Thermal decomposition and mass spectra of phosphoramidate esters

Article abstract of DOI:10.1246/bcsj.63.370

Thermal decomposition of diphenyl phosphoramidate (1) and phenyl phosphordiamidate (2) was investigated by DTA-TG, IR, ¹H NMR, ³¹P NMR, mass spectroscopy, and TG-GC/MS. The DTA-TG/DTG curve showed that the thermal decomposition of 1 occurred in one stage. Compound 1 melted at about 150°C and decomposed to polyphosphates accompanied with a weight loss of about 60% in the temperature region of 200 to 350°C. It was confirmed from the results of IR, ¹H NMR, and TG-GC/MS that this weight loss in TG of 1 is attributed to the liberation of ammonia and phenol and to the production of an insoluble polyphosphate through triphenyl phosphate or a soluble oligophosphate. The fragment ions of diphenyl ether (m/z 170) and aniline (m/z 93) were recognized in the mass spectrum of 1. This result indicates that phenyl radical and hydrogen atom in both samples transfer between three oxygen atoms and a nitrogen atom around a phosphorus atom. The activation energy of the thermal decomposition was estimated to be 151 kJmol^-1 for 1 and 220 kJmol^-1 for 2. From the DTA-TG/DTG curve of 2, the decomposition in TG showed two stages and proceeded in a similar process to 1. The cleavage of 2 by the electronic impact was also similar to that of 1.