Complex aspects of reaction kinetics between the 2,3-dichloro-5,6-dicyano-1,4-benzoquinone dianion and alkali metal cations in acetonitrile solution

Abstract

The reactions between the electrogenerated 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) dianion (DDQ²⁻) and the alkali metal cations (M⁺: Li⁺, Na⁺, K⁺) in homogeneous acetonitrile solutions were studied using a pulse electrolysis stopped-flow method. Changes in the absorption spectra were observed after the ion pair formation reaction of DDQ²⁻ with Na⁺ to form Na₂DDQ. From the decay profile of free DDQ²⁻, it became clear that the reaction of DDQ²⁻ with Na⁺ reached equilibrium through two steps, one fast (several tens of milliseconds) and one slow (several seconds). This complex behavior could be understood by the following two-step mechanism.

In addition, a difference of the reactivity toward DDQ²⁻ depending on the size of M⁺ was evident, though the reaction of DDQ²⁻ and Li⁺ was too fast to be followed.