Electrochemical study of the reaction between progressively alkylated thiazine leucodyes and Fe(lll) on a glassy carbon electrode Abstract:An electrochemical investigation on five progressively alkylated thiazine dyes in the presence of Fe(II1) ions is reported. The theory of the catalytic regeneration mechanism involving an electrode reaction followed by a coupled chemical reaction is applied to derive kinetic parameters of homogeneous reaction. The second-order rate constant for the reaction of thiazine leucodyes with Fe(II1) ions was found to increase from 0.25 x lo4 to 1.6 x lo4 dm3 mol-' s-' upon monomethylation and to vary from 0.7 x lo4 for the dimethyl derivative to 1.4 x lo4 dm3 mol-I s-I for the tetramethyl one. The electron-donating nature as well as the hydrophobic characteristics of the methyl group influence the kinetics of the homogeneous reaction.

Cyclic voltammetric investigations have been performed on the clean glassy carbon electrode (GCE) at (25 ± 0.1) °C on five progressively alkylated thiazine dyes, namely, thionine (Th), methyl thionine (Azure C), dimethyl thionine (Azure A), trimethyl thionine (Azure B), and tetramethyl thionine (methylene blue) in water, water−ethanol, and water−Triton X-100 media. Diffusion coefficient values of the dyes, measured from the electrochemical data in different media, are clearly influenced by the effect of progressive alkylation to the thionine moiety along with the solvent property. In aqueous media the values of diffusion coefficient fall in the range of (2.66·106 to 5.70·106) cm2·s−1, whereas in presence of ethanol and Triton X-100 the rather lower ranges of (1.16·106 to 3.70·106) cm2·s−1 and (0.76·106 to 1.80·106) cm2·s−1 are observed, respectively. At higher pH’s the voltammograms display cathodic and anodic post/prepeaks which are the characteristics of the strong adsorption of reactants and/or products. Along with different electrochemical parameters the kinetic parameters of electrode processes have also been determined.

Solubility and equilibrium data for phenol-aqueous sodium salicylate (54 per cent)-a-methyl naphthalene system at 34) C. are reported. The system exhibits two types of curves the ordinary bite type curve and a small convex loop with a solid and liquid phase typical of systems containing water and an inorganic salt. The tie-line data fit with most of the empirical relationships reported in literature. The plait point for the system is at 360 per cent phenol concentration. AND The use of aqueous saturated sodium salicylate for the extraction of tar acids from a low-temperature tar fraction is discussed. Solubility and equilibrium data for the system neutral oil-tar acids-aqueous sodium salicylate when plotted on a ternary diagram showed two types of curves: an ordinary bite type and another a loop containing solid and liquid phases. The tie-line data agree with most of the empirical relationships reported in the literature. The plait point for the system had a tar acid concentration of 47%. The results have been compared with the earlier data for the system: phenol-a-methylnaphthalene-aqueous sodium salicylate