SOLVATION IN DIPOLAR APROTIC SOLVENTS . IONIC ENTHALPIES OF TRANSFER

Enthalpies of solution have been determined for a series of alkali perchlorates and tetraethylammonium salts in sulfolane. Further measurements were carried out in propylene carbonate (PC), dimethylformamide, dimethyl sulfoxide, and methanol, to complement literature data. Cationic and anionic enthalpies of transfer (from water to solvent) were separated with the single extrathermodynamic assumption [formula-omitted]. The behavior of ionic enthalpies of transfer from PC to the other dipolar aprotic solvents cannot be explained only in terms of coulombic interactions. Cationic solvation is related to solvent basicity whereas anionic solvation does not depend in a simple way on ionic radius. The order of solvation enthalpies is Cl- > Br- > I- > [formula-omitted], and is the same for the aprotic solvents, water, and methanol. Some comments are made on the protic-dipolar aprotic solvent effects on the enthalpy changes of some charged nucleophiles and transition states. © 1969, American Chemical Society. All rights reserved.