2492-36-6Relevant articles and documents
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.
The Nucleophilicity of Superoxide towards Different Alkyl Halides Estimated from Kinetic Measurements
Daasbjerg, Kim,Lund, Henning
, p. 597 - 604 (2007/10/02)
Values of the rate constant ksub are measured for the substitution reaction between superoxide O2 anion-radical and the alkyl halides butyl chloride, 2-butyl chloride, benzyl chloride, ethyl bromide, butyl bromide, 2-butyl bromide, neopentyl bromide, benzyl bromide, (1-bromo-2,2-dimethylpropyl)benzene and 1-iodoadamantane.These rate constants are compared with the expected rate constant kET for the electron transfer reaction between the same alkyl halides and an aromatic anion radical A anion-radical with the same standard oxidation potential as O2 anion-radical.The ksub/kET ratios show that the mechanism of the substitution reaction amy shift from SN2-like to ET-like on changes in the steric hindrance and the acceptor ability of the alkyl halide.The influence on ksub/kET of the difference in self-exchange reorganization energy λ(0) between O2 anion-radical/O2 and A anion-radical/A is discussed.
Single-Pulse Shock Tube Studies on the Thermal Decomposition of n-Butyl Phenyl Ether, n-Pentylbenzene, and Phenotole and the Heat of Formation of Phenoxy and Benzyl Radicals
Walker, James A.,Tsang, Wing
, p. 3324 - 3327 (2007/10/02)
n-Butyl phenyl ether, n-pentylbenzene, and phenotole have been decomposed in single-pulse shock tube experiments.The main reaction for all these processes involves bond cleavage leading to the formation of an alkyl and a resonance-stabilized radical.In the case of n-butyl phenyl ether decomposition, a molecular mechanism involving the direct formation of 1-butene has also been detected.The rate expressions for the decomposition processes are k(n-C4H9-OC6H5 -> n-C4H9 + C6H5O) = 1.0 * 1016 exp(-33000/T) s-1, k(n-C4H9-OC6H5 -> 1-C4H8 + C6H5OH) = 4.0 * 1013 exp(-28900/T) s-1, k(n-C4H9-CH2C6H5 -> n-C4H9 + CH2C6H5) = 1 * 1016 exp(-36500/T) s-1, and k(n-C2H5-OC6H5 -> C2H4 + C6H5OH and C2H5 + C6H5O) = 5.7 * 1015 exp(-32300/T) s-1 over the temperature range of 940-1100 K and pressures of 2-3 atm.The assumption that the primary C-H bond strength for butane is 421.5 kJ mol-1 leads to heat of formation of the phenoxy radical of 55.3 kJ mol-1 and that of benzyl radical, 203 kJ mol-1.The A factors for the bond cleavage reactions are all significantly higher than previously reported for analogous processes.In the case of the benzyl-forming process they are now in accord with combination rates and the geometric mean rule.
