Examining thermolysis reactions and tautomerism of 2-mercapto-5-methyl-1,3,4-thiadiazole and 2,5-dimercapto-1,3,4-thiadiazole

A series of high-vacuum thermolysis experiments with 2,5-dimercapto-1,3,4-thiadiazole and 2-mercapto-5-methyl-1,3,4-thiadiazole was performed between ambient temperature and 800 °C. The thermolysis products were trapped by matrix-isolation techniques and characterised by IR spectroscopy. Thermolysis of 2,5-dimercapto-1,3,4-thiadiazole gave HNCS, CS₂ and HCN, whereas 2-mercapto-5-methyl-1,3,4-thiadiazole shows a more complex fragmentation pattern forming HNCS, CH₃NCS, HCN and CS₂. Formation of CH₃CN was not observed. The molecular structures of different isomers of both mercaptothiadiazoles were studied by ab initio and DFT computations.