Competing Channels in the Thermal Decomposition of Azidoacetone Studied by Pyrolysis in Combination with Molecular Beam Mass Spectrometric Techniques
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- 作者：Patrick O'Keeffe ; Giorgio Scotti ; Domenico Stranges ; Paula Rodrigues ; M. Teresa Barros ; Maria L. Costa
- 刊名：Journal of Physical Chemistry A
- 出版年：2008
- 出版时间：April 10, 2008
- 年：2008
- 卷：112
- 期：14
- 页码：3086 - 3093
- 全文大小：201K
- 年卷期：v.112,no.14(April 10, 2008)
- ISSN：1520-5215
文摘
The thermal decomposition of azidoacetone (CH3COCH2N3) was studied using a combined experimental andcomputational approach. Flash pyrolysis at a range of temperatures (296-1250 K) was used to induce thermaldecomposition, and the resulting products were expanded into a molecular beam and subsequently analyzedusing electron bombardment ionization coupled to a quadrupole mass spectrometer. The advantages of thistechnique are that the parent molecules spend a very short time in the pyrolysis zone (20-30 
s) and that thesubsequent expansion permits the stabilization of thermal products that are not observable using conventionalpyrolysis methods. A detailed analysis of the mass spectra as a function of pyrolysis temperature revealed theparticipation of five thermal decomposition channels. Ab initio calculations on the stable structures and transitionstates of the azidoacetone system in combination with an analysis of the dissociative ionization pattern ofeach channel allowed the identity and mechanism of each channel to be elucidated. At low temperatures(296-800 K) the azide decomposes principally by the loss of N2 to yield the imine (CH3COCHNH), whichcan further decompose to CH3CO and CHNH. At low and intermediate temperatures a process involving theloss of N2 to yield CH3CHO and HCN is also open. Finally, at high temperatures (800-1250 K) a channelin which the azide decomposes to a stable cyclic amine (CO(CH2)2NH) (after loss of N2) is active. The lastchannel involves subsequent thermal decomposition of this cyclic amine to ketene (H2CCO) and methanimine(H2CNH).
s) and that thesubsequent expansion permits the stabilization of thermal products that are not observable using conventionalpyrolysis methods. A detailed analysis of the mass spectra as a function of pyrolysis temperature revealed theparticipation of five thermal decomposition channels. Ab initio calculations on the stable structures and transitionstates of the azidoacetone system in combination with an analysis of the dissociative ionization pattern ofeach channel allowed the identity and mechanism of each channel to be elucidated. At low temperatures(296-800 K) the azide decomposes principally by the loss of N2 to yield the imine (CH3COCHNH), whichcan further decompose to CH3CO and CHNH. At low and intermediate temperatures a process involving theloss of N2 to yield CH3CHO and HCN is also open. Finally, at high temperatures (800-1250 K) a channelin which the azide decomposes to a stable cyclic amine (CO(CH2)2NH) (after loss of N2) is active. The lastchannel involves subsequent thermal decomposition of this cyclic amine to ketene (H2CCO) and methanimine(H2CNH).