Pyrolysis of Benzotriazoles. Relationships between 1- and 2-Vinylbenzotriazoles, α- and β-Azidostyrenes, N-Phenylketenimine and Indole. Pitfalls in the use of Pyrolysis-Mass Spectrometry in Mechanistic Studies

Wentrup, Curt and Freiermuth, Beat (2016) Pyrolysis of Benzotriazoles. Relationships between 1- and 2-Vinylbenzotriazoles, α- and β-Azidostyrenes, N-Phenylketenimine and Indole. Pitfalls in the use of Pyrolysis-Mass Spectrometry in Mechanistic Studies. Journal of Analytical and Applied Pyrolysis, 121 67-74. doi:10.1016/j.jaap.2016.07.003


Author Wentrup, Curt
Freiermuth, Beat
Title Pyrolysis of Benzotriazoles. Relationships between 1- and 2-Vinylbenzotriazoles, α- and β-Azidostyrenes, N-Phenylketenimine and Indole. Pitfalls in the use of Pyrolysis-Mass Spectrometry in Mechanistic Studies
Journal name Journal of Analytical and Applied Pyrolysis   Check publisher's open access policy
ISSN 0165-2370
1873-250X
Publication date 2016-07-02
Year available 2016
Sub-type Article (original research)
DOI 10.1016/j.jaap.2016.07.003
Open Access Status Not Open Access
Volume 121
Start page 67
End page 74
Total pages 31
Place of publication Amsterdam, Netherlands
Publisher Elsevier BV
Collection year 2017
Language eng
Formatted abstract
Contrary to a previous report based on pyrolysis-mass spectrometry, it is shown that 1-vinylbenzotriazole 4 undergoes flash vacuum pyrolysis (FVP) to N-phenylketenimine (PhNdouble bond; length as m-dashCdouble bond; length as m-dashCH2) 7 and indole 5 in parallel, not consecutive, reactions. N-Phenylketenimine does not rearrange to indole to any significant extent, but on FVP at 950 °C it decomposes in a free radical reaction to yield phenylacetonitrile, acetonitrile, benzene, biphenyl and o-tolunitrile. Phenylacetonitrile itself at 1000 °C yields essentially the same products. 1-(2-Methylpropeny)benzotriazole 22 pyrolyzes to C,C-dimethyl-N-phenylketenimine 23, and at higher temperature to methacrylonitrile 25 and benzene in a free radical reaction. 2-Vinylbenzotriazole 21 rearranges to 1-vinylbenzotriazole, which then affords N-phenylketenimine, phenylacetonitrile and indole at 900 °C. 2-Phenyl-1-azirine 10, phenylacetonitrile and a trace of N-phenylketenimine are formed by FVP of α-styryl azide 8. 2-Phenyl-1-azirine itself pyrolyzes to phenylacetonitrile, benzonitrile and a trace of indole at 900 °C. 3-Phenyl-1-azirine 12, phenylacetonitrile and indole are formed on pyrolysis of β-styryl azide 11, and matrix photolysis of 11 yields 3-phenyl-1-azirine and 1-phenylketenimine (PhCHdouble bond; length as m-dashCdouble bond; length as m-dashNH) 13. The paper emphasizes the dangers of relying solely on mass spectrometry in investigations of mechanisms of pyrolysis reaction. Observed mass spectra may on occasion correspond to very low yields of products that are not characteristic of the main reaction paths. Moreover, there are cases where major FVP reaction products have been nearly impossible to observe by online mass spectrometry.
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: HERDC Pre-Audit
School of Chemistry and Molecular Biosciences
 
Versions
Version Filter Type
Citation counts: TR Web of Science Citation Count  Cited 0 times in Thomson Reuters Web of Science Article
Scopus Citation Count Cited 0 times in Scopus Article
Google Scholar Search Google Scholar
Created: Fri, 15 Jul 2016, 13:56:46 EST by Mrs Louise Nimwegen on behalf of School of Chemistry & Molecular Biosciences