Production of Organic Acids from Cashew Nut Shell Liquid (CNSL) via Electrochemical Synthesis

Environmental problems arising from conventional production models have posed a significant challenge in the search for renewable sources as raw materials for the production of everyday chemical compounds through more sustainable alternatives. The objective of the present work was the electrochemical synthesis of organic acids from the liquid of the natural and technical cashew nut shell (CNSLn and CNSLt), employing chronopotentiometry using a potentiostat and a graphite working electrode. Two concentrations (0.01-0.1% <i>v</i>/<i>v</i>) of CNSLn and CNSLt, two concentrations of NaOH as supporting electrolyte (0.125-2 M), and two current densities (40-60 mA/cm²) were tested in the experiments. Organic acids were detected and quantified by HPLC. To characterize the redox processes occurring in the constituents of CNSL, spectroelectrochemical analysis (FTIR-cyclic voltammetry), FTIR, and chronoamperometry were performed. The maximum concentrations obtained in the treatments were: acetic acid (828.86 mg/L), lactic acid (531.78 mg/L), and formic acid (305.4 mg/L), while other acids present in lower concentrations included oxalic, propionic, citric, and malonic acids. Voltammetry characterizations showed three irreversible oxidation processes in the anodic wave during the first cycle, indicating that the first process involved the formation of the phenoxy radical, the second process the formation of hydroquinones and benzoquinones, and the third process the cleavage of the aromatic ring and the aliphatic chain to form the organic acids. Furthermore, another oxidation pathway was observed, consisting of a fourth process in the second voltammetry cycle, corresponding to the nucleation of the phenoxy radical, evidenced as the formation of the C-O-C bond visible at 1050 cm^-1 in the infrared spectrum. From this route, a polymer was formed on the electrode surface, which limited the yield of organic acid synthesis. Finally, this research provides new insights in the field of electrochemistry, specifically in the synthesis of organic acids from CNSL as a renewable feedstock, with the novelty being the production of oxalic, propionic, citric, and malonic acids.