Thermal behavior of guanidinium dihydrogenphosphate and diguanidinium hydrogenphosphate

The thermal decompositions of four kinds of guanidinium salts, such as guanidinium dihydrogenphosphate(1), diguanidinium hydrogenphosphate(2), diguanidinium carbonate(3), and guanidinium nitrate(4), were investigated. The thermal behaviors of these samples under a nitrogen atmosphere differ from one another. In GC/MS measurements of volatile products generated by the thermal decomposition for these samples, major fragment ions were confirmed as water, ammonia, isocyanic acid, and carbon dioxide. Further, from the mass spectrometry and IR analysis of volatile products for four kinds of samples, the formation of identical guanidine derivative during thermal decomposition process was confirmed in all cases. In IR analyses for residues of 1 and 2 heated to various temperatures, their spectra differed from each other until temperature raised at 300 degrees C. Above 300 degrees C, the infrared band of guanidinium ion completely disappeared and then the thermal products of both samples showed identical spectra. Above 500 degrees C, polymetaphosphates and diphosphorus pentaoxides were formed by the thermal decomposition and subsequently occurred condensation reactions. The kinetics were partially resolved and activation energies were estimated for the thermal decomposition of guanidinium phosphates. The highest value of activation energies for 1 and 2 were observed at weight loss of about 20%. We suggest that guanidinium phosphates decomposed through the formation of guanidine and urea derivatives, such as biguanide and amidinourea.