The present invention provides a process for preparation of halogenated methylpyridines of formula I

Formula-I
wherein X represents halogen, amino, aryloxy, alkoxy, cyano, alkyl or carboxy; X1 represent halogen; n represents an integer 1 to 3 and m is 1 or 4.

BACKGROUND OF THE INVENTION
Halogenated methylpyridines serve as important intermediates in agrochemical and pharmaceutical industries.
US Patent No. 4,260,766 discloses a process for the preparation of dichloromethylpyridines by reductive dechlorination of trichloromethylpyridines using metallic iron or a ferrous iron compound and an acid.
The process involving iron or its compound for reductive dechlorination is usually a slow process and suffers from poor selectivity of desired product.
Thus it is an object of the present invention to provide a process for producing halogenated methylpyridines with a high reaction rate and high selectivity.

OBJECT OF THE INVENTION
The main object of present invention is to provide an industrially applicable process for preparation of halogenated methylpyridines.

SUMMARY OF THE INVENTION
The present invention provides a process for preparation of a compound of formula I,

Formula-I
wherein X represents halogen, amino, aryloxy, alkoxy, cyano, alkyl or carboxy; X1 represent halogen; n represents an integer 1 to 3 and m is 1 or 4,
comprising reductive dehalogenation of a compound of Formula II,

Formula-II
wherein X represents halogen, aryloxy, alkoxy, cyano, alkyl or carboxy; X1 represent halogen; n represents an integer 1 to 3 and m is 1 or 4,
using elemental zinc in presence of an acid to obtain the compound of Formula I.

DETAILED DESCRIPTION OF THE INVENTION
As used herein, “an acid” is selected from a group consisting of an organic or an inorganic acid. The examples of organic acid includes acetic acid, p-toluenesulfonic acid, formic acid, trifluoroacetic acid or the like. The examples of inorganic acid includes hydrochloric acid, hydrobromic acid or the like. The examples of inorganic acid salts includes ammonium chloride, ammonium bromide or the like.
The present invention provides a process for preparation of halogenated methylpyridines, comprising the steps of selective reductive dehalogenation of halosubstituted methylpyridine using zinc and an acid.
In an embodiment, the present invention provides a process for preparation of 2-chloro-4-difluoromethylpyridine, comprising a dehalogenation of 2-chloro-4-difluorochloromethylpyridine using zinc and an acid.
In another embodiment, the present invention provides a process for preparation of 2-fluoro-4-difluoromethylpyridine, comprising a dehalogenation of 2-fluoro-4-difluorochloromethylpyridine using zinc and an acid.
In another embodiment, the present invention provides a process for preparation of 2-chloro-4-chlorofluoromethylpyridine, comprising a dehalogenation of 2-chloro-4-dichlorofluoromethylpyridine using zinc and an acid.
In another embodiment, the present invention provides a process for preparation of 2-fluoro-4-chlorofluoromethylpyridine, comprising a dehalogenation of 2-fluoro-4-dichlorofluoromethylpyridine using zinc and an acid.
In another embodiment, the present invention provides a process for preparation of 2-fluoro-4-fluoromethylpyridine, comprising a dehalogenation of 2-fluoro-4-chlorofluoromethylpyridine using zinc and an acid.
In preferred embodiment, the present invention provides a process for preparation of 2-chloro-4-fluoromethylpyridine, comprising a dehalogenation of 2-chloro-4-chlorofluoromethylpyridine using zinc and an acid.
In preferred embodiment, the present invention provides a process for preparation of 2-fluoro-4-methylpyridine, comprising a dehalogenation of 2-fluoro-4-chloromethylpyridine using zinc and an acid.
In preferred embodiment, the present invention provides a process for preparation of 2-chloro-4-methylpyridine, comprising a dehalogenation of 2-chloro-4-chloromethylpyridine using zinc and an acid.
In an embodiments of the present invention, the acid used is selected from organic or inorganic. Preferred acids include hydrochloric acid or acetic acid or the mixture thereof.
In another embodiment of the present invention, the selective hydro-dehalogenation is carried out at a temperature of 30 to 40ºC.
The compound of Formula I so obtained by the present invention has a purity greater than 90 %, more preferably greater than 93% by gas chromatography.
The compound of Formula I so obtained by the present invention has a yield greater than 90 %, more preferably greater than 96%.
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 completion of the reaction can be monitored by any one of chromatographic techniques such as thin layer chromatography (TLC), high pressure liquid chromatography (HPLC), ultra-pressure liquid chromatography (UPLC), Gas chromatography (GC) and alike.
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: Preparation of 2-chloro-4-difluoromethylpyridine
2-chloro-4-chlorodifluoromethylpyridine (1.08mol, Purity-95%) acetic acid (11.4mol) and water (12.5mol) were charged in a reactor equipped with thermometer pocket, condenser and stopper at 25°C. Thereafter zinc dust (82.0g, 1.26mol) was added lot-wise to the reaction mixture below 40°C. After completion of addition, reaction mass stirred for one hour and then filtered to remove the solid particles. Filtrate was extracted with dichloromethane, followed by evaporation to obtain 2-chloro-4-difluoromethylpyridine (182.0g).
Purity: 93% (GC-area %); Yield: 96%.
Example 2: Preparation of 2-fluoro-4-difluoromethylpyridine
2-fluoro-4-difluorochloromethylpyridine (1.08mol, Purity-95%) acetic acid (11.4mol) and water (12.5mol) were charged in a reactor equipped with thermometer pocket, condenser and stopper at 25°C. Thereafter zinc dust (82.0g, 1.26mol) was added lot-wise to the reaction mixture below 40°C. After completion of addition, reaction mass stirred for one hour and then filtered to remove the solid particles. Filtrate was extracted with dichloromethane, followed by evaporation to obtain 2-fluoro-4-difluoromethylpyridine.
Purity: 92% (GC-area %); Yield: 96%.
Example 3: Preparation of 2-chloro-4-chlorofluoromethylpyridine
2-chloro-4-dichlorofluoromethylpyridine (1.08mol, Purity-95%) acetic acid (11.4mol) and water (12.5mol) were charged in a reactor equipped with thermometer pocket, condenser and stopper at 25°C. Thereafter zinc dust (82.0g, 1.26mol) was added lot-wise to the reaction mixture below 40°C. After completion of addition, reaction mass stirred for one hour and then filtered to remove the solid particles. Filtrate was extracted with dichloromethane, followed by evaporation to obtain 2-chloro-4-chlorofluoromethylpyridine.
Purity: 94% (GC-area %); Yield: 97%.
Example 4: Preparation of 2-fluoro-4-chlorofluoromethylpyridine
2-fluoro-4-dichlorofluoromethylpyridine (1.08mol, Purity-95%) acetic acid (11.4mol) and water (12.5mol) were charged in a reactor equipped with thermometer pocket, condenser and stopper at 25°C. Thereafter zinc dust (82.0g, 1.26mol) was added lot-wise to the reaction mixture below 40°C. After completion of addition, reaction mass stirred for one hour and then filtered to remove the solid particles. Filtrate was extracted with dichloromethane, followed by evaporation to obtain 2-fluoro-4-chlorofluoromethylpyridine.
Purity: 96% (GC-area %); Yield: 94%.
Example 5: Preparation of 2-fluoro-4-fluoromethylpyridine
2-fluoro-4-chlorofluoromethylpyridine (1.08mol, Purity-95%) acetic acid (11.4mol) and water (12.5mol) were charged in a reactor equipped with thermometer pocket, condenser and stopper at 25°C. Thereafter zinc dust (82.0g, 1.26mol) was added lot-wise to the reaction mixture below 40°C. After completion of addition, reaction mass stirred for one hour and then filtered to remove the solid particles. Filtrate was extracted with dichloromethane, followed by evaporation to obtain 2-fluoro-4-fluoromethylpyridine.
Purity: 98% (GC-area %); Yield: 92%.
Example 6: Preparation of 2-chloro-4-fluoromethylpyridine
2-chloro-4-chlorofluoromethylpyridine (1.08mol, Purity-95%) acetic acid (11.4mol) and water (12.5mol) were charged in a reactor equipped with thermometer pocket, condenser and stopper at 25°C. Thereafter zinc dust (82.0g, 1.26mol) was added lot-wise to the reaction mixture below 40°C. After completion of addition, reaction mass stirred for one hour and then filtered to remove the solid particles. Filtrate was extracted with dichloromethane, followed by evaporation to obtain 2-chloro-4-fluoromethylpyridine.
Purity: 95% (GC-area %); Yield: 95%.
Example 7: Preparation of 2-fluoro-4-methylpyridine
2-fluoro-4-chloromethylpyridine (1.08mol, Purity-95%) acetic acid (11.4mol) and water (12.5mol) were charged in a reactor equipped with thermometer pocket, condenser and stopper at 25°C. Thereafter zinc dust (82.0g, 1.26mol) was added lot-wise to the reaction mixture below 40°C. After completion of addition, reaction mass stirred for one hour and then filtered to remove the solid particles. Filtrate was extracted with dichloromethane, followed by evaporation to obtain 2-fluoro-4-methylpyridine.
Purity: 99% (GC-area %); Yield: 98%.
Example 8: Preparation of 2-chloro-4-methylpyridine
2-chloro-4-chloromethylpyridine (1.08mol, Purity-95%) acetic acid (11.4mol) and water (12.5mol) were charged in a reactor equipped with thermometer pocket, condenser and stopper at 25°C. Thereafter zinc dust (82.0g, 1.26mol) was added lot-wise to the reaction mixture below 40°C. After completion of addition, reaction mass stirred for one hour and then filtered to remove the solid particles. Filtrate was extracted with dichloromethane, followed by evaporation to obtain 2-chloro-4-methylpyridine.
Purity: 98% (GC-area %); Yield: 95%.

WE CLAIM:

1. A process for preparation of a compound of formula I,

Formula-I
wherein X represents halogen, amino, aryloxy, alkoxy, cyano, alkyl or carboxy; X1 represent halogen; n represents an integer 1 to 3 and m is 1 or 4,
comprising reductive dehalogenation of a compound of Formula II,

Formula-II
wherein X represents halogen, aryloxy, alkoxy, cyano, alkyl or carboxy; X1 represent halogen; n represents an integer 1 to 3 and m is 1 or 4,
using elemental zinc in presence of an acid to obtain the compound of Formula I.
2. The process as claimed in claim 1, wherein the acid is selected from a group consisting of an organic or an inorganic acid.
3. The process as claimed in claim 2, wherein the organic acid is selected from acetic acid, p-toluenesulfonic acid, formic acid, trifluoroacetic acid and inorganic acid is selected from hydrochloric acid and hydrobromic acid.
4. The process as claimed in claim 1, wherein the reaction is carried out at a temperature of 30 to 40ºC.
5. The process as claimed in claim 1, wherein the compound of Formula I is obtained with a purity greater than 90%.
6. The process as claimed in claim 1, wherein the compound of Formula I is obtained with a yield greater than 90%.