The electrochemical study of the formation and decomposition of 2-halo-2-nitropropane anion radicals

Abstract

The initial reduction of 2-bromo- and 2-chloro-2-nitropropane in acetonitrile is a one-electron process which yields the corresponding anion radical. The anion radical is short-lived, however, and decomposes rapidly with loss of halide ion to form the 2-nitropropyl radical. In the presence of a hydrogen-atom donor, such as thiophenol, the 2-nitropropyl radical abstracts a hydrogen atom to form 2-nitro-propane in nearly quantitative yield. In the absence of either a hydrogen-atom or proton donor the 2-nitropropyl radical is reduced, either electrochemically or chemically, to 2-nitropropyl anion. The 2-nitropropyl anion then couples with 2-nitropropyl radical to give 2,3-dimethyl-2,3-dinitrobutane anion radical, which immediately undergoes electron transfer with the 2-halo-2-nitropropane to form the stable product, 2,3-dimethyl-2,3-dinitrobutane, and the unstable 2-halo-2-nitro-propane anion radical. In the presence of proton donors, such as acetic acid and hydroquinone, protonation of the intermediate 2-nitropropyl anion precludes coupling of 2-nitropropyl anion and 2-nitropropyl radical. Thus, reduction of 2-halo-2-nitropropane in the presence of a proton donor is a two-electron process which produces 2-nitropropane as the product.