Infrared spectroelectrochemical study of the oxidation of substituted phenols of relevance to the surface oxidation of polystyrene (original) (raw)
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International Journal of Electrochemical Science
The unknown electrochemical properties of phenoxyethanol (PE)-the most commonly used preservative in cosmetics were studied. The measurements were performed on platinum micro-and macroelectrodes by linear sweep (LSV), cyclic (CV) and differential pulse voltammetry (DPV) in mixed solvent acetic acid-acetonitrile (20%, v/v) containing NaClO4 as a supporting electrolyte. The anodic oxidation process has proved to be quasireversible, diffusion-controlled and proceeding with exchange of one electron giving the unstable cation radical as a primary product (EqCi mechanism). Very good reproducibility of the DPV curves and the wide linearity range up to 1 mmol L-1 indicate that the proposed medium can be successfully applied to develop the first voltammetric method of this preservative determination in pharmaceutical and cosmetic products.
Phenol and para-substituted phenols electrochemical oxidation pathways
Journal of Electroanalytical Chemistry, 2011
The electrochemical behaviour of phenol, catechol, hydroquinone, resorcinol, dopamine, and para-substituted phenolic compounds, 4-ethylphenol, tyrosine, and tyramine, was studied over a wide pH range using a glassy carbon electrode. The oxidation of phenol is pH dependent and irreversible, occurring in one step, and followed by hydrolyse in ortho-and para-positions, leading to two oxidation products, catechol and hydroquinone. The oxidation of phenol oxidation products, ortho-phenol and para-phenol, is reversible and pH dependent. The oxidation potential of parasubstituted phenols varies slightly due to their substituent group in position C4, and occurs in one oxidation step corresponding to the oxidation of phenol. The oxidation products of this group of para-substituted phenols are reversibly oxidised and adsorb on the electrode surface.
The Electrooxidation of 2Propanol: An Example of an Alternative Way to Look at In Situ FTIR Data
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This work investigates the electrochemical behavior of 2-propanol in acidic media on polycrystalline Pt surfaces as an attempt to apply a differential methodology to the analysis and handling of FTIR data in order to achieve a better correlation among electrochemical and spectroscopic signals and help to understand the mechanistic aspects involving the electrooxidation of complex molecules. By assumption that acetone is the main product of 2-propanol oxidation, we have used a simple procedure which consists in the differentiation of integrated absorbancies relative to acetone production. The procedure is justified by the Lambert–Beer law, and the results show a good qualitative correlation between the voltammetric profile and spectroscopic signal corresponding to changes in the moieties of acetone during the voltametric sweep.
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Electrochemistry Communications, 2003
Electrochemical oxidation of phenolic compounds generally produces unstable phenoxy radicals that readily polymerize to passivate the surface of solid electrodes. In this study, the electrocatalytic oxidation of phenol in the presence and absence of methanol was investigated by cyclic voltammetry on a platinum electrode. The cyclic voltammogram of phenol in a mixture of phosphate buffer/methanol solution showed well-defined peaks at $600 mV vs. Ag/AgCl reference electrode, which surprising, gradually increased with repetitive scanning, stabilizing after 50 cycles. This unexpected behavior is in contrast to previous studies involving phenolic compounds, which always show a decrease in intensity during continuous potential scanning. Scanning electrochemical spectroscopy (SEM) was further used to investigate the changes in the surface morphology of the Pt electrode after electrodeposition. A new electrocatalytic mechanism for phenol oxidation on the surface of a Pt electrode is suggested in the presence of methanol. The proposed mechanism is based on the formation of a film of Pt oxide/hydroxides onto which the phenol and the products of its electrochemical oxidation are further deposited. The mechanism was also studied using more complex phenolic compounds including resveratrol, quercetin and bisphenol A. The results emphasized the effect of aryl substituents on the electrochemistry of this particular class of compounds.
Data in Brief, 2019
The data collected in the present work correspond to percentages of phenol degradation by means of photoelectrochemical oxidation (PEC). Also, the information related to the energetic and kinetic performance of this advanced oxidation process (AOPs) is shown. The tests were divided into two stages: 1. Supporting electrolytes tests to determine the electrolyte that presents a better response to photocurrent and 2. Degradation of phenol to obtain the adequate conditions for the elimination of the contaminant. A central rotary composite design with uniform precision at two levels was used to analyze the influence of the initial pH, electrode potential and the initial concentration of substrate. Finally, with all the data obtained, calculation of degradation rates and the electrical energy per order EEO were made.
Spectroelectrochemical study of the oxidation of aminophenols on platinum electrode in acid medium
Journal of Electroanalytical Chemistry, 2004
The electrochemical oxidation of para-, meta-and ortho-aminophenols was carried out using a platinum electrode in aqueous acid medium. The spectroscopic results indicate that p-aminophenol suffers hydrolysis giving the formation of hydroquinone/pbenzoquinone. CO 2 has been detected by in situ FTIR spectroscopy as the main soluble oxidation product. The m-aminophenol oxidation produces a blocking polymeric film on the platinum surface. The main oxidation products detected by in situ infrared spectroscopy were CO 2 and quinone. Cyclic voltammetry and in situ FTIR spectroscopy were combined to study the redox processes of the conducting polymer obtained in the o-aminophenol oxidation. The spectroscopic results indicate that phenoxazine units are produced during the oxidation/reduction of poly(o-aminophenol).
Electrochimica Acta, 2004
The oxidation of p-chlorophenol (pcp) and p-nitrophenol (pnp) was studied at Bi-doped PbO 2 (Bi-PbO 2 ) electrodes. The mass balance between solution composition and flowing charge was obtained from deconvolution of UV-Vis spectra recorded during electrolysis at constant potential. It is shown that the time-dependent production of CO 2 is different for the oxidation of pcp and pnp, indicating different reaction mechanisms for the oxidation of each of these compounds. The reaction kinetics was also followed under thin layer conditions by SNIFTIRS; the similarly increasing signals associated to the generation of CO 2 obtained during oxidation of both compounds indicates that under conditions of restricted mass transfer the mineralization rates of pcp and pnp are similar. The results show that benzoquinone (bq) formed from oxidation of phenols desorbs prior to further oxidation to yield maleic acid (ma), in turn oxidizing further to CO 2 .
Synthetic Metals, 1997
The electrooxidation of p-dimethoxybenzene on platinum electrodes in strictly dried acetonitrile solutions was studied by in situ spectroscopic methods (UV-Vis differential reflectance, FT-IR reflectance and electron spin resonance (ESR) spectroscopies). The UV-Vis and IR spectra allowed us to investigate the early stages of polymerization and to monitor the film growth, as a function of the electrode potential and the number of potential cycles. The use of both p-and s-polarized IR radiations allowed us to observe the initial step of formation of the radical-cation and its dimerization at the electrode surface or its diffusion in solution. These observations were corroborated by ESR spectroscopy, which showed clearly the participation of the monomer and oligomer radicals in the electropolymerization process. On the other hand, the monomer concentration is a very important factor for molecular orientation at the electrode surface and formation of the polymer film.