A process for the preparation of thiencarbazone-methyl

Abstract

The present invention relates to a process for the preparation of thiencarbazone-methyl. The present invention more particularly relates to a process for the preparation of thiencarbazone-methyl and a crystalline form thereof.

Description

[0001] A PROCESS FOR THE PREPARATION OF THIENCARBAZONE- METHYL

[0002] Field of the invention

[0003] The present invention relates to a process for the preparation of thiencarbazone- methyl. The present invention more particularly relates to a process for the preparation of thiencarbazone-methyl and a crystalline form thereof.

[0004] Background of the invention:

[0005] Thiencarbazone is a herbicidal active ingredient which is used to control grass and broadleaf weeds. It acts as ALS (acetolactate synthase) inhibitor, systemic, absorbed by roots and leaves. It is solely used as its methyl- derivative, i.e., thiencarbazone-methyl, individually or in combination with other herbicides and safeners; and can be formulated in the form of oil dispersions, flowable concentrates and water dispersible granules.

[0006] US Patent No. 6964939 (hereinafter referred to as US’939) broadly discloses thiencarbazone-methyl. US’939 also discloses the preparation method of substituted thiene-3-yl- sulfonyl amino(thio)carbonyl-triazolin(thi)ones by reacting substituted thiophene-3-sulphonamides with substituted triazolin(ethi)ones in presence of an organic base such as l,8-diazabicyclo-5.4.0-undec-7-ene (DBU). The effluent treatment of processes which involves use of organic base such as those described in US’939 is laborious and costly. Additionally, DBU is considered hazardous by the 2012 OSHA Hazard Communication Standard (29 CFR 1910.1200).

[0007] US Patent No.10906893 (hereinafter referred to as US’893) discloses preparation of thiencarbazone-methyl by reacting substituted thiophene-3-sulfonyl chlorides with imidazole compound and metal cyanate. Metal cyanates have tendency to undergo rapid hydrolysis to carbonates and ammonia in a moist atmosphere, making it difficult for storage and transportation in humid conditions. This results in metal cyanates being used in the larger quantities for the reaction than actually required, making the process less economical.

[0008] Therefore, there is a need for a process for preparing thiencarbazone-methyl which can avoid drawbacks associated in the prior art processes. The inventors of the present invention have developed a novel process for preparing thiencarbazone-methyl by employing advantageous reagents thereby making the process cost effective and industrially viable.

[0009] Object of the Invention:

[0010] An object of the present invention is to provide a process for the preparation of thiencarbazone-methyl of Formula (I).

[0011] Formula (I)

[0012] Another object of the present invention is to provide cost effective and industrially viable process for preparing thiencarbazone-methyl.

[0013] Yet another object of present invention to provide a crystalline form of thiencarbazone-methyl.

[0014] Summary of the Invention:

[0015] It is an aspect of the present invention to provide a process for preparing thiencarbazone-methyl of Formula (I), the process comprising: reacting methyl 5-methyl-4-sulfamoylthiophene-3-carboxylate of Formula (II), with phenyl 4,5-dihydro-3-methoxy-4-methyl-5-oxo-lH-l,2,4-triazole-l- carboxylate of Formula (III), in presence of an inorganic base and a catalyst to get thiencarbazone-methyl of Formula (I).

[0016] In another aspect, the present invention provides a crystalline form of thiencarbazone- methyl.

[0017] In yet another aspect, the present invention provides a process of preparing crystalline form of thiencarbazone-methyl, wherein the process comprises: treating thiencarbazone- methyl with a solvent selected from C1-C2 alcohol, hydrocarbons, ethers, ketonic solvents or mixtures thereof. It is another aspect of the present invention to provide a process for preparing a crystalline form of thiencarbazone-methyl of Formula (I), the process comprising: a. reacting methyl 5-methyl-4-sulfamoylthiophene-3-carboxylate of Formula (ID, with Phenyl 4,5-dihydro-3-methoxy-4-methyl-5-oxo-lH-l,2,4-triazole-l- carboxylate of Formula (III), in presence of an inorganic base and a catalyst to obtain a crude thiencarbazone-methyl, b. treating crude thiencarbazone-methyl with a solvent selected from the group comprising of C1-C2 alcohol, hydrocarbons, ethers, ketonic solvents and mixtures thereof.

[0018] In another aspect of the present invention, there is provided thiencarbazone- methyl, having bulk density from about 0.1 g / ml to 1.0 g / ml.

[0019] In a yet another aspect of the present invention, there is provided thiencarbazone-methyl, further characterized by having a volume average particle size distribution D50 of less than or equal to 100 pm, preferably less than or equal to 75 pm.

[0020] In an aspect of the present invention, there is provided an agrochemical composition comprising thiencarbazone-methyl according to the present invention. In another aspect of the present invention, there is provided a method for the control of undesired plant growth, comprising subjecting the plants or their locus to the action of an agrochemical composition comprising thiencarbazone-methyl according to the present invention.

[0021] Brief description of drawings:

[0022] FIG. 1 illustrates powder X-ray diffraction pattern (PXRD) of thiencarbazone- methyl prepared according to example 1(a) of the present invention.

[0023] FIG. 2 is a differential scanning calorimetry (DSC) curve of thiencarbazone-methyl prepared according to example 1(a) of the present invention.

[0024] FIG. 3 is an Infrared (IR) spectrum of thiencarbazone-methyl prepared according to example 1(a) of the present invention.

[0025] FIG. 4 is a single crystal structure of thiencarbazone-methyl prepared according to example 1(a) of the present invention.

[0026] Detailed Description of the invention:

[0027] Those skilled in art will be aware that invention described herein is subject to variations and modifications other than those specifically described. It is to be understood that the invention described herein includes all such variations and modifications. The invention also includes all such steps, features, compositions, and methods referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more said steps or features.

[0028] Definitions:

[0029] For convenience, before further description of the present invention, certain terms employed in the specification, examples are described here. These definitions should be read considering the remainder of the disclosure and understood as by a person of skill in the art. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by a person of ordinary skill in the art. The terms used throughout this specification are defined as follows, unless otherwise limited in specific instances.

[0030] The terms used herein are defined as follows.

[0031] As used in this specification the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “include” and “includes”) or “containing” (and any form of containing, such as “contain” and “contains”), "characterized by" or any other variation thereof are inclusive or open- ended and do not exclude additional, unrecited elements or process steps.

[0032] Furthermore, unless stated otherwise, "or" refers to an inclusive "or" and not to an exclusive "or".

[0033] As used herein, the term “treatment", "treating", "treated" refers to mixing of product with solvent under stirring at room temperature or at boiling point of the solvent.

[0034] As used herein, the term “room temperature” unless stated otherwise, essentially means temperature in range of 20°C to 35 °C.

[0035] As used herein, the term “crude thiencarbazone-methyl” used herein refers to thiencarbazone-methyl having HPLC purity less than 90 %.

[0036] As used herein Dio refers to 10% particles of the total volume having size of less than or equal to 50 pm,

[0037] As used herein D50 refers to 50% particles of the total volume having size of less than or equal to 100 pm,

[0038] As used herein D90 refers to 90% particles of the total volume having size of less than or equal to 150 pm,

[0039] The inventors of present invention have developed a cost-effective process for preparing thiencarbazone-methyl with high yield and purity. It was surprisingly found that when thiophene compound of Formula (II) is reacted with triazole compound of Formula (III) using cheaper inorganic base and a catalyst as against costlier organic base used in prior art, thiencarbazone-methyl of Formula (I) is obtained in good yield. After rigorous attempts, the inventors of present invention have developed a process for preparation of thiencarbazone-methyl of Formula (I) wherein the process doesn’t involve use of the organic base, such as 1,8- diazabicyclo-5.4.0-undec-7-ene (DBU) and avoids its remains in the residual amount with the final product.

[0040] Accordingly, in an embodiment, the present invention provides a process for preparing thiencarbazone-methyl of Formula (I), the process comprising: reacting methyl 5-methyl-4-sulfamoylthiophene-3-carboxylate of Formula (II),

[0041] Formula (II) with Phenyl-4,5-dihydro-3-methoxy-4-methyl-5-oxo-lH-l,2,4-triazole-l- carboxylate of Formula (III), in presence of an inorganic base and a catalyst to get thiencarbazone-methyl of Formula (I). In another embodiment, methyl 5-methyl-4-sulfamoylthiophene-3-carboxylate of Formula (II) and Phenyl-4,5-dihydro-3-methoxy-4-methyl-5-oxo-lH- 1,2,4- triazole-1 -carboxylate of Formula (III) are prepared according to known methods. In accordance with the above embodiment, the inorganic base used is selected from the group comprising of hydroxides of alkali metal, hydroxides of alkaline earth metal, alkali metal carbonates and bicarbonates.

[0042] In accordance with the above embodiment, the inorganic base used is selected from hydroxides of alkali metal, such as, sodium hydroxide and potassium hydroxide or hydroxides of alkaline earth metal such as, calcium hydroxide; alkali metal carbonates, such as sodium carbonate, potassium carbonate, or cesium carbonate; alkali metal bicarbonates such as sodium bicarbonate, potassium bicarbonate, calcium bicarbonate;

[0043] In an embodiment, inorganic base is alkali metal carbonates, selected from the group comprising sodium carbonate, potassium carbonate or cesium carbonate. Preferably potassium carbonate is used as a base.

[0044] In another embodiment, the inorganic base used is present in an amount of 1 to 2 equivalent of methyl 5-methyl-4- sulfamoylthiophene-3 -carboxylate of Formula (II); preferably 1 to 1.5 equivalent of inorganic base is used.

[0045] In an embodiment, the reaction is carried out at a temperature in a range from about 0°C to about 120°C; preferably about 20°C to about 90°C; more preferably about 40°C to about 70°C.

[0046] In another embodiment, the catalyst used in the reaction is a phase transfer catalyst and is selected from the group comprising of quaternary ammonium and phosphonium salts; macrocyclic polyethers (crown ethers); macrobicyclic ethers (cryptands), and open-chain polyethers (polyethylene glycols, PEGs, and their dimethyl ethers, glymes). Preferably, quaternary ammonium salt is used as a catalyst.

[0047] In a subsequent embodiment, the catalyst used is selected from quaternary ammonium and phosphonium salts such as tetramethylammonium chloride, tetramethylammonium bromide, benzyltriethylammonium chloride, methyltrioctylammonium chloride tetra-n-Butylammonium chloride, tetra-n- butylammonium bromide, tetra-n-butylammonium hydrogensulfate, tetra-n- butylphosphonium chloride, tetraphenylphosphonium bromide, tetraphenylphosphonium chloride, triphenylmethylphosphonium bromide and triphenylmethyl; cryptands such as bis-l,3,5-phenylene cryptands, trimethyltriazacyclononane; open-chain polyethers such as polyethylene glycols and their dimethyl ethers, glymes.

[0048] In an embodiment, catalyst used is quaternary ammonium salt selected from tetramethylammonium chloride, tetramethylammonium bromide, benzyltriethylammonium chloride, methyltrioctylammonium chloride tetra-n- Butylammonium chloride, tetra-n-butylammonium bromide or tetra-n- butylammonium hydrogensulfate.

[0049] In an embodiment, the catalyst used is tetra-n-butylammonium bromide.

[0050] In another embodiment, the catalyst used is in an amount of 0.01 to 0.1 equivalent with respect to methyl 5-methyl-4-sulfamoylthiophene-3-carboxylate of Formula (II); preferably 0.01 to 0.05 equivalent of catalyst is used.

[0051] In an embodiment, the solvent used for reaction is selected from hydrocarbons, ketones, ethers, esters, nitriles, or mixtures thereof.

[0052] In an embodiment, the solvent used for reaction is selected from hydrocarbons comprising of aliphatic hydrocarbons such as pentane, hexane, heptane, and the like; aromatic hydrocarbons such as toluene, xylene benzene, and the like; cyclic hydrocarbons such as cyclohexane, and the like ; halogenated hydrocarbons such as methylene chloride, ethylene chloride, chloroform, carbon tetrachloride, chlorobenzene and the like; ketones such as acetone, methyl isobutyl ketone; ethers such as diethyl ether, dibutyl ether, glycol dimethyl ether, diglycol dimethyl ether, tetrahydrofuran; esters such as, methyl acetate, ethyl acetate; nitriles such as acetonitrile, propionitrile or other solvents such as N-methyl pyrollidone , dimethyl formamide(DMF), dimethylacetamide (DMAC). Preferably acetonitrile is used as a solvent for reaction.

[0053] In an embodiment, the solvent used for reaction is nitrile solvent selected from the group comprising of acetonitrile and propionitrile.

[0054] In an embodiment, preferably acetonitrile is used for reaction.

[0055] In yet another embodiment, the reactants, and / or reagents can be added to reactor in any sequence as practiced by a person skilled in the art, to carry out the reaction. In a subsequent embodiment, methyl 5-methyl-4-sulfamoylthiophene-3- carboxylate of Formula (II) and solvent can be added to the reactor first, followed by addition of Phenyl-4,5-dihydro-3-methoxy-4-methyl-5-oxo-lH-l,2,4-triazole- 1 -carboxylate of Formula (III), inorganic base and catalyst. The reaction can also be carried out by reversing the order of addition of raw materials, reagents, and solvents.

[0056] In an embodiment, the present invention provides a process for preparing thiencarbazone-methyl of Formula (I),

[0057] Formula (I) the process comprising: reacting methyl 5-methyl-4-sulfamoylthiophene-3-carboxylate of Formula (II),

[0058] Formula (II) with Phenyl-4,5-dihydro-3-methoxy-4-methyl-5-oxo-lH-l,2,4-triazole-l- carboxylate of Formula (III), in presence of potassium carbonate and tetra-n-butylammonium bromide in acetonitrile at a temperature in a range from about 40°C to about 70°C to get thiencarbazone-methyl of Formula (I). In a subsequent embodiment, the reaction of methyl 5-methyl-4- sulfamoylthiophene-3-carboxylate of Formula (II) with Phenyl-4,5-dihydro-3- methoxy-4-methyl-5-oxo-lH-l,2,4-triazole-l-carboxylate of Formula (III) is carried out at a temperature in a range from about 0°C to about 120°C, preferably in a range from about 20°C to about 90°C, more preferably in a range from about 40°C to about 70°C.

[0059] In an embodiment, the reaction is carried out at room temperature.

[0060] In an embodiment, the reaction is carried out at a temperature in a range from about 20°C to about 90°C.

[0061] In an embodiment, the reaction is carried out at a temperature in a range from about 30°C to about 70°C.

[0062] In an embodiment, the reaction is carried out at a temperature in a range from about 40°C to about 70°C.

[0063] In an embodiment, the reaction mass is concentrated after reaction to remove solvent, followed by water addition to the concentrated mass to obtain a slurry.

[0064] In a subsequent embodiment, slurry thus obtained is filtered and wet cake obtained is treated with a mixture of aq. inorganic acid and halogenated solvent.

[0065] In an embodiment, aqueous and organic phase are separated and crude thienecarbazone-methyl is isolated from organic phase.

[0066] In an embodiment, aq. inorganic acid is aq. hydrochloric acid, aq. sulfuric acid, aq. nitric acid; preferably aq. hydrochloric acid is used.

[0067] In another embodiment, halogenated solvent is selected from dichloromethane, dichloroethane, carbon tetrachloride; preferably dichloromethane is used.

[0068] In an embodiment, thiencarbazone-methyl of Formula (I) is obtained in yield of more than 60 %.

[0069] In another embodiment, thiencarbazone-methyl of Formula (I) is obtained in yield of more than 70 %. In another embodiment, the present invention provides a crystalline form of thiencarbazone- methyl.

[0070] In a subsequent embodiment, present invention provides a crystalline form of thiencarbazone- methyl characterized by an X-ray powder diffraction pattern exhibiting at least three peaks selected from 7.2, 9.4, 11.9, 13.1, 15.4, 18.8, 19.6, 20.0, 20.3, 21.0, 21.6, 22.5, 23.5, 23.8, 24.7, 24.8, 25.5, 26.5, 30.7, 33.2. ± 0.2° 20.

[0071] In yet another embodiment, present invention provides a crystalline form of thiencarbazone- methyl characterized by single crystal which exhibit a basic crystal structure that is monoclinic and has a space group P2i / c. The characteristic data of the crystal structure of crystalline form of thiencarbazone- methyl is shown in Table 1.

[0072] Table 1

[0073] In yet another embodiment, there is provided a crystalline form of thiencarbazone- methyl characterized by powder X-ray diffraction (PXRD) pattern as depicted in Figure 1.

[0074] In another embodiment, the thiencarbazone- methyl is characterized by a differential scanning calorimetry (DSC) that comprises an endothermic peak in the range of 205-208 °C ±3°C. In yet another embodiment, there is provided a crystalline form of thiencarbazone- methyl characterized by a differential scanning calorimetry (DSC) as depicted in Figure 2.

[0075] In yet another embodiment, the thiencarbazone- methyl is characterized by an Infrared (IR) spectrum at the 3207, 3106, 2162, 1748, 1720, 1638, 1507, 1450, 1364, 1337, 1288, 1187, 1156, 1137, 1096, 1043, 988, 912, 854 cm-1± 2 cm’1.

[0076] In yet another embodiment, there is provided a crystalline form of thiencarbazone- methyl characterized by an Infrared (IR) spectrum as depicted in Figure 3.

[0077] In another embodiment, there is provided a crystalline form of thiencarbazone- methyl characterized by a single crystal structure as depicted in Figure 4.

[0078] In another embodiment, the present invention provides a process of preparing a crystalline form of thiencarbazone-methyl, wherein the process comprises: treating crude thiencarbazone-methyl with a solvent selected from the group comprising of C1-C2 alcohol, hydrocarbons, ethers, ketonic solvents and mixtures thereof.

[0079] In yet another embodiment, the present invention provides a process for preparing a crystalline form of thiencarbazone-methyl, wherein the process comprises treating thiencarbazone-methyl having purity less than 90 % with a solvent selected from the group comprising of C1-C2 alcohol, hydrocarbons, ethers, ketonic solvents or mixtures thereof.

[0080] In an embodiment, crude thiencarbazone-methyl used as a starting material is prepared by any known method in the art. One such method involves reacting methyl 5-methyl-4-sulfamoylthiophene-3-carboxylate of Formula (II), with Phenyl-4,5-dihydro-3-methoxy-4-methyl-5-oxo-lH-l,2,4-triazole-l- carboxylate of Formula (III).

[0081] In another embodiment, crude thiencarbazone-methyl having purity less than 90% is used as starting material.

[0082] In another embodiment, crude thiencarbazone-methyl having purity less than 80 % is used as starting material.

[0083] In another embodiment, crude thiencarbazone-methyl having purity less than 70 % is used as starting material.

[0084] In a subsequent embodiment, solvent for treating crude thiencarbazone- methyl is selected from C1-C2 alcohol such as methanol, ethanol; hydrocarbons selected from aliphatic or aromatic hydrocarbons such as pentane, hexane, heptane, toluene, xylene cyclohexane, benzene; halogenated hydrocarbons such as dichloromethane, dichloroethane, chloroform, carbon tetrachloride, chlorobenzene; ketonic solvents such as acetone, methyl isobutyl ketone; ethers such as diethyl ether, dibutyl ether, glycol dimethyl ether, diglycol dimethyl ether, tetrahydrofuran. Preferably C1-C2 alcohol or ketone solvent is used; more preferably ketone, such as acetone is used. In an embodiment, ketone solvent such as acetone, methyl isobutyl ketone is used for treating crude thiencarbazone- methyl.

[0085] In an embodiment, acetone is used for treating crude thiencarbazone- methyl.

[0086] In an embodiment, the present invention provides a process for preparing a crystalline form of thiencarbazone-methyl of Formula (I), the process comprising: a. reacting methyl 5-methyl-4-sulfamoylthiophene-3-carboxylate of Formula (ID, with Phenyl 4,5-dihydro-3-methoxy-4-methyl-5-oxo-lH-l,2,4-triazole-l- carboxylate of Formula (III), in presence of an inorganic base and a catalyst, to obtain a crude thiencarbazone-methyl, b. treating crude thiencarbazone-methyl, with a solvent selected from the group comprising of C1-C2 alcohol, hydrocarbons, esters, ethers, ketonic solvents and mixtures thereof.

[0087] In accordance with the above embodiment, step-a is carried out as per the preferred embodiments of the invention as described hereinabove.

[0088] In a subsequent embodiment, in step-b, crude thiencarbazone-methyl as obtained in step-a is treated with solvent selected from C1-C2 alcohol such as methanol, ethanol; hydrocarbons selected from aliphatic or aromatic hydrocarbons such as pentane, hexane, heptane, toluene, xylene cyclohexane, benzene; halogenated hydrocarbons such as dichloromethane, dichloroethane, chloroform, carbon tetrachloride, chlorobenzene; ketonic solvents such as acetone, methyl isobutyl ketone; esters such as methyl acetate, ethyl acetate; ethers such as diethyl ether, dibutyl ether, glycol dimethyl ether, diglycol dimethyl ether, tetrahydrofuran. Preferably C1-C2 alcohol or ketone solvent is used; more preferably ketone, such as acetone is used.

[0089] In one embodiment, step b is performed at a temperature in the range from about 25°C to about 120°C, preferably about 25°C to about 90°C.

[0090] In another embodiment, crude thiencarbazone-methyl is treated with one or more of the aforementioned solvents at room temperature or at high temperature, up to the boiling point of the solvent.

[0091] In an embodiment solvent treatment is carried out by heating the solution of crude thiencarbazone-methyl and solvent to the boiling point of the solvent, gradually cooling the solution and isolating the crystals. Optionally, the solution may be seeded with seed crystals of thiencarbazone-methyl, in order to instigate crystallization.

[0092] In accordance with above embodiment, the solution is cooled to room temperature; optionally, the solution can be cooled to lower temperature and crystalline solids of thiencarbazone-methyl are isolated.

[0093] In an embodiment, the present invention provides crystalline form of thiencarbazone-methyl according to the present invention having bulk density from about 0.1 g / ml to 1.0 g / ml; preferably about 0.4 g / ml to 0.8 g / ml which is used for preparation of an agrochemical compositions.

[0094] In a yet another embodiment of the present invention, there is provided crystalline form of thiencarbazone-methyl according to the present invention, having a volume average particle size distribution Dio of less than or equal to 50 pm, preferably less than or equal to 25 pm, which is used for preparation of an agrochemical composition.

[0095] In a yet another embodiment of the present invention, there is provided crystalline form of thiencarbazone-methyl according to the present invention having a volume average particle size distribution D50 of less than or equal to 100 pm, preferably less than or equal to 75 pm, which is further used for preparation of an agrochemical composition.

[0096] In a yet another embodiment of the present invention, there is provided crystalline form of thiencarbazone-methyl according to the present invention, having a volume average particle size distribution D90 of less than or equal to 150 pm, preferably less than or equal to 120 pm, which is used for preparation of an agrochemical composition.

[0097] In yet another embodiment, crystalline form of thiencarbazone-methyl prepared according to present invention is used for preparing agrochemical compositions.

[0098] In an embodiment, the present invention provides use of crystalline form of thiencarbazone-methyl for the preparation of an agrochemical composition.

[0099] According to another embodiment, the present invention provides an agrochemical composition comprising a crystalline form of thiencarbazone-methyl according to the present invention.

[0100] In an embodiment, the present invention provides an agrochemical composition comprising a crystalline form of thiencarbazone-methyl according to the present invention and at least one agriculturally acceptable excipient or carrier.

[0101] In an embodiment, the present invention provides the agrochemical composition wherein the excipient is selected from at least one surfactant, solid diluent, liquid diluent, or a combination thereof.

[0102] In an embodiment, agriculturally acceptable excipient / carriers can be selected from one or more solid or liquid diluentsemulsifiers, fillers, anti-foaming agents, thickening agents, anti-freezing agents, freezing agents, a surfactant, a preservative, a colouring agent, a pH adjusting agent, dispersing agent, wetting agent, anti-caking agent and solvent. However, it should be appreciated that any other agriculturally acceptable excipients, as known to a person skilled in the art, may be used to serve its intended purpose.

[0103] The examples of the agrochemical composition comprising a crystalline form of thiencarbazone-methyl according to the present invention are water-soluble concentrate (SL), an emulsifiable concentrate (EC) , an emulsion (EW) , a microemulsion (ME) , a suspension concentrates (SC), an oil dispersion (OD) , a flowable suspension (FS), a water-dispersible granule (WG) , water-soluble granule (SG) , a water-dispersible powder (WP) , a water soluble powder (SP) , a granule (GR) , an encapsulated granule (CG) , a fine granule (FG) , a macrogranule (GG) , an aqueous suspo-emulsion (SE) , capsule suspension (CS) and a microgranule (MG).

[0104] In an embodiment, the present invention provides the agrochemical composition comprising a crystalline form of thiencarbazone-methyl according to the present invention and a second agrochemically active ingredient.

[0105] In an embodiment, the present invention provides a method for the control of undesired plant growth, comprising subjecting the plants or their locus to the action of an agrochemical composition.

[0106] Analytical methods:

[0107] Samples were analyzed on high performance liquid chromatograph (HPLC) with UV detector using YMC Triart Phenyl (250 mm x 4.6 mm, 5 pm).

[0108] Following analytical methods and instruments were used for characterization of crystalline form of thiencarbazone-methyl:

[0109] 1. PXRD: powder X-ray diffractogram was recorded using Bruker make 2nd generation D2 Phaser Powder X-Ray diffractometer.

[0110] 2. DSC: Differential Scanning Calorimetry was carried out using Differential Scanning Calorimeter Mettler Toledo DSC-3 Heating rate: 10 °C / min.

[0111] 3. ATR-FTIR: IR analysis was conducted using PerkinElmer, SpectralOO IR spectrophotometer.

[0112] Examples:

[0113] The preferred embodiments of the present invention are illustrated by way of following non-limiting examples. However, the scope of the present invention is not to be construed to be limited by the examples in any way. Example 1: Preparation of thiencarbazone-methyl:

[0114] To a mixture of Potassium carbonate (82.1 g; 0.6 moles), acetonitrile (670 ml) and Methyl 5-methyl-4-sulfamoylthiophene-3-carboxylate (117.3 g; 0.5 moles) was added Tetra butyl ammonium bromide (TBAB) (3.46 g) and Phenyl 4,5-dihydro-3- methoxy-4-methyl-5-oxo-lH-l,2,4-triazole-l-carboxylate (137.2 g; 0.55 moles). This reaction mixture was heated at 50-55°C for 10 hours and then acetonitrile was distilled out under reduced pressure. To the concentrated mass, water was added. The mixture was stirred and filtered to obtain a wet cake. To the wet cake was added mixture of ~5% aqueous hydrochloric acid and dichloromethane (530 ml). The organic layer was separated out and solvent was distilled out to get crude product having purity 68.9 %.

[0115] Example 1(a): Crystallization of thiencarbazone-methyl

[0116] Thiencarbazone-methyl as obtained in example 1 was taken in acetone, heated to 60°C to obtain saturated solution. The solution was cooled to 25- 30°C and filtered out to get the crystalline thiencarbazone-methyl and dried (147 g) (75 % yield) having purity 98.6 % (DSC - 205°C as depicted in figure 2). Crystalline product was also analyzed by PXRD, FTIR techniques as depicted in figures 1,3 and 4.

[0117] Particle Size Distribution: Dio = 16.9pm; D50 = 42.1pm and D90 = 85.2pm.

[0118] Bulk density: 0.56 g / ml.

[0119] Example 2: Preparation of thiencarbazone-methyl (using potassium carbonate alone)

[0120] Phenyl 4,5-dihydro-3-methoxy-4-methyl-5-oxo-lH-l,2,4-triazole-l-carboxylate (27.4 g 0.11 moles) was dissolved in acetonitrile (1500 ml) at room temperature added Methyl 5-methyl-4-sulfamoylthiophene-3-carboxylate (28.6 g 0.12 moles) and potassium carbonate (16.5 g; 0.11 moles). The reaction mixture was stirred at room temperature for 12 hours. Reaction mass sample was analyzed for product formation. Only 34 % product formation was observed, and no further progress of reaction observed. Hence, reaction was terminated. Example 3: Preparation of thiencarbazone-methyl (as per process provided in US6964939):

[0121] Phenyl 4,5-dihydro-3-methoxy-4-methyl-5-oxo-lH-l,2,4-triazole-l-carboxylate (2.9 mmoles) and acetonitrile (53 volumes) were charged in the reactor at room temperature. Methyl 5-methyl-4-sulfamoylthiophene-3-carboxylate (3.2 mmoles) and l,8-diazabicyclo-5.4.0-undec-7-ene (3.2 mmoles) (DBU) was added to above mixture at room temperature under stirring. The reaction mixture was stirred at room temperature for 12 hours and acetonitrile was distilled out under reduced pressure. To the concentrated mass, dichloromethane and water was added stirred for 15 minutes. The organic layer was separated and washed with IN HC1, followed by water wash. Dichloromethane was distilled out to get title product, which was slurried in 2-propanol and stirred for 15 minutes. Solids obtained were filtered to get thiencarbazone-methyl, having 51 % yield.

[0122] Above performed experiments are summarized in table 2:

[0123] Table 2

[0124] From the above table it is evident that the process of the present invention as exemplified in example 1 provides thiencarbazone-methyl with better yield as compared to example 2 and 3.

Claims

CLAIMS:

1. A process for preparing thiencarbazone-methyl, the process comprising: reacting methyl 5-methyl-4-sulfamoylthiophene-3 -carboxylate with phenyl 4, 5-dihydro-3-methoxy-4-methyl-5-oxo-lH-l, 2, 4-tri azole- 1 -carboxylate, in presence of an inorganic base and a catalyst to get thiencarbazone-methyl.

2. The process as claimed in claim 1, wherein said inorganic base is selected from group comprising of hydroxides of alkali metal, hydroxides of alkaline earth metal, alkali metal carbonates or bicarbonates.

3. The process as claimed in claim 1, wherein said inorganic base is alkali metal carbonates, selected from the group comprising of sodium carbonate, potassium carbonate or cesium carbonate.

4. The process as claimed in claim 1, wherein said catalyst is selected from the group comprising of quaternary ammonium and phosphonium salts, macrocyclic polyethers, macrobicyclic ethers or open-chain polyethers.

5. The process as claimed in claim 4 , wherein said catalyst is quaternary ammonium salt selected from tetramethyl ammonium chloride, tetramethyl ammonium bromide, benzyltriethylammonium chloride, methyltrioctylammonium chloride tetra-n-Butylammonium chloride, tetra- n-butylammonium bromide or tetra-n-butylammonium hydrogensulfate6. The process as claimed in claim 1, wherein the reaction is carried out at a temperature in a range from about 40°C to about 70°C.

7. The process as claimed in claim 1, wherein the reaction is carried in a nitrile solvent selected from the group comprising of acetonitrile or propionitrile.

8. The process as claimed in claim 1, wherein the process further comprises treating thiencarbazone-methyl with a solvent selected from the group comprising of C1-C2 alcohol, hydrocarbons, ethers, ketonic solvents or mixtures thereof.

9. A crystalline form of thiencarbazone-methyl which exhibits an X-ray powder diffraction pattern having at least three peaks selected from 7.2, 9.4, 11.9, 13.1, 15.4, 18.8, 19.6, 20.0, 20.3, 21.0, 21.6, 22.5, 23.5, 23.8, 24.7, 24.8, 25.5, 26.5, 30.7, 33.

2. ± 0.2° 20.

10. The crystalline form of thiencarbazone-methyl as claimed in claim 9, is further characterized by an infrared absorption spectrum having at least one peak selected from 3207, 3106, 2162, 1748, 1720, 1638, 1507, 1450, 1364, 1337, 1288, 1187, 1156, 1137, 1096, 1043, 988, 912, 854 ± 4 cm'1.

11. The crystalline form of thiencarbazone-methyl as claimed in claim 9, is further characterized by differential scanning calorimetry thermogram comprising an endothermic peak in the range of 205-208 °C ±3°C.

12. The crystalline form of thiencarbazone-methyl as claimed in claim 9, having a volume average particle size distribution D50 of less than or equal to 100 pm and having bulk density from about 0.1 g / ml to 1.0 g / ml.

13. A process for preparing a crystalline form of thiencarbazone-methyl, the process comprising: treating thiencarbazone-methyl having purity less than 90 % with a solvent selected from the group comprising of C1-C2 alcohol, hydrocarbons, ethers, ketonic solvents or mixtures thereof.

14. The process as claimed in claim 13, wherein said treatment is carried out in ketonic solvent comprising of acetone or methyl isobutyl ketone.

15. Use of crystalline form of thiencarbazone-methyl according to claim 9 for the preparation of an agrochemical composition.

16. An agrochemical composition comprising crystalline form of thiencarbazone-methyl according to claim 9 and at least one agrochemically acceptable excipient.

17. A method for the control of undesired plant growth, comprising subjecting the plants or their locus to the action of an agrochemical composition as claimed in claim 16.

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