Aryl sulfones with strongly electron-withdrawing substituents - Do their electrogenerated radical anions always undergo a single cleavage reaction?

Electrochemical reduction of p-nitrophenyl methyl sulfone (1) and p-cyanoph enyl methyl sulfone (2) at mercury and platinum cathodes in dimethylformami de containing tetra-n-butylammonium tetrafluoroborate has been investigated . Electrogenerated radical anions of these compounds are long-lived and do not undergo classic two-electron cleavage of the aliphatic carbon-sulfur bo nd. Instead, due to the electron-withdrawing nitro and cyano substituents, other reactions occur. For 1, the principal product is p-nitrophenolate, wh ich can he trapped as a p-nitrophenyl alkyl ether upon treatment with an al kyl iodide or which can be protonated to give p-nitrophenol. The radical an ion of 2 can lose CN- or CH3SO2- to give radicals which couple to form 4,4' -dicyano-, 4,4'-bis(methanesulfonyl)-, and 4-cyano-4'-(methanesulfonyl)biph enyl; furthermore, when 1-iodobutane is added to an electrolyzed solution o f 2, 1-butoxy-4-(methanesulfonyl)benzene results. These and other unexpecte d processes have been characterized by means of gas chromatography-mass spe ctrometry. (C) 2001 The Electrochemical Society. All rights reserved.