Evaluate the pyrolysis pathway of glycine and glycylglycine by TG–FTIR

An online-coupled TG–FTIR evolved gas analysis (EGA) instruments has been used to identify and monitor the evolution of gaseous products during thermal decomposition of glycine and its dipeptide in flowing N2 atmosphere up to 800 °C. The first gaseous products of glycine pyrolysis, evolved around 260 °C are NH3, H2O and CO2. The max releasing rates of both NH3 and H2O are reached at 282 °C and that of CO2 is reached at 308 °C. At 400 °C HNCO becomes the main product, accompanied by CO, HCN and some other species. HCN is the main gaseous species released around 700 °C. Compared with glycine, glycylglycine has lower thermal stability, which begins to decompose at 214 °C. However, that the evolution profiles of gaseous products from glycine and glycylglycine are similar, which suggests the decomposition of them may occur through similar pathways. Our results indicate that the primary decomposition steps include deamination and dehydration. CO2 is mainly formed through the secondary reactions. And the crack of cyclic amide, 2,5-diketopiperazine (DKP), is suggested to be the main origin of HNCO and HCN at higher temperature.