FIELD OF THE INVENTION
The present invention provides a one pot process for preparation of chlorinated trifluoromethylpyridines. They are valuable intermediates for synthesis of active agrochemical and pharmaceutical ingredients.

BACKGROUND OF THE INVENTION
Halogenated pyridines such as chlorinated trifluoromethylpyridines serve as important intermediates in agrochemical industry for example for synthesis of fluazinam and fluopicolide.
Several methods for preparation of chlorinated trifluoromethylpyridines are known in literature.
CN-A-102382048 discloses a process for preparation of 2,3-dichloro-5-trifluoromethylpyridine by chlorination of 5-methylpyridine with chlorine gas in carbon tetrachloride at 350-450? to form 2,3-dichloro-5-trichloromethylpyridine, which on reaction with hydrogen fluoride and potassium fluoride produces 2,3-dichloro-5-trifluoromethylpyridine. The process involves two steps for preparation of titled compound involving chlorination followed by fluorination.
EP-A-0110690 discloses a process for the preparation of 2,3-dichloro-5-trifluoromethylpyridine by reacting 2,3-dichloro-5-trichloromethylpyridine with anhydrous hydrogen fluoride in presence of metal catalysts. The process is tedious as it results undesirable amount of organic fluoride waste that needs to be treated and removed.
U.S. 4,288,599 discloses a process for chlorinating and fluorinating ß-picoline in a vapour phase in presence of a diluent or solvent, yielding a mixture of products containing fluorinated side chain methyl group and chlorinated a-position such as 2-chloro-5-trifluoromethylpyridine and 2,6-dichloro-5-trifluoromethylpyridine.
Further, it has been found that it is difficult to produce trifluoromethylpyridine derivatives having chlorine atoms at meta and para positions to the trifluoromethyl group on the pyridine ring. However, due to an increasing demand in recent years it is desirable to develop an industrially advantageous process for production of 5-trifluoromethylpyridine derivatives mainly having chlorine at 2 and 3-positions of the pyridine ring.
The cited references have several drawback such as unnecessary use of solvent, need complex systems, longer reaction time and have low selectivity towards the desired product.
Therefore, there is a need to develop a process, that is, economical and industrially viable and overcome the drawback of existing processes.
Thus it is an object of the present invention to provide a simple process for the preparation of chlorinated trifluoromethylpyridine in single synthetic step without involving use of any solvent.

OBJECT OF THE INVENTION
The main object of present invention is to provide a cost-effective and a scalable one pot process for preparation of chlorinated trifluoromethylpyridines using a catalyst to increase the overall efficiency of the process at industrial scale.

SUMMARY OF THE INVENTION
The present invention provides a one pot process for preparation of chlorinated trifluoromethylpyridine derivatives, comprising the step of simultaneous fluorination and chlorination of methylpyridines in presence of a catalyst.

DETAILED DESCRIPTION OF THE INVENTION
The term about as used herein describes 10% variation from the specified value.
The present invention provides a one pot process for preparation of chlorinated trifluoromethylpyridine derivatives, comprising the steps of simultaneous fluorination and chlorination of methylpyridines in presence of a catalyst.
The chlorinated trifluoromethylpyridines may be selected from 2,3-dichloro-5-trifluoromethylpyridine, 2,3-dichloro-6-trifluoromethylpyridine and 2,6-dichloro-4-trifluoromethylpyridine.
In an embodiment, the present invention provides a one pot process for preparation of 2,3-dichloro-5-trifluoromethylpyridine comprising the step of simultaneous fluorination and chlorination of 3-methylpyridine in presence of a catalyst.
In another embodiment, the present invention provides a one pot process for preparation of 2,3-dichloro-6-trifluoromethylpyridine comprising the step of simultaneous fluorination and chlorination of 2-methylpyridine in presence of a catalyst.
In another embodiment, the present invention provides a one pot process for preparation of 2,6-dichloro-4-trifluoromethylpyridine comprising the step of simultaneous fluorination and chlorination of 4-methylpyridine in presence of a catalyst.
In an embodiment of the present invention, the catalyst may be selected from chromium oxide, aluminium oxide, fluorinated chromium oxide, fluorinated aluminium oxide, Lewis acids such as aluminium trichloride, ferric chloride, ferrous chloride, titanium tetrachloride, zinc chloride, cuprous chloride, cupric chloride, nickel chloride, zirconium chloride, aluminium chloride, lanthanum chloride, tin chloride, antimony chloride or the mixture thereof.
In another embodiment of the present invention, the catalyst may be a mixture of activated chromium oxide and/or aluminium oxide and a Lewis acid.
In another embodiment of the present invention, the activation of the catalyst may be performed by heating the catalyst in anhydrous hydrogen fluoride.
In another embodiment of the present invention, the catalyst is heated with anhydrous hydrogen fluoride at a temperature of 100 to 400ºC.
In another embodiment of the present invention, the heating of chromium oxide/aluminium oxide is carried out together in a reactor.
In another embodiment of the present invention, the heating of chromium oxide/aluminium oxide and Lewis acid may be carried out together in a reactor.
In another embodiment of the present invention, the heating of chromium oxide/aluminium oxide and Lewis acid may be carried out separately.
In another embodiment of the present invention, the Lewis acid may be doped on activated carbon.
In another embodiment of the present invention, the process may be carried out in absence of a solvent or a diluent.
The “absence of solvent” refers to the process in which no solvent is used to aid the reaction. The absence of solvent reduces cost of process and generate less effluent after reaction.
In another embodiment of the present invention, the process is carried out in vapour phase.
In another embodiment of the present invention, the process may be carried out in a corrosion resistant reactor.
In another embodiment of the present invention, the corrosion resistant reactor comprised of materials which are resistant to corrosion as Hastelloy, Inconel, Monel and/or fluoropolymers linings.
In another embodiment, a mixture of 3-methylpyridine and hydrofluoric acid is preheated to about 250°C to 300°C.
In another embodiment, a chlorine gas is preheated to about 280°C to 300°C.
In another embodiment, the one pot process for preparation of chlorinated trifluoromethylpyridines produces small amounts of mono chloro trifluoromethylpyridine that can be recycled back to the reactor to enhance the overall efficiency of the process.
In another embodiment, the one pot process for preparation of 2,3-dichloro-5-trifluoromethylpyridine produces small amounts of 2-chloro-5-trifluoromethylpyridine that can be recycled back to the reactor to enhance the overall efficiency of the process.
The methylpyridines used as a raw material in the present invention may be prepared by known method or can be obtained commercially.
The completion of the reaction may 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), liquid chromatography (LC) and alike.
The reagents used in the above process are obtained commercially.
Unless stated to the contrary, any of the words “comprising”, “comprises” and includes 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 example is given by way of illustration and therefore should not be construed to limit the scope of the present invention.

EXAMPLES
Example 1: Preparation of 2,3-dichloro-5-trifluoromethylpyridine
A mixture of fluorinated chromia & ferric chloride doped on carbon catalyst (150g) was packed in an Inconel tubular reactor. The reaction tube was heated to a temperature of 300°C. The preheated mixture of 3-methylpyridine and hydrofluoric acid at about 280°C was fed into the first reaction mixture of tube at such a rate that the former goes 0.14g/min and the latter was 0.9g/min for 5 hours to form a gaseous mixture. Thereafter preheated chlorine gas at about 280°C was fed into the reaction tube of a gaseous mixture at a rate of 1g/min for 5 hours. Then the gas discharged from the reactor was condensed by passing it through a water scrubbing column followed by alkaline scrubbing column. The resulting product was extracted by dichloromethane (100g), washed with 10% aqueous potassium carbonate solution (100 ml) and dried over sodium sulfate. The crude product was analysed by gas chromatography.
Example 2: Preparation of 2,3-dichloro-5-trifluoromethylpyridine
A mixture of fluorinated alumina and fluorinated chromia catalyst (150g) was packed in an Inconel tubular reactor. The reaction tube was heated to a temperature about 300°C. The preheated mixture of 3-methylpyridine and hydrofluoric acid at about 280°C was fed into the first reaction mixture of tube at such a rate that the former goes 0.14g/min and the latter was 0.9g/min for 5 hours to form a gaseous mixture. Thereafter preheated chlorine gas at about 280°C was fed into the reaction tube of a gaseous mixture at a rate of 1g/min for 5 hours. Then the gas discharged from the reactor was condensed by passing it through a water scrubbing column followed by alkaline scrubbing column. The resulting product was extracted by dichloromethane (102g), washed with 10% aqueous potassium carbonate solution (110 ml) and dried over sodium sulfate. The crude product was analysed by gas chromatography.

Example 3: Preparation of 2,3-dichloro-6-trifluoromethylpyridine
A mixture of fluorinated alumina and fluorinated chromia catalyst was packed in an Inconel tubular reactor. The reaction tube was heated to a temperature about 300°C. The preheated mixture of 2-methylpyridine and hydrofluoric acid at about 280°C was fed into the first reaction mixture of tube at such a rate that the former goes 0.14g/min and the latter was 0.9g/min for 5 hours to form a gaseous mixture. Thereafter preheated chlorine gas at about 280°C was fed into the reaction tube of a gaseous mixture at a rate of 1g/min for 5 hours. Then the gas discharged from the reactor was condensed by passing it through a water scrubbing column followed by alkaline scrubbing column. The resulting product was extracted by dichloromethane (104g), washed with 11% aqueous potassium carbonate solution (104 ml) and dried over sodium sulfate. The crude product was analysed by gas chromatography.
Example 4: Preparation of 2,3-dichloro-4-trifluoromethylpyridine
A mixture of fluorinated alumina & ferric chloride doped on carbon catalyst was packed in an Inconel tubular reactor. The reaction tube was heated to a temperature about 300°C. The preheated mixture of 4-methylpyridine and hydrofluoric acid at about 280°C was fed into the first reaction mixture of tube at such a rate that the former goes 0.14g/min and the latter was 0.9g/min for 5 hours to form a gaseous mixture. Thereafter preheated chlorine gas at about 280°C was fed into the reaction tube of a gaseous mixture at a rate of 1g/min for 5 hours. Then the gas discharged from the reactor was condensed by passing it through a water scrubbing column followed by alkaline scrubbing column. The resulting product was extracted by dichloromethane (100g), washed with 10% aqueous potassium carbonate solution (100 ml) and dried over sodium sulfate. The crude product was analysed by gas chromatography.

CLAIMS:WE CLAIM:
1. A one pot process for preparation of chlorinated trifluoromethylpyridines, comprising the step of simultaneous fluorination and chlorination of methylpyridines in presence of a catalyst.
2. The process as claimed in claim 1, wherein the chlorinated trifluoromethylpyridine is selected from a group consisting of 2,3-dichloro-5-trifluoromethylpyridine, 2,3-dichloro-6-trifluoromethylpyridine and 2,6-dichloro-4-trifluoromethylpyridine.
3. The process as claimed in claim 1, wherein the methylpyridine is selected from a group consisting of 2-methylpyridine, 3-methylpyridine and 4-methylpyridine.
4. The process as claimed in claim 1, wherein the catalyst is selected from a group consisting of chromium oxide, aluminium oxide, fluorinated chromium oxide, and fluorinated aluminium oxide or a mixture thereof either alone or in combination with a Lewis acid.
5. The process as claimed in claim 4, wherein, the Lewis acid is selected from a group consisting of aluminium trichloride, ferric chloride, ferrous chloride, titanium tetrachloride, zinc chloride, cuprous chloride, cupric chloride, nickel chloride, zirconium chloride, aluminium chloride, lanthanum chloride, tin chloride, and antimony chloride or a mixture thereof.
6. The process as claimed in claim 1, wherein the activation of the catalyst is performed by heating the catalyst with anhydrous hydrogen fluoride in a temperature range of 100 to 400ºC.
7. The process as claimed in claim 1, wherein the process is carried out in absence of a solvent.
8. The process as claimed in claim 1, wherein a mixture of 3-methylpyridine and hydrofluoric acid is preheated to 250°C to 300°C.
9. The process as claimed in claim 1, wherein a chlorine gas is preheated to 280°C to 300°C.
10. The process as claimed in claim 1, wherein the catalyst is a mixture of activated chromium oxide and/or aluminium oxide and a Lewis acid.