Matrix-isolation pyrolysis investigation of mercapto-functionalized 1,3,4-thiadiazoles: Thermal stability of thiadiazole lubricant additives

A series of high-vacuum thermolysis experiments with alkyldithio thiadiazoles was performed between ambient temperature and 900 °C to investigate the thermal stability of thiadiazole type lubricant additives. The thermolysis products were trapped by matrix-isolation techniques and characterized by IR spectroscopy. Thermolysis of 2-(tert-butyldithio)-5-methyl- 1,3,4-thiadiazole (TB1) gave 2-methylpropene, isothiocyanic acid (HNCS), 2-mercapto-5-methyl-1,3,4-thiadiazole (McMT), hydrogen cyanide (HCN), carbon disulfide (CS₂), acetonitrile (CH₃CN), and elemental sulfur S_x [x = (2), 4, 6, 8]. A decomposition mechanism is discussed explaining the temperature-dependent composition of product mixtures, and a general precursor concept for organosulfur type anti-wear additives is presented.