Electrochemical Oxidation of Resorcinol: An Integrated Experimental and Theoretical Study
Authors: Bonechi Marco , Giurlani Walter , Mariani Elena , Biffoli Fabio , Pappaianni Giulio , Stefani Andrea , Marchetti Andrea , Fontanesi Claudio , Innocenti Massimo 
Published: February 2024

Resorcinol polymerization is a quite important chemical reaction, also in connection with applicative aspects related to the production of industrial resins [1].

In this work, we studied the electrochemical oxidation of resorcinol on platinum, palladium and glassy carbon (GC) electrodes. We propose an oxidation-polymerisation mechanism for the resorcinol molecule, which is based on the Kane-Maguire polymerization scheme. The results of an exhaustive electrochemical characterization are integrated with the outcome of complementary chromatographic analytical techniques: LC-DAD (high performance Liquid Chromatography, equipped with Diode Array Detector) and LC-MS (mass-spectroscopy by means of Ion Trap mass analyzer). We demonstrate that upon electrochemical oxidation, resorcinol polymerizes following an efficient and facile process and an organic film is obtained on the electrode surface.

We used cyclic voltammetry (CV), and a three-electrode cell to perform electrochemical oxidation. Then we used LC-DAD and LC-MS to study the intermediates involved in the electro-polymerization of resorcinol. Electrochemical experiments were performed under different condition of pH and solvent. CVs in a 0.5M H2SO4 solution shows an irreversible oxidation peak at 1.0 V that is pH dependent, consistent with a one-proton, one electron oxidation reaction. Applying potentials higher than the oxidation potential we obtained an organic film adhering to the electrode surface [2]. The polymer film was characterized by atomic force microscopy (AFM) and Scanning Electron Microscopy combined with Energy-Dispersive X-ray spectroscopy (SEM-EDS).

We also perform a theoretical study on the first steps of resorcinol electro oxidation using ab-initio quantum mechanical based methods and molecular dynamics analysis (DRC algorithm) at the B3LYP/6-31G(d) and B3LYP/cc-pVTZ level of theory [3]. The resorcinol polymerization is considered to proceed via the dissociation of one (or two) hydrogen atom to form C-C and C-O dimers.

The proposed mechanism for the resorcinol electrochemical oxidation is fully consistent with experimental results. Moreover, the film obtained on the electrode surface could be a potential substrate for electrodepositions or electroless deposition of metals and could be a promising candidate for the development of new materials of technological and industrial interest.

[1] Formaldehyde and Phenol-Resorcinol-Formaldehyde Condensation Reactions: A Theoretical Study. Polymers
2017, 9, 426, doi:10.3390/polym9090426.

[2] Bonechi, M.; Giurlani, W.; Stefani, A.; Marchetti, A.; Innocenti, M.; Fontanesi, C. Resorcinol Electropolymerization Process Obtained via Electrochemical Oxidation. Electrochimica Acta
2022, 428, 140928, doi:10.1016/j.electacta.2022.140928.

[3] Bonechi, M.; Innocenti, M.; Vanossi, D.; Fontanesi, C. The Fundamental and Underrated Role of the Base Electrolyte in the Polymerization Mechanism. The Resorcinol Case Study. J. Phys. Chem. A
2021, 125, 34–42, doi:10.1021/acs.jpca.0c07702.