ALPHA-CARBON-SULFUR OXIDATION-REDUCTION REACTIONS OF SULFOXIDES . CASE OF BENZYLIC SULFOXIDES

In refluxing glacial acetic acid, α-(benzylsulfinyl)-p-mtrotoluene (1) readily gives α,α-di(benzylthio)-p-nitrotoluene (2) and p-nitrobenzaldehyde (4), while benzyl sulfoxide (6) and phenyl benzyl sulfoxide (8) are unreactive. In contrast, 1, 6, and 8 all undergo redox reactions with hydrogen chloride in dry ether or alcohol. Isotope dilution analysis shows that, with hydrogen chloride in ether, 1 forms both 2 and α, α-di(p-nitrobenzylthio) toluene (3) in comparable amounts. Dimethyl sulfoxide (DMSO) in refluxing acetic acid is an efficient trapping agent for thiols, oxidizing them to disulfides. When 1 or α-(phenylsulfinyl)acetic acid (11) is refluxed in acetic acid with DMSO, disulfide and aldehyde are formed. The behavior of α-(benzylthio)-p-nitrobenzyl alcohol (10) with DMSO in acetic acid is equivocal. The products are 4 and either 2 or disulfide, depending on the reaction conditions. The existence of an equilibrium between thiol and aldehyde on the one hand and monothiohemiacetal on the other is demonstrated. The behavior of 10 is readily interpreted in terms of this equilibrium. Mechanistic consequences of these results are discussed and it is concluded that it is unrealistic to talk of a single mechanism for these redox reactions of sulfoxides. © 1969, American Chemical Society. All rights reserved.