Fast cleavage reactions following electron transfer. Reduction of 1,1-dinitrocyclohexane

Article abstract of DOI:10.1021/ja00014a007

One-electron reduction of 1,1-dinitrocyclohexane is followed by rapid cleavage of a C-N bond, giving nitrite and 1-nitrocyclohexyl radical. The rate constant has been determined in dimethylformamide by homogeneous redox catalysis (1.6 × 10⁶ s^-1) and in aqueous solution by pulse radiolysis (1.1 × 10⁶ s^-1). These values are of the order of 10⁶ larger than the rate constant for cleavage of mononitroalkane radical anions. In the case of electrochemical reduction, the electron transfer and bond cleavage are followed by further reduction of the nitroalkyl radical to give the nitronate anion of nitrocyclohexane. For scan rates exceeding about 0.1 V/s in cyclic voltammetry, the 1-nitrocyclohexyl radical is reduced by the anion radical of 1,1-dinitrocyclohexane rather than at the electrode. Controlled potential electrolysis and product analysis showed that about 1.2 electrons were required per molecule of 1,1-dinitrocyclohexane; essentially no nitronate was found, but instead some nitrocyclohexane and substantial amounts of 1,1′-dinitrobicyclohexyl (5) were produced. This latter product arises from the radical chain reaction of nitronate with starting material. A key chain-carrying step in this reaction scheme is the reaction of 1-nitrocyclohexyl radical with the nitronate to give the anion radical of 5. The rate constant for this step was found to be 2.6 × 10⁶ L mol^-1 in water by pulse radiolysis. Fitting of fast-scan cyclic voltammograms by digital simulation showed that this rate constant must be about 5 × 10⁸ L mol^-11 s^-1 in dimethylformamide with a termination reaction (k_t = 2 × 10⁴ s^-1) of hydrogen atom abstraction by 1-nitrocyclohexyl to produce the nitrocyclohexane found in the electrolyzed solutions.