| 摘要 |
PURPOSE:To recover phthalic acid in extremely high yield, by adding an alkali to an aqueous solution obtained by removing a reaction product from a reaction solution of a phthalate and an alkenyl chloride so that esters in the aqueous solution are hydrolyzed. CONSTITUTION:In obtaining a dialkyl ester by reacting sodium phthalate with an alkenyl chloride, an alkali substance is added or in not added (preferably added to carry out hydrolysis) to unreacted phthalic acid, phthalic acid monoalkenyl ester or sodium salt thereof as a by-product and not recovered phthalic acid dialkenyl ester existing in an aqueous solution from which an organic layer comprising dialkenyl phthalates as a main component are separated to form phthalates, then an acidic substance such as sulfuric acid, etc., are added to the aqueous solution and the solution is adjusted to pH <=3, preferably <=2.5 to precipitate free phthalic acid, which is separated and recovered.
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