PURPOSE: To obtain quinoionecarboxylnc acids having large particle size and excellent filterability and useful for pharmaceuticals, agrochemicals, etc., in high yield and purity by pouring an aqueous solution of a quinolonecarboxylic acid alkali metal salt together with an acid while controlling the final pH of the reaction liquid within a specific range. ;CONSTITUTION: The objective carboxylic acid of formula II is produced by reacting (A) an aqueous solution of a quinolonecarboxylic acid alkali metal salt of formula I (R is a lower alkyl; M is an alkali metal) with (B) an acid. The reaction is carried out by simultaneously pouring the component A and the component B while controlling the final pH of the reaction liquid to 6.0-8.5. Preferably, the quinolonecarboxylic acid is 1-ethyl-6,7-methylenedioxy-4- quinolone-3-carboxylic acid, the alkali metal salt is Na salt or K salt and the acid is an inorganic acid.;COPYRIGHT: (C)1995,JPO
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