Syntheses of Cyanine Dyes

IV. Action of K₃Fe(CN)₆ on Thioacetanilide in Alkaline Solution

Abstract

Dissolution of thioacetanilide in aqueous alkali results in the solution of its sodium salt but in alkaline concentrations of over 2N, sodium salt formation is difficult by the effect of OH radical so that the solubility of thioacetanilide in this concentration range decreases. On the other hand, formation of 2-methylbenzothiazole from thioacetanilide in alkaline aqueous solution by the oxidation with K₃Fe(CN)₆, also decreases its rate of formation when the alkaline concentration is raised above 2N, which shows that the same relationship exists between the solubility of thioacetanilide and the concentration of its alikaline solution. This is due to the two tautomeric structures of thioacetanilide molecule which change according to the concentration of alkali. It is assumed that thio-enol form of thioacetanilide is more liable to form sodium salt and also is more liable to be oxidized.