Photoinduced formation of 9-diarylaminoacridines from diarylamines and tetrabromomethane: reaction mechanism

Abstract

The UV irradiation of di-para-substituted diphenylamines and CBr 4 results in the formation of 2,7-disubstituted 9-diarylaminoacridines (DAAAs) with quantum yields of 0.035–0.080. The yield of DAAA is linearly dependent on the light intensity. An intermediate (IM1) with a lifetime varying from several minutes to tens of minutes is observed. IM1 is transformed into DAAA with pseudo-first-order kinetics, the observed rate constant being proportional to the amine concentration. A detailed examination of the spectral and kinetic properties of IM1, and a comparison with the reaction of amines with CHBr 3, leads to the conclusion that an intermediate (IM2) is formed during the transformation of IM1 to DAAA. The general reaction scheme of the photoinduced formation of DAAA is assumed to involve five principal stages: the formation of an electron donor-acceptor complex between the reactants; photodissociative electron transfer from the amine to CBr 4 on irradiation of the complex; recombination of the CBr 3 radical predominantly on the nitrogen atom of the amine cation radical and/or neutral radical, resulting in the formation of IM1; interaction of IM1 with the second amine molecule and formation of IM2 (this is the rate-limiting state); fast cyclization of IM2 to DAAA.