The enthalpies of transfer ΔHtr�, between water and the aprotic
solvents pyridine and acetonitrile have been
determined for a number of 1-1 electrolytes. To calculate ΔHtr�
for the single ions, the tatb assumption that ΔHtr�,(Ph4As+) = ΔHtr�BPh4-)
for all solvents has been applied. The results are compared with those found
earlier for the transfer between water and dimethyl sulfoxide. The values of ΔHtr�, differ widely between different
ions, from exothermic by c. 30 kJ/mol to endothermic by about the same amount.
Endothermic values are found for Cl- and, though much smaller, for Br-, and
also for the large tetraalkylammonium ion Bu4N+.
Compared to the differences in ΔHtr�,
found between the various ions, the differences found for a certain ion between
different solvents are small. The decrease of AH,", in the sequence Cl-
> Br- > I- runs almost parallel in the three aprotic solvents, and is
much less steep than in water. This reflects the influence of ligand hydrogen
bonding in the protic solvent.