Quantitative aspects of Lewis acidity. Part XII. Equilibria between aluminium chloride and substituted anilines in ether solution

Abstract

In diethyl ether solution aluminium choride and substituted anilines form 1 : 1 adducts in reversible equilibria. Equilibrium constants (K) have been measured at 25° for ten anilines. For unhindered anilines pK=– 0·60pK_a–0·75. Alkyl substituents ortho to the amino-group hinder adduct formation. Towards anilines, aluminium choride is about as strong an acid as are boron fluoride and the gallium halides. The pattern of the ultraviolet spectra of the adducts resembles that for the analogous aluminium bromide systems. Aluminium chloride is monomeric in ether at 35° at concentrations <0·2M.