IODINE ATOMS AND IODOMETHANE RADICAL CATIONS - THEIR FORMATION IN THE PULSE-RADIOLYSIS OF IODOMETHANE IN ORGANIC-SOLVENTS, THEIR COMPLEXES, AND THEIR REACTIVITY WITH ORGANIC REDUCTANTS

Pulse radiolysis of iodomethane in various organic solvents leads to formation of iodine atoms or iodomethane radical cations, which in turn form complexes with iodomethane or with the solvent. Radiolysis in cyclohexane gives CH3I.I, which exhibits an absorption peak at 390 nm, whereas radiolysis in benzene forms the solvent complex, C6H6.I, which exhibits an intense broad absorption centered at 490 nm. Radiolysis of iodomethane in acetone, benzonitrile, and halogenated hydrocarbons results in formation of the radical cation CH3I+. In the former two solvents, this species forms a complex with another molecule of iodomethane to give (CH3I)2+, which absorbs at 420 nm, in agreement with previous results in aqueous solutions, but in halogenated hydrocarbons it forms complexes with the solvents, absorbing at 320-360 nm, i.e., near the absorption of monomeric CH3I.+ in water. Complexes of I atoms oxidize phenol and triphenylamine relatively slowly whereas complexes of CH3I.+ react more rapidly. The reactivity of the CH3I.+.RX complexes increases in the order of RX = CH2Cl2, CHCl3, CH2Br2, CCl4, CH3I, and for each complex the reactivity with phenol increases with increase in electron donating power of substituents. Replacing the methyl group of iodomethane radical cation with ethyl or isopropyl decreases the reactivity, whereas trifluoromethyl increases the reactivity. These oxidation reactions proceed via an intermediate complex between the iodine species and the organic reductant.