Selectivity engineering of solid base catalyzed O-methylation of 2-naphthol with dimethyl carbonate to 2-methoxynaphthalene
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.
Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (88 K)Download as PowerPoint slideHighlights► Alkylation of 2-naphthol with dimethyl carbonate to produce 2-methoxynaphthalene. ► 20% calcinted hydrotalcite (CHT)/hexagonal mesoporous silica (HMS) as best catalyst. ► 92% conversion and 90% selectivity at 463 K. ► Zero order kinetics with strong adsorption of reactants. ► The activation energy for the reaction is 33.348 kcal/mol.
Journal: Catalysis Today - Volume 207, 30 May 2013, Pages 180–190