Investigation of the electrochemical behavior of some dihydroxybenzoic acids in aqueous solution

The electrochemical oxidation of some dihydroxybenzoic acids (DHBAs), 2,5-, 2,3-, and 3,4-dihydroxybenzoic acid, has been studied using cyclic voltammetry and chronocoulometry. It was found that the position of the carboxylic acid group on the phenyl ring is an effective factor in electrochemical oxidation of these molecules. The electrochemical oxidation of 2,5-DHBA and 2,3-DHBA shows the features of an ECE mechanism. Based on the voltammetric results, hydroxylation is considered to be the subsequent chemical reaction of electrochemical oxidation of 2,5-DHBA and 2,3-DHBA. In addition, the pH values were found to have great impacts on the hydroxylation rate of oxidized forms of 2,5-DHBA and 2,3-DHBA, which decreases with increasing pH. In contrast with 2,5-DHBA and 2,3-DHBA, our results show that the electrochemical oxidation of 3,4-DHBA is a simple electron transfer (E (r)). In addition, our results show that both diffusion and adsorption processes control the electrochemical oxidation pathway. Using chronocoulometry, the amount of surface excess for each species was obtained, and their orientations on the surface of a glassy electrode were estimated.