Estimation of the standard reduction potentials of some 1-arylethyl radicals in acetonitrile

The redox properties of some arylethyl radicals, which are involved in the electrochemical synthesis of important anti-inflammatory agents, have been investigated in CH3CN by an indirect electrochemical method based on the catalytic reduction of the corresponding arylethyl halides (RX) by electrogenerated aromatic or heteroaromatic anion radicals (D-). The reaction between RXand D- leads to aradical R, which can react with D- eitherbyradical coupling (k3) or by electron transfer (k4). Examination of the competition between these reactions, which can be expressed by a dimensionless parameter q =k4/(k3 + k4), as a function of E° D/D- allows estimation of the reduction potentials of the arylethyl radicals. The standard reduction potentials obtained for the radicals 1-(4-isobutylphenyl)ethyl, 1-(6-methoxy-2-naphthyl)ethyl, and 1-(4-biphenyl)ethyl are -1.64, -1.62, and -1.15 V vs. SCE, respectively.