Kinetics, Thermodynamics and Mechanistic Investigation of the Reaction between AuCl3(OH)]- and Propanol in Acidic Medium

Reaction of Gold(III) complex ion, [AuCl3(OH)]-, with propanol (PrOH) was studied spectrophotometrically in perchloric acid medium at ionic strength (µ) = 0.05 mol dm–3 (NaClO4) and T = 30.0 ± 1 °C. Stoichiometry of the reaction revealed that one mole of [AuCl3(OH)]- was reduced by one mole of propanol. The rate of reaction was first order in [AuCl3(OH)-] as well as in [C3H7OH] with a second order overall, having mean second order rate constant of 0.8649±0.061 dm3 mol-1 s-1. Addition of acid within the range 5.0 x10-4 to 1.0 x 10-2 mol dm-3 decreased the rate of reaction from 0.940 to 0.307 dm3 mol-1 s-1. Increasing µ from 2.0 x10-2 to 1.2 x10-1 mol dm-3 (NaClO4) had no 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 was linear and with negligible intercept. Entropy of activation was found to be -206.56 JK-1mol-1 while activated enthalpy was 3.668 kJ mol-1. Au(I) was the product of [AuCl3(OH)]- reduction while propanal was obtained from propanol oxidation. FTIR spectral showed band for propanal formation (C=O) at 1764 cm-1. Based on negligible intercept from Michaelis – Menten’s type plot and the absence of spectroscopically determinable intermediate complex, the reaction was proposed to have occurred by outer-sphere mechanistic route.