MECHANISM OF NITROUS-OXIDE FORMATION BY METAL-CATALYZED REDUCTION OF NITRIC-OXIDE IN AQUEOUS-SOLUTION

Kinetics data were collected for the palladium-catalyzed reduction of nitric oxide (NO) to nitrous oxide (N2O) with cuprous chloride reducta nt in 2 M hydrochloric acid (2NO + 2CuCl + 2HCl --> N2O + 2CuCl(2) + H 2O). The rate-determining step was first order in the palladium concen tration and NO partial pressure. The cuprous chloride dependence was f irst order below 0.1 M; at higher concentrations saturation kinetics w ere observed. The rate of reaction was independent of H+ and Cl- conce ntrations. Kinetics results were consistent with the initial, reversib le attack (k(1)/k(-1)) of free NO on the bound nitrosyl of [PdCl3NO](2 -) yielding [PdCl3(N2O2)](2-), which is then reduced by Cu(I) (k(2)) t o generate products and recycle the palladium. A k(1) value of (6.0 +/ - 0.4) x 10(-6) (P-NO)(-1) s(-1) at 20 degrees C was calculated, with a k(-1)/k(2) ratio of 0.116 +/- 0.004 M. Rate measurements show that N O reduction by Cu(I) is the rate-limiting step in the Wacker-style cat alysis of the CO + 2NO --> CO2 + N2O reaction. The current mechanism r esembles the nitric oxide reductase activities of cytochrome c oxidase s, which proceed by Cu(I) reduction of a heme bound nitrosyl, and cyto chrome P450nor.