Cholesterol complexes with tri-n-butylphosphate, tri-n-octylamine and cyclohexanone in chlorinated hydrocarbon solvents

The hydrogen bonding interactions of moderately associated cholesterol with tri-n-butylphosphate, tri-n-octylamine and cyclohexanone in dilute solutions of tetrachloromethane, 1,2-dichloroethane and trichloromethane were studied by conventional IR spectroscopy. Information on the stoichiometry of the complexes formed was derived from least squares plots of the linearized expressions of Bjerrum's degree of system formation. The formation constants of the complexes were also determined in this way. The spectra recorded in the OH region from 3100 to 3700 cm−1 were resolved in to the bands of the cholesterol species and the complexes formed. The complexes responsible for the observed bands were recognized from the dependence of their intensity on cholesterol monomer and free base concentration and from their frequency locations. The presence of the complexes B···HO(R) and B···HO(R)···HO(R) with tri-n-butylphosphate and tri-n-octylamine was established in all of the solutions and also for the system cholesterol + cyclohexanone in 1,2-dichloroethane. On the other hand, for cholesterol bonding to cyclohexanone in tetrachloromethane, the model considering complexes with 3:1 and 1:1 stoichiometry seemed the most appropriate.