808756-15-2Relevant academic research and scientific papers
Kinetics of radical heterolysis reactions forming alkene radical cations
Horner, John H.,Bagnol, Laurent,Newcomb, Martin
, p. 14979 - 14987 (2007/10/03)
Rate constants for heterolytic fragmentation of β-(ester)alkyl radicals were determined by a combination of direct laser flash photolysis studies and indirect kinetic studies. The 1,1-dimethyl-2-mesyloxyhexyl radical (4a) fragments in acetonitrile at ambient temperature with a rate constant of khet > 5 × 109 s-1 to give the radical cation from 2-methyl-2-heptene (6), which reacts with acetonitrile with a pseudo-first-order rate constant of k = 1 × 106 s-1 and is trapped by methanol in acetonitrile in a reversible reaction. The 1,1-dimethyl-2-(diphenylphosphatoxy)hexyl radical (4b) heterolyzes in acetonitrile to give radical cation 6 in an ion pair with a rate constant of khet = 4 × 106 s-1, and the ion pair collapses with a rate constant of k ≤ 1 ± 109 s -1. Rate constants for heterolysis of the 1,1-dimethyl-2-(2,2- diphenylcyclopropyl)-2-(diphenylphosphatoxy)ethyl radical (5a) and the 1,1-dimethyl-2-(2,2-diphenylcyclopropyl)-2-(trifluoroacetoxy)ethyl radical (5b) were measured in various solvents, and an Arrhenius function for reaction of 5a in THF was determined (log k = 11.16-5.39/2.3RT in kcal/mol). The cyclopropyl reporter group imparts a 35-fold acceleration in the rate of heterolysis of 5a in comparison to 4b. The combined results were used to generate a predictive scale for heterolysis reactions of alkyl radicals containing β-mesyloxy, β-diphenylphosphatoxy, and β-trifluoroacetoxy groups as a function of solvent polarity as determined on the ET(30) solvent polarity scale.
