Base catalysed addition of phenols to aryl vinyl sulphones

Abstract

The addition of some phenols to aryl vinyl sulphones was studied in 1:1 (v/v) aqueous ethanol at 25°C in the presence of a basic catalyst. The reaction follows second-order kinetics, being first order in the sulphone and first order in the phenolate ion, the only active nucleophile. The Hammett and Brønsted equations were used to correlate the effects of substituents in the aromatic ring of the substrate and of the nucleophile. These both indicate that while there is a large accumulation of negative charge on the carbon α to the sulphonyl group in the transition state, the degree of formation of the C–O bond depends on the substituent in the ring of the sulphone. The reactivity of the phenolates, despite their greater basicity, is lower by a factor of some 4 × 10⁴ than that of the arenethiolates studied previously. The following order of reactivity has been estabilished: PhO^– < OH^– < EtO^– PhS^–; this indicates that polarizability and/or solvation are more important than Brønsted basicity in determining the reactivity in the addition of anionic nucleophiles to aryl vinyl sulphones.