41876-35-1Relevant academic research and scientific papers
EPR investigation of HO· radical initiated degradation reactions of sulfonated aromatics as model compounds for fuel cell proton conducting membranes
Huebner, Gerold,Roduner, Emil
, p. 409 - 418 (1999)
In order to predict hydroxy radical initiated degradation of new proton conducting polymer membranes based on polystyrene, polyethersulfone, polyetheretherketone, or on polymers obtained by radiation grafting of styrene on different fluoropolymers, eight sulfonated aromatics were chosen as model compounds for EPR experiments, aiming at the identification of products of HO· radical reactions with these polymers. Photolysis of H2O2 was employed as the source of hydroxyl radicals. A detailed investigation of the pH profile was carried out for p-toluenesulfonic acid. Besides benzyl- and hydroxy-cyclohexadienyl radicals at lower pH values, phenoxyl radicals were identified, predominating in the pH range 10.5-13.0. A large number of new radicals give evidence of multiple hydroxylation of the aromatic rings, confirming reaction mechanisms proposed on the grounds of product analysis, but no evidence of dimerisation was found. The result as regards stability of organic proton exchange membranes for fuel cells is, that all unsaturated bonds and weakly bound atoms are subject to immediate attack by HO·. Ether links open by HO· ipso addition. Strategies for the reduction of membrane degradation should focus on a minimisation of HO· formation and of its access to the interior of the membrane.
Are Positive Ion Radicals Formed in Pulse Radiolysis of Alkylbenzenesulfonates?
Behar, David
, p. 4342 - 4347 (2007/10/02)
Oxidation of alkylbenzenesulfonates by OH radicals proceeds via two routes: 75-85 percent of the OH radicals react via addition to the benzene ring, while the rest abstract an H atom from the alkyl group.The relative distribution between the two paths of reaction depends on the nature of the alkyl group.No evidence for the formation of cation radicals from OH adducts was found.H radicals add to the benzene ring to form cyclohexadienyl type radicals, but when reacted with isopropylbenzenesulfonate about 15 percent of the H radicals abstract hydrogen from the alkyl to form the benzyl type radical.The reaction of SO4(.-) with alkylbenzenesulfonates produces 50-70 percent OH adducts and the rest are the benzyl type radicals.At high concentrations of solute and persulfate a short-lived precursor to the benzyl radicals has been observed.The precursors observed with p-toluenesulfonate, isopropylbenzenesulfonate, and m-toluenesulfonate decay in a first-order process with the rates 1.4*106, 9.4*105, and 2.5*105 s-1, respectively.The short-lived precursor is identified as an unstable OH adduct to the benzene ring.
