Synthesis, characterization and electrochemical behaviour of some substituted 3-arylazo-8-aldehydo-4-methylcoumarins at dropping mercury and glassy carbon electrodes

Abstract

A series of 3-arylazo-8-aldehydo-4-methylcoumarins have been synthesized in excellent yields (80-90%) and their structures established on the basis of IR, ¹H NMR and elemental analysis. Their purity has been ascertained by chromatographic resolution using acetic acid-toluene (6:4, v/v) as eluent. The electrochemical reduction of 3-arylazo-8-aldehydo-4-

methylcoumarins have been studied over a wide <i>p</i>H range at dropping mercury and glassy carbon electrodes. All the compounds found to exhibit well-defined, diffusion-controlled irreversible wave. They give two-electron wave corresponding to the reduction of azo group. On the basis of cyclic voltammetry, coulometry, spectrophotometry, number of protons involved in the rate-determining step, the number of electrons in the reduction and product identification, a plausible reduction mechanism is suggested. Kinetic parameters, i.e. charge-transfer coefficient (α_n) and forward rate constant (<i>K</i>^o_f,h) have also been calculated. The <i>p</i>K values are calculated by polarographic and spectrophotometric method.