Practical and efficient recyclable oxidative system for the preparation of symmetrical disulfides under aerobic conditions

An efficient and practical oxidative coupling of thiols to symmetrical disulfides is developed at room temperature under aerobic conditions. The commercially available sodium methoxide solution 30 wt. % in methanol together with the air was used as a retrievable promoter system and green oxidant, respectively, for the preparation of symmetrical disulfides. The desired products were obtained in good to high yields by an economical procedure. No overoxidation of the symmetrical disulfides was observed, and various functional groups were well tolerated in the current protocol. Moreover, the new reagent reduces the generation of hazardous waste due to its high reusability. The reaction proceeded in the absence of light, and it was not inhibited by TEMPO. Also, the low yield of TEMPO-benzyl thiol adduct was detected under these conditions. Based on our experiments, a possible mechanism was proposed in the absence and presence of TEMPO.