Autoprotolysis in aqueous organic solvent mixtures. Water-amide and water-amine binary systems

The contribution of the autoionization of water and organic solvent, and the proton transfer between them to the overall autoprotolysis of mixtures of water with amides (N,N-dimethylacetamide, N-methylacetamide, acetamide, N,N-dimethylformamide, N-methylformamide and formamide) and with amines (butylamine, N,N-diethylaminoethanol and ethanolamine) is studied and compared. Proton transfer from water to the more basic amide, and specially amine, produces the autoprotolysis in the intermediate solvent compositions and predominates over a wide range of solvent compositions. Autoionization of water predominates only for very low amide or amine contents. Autoionization of the amide or the amine can be important at intermediate and high organic solvent compositions if the pure amide or amine has a high autoprotolysis constant (pKap value lower than that of pure water). Because of the higher basicity of amines over amides, proton transfer from water to the amine produces very high autoprotolysis constants for water-amine mixtures.