Process for the preparation of isosulfan blue

1. A process for preparation of Isosulfan blue having Formula I, substantially free of desethyl impurity, wherein

the process comprises steps of:

a) oxidizing isoleuco acid by an oxidizing agent in a solvent;

b) treating isosulfan blue of step (a) with water and hydrochloric acid to provide isosulfan blue hydrochloric acid salt;

c) treating Isosulfan blue hydrochloric acid salt of step (b) with water and an inorganic salt to provide crude isosulfan blue;

d) treating crude isosulfan blue of step (c) with water and an inorganic or an organic salt.

2. The process as claimed in claim 1 , wherein the oxidizing agent is selected from potassium dichromate, lead dioxide, chloranil, sodium hypochlorite, ammonium persulphate, manganese dioxide, and potassium permanganate.

3. The process as claimed in claim 2 , wherein the amount of permanganate salts ranges from 1.0 to 2.0 molar equivalent.

4. The process as claimed in claim 1 , wherein the solvent is selected from alcohols, ketones, nitriles and water or mixtures thereof.

5. The process as claimed in claim 4 , wherein the alcohol is selected from methanol, ethanol, butanol, tertiary butanol or mixture thereof.

6. The process as claimed in claim 4 , wherein, the nitrile is selected from acetonitrile and propionitrile.

7. The process as claimed in claim 4 , wherein the ketone is selected from acetone, methyl ethyl ketone and methyl isobutyl ketone.

8. The process as claimed in claim 1 , wherein the oxidation is carried out at a temperature ranging from −20° C. to 25° C.

9. The process as claimed in claim 1 , wherein step of oxidation is followed by a step of recrystallization.

10. The process as claimed in claim 9 , wherein the recrystallization comprises the steps of:

a) dissolving of isosulfan blue in a solvent; and

b) precipitation of isosulfan blue by adding an anti-solvent.

11. The process as claimed in claim 10 , wherein the solvent for dissolution is water.

12. The process as claimed in claim 10 , wherein the anti-solvent is tertiary butanol.

13. The process as claimed in claim 1 , wherein step (b) is carried out at a temperature ranging from 20° to 35° C.

14. The process as claimed in claim 1 , wherein in step (c) the inorganic salt is selected from carbonate, bicarbonate, and hydroxide salts of sodium, potassium, and ammonium.

15. The process as claimed in claim 1 , wherein in step (c) the concentration the inorganic salt is about 30% in the solution.

16. The process as claimed in claim 1 , wherein in step (c) the reaction is carried out at pH 6 to 7.5.

17. The process as claimed in claim 1 , wherein in step (d), wherein the inorganic or organic salt is selected from carbonate, bicarbonate, hydroxide, and acetate salts of sodium, potassium, and ammonium.

18. The process as claimed in claim 1 , wherein step (d) is reaction carried out at pH 7 to 13.

19. The process as claimed in claim 1 , wherein in step (d) the concentration of the inorganic salt is about 2% to 30% in solution.

20. The process as claimed in claim 1 , wherein the isosulfan blue contains less than 0.15% of desethyl impurity.

21. The process as claimed in claim 1 , wherein the purity of isosulfan blue is greater than 99.8%.

22. Isosulfan blue of formula (I) prepared by the process as claimed in claim 1 , wherein the isosulfan blue contains less than 0.15% of desethyl impurity.

23. The process as claimed in claim 1 , wherein in step (c) the inorganic salt is selected from sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, and ammonium carbonate.

24. The process as claim in claim 1 , wherein in step (d), wherein the inorganic or organic salt is selected from sodium carbonate, sodium bicarbonate, sodium acetate, potassium carbonate, potassium bicarbonate, and ammonium carbonate.

25. The process as claim in claim 1 , wherein in step (c), the reaction is carried out at pH 6. to 7.5.

26. The process as claim in claim 1 , wherein step (d) is reaction carried out at pH 7.5 to 12.