Process for the preparation of 4,5,6-trichloropicolinic acid
View Patent ↗4,5,6-Trichloropicolinic acid is prepared by selectively dechlorinating 3,4,5,6-tetrachloropicolinic acid with zinc and a catalyst prepared from a nickel compound and a bidentate ligand in a polar solvent.
1. A process for the preparation of 4,5,6-trichloropicolinic acid (Formula I)
which comprises, selectively dechlorinating 3,4,5,6-tetrachloropicolinic acid (Formula II)
with zinc and a catalyst prepared from a nickel compound and a bidentate ligand in a polar solvent.
2. The process of claim 1 , wherein the nickel compound is NiCl 2 .6H 2 O.
3. The process of claim 1 , wherein the polar solvent is acetone, acetonitrile, dimethyl sulfoxide (DMSO), ethyl alcohol, methyl alcohol, isopropyl alcohol (iPrOH), N-methylpyrrolidinone (NMP), tetrahydrofuran (THF), N,N-dimethyl-formamide (DMF), N,N-dimethylacetamide (DMA), hexamethylphosphoramide (HMPA) or sulfolane.
4. The process of claim 3 , wherein the polar solvent is methyl alcohol, ethyl alcohol, iPrOH, THF, NMP, DMF, DMA or mixtures thereof.
5. The process of claim 3 or 4 , wherein the polar solvent is a mixture of the polar solvent with water.
6. The process of claim 4 , wherein the polar solvent is N,N-dimethylformamide.
7. The process of claim 5 , wherein the aqueous polar solvent is a mixture from about 75 to about 95 weight percent polar solvent and from about 5 to about 25 weight percent water.
8. The process of claim 1 , wherein the bidentate ligand is 6,6′-dimethyl-2,2′-bipyridyl, 4,4′-dimethyl-2,2′-bipyridyl, 5-methyl-1,10-phenanthroline, 1,10-phenanthroline or 2,2′-bipyridine.
9. The process of claim 8 , wherein the bidentate ligand is 2,2′-bipyridine.
10. The process of claim 1 , wherein the zinc is zinc powder or zinc dust.
11. The process of claim 1 , wherein the pH of the solution is neutral or acidic.
12. The process of claim 10 , wherein the zinc powder is <150 μm.
13. The process of claim 10 , wherein the zinc dust is <10 μm.