Thermal decomposition of methyl 2-azidopropionate studied by UV photoelectron spectroscopy and matrix isolation IR spectroscopy: heterocyclic intermediate vs imine formation
| Autor: | Maria Teresa Barros, J. S. Ogden, Paula Rodrigues, Melchiorre Costa, John M. Dyke, A.A. Dias, Rui M. Pinto |
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| Rok vydání: | 2011 |
| Předmět: |
Models
Molecular Azides Spectrophotometry Infrared Methyl formate Ultraviolet Rays Photoelectron Spectroscopy Imine Thermal decomposition Matrix isolation Analytical chemistry Infrared spectroscopy chemistry.chemical_compound chemistry X-ray photoelectron spectroscopy Heterocyclic Compounds Physical chemistry Quantum Theory Thermodynamics Imines Physical and Theoretical Chemistry Propionates Spectroscopy Ultraviolet photoelectron spectroscopy |
| Zdroj: | The journal of physical chemistry. A. 115(30) |
| ISSN: | 1520-5215 |
| Popis: | Methyl 2-azidopropionate (N(3)CH(3)CHCOOCH(3), 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 N(2), CO, CO(2), CH(3)CN, and CH(3)OH as the final decomposition products. Methyl formate (MF) and CH(4) 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 N(2) 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, CH(3)OH, and CH(3)CN (ΔE(G3) = 260.2 kJ/mol) and another leading to CO(2), CH(4), and CH(3)CN (ΔE(G3) = 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-CH(3) group, together with the N(2) elimination (ΔE(G3) = 260.2 kJ/mol). Finally, a third pathway which accounts for the formation of MF through an M2AP isomer is envisioned. |
| Databáze: | OpenAIRE |
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