DESC:FIELD
The present disclosure relates to a process for preparing crystalline sulfentrazone.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicates otherwise.
Herbicide: The term “Herbicide” refers to a chemical substance that inhibits and/or kills unwanted plants, such as sedges, weeds, grasses, and broadleaf plants, and that can be used for crop protection.
Alkali Salts: The term “Alkali salts” refers to soluble hydroxides of alkali metals and alkaline earth metals.
Ambient Temperature: The term “ambient temperature” refers to a temperature between 15 °C and 30 °C.
Crystallization: The term “Crystallization” refers to the precipitation of a solid material (a precipitate), which includes a crystalline material, from a liquid solution of the solid material.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
N-[2,4-dichloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl] phenyl] methanesulfonamide is commonly known as sulfentrazone, which is used as a herbicide. Sulfentrazone is known to inhibit protoporphyrinogen oxidase (PPO) in weeds and unwanted plants, thereby disrupting membranes and inhibiting photosynthesis in weeds and plants. On treatment of soil with sulfentrazone, plants emerging from the soil primarily take up sulfentrazone through the roots, resulting in necrosis followed by death of the exposed plants on exposure to light. Treatment of plants with sulfentrazone results in rapid dessication of the exposed plant tissue followed by death. Sulfentrazone is highly effective against sedges, grasses, tall fescue, and broadleaf weeds.
Commercially available partially amorphous solid form of technical grade sulfentrazone contains entrapped solvents. Amorphous sulfentrazone can be crystallized to obtain crystalline sulfentrazone. However, conventional processes for preparing crystalline sulfentrazone use large amounts of organic solvents, which are environmentally toxic and require subsequent energy intensive processes for their removal.
There is, therefore, felt a need for providing a process for preparing a crystalline sulfentrazone that mitigates the drawbacks mentioned herein above.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure is to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
It is another object of the present disclosure is to provide a process for preparing crystalline sulfentrazone.
It is still another object of the present disclosure is to provide a simple, environmentally friendly, economical, and efficient process for preparing crystalline sulfentrazone.
It is yet another object of the present disclosure is to provide crystalline sulfentrazone having relatively high purity and in high yields.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
In a first aspect, the present disclosure provides a process for preparing crystalline sulfentrazone, the process comprises treating sulfentrazone with an aqueous solution of an alkali salt, under stirring at a temperature in the range of 15 to 55 °C, for a time period in the range of 0.1 to 2 hours to obtain a mixture. The mixture is dissolved in a fluid medium and filtered to obtain a clear solution. Sulfentrazone dissolved in the clear solution is crystallized by acidifying the aqueous solution with an aqueous acid, until its pH is in the range of 2 to 4, to obtain a slurry comprising crystalline sulfentrazone form G. The crystalline sulfentrazone form G, is isolated from the slurry. The crystalline sulfentrazone form G, has purity in the range of 98% to 99.8%.
The crystalline sulfentrazone form G exhibits at least 3 of the following reflexes, in any combination, as 2? ± 0.2 degree in an X-ray powder diffractogram (X-RPD) recorded using Cu-Ka radiation at 25 °C.
2 theta
10.23
12.6
16.1
17.29
17.7
18.45
20.58
21.65
22.55
24.14
24.93
25.3
26.83
28.77
30.9
31.29
33.88

In accordance with the present disclosure, the step of isolating crystalline sulfentrazone form G from the slurry involves a step of equilibrating the slurry under stirring for a time period in the range of 0.25 to 0.75 hours, followed by filtering to collect the crystalline sulfentrazone form G, which is washed with water until the pH of the water washings is neutral, to obtain wet crystalline sulfentrazone form G that is dried under reduced pressure to obtain dried crystalline sulfentrazone form G.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The present disclosure will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates an X-ray powder diffractogram (X-RPD) of crystalline sulfentrazone form G; and
Figure 2 illustrates a differential scanning calorimetry (DSC) thermogram of crystalline sulfentrazone form G.
DETAILED DESCRIPTION
Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details, are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
Sulfentrazone is a broad spectrum herbicide, which can be applied as a foliar spray or a soil-treatment prior to planting, as it has a residual effect. It acts as a systemic herbicide which has curative, translaminar and preventative action.

Sulfentrazone
Chemical Name: N-[2,4-dichloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl]phenyl]methanesulfonamide
CAS no.: 122836-35-5
The present disclosure provides a simple, environmentally friendly, economical, and efficient process for preparing crystalline sulfentrazone having relatively high purity and in high yields.
In the present disclosure the crystalline form of N-[2,4-dichloro-5-[4-(difluoromethyl)4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl] phenyl] methanesulfonamide, is referred to as “crystalline sulfentrazone form G”.
In a first aspect, the present disclosure provides a process for preparing crystalline sulfentrazone, the process comprises treating sulfentrazone with an aqueous solution of an alkali salt, under stirring at a temperature in the range of 15 to 55 °C, for a time period in the range of 0.1 to 2 hours to obtain a mixture. The mixture is dissolved in a fluid medium and filtered to obtain a clear solution. The dissolved sulfentrazone in the clear solution is crystallized by acidifying the clear solution with an aqueous acid, until its pH is in the range of 2 to 4, to obtain a slurry comprising crystalline sulfentrazone form G. The crystalline sulfentrazone form G, is isolated from the slurry. The crystalline sulfentrazone form G has purity in the range of 98% to 99.8%.
In accordance with the embodiments of the present disclosure, the molar ratio of the sulfentrazone to the alkali salt is in the range from 1:1 to 1.2:1.
In accordance with one embodiment of the present disclosure, the molar ratio of sulfentrazone to the alkali salt is 1.1 to 1.
In accordance with the embodiments of the present disclosure, the sulfentrazone is in any form of sulfentrazone other than form G of sulfentrazone.
In accordance with the embodiments of the present disclosure, the aqueous solution of the alkali salt has a concentration in the range of 0.1 to 0.5 N.
In accordance with the embodiments of the present disclosure, the alkali salt is selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, and calcium hydroxide.
In accordance with one embodiment of the present disclosure, sulfentrazone is treated with an aqueous solution of an alkali salt, at a temperature in the range of 15 to 55. °C for 0.5 hours.
In accordance with the embodiments of the present disclosure, the molar ratio of the fluid medium to the sulfentrazone is in the range of 5:1 to 20:1.
In accordance with the embodiments of the present disclosure, the fluid medium is selected from the group consisting of methanol, ethanol, and propanol.
In accordance with one embodiment of the present disclosure, the fluid medium is water.
The process of the present disclosure does not use environmentally toxic organic solvents. Thus, the process of the present disclosure is environment friendly.
In accordance with the embodiments of the present disclosure, the aqueous acid has a concentration in the range of 8 to 12 N.
In accordance with one embodiment of the present disclosure, the aqueous acid has a concentration of 10 N.
In accordance with the embodiments of the present disclosure, the aqueous acid is selected from aqueous hydrochloric acid (HCl) and aqueous sulfuric acid (H2SO4).
In accordance with one embodiment of the present disclosure, the aqueous acid is aqueous hydrochloric acid (HCl).
In accordance with one embodiment of the present disclosure, the pH of the acidified solution is 3.
In accordance with the embodiments of the present disclosure, the step of isolating crystalline sulfentrazone form G from the slurry comprising crystalline sulfentrazone form G, further involves a step of equilibrating the slurry under stirring for a time period in the range of 0.25 to 0.75 hours, followed by filtering to collect the crystalline sulfentrazone form G, which is washed with water until the pH of the water washings is neutral, to obtain wet crystalline sulfentrazone form G that is dried under reduced pressure to obtain dried crystalline sulfentrazone form G.
In accordance with the embodiments of the present disclosure, the separation of the crystalline sulfentrazone form G from the slurry is achieved by a simple physical process such as filtration. Therefore the process of the present disclosure is cost effective.
In one embodiment of the present disclosure, the dried crystalline sulfentrazone form G is 99.51% pure.
In another embodiment of the present disclosure, the dried crystalline sulfentrazone form G is 98.49% pure.
In still another embodiment of the present disclosure, the dried crystalline sulfentrazone form G is 98.42% pure.
The present disclosure provides crystalline sulfentrazone form G, which is polymorphic form G of sulfentrazone and exhibits at least 3 of the following peaks;
2 theta
10.23
12.6
16.1
17.29
17.7
18.45
20.58
21.65
22.55
24.14
24.93
25.3
26.83
28.77
30.9
31.29
33.88

in any combination, as 2? ± 0.2 degree in an X-ray powder diffractogram (X-RPD) recorded using Cu-Ka radiation at 25 °C.
In the present disclosure, the crystalline sulfentrazone form G is characterized by X-ray powder diffraction pattern as represented in Figure 1.
In the present disclosure, the crystalline sulfentrazone form G exhibits an endothermic melting peak having a maximum at 124°C to 125°C in its differential scanning calorimetry (DSC) thermogram as represented in Figure 2.
The crystalline sulfentrazone form G of the present disclosure can be used as herbicidal or in a herbicidal composition in the form of water dispersible granules, wettable powder, a suspension concentrate, an oil suspension, suspoemulsion and a capsule suspension.
The crystalline sulfentrazone form G of the present disclosure can be included in herbicidal compositions or formulations in a suitable manner known the art using auxiliaries,carriers and solvents and the like, in a known manner analogous to that for amorphous sulfentrazone.
The crystalline sulfentrazone form G of the present disclosure has enhanced herbicidal activity as well as enhanced biocidal activity in controlling unwanted plant growth.
It is observed that the crystalline sulfentrazone form G of the present disclosure is stable and shows enhanced efficacy when used as a herbicide or in a herbicidal composition.
The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
The present disclosure is further illustrated herein below with the help of the following experiments. The experiments used herein are intended merely to facilitate an understanding of the ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the experiments should not be construed as limiting the scope of embodiments herein. These laboratory scale experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial/commercial scale.
EXPERIMENTAL DETAILS
Example 1: Preparation of Crystalline Sulfentrazone form G:
Procedure: Sulfentrazone (52 g, 0.134 moles, purity by GLC 98.93%) was added in water (400 ml) and NaOH (8.2 ml) under stirring at room temperature for ½ hour to obtain a mixture. The mixture was dissolved in methanol (100 ml, 2.47 moles) and filtered to obtain a methanolic solution, which was acidified using 10N HCl solution until the pH of the solution was 3, at which the dissolved product crystallized from the acidified solution to obtain a slurry comprising crystals of sulfentrazone form G. The slurry was equilibrated under stirring for ½ hour, filtered to collect the crystals of sulfentrazone form G, which were washed with water (500ml) until the pH of the water washings was neutral, to obtain wet crystals of sulfentrazone form G. The wet crystals were dried under reduced pressure to obtain dried crystals of sulfentrazone form G (48 g, 0.124 moles, yield 92.5%, purity 99.51% (by GLC), melting point: 124.40°C (by DSC)).
The X-ray powder diffractogram of crystals exhibited peaks as shown in Figure 1.
Example 2:
Procedure: Sulfentrazone (33 g, 0.085 moles, purity by GLC 92.41%) was added in water (400 ml) and NaOH (5.2 ml) under stirring at room temperature for ½ hour to obtain a product mixture. The product mixture was dissolved in methanol (50 ml, 1.24 moles) and filtered to obtain a methanolic solution, which was acidified using 10N HCl solution until the pH of the solution was 3, at which the dissolved product crystallized from the acidified solution to obtain a slurry comprising crystals of sulfentrazone form G. The slurry was equilibrated under stirring for ½ hour, filtered to collect the crystals of sulfentrazone form G, which were washed with water (200 ml) until the pH of the water washings was neutral, to obtain wet crystals of sulfentrazone form G, which were dried under reduced pressure to obtain dried crystals of sulfentrazone form G (30 g, 0.077 moles, yield 90.6%, purity 98.49% (by GLC), melting point: 124.73°C (by DSC)).
Example 3:
Procedure: Sulfentrazone (529 g, 1.37 moles) was slowly added in water (6 litres) and NaOH (83 ml) under stirring at room temperature for ½ hour and further stirred at 37 °C for ½ hour to obtain a product mixture. The product mixture was acidified using 10N HCl solution until the pH of the solution was 3, at which the dissolved product crystallized from the acidified solution to obtain a slurry comprising crystals of sulfentrazone form G. The slurry was equilibrated under stirring for ½ hour, filtered to collect the crystals of sulfentrazone form G, which were washed with water (2 × 500 ml) until the pH of the water washings was neutral, to obtain wet crystals of sulfentrazone form G, which were dried under reduced pressure to obtain dried crystals of sulfentrazone form G (454 g, 1.17 moles, yield 85.8%, purity 98.42% (by GLC), melting point: 124.54°C (by DSC)).
Table 1: 2? values of Crystalline Sulfentrazone form G, recorded in an X-ray powder diffractogram (X-RPD)
2 theta I/I0
10.23 33
12.6 35
16.1 55
17.29 42
17.7 22
18.45 26
20.58 42
21.65 100
22.55 30
24.14 68
24.93 57
25.3 49
26.83 42
28.77 31
30.9 24
31.29 26
33.88 21

TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of:
- a simple, environmentally friendly, economical, and efficient process for preparing crystalline sulfentrazone; and
- provide crystalline sulfentrazone having relatively high purity and in high yields.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
,CLAIMS:We Claim:
1. A process for preparing crystalline sulfentrazone, the process comprising the following steps:
i) treating sulfentrazone with an aqueous solution of an alkali salt, under stirring at a temperature in the range of 15 to 55 °C, for a time period in the range of 0.1 to 2 hours to obtain a mixture;
ii) dissolving the mixture in a fluid medium and filtering to obtain a clear solution;
iii) crystallizing the dissolved sulfentrazone in the clear solution, by acidifying the clear solution with an aqueous acid, until its pH is in the range of 2 to 4, to obtain a slurry comprising crystalline sulfentrazone form G; and
iv) isolating the crystalline sulfentrazone form G, from the slurry,
wherein the crystalline sulfentrazone form G in step (iv), has purity in the range of 98% to 99.8%; and
wherein the crystalline sulfentrazone form G exhibits at least 3 of the following reflexes, in any combination, as 2? ± 0.2 degree in an X-ray powder diffractogram (X-RPD) recorded using Cu-Ka radiation at 25 °C.
2 theta
10.23
12.6
16.1
17.29
17.7
18.45
20.58
21.65
22.55
24.14
24.93
25.3
26.83
28.77
30.9
31.29
33.88

2. The process as claimed in claim 1, wherein the molar ratio of the sulfentrazone to the alkali salt is in the range from 1:1 to 1.2:1.
3. The process as claimed in claim 2, wherein the molar ratio of sulfentrazone to the alkali salt is 1.1 to 1.
4. The process as claimed in claim 1, wherein the sulfentrazone is in any form other than form G of sulfentrazone.
5. The process as claimed in claim 1, wherein the aqueous solution of the alkali salt has a concentration in the range of 0.1 to 0.5 N.
6. The process as claimed in claim 1, wherein the alkali salt is selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide and calcium hydroxide.
7. The process as claimed in claim 1, wherein the molar ratio of the fluid medium to the sulfentrazone is in the range of 5:1 to 20:1.
8. The process as claimed in claim 1, wherein the fluid medium is selected from the group consisting of methanol, ethanol, and propanol.
9. The process as claimed in claim 1, wherein the aqueous acid has a concentration in the range of 8 to 12 N.
10. The process as claimed in claim 1, wherein the aqueous acid is selected from aqueous hydrochloric acid (HCl) and aqueous sulfuric acid (H2SO4).
11. The process as claimed in claim 1, wherein the step of isolating crystalline sulfentrazone form G from the slurry, involves a step of equilibrating the slurry under stirring for a time period in the range of 0.25 to 0.75 hours, followed by filtering to collect the crystalline sulfentrazone form G, which is washed with water until the pH of the water washings is neutral, to obtain wet crystalline sulfentrazone form G that is dried under reduced pressure to obtain dried crystalline sulfentrazone form G.
Dated this 4th Day of September, 2019

_______________________________
MOHAN DEWAN, IN/PA - 25
of R.K.DEWAN & CO.
Authorized Agent of Applicant

TO,
THE CONTROLLER OF PATENTS
THE PATENT OFFICE, AT MUMBAI