QUANTITATIVE-EVALUATION OF SOLUTE-SOLVENT INTERACTIONS - ENVIRONMENTAL-EFFECTS ON THE NORMAL-BUTYLAMINOLYSIS OF TETRACHLORO-N-NORMAL-BUTYLPHTHALIMIDE

Tetrachloro-N-n-butylphthalimide reacts readily with n-butylamine in aprotic media to form the corresponding diamide. The reaction is third order with respect to butylamine both at low and high amine concentrations. The substrate and the nucleophile form a n-π type complex whose catalyzed transformation leads to the final product. Compared to cyclohexane as a standard, all other solvents used (cyclohexene, benzene, toluene, m-xylene, p-xylene, mesitylene, and α-methylnaphthalene) solvate the substrate preferentially and partially inhibit the reaction. Since the dielectric constant has been fixed detailed analysis shows that specific solvent effects (π-π interactions) are responsible for the observed effects. Therefore the reaction performed in cyclohexane with added aromatic solvent represents a case where an external complexing agent influences the reactivity. The use of liquid complexing agents made it possible to extend their concentration up to 100% in a series of stripping experiments where cyclohexane has been gradually replaced by π-donor solvents. Thus a connection between complexation and solvation has been realized. The results obtained in these mixed solvents cannot be interpreted along traditional lines. Therefore a new model, called the competitive preferential solvation theory, is proposed which allows the interpretation of the observed kinetic anomalies and throws new light on the solvating-complexing role of the solvent. For the first time a linear free energy relationship is established which connects the interacting power of the solvent to its catalytic activity. © 1979 American Chemical Society.