Kinetics and Mechanism of the Reduction of Tartrazine by Nitrite Ion in Aqueous Acid Phase

Abstract

Kinetics and mechanism of the reduction of tartrazine (TZ+) by nitrite ion (NO2-) was conducted in aqueous acidic phase under pseudo-first order condition in excess of [NO2-] at T = 28 ± 1°C, [H+] = 1 × 10-4 mol/dm3, λmax = 560 nm and ionic strength I = 1.0 mol/dm3 (NaCl). The stoichiometry of the reaction displayed 1:2 mole ratio for tartrazine and nitrite ion. The redox reaction was first order with respect to [TZ+] and first order with respect to [NO2-]. A second order rate constant was observed for the reaction. The rate also shows first order dependence on acid ion concentration. The overall reaction conforms to the rate law: [TZ+] = a[H+][TZ+][NO2-] Where a = 6.7343 dm6 mol-2 s-1. The rate of reaction increased with increase in ionic strength. There was no positive polymerization in the reaction. The investigation of spectroscopic and Michaelis- Mentens plot studies did not indicate any complex formation. A plausible mechanism in support of an outer-sphere mechanism is proposed for the reaction.