Kinetics and Mechanism of the Silver (I)-Catalyzed Autoxidation of SO2 in Aqueous Solution and Its Inhibition by Benzoate and Amide Ions

Abstract

In this paper we report that sodium benzoate and benzamide both are organics works as good inhibitor for SO2 oxidation in pH range 4.02-5.25 in the presence of silver (I). Based on the observed results following rate law given and a free radical mechanism have been proposed.      k           d S IV dt B organics 1       2 k Ag I S lV 1      Experiments were carried out at 30≤T°C≤40, 4.02≤pH≤5.25, 1×10−3mol/dm3≤ [S(lV)≤10×10−3 mol/dm3, 5×10−6mol/dm3 ≤ [Ag(I)] ≤2.5×10−5mol/dm3, 5×10−6mol/dm3≤ [Sodium Benzoate]≤8×104mol/dm3, 5×10−7mol/dm3≤ [Benzamide] ≤8×10-4mol/dm3. Rate constants and order of reaction were calculated and found pseudo- first order in all cases. The effect of pH and temperature were also discussed. The kinetic and thermodynamic parameters along with inhibition parameter have been reported. It is concluded by activation energy and inhibition values (B) is higher for benzamide, so it is better inhibitor for SO2 inhibition compared to sodium benzoate.