Kinetic studies on fast reactions in solution VI : the kinetic studies on the reaction between tetrahalogeno-p-benzoquinones and alkali iodides

Abstract

The reactions to produce the semiquinone ion radicals by the electron transfer between tetrahalogeno-p-benzoquinones (fluoranil, chloranil, bromanil and iodanil) and alkali iodides (NaI and KI) were investigated photometrically in acetone solution in the temperature range, 20°～35℃, from the view point of kinetics. The rate of semiquinone ion radical formation is of first order for p-benzoquinones and of second order for alkali iodides. Activation energies and entropies are as follows: for chloranil-NaI, ΔE≠6.8 kcal/mole, ΔS≠=-19.4 e.u.; for chloranil-KI, ΔE≠=7.6 kcal/mole, ΔS≠=-18.6 e.u.; for bromanil-NaI, ΔE≠=9.7 kcal/mole, ΔS≠=-16.6 e.u.; for bromanil-KI, ΔE≠=9.8 kcal/mole, ΔS≠=-16 .3 e.u. Moreover, it was considered that 1) the electron donor is not a dissociated ion but the ion pair of alkali iodide. 2) a kind of charge transfer complex is formed as an intermediate in the electron transfer process and that 3) the rate of reaction is in the following order for the substituted halogen, F>Cl>Br>I. But the reaction rate can not be successfully explained in terms of electron affinity of the electron acceptor.