Kinetics of silver(I)-catalyzed oxidation of formic acid by the (ethylenebis(biguanidine))silver(III) cation in acid perchlorate media

In the presence of added Ag+, the title reaction follows the rate law-d[complex]/dt = ko = Kk1[Ag+]2[HCO2H]/([H+] + K[HCO2H]), where ko is the observed zero-order rate constant for a large excess of Ag+,H+, and HCO2H over the complex. 103k1 was found to be 1.0 ± 0.1M-1 min-1 at 30°C and I=1.0M. Corresponding ΔH* and ΔS* values are 13 ± 1 kcal/mol and -37 ± 3eu, respectively. Under these conditions, K, the formation constant of Ag(HCO2) from HCO2H and Ag+, was found from kinetic results to be 0.1 ± 0.01. The acid dissoication constants (pK1 and pK2) of the complex cation under similar conditions in a 50% (v/v) aqueous-DMF medium are 3.0 ± 0.2 and 6.8 ± 0.3. There is evidence fro the Ag+ ion acting here as the actual oxidant for HCO2H with use of the complex as an oxidant regenerating Ag+ from Ag0 formed as an intermediate. Under the experimental conditions where Ag(II) is detectable in concentrations less than about 10-4M, the whole reaction course is EPR silent. This has been discussed in terms of possible reaction schemes