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Methanolysis of phthalic anhydride; Phthalic acid monomethyl ester

SyntheticPage 428
DOI: 10.1039/SP428
Submitted Jul 01, 2010, published Jul 05, 2010
Christopher Cooksey (
A contribution from R J H Clark Group, UCL

			Reaction Scheme: Methanolysis of <SPAN class=csm-chemical-name id=csm1285705409922 title="phthalic anhydride">phthalic anhydride</SPAN>

Chemicals Used

phthalic anhydride (Aldrich)


Powdered phthalic anhydride (74 g, 0.5 mol) and methanol (100 cm3, 2.47 mol) were heated under reflux with magnetic stirring on an oil bath for 8 h. The clear solution was distilled to remove most of the methanol. Toluene (100 cm3) was added to the residue and distillation was continued until the still-head temperature reached 110 ºC. After cooling to 30 ºC, the resulting thick white precipitate was filtered and the residue washed with toluene (50 cm3). Petroleum ether (30/40, 100 cm3) was added to the combined filtrates to give a dense oil which crystallised as long white needles after standing overnight. Filtration and washing with petroleum ether (60/80, 50 cm3) gave the product, 44.5 g, 49% yield.

Author's Comments

A subsequent perusal of the literature reveals a much simpler procedure, 0.5 h reflux and no toluene: "Under a nitrogen atmosphere, a mixture of 75.0 grams (0.506 mole) of phthalic anhydride in 120.0 grams (3.75 moles) of methanol was stirred and heated under reflux for 30 minutes. During this time a complete solution was attained. The reaction mixture was concentrated under reduced pressure to a residual oil. The oil was placed in a refrigerator where it solidified to yield when dried, 93.0 grams of phthalic acid, mono-methyl ester; m.p. 80-81.5 ºC." in quantitative yield.

Chang Jun H, Baum J S, US 4892578 (9 Jan 1990)


δH (CDCl3, 200 MHz) 7.68m (1H), 7.61m (1H), 7.56m (2H), 3.92s (3H)

Lead Reference

E L Eliel, A W Burgstahler, J Amer Chem Soc, 1949, 71, 2251-2252. doi: 10.1021/ja01174a509

Other References

Chang Jun H, Baum J S, US 4892578 (9 Jan 1990)

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Keywords: addition, alcohols, carboxylic acids, esters, nucleophilic

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