Issue 11, 2013

Formation of dimethylketene and methacrolein by reaction of the CH radical with acetone

Abstract

The reaction of the methylidyne radical (CH) with acetone ((CH3)2C[double bond, length as m-dash]O) is studied at room temperature and at a pressure of 4 Torr (533.3 Pa) using a multiplexed photoionization mass spectrometer coupled to the tunable vacuum ultraviolet synchrotron radiation of the Advanced Light Source at Lawrence Berkeley National Laboratory. The CH radicals are generated by 248 nm multiphoton photolysis of bromoform and react with acetone in an excess of helium and nitrogen gas flow. The main observed reaction exit channel is elimination of a hydrogen atom to form C4H6O isomers. Analysis of photoionization spectra identifies dimethylketene and methacrolein as the only H-elimination products. The best fit to the data gives branching ratios of 0.68 ± 0.14 for methacrolein and 0.32 ± 0.07 for dimethylketene. A methylketene spectrum measured here is used to reanalyze the photoionization spectrum obtained at m/z = 56 for the CH + acetaldehyde reaction, (Goulay et al., J. Phys. Chem. A, 2012, 116, 6091) yielding new H-loss branching ratios of 0.61 ± 0.12 for acrolein and 0.39 ± 0.08 for methylketene. The contribution from methyleneoxirane to the reaction product distribution is revised to be negligible. Coupled with additional product detection for the CD + acetone reaction, these observations pave the way for development of general set of reaction mechanisms for the addition of CH to compounds containing an acetyl subgroup.

Graphical abstract: Formation of dimethylketene and methacrolein by reaction of the CH radical with acetone

Supplementary files

Article information

Article type
Paper
Submitted
30 Oct 2012
Accepted
29 Jan 2013
First published
29 Jan 2013

Phys. Chem. Chem. Phys., 2013,15, 4049-4058

Formation of dimethylketene and methacrolein by reaction of the CH radical with acetone

F. Goulay, A. Derakhshan, E. Maher, A. J. Trevitt, J. D. Savee, A. M. Scheer, D. L. Osborn and C. A. Taatjes, Phys. Chem. Chem. Phys., 2013, 15, 4049 DOI: 10.1039/C3CP43829E

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