Thermodynamics of metal ion cryptates and cryptand 222 in dipolar aprotic solvents.

Thermodynamic parameters of transfer of single-ions from water to nitromethane are obtained using the Ph4AsPh4B convention suggested by Parker. Enthalpies of complexing of alkali-metal and silver cations with cryptand 222 in N,N-dimethylformamide, dimethylsulphoxide, propylene carbonate, acetonitrile and nitromethane were determined calorimetrically. The stability constants of alkali-metal and silver cryptates in nitromethane were determined by potentiometric titration. This is the first set of data ever reported for the thermodynamic parameters of complexing of metal-ions with cryptand 222 in nitromethane. Free energies and enthalpies are combined to give entropies of complexing of metal-ion cryptates in the dipolar aprotic solvents. Some enthalpy of complexing data in methanol are reviewed. A correlation is found between the enthalpy of transfer of a given cation and the difference in enthalpy of complexing of metal cation with cryptand 222 among two dipolar aprotic solvents. This correlation could provide a means of evaluating single-ion enthalpies of transfer among dipolar aprotic solvents from enthalpy of complexing data. Enthalpies and free energies of complexation of metal-ion cryptates in N,N-dimethylformamide, dimethylsulphoxide, propylene carbonate, acetonitrile and nitromethane are used with relevant data to obtain the thermodynamic parameters for transfer of metal-ion cryptates from water to these solvents, and from propylene carbonate to the other dipolar aprotic GO solvents. The results obtained show variation in DeltaG°t, DeltaH°t and Deltas°t values for the metal-ion cryptates are predominantly found in transfers from water, with unappreciable variations in these parameters for transfer among dipolar aprotic solvents. The latter conclusion is based on a large number of experimental calorimetric data and suggests that cryptate conventions seem to be valid among dipolar aprotic solvents. The use of cryptand 222 for the extraction of alkali-metal salts from water into nitromethane is discussed. The thermodynamic parameters for extraction process in water-pure nitromethane system are obtained