Remarkable 3-methyl substituent effects on the cyclization reaction of diphenylamine derivative cation radicals in acetonitrile

摘要

Reactions of methyl substituted diphenylamine cation radicals in acetonitrile were observed using an electronntransfer stopped-flow (ETSF) method. In the reactions of the 4-methylphenyl(phenyl)amine cation radicaln(4M–DPAu0001u0001), the main reaction route was the formation of the benzidine dimer, which is similar to the case of thendiphenylamine cation radical (DPAu0001u0001). The dimerization rate of 4M–DPAu0001u0001 was 2.3 × 104n Mu00021n snu00021n, which was slowernthan for DPAu0001u0001 (dimerization rate 1.0 × 106n Mu00021n snu00021n), due to the 4-methyl substituent. Also, in the cases of 4-methylnand 4,4u0003-dimethyl DPAu0001u0001, the formation of the cyclized dimer compounds was inferred from the presence of a largenexcess of the neutral molecules acting as a base. In contrast, the formation of the cyclized dimer compounds wasncharacterized for 3-methyl- and 3,3u0003-dimethyl substituted DPAu0001u0001 using cyclic voltammetry. In the ETSF method, thendimerization reaction was determined to be second-order in the cation radical and totally independent of the neutralnmolecule. The dimerization rates were ca. 1.0 × 107n Mu00021n snu00021n, which are faster than the reaction of DPAu0001u0001. In spite ofnthe complex pathway of the cyclization reaction, the 3-methyl substituent was found to promote the reaction betweennthe 6-position of the phenyl ring and the nitrogen molecule of 3M–DPAu0001u0001 or 3,3u0003M–DPAu0001u0001.