Electrochemical synthesis of 1,3,4-thiadiazol-2-ylthio-substituted catechols in aqueous medium

Anodic oxidation of catechols 1a–e in the presence of 5-methyl-2-mercapto-1,3,4-thiadiazole 2 has been studied in acetate buffer solution by cyclic voltammetry and controlled-potential electrolysis techniques. The effects of various electrolytic conditions (amount of passed charge, anodic materials, pH of the electrolytic solution, applied potential, and concentration of substrates) on the yield have also been investigated. The results showed that the position of the initial substituent of the starting catechol derivatives dominated the formation of monothiadiazol-2-ylthio-substituted or/and dithiadiazol-2-ylthio-substituted products. For 4-substituted catechols 1a–b, monothiadiazol-2-ylthio-substituted products (3a–b) were exclusively produced in high to excellent yields. However, in the cases of catechol itself (1c) and 3-substituted catechols (1d–e), both monothiadiazol-2-yl-substituted (3c–e and 5d–e) and dithiadiazol-2-ylthio-substituted products (4c–e) were isolated. In addition, the nature of the initial substituent of the starting 3-substituted catechols (1d and 1e) affected the relative ratio of the two monothiadiazol-2-ylthio-substituted isomers (3d–e vs 5d–e).