Acetonitrile (MeCN) is a common solvent in synthetic chemistry and electrochemistry where it is often used when a polar, aprotic solvent is needed.^1,2 In the past few years, the importance of controlling water content of aprotic solvents has been pointed out several times^2,3 and the suggestion of allowing the solution to sit for a time over 3A molecular sieves has been proposed.⁴ There should be no surprise that there is a definite limit to the utility of this method, as complexes with closely spaced Lewis acids and bases have been shown to have catalytic effects in the past⁵ and molecular sieves often consist of main group metal oxides and halides.

We report here a definite limit to solvent dryness where MeCN left over 3A molecular sieves for more than a few days will decay into one or more products that include acidic goups, aromatic groups, and one or more functional groups that will adhere to an electrode surface after a reduction/oxidation cycle. We present CV experiments involving duroquinone (DQ) as a probe molecule to show how surface coverage of the electrode differs between three common electrode materials—Pt, Au, and glassy carbon—changes over time, and also how CV characteristics typical of protonation show up after just allowing the MeCN to sit over the molecular sieves for a little while. Finally, we use NMR spectroscopy, Raman spectroscopy, and mass spectrometry to gain some understanding of the identity of the one or more decay products.

1. D. Bradley, G. Williams, and Michelle Lawton. “Drying fo Organic Solvents: Quantitative Evaluation of the Efficiency of Several Desiccants”. J. Org. Chem. (2010) Vol. 75, iss. 24, pp. 8351-8354.

2.Yanlan Hui, Elaine Lay Khim Chng, Cheryl Yi Lin Chng, Hwee Ling Poh, and Richard D. Webster. “Hydrogen-Bonding Interactions between Water and the One- and Two- Electron-Reduced Forms of Vitamin K1: Applying Quinone Electrochemistry To Determine the Moisture Content of Non-Aqueous Solvents”. J. Am. Chem. Soc. (2009) Vol. 131, iss. 4, pp. 1523-1534.

3. Patrick A. Staley, Eric M. Lopez, Laurie A. Clare, and Diane K. Smith. “Kinetic Stabilization of Quinone Dianions via Hydrogen Bonding by Water in Aprotic Solvents”. J. Phys. Chem. C. (2015) Vol. 119, iss. 35, pp. 20319-20327.

4. Malcolm E. Tessensohn, Hajime Hirao, and Richard D. Webster. “Electrochemical Properties of Phenols and Quinones in Organic Solvents are Strongly Influenced by Hydrogen-Bonding with Water”. J. Phys. Chem. C. (2013) Vol. 117, iss. 2, pp. 1081-1090.

5. Deng Zhaoxiang, Qui Wenfeng, Li Weijia, and Li Yadong. “Cyclotrimerization of nitriles catalyzed by Li3N”. Chinese Science Bulletin. (2004) Vol. 49, No. 2, pp. 127-130.