STUDY OF ACID-BASE AND REDOX EQUILIBRIA FOR THE C-60 C60H2 SYSTEM IN DIMETHYL-SULFOXIDE SOLVENT

Voltammetric techniques have been used to monitor the acid-base reacti ons of reduced forms of C-60 in dimethyl sulfoxide (DMSO) solution. In agreement with earlier work, the dihydrofullerene, C60H2, was found t o show three reversible reduction processes with potentials about 0.1 V negative of the corresponding C-60 potentials in toluene/DMSO (67/33 , v/v). For C60H2, the first and second acid dissociation constants ar e 4.7 and 16, respectively. Also, the reversible potentials for the C6 0H./C60H- and C60H-/C60H.- couples were found to be identical to the f irst two reduction potentials for C-60, within experimental error. The reversible potentials and pK(a) values were combined to compute the p K(a) of related species. For example, pK(a) for C60H. was computed to be 9. The titration of electrogenerated C-60(.-) with 4-nitrobenzoic a cid (pK(a) = 9) was consistent with this calculation.