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The enthalpies of solution of LiI, NaI, KF, KCl, KBr, KI, RbI and CsI in anhydrous N‐methylformamide (NMF) at concentrations of about 5 × 10−3 molal have been measured with an adiabatic calorimeter. The enthalpies of dilution in NMF were calculated with the aid of the extended Debye‐Hückel theory. The differences in enthalpy of solution of the alkali iodides between (1) water and formamide and (2) water and NMF are compared with the results of van Eck's theory of ionic solvation.

Measurements of the enthalpies of solution of LiI, NaI, KF, KC1, KBr, KI, RbI and CsI in N-methylacetamide at 35" with an adiabatic calorimeter are reported.A calculation of the ionic enthalpies of solvation of the alkali metal and halide ions in N-methylformamide and N-methylacetamide is given. From the ditference in ionic enthalpy of solvation of the fluoride and the potassium ions in water, formamide, N-mc:thylformamide and N-methylacetaniide, respectively, the quadrupole moments of these solvent molecules have been calculated. IntroductionIn previous papers measurements of the enthalpies of solution of alkali halides in formarnide and N-methylformamide 2 (NMF) have been reported. In order to get a broader experimental basis for the solvation of simple ions in non-aqueous solvents the enthalpies of solution in N-methylacetamide (NMA) should be interesting. The solubility of most salts in NMA is good, only the rate of dissolution is lower than in formamide and NMF.

Enthalpies of solution of alkali halides in formamide, N-methylforrnamide, N,N-dimethylformamide, N-methylacetamide, dimethyl sulfoxide, water, methanol and ammonia are discussed. The ensuing enthalpies of transfer between any two solvents are nearly constant for salts with a common anion. The enthalpies of solution of a single salt in the different liquids can be correlated with the structure of the solvent.

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).