Effect of Hydrogen Bonding on Acid‐Base Equilibria and Titrations in Organic Aprotic Solvents

For convenience a distinction is made in the literature between amphiprotic and aprotic solvents. It would be fair to consider a solvent amphiprotic when it yields a stable lyate ion. Our work has been confined mainly to two solvents, acetonitrile, AN (ϵ = 36), and dimethylsulfoxide, DMSO (ϵ = 46). In the literature DMSO is usually considered as an aprotic solvent; however, it yields a stable lyate ion, called dimsyl 1 . The analytical uses of sodium and K dimsyl are discussed later on. We have selected AN and DMSO as solvents, as their dielectric constant E is of the order of 40 and tetraalkyl salts in dilute solutions can be considered to be completely dissociated. AN is a very much weaker base than water, and has been classified as a protophobic aprotic solvent, while DMSO is a stronger base than water and is classified as protophilic. As will be seen, AN is a very poor H bond acceptor, being much weaker than water, while DMSO is a stronger H bond acceptor than water. The effects of H bonding on monoprotic acid‐base equilibria in these two solvents has been reviewed in a recent paper 2 . To avoid repetition, only the main effects will be summarized.