Kinetic and isotopic studies on the reaction between trioxodinitrate and the hexaammineruthenium(III) cation

The reaction between trioxodinitrate and the hexaammineruthenium(III) cation has been studied over the pH range 4.7-13.4. The products are nitrite, N/sub 2/O, NO, and a trace of N/sub 2/. Isotopic-labeling experiments confirm that the major source of the gaseous products is the N-1 nitrogen atom in trioxodinitrate, with a small contribution from the N-2 (two-oxygen-containing) position. The reaction is first order in both ruthenium complex and in trioxodinitrate. The rate exhibits a maximum at about pH 11.2, with a second-order rate constant k/sub 2/ = 45.8 M/sup -1/ s/sup -1/ at 2/sup 0/C. Variation of rate constant with pH allows the determination of pK/sub a/ values of 9.25 and 13.20 for HN/sub 2/O/sub 3//sup -/ and Ru(NH/sub 3/)/sub 6//sup 3 +/, respectively, in good agreement with literature values. The kinetic data are consistent with pathways involving N/sub 2/O/sub 3//sup 2 -/ and Ru(NH/sub 3/)/sub 6//sup 3 +/ as reactive species, or HN/sub 2/O/sub 3//sup -/ and Ru(NH/sub 3/)/sub 5/(NH/sub 2/)/sup 2 +/. The latter alternative leads to an unreasonably high value of the second-order rate constant (k/sub 2/' = k/sub 2/K/sub a/(HN/sub 2/O/sub 3//sup -/)/K/sub a/(Ru) = 2.5 x 10/sup 5/ M/sup -1/ s/sup -1/), however, and is considered unlikely. 20 references, 1 figure, 4 tables.