Facile Rearrangement of 3-Oxoalkyl Radicals is Evident in Low-Temperature Gas-Phase Oxidation of Ketones
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.
- Research Organization:
- Sandia National Lab. (SNL-CA), Livermore, CA (United States); Sandia National Laboratories (SNL), Albuquerque, NM, and Livermore, CA (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA)
- DOE Contract Number:
- AC04-94AL85000
- OSTI ID:
- 1082217
- Report Number(s):
- SAND2013-4534J; 456028
- Journal Information:
- Journal of the American Chemical Society, Vol. 135, Issue 38; Related Information: Proposed for publication in Journal of the American Chemical Society.; ISSN 0002-7863
- Publisher:
- American Chemical Society (ACS)
- Country of Publication:
- United States
- Language:
- English
Similar Records
Resonance stabilization effects on ketone autoxidation: Isomer-specific cyclic ether and ketohydroperoxide formation in the low-temperature (400–625 K) oxidation of diethyl ketone
A Theoretical Investigation of the Structure and Reactivity of the Molecular Constituents of Oil Sand and Oil Shale