The present invention relates to a process for separation of substituted trihalomethylpyridines.

BACKGROUND OF THE INVENTION
Substituted trihalomethyl pyridine compounds are useful as intermediates for pharmaceuticals or agrochemicals.
Most of the techniques known for preparation of substituted trihalomethylpyridines involves substitution reaction on the ring resulting in the formation of mixture of mono, di, tri or more ring substitution. These compounds are usually separated by distillation. However, distillation of some high boiling substituted trihalomethylpyridines become tedious and cost intensive process.
An object of the present invention is separation of substituted trihalomethylpyridines using cost effective and commercially viable techniques.
Further, it has been found that it is difficult to produce such type of trihalomethyl substituted pyridine compounds having halo groups at ortho position to the trihalomethyl group on the pyridine ring. Therefore their separation with high purity is also challenging.
Thus, it is another object of the present invention to provide a process for separation of mono and di-halo substituted trihalomethylpyridines with high purity.

OBJECT OF THE INVENTION
The main object of present invention is to provide process for separation of mono and di-halo substituted trihalomethylpyridines.

SUMMARY OF THE INVENTION
The present invention provides a process for separation of a mixture of substituted trihalomethylpyridines of Formula I and Formula II,

Formula-I Formula-II
wherein X is independently selected from F, Cl and Br; n is an integer from 1-3, n1 and n2 are an integer from 1-4 provided that n2 >n1,
comprising the steps of adding an acid to a mixture of substituted trihalomethylpyridines of Formula I and II to separate out substantially pure compound of formula I and II, having purity >95%.

DETAILED DESCRIPTION OF THE INVENTION
As used herein, an acid is selected from a group consisting of an organic or an inorganic acid. Examples of inorganic acid includes hydrochloric acid, sulfuric acid, methanesulfonic acid etc. Examples of organic acids includes trifluoroacetic acid and trifluoromethanesulfonic acid.
In an embodiment of the present invention, the process can be carried out in a nonpolar solvent selected from hexane, heptanes, toluene and cyclohexane.
In another embodiment, the compound of formula I is isolated from an acid layer using a solvent selected from a group consisting of chlorinated solvents such as dichloromethane or carbontetrachloride, dichloroethane, 1,1,2,2-tetrachloroethane, an ether such as diethylether, diisopropyl ether, tert-butyl methyl ether, tetrahydrofuran, a nitrile such as acetonitrile or an ester solvent such as methyl acetate, ethyl acetate, propyl acetate, butyl acetate or a mixture thereof.
In another embodiment the process of the present invention is carried out in absence of solvent.
In another embodiment of the present invention is to provide methods whereby 'highly chlorinated heterocyclic nitrogen compounds may be prepared substantially as a single or major component of a reaction product composition or may be prepared in such amounts as to make recovery of products practicable as a production method.
In another embodiment of the present invention, the process is carried out at reaction temperature between 0-15°C.
In an embodiment, the present invention provides a process for separation 2-chloro-4-trichloromethylpyridine from its mixture with 2,6-dichloro-4-trichloromethylpyridine, comprising the steps of adding an acid to a mixture to separate out substantially pure 2-chloro-4-trichloropyridine.
In an embodiment, the present invention provides a process for separation 2-chloro-4-trichloromethylpyridine from its mixture with 2,6-dichloro-4-trichloromethylpyridine, comprising the steps:
a) adding an acid to a mixture of 2-chloro-4-trichloromethylpyridine and 2,6-dichloro-4-trichloromethylpyridine in a non-polar solvent at a temperature of 0-15°C;
b) isolating 2,6-dichloro-4-trichloromethylpyridine from the organic layer;
c) isolating 2-chloro-4-trichloromethylpyridine from the acid layer.
In another embodiment of the present invention, 2-chloro-4-trichloromethylpyridine is isolated from the acid layer by extracting it in an organic solvent followed by evaporation. The organic solvent for this purpose is selected from a group consisting of chlorinated solvents such as dichloromethane or carbontetrachloride, dichloroethane, 1,1,2,2-tetrachloroethane, an ether such as diethylether, diisopropyl ether, tert-butyl methyl ether, tetrahydrofuran, a nitrile such as acetonitrile or an ester solvent such as methyl acetate, ethyl acetate, propyl acetate, butyl acetate or a mixture thereof.
In an embodiment, the present invention provides a process for separation 2-chloro-4-trifluoromethylpyridine from its mixture with 2,6-dichloro-4-trifluoromethylpyridine, comprising the steps of adding an acid to a mixture to separate out substantially pure 2-chloro-4-trifluoromethylpyridine.
In an embodiment, the present invention provides a process for separation 2-chloro-4-trifluoromethylpyridine from its mixture with 2,6-dichloro-4-trifluoromethylpyridine, comprising the steps:
a) adding an acid to a mixture of 2-chloro-4-trifluoromethylpyridine and 2,6-dichloro-4-trifluoromethylpyridine in a non-polar solvent at a temperature of 0-15°C;
b) isolating 2,6-dichloro-4-trifluoromethylpyridine from the organic layer;
c) isolating 2-chloro-4-trifluoromethylpyridine from the acid layer.
In another embodiment of the present invention, 2-chloro-4-trifluoromethylpyridine is isolated from the acid layer by extracting it in an organic solvent followed by evaporation. The organic solvent for this purpose is selected from a group consisting of chlorinated solvents such as dichloromethane or carbontetrachloride, dichloroethane, 1,1,2,2-tetrachloroethane, an ether such as diethylether, diisopropyl ether, tert-butyl methyl ether, tetrahydrofuran, a nitrile such as acetonitrile or an ester solvent such as methyl acetate, ethyl acetate, propyl acetate, butyl acetate or a mixture thereof.
Unless stated to the contrary, any of the words “comprising”, “comprises” mean “including without limitation” and shall not be construed to limit any general statement that it follows to the specific or similar items or matters immediately following it.
Embodiments of the invention are not mutually exclusive, but may be implemented in various combinations. The described embodiments of the invention and the disclosed examples are given for the purpose of illustration rather than limitation of the invention as set forth in the appended claims.
The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention.

EXAMPLES
Example 1: Process for the separation of mono and di-halo substituted 4-trihalomethyl pyridines
Chlorinated mixture (1200g) containing 2-chloro-4-trichloromethylpyridine (content-45%) and 2,6-dichloro-4-trichloromethylpyridine (content-47%) was mixed in hexane (800.0g, 9.3mol). Then, the mixture was added to 68% of sulfuric acid (2000g, 13.8mol) at the reaction temperature between 0-15°C under stirring and maintained the temperature for 30 minutes. Thereafter, the reaction mixture was followed by layer separation. The organic layer was separated and evaporated to get 2,6-dichloro-4-trichloromethylpyridine (596.0g) having purity of 92%, further sulfuric layer was diluted with water (1000g) and extracted with dichloromethane (1000g) followed by evaporation to obtain 2-chloro-4-trichloromethyl pyridine (525.0g) having purity of >95%. Recovery percentage of 2-chloro-4-trichloromethylpyridine is 92.7% and recovery percentage of 2,6-dichloro-4-trichloromethylpyridine is 97.2%.
Example 2: Process for the separation of mono and di-halo substituted 4-trihalomethyl pyridines
A mixture (1000g) containing 2-chloro-4-trifluoromethylpyridine (content-60%) and 2,6-dichloro-4-trifluoromethylpyridine (content-35%) was mixed in hexane (800.0g, 9.3mol). Then, the mixture was added to 68% of sulfuric acid (2000g, 13.8mol) at the reaction temperature 0-15°C under stirring and maintained the temperature for 30 minutes. Thereafter, the reaction mixture was followed by layer separation. The organic layer was separated and evaporated to form 2,6-dichloro-4-trifluoromethylpyridine (358.0g) having purity of 94%, further sulfuric layer was diluted with water (1000g) and extracted with dichloromethane (1000g) followed by evaporation to obtain 2-chloro-4-trifluoromethyl pyridine (601.0g) having purity of >95%. Recovery percentage of 2-chloro-4-trifluoromethylpyridin is 95.2% and recovery percentage of 2,6-dichloro-4-trifluoromethylpyridine is 96.1%.

WE CLAIM:

1. A process for separation of a mixture of compounds of Formula I and Formula II,

Formula-I Formula-II
wherein X is independently selected from F, Cl and Br; n is an integer from 1-3, n1 and n2 are an integer from 1-4 provided that n2 >n1,
comprising the step of adding an acid to a mixture of compounds of Formula I and II to isolate substantially pure compounds of Formula I and II.

2. The process as claimed in claim 1, wherein the acid is selected from a group consisting of trifluoroacetic acid, trifluoromethanesulfonic acid and inorganic acid is selected from hydrochloric acid, sulfuric acid and methanesulfonic acid.

3. The process as claimed in claim 1, wherein an acid is added to a mixture of compounds of Formula I and II in a nonpolar solvent at a temperature of 0-15°C, followed by isolating the compound of formula II from the organic layer and isolating the compound of formula I from the acid layer.

4. The process as claimed in claim 3, wherein nonpolar solvent is selected from a group consisting of hexane, heptanes, toluene and cyclohexane or a mixture thereof.

5. The process as claimed in claim 3, wherein the compound of formula I is isolated from an acid layer using a solvent selected from a group consisting of chlorinated solvents such as dichloromethane or carbontetrachloride, dichloroethane, 1,1,2,2-tetrachloroethane, an ether solvent such as diethylether, diisopropyl ether, tert-butyl methyl ether, tetrahydrofuran, a nitrile solvent such as acetonitrile or an ester solvent such as methyl acetate, ethyl acetate, propyl acetate and butyl acetate or a mixture thereof.