Enthalpies of solvation of macrocyclic ether of dibenzo-24-crown-8 in solvents of different polarity

Enthalpies of solution of dibenzo-24-crown-8 in tetrachlormethane, benzene, chloroform, pyridine, acetone, acetonitrile, DMF, DMSO and propylene carbonate have been determined by calorimetric method at 298.15 K. The changes in enthalpy of solute-solvent interaction for the transfer the ether from inert tetrachlormethane into various solvents have been calculated from the obtained data. The thermochemical characteristics obtained for dibenzo-24-crown-8 have been compared with similar ones for dibenzo-18-crown-6 having a smaller cycle size. It has been found that an exothermicity of solute-solvent interaction changes to a lesser extent for transfer of the larger cyclic ether into polar solvents. But the effect increases more sharply for the transfer to chloroform. It has been concluded that the contribution from electrostatic interaction with solvent decreases with an increase of the cycle size as result of the increasing structural flexibility and decreasing polarity of cycle. But the contribution from hydrogen bonding with chloroform becomes larger due to an increase in the number of donor atoms of the ether molecules. It was ascertained that the ability to bind specifically acetonitrile molecules disappears in going from 18-merous to 24-merous cycle.