KINETICS AND MECHANISM OF OXIDATION OF NITROGEN(III) BY [ETHYLENEBIS(BIGUANIDE)]SILVER(III) CATION AND ITS CONJUGATE BASES IN AQUEOUS PERCHLORATE-MEDIA

The complex cation [ethylenebis(biguanide)]silver(III), [Ag(H2L)]3+, oxidised N(III) quantitatively to N(V), being reduced to Ag(I). Free ethylenebis(biguanide) was recovered in near-quantitative yield. In the investigated pH range (1-7.5) the reaction is first order in [complex] and [N(III)]T. The reaction proceeds through four parallel paths: (Ag(H2L)]3+-HNO2 (k1), [Ag(H2L)]3+-NO2- (k2), [Ag(HL)]2+-NO2- (k3) and [AgL]+-NO2-(k4), where [Ag(HL)]2+ and [AgL]+ are two conjugate bases of [Ag(H2L)]3+. The respective rate constants (10(2) k dm3 mol-1 S-1) are k1 = 2.4, k2 = 42.5, k3 = 11.4 and k4 = 4.4 at 30-degrees-C and I = 1.0 mol dm-3 (NaClO4). The associated DELTAH(double-dagger) values are all moderately low and DELTAS(not-equal) are significantly negative. Nitrogen(III) reduces the silver(III) complex much faster than do alcohols and hydrogen peroxide. No silver(I)-catalysed path was detected. The present reactions appear to be outer sphere in nature.