with Benzidine and Its Derivatives

Abstract The preparation of picric acid complexes with benzidine, o-tolidine, 3,3′-dichloro-o-tolidine, 3,3′-dibromo-o-tolidine, o-dianisidine, and N,N,N′,N′-tetramethylbenzidine was attempted in the following three solvents: benzene, chloroform, and ethanol. From benzene and chloroform, 3,3′-dibromo-o-tolidine forms a 1 : 1 complex of the charge-transfer type, but the other five diamines give yellow salts formed by means of proton-transfer. Some complexes prepared in ethanol are of an unfamiliar nature. The spectroscopic examination of the 1 : 1 complexes with o-tolidine, o-dianisidine, and tetramethylbenzidine revealed that a half of the diamine molecule acts as a proton-acceptor, while the other half has a charge-transfer interaction with the picrate ion. The simultaneous operation of charge-transfer and proton-transfer interactions was also demonstrated in the black-colored complex with benzidine of a 2 : 1 composition.