The standard molar enthalpies of solution of linear polyethers (LPs) such as 1,2-dimethoxyethane (monoglyme), diethyleneglycol dimethyl ether (diglyme), triethyleneglycol dimethyl ether (triglyme), tetraethyleneglycol dimethyl ether (tetraglyme), and pentaethyleneglycol dimethyl ether (pentaglyme) in a mixture of water and N,N-dimethylformamide were measured at a temperature of 298.15 K. The values of standard molar enthalpy of solution, Δsol H m o, the enthalpic effect of hydrophobic hydration, Hb(H2O), and the enthalpic effect of cyclization of these glymes have been determined. The values of standard molar enthalpy of solution of LPs are more negative than those of their cyclic equivalents. The exothermic enthalpic effect of hydrophobic hydration of LPs increases linearly with the increase in the number of −CH2− groups. The values of the standard molar enthalpy of solution and the enthalpic effect of hydrophobic hydration of LPs calculated in this paper have been compared to those data for cyclic polyethers (CPs) obtained earlier. The contributions of particular groups (−CH2−, −O−, and −CH3) to the enthalpic effect of hydrophobic hydration have been calculated.

The dissolution enthalpy of 1,4-dioxane and 12-crown-4 ethers in the mixture of water and N,Ndimethylformamide was measured at four temperatures within the range from (293.15 to 308.15) K. The values of partial molar heat capacity (C p,2 o ) and hydrophobic hydration effect, Hb(W), were determined. The effect of temperature on the process of hydrophobic hydration of cyclic ethers has been interpreted. An increase in temperature results in the increased values of the standard enthalpies of solution, ∆ sol H m o (a lower exothermic effect), while the exothermic enthalpic effect of hydrophobic hydration, Hb(W), decreases with increasing temperature.

The dissolution enthalpy of 1,4,7,10,13-pentaoxacyclopentadecane (15-crown-5) and 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6) ethers in the mixture of water and N,N-dimethylformamide (DMF) was measured within the range from (293.15 to 308.15) K. The values of standard molar enthalpies of solution, Δsol H m o, of crown ethers: 15-crown-5 and 18-crown-6 in the mixture of water and N,N-dimethylformamide within the range of the mixture composition under investigation, increase linearly with increasing temperature. The values of partial molar heat capacity, C p,2 o, and hydrophobic hydration effect, Hb(H2O), were determined. The effect of temperature on the process of hydrophobic hydration of crown ethers has been interpreted. The values of the enthalpic effect of hydrophobic hydration are more negative for 18-crown-6 than those for 15-crown-5. The exothermic enthalpic effect of hydrophobic hydration, Hb(H2O), of the crown ethers under investigation decreases linearly with increasing temperature.

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