Temperature Effect on the Distribution of Some Phenolic Compounds: An Experimental Measurement of 1-Octanol/Water Partition Coefficients

Abstract

The partition coefficient, KOW, of some phenolic compounds, PhC, between water and 1-octanol, was determined at six temperatures from (293.15 to 318.15) K using a slow-stirring method. The log KOW values of protocatechuic acid, vanillic acid, and vanillin range from (0.78 to 0.61), (1.46 to 1.18), and (1.25 to 0.99), respectively, over the temperature range studied. Obtained values at 298.15 K agree well with literature data. The van’t Hoff plots of log KOW versus T−1 exhibit linearity with values of KOW increasing by 13 % to 21 % over this temperatures range. On the basis of the fluid phase equilibrium theory, a temperature-dependent thermodynamic relationship of the 1-octanol/water partition coefficient is proposed, and the changes of enthalpy, entropy, and the Gibbs energy function for phenolic compounds partitioning in 1-octanol/water were determined. In all cases, the thermodynamic functions of transfer of PhC from the water to the organic phase were negative. The Gibbs energy of transfer ranges from (3.69 to 8.29) kJ·mol−1. The temperature effect coefficient of the 1-octanol/water partition coefficient is also discussed, showing slight and negative values.