Resonance stabilization effects on ketone autoxidation: Isomer-specific cyclic ether and ketohydroperoxide formation in the low-temperature (400–625 K) oxidation of diethyl ketone

Journal Article · Tue Oct 11 00:00:00 EDT 2016 · Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory

DOI:https://doi.org/10.1021/acs.jpca.6b07370· OSTI ID:1356327

Scheer, Adam M. ^[1]; Eskola, Arkke J. ^[2]; Osborn, David L. ^[3]; Sheps, Leonid ^[3]; Taatjes, Craig A. ^[3]

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1. Sandia National Lab. (SNL-CA), Livermore, CA (United States); Pacific Gas and Electricity Co., San Francisco, CA (United States)
2. Sandia National Lab. (SNL-CA), Livermore, CA (United States); Univ. of Helsinki, Helsinki (Finland)
3. Sandia National Lab. (SNL-CA), Livermore, CA (United States)

Here, the pulsed photolytic chlorine-initiated oxidation of diethyl ketone [DEK; (CH₃CH₂)₂C=O], 2,2,4,4-d₄-DEK [d₄-DEK; (CH₃CD₂)₂C=O], and 1,1,1,5,5,5-d₆-DEK [d₆-DEK; (CD₃CH₂)₂C=O] is studied at 8 torr and 1–2 atm and from 400–625 K. Cl atoms produced by laser photolysis react with diethyl ketone to form either primary (3-pentan-on-1-yl, R_P) or secondary (3-pentan-on-2-yl, R_S) radicals, which in turn react with O₂. Multiplexed time-of-flight mass spectrometry, coupled to either a hydrogen discharge lamp or tunable synchrotron photoionizing radiation, is used to detect products as a function of mass, time, and photon energy. At 8 torr, the nature of the chain propagating cyclic ether + OH channel changes as a function of temperature. At 450 K, the production of OH is mainly in conjunction with formation of 2,4-dimethyloxetan-3-one, resulting from reaction of the resonance-stabilized secondary R_S with O₂. In contrast, at 550 K and 8 torr, 2-methyl-tetrahydrofuran-3-one, originating from oxidation of the primary radical (RP), is observed as the dominant cyclic ether product. Formation of both of these cyclic ether production channels proceeds via a resonance-stabilized hydroperoxy alkyl (QOOH) intermediate. Little or no ketohydroperoxide (KHP) is observed under the low-pressure conditions. At higher O₂ concentrations and higher pressures (1–2 atm), a strong KHP signal appears as the temperature is increased above 450 K. Definitive isomeric identification from measurements on the deuterated DEK isotopologues indicates the favored pathway produces a γ-KHP via resonance-stabilized alkyl, QOOH, and HOOPOOH radicals. Time-resolved measurements reveal the KHP formation becomes faster and signal more intense upon increasing temperature from 450 to 575 K before intensity drops significantly at 625 K. The KHP time profile also shows a peak followed by a gradual depletion for the extent of experiment. Several tertiary products exhibit a slow accumulation in coincidence with the observed KHP decay. These products can be associated with decomposition of KHP by β-scission pathways or via isomerization of a γ-KHP into a cyclic peroxide intermediate (Korcek mechanism). The oxidation of d₄-DEK, where kinetic isotope effects disfavor γ-KHP formation, shows greatly reduced KHP formation and associated signatures from KHP decomposition products.

• Research Organization: Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC04-94AL85000
• OSTI ID: 1356327
• Report Number(s): SAND-2017-3007J; 651896
• Journal Information: Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory, Vol. 120, Issue 43; ISSN 1089-5639
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

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