Potassium phosphate as a high-performance solid base in phase-transfer-catalyzed alkylation reactions

摘要

Potassium phosphate is reported as a remarkably active and selective solid base in phase-transfer-catalyzed alkylation reactions of alkaline-sensitive substrates such as esters and halides. The performance of potassium phosphate exceeded that of common bases such as hydroxides, carbonates, fluorides, and oxides. Even though potassium phosphate is not porous and the number of basic sites exposed at the surface is relatively low (0.05 mequiv/g), it is still fully consumed in the alkylation process and converted into K2HPO4. The heterogeneous process follows a second-order rate law, and the rate constant was found to depend strongly on particle size, presence of water in the system, thermal pretreatment of the base, structure of the phase transfer catalyst, nature of the solvent, and reaction temperature. Some surface properties of K3PO4 have been determined and are discussed with relevance to the above catalytic alkylation reactions.