Solvatochromic Study of Poly(vinyl chloride) Plasticizers and Their Solutions in Chloroform: Application to Phenobarbital Partitioning and Molecular Recognition of Phenobarbital

Abstract

The possibility now exists, with the availability of several families of artificial molecular receptors, to create selective extraction media. More selective extractions will lead to cleaner chromatograms, with lower detection limits and perhaps higher accuracy for trace organic analysis by chromatography. Furthermore, laboratories will be expected to minimize the use of volatile organic solvents. Consequently, nonvolatile, reusable solvents will be the basis for extractions. In addition, as artificial molecular receptors become more widely available, these solvents will be used to support molecular recognition. We have focused on plasticizers of poly(vinyl chloride) as examples of these solvents. We have determined solvatochromic parameters of several plasticizers and their solutions in chloroform. These parameters, along with cohesive energy density and solvent molar volume, were used to derive linear free energy relationships for the free energies of phenobarbital partitioning between solvent and aqueous solution, receptor solubility, formation of a complex with a barbiturate receptor [1,3-bis[[[6-(1-butyrylamino)pyrid-2-yl]amino]carbonyl]benzene (2)], and the transfer of the complex (artificial receptor and phenobarbital) from chloroform to other solvents. Solvent dipolarity/polarizability and hydrogen bond basicity, but not acidity, support complex dissociation. Solvents with large molar volumes dissolve the polar solutes, phenobarbital, receptor, and complex more poorly than solvents with lower molar volume, but there is no influence of molar volume on complex formation.