Effect of Base-Acid Properties of Mixtures of Ethanol with Water on the Enthalpy of Solution of Cyclic Ethers in these Mixtures at T = 298.15 K.

The enthalpies of solution of the cyclic ethers 1,4-dioxane, 12-crown-4 and 18-crown-6 in mixtures of ethanol and water have been measured within the whole mole fraction range at T = 298.15 K. The enthalpy of solvation has been calculated. In pure ethanol and pure water, the solvation enthalpy of the investigated cyclic ethers depends linearity on the number of -CH(2)CH(2)- groups in the cyclic ether molecules. Based on the analysis of the preferential solvation model proposed by Waghorne, it can be concluded that the 1,4-dioxane, 15C5 and 18C6 molecules are preferentially solvated by water molecules in the range of low water content in these mixtures. The effect of base-acid properties of ethanol-water mixtures on the enthalpy of solution of cyclic ethers in these mixtures has been analyzed. The enthalpy of solution of cyclic ethers correlates with the acidic properties of ethanol-water mixtures in the range of high and medium water content. The results presented are compared with analogous data obtained for the methanol-water and propan-1-ol-water mixtures.