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

Abstract

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 asmore » 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.« less

Authors:

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

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+ Show Author Affiliations

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)

Publication Date:

Tue Oct 11 00:00:00 EDT 2016

Research Org.:

Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1356327

Report Number(s):

SAND-2017-3007J
Journal ID: ISSN 1089-5639; 651896

Grant/Contract Number:  

AC04-94AL85000

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory

Additional Journal Information:

Journal Volume: 120; Journal Issue: 43; Journal ID: ISSN 1089-5639

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY