Theoretical study on the thermal decomposition of thiourea

Abstract

Thermal stability of thiourea determines its successful application in electronic devices. For this reason, the primitive reactions in thiourea decomposition have been studied using HF, MP2 and DFT methods at various basis sets. Under thermal condition, thiourea isomerizes to carbamimidothioic acid via a hydrogen shift from an amino group to the nearby sulfur atom. This carbamimidothioic acid can then isomerize to its isomers. From carbamimidothioic acid intermediates, a total of four pairs of products can be generated from the studied primitive reactions, including: ammonia and isothiocyanic acid (NH3+HNCS), hydrogen sulfide and carbodiimide (H2S+HNCNH), hydrogen sulfide and cyanoamine (H2S+NH2CN), and ammonia and thiocyanic acid (NH3+HSCN). However, computational results show that product pairs of NH3+HNCS and H2S+HNCNH can be easily formed, whilst the formation of the other two product pairs are much less competitive due to their high activation energies. In addition, the calculated data can explain the reported results from thermal decomposition of thiourea and thiourea complexes.