Kinetic Analysis of Reactions of p-Anisidine and N-Methyl-p-anisidine Cation Radicals in Acetonitrile Using an Electron-Transfer Stopped-Flow Method

摘要

The chemical follow-up reactions after one-electron oxidation of p-anisidine (PA), N-methyl-p-anisidine (MPA), and N-benzyl-p-anisidine (BPA) in acetonitrile (AN) were analyzed with a stopped-flow method utilizing the electron-transfer reaction with the tris(p-bromophenyl)amine (TBPA) cation radical. The reactions of these p-anisidine derivative cation radicals in AN were found to be faster than that of N,N-dimethyl-p-anisidine (DMPA) cation radical, which proceeds via the acid-base interaction between DMPA~(·+) and DMPA. In addition, while the rate law of the decay reaction of DMPA~(·+) was expressed as -d[DMPA~(·+)]/dt = k[DMPA+][DMPA], that of PA~(·+) has been determined to be -d[PA~(·+)]/dt = k[PA~(·+)]~2[PA] when PA+ was generated in the presence of PA. On the other hand, in the case that PA~(·+) was quantitatively formed without PA via equimolar mixing with TBPA+, the rate was determined to be -d[PA~(·+)]/dt = k[PA~(·+)]~2. Also, for the reactions of MPA~(·+) and BPA~(·+), the rate laws were identical to those of PA~(·+). From these results, the reaction mechanisms and the effects of the methyl groups on the reaction kinetics of the p-anisidine derivative cation radicals in AN were discussed.