Ionic solvation in water–cosolvent mixtures. Part 13.—Free energies of transfer of single ions from water into water–tetrahydrofuran mixtures

Abstract

The free energy of transfer of the proton between water and water-rich mixtures of water and tetrahydrofuran (THF), AG:(H+), has been found by examining spectrophotometrically the redistribution of solvent molecules around the aqua-proton after the latter charged sphere has been transferred into the mixture. Values for AG,"(HX) calculated from electrochemical data are combined with the new AG,"(H+) to produce AG,"(X-) for the transfer of halide ions and of OHfrom water into water-THF mixtures. These AG,"(X-) are then used with values for AG,"(MX) derived from electrochemical and vapour-pressure measurements to give values for AG,"(M+) for alkali-metal ions and for ButN+ ions. pK values for two carboxylic acids and for a range of anilinium cations in water-THF mixtures are combined with AG:(H+) to produce AG: & the free energy of transfer from water into water-THF of the charge on the carboxylate anion or the anilinium cation with the effect of transferring the molecular bulk of the ion removed.The spectrophotometric solvent sorting m e t h ~d l -~ for the determination of the free energy of transfer of the proton from water into water<osolvent mixtures has been used with a range of acyclic organic cosolvent m o l e c ~l e s ~* ~ and with one cyclic cosolvent molecule, d i ~x a n . ~We now report the application of this method to mixtures of water with the cyclic cosolvent molecule, tetrahydrofuran. The positive values obtained6 for the structural contribution ATSt to the increase in the temperature of the maximum density of water when tetrahydrofuran is added to water indicate that the former has a structure-forming effect on the latter. This conclusion is supported by the minimum found in the relative partial molar volume of tetrahydrofuran, B-c, at a mol fraction x , x 0.03-0.04,7 the minima in the excess thermodynamic properties of mixing of water and tetrahydrofuran, the volume at x , z 0.35, the enthalpy at x, z 0.1-0.15 and the entropy at x, x 0.35,* the maximum in the ultrasonic absorption at x, z 0.299 and the maximum found in the viscosity at x , x 0.14.lo

Gibbs energies of transfer of the proton from water into mixtures of water with chain multiple ethers: Equilibria involving changes of solvation of the proton

“…( 5). [3][4][5][6][7][20][21][22] As c o is reduced, the intercept approaches 23 zero, as expected from eqn. ( 5) and, with pK a $ 1 for 4-nitroaniline, the changes in c x and c w become smaller 23 when [HCl] is reduced below the above range, producing larger errors in the derived functions.…”

“…For a total added concentration of B ¼ c o , the actual concentration of B found in the mixture, c x , for a range of [HCl] at a fixed total concentration of S ¼ [S] T should vary as in eqn. ( 5), [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][20][21][22] g i ! 1.0 at S[i] !…”

“…( 5) at constant ionic strength ¼ 1.00 mol dm À3 using added NaCl. [3][4][5][6][7][20][21][22] As expected for a balanced equilibrium between two similarly sized, singly charged species, K c for simple alcohols was found to be independent of ionic strength 20 varying 0.25-2.00 mol dm À3 and is not dependent on the specific presence of Cl À ions. The possible existence 23 of a non-basic form of 4-nitroaniline B 0 in equilibrium with the basic form B with…”

“…(6), leaving K c unaffected. Alternatively, [3][4][5][6][7][20][21][22] the concentration quotient K 2 F 2 determined from the ratio slope/intercept of the plots of eqn. ( 5) is used to calculate K c via eqns.…”

“…However, no sharp movement of equilibrium (2) occurs between S ¼ tetrahydrofuran and S ¼ dioxane. 3,6,7 To investigate the effect of multiple -O-groups on the free energy of transfer of H + , we now report the investigation of equilibrium (2) using the dimethyl ethers of diethylene glycol and triethylene glycol. These will be referred to throughout as diglyme and triglyme respectfully.…”