Rhodium-catalyzed synthesis of isothiocyanate from isonitrile and sulfur

Rhodium complexes RhH(PPh3)4 and Rh(acac)(CH2CH2)2 catalyze sulfuration of isonitrile with sulfur giving isothiocyanates in high yields. The metal-catalyzed reaction is rapid in refluxing acetone, and completes within 3 h in most cases. The reaction exhibits induction period, which disappeared by preheating sulfur in refluxing acetone for 1.5 h. Use of several organic polysulfides in this transformation was examined in order to compare the reactivity.