Kinetic Studies of Spin-trapping Reactions. I. The Trapping of the t-Butyl Radical Generated by the Photodissociation of 2-Methyl-2-nitrosopropane by Several Spin-trapping Agents

The photochemical reaction of 2-methyl-2-nitrosopropane (a spin-trapping agent) in benzene was studied at 299 K by monitoring the optical absorption intensity of the spin-trapping agent and the ESR signal intensity of the spin-adduct radical (di-t-butyl nitroxide). The observed kinetic feature was interpreted in terms of three elementary processes; the photodissociation of the spin-trapping agent giving a t-butyl radical, the spin trapping of the t-butyl radical by the trapping agent giving the spin adduct radical, and the reaction of the spin-adduct radical with the t-butyl radical giving diamagnetic products. The rate constant of the last process was found to be 10 times as large as that of the spin-trapping process, which was determined to be 3.3×106 mol−1 dm3 s−1 based on the reported rate constant for the scavenging of the t-butyl radical by tributylstannane. The relative spin-trapping rate constants toward the t-butyl radical were also determined to be 0.07, 1.0, 41, 63, and much higher than 50 for 2,4,6-tri-t-butylnitrosobenzene, 2-methyl-2-nitrosopropane, pentamethylnitrosobenzene, nitrosodurene and nitrosobenzene, respectively. C-phenyl-N-t-butylnitrone was found to be much less reactive by a factor of less than 0.003.