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 1,2-dichloroethane is found to increase the yield of solute radical cations (G=0.68 molecules 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 ∼1.1 V (vs. SCE) or below for the S+·/S couple and is due to reaction of the chlorine atom:toluene (π-Cl·) complex with the solute. A similar species forms with benzene. π-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 λmax 460 nm, εmax=1800 M-1 cm-1 and decays with an observed first-order rate constant k=1.12x106 s-1. The rate of reaction of the π-Clbullet with added solutes ranges from 2.5 to 5x109 M-1 s-1. 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=1.35x1010 M-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=1-2x1010 M-1 s-1