No abstract

No abstract

No abstract

From the enthalpies of solution of various electrolytes and some non-electrolytes in binary solvent systems containing water and different amides, several enthalpic pair-interaction coefficients have been evaluated. They refer to the interactions of different quarternary ammonium bromides, some trialkylphosphates and triethylamine with formamide, N-methylformamide, NN-dimethylformamide and NNdimethylacetamide in aqueous solution and with water in the non-aqueous solvent NN-dimethylformamide. In aqueous solution a much larger variety of values for pair-interaction coefficients is found than in the non-aqueous systems. The different pair-interaction coefficients in water can be related to the structure of the solutes. A functional group additivity concept, introduced by Savage and Wood for non-ionic solutes, is also applicable to the interactions between electrolytes and non-electrolytes. The values of the functional-group parameters for the electrolytes in water are in reasonable agreement with those obtained from non-electrolytic interactions. In non-aqueous solutions the additivity concept gives a better correlation of the experimental values than in aqueous systems.

Enthalpies of solution of tetra-n-pentylammonium bromide in mixtures of water and Ar,ZV-dimethylformamide (DMF) and of tetra-n-butylammonium bromide in mixtures of water and dimethyl sulfoxide (Me2SO) and of water and IV.lV-dimethylacetamide (DMA) have been measured calorimetrically at 298.15 K over the whole mole fraction range. All profiles of the enthalpy of solution vs. solvent composition show endothermic maxima. The results are interpreted in terms of a simple hydration model with two parameters: the enthalpic effect of hydrophobic hydration in pure water, and the number of solvation sites of one alkyl group. After elimination of the influence of the Br~i on, both parameters are in good agreement with those found for some nonelectrolytes. Finally, the role of the cosolvent is considered more systematically.