Method for crystallization of hydroxycarboxylic acids

1. 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.

2. The method for crystallization according to claim 1 ,

wherein the alkali salt of compound (1) is an alkali metal salt or an amine salt.

3. The method for crystallization according to claim 2 ,

wherein the alkali metal salt is a lithium salt, a sodium salt or a potassium salt.

4. The method for crystallization according to claim 2 ,

wherein the amine salt is an ammonium salt, a pyridinium salt, a trimethylamine salt or a triethylamine salt.

5. The method for crystallization according to claim 1 ,

wherein the organic solvent to be concomitantly present is selected from among C 6-12 aromatic hydrocarbons.

6. The method for crystallization according to claim 1 ,

wherein the organic solvent to be concomitantly present is a solvent selected from among pentane, n-hexane, isohexane, n-heptane, octane, methylcyclohexane, ethylcyclohexane, 1-hexene, benzene, toluene, xylene, ethylbenzene, tetrahydrofuran, 1,4-dioxane, tert-butyl methyl ether, ethyl acetate, isopropyl acetate, butyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, dichloromethane, 1,2-dichloroethane, acetonitrile, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, tert-butanol, 1-hexanol, and 2-hexanol or a mixture of two or more such solvents.

7. The method for crystallization according to claim 1 ,

wherein the organic solvent to be concomitantly present is a solvent selected from among pentane, n-hexane, isohexane, n-heptane, octane, methylcyclohexane, benzene, toluene, xylene, tert-butyl methyl ether, ethyl acetate, acetone, methyl isobutyl ketone, dichloromethane, acetonitirle, and 2-propanol or a mixture of two or more such solvents.

8. The method for crystallization according to claim 1 ,

wherein the organic solvent to be concomitantly present is a solvent selected from among benzene, toluene, and xylene or a mixture of two or more such solvents.

9. The method for crystallization according to claim 1 ,

wherein the acidification is effected with an inorganic acid, formic acid, trifluoroacetic acid, trichloroacetic acid, p-toluenesulfonic acid, or methanesufonic acid.

10. The method for crystallization according to claim 1 ,

wherein the acidification is effected with an inorganic acid.

11. The method for crystallization according to claim 10 ,

wherein the inorganic acid is sulfuric acid.

12. The method for crystallization according to claim 1 ,

wherein the acidification is effected to a final pH not higher than pH 6.

13. The method for crystallization according to claim 12 ,

wherein the acidification is effected to a final pH not higher than pH 5.

14. The method for crystallization according to claim 12 ,

wherein the temperature of the system at pH 6 or less is not over 70° C.

15. The method for crystallization according to claim 12 ,

wherein the temperature of the system at pH 5 or less is 0 to 60° C.

16. The method for crystallization according claim 1 ,

wherein the solution of an alkali salt of compound (1) is a reaction solution resulting from deacylation of a compound (2) of the following general formula (2):

wherein R, a, and b are as defined in claim 1 , or a solution obtainable by subjecting said reaction solution to concentration or solvent substitution.

17. The method for crystallization according to claim 16 ,

wherein an impurity or color contaminant by-produced in the course of deacylation is removed with an adsorbent in advance of crystallization.

18. The method for crystallization according to claim 1 ,

wherein R is CH 3 or OH.

19. The method for crystallization according to claim 1 ,

wherein R is CH 3 .