Effect of Temperature on the Process of Hydrophobic Hydration. Part II. Hydrophobic Hydration of 15-Crown-5 and 18-Crown-6 Ethers

Abstract

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, ΔsolHmo, 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, Cp,2o, 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.