Gas chromatographic studies of the solvent extraction systems-I. DI-n-butyl phosphoric acid and mono-n-butyl phosphoric acid

Activity coefficients and excess thermodynamic functions at infinite dilution were determined in diluent-DBP and diluent-MBP systems using gas chromatography. The diluents include benzene, toluene, hexane, cyclohexane, carbon tetrachloride, chloroform, acetone, methanol, carbon disulphide, and water. The standard thermodynamic functions of the association reaction, the equilibrium constants and the energy of the hydrogen bond formation were calculated according to the theory of the associated regular solutions. It is postulated that the undiluted DBP exists predominantly as a cyclic trimer with a bond energy of about 5 kcal/mole, while MBP forms an octadecamer with a small thermal effect. The behavior of the diluents (polymerization or depolymerization properties) in the considered systems, agree well with that observed in infra-red, partition and molecular weight determinations.