Heats of solution of some trifluoroacetates, tetraphenylborates, iodides, and perchlorates in water and in propylene carbonate and the relative enthalpies of solvation of the alkali metal ions in propylene carbonate

Abstract

The enthalpies of transfer of the alkali metal ions from water to propylene carbonate (dielectric constant 65.1) at 25° have been determined calorimetrically with the following results for the ΔH relative to that for Na+: Li+, 3.17; Na+, 0; K+, -2.80; Rb+, -3.43; Cs+, -3.96 kcal./mole. Each of these values has been derived from two independent sets of data with the disparity between independently determined values being, at most, 0.26 kcal./mole. The solvation enthalpies and their correlation, by means of the theory of Latimer, Pitzer, and Slansky, are derived and discussed. Lithium trifluoroacetate is a very weak electrolyte in propylene carbonate, Λ/Λ0 being only 0.6 in 0.001 M solution. The association produces not only ion pairs but also a large proportion of a larger aggregate.