The Synthesis of Phthalic Anhydride via Ozonation of Naphthalene

Abstract

The oxidation of naphthalene (1) (Scheme 1) in dichloromethane or acetonitrile with excess ozone gives phthalic aldehyde (3), 2-formyl benzoic acid (4) and phthalic anhydride (8). Small amounts of the (E)- and (Z)-isomer of 3-phenyl-(2-formyl)-propenal (10) and (11) are also observed in some cases. The reaction is faster in acetonitrile than in dichloromethane owing to the higher solubility of ozone in the former solvent. The reaction is faster on lowering the temperature because of the increase of the concentration of ozone in solution at lower temperature. With a 1:1 or a 1:2 naphthalene:ozone ratio high conversion and low selectivity for the anhydride (8) is observed.

Keywords:

• Ozone
• Oxidation
• Chemical Synthesis
• Naphthalene
• Phthalic Anhydride

ACKNOWLEDGMENTS

We thank our students Cecilia Butti, Francesco Conti, Matteo Locaso, Maria Giner Vano and Stefano Zanirati for their collaboration in the experimental work.