Molecular recognition of phenobarbital in plasticizers. Equilibrium investigations on the solubility of the barbiturate artificial receptor and its binding to phenobarbital in plasticizers

Environmental concern is renewing interest in selective, waste-free extractions. A recent report demonstrated an improved extraction of phenobarbital by means of a specifically designed molecular receptor. In that work, the solvent was CHCl3. The current work is the first step in extending extractions based on molecular recognition to reusable solvents, namely plasticizers. Phenobartital aqueous/organic partition coefficients, receptor solubility, and phenobarbital-receptor-formation constants in several plasticizers and in their CHCl3 solutions are reported. In addition, by a thermodynamic cycle, the free energy for transfer of the barbiturate-receptor complex from CHCl3 to plasticizers has been calculated. Finally, the data have been displayed in coordinate systems representing extraction efficiency and selectivity. The most selective extraction medium yielding useful extraction efficiency is dioctyl phthalate.