Thermodynamic properties of the acetonitrile-water system

Abstract

Acetonitrile is attracting increasing use as a solvent in electrochemical studies, and as a reaction medium for both organic and inorganic processes. It is a comparatively inert solvent with a distinct lack of hydrogen bond donor power, although having strong H-bond acceptor characteristics. It does not generally show as great a solvation ability as water, although steric effects may alter this (viz: the case of the acidity of the tertiary ammonium ion being more acidic than either of the corresponding secondary or primary ions, while on the basis of the inductive effect alone, the tertiary ion should be the weakest acid). Specific practical requirements, such as inadequate water solubility, or undesirable side reactions (eg: hydrolysis) may also force the use of a non-hydrogen bonding solvent such as acetonitrile. Finally, the large bulk of empirical information on the properties of electrolytes in acetonitrile-water systems encourages further investigation in this area. Due to the lower occurrence of specific solvent-solute interactions, acetonitrile provides a clearer picture of the intrinsic solute properties than presented by aqueous systems.