Kryn G. Ihrman

Potassium hydroxide as a promoter for the potassium-metal catalyzed side-chain alkylation of toluene

Abstract Potassium hydroxide acts synergistically with catalyst supports such as alumina, diatomaceous earth, or potassium carbonate to promote the potassium-metal catalyzed side-chain alkylation of toluene with propene. Carrying out the reaction with wet toluene to generate KOH in situ is a particularly effective method for promoting the reaction. The catalyst supports are not inert in the absence of the promoter, because they alter alkylation regiochemistry and increase the formation of methylindan by-products. As a mechanistic probe, the amounts of benzylpotassium that form are compared with propylation reaction rates. This is the first report concerning the amount of benzylpotassium that forms under side-chain alkylation conditions. From this and other data, a previously unrecognized mechanism for the promotion of side-chain alkylation is identified.