Field of the invention
The present invention relates to a novel process for producing mono or di halo substituted trichloromethyl pyridine selectively by reacting 4-methyl pyridine (also known as 4-picoline) with chlorine in gaseous phase to give mono or di halo substituted trichloromethyl pyridine selectively by using a specific range of temperature.
Background of the invention
Mono or di halo substituted trichloromethyl pyridine are used as an intermediate for medicines, agricultural chemicals and dyes especially herbicides. The mono or di halo substituted trichloromethyl pyridine compounds can be prepared by rapidly mixing, in the vapor phase, chlorine, an appropriate methyl pyridine compound in an inert diluent and subjecting the mixture to temperatures of about 400-490°C or 240-270°C for a brief contact time. The desired products can then be distilled from the resulting product stream.
U.S. Patent no. 3,412,095 discloses vapor phase chlorination of 4-picoline at a temperature in the range of 230-260°C using steam as inert medium and with a contact time of 3.8 seconds to give 4-trichloromethylpyridine.
The said patent is silent about the synthesis of mono or di halo substituted trichloromethyl pyridine. Moreover, the present invention involves chlorination of 4-picoline to obtain mono or di halo substituted trichloromethyl pyridine.
It has been observed that selective preparation of mono or di halo substituted trichloromethyl pyridine has not been reported in prior art.
Therefore, there is an urgent need to develop a process for preparing mono or di halo substituted trichloromethyl pyridine, selectively.

Object of the invention
The main object of the present invention is to provide simple, cost effective and industrially applicable selective process for preparation of mono or di halo substituted trichloromethyl pyridine by vapour phase chlorination by using a specific range of temperature. Summary of the invention
A first aspect of the present invention provides a process for preparation of a compound of formula I,
Formula I wherein Xcan independently be selected from H or CI;
comprises of reacting 4-picoline with chlorine in the presence of inert diluent at a temperature in the range of 300-450°C to obtain compound of formula I.
A second aspect of the present invention provides a process for preparation of an enriched compound of formula la,
Formula la comprises of:
a) reacting 4-picoline with chlorine in the presence of inert diluent at a temperature in the range of 300-370°C to obtain an enriched compound of formula la and
b) optionally, isolating the enriched compound of formula la from the step a).
A third aspect of the present invention provides a process for preparation of an enriched compound of formula lb,

Formula lb comprises of:
a) reacting 4-picoline with chlorine in the presence of inert diluent at a temperature in the range of 370-450°C to obtain an enriched compound of formula lb and
b) optionally, isolating the enriched compound of formula lb from the step a).
Detailed description of the invention
As used herein enriched compound refers to a compound having purity percentage at least 40% or preferably at least 50% in the crude compound.
As used herein crude compound refers to a mixture of compound of formulae la and lb.
The present invention provides a process for preparation of a compound of formula I by vapour phase chlorination of 4-picoline.
In the said vapour phase chlorination process, 4-picoline is reacted with chlorine in the presence of inert diluent at a temperature in the range of 300-450°C to obtain a compound of formula I.
In one embodiment of the present invention, 4-picoline is pre-heated to obtain vapours of 4-picoline and chlorine is pre-heated at a temperature in the range of 200-300°C. Thereafter, 4-picoline and the pre-heated chlorine gas is reacted in the presence of inert diluent at a temperature in the range of 300-450°C.
In one embodiment of the present invention, inert diluent used in the reaction is preferably nitrogen gas.
In one embodiment of the present invention, the reaction time of vapour phase chlorination is between 20-50 hours.
In one embodiment of the present invention, the reaction time of vapour phase chlorination is preferably between 30-50 hours.

In one specific embodiment, the present invention provides a process for the preparation of an enriched compound of formula la; wherein 4-picoline is reacted with chlorine in the presence of inert diluent at a temperature in the range of 300-370°C for the time upto 50 hours to obtain an enriched compound of formula la. Optionally, the enriched compound of formula la may be isolated.
In other embodiment, the present invention provides a process for the preparation of an enriched compound of formula lb; wherein 4-picoline is reacted with chlorine in the presence of inert diluent at a temperature in the range of 370-450°C for the time upto 40 hours to obtain an enriched compound of formula lb. Optionally, the enriched compound of formula lb may be isolated.
The enriched compound of formulae la or lb may be isolated by using techniques known in the art for example distillation, extraction, evaporation, column chromatography and layer separation or combination thereof.
In one embodiment of the present invention, the compounds of formulae la or lb is isolated by layer separation or followed by distillation. The layer may optionally be washed with water or with a solution of a base.
The base may be selected from the group consisting of sodium bicarbonate, sodium carbonate, potassium bicarbonate and potassium carbonate or a like.
4-picoline can be prepared by using processes known in the art or it can be purchased from market.
Unless stated to the contrary, any of the words "comprising" and
"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: Process for preparing 2,6-dichloro-4-(trichloromethyl)pyridine
Pre-heated 4-methylpyridine (0.2g /min, 2.14 mmole) and chlorine (l.Og/min, 14
mmole) was added into a one meter glass reactor packed with spiral glass packing at 380°C for 32 hours. Along with 4-methylpyridine and chlorine, nitrogen gas was fed into the reactor at rate of 40cc/minute as a diluent. Reactor outlet material was diluted with dichloromethane and then washed with water followed by sodium carbonate solution. Dichloromethane layer was concentrated and obtained 740g of crude product having enriched amount of the titled compound, analysed by GC and showing below results:

Example 2: Process for preparing 2-chloro-4-(trichloromethyl) pyridine
Pre-heated 4-methylpyridine (0.2g /min, 2.14 mmole) and chlorine (l.Og/min, 14
mmole) was added into a one meter glass reactor packed with spiral glass packing at 365°C for 46 hours. Along with 4-methylpyridine and chlorine, nitrogen gas was fed into the reactor at rate of 40cc/min as a diluent. Reactor outlet material was diluted with dichloromethane and then washed with water followed by sodium carbonate solution. Dichloromethane layer was evaporated to get 1183g of crude product having enriched amount of the titled compound, analysed by GC and showing below results:
It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention and specific examples provided herein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention that come within the scope of any claims and their equivalents.

We Claim:
1. A process for preparation of compounds of formula I,
Formula I wherein Xcan independently be selected from H or CI;
comprises of reacting preheated 4-picoline with preheated chlorine in presence of inert diluent at a temperature in the range of 300-450°C to obtain the compounds of formula I,
wherein inert diluent is nitogen or argon. 2. A process for preparation of an enriched compound of formula la,
Formula la comprising the steps of:
a) reacting preheated 4-picoline with preheated chlorine in presence of inert diluent at a temperature in the range of 300-370°C to obtain an enriched compound of formula la; and
b) optionally, isolating the enriched compound of formula la from the step a), wherein inert diluent is nitogen or argon.
3. A process for preparation of an enriched compound of formula lb,
Formula lb

comprising the steps of:
a) reacting preheated 4-picoline with preheated chlorine in the presence of inert diluent at a temperature in the range of 370-450°C to obtain an enriched compound of formula lb; and
b) optionally, isolating the enriched compound of formula lb from the step a), wherein inert diluent is nitogen or argon.

4. The process as claimed in claims 1, 2, and 3, wherein chlorine and 4-picoline is pre-heated at a temperature in the range 200-300°C to form vapours.
5. The process as claimed in claims 1, 2, and 3, wherein reaction time is 20-50 hours.
6. The process as claimed in claims 3 and 4, wherein enriched compound refers to a compound having purity percentage at least 40% or preferably at least 50%.
7. The process as claimed in claims 1, 2, and 3, wherein, nitrogen gas is fed into the reactor at a rate of 30cc/minute to 60cc/minute.