The reactions between the electrogenerated 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) dianion (DDQ(2-)) 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 DDQ(2-) with Na+ to form Na(2)DDQ. From the decay profile of free DDQ(2-), it became clear that the reaction of DDQ(2-) 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.
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In addition, a difference of the reactivity toward DDQ(2-) depending on the size of M+ was evident, though the reaction of DDQ(2-) and Li+ was too fast to be followed.