Theoretical study on the formation of carbon disulfide and ammonia from thermal decomposition products of thiourea

Abstract

The formation of carbon disulfide ( CS 2) and ammonia ( NH 3) from the thermal decomposition products of thiourea has been studied with MP2, and hybrid module-based density functional theory methods (B3LYP, MPW1PW91 and PBE1PBE), each in conjunction with five different basis sets (6-31+G(2d,2p), 6-311++G(2d,2p), DGDZVP, DGDZVP2 and DGTZVP). The free energy changes and activation energies for all the five primitive reactions involved in the formation of CS 2 and NH 3 have been compared and discussed. The results indicate that CS 2 is most likely formed in a consecutive reaction path that consists of the addition of hydrogen sulfide ( H 2 S ) to isothiocyanic acid (HNCS) to generate carbamodithioic acid and subsequent decomposition of carbamodithioic acid. By contrast, thiocyanic acid (HSCN) as the structural isomer of isothiocyanic acid is not likely the source of CS 2.