A Theoretical Study of the Gas-Phase Pyrolysis of 2-Azidoacetic Acid

DFT and ab initio calculations up to the MP2 level have been performed to study the pyrolysis of 2-azidoacetic acid (N 3 CH 2 COOH). Several molecular properties, such as conformational equilibrium, optimal geometry, ionization energies, and vibrational frequencies, have been computed for this acid. Other species involved in its pyrolysis were also fully optimized and corrected for zero-point energies. In all cases, the calculated properties agree quite well with the observed experimental data. Two types of mechanisms were analyzed for the decomposition of N 3 CH 2 COOH. The first analyzed mechanism is a multistep process analogous to the one traditionally proposed for alkyl azides. First, either the imine NHCHCOOH or the nitrene NCH 2 COOH is formed by the release of molecular N 2 . Then, from these species, ejection of CO 2 will produce methanimine (NHCH 2 ), although other reaction channels may be expected. The second mechanism involves, after an initial distortion of the N 3 CH 2 COOH minimum geometry, a concerted dissociation step where N 2 and CO 2 are simultaneously ejected, yielding directly the imine NHCH 2 . Accordingly to the present calculations, the second mechanism is the most favorable one, in clear agreement with recent experimental work ( J. Am. Chem. Soc. 1997, 119, 6883).