1. A process for the preparation of 3-[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl) pyrazol-4-ylmethylsulfonyl]-4,5-dihydro-5,5-dimethyl-l,2-oxazole i.e. Pyroxasulfone, wherein said process comprises the step of oxidizing 3-([[5-(Difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-pyrazol-4-yl]methyl] sulfanyl)-5,5-dimethyl-4,5-dihydro-1,2-oxazole of Formula II in presence of solvent system comprising at least one ether solvent, .

2. The process as claimed in claim 1, wherein said solvent system comprises atleast one ether solvent used either alone or in combination with other organic solvent.

3. The process as claimed in claim 2, wherein said organic solvent is selected from the group comprising of 1,4-dioxane, tetrahydrofuran, methyl-tetrahydrofuran, 1,2-dimethoxyethane, diethyl ether, n-hexane, n-heptane, cyclohexane, petroleum ether, benzene, toluene, xylene, dichloromethane, dichloroethane, chloroform, carbon tetrachloride, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, acetone, and methyl ethyl ketone, acetonitrile, propionitrile, isobutyronitrile, water and mixture thereof.

4. The process as claimed in claims 1 and 2, wherein said ether solvent is selected from 1,4-dioxane, tetrahydrofuran, methyl-tetrahydrofuran, 1,2-dimethoxyethane, diethyl ether and mixture thereof.

5. The process as claimed in claim 1, wherein said oxidising reaction is carried out in presence of atleast one metal catalyst, one oxidising agent and acid, at a temperature ranging from 40 to 85oC.

6. The process as claimed in claim 5, wherein said oxidising agent is selected from m-chloroperbenzoic acid, performic acid, peracetic acid, hydrogen peroxide (aqueous), and potassium permanganate; wherein said metal catalyst is selected from the group comprising of sodium tungsten catalyst, molybdenum catalyst, titanium catalyst, zirconium catalyst or mixture thereof; and wherein said acid is selected from hydrochloric, hydrobromic, sulfuric, and phosphoric acids.

7. The process as claimed in claims 5 and 6, wherein said oxidising agent is present in an amount ranging from 0.1 to 1.0 moles; wherein said metal catalyst is present in an amount ranging from 0.0001 to 0.1 moles; and wherein said acid is present in an amount ranging from 0.001 to 0.05 moles.

8. The process as claimed in any of the preceding claim, wherein said oxidising reaction is followed by neutralization using base in an amount ranging from 0.1 to 0.5 moles.

9. The process as claimed in claim 8, wherein said base is selected from the group comprising of sodium carbonate, potassium carbonate, lithium carbonate, sodium bicarbonate, potassium bicarbonate, sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium hydride, potassium hydride, lithium hydride, sodium amide, potassium amide, lithium amide, sodium sulphite, sodium metabisulphite potassium sulphite, dimethylamine, diethylamine, diisopropylamine, trimethylamine, tert-butylamine, benzylamine, pyridine, 4-dimethylaminopyridine and sodium methoxide.

10. A process for the preparation of 3-[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl) pyrazol-4-ylmethylsulfonyl]-4,5-dihydro-5,5-dimethyl-l,2-oxazole i.e. Pyroxasulfone of Formula I, wherein said process comprises the step of oxidizing 3-([[5-(Difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-pyrazol-4-yl]methyl] sulfanyl)-5,5-dimethyl-4,5-dihydro-1,2-oxazole of Formula II in presence of solvent system comprising at least one ether solvent alone or in combination of organic solvent, to give compound of Formula I, . wherein said compound of Formula I is crystallized in hot water at 40-70oC.

Description:
FIELD OF THE INVENTION
The present invention relates to a process for the preparation of Pyroxasulfone in high yields, by oxidizing a compound of Formula (II) in solvent system containing at least one ether solvent
.

Present invention further provides process of crystallizing Pyroxasulfone of Formula I,
.

BACKGROUND OF THE INVENTION
Pyroxasulfone was first disclosed in U.S. Pat. No. 7,238,689. There are certain methods known for the production of Pyroxasulfone however, few methods are known to produce Pyroxasulfone by oxidation method. One of such method is described in US20120264947 which involves the oxidation of compound of Formula (II) in presence of sodium tungstate dihydrate, hydrogen peroxide and acetic acid at room temperature for 16 hours. The reaction can be represented as follows:

The major drawback of the above disclosed method is poor yield. The yield of the Pyroxasulfone obtained using this process is only 30-35% which is not acceptable at industrial scale production.

US2023012374 discloses the preparation of pyroxasulfone (3-[[5-(difluoromethoxy)-l-methyl-3- (trifluoromethyl)pyrazol-4-yl] methyl sulfonyl]-5,5-dimethyl-4H-l,2-oxazole) by oxidizing 3-[(5-difluoromethoxy-l-methyl-3-trifluoromethylpyrazol-4-yl)methylthio]-4,5-dihydro-5,5-dimethylisoxazole in the presence of a metal catalyst and hydrogen peroxide. The yields of the reaction are typically lowered by incomplete oxidation of the thio group to the corresponding sulfoxide. Different organic solvents are tested in US2023012374, for example, butyl acetate, isopropyl acetate, ethyl acetate, methanol, butanol, ethanol, acetonitrile, DMF, or NMP, each solvent and solvent amount having a different effect on the amount pyroxasulfone formed and the resulting amounts of the sulfone impurity, however it is observed that detectable amount of sulfone impurity is formed in each case.

OBJECT OF THE PRESENT INVENTION
It is an object of the present invention to provide a process for preparation of a compound of Pyroxasulfone of Formula I
.

It is another objective of the present invention to provide an improved, simple, cost effective and industrially viable process for preparation of compound of Pyroxasulfone of Formula I.

It is another objective of the present invention to provide an improved oxidation process of intermediate of Formula II, to provide desired compound of Formula I in high yields and purity
.

SUMMARY OF THE INVENTION
The main aspect of the present invention provides a process for the preparation of 3-[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl)pyrazol-4-ylmethylsulfonyl]-4,5- dihydro-5,5-dimethyl-l,2-oxazole i.e. Pyroxasulfone of Formula I, by oxidizing 3-([[5-(Difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-pyrazol-4-yl] methyl] sulfanyl)-5,5-dimethyl-4,5-dihydro-1,2-oxazole of Formula II.

In another aspect, the present invention provides process for the preparation of 3-[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl) pyrazol-4-yl methylsulfonyl]-4,5-dihydro-5,5-dimethyl-l,2-oxazole i.e. Pyroxasulfone of Formula I, wherein said process comprises the step of oxidizing 3-([[5-(Difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-pyrazol-4-yl] methyl] sulfanyl)-5,5-dimethyl-4,5-dihydro-1,2-oxazole of Formula II in presence of solvent system comprising at least one ether solvent
.

In another aspect, the present invention provides process for the preparation of 3-[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl)pyrazol-4-ylmethylsulfonyl]-4,5-dihydro-5,5-dimethyl-l,2-oxazole i.e. Pyroxasulfone of Formula I, wherein said process comprises the step of oxidizing 3-([[5-(Difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-pyrazol-4-yl]methyl]sulfanyl)-5,5-dimethyl-4,5-dihydro-1,2-oxazole of Formula II in presence of oxidizing agent and a metal catalyst in a solvent system comprising at least one ether solvent
,
wherein said ether solvent is selected from group comprising of 1,4-dioxane, tetrahydrofuran, methyl-tetrahydrofuran, 1,2-dimethoxyethane, diethyl ether and mixture thereof.

DETAILED DESCRIPTION
Those skilled in the art will appreciate that the invention described herein may be implemented with various changes or adaptations beyond the embodiments expressly outlined. All such modifications and alternatives are deemed to fall within the scope of the present invention. The invention further encompasses any features, steps, compositions, or methods mentioned in this specification, whether described individually, collectively, or in any combination thereof.

For clarity, before detailing further aspects of the invention, certain terms used throughout this specification and accompanying examples are defined below. These definitions should be interpreted in the context of the entire disclosure and in a manner consistent with how a person of ordinary skill in the art would understand them. Unless otherwise specified, technical and scientific terminology used here carries the meaning commonly attributed to it by those skilled in the field. The terms provided herein apply unless explicitly restricted in particular sections.

The terms “about” or “approximately,” as used in this disclosure, include the stated numerical value and a reasonable range around it, as would be recognized by a person of ordinary skill in the art. This range accounts for standard measurement variations, instrument limitations, and experimental error. For instance, “about” may refer to a deviation within one or more standard deviations or within ±5% of the stated value. Any reference to numerical ranges should be interpreted as including each individual value within the range unless otherwise specified, and each endpoint is considered part of the range and may be combined independently. Where a parameter range is provided, all whole numbers and decimal increments falling within that range are also intended to be included.

As used herein, the terms “comprising,” “including,” “having,” “containing,” “involving,” and similar expressions are intended to be open-ended and indicate that additional elements or steps may be present. The terms “preferred” and “preferably” denote embodiments that may offer certain advantages under specific conditions. In the context of this disclosure, any instance of “comprising” may also be interpreted, where appropriate, as “consisting of,” “consisting essentially of,” or “consisting substantially of.”

As used herein, the term “solvent system” refers to either a mixture comprising an organic solvent together with at least one ether solvent, or a system consisting solely of an ether solvent. The expression “organic solvent” encompasses, without limitation, the following categories and examples:
Ether solvents such as 1,4-dioxane, tetrahydrofuran, methyl-tetrahydrofuran, 1,2-dimethoxyethane, diethyl ether, or mixtures thereof; Non-polar (hydrocarbon) solvents such as n-hexane, n-heptane, cyclohexane, petroleum ether, benzene, toluene, xylene, or combinations thereof; Chloro-containing solvents such as dichloromethane, dichloroethane, chloroform, carbon tetrachloride, or mixtures thereof; Polar aprotic solvents including dimethylacetamide, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, or mixtures thereof; Ketone solvents such as acetone, and methyl ethyl ketone; Nitrile solvents including acetonitrile, propionitrile, isobutyronitrile, or mixture thereof; and Polar solvents such as water; and mixture of any above solvent.

In this disclosure, the term “acid” includes both mineral and organic acids.
Examples of inorganic acids include hydrochloric, hydrobromic, sulfuric, and phosphoric acids. Examples of organic acids include, but are not limited to, formic acid, acetic acid, propionic acid, methane sulfonic acid, para-toluenesulfonic acid, and related derivatives.

As used herein, the term “base” includes inorganic and organic bases. Suitable inorganic bases include, but are not limited to Alkali metal carbonates such as sodium, potassium, or lithium carbonate; Alkali metal bicarbonates such as sodium or potassium bicarbonate; Alkali metal hydroxides such as sodium, potassium, or lithium hydroxide; Alkali metal hydrides such as sodium, potassium, or lithium hydride; Alkali metal amides such as sodium, potassium, or lithium amide; Alkali sulphites such as sodium sulphite, sodium metabisulphite, potassium sulphite. Representative organic bases include lower alkylamines (e.g., dimethylamine, diethylamine, diisopropylamine), branched or tertiary amines such as triethylamine and tert-butylamine, benzylamine, heteroaromatic bases such as pyridine or 2,6-lutidine, and like specialized reagents 4-dimethylaminopyridine (DMAP). The category also encompasses alkoxides formed from alkali metals, such as sodium or potassium methoxide/ethoxide, and tert-butoxides of sodium, potassium, or lithium.

The embodiments described herein serve merely as illustrative examples, and the scope of the present disclosure should not be limited solely to these specific descriptions.

Accordingly, in main embodiment, the present invention provides process for the preparation of 3-[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl) pyrazol-4-ylmethylsulfonyl]-4,5-dihydro-5,5-dimethyl-l,2-oxazole i.e. Pyroxasulfone of Formula I, wherein said process comprises the step of oxidizing 3-([[5-(Difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-pyrazol-4-yl]methyl] sulfanyl)-5,5-dimethyl-4,5-dihydro-1,2-oxazole of Formula II in presence of solvent system comprising at least one ether solvent
.

In another embodiment, the present invention provides process for the preparation of 3-[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl) pyrazol-4-ylmethylsulfonyl]-4,5-dihydro-5,5-dimethyl-l,2-oxazole i.e. Pyroxasulfone of Formula I, wherein said process comprises the step of oxidizing 3-([[5-(Difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-pyrazol-4-yl] methyl] sulfanyl)-5,5-dimethyl-4,5-dihydro-1,2-oxazole of Formula II in presence of oxidizing agent and a metal catalyst in a solvent system comprising at least one ether solvent
, ,
wherein said ether solvent is selected from group comprising of 1,4-dioxane, tetrahydrofuran, methyl-tetrahydrofuran, 1,2-dimethoxyethane, diethyl ether and mixture thereof.

In another embodiment, the oxidising agent is selected from, but not limited to, m-chloroperbenzoic acid, performic acid, peracetic acid, hydrogen peroxide (aqueous), and potassium permanganate.

In another embodiment, the said oxidation reaction is carried out at the temperature ranging from 40 to 85oC, preferably 70-85oC.

In another embodiment, the metal catalyst is selected from the group comprising of, but not limited to, sodium tungsten catalyst, molybdenum catalyst, titanium catalyst, zirconium catalyst or mixture thereof.

In another embodiment, the metal catalyst is used in the amount ranging from 0.0001 to 0.1 moles.

In another embodiment, the oxidising agent is used in the amount ranging from 0.1 to 1.0 moles.

In another embodiment, the above oxidising reaction is carried out in presence of acid used in the amount ranging from 0.001 to 0.05 moles.

In another embodiment, the said acid is selected from, but not limited to, mineral and organic acids.
Examples of inorganic acids include hydrochloric, hydrobromic, sulfuric, and phosphoric acids. Examples of organic acids include, but are not limited to, formic acid, acetic acid, propionic acid, methane sulfonic acid, para-toluenesulfonic acid, and related derivatives.

In another embodiment, said oxidising reaction is carried out in presence of solvent system comprising atleast one ether solvent. Said solvent system is either a mixture comprising an organic solvent together with at least one ether solvent, or a system consisting solely of an ether solvent, wherein said organic solvent is selected from the ether solvent, non-polar solvent, chloro-containing solvent, polar aprotic solvent, nitrile solvent, ketone solvent, polar solvent, and mixture thereof.

In another embodiment, said organic solvent is selected from, but not limited to, the group comprising of 1,4-dioxane, tetrahydrofuran, methyl-tetrahydrofuran, 1,2-dimethoxyethane, diethyl ether, n-hexane, n-heptane, cyclohexane, petroleum ether, benzene, toluene, xylene, dichloromethane, dichloroethane, chloroform, carbon tetrachloride, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, acetone, and methyl ethyl ketone, acetonitrile, propionitrile, isobutyronitrile, water and mixture thereof.

In another embodiment, atleast one ether solvent used in either alone or combination of organic solvent is selected from, 1,4-dioxane, tetrahydrofuran, methyl-tetrahydrofuran, 1,2-dimethoxyethane, diethyl ether and mixture thereof.

In another embodiment, after completion of oxidation reaction, reaction system is neutralized using base in the minimal amount ranging from 0.1 to 0.5 moles.

In another embodiment, said base is selected from the group comprising of sodium carbonate, potassium carbonate, lithium carbonate, sodium bicarbonate, potassium bicarbonate, sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium hydride, potassium hydride, lithium hydride, sodium amide, potassium amide, lithium amide, sodium sulphite, sodium metabisulphite potassium sulphite, dimethylamine, diethylamine, diisopropylamine, trimethylamine, tert-butylamine, benzylamine, pyridine, 4-dimethylaminopyridine and sodium methoxide.

In another embodiment, Pyroxasulfone obtained by present process is crystallized in hot water at 40-70oC, followed by washing with water

In another embodiment, Pyroxasulfone is obtained in yield of more than 85%, preferably more than 92%.

In a preferred embodiment, the present invention provides process for the preparation of 3-[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl) pyrazol-4-ylmethylsulfonyl]-4,5-dihydro-5,5-dimethyl-l,2-oxazole i.e. Pyroxasulfone of Formula I, wherein said process comprises the step of oxidizing 3-([[5-(Difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-pyrazol-4-yl]methyl] sulfanyl)-5,5-dimethyl-4,5-dihydro-1,2-oxazole of Formula II

in presence of solvent system comprising at least one ether solvent alone or in combination of organic solvent, to give compound of Formula I,

wherein said compound of Formula I is crystallized in hot water at 40-70oC.

In another preferred embodiment, the present invention provides process for the preparation of 3-[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl) pyrazol-4-ylmethylsulfonyl]-4,5-dihydro-5,5-dimethyl-l,2-oxazole i.e. Pyroxasulfone of Formula I, wherein said process comprises the step of oxidizing 3-([[5-(Difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-pyrazol-4-yl]methyl] sulfanyl)-5,5-dimethyl-4,5-dihydro-1,2-oxazole of Formula II

in presence of solvent system comprising at least one ether solvent present alone or in combination of organic solvent, along with atleast one metal catalyst, one oxidising agent and acid, to give compound of Formula I,

wherein said ether solvent is selected from 1,4-dioxane and tetrahydrofuran,
wherein said organic solvent is selected from acetone, dimethylformamide and acetonitrile,
wherein said metal catalyst is selected from sodium tungstate used in the ratio of 0.0001 to 0.1 moles, and
wherein said oxidisation reaction is followed by neutralization using base, selected from, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sodium hydroxide, sodium sulphite, sodium metabisulphite and potassium sulphite, used in the ratio of 0.1 to 0.5 moles.

The following examples are presented to provide what is believed to be the most useful and readily understood description of procedures and conceptual aspects of this invention. The examples provided below are merely illustrative of the invention and are not intended to limit the same to disclosed embodiments. Variations and changes obvious to one skilled in the art are intended to be within the scope and nature of the invention.

EXAMPLES

Example 1:
Synthesis of Pyroxasulfone technical using 1,4-Dioxane as a solvent
Charge 1,4-Dioxane (100gm) and 3-[[5-(Difluoromethoxy)-1-methyl-3-(trifluoromethyl) pyrazol-4-yl] methylsulfanyl]-5,5-dimethyl-4H-1,2-oxazole, compound of Formula II (100 gm, 0.278 Mol.) Stir till clear at room temperature. Charge Sodium tungstate dihydrate (Na2WO4 .2H2O) (1.0 gm). Heat to 55-60oC. Slowly add 50% hydrogen peroxide (56 gm, 3.0 M.eq.) to the above mass maintaining temperature 55-85oC in 1-2 hr. Slowly raise the temperature up to 83-85oC. Maintain reaction under stirring at 83-85oC for 3-5 hrs. Cool to 50-55oC, and slowly add 1 gm Sodium metabisulfite in above mass to kill peroxide contents. Recover the 1,4-Dioxane under mild vacuum at 50-60oC. Add hot water (200 gm) at 55oC and maintain for 1 hr. Slowly cool to 25-30oC and maintain for 1 hr. Filter the mass on Buckner at 25-30oC. Wash the wet solid with water (100 gm). Dry the solid at 60oC for 5-6 hrs.
HPLC Purity: 99.30%
Sulfoxide (Area): 0.2%
Moisture contents: 0.3%
Colour: White colour powder.
Yield w/w: 98 %

Example 2: Synthesis of Pyroxasulfone technical using tetrahydrofuran as a solvent
Added tetrahydrofuran instead of 1,4-dioxane keeping all other parameter similar to example 1.
HPLC Purity: 99.0%
Sulfoxide (Area): 0.25%
Moisture contents: 0.25%
Colour: White colour crystalline powder.
Yield w/w: 96 %

Example 3: Synthesis of Pyroxasulfone technical using 1,4-Dioxane and acetonitrile combination as a solvent
Charge 1,4 Dioxane (140g) and Acetonitrile (60 gm) in 1 L RBF. Charge 100g of compound of Formula II to above solution at 25-30°C. Charge 2.0g of Sulfuric acid to above reaction mass at 25-30°C. Charge 2.0g of Sodium tungstate dehydrate to above reaction mass at 25-30°C. Raise the temperature of reaction mass at 70°C. Slowly add 47g of 50% Hydrogen peroxide in reaction mass in 1-2 hr at 70-80°C. After addition completion, raise the temperature of reaction mass at 75-80°C and maintain the reaction mass for 3-4 hr at 75-80°C. Cool the reaction mass at 55-60oC. Slowly add 20% Sodium sulphite solution (67g) in reaction mass at 55-60°C. Distil out and recover acetonitrile & 1,4-dioxane completely under vacuum below 65-70°C. Charge 200g water in reaction mass at 65-70°C. and stir for 1.0hr at same temperature. Cool the reaction mass at 25-30°C and stir for 1.0hr. Filter the material at 25-30°C and wash with hot water. Dry the material at 50-55oC.
Purity by HPLC: = 99.80%
Moisture contents: = 0.20%
Colour: White solid crystalline powder.
Yield: = 96.41%.

Example 4: Synthesis of Pyroxasulfone technical using 1,4-Dioxane and acetone combination as a solvent
Charge 1,4 Dioxane (140g) and Acetonitrile (50 gm) in 1 L RBF. Charge 100g of compound of Formula II to above solution at 25-30°C. Charge 2.0g of Sulfuric acid to above reaction mass at 25-30°C. Charge 2.0g of Sodium tungstate dehydrate to above reaction mass at 25-30°C. Raise the temperature of reaction mass at 70°C. Slowly add 47g of 50% Hydrogen peroxide in reaction mass in 1-2 hr at 80°C. After addition completion, raise the temperature of reaction mass at 80°C and maintain the reaction mass for 3-4 hr at 80°C. Cool the reaction mass at 55-60oC. Slowly add 20% Sodium sulphite solution (67g) in reaction mass at 55-60°C. Distil out and recover acetone & 1,4-dioxane completely under vacuum below 65-70°C. Charge 200g water in reaction mass at 65-70°C and stir for 1.0hr at same temperature. Cool the reaction mass at 25-30°C and stir for 1.0hr. Filter the material at 25-30°C and wash with hot water. Dry the material at 50-55oC.
Purity by HPLC: = 99.10%
Moisture contents: = 0.35%
Colour: White solid crystalline powder.
Yield: = 93.00%.

Example 5: Synthesis of Pyroxasulfone technical using 1,4-Dioxane and dimethyl formamide combination as a solvent
Charge 1,4 Dioxane (140g) and Dimethylformamide (60 gm) in 1 L RBF. Charge 100g of compound of Formula II to above solution at 25-30°C. Charge 2.0g of Sulfuric acid to above reaction mass at 25-30°C. Charge 2.0g of Sodium tungstate dehydrate to above reaction mass at 25-30°C. Raise the temperature of reaction mass at 80°C. Slowly add 47g of 50% Hydrogen peroxide in reaction mass in 1-2 hr at 85°C. After addition completion, raise the temperature of reaction mass at 85°C and maintain the reaction mass for 3-4 hr at 85°C. Cool the reaction mass at 55-60oC. Slowly add 20% Sodium sulphite solution (67g) in reaction mass at 55-60°C. Quench the reaction with addition of additional water and extract the compound in ethyl acetate. Distil the ethyl acetate layer under vacuum below 65-70°C. Charge 200g water in reaction mass at 65-70°C and stir for 1.0hr at same temperature. Cool the reaction mass at 25-30°C and stir for 1.0hr. Filter the material at 25-30°C and wash with hot water. Dry the material at 50-55oC.
Purity by HPLC: = 99.80%
Moisture contents: = 0.20%
Colour: White solid crystalline powder.
Yield: = 97%.
, Claims:WE CLAIM
1. A process for the preparation of 3-[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl) pyrazol-4-ylmethylsulfonyl]-4,5-dihydro-5,5-dimethyl-l,2-oxazole i.e. Pyroxasulfone, wherein said process comprises the step of oxidizing 3-([[5-(Difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-pyrazol-4-yl]methyl] sulfanyl)-5,5-dimethyl-4,5-dihydro-1,2-oxazole of Formula II in presence of solvent system comprising at least one ether solvent,
.

2. The process as claimed in claim 1, wherein said solvent system comprises atleast one ether solvent used either alone or in combination with other organic solvent.

3. The process as claimed in claim 2, wherein said organic solvent is selected from the group comprising of 1,4-dioxane, tetrahydrofuran, methyl-tetrahydrofuran, 1,2-dimethoxyethane, diethyl ether, n-hexane, n-heptane, cyclohexane, petroleum ether, benzene, toluene, xylene, dichloromethane, dichloroethane, chloroform, carbon tetrachloride, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, acetone, and methyl ethyl ketone, acetonitrile, propionitrile, isobutyronitrile, water and mixture thereof.

4. The process as claimed in claims 1 and 2, wherein said ether solvent is selected from 1,4-dioxane, tetrahydrofuran, methyl-tetrahydrofuran, 1,2-dimethoxyethane, diethyl ether and mixture thereof.

5. The process as claimed in claim 1, wherein said oxidising reaction is carried out in presence of atleast one metal catalyst, one oxidising agent and acid, at a temperature ranging from 40 to 85oC.
6. The process as claimed in claim 5, wherein said oxidising agent is selected from m-chloroperbenzoic acid, performic acid, peracetic acid, hydrogen peroxide (aqueous), and potassium permanganate;
wherein said metal catalyst is selected from the group comprising of sodium tungsten catalyst, molybdenum catalyst, titanium catalyst, zirconium catalyst or mixture thereof; and
wherein said acid is selected from hydrochloric, hydrobromic, sulfuric, and phosphoric acids.

7. The process as claimed in claims 5 and 6, wherein said oxidising agent is present in an amount ranging from 0.1 to 1.0 moles;
wherein said metal catalyst is present in an amount ranging from 0.0001 to 0.1 moles; and
wherein said acid is present in an amount ranging from 0.001 to 0.05 moles.

8. The process as claimed in any of the preceding claim, wherein said oxidising reaction is followed by neutralization using base in an amount ranging from 0.1 to 0.5 moles.

9. The process as claimed in claim 8, wherein said base is selected from the group comprising of sodium carbonate, potassium carbonate, lithium carbonate, sodium bicarbonate, potassium bicarbonate, sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium hydride, potassium hydride, lithium hydride, sodium amide, potassium amide, lithium amide, sodium sulphite, sodium metabisulphite potassium sulphite, dimethylamine, diethylamine, diisopropylamine, trimethylamine, tert-butylamine, benzylamine, pyridine, 4-dimethylaminopyridine and sodium methoxide.

10. A process for the preparation of 3-[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl) pyrazol-4-ylmethylsulfonyl]-4,5-dihydro-5,5-dimethyl-l,2-oxazole i.e. Pyroxasulfone of Formula I, wherein said process comprises the step of oxidizing 3-([[5-(Difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-pyrazol-4-yl]methyl] sulfanyl)-5,5-dimethyl-4,5-dihydro-1,2-oxazole of Formula II

in presence of solvent system comprising at least one ether solvent alone or in combination of organic solvent, to give compound of Formula I,
.
wherein said compound of Formula I is crystallized in hot water at 40-70oC.