Patent ID: 7034180

Claim:
A method for crystallization of a compound (1) of the following general formula (1): in which R is CH 3 , CH 2 OH, CH 2 OCOR 1 , CO 2 R 2 , CONR 3 R 4 , OH, CH 2 OR 1 or CH 2 NR 3 R 4 ; R 1 is a C 1-5 alkyl group; R 2 is H or a C 1-5 alkyl group; R 3 and R 4 are independently selected from among H and C 1-5 alkyl groups; a and b each is a double bond, one of a and b is a single bond with the other being a double bond or a and b each is a single bond, which comprises acidifying a mixture of a solution of an alkali salt of the compound (1) and an organic solvent in such a manner that the solubility of the compound (1) at completion of crystallization will be 3 weight % or less and isolating the obtained crystals wherein the organic solvent to be concomitantly present is a solvent selected from among C 5-12 saturated hydrocarbons represented by C n H 2n+2 or C n H 2n , C 5-12 unsaturated hydrocarbons represented by C n H 2n or C n H 2n−2 , C 6-12 aromatic hydrocarbons, C 4-10 ethers, C 3-10 esters, C 3-10 ketones, C 1-8 halogenated hydrocarbons, C 2-6 nitriles, and C 1-8 alcohols or a mixture of two or more such solvents.