Enthalpies of solution of some alkali halides in N,N‐dimethylformamide at 25°C: (Short communication)

Abstract

In connection with our investigations about the enthalpies of solvation of univalent ions in non-aqueous solvents we previously reported enthalpies of solution of alkali halides in formamide 1, N-methylformamide (NMF) and N-methylacetamide (NMA) 3. In this short communication we give a brief account of the measurements of the enthalpies of solution of LiCI, LiBr, LiI, NaI, KI, RbI and CsI in N,N-dimethylformamide (DMF).The adiabatic calorimeter and the experimental technique were described previously. DMF was taken from stock (Merck, Darmstadt; Uvasole fur die Spektroskopie). The small amount of water still present was removed by drying over KOH and distilling twice under reduced pressure. An upper limit for the water content of 0.02% was observed (Karl Fischer titration).In order to obtain the standard molar enthalpy of solution, AHosol, (at infinite dilution) the enthalpy of dilution, AHmdil, from molality m (the concentration of the solution reached on dissolving the salt) to m = 0 must be known. Measurements 4 9 5 of the conductivity of alkali halides in D M F indicate that there is no association of the ions at the low concentrations used (< 10-2 molal). Consequently it is allowable to use the Debye-Huckel theory for calculating AHmdil-values. The result of this calculation was :A H m d i l = -6350 m'" (1 -2.04 m'k) J . mole-', using the physical constants reported in the literature 6-9, G. Somsen and J. Coops, Rec. Trav. Chim. 84, 985 (1965). L. Weeda and G. Somsen, ibid. 85, 159 (1966).

Solubility of Sodium Halides in Aqueous Mixtures with ε-Increasing Cosolvents: Formamide, N-Methylformamide, and N-Methylacetamide at 298.15 K

“…The immense majority of experimental studies on the solubility of salts have been carried out in water, , pure organic solvents, or aqueous–organic mixtures with cosolvents that have a dielectric constant lower than that of water (ε-decreasing system). Among the systems of this kind, the most studied are those containing alcohols − ,− ,− and ketones, esters and ethers, among other chemical compounds. ,,,,− Data on systems with cosolvents with dielectric constants greater than the dielectric constant of pure water (ε-increasing system) are somewhat more scarce and usually include some amides as the cosolvent. − Aqueous mixtures containing amides (in particular, cyclic amides) constitute an essential tool in the understanding of the behavior of complex molecules of biological interest. , Extensive work has been published on water–amide systems to discover the mode in which water exercises kinetic and thermodynamic control of the chemical activities of polypeptides. The unusually high density of hydrogen bonds in water (strongly self-associated) and the character of the acceptor–donor (−CO–NH–peptide bond) make these water–amide systems very interesting from a structural point of view.…”