Mechanism of the oxidation of carbon monoxide by tetrachloroplatinate(2-). An investigation into the nature of the intermediates by isotopic labeling

Abstract

The oxidation of CO by PtCl/sub 4//sup 2/minus//-CuCl/sub 2/ in the presence of /sup 18/O-enriched water produces CO/sub 2/ of which the /sup 18/O distribution indicates that statistically 1.5 of the 2 oxygens are derived from water. During the reaction, PtCl/sub 3/(CO)/sup /minus// may be isolated by quenching with (AsPh/sub 4/)/sup +/Cl/sup /minus//. This monocarbonyl species undergoes oxygen exchange with /sup 18/O-enriched water reaching isotopic equilibrium within 5 min at ambient temperature. Under a /sup 13/CO atmosphere, a solution of PtCl/sub 3/(CO)/sup /minus// yields CO/sub 2/ of which the /sup 13/C abundance reveals that half the CO/sub 2/ comes from gaseous CO and the other half is from PtCl/sub 3/(CO)/sup /minus//. These results strongly imply that PtCl/sub 3/(CO)/sup /minus// reacts with gaseous CO to give PtCl/sub 2/(CO)/sub 2/ prior to CO/sub 2/ formation. The rapid oxygen exchange of PtCl/sub 3/(CO)/sup /minus// with water and the irreversible attack of PtCl/sub 2/(CO)/sub 2/by water to give CO/sub 2/ are proposed to explain the observation that statistically 1.5 of the 2 oxygens in CO/sub 2/ are from water. Isotopic analysis of the CO/sub 2/ produced from the reaction of /sup 13/CO with PtCl/sub 3/(CO)/sup /minus// in /sup 18/O-enriched aqueous solution demonstrates that onemore » oxygen in (/sup 13/C)carbon dioxide is originally from water, while both oxygens in (/sup 12/C) carbon dioxide are derived from water. This double-labeling experiment further confirms the results obtained from /sup 18/O and /sup 13/C labeling studies. A detailed mechanism based on the results of these isotopic labeling studies is proposed. 19 references, 1 figure, 3 tables.« less