Potassium salts catalyzed oxidative coupling of alkanethiols with sulfur: the effect of solid-liquid phase transfer of crown ether

Abstract

Potassium salts (KA, A = anion) that catalyzed the oxidative coupling of alkanethiols (RSH) to dialkyl disulfide (R2S2) were investigated by using sulfur as oxidant and 18-crown-6 ether as phase transfer agent under solvent-free conditions at atmospheric pressure. Crown ether (15-crown-5 ether, 18-crown-6 ether, dibenzo-18-crown-6 ether) showed excellent solid-liquid phase transfer effect in solid KA catalyzed reaction. RS− is the key active species of the KA catalyzed reaction. The catalytic activity of KA is affected by the pKa of conjugated acid (HA) of anion A− in KA. The larger the pKa of the corresponding HA, the more active for KA to activate RSH to generate RS−. Among the KA investigated, the yield of (n-C8H17)2S2 for the K2CO3, K3PO4·3H2O and K2SnO3·3H2O catalyzed reaction reached more than 98.0%. The yield of R2S2 can reach more than 95.0% by 0.1 mol% 18-C-6 (based on sulfur) and 0.1 mol% K2CO3 (based on sulfur) catalyzed the oxidative coupling of different alkanethiols.