Conversion of hydroxycyclohexadienyl radicals of methylated benzenes to cation radicals in acid media

Abstract

Publication costs assisted by Ris4 National Laboratory Formation of radical cations from the OH adducts of methylated benzenes in acidic aqueous solutions is demonstrated. The radical cation is formed as an intermediate species in the water elimination reaction in which the OH adduct is transformed into the corresponding methylbenzyl radical. The radical cations are also produced in neutral aqueous solution by reacting SOf radical ions with the methylated benzenes. The cations have two absorption bands, an UV band, 280-300 nm, and a visible band, 430-470 nm, with extinction coefficient of about 6500 and 2000 NT1 cnf1, respectively. The formation of the radical cations from the OH adducts depends on the hydrogen ion concentration, feoH adduct+H+ = (1.5 ± 0.5) X 109 M"1 s_1. The radical cations decay in acid solution exclusively into the corresponding methylbenzyl radicals.

Ultrafast photoactivation of C─H bonds inside water-soluble nanocages

“…For both 9-MA and 1-MeNap, we observed sharp features in the 675- to 750-nm region, while for Tol, a sharp peak at 450 nm was observed. Notably, the radical cation features for all the three molecules were slightly redshifted by ~10 to 20 nm from their respective free-solution absorption maxima, providing evidence for confinement of the radical cations ( 42 , 43 ). The cage-incarcerated radical cationic state of the aromatic substrates was observed to decay in a picosecond time scale to form the corresponding neutral benzyl radicals after donating a proton to the solvent water molecule since it is an exergonic process ( 41 ).…”

Reaction of SO4˙− with an oligomer of poly(sodium styrene sulfonate). Probing the mechanism of damage to fuel cell membranes

“…[3][4][5][6] The estimated steady-state concentration of HO under fuel cell operating conditions is on the order of 10 À16 M. 7 Recently, we studied the reaction of HO with a model compound of a polystyrenesulfonic acid based ionomer, an oligomer with an average molecular weight of 1100 Da, poly(sodium styrene sulfonatew) (PSSS-1100) in oxygenated solution. 8 90% of HO react by addition to the aromatic ring, forming a HO-adduct.z At low pH, water elimination by reaction of protons with HO-adducts yields a radical cation, [9][10][11][12] (reaction (1)), as follows from electron paramagnetic resonance spectroscopy, UV/Vis-spectrophotometry, and conductivity measurements. 9,11,13,14 ð1Þ By means of electron paramagnetic resonance spectroscopy, Hu¨bner and Roduner observed that the reaction of HO with toluenesulfonate-used as a model compound for fuel cell membranes-yields benzyl radicals at pH 0.5-1.5, analogous to reaction (1).…”

Electron spin resonance studies. Part 71. Side-chain oxidation pathways in the reactions of ˙OH and SO4–˙ with some phenyl-substituted carboxylic acids, their anions, and some related compounds

“…The effect of acid in inducing deprotonation rather than decarboxylation may then be interpreted in several ways. First, if decarboxylation occurs via direct electrontransfer (from C0,H or C0,-to the ring) then it would be anticipated that this would occur more readily from the carboxylate anion (a radical-zwitterion) (10) than from (9). Secondly, it is conceivable that the overall electron-transfer occurs via the formation and decomposition of a bicyclic species, e.g.…”