LIQUID-PHASE ALKYLTHIOLATION REACTION OF PHENOL BY DIMETHYLDISULFIDE OVER ZEOLITES

The alkylthiolation reaction of phenol by dimethyldisulfide has been studied over various zeolites, in toluene as solvent. Over faujasite-type zeolites, this reaction leads to the formation of 2-(methylthio)phenol and 4-(methylthio)phenol with an initial ortho/para ratio in favor of the para isomer. Such a ratio changes with time; moreover, side reactions, mainly disubstitution and isomerisation of the para into the ortho derivative, are observed consecutively to the monosubstitution reaction. The role of the composition of the initial reaction mixture has been shown to be essential in the orientation of the reaction. A large excess of phenol leads to a decrease in the rates of the side reactions, and the monosubstitution step can be oriented towards the predominant formation of either the para or the ortho isomer, depending on the excess of phenol used. Such results are interpreted in terms of the competitive adsorption of the two reactants on the catalyst.