TG-FTIR, Py-two-dimensional GC-MS with heart-cutting and LC-MS/MS to reveal hydrocyanic acid formation mechanisms during glycine pyrolysis

To elucidate the formation process of HCN from the pyrolysis of glycine, the small molecule gaseous pyrolysates, H2O, NH3, CO2, CO, HNCO, and HCN, were analyzed in real-time by TG-FTIR. The appearance of the volatile pyrolysis products and the solid residue was determined in real-time at their corresponding formation temperatures by online Py-two-dimensional GC-MS with heart-cutting and LC-MS/MS. The pyrolysis of 2,5-diketopiperazine, a thermolytic by-product of glycine pyrolysis, was also studied. The results showed that: (1) the pyrolysis of glycine can be divided into three temperature ranges 200-300, 300-440, and 440-900 A degrees C; HCN forms in each range with three peaks appearing at 273, 422, and 763 A degrees C, respectively. (2) The mechanistic pathways of HCN formation from glycine in the low- and high-temperature heating stages are different. Below 273 A degrees C, glycine undergoes a decarboxylation reaction to produce methylamine, which subsequently forms HCN by means of dehydrogenation. Above 300 A degrees C, glycine gives relatively large amounts of HCN via 2,5-diketopiperazine and subsequent HNCO or methylenimine formation.