Stability of arenide ions. Cleavage of unsymmetrical diaryl ketones with potassium t-butoxide

Abstract

Diaryl ketones (RC₆H₄·COPh) were cleaved by heating with potassium t-butoxide in the absence of a solvent. After addition of water the products were the two carboxylic acids RC₆H₄·CO₂H and PhCO₂H. and the two neutral compounds HPh and RPh. The relative proportions of the products indicated the preferred direction of cleavage. It is assumed that the aryl groups were produced as arenide ions, and that the propensity for cleavage is in the same order as the stability of the arenide ions. Substituents R were found to favour cleavage in the order 2-F > 3-F ∼ 2-Me > 4-F > 4-CF₃ > H > 3-Me ∼ 4-Me > 4-MeO. Though the actual species undergoing cleavage was ArAr'C(OBu^t)O^–(2)[unlike previous investigations in which the cleaved species was ArAr'C(OH)O^–(1) or ArAr'C(O^–)₂(6)], the results are in accord with previous work.