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

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 beta-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 degrees 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.