Thermodynamic study of aqueous dilute solutions of organic compounds. Part 3.—Morpholines and piperazines

Abstract

Free energy, enthalpy and entropy changes associated with the transfer of six membered ring molecules (containing O, NH or NCH₃ groups in 1 and 4 positions) from the condensed or gas phase to dilute aqueous solution have been determined. Comparisons are made with data for similar cyclic molecules containing only one hetero-atom.

The free energies of hydration of the bifunctional compounds are lower than those of the monofunctional molecules of the same size. This relative lowering of free energy is determined by the entropy term when the second hydrophilic centre introduced is an ether oxygen atom, but by the enthalpy term otherwise. Interactions between hydrophilic centres in 1,4 positions are evident and a tentative interpretation is given.