Process for preparation of azelaic acid

1. A process for the preparation of azelaic acid, wherein the level of any single impurity selected from the group consisting of C 3 -C 18 aliphatic mono carboxylic acids, C 3 -C 8 aliphatic dicarboxylic acids, C 10 -C 18 aliphatic dicarboxylic acids, and C 1-5 alkyl esters of azelaic acid, is less than about 0.15% w/w with respect to azelaic acid as measured by HPLC, the process comprising

(a) treating crude azelaic acid containing one or more impurities from the group consisting of C 3 -C 18 aliphatic mono carboxylic acids, C 3 -C 8 aliphatic dicarboxylic acids, C 10 -C 18 aliphatic dicarboxylic acids, and C 1-5 alkyl esters of azelaic acid with an acid; and

(b) treating the treated crude azelaic acid of step (a) with a hydrocarbon solvent and an ester solvent, wherein the hydrocarbon solvent is cyclohexane and the ester solvent is ethyl acetate.

2. The process as claimed in claim 1 , wherein the level of total impurities is less than about 1% w/w with respect to azelaic acid as measured by HPLC.

3. The process as claimed in claim 1 , wherein treating step (b) comprises washing with a hydrocarbon solvent and an ester solvent, or slurring with a hydrocarbon solvent and an ester solvent, or recrystallizing with a hydrocarbon solvent and an ester solvent, or adding to a hydrocarbon solvent and an ester solvent, heating and optionally cooling, or dissolving in a hydrocarbon solvent and ester solvent at a higher temperature optionally followed by cooling, wherein the hydrocarbon solvent is cyclohexane and the ester solvent is ethyl acetate.

4. The process as claimed in claim 1 , wherein the C 3 -C 18 aliphatic mono carboxylic acid is a saturated aliphatic monocarboxylic acid or an unsaturated aliphatic monocarboxylic acid optionally substituted with hydroxy group.

5. The process as claimed in claim 1 , wherein the C 3 -C 18 unsaturated aliphatic monocarboxylic acid is selected from the group consisting of oleic acid, linoleic acid, linolenic acid and ricinoleic acid.

6. The process as claimed in claim 4 , wherein the C 3 -C 18 saturated aliphatic mono carboxylic acid is selected from the group consisting of propanoic acid, hexanoic acid, nonanoic acid, palmitic acid and stearic acid.

7. The process as claimed in claim 1 , wherein the C 3 -C 8 aliphatic dicarboxylic acid is selected from the group consisting of malonic acid, adipic acid, pimelic acid and suberic acid.

8. The process as claimed in claim 1 , wherein the C 10 -C 18 aliphatic dicarboxylic acid is selected from the group consisting of sebacic acid, undecane dioic acid, dodecanedioc acid, tridecanedioic acid and tetradecane dioic acid.

9. The process as claimed in claim 1 , wherein the C 1-5 alkyl ester of azelaic acid is selected from the group consisting of monomethyl azelate and diethyl azelate.

10. The process as claimed in claim 1 , wherein any single impurity selected from the group consisting of pimelic acid, suberic acid, sebacic acid, undecanedioc acid and azelaic acid monomethyl ester in the azelaic acid obtained by the process of claim 1 is not more than 0.15% w/w with respect to azelaic acid as measured by HPLC.

11. The process as claimed in claim 1 , wherein the acid used in step (a) is an organic or inorganic acid.

12. The process as claimed in claim 1 wherein the acid used in step (a) is an inorganic acid.