The present invention provides a process for preparation of a compound of formula I,

Formula I
wherein X and X1 are independently selected from a halogen, CX13 is present at either 3-position or 5-position; R is independently selected from C1-C3 alkyl; n ranges from 0-3.

BACKGROUND OF THE INVENTION
The halogen substituted halomethylalkoxypyridines are valuable building blocks in organic systems such as pharmaceutical or agrochemical synthesis, e.g. herbicide, fungicide or insecticides.
Various methods are known in the art for preparation of halogen substituted trihalomethylalkoxypyridine.
The Journal of Fluorine Chemistry 79 (1996) 9-12 discloses methoxylation of 2,3-dichloro-5-trifluoromethylpyridine using sodium hydride, dimethylformamide and methanol at room temperature to give 2-methoxy-3-chloro-5-trifruoromethylpyridine in 60% yield.
PCT No. WO2013088404A1 discloses a process for preparation of 2-methoxy-3-trifluoromethylpyridine by reacting 2-chloro-3-trifluoromethylpyridine with a solution of sodium methoxide in methanol to form 2-methoxy-3-trifluoromethylpyridine in 89% yield.
The processes available in literature provides very less yield or take longer time for reaction completion or both, therefore there is a need to develop a cost effective and economical process for preparation of substituted alkoxypyridine at commercial scale.

OBJECT OF THE INVENTION
An object of the present invention is to provide a novel, commercially viable and an alternate process for producing substituted alkoxypyridine.

SUMMARY OF THE INVENTION
In an aspect, the present invention provides a process for preparation of a compound of formula I,

Formula I
wherein X and X1 are independently selected from a halogen, CX13 is present at either 3-position or 5-position; R is independently selected from C1-C3 alkyl; n ranges from 0-3.
comprising the step of reacting a compound of formula II,

Formula II
wherein L is a leaving group, X and X1 are independently selected from a halogen, n ranges from 0-3,
with alkali metal alkoxide in presence of a solvent to obtain the compound of formula 1, wherein the compound of formula I is obtained with a yield greater than 98%.

DETAILED DESCRIPTION OF THE INVENTION
As used herein, “L” is a leaving group selected from halogen, or mesylate, tosylate or the like.
As used herein, the group “X” is a halogen selected from fluorine, chlorine, bromine or iodine. The group “X” can be present at any position on the ring such as at position 2-, 3-, 4-, or 6- with respect to the ring nitrogen. The preferred position is 3- with respect to the ring nitrogen.
As used herein, “CX13” is selected from CClF2, CCl2F, CF3, CCl3 or the like. It is further provided that when L is chloro, then CX13 is either CF2Cl, or CFCl2.
As used herein, “R” is C1-C3 alkyl group. The C1-C3 alkyl group is selected from methyl, ethyl, propyl and isopropyl or the like.
As used herein, alkali metal alkoxide is sodium alkoxide or potassium alkoxide selected from the group comprising sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, sodium propoxide and potassium propoxide or the like.
In another embodiment, the present invention provides a process for preparation of a compound of formula I,

Formula I
wherein X and X1 are independently selected from a halogen, CX13 is present at either 3-position or 5-position; R is independently selected from C1-C3 alkyl; n ranges from 1-3
comprising a step of reacting a compound of formula II, with alkali metal alkoxide in presence of a solvent to obtain the compound of formula I with a yield of greater than 98%, wherein, the reaction is carried out at a temperature in the range of 40 to 100°C.
The process may be carried out in a solvent selected from water, alcohols such as methanol, ethanol, isopropanol, propanol and n-propanol or like.
In an embodiment of the present invention, the reaction is carried out at a temperature in the range of 40 to 100°C, preferably in the range of 65-70°C.
In an embodiment, alkyloxylation takes place in 1-2 hours. The short reaction time is advantageous in achieving high yield and prevent impurity formation under pressure.
In another embodiment of the present invention, the process is carried out in absence of any catalyst.
In another embodiment of the present invention, the process is carried out in absence of any phase transfer catalyst.
In an embodiment, the present invention provides a process for preparation of compound of formula I having yield greater than 98% and more preferably greater than 99%.
The compound of formula I refers to a compound selected from 3-chloro-2-methoxy-5-(trifluoromethyl)pyridine, 3-chloro-2-methoxy-5-(chlorodifluoromethyl)pyridine, 5-(chlorodifluoromethyl)-2-methoxy-pyridine, 3-bromo-2-ethoxy-5-(trifluoromethyl)pyridine, 3-fluoro-2-propoxy-5-(trifluoro methyl)pyridine, 2-methoxy-5-(trifluoromethyl)pyridine, 3-chloro-2-methoxy-5-(dichlorofluoromethyl)pyridine, 2-methoxy-5-(dichlorofluoromethyl)pyridine, 2-chloro-6-methoxy-3-dichlorofluoromethylpyridine, 2-bromo-6-methoxy-3-dichlorofluoromethylpyridine, 2-bromo-6-methoxy-3-trifluoro methylpyridine, 5-chloro-2-methoxy-3-dichlorofluoromethylpyridine, 2-methoxy-3-(dichlorofluoromethyl)pyridine, 5-bromo-2-methoxy-3-(trifluoro methyl)pyridine, 2-methoxy-3-(trifluoromethyl)pyridine, 5-chloro-2-methoxy-3-(chlorodifluoromethyl)pyridine and 2-methoxy-3-(chlorodifluoromethyl)pyridine or the like.
The compound of formula II may refer to a compound selected from 3-chloro-2-fluoro-5-trifluoromethylpyridine, 2,3-dichloro-5-chlorodifluoromethylpyridine, 2,3-dichloro-5-trifluoromethylpyridine, 5-chloro-2-fluoro-3-(dichlorofluoro methyl)pyridine, 2,5-dichloro-3-(dichlorofluoromethyl)pyridine, 5-chloro-2-fluoro-3-(chlorodifluoromethyl)pyridine, 2-fluoro-3-(chlorodifluoromethyl) pyridine, 5-bromo-2-fluoro-3-(trifluoromethyl)pyridine, 2-fluoro-3-(trifluoromethyl)pyridine, 2,5-dibromo-3-(trifluoromethyl)pyridine and 2-chloro-3-(dichlorofluoromethyl)pyridine or like.
The compound of the present invention can be isolated using various isolation techniques known in the art, for example, chemical separation, extraction, acid-base neutralization, distillation, evaporation, column chromatography and filtration or a mixture thereof.
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.
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: Preparation of 3-chloro-2-methoxy-5-(trifluoromethyl)pyridine
A solution of sodium methoxide (28g, 0.154mol, 30%) and methanol (250ml) was charged into a round bottle flask (250ml). The reaction mixture was heated to 68°C. Thereafter 2,3-dichloro-5-(trifluoromethyl)pyridine (25g, 0.1157mol) was added drop wise to the reaction mixture and refluxed at 65-70°C for 1 hour. After completion of the reaction, water (100g, 5.55mol) was added into reaction mass at 25-30°C to obtain the 3-chloro-2-methoxy-5-(trifluoromethyl)pyridine.
Purity: 99.0 %; Yield: 98.3 %.
Example 2: Preparation of 3-chloro-2-methoxy-5-(trifluoromethyl)pyridine
A solution of sodium methoxide (30g, 0.166mol, 30%) and methanol (250ml) was charged into a round bottle flask (250ml). The reaction mixture was heated to 68°C. Thereafter 3-chloro-2-fluoro-5-(trifluoromethyl)pyridine (25g, 0.125mol) was added drop wise to the reaction mixture and refluxed at 70°C for 1 hour. After completion of the reaction, water (100g, 5.55mol) was added into reaction mass at 30°C to obtain 3-chloro-2-methoxy-5-(trifluoromethyl)pyridine.
Purity: 99.0 %; Yield: 99.2 %.
Example 3: Preparation of 3-chloro-2-ethoxy-5-(trifluoromethyl)pyridine
A solution of sodium ethoxide (50g, 0.154mol, 21%) and ethanol (250ml) was charged into a round bottle flask (250ml). The reaction mixture was heated to 65°C. Thereafter 2,3-dichloro-5-(trifluoromethyl)pyridine (25g, 0.1157mol) was added drop wise to the reaction mixture and refluxed at 67°C for 1 hour. After completion of the reaction, 100g (5.55mol) of water was added into reaction mass at 25-30°C to obtain 3-chloro-2-ethoxy-5-(trifluoromethyl)pyridine.
Purity: 98.7 %; Yield: 98.8 %.
Example 4: Preparation of 3-chloro-2-methoxy-5-(dichlorofluoromethyl) pyridine
A solution of sodium methoxide (24g, 0.133mol, 30%) and methanol (250ml) was charged into a round bottle flask (250ml). The reaction mixture was heated to 68°C. Thereafter 2,3-dichloro-5-(dichlorofluoromethyl)pyridine (25g, 0.100mol) was added drop wise to the reaction mixture and refluxed at 67-70°C for 1 hour. After completion of the reaction, water (100g, 5.55mol) was added into reaction mass at 25-30°C to obtain 3-chloro-2-methoxy-5-(dichlorofluoromethyl)pyridine.
Purity: 99.0 %; Yield: 98.9%.

WE CLAIM:

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

Formula I
wherein X and X1 are independently selected from a halogen, CX13 is present at either 3-position or 5-position; R is independently selected from C1-C3 alkyl; n ranges from 0-3.
comprising the step of reacting a compound of formula II,

Formula II
wherein L is a leaving group, X and X1 are independently selected from a halogen, n ranges from 0-3,
with alkali metal alkoxide in presence of a solvent to obtain the compound of formula 1, wherein the compound of formula I is obtained with a yield greater than 98%.
2. The process as claimed in claim 1, wherein the reaction is carried out at a temperature in the range of 40 to 100°C.
3. The process as claimed in claim 1, wherein the reaction is carried out at a temperature in the range of 65 to 70°C.
4. The process as claimed in claim 1, wherein the alkali metal alkoxide is sodium alkoxide or potassium alkoxide selected from a group consisting of sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, sodium propoxide and potassium propoxide.
5. The process as claimed in claim 1, wherein the solvent is selected from a group consisting of water, methanol, ethanol, isopropanol, propanol and n-propanol or a mixture thereof.