Kinetic studies on fast reactions in solution VII : the kinetic studies on the reactions of p-benzoquinone and its derivatives with alkoxy ions

Abstract

The fast reactions to produce semiquinone ion radicals by electron transfer from alkoxy ions (RO^-) to p-benzoquinone (BQ), 2-methyl-p-benzoquinone (MeBQ), 2-chloro-p-benzoquinone (CIBQ) and 2-bromo-p-benzoquinone (BrBQ) were kinetically studied using the stopped flow apparatus in alcoholic solutions corresponding to the alkoxy ions, by means of the spectrophotometric and ESR methods. In the reactions of BQ and MeBQ with MeO^-. EtO^-, n-PrO^- and with n-BuO^-, the corresponding semiquinone ion radicals were first produced. And then it was found that the substitution reactions of alkoxy ion follows consecutively or concurrently, in the reaction of BQ and CIBQ with MeO^- and EtO^-. But is the case of BrBQ, the formation is presumed to be too fast to be detected. The rates of the semiquinone formation is of first order for benzoquinones and also of first order for RO^- in the cases of BQ and CIBQ, but of non-integral order for RO^- is the case of MeBQ. From these results, the reaction scheme was considered assuming a kind of the charge-transfer complex. The activation parameters were obtained, and the reaction rate was discussed in terms of electron affinities of benzoquinones and the influence of Z-value of the solvent.