REDOX PROCESSES AND ALKYLATION REACTIONS OF C-60 AS STUDIED BY PULSE-RADIOLYSIS

Redox and alkylation (radical addition) reactions with C60 have been investigated by means of radiation chemical methods, particularly time-resolved pulse radiolysis measurements. All experiments were conducted in solutions at room temperature. The primary radical products, namely, the C60.- radical anion, the C60.+ radical cation, and radical adducts (C60-R)., exhibit distinct absorption bands in the IR at 1080, 980 (corroborating earlier low-temperature matrix and photochemical experiments), and around 900 nm, respectively. Reductions, to yield the C60.- radical anion (and at longer steady-state irradiations also more highly reduced states), could be achieved by solvated electrons and (CH3)2C(OH). radicals in 2-propanol solutions and toluene/acetone/2-propanol mixtures with rate constants of greater-than-or-equal-to 10(10) and 8.5 x 10(8) M-1 s-1, respectively. The reaction of a water-soluble C60-gamma-cyclodextrin complex (C60/gamma-CD) with alpha-hydroxyalkyl radicals also involves electron transfer, as indicated by the dependence of the rate constants on the redox potential of the reducing radicals: 2.7 x 10(8) M-1 s-1 for (CH3)2C(OH)., 1.4 x 10(8) M-1 s-1 for CH3CH(OH)., and 0.5 x 10(8) M-1 s-1 for .CH2(OH). Oxidation of C60 to yield the C60.+ radical cation through radiation-generated solvent radical cations occurs generally very fast, with rate constants greater-than-or-equal-to 2 x 10(10) M-1 s-1 (1,2-dibromomethane, dichloro- and dibromomethane, cyclohexane as solvent). The decay of the C60.+ radical cation appears to proceed via a (C60)2.+ dimer complex with a rate constant for the C60.+ + C60 reaction of 6.0 x 10(9) M-1 s-1. The addition of .CH3, .CH2Br, .CH2CH2Cl, and CH2C(CH3)2OH to the pi-system of C60 occurs with rate constants of 4.8 x 10(9), 1.7 X 10(9), 2.2 X 10(9), and 1.8 x 10(9) M-1 s-1, respectively. The decay of the adduct radicals involves both a second-order component (presumed to be radical dimerization) and a pseudo-first-order reaction dependent on the C60 concentration. The latter (1.0 X 10(8) M-1 s-1 for the .CH2CH2Cl adduct) is suggested to be an initial step of a polymerization process.