Aromatic nucleophilic substitution with sulphoxides: The interaction of dimethyl sulphoxide with chloronitrobenzenes

Abstract

Activated chlorine atoms are displaced by sulphoxide oxygen when di- and tri-nitrochlorobenzenes are heated in dimethyl sulphoxide. The corresponding phenols, thiomethoxymethyl- and formyl- substituted phenols, thioanisoles and decomposition products of chlorodimethyl sulphide are formed. Monochloronitrobenzenes do not undergo reaction with Me₂SO even at 190º, but in the presence of added sodium acetate or sodium benzoate, phenols and thioanisoles are obtained together with products derived from the sulphonium ylid CH₃S⁺=CH₂. These observations are rationalized mechanistically. The reaction mixtures are shown to oxidize benzyl alcohol to benzaldehyde. These results do not substantiate the presence of an intermediate sulphonium complex, however, because benzyl alcohol competes more favourably for the chloroaromatic system than does Me₂SO; benzyl alcohol forms the chloride which then undergoes a Kornblum oxidation to yield benzaldehyde.