Selectivity engineering in multiphase transfer catalysis in the preparation of aromatic ethers

Abstract

Phase transfer catalysis (PTC) is a very mature discipline now. However, there are hardly any studies on the theoretical and experimental analysis of the effect of nature and number of phases on enhancement of rates and selectivities. PTC reactions can be carried out in liquid–liquid (L–L), solid–liquid (S–L), and liquid–liquid–liquid (L–L–L) and solid–liquid–liquid (S–L–L) conditions bringing into picture dominance of mass transfer effects. The current work addresses these issues in the alkylation reaction of β-naphthol with benzyl chloride with the C- and O-alkylation being the competing reactions. The role of various phases in enhancing the selectivity towards benzyl-2-naphthyl ether has been extensively investigated. The L–L–L PTC process has been found to be the most effective and economical route giving only the desired ether within a short reaction times and high catalyst reusability, unlike the L–L PTC process. A mathematical model is developed to establish the rate constant.