Kinetic study on electrochemical oxidation of catechols in the presence of cycloheptylamine and aniline: Experiments and digital simulation

Abstract

Oxidative coupling reaction of some catechols has been studied by cyclic voltammetry at the glassy carbon electrode in different experimental conditions. The electrogenerated o-banzoquinone participates in a coupling reaction with anionic and dianionic forms of catechol. Based on EC mechanism, the observed homogenous rate constants of the coupling reaction of catechols were estimated by analyzing the cyclic voltammetric responses using the simulation software DIGIELCH. This paper deals with reaction of o-benzoquinones derived by the oxidation of catechol (CAT), 3-methylcatechol (3-MC), 3-methoxycatechol (3-MOC) and 3,4-dihydroxybenzoic acid (3,4-DHBA) with cycloheptylamine (a primary aliphatic amine) and aniline (a primary aromatic amine) as nucleophiles to gain mechanistic insight. The outcome indicates participation of o-benzoquinone in the Michael addition reaction with the studied primary amines. The best fit of the experimental and simulated results was obtained for ECE mechanism. The calculated/estimated homogeneous rate constants (k obs) for Michael addition reaction were found to vary in the order CAT >3-MC >3-MOC >3,4-DHBA and CAT >3,4-DHBA >3-MC >3-MOC for cycloheptylamine and aniline, respectively. These data are in agreement with the trend of electronic properties (electron-donating/-withdrawing) of the substitutions on the catechol ring.