Selective O-alkylation of 2-naphthol using phosphonium-based ionic liquid as the phase transfer catalyst

Abstract

The selective preparation of O-alkylated aromatic products from substituted phenol and naphthols is challenging. The O-alkylation of 2-naphthol with benzyl chloride has been studied in this work using phosphonium-based ionic liquids as catalysts such as trihexyl(tetradecyl)phosphonium chloride (THTDPC), trihexyl(tetradecyl)phosphonium bromide (THTDPB), trihexyl(tetradecyl)phosphonium decanoate (THTDPD), and trihexyl(tetradecyl)phosphonium hexafluorophosphate (THTDPH). This is a liquid−liquid phase-transfer-catalysed reaction with reuse of catalyst. The effects of various parameters such as agitation speed, various phosphonium-based ionic liquids, phase volume ratio, catalyst concentration, NaOH concentration, mole ratio of starting materials, and temperature were studied systematically to understand the conversion patterns and the selectivity of the desired product. A mechanism of the reaction and a kinetic model are proposed.