Abstract

AVILA-GUTIERREZ, Mario; GUTIERREZ-PORTOCARRERO, Salvador; CORONA-ELIZARRARAS, Luis  and  ALPUCHE-AVILES, Mario A.. A Practical and Instructive Approach to Purify Acetonitrile for a Wide Electrochemical Window. J. Mex. Chem. Soc [online]. 2023, vol.67, n.4, pp.393-402.  Epub Apr 26, 2024. ISSN 1870-249X.  https://doi.org/10.29356/jmcs.v67i4.2013.

Because of its large electrochemical window, acetonitrile (MeCN) is one of the most widely used solvents in electrochemistry. It is a suitable solvent for nonaqueous electrolytes that allows studies of cathodic and anodic processes, but electrolyte purification remains challenging. As received, the high-performance liquid chromatography (HPLC) grade is unsuitable for most electroanalytical applications. We present an approach to optimize the purification of HPLC-grade acetonitrile to yield a tetrabutylammonium perchlorate (TBAP)/MeCN electrolyte for experiments in nonaqueous media. We used cyclic voltammetry (CV) to show the background due to impurities and to guide the experimental design to a background current acceptable for CVs of a 1 mM typical concentration of a redox-active molecule. We use 3A molecular sieves, followed by distillation over CaH2 with a final treatment with Al2O3. The optimized procedure yields CH3CN with small background currents, increasing the signal-to-noise ratio and minimizing chemical complications over a wide potential window. Our approach includes discriminating between impurities in the solvent and electrolyte salts; for TBAP, we recrystallize from ethyl acetate and 95 % ethanol. The process and theoretical guidelines apply to other nonaqueous electrolytes dealing with electroactive impurities, including organic molecules, oxygen, and water.

Keywords : Acetonitrile purification; electrolyte purification; electrochemical window; nonaqueous electrolytes; CH₃CN.