Determination of the transfer thermodynamic functions for some monovalent ions from water to N,N′-dimethylpropyleneurea

Abstract

The transfer thermodynamic functions for 19 monovalent ions from water to N,N′-dimethylpropyleneurea (1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidione) are reported. The Gibbs energies of transfer, Δ_tG^o, have been determined from solubility product or potentiometric measurements, and the heats of transfer, Δ_tH^o, have been determined calorimetrically. The entropies of transfer, Δ_tS^o, have been calculated from these Δ_tG^o and Δ_tH^o values. The extrathermodynamic tetraphenylarsonium tetraphenylborate (TATB) assumption has been applied in order to calculate the contribution from the individual ions. The hard alkali metal ions are strongly solvated by N,N′-dimethylpropyleneurea as is the soft silver(I) ion. The inorganic anions are all more strongly solvated in water than in N,N′-dimethylpropyleneurea, and the Δ_tS^o values are markedly negative. In spite of the stronger solvation of the anions in water, the heats of transfer for some of these are exothermic. The exothermic heats of transfer arise from the difference in bulk order between water, which is well-ordered through hydrogen bonding, and N,N′-dimethylpropyleneurea, which has a significantly lower bulk order than water. The solvation of monovalent ions shows a similar pattern in N,N′-dimethylpropyleneurea to that previously found in dimethylsulfoxide.