Gibbs transfer energies of macrocyclic ligands in methanol+N-methyl-2-pyrrolidinone mixtures by solubility and partition measurements

The standard Gibbs transfer energies of 18-crown-6, dibenzo-18-crown-6, cryptands 21, 22 and 222 from methanol to methanol + N-methyl-2-pyrrolidinone (NMP) mixtures were determined from solubility and partition measurements at 30 °C. While the Gibbs energy of transfer of 18-C-6 is positive, increases up to XNMP = 0.7 and thereafter decreases, the transfer energy of dibenzo-18-C-6 is negative and decreases with the addition of NMP. However, the transfer energy of cryptand 21 becomes increasingly negative with the addition of NMP while that of cryptand 22 is positive and increases under the same conditions. For cryptand 222, the transfer energy is slightly negative up to XNMP = 0.5 but decreases markedly at higher compositions of NMP. These results have been explained in terms of the various types of interaction between the ligand molecules, solvent components and the effect of solvent-solvent interactions on them.