1981-80-2Relevant articles and documents
Mechanism of thermal decomposition of allyltrichlorosilane with formation of three labile intermediates: dichlorosilylene, allyl radical, and atomic chlorine
Boganov,Promyslov,Krylova,Zaitseva,Egorov
, p. 1216 - 1224 (2017/02/05)
It is experimentally found that allyltrichlorosilane dissociates under vacuum pyrolysis (~10–2 Torr) at temperatures above 1100 K to form three labile intermediates: allyl radical, dichlorosilylene, and monoatomic chlorine. On the basis of experimental and theoretical data obtained, it is shown that the decomposition reaction proceeds in two steps. The first step is a typical reaction of homolytic decomposition to two radicals (C3H5 and SiCl3) at the weakest Si—C bond. Due to weakness of the Si—Cl bond in the SiCl3 radical, the energy of which is even somewhat lower than the dissociation energy of the Si—C bond in starting AllSiCl3, this radical undergoes further dissociation to SiCl2 and Cl, thus resulting in three intermediates of different classes of highly reactive species formed from AllSiCl3.
Experimental study of the reaction between vinyl and methyl radicals in the gas phase. Temperature and pressure dependence of overall rate constants and product yields
Stoliarov, Stanislav I.,Knyazev, Vadim D.,Slagle, Irene R.
, p. 9687 - 9697 (2007/10/03)
The vinyl-methyl radicals are critical intermediates in hydrocarbon combustion systems with elementary reactions of CH3 and C2H3 influencing the rate and products of the overall combustion process. The vinyl-methyl cross-radical reaction was studied using laser photolysis/photoionization MS. C2H2 yields did not experience any pressure dependence at 310, 500, and 900 K. The C3H5 decreased with an increasing pressure, which was well resolved at 310 and 500 K. The overall C2H3 + CH3 rate constants and quantitative product yields were obtained in direct real-time experiments at 300-900 K and bath gas (He) density (3-12) x 1016 molecules/cc. The primary products of the C2H3 + CH3 reaction were propylene, acetylene, and allyl radicals. A mechanism consisting of two major routes was proposed, i.e., via direct abstraction of a hydrogen atom from the vinyl radical by the methyl radical resulting in the formation of acetylene and methane and via the formation of chemically activated propylene that can undergo collisional stabilization or further decomposition into allyl radical and hydrogen atom.
Exploitation of aldoxime esters as radical precursors in preparative and EPR spectroscopic roles
McCarroll, Andrew J.,Walton, John C.
, p. 2399 - 2409 (2007/10/03)
Photolyses of aldoxime esters, containing a considerable range of alkyl groups, lead to cleavage of their N-O bonds and formation of aryliminyl and alkyl radicals. The process was found to be favoured by 4-methoxyacetophenone as a photosensitiser and by methoxy substituents in the aryl rings. 4-Nitro- and pentafluoro-substitutions of the aryl rings were, on the other hand, deleterious. The intermediate iminyl radicals, together with primary, secondary and tertiary alkyl radicals were characterised by 9 GHz EPR spectroscopy. Cyclopropyl, CF3, and CCl3 radicals were probably also formed, but were too reactive for direct EPR spectroscopic detection. Photosensitised reaction of benzophenone oxime O-nonanoyl ester produced the diphenylmethaniminoxyl, as well as the expected n-octyl and iminyl radicals. This indicated that O-C bond scission accompanied O-N scission for this ketoxime ester. At higher temperatures the C-centred radicals added to the starting oxime esters to produce alkoxyaminyl radicals that were also spectroscopically detected in some cases. No evidence for abstraction of the iminyl hydrogen by tertbutoxyl radicals was obtained. Instead, the t-BuO radicals added to the C=N double bonds of the oxime esters. Similarly, chlorine abstraction from alkylbenzohydroximoyl chlorides by trimethyltin radicals did not take place. Preparative scale experiments with oxime esters containing suitably unsaturated alkyl groups showed that good yields of cyclised products could be obtained in the presence of the photosensitiser. This process constitutes a general method by which carboxylic acids or acid chlorides can be converted into alkyl radicals and hence to cyclised derivatives.