Quantitative aspects of Lewis acidity. Part VI. Boron trifluoride–aniline equilibria in ether

Abstract

In ether solution boron trifluoride and substituted anilines interact initially to give 1 : 1 co-ordination adducts, which may subsequently disproportionate to yield anilinium tetrafluoroborates and arylaminoboron difluorides. Equilibrium constants, K, for the initial 1 : 1 adduct formation are reported. o-Methyl and o-chloro substituents hinder adduct formation. For unhindered bases at 25° pK=–0·96 pKa–0·29, where Ka is the dissociation constant of the corresponding anilinium ion in water. The ultraviolet spectra of the adducts in ether very closely resemble those of the corresponding anilinium ions in a similar solvent.