DESC:
FIELD OF THE INVENTION
The present invention relates to an improved process for preparation of an anthranilic ester compound of formula (I).

Formula (I)

BACKGROUND OF THE INVENTION
Anthranilic esters are versatile and low-cost starting material/ intermediates for preparing many pharmaceutical and agricultural products.

Anthranilic esters are known to be used for preparing an important synthetic class of insecticides i.e. diamides. The diamide insecticide molecules share the same target site, the ryanodine receptor, and are grouped together under group 28, the ryanodine receptor modulators, of the Insecticide Resistance Action Committee (IRAC) mode of action classification. Diamide insecticides such as Chlorantraniliprole, Cyantraniliprole, Cyclaniliprole, Tetrachlorantraniliprole and Tetraniliprole are well known and are highly potent.

The existing prior arts have disclosed various routes of synthesis for preparing diamide insecticides, many processes proceed through anthranilic ester compound of formula (I).

Formula (I)

Processes for preparation of the intermediate i.e. anthranilic ester of formula (I) are known in the art. However, the sequence of reaction disclosed in prior arts is tedious to perform and less suitable for commercial production. Some of these processes involves use of expensive chlorinating agents such as hypochlorous sodium solution, N-Chlorosuccinimide and the like. Use of such expensive reagents on large scale is not economically feasible.

WO2006062978 discloses a process for preparation of anthranilic ester compound of formula (I) by chlorinating methyl-2-amino-3-methylbenzoate using sulfuryl chloride in acetonitrile. Said process involves addition of small amount sulfuryl chloride over 3-3.5 hours maintaining temperature at 50-55°C followed by immediate cooling to 5°C, and then the work up procedure is carried out. Pointing to the limitation of the process, the process required very slow addition of sulfuryl chloride and then immediate cooling to 5°C. Furthermore, the solvent used for the reaction is acetonitrile which is hygroscopic in nature and may lead to increase in moisture content in the reaction mixture. It is well known that sulfuryl chloride readily reacts with water, thereby leaving the possibility of formation of gaseous by-products in form of oxides of sulfur and this formation of gaseous by-products may continue when the reaction proceeds. At large scale production, the gas evolution is very copious and at any unpredictable time, it can take a form of sudden surge leading to a run-away-reaction like situation leading to reactants getting thrown out of reactor. These limitations and the problems associated with the process make this process cumbersome, inefficient, and risky at commercial scale.
It is therefore necessary to find out a safe way of conducting this reaction on commercial scale and overcoming one or more problems associated with prior art.

OBJECT OF THE INVENTION
It is an object of the present invention to provide a process for the preparation of an anthranilic ester compound of formula (I).

It is another object of the present invention to provide an improved, cost-effective and industrially viable process for preparation of an anthranilic ester compound of formula (I).

It is another object of the present invention to provide a process for preparation of an anthranilic ester compound of formula (I) which does not require extreme temperature conditions, complicated work-up steps.

SUMMARY OF THE INVENTION
According to an aspect of the present invention, there is provided a process for preparation of a compound of formula (I), without isolating the compound of formula (IV)

Formula (I) Formula (IV)

According to another aspect of the present invention, there is provided a process for preparation of an anthranilic ester compound of formula (I),

Formula (I)
comprising
a) methylating a compound of formula (III) with a methylating agent to obtain a compound of formula (IV);

Formula (III) Formula (IV)

b) extracting the compound of formula (IV) with a chlorinated solvent; and treating the separated organic layer with sulfuryl chloride to get an anthranilic ester compound of formula (I).

Formula (IV) Formula (I)

According to another aspect of the present invention, there is provided a process for preparation of an anthranilic ester compound of formula (I),

Formula (I)
comprising
a) methylating a compound of formula (III) with a methylating agent to get a compound of formula (IV)

Formula (III) Formula (IV)
b) treating the compound of formula (IV) with chlorinated solvent and treating the separated organic layer with sulfuryl chloride to get an anthranilic ester compound of formula (I),

Formula (IV) Formula (I)
wherein the compound of formula (III) used in step a) is prepared by reducing the compound of formula (II).

Formula (II) Formula (III)
According to yet another aspect of the present invention, there is provided a process for preparation of anthranilic ester compound of formula (I),

Formula (I)
comprising
a) methylating compound of formula (III) with a methylating agent to obtain compound of formula (IV);

Formula (III) Formula (IV)
b) extracting the compound of formula (IV) with a chlorinated solvent and treating the separated organic layer with sulfuryl chloride to obtain anthranilic ester compound of formula (I),

Formula (IV) Formula (I)
wherein the compound of formula (III) used in step a) is prepared by reducing compound of formula (II) in presence of platinum catalyst.

Formula (II) Formula (III)

DESCRIPTION OF THE INVENTION
The following description is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. The invention also includes all such steps, features, compositions and methods referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more said steps or features.

Definitions:
For convenience, before further description of the present invention, certain terms employed in the specification, examples are described here. These definitions should be read in light of the remainder of the disclosure and understood as by a person of skill in the art. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by a person of ordinary skill in the art. The terms used throughout this specification are defined as follows, unless otherwise limited in specific instances.

The term ‘room temperature’ unless stated otherwise, essentially means temperature in range of 20-35 °C.

The term "purity" means purity as determined by HPLC ("High Pressure Liquid Chromatography").

The term “about” or “approximately” as used herein is inclusive of the stated value and means within an acceptable range of deviation for particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (i.e., the limitations of the measurement system). For example, “about” can mean within one or more standard deviations, or within ± 10 or ± 5 of the stated value. Recitation of ranges of values are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. The endpoints of all ranges are included within the range and independently combinable. It is understood that where a parameter range is provided, all integers within that range, and tenths thereof, are also provided. For example, “0.1-80%” includes 0.1%, 0.2%, 0.3%, etc. up to 80%.As used herein, the terms “comprising” “including,” “having,” “containing,” “involving,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to.

The terms “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. In an embodiment, the aspects and embodiments described herein shall also be interpreted to replace the clause “comprising” with either “consisting of” or with “consisting essentially of” or with “consisting substantially of”.

The present invention describes an improved process for the preparation of anthranilic ester compound of formula (I). The process of the present invention is based on a new sequence of reactions which can be easily implemented at large production batches to provide desired compound in high yield without involving any risk of release of violent gaseous by-products, arising due to use of sulfuryl chloride. Hence, process provided in the present invention is economical, environment friendly and safe.

According to an aspect of the present invention, there is provided a process for preparation of an anthranilic ester compound of formula (I), without requiring isolation of compound of formula (IV)

Formula (I) Formula (IV)

In an embodiment, there is provided a process for preparation of an anthranilic ester of formula (I),

Formula (I)
comprising
i) methylating compound of formula (III) with a methylating agent to obtain compound of formula (IV); and
ii) treating the obtained compound of formula (IV) with sulfuryl chloride to get an anthranilic ester of formula (I).

Formula (III) Formula (IV) Formula (I)
wherein the process is carried out without isolation of the compound of formula (IV).

In an embodiment, the methylating agent used is selected from iodomethane, dimethyl carbonate, dimethyl sulphate, diazomethane, dimethoxypropane, dimethylzinc, methyl fluorosulphonate, methyl triflate and the like, preferably dimethyl sulphate is used.

The amount of methylating agent used with respect to compound of formula (III) is in the range of 1 to 3 moles.

In an embodiment, said methylation is carried out in presence of a solvent.

The solvent used is selected from organic solvents such as dichloromethane, dichloroethane, acetonitrile, dimethyl formamide, dimethylacetamide, N-Methyl pyrrolidone and mixture thereof.

In an embodiment, the methylation reaction is carried out in presence of dimethyl formamide as a solvent.

In an embodiment, the methylation reaction is carried out in presence of dimethylacetamide as a solvent.

The amount of the solvent used with respect to compound of formula (III) is about 4 to 10 times.

In an embodiment, the methylation reaction is carried out in presence of a base.

Typically, the base used is selected from sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate and the like.

The amount of the base used with respect to compound of formula (III) is in the range of 1 to 1.5 moles.

In an embodiment, methylation reaction is carried out at temperature ranging from 20 to 100°C.

In an embodiment, methylation reaction is carried out for a time period ranging from 0.5 to 6 hours.

In an embodiment, the step i) of the process further comprises isolating the compound of formula (IV) with a chlorinated solvent and reducing the moisture content of the organic layer to less than 0.5% wt/wt.

In an embodiment, the chlorinated solvent used is selected from the group of methylene dichloride, ethylene dichloride, chloroform, 1,1,2-trichloroethane, chlorobenzene, o-dichlorobenzene and the like.

In an embodiment, the chlorinated solvent used is ethylene dichloride.

The amount of the chlorinated solvent used with respect to the compound of formula (III) is about 3 to 10 times.

In an embodiment, the moisture content of the organic layer is reduced to less than 0.5% w/w.

In an embodiment, the compound of formula (IV) obtained in step i) is not isolated and the organic layer obtained in step i) is used directly in step ii) for further treatment.

In an embodiment, the compound of formula (IV) obtained in step i) can be isolated by conventionally known processes, such as distillation, precipitation and so on; and then used in step ii).

In an embodiment, in step ii) the amount of sulfuryl chloride used with respect to compound of formula (III) is in the range of 0.5 to 1.5 moles.

In an embodiment, the treatment with sulfuryl chloride is carried out at temperature ranging from 20 to 100°C. In an embodiment, the treatment with sulfuryl chloride is carried out at temperature ranging from 40 to 70°C.

In an embodiment, the treatment with sulfuryl chloride is carried out for time period ranging from 10 minutes to 3 hours.

According to another aspect of the present invention, there is provided a process for preparation of an anthranilic ester compound of formula (I),

Formula (I)
comprising
i) methylating a compound of formula (III) with a methylating agent to obtain compound of formula (IV);

Formula (III) Formula (IV)
ii) isolating the compound of formula (IV) by treating with a chlorinated organic solvent; and further treating the separated organic layer with sulfuryl chloride to get an anthranilic ester compound of formula (I)

Formula (IV) Formula (I)

In an embodiment, the chlorinated solvent used is selected from the group of methylene dichloride, ethylene dichloride, chloroform, 1,1,2-trichloroethane, chlorobenzene, o-dichlorobenzene and the like.

In an embodiment, the chlorinated solvent used is ethylene dichloride.

The amount of the chlorinated solvent used with respect to the compound of formula (III) is about 3 to 10 times.

In an embodiment the step ii) of the process further comprises reducing the moisture content of the organic layer to less than 0.5% w/w before treating with sulfuryl chloride.

In an embodiment, the moisture content of the organic layer is reduced by azeotropic distillation.

In an embodiment, the moisture content is reduced to less than 0.5% w/w.

Preferably, the moisture content of the organic layer is adjusted to less than 0.1% w/w.

In an embodiment, the amount of sulfuryl chloride used with respect to compound of formula (III) is in the range of 0.5 to 1.5 moles.

In an embodiment, step ii) is carried out in presence of a catalyst. Preferably, the catalyst used is dimethyl formamide.

In an embodiment, the treatment with sulfuryl chloride is carried out at temperature ranging from 20 to 100°C. In an embodiment, the treatment with sulfuryl chloride is carried out at temperature ranging from 40 to 70°C.

In an embodiment, the treatment with sulfuryl chloride is carried out for time period ranging from 10 minutes to 3 hours.

The inventors of the present invention have skilfully designed the inventive process by mindful selection of solvent used in the process which is not hygroscopic in nature. Use of this solvent makes it possible to adjust the moisture content to a great extent.

Furthermore, the use of multiple solvents in the process is also avoided by using chlorinated organic solvent for extracting the compound of formula (IV). Typically, the organic layer after adjusting the moisture content can be directly used for chlorination reaction without requiring isolation of compound of formula (IV), thereby making the process efficient, environment friendly and economical for large scale production.

Also, as the compound of formula (IV) is not required to be isolated the possibility of loss of yield due to solid handling steps such as crystallization or precipitation or filtration is reduced.

According to an embodiment of the present invention, the compound of formula (III) is prepared by reducing the compound of formula (II).

Formula (II) Formula (III)

In an embodiment, the step of reducing compound of formula (II) to compound of formula (III) is carried out in presence of a catalyst and a solvent.

Typically, the catalyst used is selected from palladium catalyst, a platinum catalyst or Raney nickel. The palladium or platinum catalyst such as palladium on carbon or platinum on carbon can be used. Preferably, a platinum catalyst is used.

In an embodiment, the platinum catalyst used in the step of reducing compound of formula (II) to compound of formula (III), can be recycled and reused for same reaction for more than 20 times thereby making the process cost effective and economically viable at industrial scale.

In an embodiment, the solvent used in the step of reducing compound of formula (II) to compound of formula (III), is selected from the group consisting of nitriles for example acetonitrile or C1-C5 alcohol for example methanol, ethanol, isopropanol, n-propanol, butanol, tert-butanol and the like.

In an embodiment, the step of reducing compound of formula (II) to compound of formula (III), is carried out at temperature ranging from 20 to 80°C.

In an embodiment, the step of reducing compound of formula (II) to compound of formula (III), is carried out for time period ranging from 1 to 10 hours.

According to another aspect of the present invention, there is provided a process for preparation of an anthranilic ester compound of formula (I),

Formula (I)
comprising
i) methylating a compound of formula (III) with a methylating agent to result a compound of formula (IV)

Formula (III) Formula (IV)
ii) extracting the compound of formula (IV) in a chlorinated organic solvent and treating the separated organic layer with sulfuryl chloride to get an anthranilic ester compound of formula (I),

Formula (IV) Formula (I)

wherein the compound of formula (III) used in step i) is prepared by reducing compound of formula (II).

Formula (II) Formula (III)

According to yet another aspect of the present invention, there is provided a process for preparation of anthranilic ester compound of formula (I),

Formula (I)
comprising
i) methylating compound of formula (III) with a methylating agent to obtain compound of formula (IV);

Formula (III) Formula (IV)
i) extracting the compound of formula (IV) with a chlorinated organic solvent and treating the separated organic layer with sulfuryl chloride to obtain anthranilic ester compound of formula (I),

Formula (IV) Formula (I)

wherein the compound of formula (III) used in step i) is prepared by reducing compound of formula (II) in presence of platinum catalyst.

Formula (II) Formula (III)

According to an aspect of the present invention, there is provided a process for preparation of an anthranilic ester compound of formula (I),

Formula (I)
comprising
i) methylating compound of formula (III) with a methylating agent to obtain compound of formula (IV);

Formula (III) Formula (IV)

ii) extracting the compound of formula (IV) in a chlorinated organic solvent and reducing the moisture content in the organic layer to less than 0.5% w/w;
iii) treating the organic layer with sulfuryl chloride to get an anthranilic ester compound of formula (I),

Formula (IV) Formula (I)
wherein the compound of formula (III) used in step i) is prepared by reducing compound of formula (II).

Formula (II) Formula (III)
According to yet another aspect of the present invention, there is provided a process for preparation of anthranilic ester compound of formula (I),

Formula (I)
comprising,
i) methylating compound of formula (III) with a methylating agent to result an ester of formula (IV)

Formula (III) Formula (IV)
ii) extracting the ester of formula (IV) in a chlorinated solvent to obtain an organic layer;
iii) reducing the moisture content of the organic layer to less than 0.5% w/w;
iv) treating the organic layer of step c) with sulfuryl chloride to get anthranilic ester compound of formula (I),

Formula (IV) Formula (I)

wherein the compound of formula (III) is prepared by reducing the compound of formula (II) in presence of platinum catalyst.

Formula (II) Formula (III)

In an embodiment the compound of formula (I) can be used to prepare the diamide insecticide compounds for example chlorantraniliprole, cyantraniliprole, cyclaniliprole, tetrachlorantraniliprole and tetraniliprole. Preferably the compound of formula (I) is used for the preparation of chlorantraniliprole.

Advantages of the Present Invention
1. A simple, cost-effective and industrially viable process for preparation of an anthranilic ester compound of formula (I).
2. Said process does not require isolation compound of Formula (IV), thereby reducing effluent generation and the number of steps of the operations.
3. Involves use of cost-effective reagents like sulfuryl chloride.
4. The platinum catalyst used for reduction of compound of formula (II) can be recycled and reused for multiple times.

EXAMPLES
The process for preparation of an anthranilic ester compound of formula (I) according to the invention is ascertained by the experiments as exemplified below. These examples are merely illustrations and are not to be understood as limiting the scope and underlying principles of the invention in any way. Indeed, various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the following examples and foregoing description.

Analytical Method Details:
Samples were analysed on high performance liquid chromatograph with UV detector using COSMOSIL -5C18-MS-II column.

Example 1: Preparation of 2-Nitro-3-methyl benzoic acid – Compound of Formula (II)
6147g of fuming nitric acid was charged into a reaction vessel and was cooled to -15 to -10°C, then 1639g of m-toluic acid was added and the reaction mixture was maintained for 2 hours at the same temperature. After the completion of reaction, the crude 2-nitro-3-methyl benzoic acid was isolated and 1180g of 50% ethanol was added. The mixture was heated to 75-80°C for 1 hour and then cooled at room temperature, the product was filtered and dried to obtain 1000g of 2-Nitro-3-methyl benzoic acid.

Example 2: Preparation of 2-Amino-3-methyl benzoic acid – Compound of Formula (III)
1032g of 2-nitro-3-methyl benzoic acid, 51g of 3 wt.% platinum on activated carbon (Pt/C) catalyst and 6640g of methanol were added to a reaction vessel. The mixture was hydrogenated at 4 to 6 kg/cm2 at 30°C then the temperature of reaction mixture was raised to 50-55°C and maintained for 6 hours. After the completion of the reaction, the reaction mixture was filtered to recover the catalyst and the filtrate was distilled to recover about 70% of solvent used and to obtain a reaction mass. This was followed by the addition of 1674g of water and the mixture was maintained for 1 hour at 20-25°C to precipitate the product. The product was filtered and dried to obtain 806g of 2-amino-3-methyl benzoic acid.

Example 3: Preparation of Methyl-3-methyl -2-amino benzoate [Compound of Formula (IV)]
To a mixture of 5250g of dimethylformamide and 806g of 2-amino-3-methyl benzoic acid, 850g of potassium carbonate was added and the reaction mixture was heated at 50-55°C. Maintaining the temperature to 50-55°C, 1380g of dimethyl sulphate was added within 2-3hours and the temperature was raised to 65-70°C. The mixture was maintained at this temperature for 3 to 4 hours. After the completion of reaction, the solvent used was distilled out and 4050g of ethylene dichloride was added to the residue thus obtained. To the mixture was then added 4850g of water and mixture was stirred for 1 hour at room temperature. After 1 hour, the layers were separated, and the organic layer was subjected to azeotropic distillation at 50-55°C under vacuum 550-650 mmHg. The moisture content of the organic layer was reduced to below 0.1% and this organic layer comprising methyl-3-methyl -2-amino benzoate was used in example 4.

Example 4: Preparation of Methyl-3-methyl -2-amino-5-chloro benzoate [Compound of Formula (I)]
To the organic layer obtained in example 3 was added 660 gm of sulfuryl chloride within 2 to 3 hours at 50-55°C and maintain the reaction for 1 hour. After completion of reaction the mixture was cooled to room temperature and 1200g of water was added, followed by addition of 920g of sodium hydroxide to adjust the pH between 5.5 to 6. The layers were separated, and the organic layer was distilled out to obtain 1000g of methyl-3-methyl -2-amino-5-chloro benzoate.

Example 5: Preparation of Methyl-3-methyl -2-amino-5-chloro benzoate – [Compound of Formula (I)]
Step 1: Preparation of 2-Nitro-3-methyl benzoic acid
735g of fuming nitric acid was charged into a reaction vessel and was cooled to -15 to -10°C. This was followed by portion wise addition of 250g of m-toluic acid and the reaction mixture was maintained for 2 hours at the same temperature. After the completion of reaction, the crude 2-nitro-3-methyl benzoic acid was isolated, and 225g of 50% ethanol was added to it. The mixture was heated to 75-80°C for 1 hour and then cooled room temperature, the product was filtered and dried to obtain 161g of 2-nitro-3-methyl benzoic acid.

Step 2: Preparation of 2-Amino-3-methyl benzoic acid
159g of 2-nitro-3-methyl benzoic acid, 7g of 3 wt.% platinum on activated carbon (Pt/C) catalyst and 1000g of methanol were added to a reaction vessel. The mixture was hydrogenated at 4 to 6 kg/cm2 at 30°C, then temperature of reaction mixture was raised to 50-55°C and maintained for 6 hours. After completion of the reaction, the reaction mixture was filtered to recover the catalyst and the filtrate was distilled to recover about 70% of solvent used and to obtain a reaction mass. 525g of water was added to the reaction mass and the mixture was maintained at 20-25°C for 1 hour to precipitate the product. The product was filtered and dried to obtain 120g of 2-amino-3-methyl benzoic acid.

Step 3: Preparation of Methyl-3-methyl -2-amino benzoate
To a mixture of 650g of dimethylformamide and 100g of 2-amino-3-methyl benzoic acid of step 2 was added 106g of potassium carbonate and the reaction mixture obtained was heated to 50-55°C. Maintaining the temperature to 50-55°C, 170g of dimethyl sulphate was added within 2-3hours and the temperature was raised to 65-70°C. The mixture was maintained at this temperature for 3 to 4 hours. After completion of reaction, the solvent used was distilled out and 600g of water was added. To the mixture was then added 500g of ethylene dichloride and the mixture was stirred for 1 hour at room temperature. After 1 hour, the layers were separated, and the organic layer was subjected to azeotropic distillation at 50-55°C under vacuum 500-650 mmHg. The moisture content of the organic layer was reduced to below 0.1% and this organic layer comprising methyl-3-methyl -2-amino benzoate was used in step 4.

Step 4: Preparation of Methyl-3-methyl -2-amino-5-chloro benzoate
To the organic layer obtained in step 3 was added 82g of sulfuryl chloride within 2 to 3 hours at 50-55° C and maintain the reaction for 1 hour. After completion of reaction the mixture was cooled to room temperature and 150g of water was added, followed by addition of 114g of sodium hydroxide to bring pH to 5.5 to 6. The layers were separated, and the organic layer was distilled out to obtain 124g of methyl-3-methyl -2-amino-5-chloro benzoate.

Example 6: Preparation of Methyl-3-methyl -2-amino-5-chloro benzoate - Compound of Formula (I)
Step 1 and step 2 were carried out in similar manner as in example 5.
Step 3: Preparation of Methyl-3-methyl -2-amino benzoate
To a mixture of 650g of dimethylacetamide and 100g of 2-amino-3-methyl benzoic acid was added 106g of potassium carbonate and the reaction mixture obtained was heated to 50-55°C. 170g of dimethyl sulphate was added to the mixture within 2-3hours and the temperature was raised to 65-75°C. The mixture was maintained at this temperature for 3 to 4 hours. After the completion of reaction, the solvent used was distilled out followed by addition of 580g of ethylene dichloride and 580g of water. The mixture was stirred and heated to 40-45°C temperature. After the layers were separated, and the organic layer was subjected to azeotropic distillation at 50-55°C under vacuum 500-650 mmHg. The moisture content of the organic layer was reduced to below 0.1% and this organic layer comprising methyl-3-methyl -2-amino benzoate was used in step 4.

Step 4: Preparation of Methyl-3-methyl -2-amino-5-chloro benzoate
To the organic layer obtained in step 3 was added 82g of sulfuryl chloride and 1g of dimethyl formamide within 2 to 3 hours at 50-55°C. The reaction mixture was then maintained for another 1-2 hour at same temperature. After the completion of reaction, the mixture was cooled to room temperature and 150g of water was added, followed by addition of 50% aqueous solution of sodium hydroxide to bring pH to 5.5 to 6. The layers were separated, and the organic layer was distilled out to obtain 124g of methyl-3-methyl -2-amino-5-chloro benzoate having HPLC purity of 99.21%.
,CLAIMS:
1. A process for the preparation of compound of formula (I) comprising

Formula (I)
i) methylating a compound of formula (III) with a methylating agent to obtain a compound of formula (IV); and
ii) reacting the obtained compound of formula (IV) with sulfuryl chloride to get a compound of formula (I),

Formula (III) Formula (IV) Formula (I)

2. The process as claimed in claim 1, wherein the process is carried out without isolation of the compound of formula (IV).

3. The process as claimed in claim 1, wherein the methylating agent is selected from iodomethane, dimethyl carbonate, dimethyl sulphate, diazomethane, dimethoxypropane, dimethylzinc, methyl fluorosulphonate and methyl triflate.

4. The process as claimed in claim 1, wherein the methylation is carried out in presence of a solvent.

5. The process as claimed in claim 4, wherein the solvent is selected from dichloromethane, dichloroethane, acetonitrile, dimethyl formamide, dimethylacetamide, N-Methyl pyrrolidone and mixtures thereof.

6. The process as claimed in claim 1, wherein the methylation is carried out in presence of a base.

7. The process as claimed in claim 6, wherein the base is selected from sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate and potassium bicarbonate.

8. The process as claimed in claim 1, wherein the step i) further comprises isolating the compound of formula (IV) in a chlorinated solvent and reducing the moisture content of the organic layer to less than 0.5% wt/wt.

9. The process as claimed in claim 8, wherein the chlorinated solvent is selected from the group consisting of methylene dichloride, ethylene dichloride, chloroform, 1,1,2-trichloroethane, chlorobenzene and o-dichlorobenzene.

10. The process as claimed in claim 1, wherein the compound of formula (III) is prepared by reducing the compound of formula (II)

Formula (II) Formula (III)
wherein said reduction of formula (II) is carried out in presence of a catalyst and a solvent.

11. The process as claimed in claim 10, wherein the catalyst is metal catalyst selected from palladium, platinum and Raney nickel.

12. The process as claimed in claim 10, wherein the catalyst is a platinum.

13. The process as claimed in claim 10, wherein the solvent is selected from group consisting of nitriles or C1-C5 alcohol.

14. A process for preparation of a compound of formula (I),
Formula (I)
comprising,
i) methylating a compound of formula (III) with a methylating agent to obtain a compound of formula (IV)

Formula (III) Formula (IV)
ii) treating the compound of formula (IV) with a chlorinated solvent to get an organic layer;
iii) reducing the moisture content of the organic layer to less than 0.5% w/w;
iv) reacting the compound of formula (IV) with sulfuryl chloride to get the compound of formula (I),

Formula (IV) Formula (I)
wherein the compound of formula (III) is prepared by reducing the compound of formula (II) in presence of platinum catalyst.

Formula (II) Formula (III)