ELECTROCHEMICAL PROPERTIES OF BENZOPHENONE IMINE AND THE USE OF THE CORRESPONDING ANION RADICAL AS A STRONG ELECTROGENERATED BASE

The electrochemical reduction of benzophenone imine (Ph2C = NH) in 0.1 M Me4NBF4 + DMF occurs in two successive one-electron steps in the absence of an added proton donor. Whereas the anion radical is stable and can be reoxidized to Ph2C = NH, the corresponding dianion is unstable (t1/2 less-than-or-equal-to 1 ms) and reacts by abstracting a proton from a component of the solvent + electrolyte system. In the presence of a nitrogen- or oxygen-centered Bronsted acid that has a pK(a) less than approximately 32, Ph2C = NH.- abstracts the proton rapidly. The redox behavior of the conjugate base of the proton donor can then be examined on a glassy carbon working electrode. In contrast, the Tate of protonation of the anion radical by weak carbon acids is often much slower than that by nitrogen- and oxygen-centered acids of similar acid strength. Kinetically controlled proton transfer from a weak carbon acid is illustrated with Ph2CH2.