Thiol synthesis from alkenes using elemental sulfur and hydrogen with cobalt-based heterogeneous catalysts

• First catalytic synthesis of thiols from alkenes using H2 and elemental sulfur. • Heterogeneous CoOx-SiOy catalyst exhibits high Markovnikov selectivity. • A wide range of alkenes were converted to thiols in up to 99% yield. • Mechanistic studies clarified the origin of regioselectivity and high catalytic activity. H 2 S-reagent-free synthesis of organosulfur compounds is an important issue from the perspective of industrial-scale synthesis. Herein, we report a synthetic method of thiols from alkenes and elemental sulfur under hydrogen pressure catalyzed by amorphous cobalt silicate (CoO x -SiO y ). This reaction employs hydrogen and elemental sulfur as alternatives to the hydrogen sulfide reagent, which is highly toxic and require high operation management cost, in the conventional industrial synthetic method of thiols from alkenes. CoO x -SiO y promoted the reaction of alkenes in the presence of elemental sulfur under 7 MPa hydrogen pressure at 130 °C to provide the corresponding secondary or tertiary thiols in 37–99% yields. Various alkene substrates such as unsaturated alcohol, allyl silane, aliphatic alkene, styrene, and cyclic alkene have been successfully applied to this catalytic system. In addition, the characterization of CoO x -SiO y using X-ray structure analyses, elemental analyses, and specific surface area measurements and the control experiments were conducted. The results suggested that the reaction involves the formation of dialkylpolysulfanes in the initial step followed by cleavage of the S–S bonds via several processes such as cobalt-catalyzed hydrogenolysis and S–S bond exchange reaction. Furthermore, DFT calculation suggested polar addition mechanism and provided a reasonable explanation for the observed Markovnikov selectivity of the reaction.