Selectivity engineering of solid base catalyzed O-methylation of 2-naphthol with dimethyl carbonate to 2-methoxynaphthalene

Abstract

2-Methoxynaphthalene is an important intermediate used in the production of naproxen which is widely used as a non-steroidal, anti-inflammatory, analgesic and antipyretic drug. In the current work, catalytic methylation of 2-naphthol was studied by using dimethyl carbonate as a greener agent vis-à-vis methyl halides and dimethyl sulfate. Catalysts based on calcined-hydrotalcite (CHT) supported on hexagonal mesoporous silica (HMS) were synthesized. Effect of CHT loading on HMS was systematically studied including full characterization. The activity and selectivity of CHT/HMS was examined by studying the effects of different operating parameters to deduce mechanism and kinetics. Conversion of 2-naphthol at 463 K and autogenous pressure was 92% with 90% selectivity toward 2-methoxynaphthalene on 20% (w/w) CHT/HMS. The catalyst was easily recovered and reused without any significant loss in activity. A kinetic model was developed. It follows zero order kinetics based on Langmuir–Hinshelwood–Hougen–Watson mechanism with strong adsorption of reactants. The apparent activation energy is 32.3 kcal/mol.