THERMODYNAMIC PROPERTIES OF NONAQUEOUS SOLUTIONS .6. ENTHALPIES OF SOLUTION OF SOME TETRAALKYLAMMONIUM IODIDES IN WATER AND N,N-DIMETHYLFORMAMIDE AT 25 DEGREES

Heats of solution of (CH3)4NI, (C2H5)4NI, and (C3H7)4NI have been measured in N,N-dimethylformamide (DMF) and in water in the concentration range 3.5 × 10-4 to 5 × 10-3 m and have been extrapolated to infinite dilution by the simple Debye-Hückel equation in order to obtain standard heats of solution in the two solvents. Enthalpies of transfer, ΔHtr°, of the salts from water to DMF have been calculated and compared with other ΔHtr° data taken from the literature. Although in every case examined there is an unexpectedly large change in ΔHtr° between CsI and (CH3)4NI, it is shown that this change cannot be fully explained in terms of the ice-like structure of water molecules around the tetraalkylammonium ions. The modified Born equation is shown to be inadequate to explain, even qualitatively, the behavior of the enthalpies of transfer for these salts and the alkali metal iodides from water to DMF and other solvents, or between two nonaqueous solvents.