Kinetics of the oxidation of 2-hydroxy-2-methylpropanoic acid by silver(II) ions complexed with 2,2′-bipyridine in aqueous nitrate media

Abstract

Stopped-flow traces show that the oxidation of 2-hydroxy-2-methylpropanoic acid (hmpa) by [Ag(bipy)₂]²⁺ proceeds in two consecutive reactions. Both are found to be first order in [Ag^II] and first order in [hmpa]. The first rapid reaction is ascribed to complex formation between Ag^II and hmpa and the second to a slower redox step. A mechanism is proposed to account for the observed orders in [Ag^II], [hmpa] and [H⁺] for each reaction and values for the enthalpies and entropies of activation are determined. To investigate the effect on the redox kinetics of oxidatively inert species close to the cation, these are compared with the transition-state parameters for the oxidation of hmpa by aqua-metal cations and for the oxidation of other substrates by metal cations complexed with 2,2′-bipyridine.