PURPOSE: To obtain a solid material by treating a water-based alkaline solution containing the solid material hardly soluble under a weak acidic or weak alkaline condition but relatively easily soluble in a strong alkaline condition in a water-based medium with carbonic acid, a carboxylic acid ester, an amide or the like.
CONSTITUTION: At the time of isolating the solid material (e.g. toluol sulfonamide, saccharin, phenol, guanine, uracil) hardly soluble in the weak acidic or weak alkaline condition but relatively easily soluble in the strong alkaline condition in the water-based medium from the waster-based alkaline solution, the solution is treated with carbonic acid and/or the carboxylic acid ester (e.g. ethyl acetate) and/or amide (e.g. formamide) hydrolyzable in the water-based alkaline medium at 10-100°C and the resultant precipitates are subjected to solid-liquid separation. The method is applied for a pharmaceutically active material or the intermediate product.
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