The investigation of thermal decomposition pathways of phenylalanine and tyrosine by TG–FTIR

An online-coupled TG–FTIR evolved gas analysis (EGA) instruments have been used to identify and monitor the evolution of gaseous products during the thermal decomposition of phenylalanine and tyrosine in flowing N2 atmosphere up to 800 °C. The results indicate that the thermolysis processes of these two compounds are similar. For both of them the main primary decomposition steps are two competing paths: the direct decarboxylation and the concerted rupturing of C–C bonds. And the primary decomposition reactions also include deamination and dehydration. The main secondary reaction is the crack of cyclic dipeptide which also presents two competing pathways. The main gaseous products are NH3, H2O, CO2, CO, HNCO, HCN and some organic compounds. However, compared with tyrosine, the decomposition of phenylalanine is more complete and involves less secondary reaction. That is caused by their different thermal stability and decomposition temperature.