The electrochemical oxidation of Pb(II) to Pb(IV) in acetonitrile solution containing benzoic acid and pyridine is possible at a basal-plane pyrolytic-graphite electrode and associated with a rapid ligand exchange at the metal center. The Pb(IV) species generated under these conditions is shown to react with diols such as 1,2:5,6-di-O-isopropylidene-D-mannitol, 1,2-ethanediol, cis- and trans-1,2-cyclopentanediol, which undergo a two-electron oxidation associated with carbon-carbon bond cleavage. Voltametric data obtained by both channel flow cell and rotating disk electrode experiments are analyzed by numerical simulation. Consistent results for a second-order EC＇ (electrocatalytic) reaction pathway were obtained. Voltammetric data obtained by systematically varying the concentration of pyridine and benzoic acid reveal a complex mechanism with a distinct trend in reaction rate for each diol expressed in terms of apparent fractional reaction orders when analyzed in terms of a chemically oversimplified EC＇ mechanism. This behavior is given mechanistic significance by analysis of the data using numerical simulation employing the following "branched" ECrevCrevCirrev＇ reaction scheme, which allows all the experimental results to be rationalized (benz = benzoic acid, py = pyridine) : Pb(II)reversible arrow Pb(IV) + 2e(-); Pb(IV)(benz)(h)(py)(i) + diol reversible arrow Pb(IV)(benz)(h)(diol)(py)(i) with rate constants k(1) and k(-1) for the forward and reverse reactions, respectively; Pb(IV)(benz)(h+j)(diol)(py)(i-k) + k(py) reversible arrow Pb(IV)(benz)(h)(diol)(py)(i) + j(benz) with rate constants k(2) and k(-2) for the forward and reverse reactions, respectively; Pb(IV)(benz)(h)(diol)(py)(i) --> Pb(II) + products with rate constant k(i). Here, the chemical processes are associated with appropriate rate constants, k(n), and the equilibrium constant of a process is given by K-n = k(n)/k(-n) (n = 1, 2). The "true" second-order rate constants K(j)k(i) obtained for the electrocatalytic cleavage of 1,2:5,6-di-O-isopropylidene-D-mannitol (k =j = 1), K(1)k(f) = (36 +/- 7) x 10(3) M-1 s(-1), 1,2-ethanediol (k = 1; j = 2), K(1)k(f) = (70 +/- 14) x 10(3) M-1 s(-1), trans-1,2-cyclopentanediol (k = 1; j = 0), K(1)k(f) = (180 +/- 36) X 10(3) M-1 s(-1), and cis-1,2-cyclopentanediol (k = j = 0), K(1)k(f) = (280 +/- 56) x 10(3) M-1 s(-1) are similar to within 1 order of magnitude. The effect of the diffusion of coexisting species coupled via fast preequilibria to the irreversible chemical process is discussed in respect to the physical meaning of the rate constants determined by applying a simplified mechanistic scheme.