BORONIC ACID-CATALYZED HYDROLYZES OF SALICYLALDEHYDE IMINES

The hydrolysis of salicylaldehyde imines is catalyzed by boric acid, substituted arylboronic acids, and diphenylborinic acid. These reactions show saturation kinetics, allowing the determination of first-order catalytic constants and dissociation constants. Dissociation constants reflect single-ionization pK values similar to the pK values of the boronic acids. Binding is best on the acid side of the pK. Use of the Bronsted and the Hammett relationships shows that the binding constants are improved by electron-withdrawing substituents on the catalysts. Catalytic constants are nearly independent of pH, of Hammett sigma, and of the pK of the catalyst. The reactions display no solvent deuterium isotope effect.