2006 Volume 55 Issue 1 Pages 1-13
We have carried out a kinetic and thermodynamic study on the hydrolysis of sodium laurate (NaLA) taking place at given water/oil interfaces in parallel with the transfer of hydrolyzed species (lauric acid, HLA) into different oil phases comprised primarily of benzene(Bz), dodecane(C12) or dodecylbenzene(C12Bz) with and without added amphiphiles such as hexadecanol(C16OH) and cholesterol(Ch) as functions of temperature and concentration of added amphiphiles. The contact of aqueous NaLA solution with the respective oil phases was found to cause enhanced hydrolysis of NaLA and lead to a pH rise in the bulk phase of aqueous solution. According to the previous kinetic sturdy, measured concentration change of OH- or HLA with time was completely simulated by computer and enabled us to determine the rate constants (k) as well as the concentration of OH- or HLA ([OH-]0 or [HLA]0, respectively) at partition equilibria. The partition coefficient, Kpt was found to depend markedly on conditions such as oil solvents with or without added amphiphile species and its concentration as well as temperature. The present paper reports upon the results of thermodynamic analysis of partition coefficients as well as discussion of the enthalpy-entropy compensation phenomenon observed in the transfer of HLA into oil phase or partition of HLA between oil/water phases.