DESC:1

FORM 2

THE PATENTS ACT, 1970
(39 of 1970)

&

THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
(See Section 10 and Rule 13)

PROCESS FOR PREPARATION OF PYROXASULFONE

SHOGUN ORGANICS LIMITED
Block A, NDM-1, 4th & 5th Floor, Netaji Subhash Place, Delhi, 110034

The following specification describes the invention and the manner in which it is to be
performed.

2

PROCESS FOR PREPARATION OF PYROXASULFONE

FIELD OF THE INVENTION
The present invention relates to a process for the preparation of Pyroxasulfone of Formula
(I) or salts thereof from a compound of Formula (II).

5 Formula (I) Formula (II)
BACKGROUND OF THE INVENTION
Pyroxasulfone is an isoxazoline herbicide, which acts by inhibition of very-long-chain fatty
acid elongase (VLCFAE). It is chemically known as [5-(difluoromethoxy)-1-methyl-3-
(trifluoromethyl)1H-pyrazol-4-yl]methyl4,5-dihydro-5,5-dimethylisoxazol-3-yl sulfone and
10 has the CAS No. 447399-55-5. Represented by compound of Formula (I)

Formula (I)
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,
15 Phalaris minor, Echinochloa colonum, Celosia argentia, Trianthema porulacastrum,
Amarthanas viridis, Digeria arvensis in crops such as Maize, Wheat and Soybean.

3

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:

5

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.
10 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

4

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
chemoselectivity.
5 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;

10 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.
In addition to these organic acids being expensive they also have problems associated with
15 contamination from undesired micro-organisms during storage.
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
20 Pyroxasulfone. Thus, a considerable amount of impurity is obtained along with
Pyroxasulfone which is difficult to isolate.
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

5

effluent treatment plants also generate air pollutants. Such problems make the entire process
unsustainable and may also cause significant hazard to the environment.
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
5 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.
OBJECT OF THE INVENTION:
10 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.
Another main object of the present invention is to provide a process that gives high yield of
Pyroxasulfone of Formula (I)
15 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)
SUMMARY OF THE INVENTION
According to an aspect of the present invention, there is provided a process for preparation
20 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.
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
25 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 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,
30 etc.

6

According to another embodiment of the present invention, the oxidizing agent is not
hydrogen peroxide.
According to yet another embodiment of the present invention, the catalyst is selected from
metal catalysts.
5 According to still another embodiment of the present invention, the acid is selected from
inorganic acids.
DETAILED DESCRIPTION OF THE INVENTION
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
10 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.
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
15 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.
The term “about” or “approximately” as used herein is inclusive of the stated value and
20 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
25 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
30 provided. For example, “0.1-80%” includes 0.1 %, 0.2%, 0.3%, etc. up to 80%.

7

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
5 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 term “room temperature” unless stated otherwise, essentially means temperature in
10 range of 20-35 °C
The term "purity" means purity as determined by HPLC ("High Pressure Liquid
Chromatography").
The term “Pyroxasulfone” as used herein, includes Pyroxasulfone free base or its salts and
is used interchangeably throughout the disclosure.
15 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.
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.
20 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.
According to an aspect of the present invention, there is provided a process for preparation
25 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.

8

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:
Reaction Scheme I:

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.
5 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.
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
10 sodium perborate, sodium peroxometaborate, sodium peroxoborate, sodium peroxoborate
hexahydrate, sodium perborate monohydrate, sodium perborate tetrahydrate, etc.
According to yet another embodiment of the present invention, the oxidizing agent is a salt
of perboric acid.

Oxidizing Agent

Metal Catalyst &
Inorganic acid &
optionally Phase
Transfer Catalyst

CAS No: 656825-92-2
3-{[5-(difluoromethoxy)-1-methyl-3-
(trifluoromethyl)pyrazol-4-yl](methylsulfanyl)}-5,5-
dimethyl-4H-1,2-oxazole
(II)

CAS No.: 447399-55-5
3-{[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-
pyrazol-4-yl](methanesulfonyl)}-5,5-dimethyl-4,5-dihydro-1,2-
oxazole
Pyroxasulfone (I)

9

According to still another preferred embodiment of the present invention, the salt of perboric
acid is Sodium Perborate or its hydrates.
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
5 formula NaBO3 • n H2O (with n ranging from 1 to 4).
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.
10 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.
15 According to yet another preferred embodiment of the present invention, the metal catalyst
is a tungsten catalyst or molybdenum catalyst.
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
20 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
25 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.
According to yet another embodiment the preferred examples of molybdenum catalyst
include molybdic acid, molybdate, molybdenum metal, molybdenum oxide, sodium
30 molybdate, potassium molybdate, ammonium molybdate, molybdenum carbide,
molybdenum chloride, molybdenum sulfide, molybdenum bromide, phosphomolybdic acid,

10

sodium phosphomolybdate, phosphorus ammonium molybdate, silicomolybdic acid,
sodium silicomolybdate and salts and mixtures thereof. More preferably ammonium
molybdate or molybdic acid.
The process according to Reaction Scheme I wherein, the inorganic acid is selected from a
5 group comprising of hydrochloric acid, hydrobromic acid, hydroiodic acid, sulphuric acid,
para toluene sulphonic acid and the like.
According to still another embodiment of the present invention, the inorganic acid is
preferably sulphuric acid, hydrochloric acid or para-toluene sulphonic acid.
In the described process, inorganic acids are used instead of organic acids since they provide
10 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
15 metal catalysts involved in the oxidation process, leading to higher yield and purity of
compound of Formula I (Pyroxasulfone).
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.
20 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.
25 According to another embodiment of the present invention, the solvent is preferably
acetonitrile or tetrahydrofuran.
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

11

In an embodiment Pyroxasulfone prepared using the method of the present invention is
substantially free of impurity.
An embodiment of the present invention provides, Pyroxasulfone of Formula (I) having
purity of more than 95%, preferably more than 99%.
5 An embodiment of the present invention provides, Pyroxasulfone of Formula (I) with the
Yield of up to 96% or more.
In another embodiment Pyroxasulfone prepared using the process disclosed in the present
invention is used in the preparation of agrochemical composition or formulation.
The further embodiment of the present invention is illustrated by the following examples
10 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.
General Process for Preparation of Pyroxasulfone of Formula (I) from Compound of
15 Formula (II)
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;
20 b) adding pre-determined amount of selected solvent;
c) feeding pre-determined amount of selected inorganic acid in 1hr 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);
25 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
70-72oC; maintain the temperature for a period of 16-20 Hrs.
h) adding Sodium Sulphite solution (after the reaction mass has cooled down to about
30 55oC) to the reaction mass till starch iodide paper turns colorless from blue.

12

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.
5 EXAMPLES
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).
Reaction Scheme II:
10

15
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 1hr at 25-30°C,
stirring continuously. Add 1gm 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
20 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%)

Example 2: Charge 42.8gm of Sodium perborate monohydrate at 25-30°C in 250ml 4-
25 neck RBF. Add 200 mL acetonitrile. Feed 30% Sulphuric acid (50gm) in 1hr at 25-30°C,
stirring continuously. Add 1gm of sodium tungstate at 25-30°C and optionally add

PBS/ H2O2
Metal Catalyst &
Inorganic acid &
optionally Phase
Transfer Catalyst

3-{[5-(difluoromethoxy)-1-methyl-3-
(trifluoromethyl)pyrazol-4-yl](methylsulfanyl)}-5,5-
dimethyl-4H-1,2-oxazole
(II)

3-{[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-
pyrazol-4-yl](methanesulfonyl)}-5,5-dimethyl-4,5-dihydro-1,2-
oxazole
Pyroxasulfone (I)

13

TBAB 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%)

5

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 1hr at 25-
30°C, stirring continuously. Add 1gm 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
10 (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%).

Example 4: Charge 45gm of Sodium perborate tetrahydrate at 25-30°C in 250ml 4-neck
15 RBF. Add 125 mL acetonitrile. Feed dil. para toluene sulphonic acid (24gm) in 1hr at
25-30°C, stirring continuously. Add 1gm 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
20 product of Formula (I) is isolated with 99.3% purity (Yield: 80%).

Example 5: Charge 47.1gm of Sodium perborate tetrahydrate at 25-30°C in 250ml 4-
neck RBF. Add 200 mL acetonitrile. Feed 40% H2SO4 (42.5gm) in 1hr at 25-30°C,
stirring continuously. Add 1gm of 85% Molybdic acid as a catalyst at 25-30°C and
25 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%).

30 Example 6: Charge 47.1gm of Sodium perborate tetrahydrate at 25-30°C in 250ml 4-
neck RBF. Add 150gm tetrahydrofuran. Feed 40% H2SO4 (42.5gm) in 1hr at 25-30°C,
stirring continuously. Add 1gm 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.

14

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%).

5 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 1hr at 25-
30°C, stirring continuously. Add 1gm 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
10 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%).

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)
15 in 1hr at 25-30°C, stirring continuously. Add 1gm 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%).
20
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
25 Sulphur oxidation.
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
30 and Purity after using Hydrogen Peroxide and PBS in presence of inorganic acids and metal
catalysts are Tabulated below:

15

Table No. 1:
Oxidizing Agent Inorganic acid Result
Yield Purity
Sodium Perborate
Monohydrate

30% Sulphuric
Acid (H2SO4)

96% (Highest) 99.7% (Highest)

Sodium Perborate
Tetrahydrate

30% Sulphuric
Acid (H2SO4)

96% (Highest) 99.7% (Highest)

Sodium Perborate
Tetrahydrate

Dil. Para Toluene
Sulphonic Acid

80% 99.3

Hydrogen Peroxide 30% Sulphuric
Acid (H2SO4)

78% 97.8%

Hydrogen Peroxide Dil. Para Toluene
Sulphonic Acid

75% (Lowest) 97.2% (Lowest)

The major advantage of using a salt of perboric acid in its crystalline hydrate form over
5 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.
The inventors of the present invention found that the crystalline form of Sodium Perborate
10 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.

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
15 are perboric acids and its salts thereof (PBS). Furthermore, the preferred inorganic acid is
Sulphuric acid for obtaining higher yield and purity.

16

Table 2:

Example
No.

Solvent Oxidizing
Agent

Inorganic
acid

Catalyst Result

Yield Purity

Example 1 200 mL of
Acetonitrile

42.8g of
Sodium
perborate
tetrahydrate

30 %
Sulphuric
acid (50gm)

Sodium
tungstate
1gm

96% 99.7%

Example 2 200 mL of
Acetonitrile

42.8g of
Sodium
perborate
monohydrate

30 %
Sulphuric
acid (50gm)

Sodium
tungstate
1gm

96% 99.7%

Example 3 125 mL of
Acetonitrile

47.1 gm
Sodium
perborate
tetrahydrate

30 %
Hydrochloric
Acid (20gm)

Sodium
tungstate
1gm

85% 99.5%

Example 4 125 mL of
Acetonitrile

45 gm of
Sodium
perborate
tetrahydrate

Dil. Para
Toluene
Sulphonic
Acid (24gm)

Sodium
tungstate
1gm

80% 99.3%

Example 5 200 mL of
Acetonitrile

47.1 gm of
Sodium
perborate
tetrahydrate

40 %
Sulphuric
Acid (42.5
gm)

Molybdic
Acid
1gm

90% 99.6%

Example 6 150 mL of
Tetrahydrofuran

47.1 gm of
Sodium

40 %
Sulphuric

Sodium
tungstate
1gm

91% 99.6%

17

perborate
tetrahydrate

Acid (42.5
gm)

Comparative
Example 1

200 mL of
Acetonitrile

39.4gm of
Hydrogen
peroxide

30%
Sulphuric
Acid (50
gm)

Sodium
tungstate
1gm

78% 97.8%

Comparative
Example 2

150 mL of
Tetrahydrofuran

39.4gm of
Hydrogen
peroxide

Dil. Para
Toluene
Sulphonic
Acid (20gm)

Sodium
tungstate
1gm

75% 97.2%

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
5 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.
10 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.
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
15 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.
Having described what is considered the best form presently contemplated for embodying
the present invention. Numerous alterations, modifications, and/or alternative applications
20 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

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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.

Dated this 15th day of June, 2024

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Dated this 15th day of June 2024

Anshu Agrawal
IN/PA - 4170
Authorized Agent of the Applicant

,CLAIMS:We Claim:

1. A process for preparing Pyroxasulfone of Formula (I) or salts thereof

(I)

from a compound of Formula (II),

(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.

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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.