Kinetics and mechanism of the reduction of gold(III) by glycine in acetate buffer

The kinetics of reduction of tetrachloroaurate(III) by glycine has been spectrophotometrically studied in NaOAc–AcOH buffer in the pH range 3.73–4.77. The reaction is first order with respect to both Au(III) and glycine. Both H⁺ and Cl⁻ ions have inhibiting effects on the reaction rate. The rate decreases with a decrease in the dielectric constant of the medium. AuCl₄⁻ and AuCl₃(OH)⁻ are presumed to be the predominant oxidizing species under the conditions of the experiment. The reaction of gold(III) and zwitterionic species of glycine proceeds with the intermediate formation of gold(I) and iminic cation and the latter subsequently hydrolyses in a fast step to produce formaldehyde and ammonium ion. Formaldehyde was identified as the only organic product by ¹H NMR spectroscopy.