Process for the preparation of indigo carmine
The present invention relates to an improved process for preparation of Indigo carmine of Formula (I), in high purity, more than 99.5%.
1. An improved process for the preparation of Indigo carmine of formula (I) having a purity of 99.5%,
the process comprising:
a) treating an Indole of compound formula (II)
with peroxide in the presence of a catalyst in an alcoholic solvent to give an indigo of compound formula (III)
b) reacting the Indigo of compound formula (III)
with sulfuric acid and adding an organic solvent then washing or purifying in an ester solvent to produce an indigodisulfonic acid of compound formula (IV)
and
c) reacting indigodisulfonic acid of formula (IV)
in an aqueous media with a sodium source compound and washing with a nitrile or a ketonic solvent to give the Indigo carmine of formula (I).
2. The process according to claim 1 , wherein in step (a) the reaction carried is out in an alcohol solvent selected from group methanol, ethanol, isopropanol, n-butanol, and tert-butanol.
3. The process according to claim 1 , wherein in step (a) the reaction is carried out in a peroxide compound selected from hydrogen peroxide and cumene hydrogen peroxide in cumene.
4. The process according to claim 1 , wherein in step (a) the reaction is carried out at a temperature ranging from 80° C. to 120° C.
5. The process according to claim 1 , wherein in step (a) the reaction is carried out in the presence of a catalyst, which is Molybledenumhexacarbonyl (Mo(CO) 6 ).
6. The process according to claim 1 , wherein in step (b) the reaction is carried out at a temperature ranging from 50° C. to 90° C.
7. The process according to claim 1 , wherein in step (b) the reaction is carried out in a solvent, which is an organic solvent.
8. The process according to claim 1 , wherein in step (b) the washing or purifying is carried out in the ester solvent, which is selected from methyl acetate and ethyl acetate.
9. The process according to claim 1 , wherein the aqueous media is only water.
10. The process according to claim 1 , wherein in step (c) the reaction is carried out at a temperature ranging from 20° C. to 40° C.
11. The process according to claim 1 , wherein in step (c) the sodium source compound is selected from sodium metal, sodium hydride, and sodium hydroxide.
12. The process according to claim 11 , wherein in step (c) the washing is carried out in a solvent selected from acetone and acetonitrile.
13. The process according to claim 2 , wherein in step (a) the alcohol solvent is tert-butanol.
14. The process according to claim 3 , wherein in step (a) the reaction is carried out in cumene hydrogen peroxide in cumene.
15. The process according to claim 4 , wherein in step (a) the reaction is carried out at a temperature ranging from 95° C. to 100° C.
16. The process according to claim 6 , wherein in step (b) the reaction is carried out at a temperature ranging from 75° C. to 85° C.
17. The process according to claim 7 , wherein in step (b) the reaction is carried out in acetic acid.
18. The process according to claim 8 , wherein in step (b) the ester solvent is ethyl acetate.
19. The process according to claim 10 , wherein in step the reaction is carried out at a temperature ranging from 25° C. to 30° C.
20. The process according to claim 12 , wherein in step the washing is carried out in acetone.