The Effect of Electrolytes Composition on the Behaviour of Saccharin and N-methylsaccharin during Ni Electrodeposition

Abstract

SUMMARYThe interaction between saccharin, N-methylsaccharin and the cathode during Ni electrodeposition in electrolytes containing different quantities of sulphate, chloride and citrate and gluconate ions was investigated by determining consumption rates (V∞) of additives and accumulation rates (Va) of cathodic reaction products. The hydroxycarboxylic acids and/or chloride anions increase Vc of saccharin and N-methylsaccharin in comparison with the anions of Watts electrolyte by accelerating either one or both cathodic reduction reactions of the carbonyl group (with and without hydrogenolysis of the endocyclic C3/4N bond). The mixtures of the cathodic reaction products of both additives in all-chloride electrolyte differ from that of Watts electrolyte, and only the cathodic reaction products mixture of saccharin differs markedly in the presence of citric and gluconic acids at concentrations of 0.04-0.10 mol dm−3. The quantity of accumulated o-toluene sulphonamide depends on the concentration of saccharin in electrolytes containing organic acids. The largest accumulation rate (Va) of the above compound was found at a concentration of ∼1.25 mM of additive. An increase in Va of o-toluene sulphonamide, N-methyl-o-toluene sulphonamide and N-methylbenzylsultame (2,3-dihydro-2-methyl-1,2- benzisothiazole-1, 1-dioxide) shows that the adsorption of additives by a carbonyl group increases. A decrease in Va of the corresponding benzamides suggests the opposite influence of investigated anions on the adsorption of additives by a sulphonyl group. The behaviour of additives in all electrolytes under study depended on their structure. The Va of benzamide and benzylsultame (2,3-dihydro-1,2-benzisothiazole-1,1-dioxide) were lower than the corresponding values of Va for N-methyl derivatives, however, Va of o-toluene sulphonamide was significantly higher than V of N-methyl-o-toluene sulphonamide. The difference of behaviour of saccharin and N-methylsaccharin in distinct electrolytes is decided by the N-methyl group, which blocked the dissociation of the latter additive.