The effect of triphenylmethyl cations on the electroreduction of O2 in nitrobenzene or acetonitrile

Abstract

Abstract The electroreduction of O 2 in two aprotic solvents (nitrobenzene and acetonitrile) was examined in the absence and in the presence of the very strong Lewis acid, triphenylmethyl cation, φ 3 C + (φ=phenyl). The addition of φ 3 C + causes the electroreduction of O 2 to change from the one-electron reduction to O 2 − into the two-electron reduction to φ 3 CO 2 Cφ 3 at a potential that is 1 V more positive than that where O 2 is reduced to O 2 − . This large positive shift in potential is used to estimate a value of the equilibrium constant for the association between O 2 2− and two φ 3 C + cations ( K =3×10 26 M −2 ). The mechanism of the reduction of O 2 to φ 3 CO 2 Cφ 3 can be regarded as an inner-sphere electron-transfer reaction between φ 3 C and O 2 or, equivalently, as a radical addition to O 2 .