Increased yields of radical cations by arene addition to irradiated 1,2-dichloroethane

Pulse radiolysis in chlorinated hydrocarbon liquids such as 1,2-dichloroethane is a versatile and effective method for the generation of solute radical cations. The addition of a large concentration of toluene or benzene to solutions of 1,2dichloroethane is found to increase the yield of solute radical cations (G=0.68molecules 100 eV 1 in 1,2-dichloroethane (J. Phys. Chem. 83(15) (1979) 1944) by a factor of 2.5. The increased yield is found for solutes which have a potential of B1.1V (vs. SCE) or below for the S/S couple and is due to reaction of the chlorine atom:toluene (p-Cl) complex with the solute. A similar species forms with benzene. p-Cl is formed with a yield of G=3.0, and arises principally as a result of geminate recombination of ions. It has an absorption in the visible with lmax 460 nm, emax=1800M 1 cm 1 and decays with an observed first-order rate constant k=1.12 10 s . The rate of reaction of the p-Cl with added solutes ranges from 2.5 to 5 10M 1 s . The other oxidant present in the 1,2-dichloroethane/toluene solutions is identified as the toluene cation dimer. This is formed from the 1,2-dichloroethane radical cation with bimolecular rate constant k=1.35 10M 1 s 1 with a radiation chemical yield G=0.5. The rate of reaction of this species with the added solutes is diffusion controlled, k=1–2 10M 1 s . r 2004 Elsevier Ltd. All rights reserved.