Reactivity of aromatic thiols toward carbon-centred radicals via hydrogen abstraction reaction: a pulse radiolysis study

Hydrogen abstraction reactions of various carbon-centred radicals from thiophenol and its methyl derivatives to produce thiyl radicals have been studied by pulse radiolysis in neutral aqueous solutions and in cyclohexane. The bimolecular rate constants in aqueous solution were found to be in the order: CCl3>C(CH3)2OH>CH(CH3)OH>CH2OH>CH2C(CH3)2OH (in the range between 2.6×109 and 0.1×109 dm3 mol−1 s−1). It was found that hydrogen abstraction from aromatic thiols by hydroxyalkyl radicals radical is not controlled by the relative bond dissociation energies but rather by the electron density at the site through a polar transition state. Cyclohexyl radicals formed in cyclohexane react considerably slower than hydroxyalkyl and trichloromethyl radicals in water with aromatic thiols (k≈5×107 dm3 mol−1 s−1).