Solute−Solvent Interactions in Amide−Water Mixed Solvents

Excess volumes, mixing viscosities, and excess Gibbs energies of activation of viscous flow of the aqueous binary mixtures of the amides formamide, N-methylformamide, N,N-dimethylformamide, pyrrolidin-2-one, and N-methyl-2-pyrrolidinone were calculated from density and viscosity measurements. The values of these functions point to strong amide−water interactions with formation of a variety of aggregates, the nature of which depends on the extent of substitution of the amides; comparison of the functions of the same amides with alkan-1-ols reveal an important hydration effect. Various one-parameter and two-parameter empirical models for prediction of mixing viscosities were in good agreement with the experimental results only for the formamide−water system; none of the models predicted satisfactorily the behavior for the aqueous mixtures of both mono- and disubstituted amides.