Electrochemical reduction of phthalide at carbon cathodes in dimethylformamide: Effects of supporting electrolyte and gas chromatographic injector-port chemistry on the product distribution

• Published in: Electrochimica acta Vol. 113; pp. 557 - 563
• Main Authors: Pasciak, Erick M., Hochstetler, Spencer E., Mubarak, Mohammad S., Evans, Dennis H., Peters, Dennis G.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.12.2013
• Subjects: Carbon; Cathodes; Catholytes; Digital simulation; Electrodes; Electrolysis; Esters; Gas chromatography; GC injector-port chemistry; Phthalide; Reduction (electrolytic); Ring-opening reaction; Supporting-electrolyte effects; Phthalide; Ring-opening reaction; Supporting-electrolyte effects; Digital simulation; GC injector-port chemistry
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2013.09.124

•Reduction of phthalide gives a radical-anion that undergoes ring-opening in 3.5s.•Phthalide reduction gives 2-methylbenzoate esters with electrolyte-derived moieties.•Electrolysis of phthalide affords products that depend on the method of analysis.•Upon reduction, phthalide undergoes deuteration in the presence of deuterium oxide. Cyclic voltammetry and controlled-potential (bulk) electrolysis have been used to investigate the direct reduction of phthalide at carbon electrodes in dimethylformamide (DMF) containing 0.10M tetramethylammonium perchlorate (TMAP) or tetra-n-butylammonium perchlorate (TBAP). Cyclic voltammograms recorded with a glassy carbon electrode exhibit a single cathodic peak and a corresponding anodic peak that arise, respectively, from one-electron reduction of phthalide to generate a radical-anion intermediate and from reoxidation of the intermediate. At a scan rate of 100mVs−1, quasi-reversible behavior is observed (due to ring-opening of the radical-anion), whereas fully reversible behavior is seen at 5Vs−1 or higher. Digital simulation of cyclic voltammograms indicates that the lifetime of the radical-anion is 3.5s. Bulk electrolysis of phthalide at a reticulated vitreous carbon cathode affords products that depend on the procedure used to analyze the catholyte. Direct injection of catholyte into a gas chromatograph shows phthalide and a 2-methylbenzoate ester bearing an alkyl moiety from the supporting-electrolyte cation. However, if the catholyte is partitioned between diethyl ether and aqueous hydrochloric acid before gas chromatographic analysis, phthalide and 2-methylbenzoic acid are observed. Thermally induced reactions that occur in the injector port of the gas chromatograph are responsible for the formation of the 2-methylbenzoate ester as well as for the phthalide found in all electrolyzed solutions.