Recent chemical, electrochemical and electron spin resonance studies of halogenated nitroaromatics have shown that loss of anionic substituents is a frequently observed pathway for anion radical decomposition 1 -14. The neutral radicals which result from loss of the anionic substituents react by numerous pathways including: dimerization of benzyl 5 and cumyl radicals 14, hydrogen atom abstraction by phenyl radicals 3, and coupling of phenyl radicals with a second anion to form a new, stable anion radical 8' 12. With the exception of the p-nitrophenylthiyl radical (p-OENC6H4 S') which is formed by the elimination of cyanide ion from p-nitrophenylthiocyanate anion radical, none of the nitroaromatic radicals is reduced at the applied potential to an anion 13.
There are two salient features of the 2-halo-2-nitroaliphatics which should distinguish the electrochemical behavior of this reaction series from the redox behavior of the halogenated nitroaromatics. First, since the 2-halo-2-nitropropanes are not reduced by the alkali metal salts of 2-nitropropyl anion in the dark 9, 2-nitropropyl radical should be reduced to its anion by the anion radical of a 2-halo-2nitropropane. Second, since the pKa relative to water for 2-nitropropane is approximately 1015, 2-nitropropyl anion will be unable to abstract a proton from such solvents as acetonitrile, dimethylformamide, and dimethylsulfoxide. The unusual stability of this anion to both proton and electron transfer should make the 2-nitropropyl anion an intermediate in the decomposition of the anion radicals of the 2-halo-2-nitropropanes and, moreover, should provide additional reaction pathways which were not observed in the decomposition of nitroaromatic anion radicals 1 -5
The first evidence for the intermediacy of the 2-nitropropyl radical in the decomposition of nitroaliphatic anion radicals was obtained by Hoffmann et al. 7. These workers observed that the polarographic reduction of 2,2-dinitropropane in glyme resulted in the formation of 2-nitropropyl anion and 2,3-dimethyl-2,3-dinitrobutane. Although these species were suggested to arise by reduction and dimerization of 2-nitropropyl radicals respectively, recent studies have shown that coupling of aromatic and aliphatic radicals with anions to form anion radicals is an extremely facile process which can compete with the hydrogen-atom abstraction and dimerization reactions of radicals 8'9'12.
The work described here is concerned principally with the reaction pathways of the 2-nitropropyl radical and anion and the effects of proton and hydrogen atom donors on the several reaction pathways. The 2-nitropropyl radical is generated in situ by the decomposition of electrolytically formed 2-halo-2-nitropropyl anion radicals.