Issue 26, 2014

Low-temperature combustion chemistry of novel biofuels: resonance-stabilized QOOH in the oxidation of diethyl ketone

Abstract

The Cl˙ initiated oxidation reactions of diethyl ketone (DEK; 3-pentanone; (CH3CH2)2C[double bond, length as m-dash]O), 2,2,4,4-d4-diethyl ketone (d4-DEK; (CH3CD2)2C[double bond, length as m-dash]O) and 1,1,1,5,5,5-d6-diethyl ketone (d6-DEK; (CD3CH2)2C[double bond, length as m-dash]O) are studied at 8 Torr and 550–650 K using Cl2 as a source for the pulsed-photolytic generation of Cl˙. Products are monitored as a function of reaction time, mass, and photoionization energy using multiplexed photoionization mass spectrometry with tunable synchrotron radiation. Adding a large excess of O2 to the reacting flow allows determination of products resulting from oxidation of the initial primary (Rp) and secondary (Rs) radicals formed via the Cl˙ + DEK reaction. Because of resonance stabilization, the secondary DEK radical (3-oxopentan-2-yl) reaction with O2 has a shallow alkyl peroxy radical (RsO2) well and no energetically low-lying product channels. This leads to preferential back dissociation of RsO2 and a greater likelihood of consumption of Rs by competing radical–radical reactions. On the other hand, reaction of the primary DEK radical (3-oxopentan-1-yl) with O2 has several accessible bimolecular product channels. Vinyl ethyl ketone is observed from HO2-elimination from the DEK alkylperoxy radicals, and small-molecule products are identified from β-scission reactions and decomposition reactions of oxy radical secondary products. Although channels yielding OH + 3-, 4-, 5- and 6-membered ring cyclic ether products are possible in the oxidation of DEK, at the conditions of this study (8 Torr, 550–650 K) only the 5-membered ring, 2-methyltetrahydrofuran-3-one, is observed in significant quantities. Computation of relevant stationary points on the potential energy surfaces for the reactions of Rp and Rs with O2 indicates this cyclic ether is formed via a resonance-stabilized hydroperoxyalkyl radical (QOOH) intermediate, formed from isomerization of the RpO2 radical.

Graphical abstract: Low-temperature combustion chemistry of novel biofuels: resonance-stabilized QOOH in the oxidation of diethyl ketone

Supplementary files

Article information

Article type
Paper
Submitted
27 Dec 2013
Accepted
14 Feb 2014
First published
14 Feb 2014
This article is Open Access
Creative Commons BY-NC license

Phys. Chem. Chem. Phys., 2014,16, 13027-13040

Low-temperature combustion chemistry of novel biofuels: resonance-stabilized QOOH in the oxidation of diethyl ketone

A. M. Scheer, O. Welz, J. Zádor, D. L. Osborn and C. A. Taatjes, Phys. Chem. Chem. Phys., 2014, 16, 13027 DOI: 10.1039/C3CP55468F

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