Partition Coefficients of Alkanols and Polyoxyethylene Alkyl Ethers in the Dodecane–Water System at 25 °C

The partition coefficients of normal alkanols (RmOH, m=2 to 6) and a number of polyoxyethylene normal alkyl ethers (RmEnOH, n=1,2 m=2 to 5; n=3, 4m=4,5) in the dodecane-water system have been determined at a high dilution at 25 °C. From the finding that the standard free energies of the transfer of the solutes from water to the dodecane phase show a linear relation with the number of methylene and oxyethylene groups, the contribution of the groups to the free energy was obtained as −0.858 for alkanols and −0.808 kcal/mol methylene group for ethers, and 0.655 kcal/mol oxyethylene group respectively. Extrapolation to zero oxyethylene in the linear relationship for the normal alkylethers gave standard free energies of transfer less than those for normal alkanols with the same alkyl chain length. Thus, the alkanol is more hydrophilic than the hypothetical “ether” with no oxyethylene group. The difference in the free energies is discussed from the viewpoint of intramolecular hydrogen-bond formation in the polyoxyethylene chain in the dodecane phase.