Method for preparing 2,6-naphthalene dicarboxylic acid

1. A method for preparing 2,6-naphthalene dicarboxylic acid, which comprises the steps of, hydrolyzing di-lower alkyl 2,6-naphthalene dicarboxylate under the presence of a basic compound to give a solution of the di-basic compound salt of 2,6-naphthalene dicarboxylic acid, and aciding out the solution to give 2,6-naphthalene dicarboxylic acid, wherein the hydrolyzing step comprises;

hydrolyzing one part by weight of di-lower alkyl 2,6-naphthalene dicarboxylate in 3-50 parts by weight of water in the presence of (A), (B) and the basic compound:

(A) 20-200 parts by weight of a hydrophobic organic solvent selected from the group consisting of an aromatic compound, a ketone and an ether per 100 parts by weight of di-lower alkyl 2,6-naphthalene dicarboxylate,

(B) 0.01-10 parts by weight of an additive selected from the group consisting of a polyalkylene glycol and a surface active agent per 100 parts by weight of di-lower alkyl 2,6-naphthalene dicarboxylate; and

separating the reaction mixture into organic phase and aqueous phase to give the aqueous solution of the di-basic compound salt of 2,6-naphthalene dicarboxylic acid.

2. The method of claim 1 , wherein the hydrophobic organic solvent is at least one selected from the group consisting of benzene, toluene, xylene, mesitylene, ethylbenzene, nitrobenzene, chlorobenzene and dichlorobenzene.

3. The method of claim 1 , wherein the additive (B) is polyalkylene glycol.

4. The method of claim 3 , wherein the polyalkylene glycol is polyethylene glycol.

5. The method of claim 1 , wherein the organic phase obtained after the hydrolyzing step is used again as the hydrophobic organic solvent in the hydrolyzing step.

6. The method of claim 1 , wherein the basic compound is selected from the group consisting of an alkaline metal hydroxide, an alkaline metal carbonate, an alkaline metal bicarbonate and an alkaline metal lower alkoxide.

7. The method of claim 1 , wherein the amount of the basic compound used in the hydrolyzing step is 1.0-5.0 equivalent per 1 equivalent of di-lower alkyl 2,6-naphthalene dicarboxylate (based on the ester group).

8. A method for preparing 2,6-naphthalene dicarboxylic acid which comprises the steps of, hydrolyzing di-lower alkyl 2,6-naphthalene dicarboxylate under the presence of a basic compound to give a solution of the di-basic compound salt of 2,6-naphthalene dicarboxylic acid, and aciding out the solution to give 2,6-naphthalene dicarboxylic acid, wherein the hydrolyzing step comprises;

hydrolyzing one part by weight of di-lower alkyl 2,6-naphthalene dicarboxylate in 3-20 parts by weight of a mixed solvent of 10/100 to 200/100 (w/w) non-water-miscible alcohol/water in the presence of the basic compound, and

separating the reaction mixture into the organic phase and aqueous phase to give the aqueous solution of the di-basic compound salt of 2,6-naphthalene dicarboxylic acid.

9. The method of claim 8 , wherein the non-water miscible alcohol is at least one selected from the group consisting of n-butanol, 2-ethyihexyl alcohol, 2-phenoxyethanol and benzyl alcohol.

10. The method of claim 8 , wherein the organic phase obtained after the hydrolyzing step is used again as the non-water miscible alcohol in the hydrolyzing step.

11. The method of claim 8 , wherein the basic compound is selected from the group consisting of an alkaline metal hydroxide, an alkaline metal carbonate, an alkaline metal bicarbonate and an alkaline metal lower alkoxide.

12. The method of claim 8 , wherein the amount of the basic compound used in the hydrolyzing step is 1.0-5.0 equivalent per 1 equivalent of di-lower alkyl 2,6-naphthalene dicarboxylate (based on the ester group).

13. A method for preparing 2,6-naphthalene dicarboxylic acid which comprises the steps of, hydrolyzing di-lower alkyl 2,6-naphthalene dicarboxylate under the presence of a basic compound to give a solution of the di-basic compound salt of 2,6-naphthalene dicarboxylic acid, and aciding out the solution to give 2,6-naphthalene dicarboxylic acid, wherein the hydrolyzing step comprises;

(1) 1st hydrolyzing step wherein one part by weight of di-lower alkyl 2,6-naphthalene dicarboxylate is reacted with the basic compound in 5-20 parts by weight of a water miscible organic solvent in the presence of water in an amount of 2-10 molar times 2,6-NDC until at least 80% of di-lower alkyl 2,6-naphthalene dicarboxylate is converted; and

(2) 2nd hydrolyzing step wherein 5-20 parts by weight of water is added to the mixture obtained by the 1st hydrolyzing step and the resulting mixture is further reacted to give the solution of the di-basic compound salt of 2,6-naphthalene dicarboxylic acid.

14. The method of claim 13 , wherein the water miscible organic solvent is at least one selected from the group consisting of an alcohol, a ketone and aprotic polar solvent.

15. The method of claim 13 , wherein the water miscible organic solvent is at least one selected from the group consisting of methanol, ethanol, isopropanol, 2-methoxyethanol, 2-ethoxyethanol, ethyleneglycol, glycerine and polyethylene glycol 200.

16. The method of claim 13 , wherein the basic compound is selected from the group consisting of an alkaline metal hydroxide, an alkaline metal carbonate, an alkaline metal bicarbonate, and an alkaline metal lower alkoxide.

17. The method of claim 13 , wherein the amount of the basic compound used in the hydrolyzing step is 1.0-5.0 equivalent per 1 equivalent of di-lower alkyl 2,6-naphthalene dicarboxylate (based on the ester group).