Kinetics and mechanism of oxidation of hydroxylamine by tetrachloroaurate(III) ion

The oxidation of H2NOH is first-order both in [NH3OH+] and [AuCl4-]. The rate is increased by the increase in [Cl-] and decreased with increase in [H+]. The stoichiometry ratio, Delta[NH3OH+]/Delta[AuCl4-], is approximate to1. The mechanism consists of the following reactions. NH3OH+ (K)(reversible arrow)a NH2OH + H+ (i) AuCl4- + NH2OH (k)(-->) AuCl2- + HNO + 2Cl(-) + 2H(+) (ii) AuCl4- + NH3OH+ + Cl- (k1)(-->) AuCl2- + HNO + 3Cl(-) + 3H(+) (iii) 2HNO (fast)(-->) N2O + H2O (iv) The rate law deduced from the reactions (i) -(iv) is given by Equation (v) considering that [H+] much greater than K-a. k(obs)/[H2NOH](o) = k(2) = (kK(a)[H+](-1) + k(1)[Cl-]) (v) The reaction (iii) is a combination of the following reactions: NH3OH+ + AuCl4- (fast)(-->) [AuCl4-..NH3OH+](precursor)double dagger (a) [AuCl4-..NH3OH+](precursor)double dagger Cl+ (k1)(-->) [Cl-...AuCl4-..NH3OH+](successor)double dagger (b) [Cl-...AuCl4-...NH3OH+](successor) -->(fast) AuCl2- HNO + 3Cl(-) + 3H(+) (c) The activation parameters for the reactions (ii) and ( iii) are consistent with an outer-sphere electron transfer mechanism.