Thermodynamic and electrochemical study of some dihydroxybenzenes in the presence of different nucleophiles

Abstract

In the current study, effects of thermodynamic on the reaction mechanisms of the electrochemical oxidation of hydroquinone and catechol in the presence of various nucleophiles have been investigated both experimentally and theoretically, using cyclic voltammetry, controlled-potential coulometry, and density functional theory. The theoretical results were calculated at DFT (B3LYP) level of theory and 6-311?G(p,d) basis set. Calculated DG tot of the oxidation of the intermediates and products indicated that thermodynamic is one of the important parameters on the reaction mechanisms. The results of this work show that depending on the DG tot of electrochemical oxidation, the intermediates which are produced on the surface of electrode will participate in the electrochemical or chemical following reactions. Graphical abstract

Thermodynamic and Mechanistic Study of the Electrochemical Oxidation of Rosmarinic Acid

“…Previous reported works on the study of the electrochemical oxidation of catechols, hematoxylin and electrochemical oxidation of RA (1) in one hand 16,[26][27][28][29][30] and our obtained results in this research on the other hand, allow us to propose an E r E r mechanism for the electrochemical oxidation of RA (1) in the time scale of cyclic voltammetry (Scheme 1). In positive going scan and in the first step oxidation, RA (1) oxidized to OX 1-1 and in the second step oxidation the produced OX 1-1 oxidized to OX 2 .…”

“…In order to answer this question the computational study was used. Because the relationship between oxidation potential and G tot were described in our previous articles, 28,30,41 the details of the calculation of G tot using Born-Haber cycle were not explained in this work.…”

“…[17][18][19][20][21][22][23][24][25] RA (1) has two electroactive catechol moieties (ring A and ring B), which are independent of each other and can participate in the electrochemical oxidation-reduction process. Our experience about electrochemical oxidation of species contains one or two catechol rings, [26][27][28][29][30][31] the importance of RA (1) and lack of electrochemical oxidation results of it prompted us to the electrochemical study of RA (1). In this paper, a mechanism was proposed for the electrochemical oxidation of RA (1), and also its adsorption behavior was investigated in the aqueous solutions at various pHs.…”

“…In the first step oxidation RA (1) is converted to OX 1-1 , and in the second step oxidation produced OX 1-1 oxidized to OX 2 . Because it was reported that the oxidation potentials of species correspond to their total change in Gibbs free ( G tot ), [28][29][30] a computational study was used to confirm the electrochemical reaction pathway. Therefore oxidation potential of RA (1) was compared with some substitute of catechol (2)(3)(4)(5) at pH = 0.0.…”

“…G tot of the electrochemical oxidation of catechol species (2)(3)(4)(5) were obtained by considering a general thermodynamic cycle (Born-Haber cycle). [28][29][30] The oxidation potential of studied species in pH = 0.0 (E p0 ) and G tot of the electrochemical oxidation of them (1-5 and OX 1-1 ) have been calculated from E-pH diagram and computational method, respectively. It was found that the more the value of positive oxidation potential, the larger the G tot oxidation of the species.…”