Abstract

Kinetic, thermodynamic and mechanistic studies of the reduction of gold(III) complex ion, [AuCl3(OH)]-, by ethanol (EtOH) was studied spectrophotometrically in perchloric acid medium at ionic strength (µ ) = 0.05 moldm–3 (NaClO4) and T = 30.0 ± 1 °C. Stoichiometric result of the reaction revealed that one mole of the oxidant, [AuCl3(OH)]-, was reduced by one mole of the reductant, ethanol. The rate of reaction was first order in [AuCl3(OH)]- as well as in [C2H5OH] with a second order overall. Varying concentration of acid within the range 5.0 x10-4 to 1.4 x 10-2 mol dm-3 decreased the rate of the reaction. Increasing µ from 2.0 x10-2 to 1.2 x10-1 mol dm-3 (NaClO4) had no noticeable effect on the rate of the reaction. The same trend was observed on varying dielectric constant from 78.40 to 73.59. Michaelis – Menten’s type plot of kobs-1against [C2H5OH]-1was linear with negligible intercept. Entropy of activation was found to be -175.74 JK-1mol-1while activation enthalpy was found to be13.010 kJ mol-1. AuI was the product of [AuCl3(OH)]- reduction while aldehyde was obtained for EtOH oxidation. FTIR spectrum showed band for ѵ(C=O) at 1762 cm-1 for aldehyde formation. Based on negligible intercept from Michaelis – Menten’s type plot and the absence of spectroscopically determinable intermediate complex, the reaction was proposed to have proceeded through the outer-sphere mechanistic pathway.