Remarkable 3-methyl substituent effects on the cyclization reaction of diphenylamine derivative cation radicals in acetonitrileElectronic supplementary information (ESI) available: results of kinetic analysis for the reactions in Figs. 4 and 5. See http://www.rsc.org/suppdata/p2/b2/b201796b/

Abstract

Reactions of methyl substituted diphenylamine cation radicals in acetonitrile were observed using an electron transfer stopped-flow (ETSF) method. In the reactions of the 4-methylphenyl(phenyl)amine cation radical (4M–DPA˙+), the main reaction route was the formation of the benzidine dimer, which is similar to the case of the diphenylamine cation radical (DPA˙+). The dimerization rate of 4M–DPA˙+ was 2.3 × 104 M−1 s−1, which was slower than for DPA˙+ (dimerization rate 1.0 × 106 M−1 s−1), due to the 4-methyl substituent. Also, in the cases of 4-methyl and 4,4′-dimethyl DPA˙+, the formation of the cyclized dimer compounds was inferred from the presence of a large excess of the neutral molecules acting as a base. In contrast, the formation of the cyclized dimer compounds was characterized for 3-methyl- and 3,3′-dimethyl substituted DPA˙+ using cyclic voltammetry. In the ETSF method, the dimerization reaction was determined to be second-order in the cation radical and totally independent of the neutral molecule. The dimerization rates were ca. 1.0 × 107 M−1 s−1, which are faster than the reaction of DPA˙+. In spite of the complex pathway of the cyclization reaction, the 3-methyl substituent was found to promote the reaction between the 6-position of the phenyl ring and the nitrogen molecule of 3M–DPA˙+ or 3,3′M–DPA˙+.