Formaldehyde → 1,3-Dihydro-1-oxoisobenzofuran-5-carboxylic acid

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Reaction Steps

In the method of the invention, the terephthalic acid is condensed with paraformaldehyde liberating water, which reacts with the SO3. When the reaction is complete, 5-carboxyphthalide may be isolated as follows. The reaction mixture is hydrolysed with water. The condensed product, 5-carboxyphthalide inclusive possible diphthalide impurities may then be filtered off, and the 5-carboxyphthalide may be dissolved in aqueous medium by adjusting pH to about 6.7 to 7.3, leaving possible diphthalide impurities in the solid phase The diphthalide present may be filtered off whereupon 5-carboxyphthalide may be precipitated by acidification, filtered off, washed with water and dried.

Provenance & Evidence