Thermal decomposition of methyl 2-azidopropionate studied by UV photoelectron spectroscopy and matrix isolation IR spectroscopy: heterocyclic intermediate vs imine formation

Pinto, R.M., Dias, A.A., Costa, M.L., Rodrigues, P, Barros, M.T., Ogden, J.S. and Dyke, J.M. (2011) Thermal decomposition of methyl 2-azidopropionate studied by UV photoelectron spectroscopy and matrix isolation IR spectroscopy: heterocyclic intermediate vs imine formation. Journal of Physical Chemistry A, 115 (30), 8447-8457. (doi:10.1021/jp2036845). (PMID:21707051)

Abstract

Methyl 2-azidopropionate (N3CH3CHCOOCH3, M2AP) has been synthesized and characterized by different spectroscopic methods, and the thermal decomposition of this molecule has been investigated by matrix isolation infrared (IR) spectroscopy and ultraviolet photoelectron spectroscopy (UVPES). Computational methods have been employed in the spectral simulation of both UVPES and matrix IR spectra and in the rationalization of the thermal decomposition results. M2AP presents a HOMO vertical ionization energy (VIE) of 9.60 ± 0.03 eV and contributions from all four lowest-energy conformations of this molecule are detected in the gas phase. Its thermal decomposition starts at ca. 400 °C and is complete at ca. 650 °C, yielding N2, CO, CO2, CH3CN, and CH3OH as the final decomposition products. Methyl formate (MF) and CH4 are also found during the pyrolysis process. Analysis of the potential energy surface of the decomposition of M2AP indicates that M2AP decomposes preferentially into the corresponding imine (M2IP), through a 1,2-H shift synchronous with the N2 elimination (Type 1 mechanism), requiring an activation energy of 160.8 kJ/mol. The imine further decomposes via two competitive routes: one accounting for CO, CH3OH, and CH3CN (?EG3 = 260.2 kJ/mol) and another leading to CO2, CH4, and CH3CN (?EG3 = 268.6 kJ/mol). A heterocyclic intermediate (Type 2 mechanism)—4-Me-5-oxazolidone—can also be formed from M2AP via H transfer from the remote O–CH3 group, together with the N2 elimination (?EG3 = 260.2 kJ/mol). Finally, a third pathway which accounts for the formation of MF through an M2AP isomer is envisioned

This record has no associated files available for download.

Contributors

Author: J.M. Dyke

Download statistics