Selective synthesis of 1-(1-naphthyloxy)-2,3-epoxypropane from 1-naphthol and epichlorohydrin under solid–liquid phase transfer catalysis: a waste minimization strategy

Abstract

Selective organic transformation is a basic theme which needs to be followed to have a waste free, clean and green process. Phase transfer catalysis (PTC) is a synthetic technique that satisfies this criterion very well in which reaction rates and selectivities are enhanced by several folds, thereby decreasing processing costs and hazardous conditions. Solid–liquid (S–L) PTC is better than liquid–liquid (L–L) PTC since the rates of reactions are intensified by order(s) of magnitude and total selectivity can be obtained due to suppression of aqueous-phase reactions. 1-(1-Naphthyloxy)-2,3-epoxypropane is an intermediate in the synthesis of β-blocker drugs propranolol and nadolol. In the current work, synthesis of 1-(1-naphthyloxy)-2,3-epoxypropane was carried out by the reaction of 1-naphthol and epichlorohydrin by using a variety of phase transfer catalysts among which tetra-n-butyl ammonium bromide (TBAB) was the best catalyst at 70 °C under S–L PTC. The effects of various parameters affecting the conversion and initial rates of O-alkylation were studied to establish kinetics and mechanism. Selectivity of 100% for 1-(1-naphthyloxy)-2,3-epoxypropane was observed. The reaction followed pseudo-first-order kinetics. S–L PTC is a waste minimization strategy since no by-products are formed and the process is intensified reducing reactor volume and processing time.