KINETICS AND ABSORPTION-SPECTRA OF TRANSIENTS IN THE RADIOLYSIS OF HEXAFLUOROBENZENE IN AQUEOUS-SOLUTION - A PULSE-RADIOLYSIS STUDY

Hexafluorobenzene reacts with hydrated electrons with a rate constant of 8.5 X 10(9) M-1 s-1. In alkaline solution, the radical anion formed has absorption maxima at 280 and 390 nm. The radical anion decays with a rate constant 2k = 4.6 X 10(9) M-1 s-1 to form carbanion which has absorption maxima at 290, 345, and 410 nm. Below pH 11, C6F6.-, is rapidly protonated to form cyclohexadienyl radical which has bands at 260 and 350 nm. The pK(a) of the C6F6H. half arrow right over half arrow left C6F6.- + H+ equilibrium was estimated to be 12.4. The radical anion derived from ethanol also reduces C6F6 with a rate constant of 2.5 x 10(6) M-1 s-1, and the radical anion formed has absorption bands at 300 and 440 nm. It decays by radical recombination to yield a carbanion which has absorption bands at 310 and 580 nm. Both the radical anion and the carbanion formed display considerable inertness and have long lifetimes. The product spectrum shows evidence for the formation of long-chain molecules, indicating the involvement of anionic polymerization. Hydroxyl radical adds to hexafluorobenzene with a rate constant of 1.4 X 10(9) M-1 s-1 to form an adduct, hydroxycyclohexadienyl radical, which has absorption bands at 280 and 400 nm. O.- adds to hexafluorobenzene with a rate constant of 9.4 X 10(7) M-1 s-1. The adduct undergoes base-catalyzed fluoride elimination to yield phenoxide radical which has absorption maxima at 300 and 430 nm. The adduct also undergoes acid-catalyzed water elimination at lower pH to yield C6F6.+, and the radical cation is also formed by electron-transfer reaction with SO4.-.