Patent ID: 8148542

Claim:
A method for producing crystal A of 2-(3-cyano-4-isobutyloxyphenyl) -4-methyl-5-thiazolecarboxylic acid, comprising dissolving 2-(3-cyano-4-isobutyloxyphenyl)-4-methyl-5-thiazolecarboxylic acid in methanol or a mixed solvent of methanol and water having a volume ratio of methanol to water of 90/10or more, adding water until the ratio of methanol to water becomes 7/3, and adding a specific amount of a seed crystal at a specific timing during the addition of water, wherein the amount of the seed crystal to be added is not less than 0.25 +(r−0.007)/(0.01175−0.007)×(0.41−0.25) (mg/mL) and not more than 1.25 (mg/mL), and the timing of adding the seed crystal is not earlier than 40+(r−0.007)/(0.01175−0.007)×(25−40) (min) and not later than 50+(r—0.007)/(0.01175−0.007)×(30−50) (min), when the initial concentration of 2-(3-cyano-4-isobutyloxyphenyl)-4-methyl-5-thiazolecarboxylic acid is 0.024 ±0.008 mol/L and the water addition rate (r) is 0.007mL/min/mL ≦r ≦0.01175 mL/min/mL.