Electrochemical Study Of Catechol In Presence Of Sulfanilic Acid And Diethytamine At Different Ph

Abstract

The electrochemical behavior of catechol in presence of diethylamide and sulfanilic acid & catechol in presence of sulfanilic acid + diethylamide have been studied by cyclic voltammetry, controlled potential coulometry, differential pulse voltammetry and chronoamperometry techniques using Glassy carbon (GC), Gold (Au) and Platinum (Pt) electrodes. The voltammetry studies have been carried out in variation of catechol, diethylamine and sulfanilic acid concentration, buffer solution of different pH, different electrodes and scan rate. Upon addition of diethyl amine and sulfanilic acid in catechol solution at the second scan of potential a new anodic peak appeared at the negative potential and the reduction peak shifted with respect of pure catechol. Also the anodic and cathodic peak current decreases significantly compared with the pure catechol that indicates the participation of reaction of o-benzoquinone with diethylamine, sulfanilic acid and their mixtures. The products generated from the reaction of catechol with diethylamine and sulfanilic acid are assumed to be 4-(diethylamino)-benzene- I ,2-diol, and 4-(bis(3,4-dihydroxyphenyl)amino) benzenesulfonic acid, respectively that undergo electron transfer at more negative potentials than the catechol. The electro-synthesized products originated from catechol with diethylamine and sulfanilic acid were isolated. The formation of new products was also confirmed by FTIR spectra. The effect of pH of catechol in presence of diethylamine and sulfanilic acid were studied by varying pH from 3 to II except sulfanilic acid 2-9. For diethylamine, it is seen that at pH 3-5, no new anodic peak appeared after repetitive cycling. In the pH 7-1 1, the o- benzoquinone undergoes nucleophilic attack by the amines that voltammetric new anodic peak A0 appeared after repetitive cycling. In contrast, for sulfanilic acid at pH 9 no new anodic peak appeared after repetitive cycling. Whereas in pH 7, the voltammogram shows a small peak. For diethylamine, the maximum peak current is obtained at pH 7 but the maximum peak current of sulfanilic acid is obtained at pH 3. The slopes of the peak potential, E vs pH plot was determined graphically as the anodic peaks of catecholdiethylamine (69 mV/pH for first anodic peak A1mV/pH for appeared peak Ao) and catechol-sulfanilic acid (36 mV/pH for first anodic peak A1 or 38 mV/pH for appeared peak Ao) at 0.1 V/s. This indicates that the oxidation reaction of catechol-diethylamine adduct proceeded via the 1e71H process whereas catechol-sulfanilic acid adduct proceeded via the 2ei2H processes. This also suggests that during the reaction not only electron but also proton are released from the catechol-amine adduct. The reaction was strongly influenced by the pH as well as concentration of diethylamine and sulfanilic acid. The reaction was mostly favorable in 250 mM of diethylamine with fixed 2 mM of catechol at pH 7. The reaction of catechol in presence of sulfanilic acid was favorable in 2 mM sulfanilic acid, 2 mM catechol at pH 3. The electro-oxidation of catechol-diethylamine adduct are facilitated in neutral media whereas catechol-sulfanilic acid in acid media. The scan rate effect on cyclic voltammogram of catechol in presence of diethylamine and sulfanilic acid were also studied. The peak current of both the anodic and the corresponding cathodic peaks increases with the increase of scan rate. The nearly proportionality of the anodic and corresponding cathodic peak suggests that the peak current of the reactant at each redox reaction is controlled by diffusion process. The current function for anodic peak A0, (I/v) of catechol-diethylamine derivative was found to be decreased exponentially with increasing scan rate. Catechol-diethylamine derivatives have been found to undergo electrochemical reaction with ECE (electron transferchemical reaction- electron transfer) type mechanism. But, the current function for the anodic peak A0, (I1,/v) of catechol-sulfanilic acid derivative was found to be decreased with increasing scan rate and such a behavior is adopted as indicative of an ECECE type mechanism.