THE KINETICS AND MECHANISM OF ACETYLENE REACTIONS IN AQUEOUS IODIDE SOLUTIONS OF PLATINUM COMPLEXES .1. REVERSIBLE STAGES OF IODOPLATINATION OF ACETYLENE IN PT(IV)-I--H2O SOLUTIONS

The stage mechanism of the previously reported catalytic acetylene hyd roiodination reaction was studied at 353 K in a Pt(IV)-NaI-H+-H2O Solu tion. Reversible acetylene binding with Pt(IV) at lower temperatures ( 313 and 333 K) was found, whereas only insignificant vinyl iodide form ation was observed. The reactiOn Of C2H2 with Pt(IV) gave products tha t were intermediates in the acetylene hydroiodination reaction. The ki netics and stoichiometry of the formation of these products were studi ed under these conditions. At 313 K, C2H2 underwent a reversible react ion, which fits the following stoichiometry: C2H2 + Pt(IV) k1 reversib le k-1 X, where X is a product of the interaction, and k1 = 0.15 +/- 0 .02 l/(mol s) and k-1 = 9 x 10(-5) s-1 are the rate constants of the r espective elementary reactions. At 333 K, this reaction was rapidly eq uilibrated (the equilibrium constant K1 = k1/k-1 = 57 +/- 9 l/mol). Ac etylene conversion is limited by the following step: X + Pt(IV) k2 rev ersible k-2 Y, where k2 = (5.8 +/- 0.5) x 10(-2)/(mol s) and k-2 = (5. 5 +/- 3.9) x 10(-4) s-1. X and Y were assumed to be the products of co nsecutive haloplatination of the acetylene triple bond.