Impurities in Nitrile Solvents Commonly Used for Electrochemistry, and their Effects on Voltammetric Data

Voltammetry experiments were performed on 1,4-benzoquinone and 1,4-phenylenediamine in acetonitrile, propionitrile (from five commercial suppliers: Acros Organics, Aldrich, Alfa Aesar, Fluka, and Merck), and butyronitrile, to which different electrochemical responses were collected across the three nitrile solvents and within the five commercial brands of propionitrile, owing to the reduced (1,4-benzoquinone) or oxidized (1,4-phenylenediamine) compounds reacting with impurities in the solvents. Of the three solvents, propionitrile suffered from the most impurities, which adversely affected the electrochemical results. Distillation of the propionitrile over phosphorus pentoxide or passing it through a flash column containing silica gel was partially effective in removing some of the impurities and resulted in the recovery of the familiar oxidation behavior of 1,4-phenylenediamine. The reduction behavior of 1,4-benzoquinone could be improved if propionitrile was purified by passing it through a column of basic activated alumina, thus a combination of distillation and flash chromatography is necessary to adequately purify propionitrile for reductive and oxidative voltammetry experiments. Purge and trap-gas chromatography–mass spectrometry analyses positively identified 2-methyl-2-pentenal among the impurities, but it was discovered to only have a mild effect on the voltammetric behavior of the quinone and not exert any influence on the electrochemical response of the phenylenediamine. The results of this study lead to the possibility of using the voltammetry of quinones and phenylenediamines as a sensitive method for determining the purity of organic solvents.