Acetonitrile + nitromethane: An example of ideal solvent mixtures

Densities, viscosities, static dielectric constants and refractive indices of acetonitrile + nitromethane mixtures in the temperature range between 5 and 45°C are reported. Density and viscosity data, analyzed in terms of molar excess volumes and molar excess fluidities, show a weak interactions field between acetonitrile and nitromethane molecules. Lorentz-Lorenz molar refractivities and Kirkwood correlation factors, obtained from refractive indices and dielectric constants data, respectively, indicate that such weak interactions can be atributed to an antiparallel alignment between neighboring dipoles of unlike solvent molecules. Such specific features do not significantly perturb the local structures of the pure components so that acetonitrile + nitromethane mixtures can be considered, in a first approximation, one of the few ideal solvent mixtures for which the physical properties can be determined by applying the additivity rules to the pure components.