Kinetic Studies of Spin Trapping Reactions. II. Radiolysis of Cyclohexane

In order to extend kinetic utilization of the spin-trapping techniques in radiation chemistry, γ-radiolysis of cyclohexane has been studied at room temperature using pentamethylnitrosobenzene as a spin trap. With increasing radiation dose, the cyclohexyl radical spin adduct has been found by ESR to form and then decay. Consumption of the spin trap has also been monitored by observing the optical absorption. The observed kinetic aspects indicate that the radiation-generated cyclohexyl radicals are completely trapped by 1.3×10−4–6.6×10−4 mol dm−3 of the spin trap, and their G-value is 3.0. The spin-trapping rate constant has been determined to be 1.6×107 mol−1 dm3 s−1 at 299 K based on the reported rate constant for the reaction between the cyclohexyl radical and tributylstannane. From the optical absorption study, dimeric pentamethylnitrosobenzene has been found to dissociate into the monomer, effective in the spin-trapping, with an equilibrium constant of 8×10−4 mol dm−3 in cyclohexane at 299 K. The monomer has an absorption coefficient of 48 mol−1 dm3 cm−1 at its absorption peak of 790 nm.