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Title: Facile Rearrangement of 3-Oxoalkyl Radicals is Evident in Low-Temperature Gas-Phase Oxidation of Ketones

Abstract

The pulsed photolytic chlorine-initiated oxidation of methyl-tert-butyl ketone (MTbuK), di-tert-butyl ketone (DTbuK), and a series of partially deuterated diethyl ketones (DEK) is studied in the gas phase at 8 Torr and 550–650 K. Products are monitored as a function of reaction time, mass, and photoionization energy using multiplexed photoionization mass spectrometry with tunable synchrotron ionizing radiation. The results establish that the primary 3-oxoalkyl radicals of those ketones, formed by abstraction of a hydrogen atom from the carbon atom in γ-position relative to the carbonyl oxygen, undergo a rapid rearrangement resulting in an effective 1,2-acyl group migration, similar to that in a Dowd–Beckwith ring expansion. Without this rearrangement, peroxy radicals derived from MTbuK and DTbuK cannot undergo HO2 elimination to yield a closed-shell unsaturated hydrocarbon coproduct. However, not only are these coproducts observed, but they represent the dominant oxidation channels of these ketones under the conditions of this study. For MTbuK and DTbuK, the rearrangement yields a more stable tertiary radical, which provides the thermodynamic driving force for this reaction. Even in the absence of such a driving force in the oxidation of partially deuterated DEK, the 1,2-acyl group migration is observed. Quantum chemical (CBS-QB3) calculations show the barrier for gas-phasemore » rearrangement to be on the order of 10 kcal mol–1. The MTbuK oxidation experiments also show several minor channels, including β-scission of the initial radicals and cyclic ether formation.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Sandia National Lab. (SNL-CA), Livermore, CA (United States); Sandia National Laboratories (SNL), Albuquerque, NM, and Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1082217
Report Number(s):
SAND2013-4534J
Journal ID: ISSN 0002-7863; 456028
DOE Contract Number:  
AC04-94AL85000
Resource Type:
Journal Article
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 135; Journal Issue: 38; Related Information: Proposed for publication in Journal of the American Chemical Society.; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Scheer, Adam M., Welz, Oliver, Sasaki, Darryl Y., Osborn, David L., and Taatjes, Craig A. Facile Rearrangement of 3-Oxoalkyl Radicals is Evident in Low-Temperature Gas-Phase Oxidation of Ketones. United States: N. p., 2013. Web. doi:10.1021/ja405892y.
Scheer, Adam M., Welz, Oliver, Sasaki, Darryl Y., Osborn, David L., & Taatjes, Craig A. Facile Rearrangement of 3-Oxoalkyl Radicals is Evident in Low-Temperature Gas-Phase Oxidation of Ketones. United States. https://doi.org/10.1021/ja405892y
Scheer, Adam M., Welz, Oliver, Sasaki, Darryl Y., Osborn, David L., and Taatjes, Craig A. 2013. "Facile Rearrangement of 3-Oxoalkyl Radicals is Evident in Low-Temperature Gas-Phase Oxidation of Ketones". United States. https://doi.org/10.1021/ja405892y.
@article{osti_1082217,
title = {Facile Rearrangement of 3-Oxoalkyl Radicals is Evident in Low-Temperature Gas-Phase Oxidation of Ketones},
author = {Scheer, Adam M. and Welz, Oliver and Sasaki, Darryl Y. and Osborn, David L. and Taatjes, Craig A.},
abstractNote = {The pulsed photolytic chlorine-initiated oxidation of methyl-tert-butyl ketone (MTbuK), di-tert-butyl ketone (DTbuK), and a series of partially deuterated diethyl ketones (DEK) is studied in the gas phase at 8 Torr and 550–650 K. Products are monitored as a function of reaction time, mass, and photoionization energy using multiplexed photoionization mass spectrometry with tunable synchrotron ionizing radiation. The results establish that the primary 3-oxoalkyl radicals of those ketones, formed by abstraction of a hydrogen atom from the carbon atom in γ-position relative to the carbonyl oxygen, undergo a rapid rearrangement resulting in an effective 1,2-acyl group migration, similar to that in a Dowd–Beckwith ring expansion. Without this rearrangement, peroxy radicals derived from MTbuK and DTbuK cannot undergo HO2 elimination to yield a closed-shell unsaturated hydrocarbon coproduct. However, not only are these coproducts observed, but they represent the dominant oxidation channels of these ketones under the conditions of this study. For MTbuK and DTbuK, the rearrangement yields a more stable tertiary radical, which provides the thermodynamic driving force for this reaction. Even in the absence of such a driving force in the oxidation of partially deuterated DEK, the 1,2-acyl group migration is observed. Quantum chemical (CBS-QB3) calculations show the barrier for gas-phase rearrangement to be on the order of 10 kcal mol–1. The MTbuK oxidation experiments also show several minor channels, including β-scission of the initial radicals and cyclic ether formation.},
doi = {10.1021/ja405892y},
url = {https://www.osti.gov/biblio/1082217}, journal = {Journal of the American Chemical Society},
issn = {0002-7863},
number = 38,
volume = 135,
place = {United States},
year = {Fri Aug 23 00:00:00 EDT 2013},
month = {Fri Aug 23 00:00:00 EDT 2013}
}