Process for preparation of pyroxasulfone

Abstract

The present invention relates to a process for the preparation of Pyroxasulfone of Formula (I) or salts thereof from a compound of Formula (II) by reacting the compound of Formula (II) with a suitable oxidizing agent in presence of a metal catalyst, an inorganic acid and optionally a phase transfer catalyst. Formula (I) Formula (II).

Description

[0001] PROCESS FOR PREPARATION OF PYROXASULFONE

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a process for the preparation of Pyroxasulfone of Formula (I) or salts thereof from a compound of Formula (II).

[0004] Formula (I) Formula (II)

[0005] BACKGROUND OF THE INVENTION

[0006] Pyroxasulfone is an isoxazoline herbicide, which acts by inhibition of very-long-chain fatty acid elongase (VLCFAE). It is chemically known as [ 5 -(difluoromethoxy )-l-methyl-3- ( trifluoromethyl)lH-pyrazol-4-yl]methyl4,5-dihydro-5,5-dimethylisoxazol-3-yl sulfone and has the CAS No. 447399-55-5. Represented by compound of Formula (I)

[0007] Formula (I)

[0008] Pyroxasulfone is a selective pre-emergence grass and broad-leaved weed herbicide. It finds application in the control of Echinochloa crusgalli, Eleusine indica, Phyllanthus niruri, Phalaris minor, Echinochloa colonum, Celosia argentia, Trianthema porulacastrum, Amarthanas viridis, Digeria arvensis in crops such as Maize, Wheat and Soybean. Pyroxasulfone was first disclosed in the US7238689. The patents US6841519, IN220938 discloses intermediates and process for preparation of Pyroxasulfone. The process disclosed in the above cited patent can be depicted as follows:

[0009] From the above scheme the compound of Formula (II) can be converted to compound of Formula (I) by using an oxidizing agent such as m-chloroperbenzoic acid (mCPBA). However, the use of said oxidizing agent at a commercial scale has problems such as waste management and poor yield.

[0010] Another popular oxidising agent is hydrogen peroxide. For e.g.: reference is made to WO2022138781 which discloses the use of hydrogen peroxide or a persulfate compound as an oxidizing agent in presence of a base for conversion of compound of Formula (II) to compound of Formula (I). The use of hydrogen peroxide in presence of a base has problems associated with by-product due to non-selective Sulphur oxidation. The process lacks chemo selectivity .

[0011] Reference is made to WO2022191292. The application discloses a process for preparing a compound of formula (2) comprising reacting a compound of formula (1) with an oxidizing agent in the presence of a metal catalyst and in the presence of a carboxylic acid, a method wherein the reaction is carried out above 35 °C;

[0012] The drawback with the above reaction scheme is that it requires the use of an acid additive such as carboxylic acid. Employing carboxylic acid poses challenges in waste management during large-scale production. It requires effluent treatment for neutralization of residual carboxylic acid.

[0013] In addition to these organic acids being expensive they also have problems associated with contamination from undesired micro-organisms during storage.

[0014] Reference is also made to WO2021002484. The application discloses converting the compound of Formula (II) to compound of Formula (I) in the presence of hydrogen peroxide and a metal catalyst. The major drawback with the said synthetic reaction is that the reaction time is too long and there is incomplete conversion of compound of Formula (II) to Pyroxasulfone. Thus, a considerable amount of impurity is obtained along with Pyroxasulfone which is difficult to isolate.

[0015] The methods already known in the art have several disadvantages such as waste management, effluent treatment, impurity profile of toxicological concern and cost of production. Effluent treatment requires high energy consumption, not only this but the effluent treatment plants also generate air pollutants. Such problems make the entire process unsustainable and may also cause significant hazard to the environment.

[0016] Thus, there is a need in the art to develop a novel and improved process that can overcome the drawbacks in the prior art. The present invention aims to solve all the above problems associated with waste management, cost of synthesis, low reaction rate, non-selective oxidation, incomplete conversion of reactant, low yield and purity. Thus, the present invention aims to provide a commercially viable, safer, environment friendly and sustainable process.

[0017] OBJECT OF THE INVENTION:

[0018] The main object of the present invention is to provide a method for preparation of Pyroxasulfone of Formula (I) from compound of Formula (II) by using a suitable oxidizing agent in presence of one or more suitable reaction chemicals.

[0019] Another main object of the present invention is to provide a process that gives high yield of Pyroxasulfone of Formula (I)

[0020] Yet another object of the present invention is to provide a simple, sustainable, cost effective, environment friendly and commercially viable process for preparation of Pyroxasulfone of Formula (I)

[0021] SUMMARY OF THE INVENTION

[0022] According to an aspect of the present invention, there is provided a process for preparation of Pyroxasulfone of Formula (I) from a compound of Formula (II) wherein the said process comprises oxidizing compound of Formula (II) at a temperature ranging from 20 to 80°C in presence of one or more suitable reaction chemicals.

[0023] According to an aspect of the present invention, there is provided a process for preparation of Pyroxasulfone of Formula (I) from a compound of Formula (II) wherein the said process comprises reacting the compound of Formula (II) with an oxidizing agent in presence of a catalyst, an inorganic acid and optionally another phase transfer catalyst.

[0024] According to another embodiment of the present invention, the oxidizing agent is selected from a group comprising of perboric acid, salt of perboric acid, peracetic acid, hypochlorite such as sodium hypochlorite, potassium hypochlorite, permanganates, manganese dioxide, etc. According to another embodiment of the present invention, the oxidizing agent is not hydrogen peroxide.

[0025] According to yet another embodiment of the present invention, the catalyst is selected from metal catalysts.

[0026] According to still another embodiment of the present invention, the acid is selected from inorganic acids.

[0027] DETAILED DESCRIPTION OF THE INVENTION

[0028] Discussed below are some representative embodiments of the present invention. The invention in its broader aspects is not limited to the specific details and representative methods. The illustrative examples are described in this section in connection with the embodiments and methods provided. The invention according to its various aspects is particularly pointed out; read in view of this specification and appropriate equivalents.

[0029] All technical and scientific terms used herein have the same meanings as commonly understood by someone ordinarily skilled in the art to which the present subject matter belongs. It is to be noted that, as used in the specification, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and / or” unless the content clearly dictates otherwise.

[0030] 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.

[0031] 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’.

[0032] The term “room temperature” unless stated otherwise, essentially means temperature in range of 20-35 °C

[0033] The term "purity" means purity as determined by HPLC ("High Pressure Liquid Chromatography " ) .

[0034] The term “Pyroxasulfone” as used herein, includes Pyroxasulfone free base or its salts and is used interchangeably throughout the disclosure.

[0035] The term “Perboric acid or its salts” as used herein is referred to as “PBS” and includes all possible forms such as crystalline, hydrate, amorphous, anhydrous, etc unless specified otherwise.

[0036] The present disclosure is not to be limited in scope by the specific embodiments described herein, which are intended for the purposes of exemplification only.

[0037] According to an aspect of the present invention, there is provided a process for preparation of Pyroxasulfone of Formula (I) from a compound of Formula (II) wherein the said process comprises oxidizing compound of Formula (II) at a temperature ranging from 20 to 80°C in presence of one or more suitable reaction chemicals.

[0038] According to an aspect of the present invention, there is provided a process for preparation of Pyroxasulfone of Formula (I) from a compound of Formula (II) wherein the said process comprises reacting the compound of Formula (II) with an oxidizing agent in presence of a catalyst, an inorganic acid and optionally another phase transfer catalyst. According to an aspect of the present invention, the optionally used phase transfer catalyst is preferably a quaternary ammonium salt. Thus, as a result of the present invention Pyroxasulfone of Formula I can be easily and effectively produced from the compound of Formula II by using the following reaction scheme:

[0039] Reaction Scheme I:

[0040] CAS No: 656825-92-2 CAS No.: 447399-55-5

[0041] 3-{[5-(difluoromethoxy)-l-methyl-3- 3-{[5-(difluoromethoxy)-l-methyl-3-(trifluoromethyl)-lH-

[0042] (trifluoromethyl)pyrazol-4-yl](methylsulfanyl)}-5,5- pyrazol-4-yl](methanesulfonyl)}-5,5-dimethyl-4,5-dihydro-l,2- dimethyl-4H-l,2-oxazole oxazole

[0043] (ID Pyroxasulfone (I)

[0044] The process according to Reaction Scheme I wherein, the oxidizing agent is selected from a group comprising of perboric acid, salt of perboric acid, peracetic acid, hypochlorite such as sodium hypochlorite, potassium hypochlorite, permanganates, manganese dioxide, etc.

[0045] According to an embodiment of the present invention, the oxidizing agent is preferably perboric acid, salt of perboric acid including its crystalline, amorphous and anhydrous forms thereof.

[0046] According to another embodiment of the present invention, the salt of perboric acid includes but is not limited to perboric acid monosodium salt trihydrate, perboric acid sodium salt or sodium perborate, sodium peroxometaborate, sodium peroxoborate, sodium peroxoborate hexahydrate, sodium perborate monohydrate, sodium perborate tetrahydrate, etc.

[0047] According to yet another embodiment of the present invention, the oxidizing agent is a salt of perboric acid. According to still another preferred embodiment of the present invention, the salt of perboric acid is Sodium Perborate or its hydrates.

[0048] Sodium Perborate is known to serve as a bleaching agent in the detergent industry. This crystalline reagent is economically available as a hydrate, represented by the general formula NaB03 • n H2O (with n ranging from 1 to 4).

[0049] The crystalline form of Sodium perborate can be encountered in both anhydrous form or a hydrate form. The hydrate forms are freely soluble in water. The hydrate forms, more commonly available are Sodium Perborate monohydrate and Sodium Perborate tetrahydrate.

[0050] The process according to Reaction Scheme I wherein, the metal catalyst is selected from a group comprising of but not limited to tungsten catalyst, molybdenum catalyst, iron catalyst, manganese catalyst, vanadium catalyst, niobium catalyst, tantalum catalyst, titanium catalyst, zirconium catalyst, copper catalyst, thallium catalyst, etc including their acid and salt forms.

[0051] According to yet another preferred embodiment of the present invention, the metal catalyst is a tungsten catalyst or molybdenum catalyst.

[0052] According to yet another embodiment the preferred examples of tungsten catalyst include tungstic acid, tungstates such as sodium tungstate including sodium tungstate dihydrate and sodium tungstate decahydrate, potassium tungstate, calcium tungstate, ammonium tungstate; tungsten metal, tungsten oxide such as tungsten (VI) oxide, tungsten (VI) oxide is also called tungsten trioxide), tungsten carbide, tungsten chloride such as tungsten chloride (VI), tungsten chloride (VI) is tungsten hexachloride, tungsten bromide (e.g., tungsten (V) bromide), tungsten sulfide (e.g., tungsten (IV) sulfide, tungsten (IV) sulfide is also referred to as tungsten disulfide), phosphotungstic acid and its salts such as phosphotungstic acid, sodium phosphotungstate, ammonium phosphotungstate, etc., silicotungstic acid and its salts such as silicotungstic acid, sodium silicotungstate, etc., and mixtures thereof. More preferably sodium tungstate or sodium tungstate dihydrate.

[0053] According to yet another embodiment the preferred examples of molybdenum catalyst include molybdic acid, molybdate, molybdenum metal, molybdenum oxide, sodium molybdate, potassium molybdate, ammonium molybdate, molybdenum carbide, molybdenum chloride, molybdenum sulfide, molybdenum bromide, phosphomolybdic acid, sodium phosphomolybdate, phosphorus ammonium molybdate, silicomolybdic acid, sodium silicomolybdate and salts and mixtures thereof. More preferably ammonium molybdate or molybdic acid.

[0054] The process according to Reaction Scheme I wherein, the inorganic acid is selected from a group comprising of hydrochloric acid, hydrobromic acid, hydroiodic acid, sulphuric acid, para toluene sulphonic acid and the like.

[0055] According to still another embodiment of the present invention, the inorganic acid is preferably sulphuric acid, hydrochloric acid or para-toluene sulphonic acid.

[0056] In the described process, inorganic acids are used instead of organic acids since they provide more consistent and stronger acidic conditions, which are essential for effective oxidation reactions in the given process. Inorganic acids such as sulfuric acid, hydrochloric acid, and para-toluenesulfonic acid are typically more stable and do not introduce additional organic residues or by-products that could potentially complicate the purification of the final product. Furthermore, inorganic acids can effectively facilitate the catalytic activity of the metal catalysts involved in the oxidation process, leading to higher yield and purity of compound of Formula I (Pyroxasulfone).

[0057] Other major drawbacks with the use of organic acids are costliness, susceptibility to contamination, need for effluent treatment due to environmental hazard from the residual waste, etc.

[0058] The process according to scheme I wherein, the solvent is selected from a group comprising of tetrahydrofuran, chlorobenzene, dichlorobenzene, dichloromethane, methanol, ethanol, propanol, 2-propanol, butanol, sec -butanol, isobutanol, tert-butanol, sec-amyl alcohol, acetonitrile, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate and its isomers, N,N-dimethylformamide (DMF), etc.

[0059] According to another embodiment of the present invention, the solvent is preferably acetonitrile or tetrahydrofuran.

[0060] According to Reaction Scheme I the optionally used phase transfer catalyst is selected from the group comprising of Quaternary ammonium salts such as Tetrabutylammonium bromide and the like, crown ethers and phosphonium compounds In an embodiment Pyroxasulfone prepared using the method of the present invention is substantially free of impurity.

[0061] An embodiment of the present invention provides, Pyroxasulfone of Formula (I) having purity of more than 95%, preferably more than 99%.

[0062] An embodiment of the present invention provides, Pyroxasulfone of Formula (I) with the Yield of up to 96% or more.

[0063] In another embodiment Pyroxasulfone prepared using the process disclosed in the present invention is used in the preparation of agrochemical composition or formulation.

[0064] The further embodiment of the present invention is illustrated by the following examples included with tables, which are provided merely to be exemplary of the inventions and is not intended to limit the scope of the invention. Certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention.

[0065] General Process for Preparation of Pyroxasulfone of Formula (I) from Compound of Formula (II)

[0066] Pyroxasulfone of Formula (I) can be prepared by reacting the compound of Formula (II) with a suitable oxidizing agent in presence of a metal catalyst, an inorganic acid and optionally a phase transfer catalyst using the following general steps: a) charging pre-determined amount of selected oxidizing agent at 25-30°C; b) adding pre-determined amount of selected solvent; c) feeding pre-determined amount of selected inorganic acid in Ihr at 25-30°C; d) stirring the mixture continuously; e) adding 1-2 gm of metal catalyst at 25-30°C and optionally adding 0.5-1 gm of a phase transfer catalyst (preferably tetrabutylammonium bromide); f) feeding pre-determined amount of compound of Formula (II) in pre-determined amount of solvent solution in 4-6hrs at 60-65°C; g) after complete addition of compound of Formula (II) the temperature rises up to 70-72°C; maintain the temperature for a period of 16-20 Hrs. h) adding Sodium Sulphite solution (after the reaction mass has cooled down to about 55°C) to the reaction mass till starch iodide paper turns colorless from blue. i) Later adding water into the residual mass and maintaining the pH 7-8 by using Caustic lye or Caustic soda solution. j) washing the filtered compound with 10% sodium bicarbonate to obtain the final product of formula (I) with up to 99% yield.

[0067] EXAMPLES

[0068] Below is an illustration of Process for Preparation of Pyroxasulfone (Formula I) from compound of Formula II using the present invention and also by using Hydrogen Peroxide (as an oxidizing agent) already known in the art (Comparative Examples).

[0069] Reaction Scheme II: Transfer Catalyst

[0070] 3-{[5-(difluoromethoxy)-l-methyl-3- 3-{[5-(difluoromethoxy)-l-methyl-3-(trifluoromethyl)-lH-

[0071] (trifluoromethyl)pyrazol-4-yl](methylsulfanyl)}-5,5- pyrazol-4-yl](methanesulfonyl)}-5,5-dimethyl-4,5-dihydro-l,2- dimethyl-4H-l,2-oxazole oxazole

[0072] (ID Pyroxasulfone (I)

[0073] Example 1: Charge 42.8gm of Sodium perborate tetrahydrate at 25-30°C in 250ml 4- neck RBF. Add 200 mL acetonitrile. Feed 30% Sulphuric acid (50gm) in Ihr at 25-30°C, stirring continuously. Add Igm of sodium tungstate at 25-30°C and optionally add TB AB 0.5gm. Heat the mixture upto 60-65°C. Feed 50gm compound of Formula (II) in 200gm acetonitrile solution in 6hrs, stirred for 4hrs at 60-65°C. Add water and stir for 30mins. Filtered wet cake is washed with 10% Sodium bicarbonate. The final product of Formula (I) is isolated with 99.7% purity (Yield: 96%)

[0074] Example 2: Charge 42.8gm of Sodium perborate monohydrate at 25-30°C in 250ml 4- neck RBF. Add 200 mL acetonitrile. Feed 30% Sulphuric acid (50gm) in Ihr at 25-30°C, stirring continuously. Add Igm of sodium tungstate at 25-30°C and optionally add TB AB 0.5gm. Heat the mixture upto 60-65°C. Feed 50gm compound of Formula (II) in 200gm acetonitrile solution in 6hrs, stirred for 4hrs at 60-65°C. Add water and stir for 30mins. Filtered wet cake is washed with 10% Sodium bicarbonate. The final product of Formula (I) is isolated with 99.7% purity (Yield: 96%)

[0075] Example 3: Charge 47.1gm of Sodium perborate tetrahydrate at 25-30°C in 250ml 4- neck RBF. Add 125 mL acetonitrile. Feed 30% Hydrochloric acid (20gm) in Ihr at 25- 30°C, stirring continuously. Add Igm of sodium tungstate at 25-30°C and optionally add TBAB 0.5gm. Heat the mixture upto 60-65°C. Feed 50gm compound of Formula (II) in 300gm acetonitrile solution in 6hrs, stirred for 4hrs at 60-65°C. Add water and stir for 30mins. Filtered wet cake is washed with 10% Sodium bicarbonate. The final product of Formula (I) is isolated with with 99.5% purity (Yield: 85%).

[0076] Example 4: Charge 45gm of Sodium perborate tetrahydrate at 25-30°C in 250ml 4-neck RBF. Add 125 mL acetonitrile. Feed dil. para toluene sulphonic acid (24gm) in Ihr at 25-30°C, stirring continuously. Add Igm of sodium tungstate at 25-30°C and optionally add TBAB 0.5gm. Heat the mixture upto 60-65°C. Feed 50gm compound of Formula (II) in 300gm acetonitrile solution in 6hrs, stirred for 4hrs at 60-65°C. Add water and stir for 30mins. Filtered wet cake is washed with 10% Sodium bicarbonate. The final product of Formula (I) is isolated with 99.3% purity (Yield: 80%).

[0077] Example 5: Charge 47. Igm of Sodium perborate tetrahydrate at 25-30°C in 250ml 4- neck RBF. Add 200 mL acetonitrile. Feed 40% H2SO4 (42.5gm) in Ihr at 25-30°C, stirring continuously. Add Igm of 85% Molybdic acid as a catalyst at 25-30°C and optionally add TBAB 0.5gm. Heat the mixture upto 60-65°C. Feed 50gm compound of Formula (II) in 300gm acetonitrile solution in 6hrs, stirred for 4hrs at 60-65°C. Add water and stir for 30mins. Filtered wet cake is washed with 10% Sodium bicarbonate. The final product of Formula (I) is isolated with 99.6% purity (Yield: 90%).

[0078] Example 6: Charge 47. Igm of Sodium perborate tetrahydrate at 25-30°C in 250ml 4- neck RBF. Add 150gm tetrahydrofuran. Feed 40% H2SO4 (42.5gm) in Ihr at 25-30°C, stirring continuously. Add Igm of sodium tungstate as a catalyst at 25-30°C and optionally add TBAB 0.5gm. Heat the mixture upto 60-65°C. Feed 50gm compound of Formula (II) in 150 mL tetrahydrofuran solution in 6hrs, stirred for 4hrs at 60-65°C. Add water and stir for 30mins. Filtered wet cake is washed with 10% Sodium bicarbonate. The final product of Formula (I) is isolated with 99.6% purity (Yield: 91%).

[0079] Comparative Example 1: Charge 39.4gm of Hydrogen peroxide at 25-30°C in 250ml 4-neck RBF. Add 200 mL of acetonitrile. Feed 30% Sulphuric acid (50gm) in Ihr at 25- 30°C, stirring continuously. Add Igm of sodium tungstate as a catalyst at 25-30°C and optionally add TBAB 0.5gm. Heat the mixture upto 60-65°C. Feed 50gm compound of Formula (II) in 200 mL of acetonitrile solution in 6hrs, stirred for 4hrs at 60-65°C. Add water and stir for 30mins. Filtered wet cake is washed with 10% Sodium bicarbonate. The final product of Formula (I) is isolated with 97.8% purity (Yield: 78%).

[0080] Comparative Example 2: Charge 39.4gm of Hydrogen peroxide at 25-30°C in 250ml 4-neck RBF. Add 150 mL tetrahydrofuran. Feed dil. para toluene sulphonic acid (20gm) in Ihr at 25-30°C, stirring continuously. Add Igm of sodium tungstate as a catalyst at 25-30°C and optionally add TBAB 0.5gm. Heat the mixture upto 60-65°C. Feed 50gm compound of Formula (II) in 150gm tetrahydrofuran solution in 6hrs, stirred for 4hrs at 60-65°C. Add water and stir for 30mins. Filtered wet cake is washed with 10% Sodium bicarbonate. The final product of Formula (I) is isolated with 97.2% purity (Yield: 75%).

[0081] It is observed that the process using salts of Perboric acid as an oxidizing agent results in significantly higher yields of Pyroxasulfone. Moreover, when combined with an inorganic acid, it produces a powerful oxidation medium for complete oxidation. Further addition of a suitable metal catalyst such as sodium tungstate or molybdic acid enhances selective Sulphur oxidation.

[0082] In contrary, process with Hydrogen Peroxide resulted in lower yields and relatively higher impurity levels as shown in Comparative examples 1&2. Hydrogen peroxide decomposes and leads to inconsistent oxidation and formation of undesired by-products leading to high impurity profile in the final product. A comparison of the Results obtained in terms of Yield and Purity after using Hydrogen Peroxide and PBS in presence of inorganic acids and metal catalysts are Tabulated below: Table No. 1:

[0083] The major advantage of using a salt of perboric acid in its crystalline hydrate form over Hydrogen Peroxide as an oxidizing agent is that it has higher oxidation potential and reactivity. Furthermore, storage and handling of PBS notably, offers low toxicity and an extended shelf life in comparison to highly concentrated Hydrogen Peroxide solutions that can also pose a significant explosion hazard.

[0084] The inventors of the present invention found that the crystalline form of Sodium Perborate acts as an excellent oxidizing agent even at a low pH as against Hydrogen Peroxide. The use of the crystalline hydrate of Sodium Perborate delivers peroxoborate anions in the reaction system for complete oxidation.

[0085] The difference in the yield and purity of Formula I is as illustrated in table 1. Thus, the preferred oxidizing agents used in the process of oxidation of Formula II to obtain Formula I are perboric acids and its salts thereof (PBS). Furthermore, the preferred inorganic acid is Sulphuric acid for obtaining higher yield and purity. Table 2:

[0086] Sodium Perborate or its hydrates are a mild, inexpensive, and air-stable oxidizing agent. Due to its high affinity for water it is usually found in its hydrated form. The process of the present invention can selectively and effectively oxidize the Sulphur in Formula (II). In nearly every instance, the process of the present invention leads to improved yield and purity of the product. The use of PBS in presence of an inorganic acid such as Sulphuric acid or Hydrochloric acid or Para toluene sulphonic acid and a suitable metal catalyst such as Sodium tungstate or Molybdic acid, provides an effective oxidation for higher yield and purity in the process of oxidizing Formula II to obtain Formula I of Pyroxasulfone.

[0087] In addition, the process of the present invention does not have problems associated with neutralization of organic acid residue in the effluent generated. Higher yield makes the overall process cost effective and reduces the problem of waste management.

[0088] Thus, the inventors of the present invention have successfully developed a novel and improved process for Synthesis of Pyroxasulfone of Formula (I) from Formula (II). The process of the present invention provides higher yield and reduced impurity profile as compared to those known in the art. The process of the present invention is simple, sustainable, efficient, improved, cost effective and commercially viable.

[0089] Having described what is considered the best form presently contemplated for embodying the present invention. Numerous alterations, modifications, and / or alternative applications of the invention will be promptly apparent to those skilled in the art. Therefore, it is to be understood that the present invention is not limited to the practical aspects of the actual preferred embodiments hereby described and that any such modifications and variations must be considered as being within the spirit and the scope of the invention, as described herein above.

Claims

Claims:

1. A novel and improved process for preparing Pyroxasulfone of Formula (I) or salts thereoffrom a compound of Formula (II),comprising: reacting the compound of Formula (II) at a temperature ranging from 20 to 80°C with an oxidizing agent in presence of a metal catalyst, an inorganic acid, and optionally a phase transfer catalyst.

2. The process as claimed in Claim 1, wherein the oxidizing agent is selected from a group comprising of perboric acid, salt of perboric acid, peracetic acid, hypochlorite and its salts such as sodium hypochlorite, potassium hypochlorite, permanganates and manganese dioxide.

3. The process as claimed in Claim 1, wherein the metal catalyst is selected from a group comprising tungsten catalyst, molybdenum catalyst, iron catalyst, manganese catalyst, vanadium catalyst, niobium catalyst, tantalum catalyst, titanium catalyst, zirconium catalyst, copper catalyst, thallium catalyst, including their acid and salt forms.

4. The process as claimed in Claim 1, wherein the inorganic acid is selected from a group comprising of hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid and para-toluenesulfonic acid.

5. The process as claimed in Claim 1 , wherein the solvent is selected from a group comprising of tetrahydrofuran, chlorobenzene, dichlorobenzene, dichloromethane, methanol, ethanol, propanol, 2-propanol, butanol, sec-butanol, isobutanol, tert-butanol, sec-amyl alcohol, acetonitrile, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate and its isomers, N,N-dimethylformamide (DMF).

6. The process as claimed in Claim 1, wherein the optionally used phase transfer catalyst is selected from Quaternary ammonium salts, crown ethers and phosphonium compounds.

7. Pyroxasulfone of formula (I) prepared from compound of Formula (II) using the process as claimed in the preceding claims is used in the preparation of agrochemical compositions or formulations.

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