Gas-phase oxygenation of benzene derivatives around 300 K with O(3P) atoms produced by microwave discharge of N2O. Part 2. Kinetic H/D isotope effects
✍ Scribed by Veronica M. Sol; Robert Louw; Peter Mulder
- Book ID
- 104589190
- Publisher
- Elsevier Science
- Year
- 2010
- Tongue
- English
- Weight
- 737 KB
- Volume
- 109
- Category
- Article
- ISSN
- 0165-0513
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✦ Synopsis
Abstract
The possible pathways for the formation of (chloro)phenol, following the addition of O(^3^P) to (chloro)benzene, have been examined using deuterated substrates: C~6~D~6~ (also in admixture with C~6~H~6~) and p‐deuterochlorobenzene. Whereas with O‐C~6~H~6~ adduct biradicals, loss of H\documentclass{article}\pagestyle{empty}\begin{document}[^\bullet]\end{document} to give phenoxy radicals predominates, only one‐third of the O‐C~5~D~6~ intermediates undergo the corresponding reaction. Phenoxy radicals lead to phenol by transfer of an H(D) atom from cyclohexadienyl‐type radicals, formed from H\documentclass{article}\pagestyle{empty}\begin{document}[^\bullet]\end{document} (D\documentclass{article}\pagestyle{empty}\begin{document}[^\bullet]\end{document}) and substrate.
Analogously, in reactions of p‐deuterochlorobenzene, loss of H is a major reaction after addition of an oxygen atom to a meta position, whereas loss of D (to give p‐chlorophenol) occurs only with 35% of the corresponding O(^3^P) adduct biradicals. The isotopic composition of phenol formed from p‐DC~6~H~4~Cl (via p‐DC~6~H~4~O\documentclass{article}\pagestyle{empty}\begin{document}[^\bullet]\end{document}; generated by ipso substitution) revealed that H transfer to phenoxy radicals primarily gives the keto tautomers as major products. Isomerization of (chloro)‐benzene‐O(^3^P) adduct biradicals to the corresponding phenols also appears to involve mainly, keto tautomers.
The reaction of O(^3^P) with p‐deuterochlorobenzene showed a slight change in the o/m/p distribution; this can be explained by the absence of a net secondary H/D kinetic isotope effect for O(^3^P) addition to the para site and a normal secondary isotope effect for meta addition.