# Patent

## Title
Process for preparing a novel crystalline form of thifensulfuron-methyl and use of the same

## Abstract

A the crystalline form of thifensulfuron-methyl of formula (I), the crystal preparation process, the analyzes of the crystal through various analytical methods and using the crystal to prepare stable agrochemical formulation. The invention also describes the use of various solvents towards the crystalline form preparation conditions.

## Background
BACKGROUND
Field
The present disclosure relates to a crystalline form of methyl 3-(4-methoxy-6-methyl-1,3,5-triazin-2-ylcarbamoylsulfamoyl)thiophene-2-carboxylate (thifensulfuron-methyl), to its preparation processes and to its use in agrochemical preparations.
Description of Related Art
Thifensulfuron-methyl, i.e., methyl 3-(4-methoxy-6-methyl-1,3,5-triazin-2-ylcarbamoylsulfamoyl)thiophene-2-carboxylate is a member of the sulfonylurea group of chemicals and used as herbicide. Thifensulfuron-methyl is a selective post-emergence sulfonylurea herbicide for the control of broadleaved weeds in cereals and soybeans. Like other sulfonylureas, the mode of action is via inhibition of the enzyme acetolactate synthase (ALS), and thus prevention of the biosynthesis of the essential amino acids isoleucine and valine.
Thifensulfuron-methyl has molecular formula of C12H13N5O6S2. Its chemical structure is




SUMMARY
The commercially available thifensulfuron-methyl, which is usually manufactured by the process described in U.S. Pat. No. 4,481,029, which is incorporated by reference in its entirety for all purposes. is present in an amorphous state. It has been found that thifensulfuron-methyl in amorphous state is highly viscous, which is not suitable for being prepared as compositions or formulations having spray equipment cleanout property. Thifensulfuron-methyl residues remain in the spray equipment after spraying. Adequate cleanout prior to reuse of the spray equipment will typically require a rinsing procedure that is not only time-consuming but also results in wastewater disposal problem. Therefore, there is a need to provide a novel form of thifensulfuron-methyl with increased solubility and decreased viscosity.
Accordingly, an embodiment of the invention provides a novel crystalline form of thifensulfuron-methyl, termed “crystalline modification I”, and a process for its preparation as well as agrochemical compositions containing it, and methods for using it in agrochemical applications, such as methods for applying it to plants, surroundings, and plant parts. The novel crystalline modification I has been advantageously found to have increased solubility, decreased viscosity and improved spray equipment clean-out properties.
Accordingly, an embodiment of the invention also provides compositions for controlling undesirable plants, such as weeds, comprising the crystalline modification I of thifensulfuron-methyl on its own, as a mixture with auxiliaries and carriers, and as a mixture with other active compounds. The use of the crystalline modification I of thifensulfuron-methyl in the control of undesired plant growth and a method for the same are also provided by an embodiment of the invention.



BRIEF DESCRIPTION OF DRAWINGS
Various features and aspects of the embodiments of the invention disclosed herein can be more clearly understood by reference to the drawings, which are intended to exemplify and illustrate, but not to limit, the scope of the invention, and wherein:
FIG. 1 is an infrared (IR) spectrum of an embodiment of crystalline modification I of thifensulfuron-methyl;
FIG. 2 is a X-ray powder diffractogram of an embodiment of crystalline modification I of thifensulfuron-methyl;
FIG. 3 is a Differential Scanning calorimetry (DSC) thermogram of an embodiment of crystalline modification I of thifensulfuron-methyl; and
FIG. 4 is a X-ray powder diffractogram of amorphous thifensulfuron-methyl.



DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
The invention can be more clearly understood by reference to the following detailed description of specific embodiments thereof, which is intended to illustrate, but not limit, the scope of the appended claims.
It has been found that the crystalline modification I of thifensulfuron-methyl has a significant increase in its solubility and a significant decrease in its viscosity, which significantly reduces the residue contamination and improve spray equipment clean-out properties. In addition, it is found that the crystalline modification I of thifensulfuron-methyl is easier to comminute or grind compared to amorphous thifensulfuron-methyl prepared in accordance with the disclosure of U.S. Pat. No. 4,481,029, which is incorporated by reference in its entirety for all purposes. This allows the preparation of commercial formulations such as suspension concentrates (SC), oil-based suspension concentrates (OD), water-dispersible granules (WG) and water-soluble granules (SG). Hence, it is possible to prepare any formulations of thifensulfuron-methyl in crystalline modification I, which will be disclosed hereinafter.
By virtue of its high solubility and low viscosity, the crystalline modification I of thifensulfuron-methyl is highly suitable for preparing compositions for controlling undesirable plants, such as weeds.
According to an embodiment of the invention, a crystalline modification I of thifensulfuron-methyl is provided, exhibiting at least 3 of the following reflexes, in any combination, as 2θ values in an X-ray powder diffractogram recorded using Cu-Kαradiation at 25° C.:

2θ=6.62±0.2  (1)

2θ=11.11±0.2  (2)

2θ=12.84±0.2  (3)

2θ=13.30±0.2  (4)

2θ=15.48±0.2  (5)

2θ=20.04±0.2  (6)

2θ=22.34±0.2  (7)

2θ=24.62±0.2  (8)

2θ=24.92±0.2  (9)

2θ=27.83±0.2  (10)

The crystalline modification I of thifensulfuron-methyl of the present invention is characterized by an X-ray powder diffractogram having at least three of the reflexes indicated above. Preferably, the crystalline modification I is one having at least four of the aforementioned reflexes, more preferably at least five of said reflexes, again in any combination thereof. An X-ray powder diffractogram of the crystalline modification I of thifensulfuron-methyl is shown in FIG. 2, which will be described in detail hereinafter.
According to a preferred embodiment the crystalline modification I exhibits at least three, four, or five or all of the reflexes from the following:

2θ=6.62±0.2  (1)

2θ=13.30±0.2  (4)

2θ=15.48±0.2  (5)

2θ=20.04±0.2  (6)

2θ=24.62±0.2  (8)

2θ=24.92±0.2  (9).

The X-ray powder diffractogram was taken using a diffractometer from in reflection geometry in the range from 3°-60° with increments of 0.03° using Cu-Ka radiation at 25° C.
Further to X-ray diffraction analysis, crystalline modification I of thifensulfuron-methyl according to an embodiment can also be characterized by IR spectroscopy. The IR spectrum was measured with the resolution of 4 cm−1 and with the number of scans of 16 for the purified sample. The IR spectrum of crystalline modification I of thifensulfuron-methyl can be identified by its characteristic functional group vibrations (characteristic bands) at one or more of 3293.22, 3075.76 and 1728.23 cm−1 as shown in FIG. 1.
All IR spectra were obtained using the following acquisition parameters:
















FT-IR spectrometer
Bruker Tensor 37



Diamond ATR unit
from Specac



Wavelength range
550-4000 cm−1



Resolution
4 cm−1



Number of scans
16










The crystalline modification I of thifensulfuron-methyl according to an embodiment of the invention may be further characterized by differential scanning calorimetry (DSC) (FIG. 3). An endothermic peak at about 181.05° C. is shown in FIG. 3. As used herein, the terms “about 181.05° C.” means a range of 179° C. to 183° C.
Methods for preparing amorphous thifensulfuron-methyl are well known in the art. Amorphous thifensulfuron-methyl is manufactured and available on a commercial scale. A particularly suitable method for preparing amorphous thifensulfuron-methyl is described in U.S. Pat. No. 4,481,029, which is incorporated herein by reference for all purposes.
According to an embodiment of the invention, the crystalline modification I of thifensulfuron-methyl can be obtained by the processes below:
Thifensulfuron-methyl in amorphous state is dissolved and then crystallized from solvents.
In one aspect, the present invention provides a process for preparing a crystalline modification I of thifensulfuron-methyl comprising steps of:

    
    
        i) dissolving an amorphous thifensulfuron-methyl in a solvent;
        ii) precipitating the dissolved compound into crystalline modification I of thifensulfuron-methyl; and
        iii) isolating the precipitated crystalline modification I.
    
    


Suitable solvents for preparing thifensulfuron-methyl crystalline modification I include halogenated hydrocarbons (for example, chlorobenzene, bromobenzene, dichlorobenzene, chlorotoluene and trichlorobenzene), ethers (for example, ethyl propyl ether, n-butyl ether, anisole, phenetole, cyclohexyl methyl ether, dimethyl ether, diethyl ether, dimethyl glycol, diphenyl ether, dipropyl ether, diisopropyl ether, di-n-butyl ether, diisobutyl ether, diisoamyl ether, ethylene glycol dimethyl ether, isopropyl ethyl ether, methyl tert-butyl ether, tetrahydrofuran, methyltetrahydrofuran, dioxane, dichlorodiethyl ether, methyl-tetrahydrofuran, polyethers of ethylene oxide and/or propylene oxide), nitrated hydrocarbons (for example, nitromethane, nitroethane, nitropropane, nitrobenzene, chloronitrobenzene and o-nitrotoluene), aliphatic, cycloaliphatic or aromatic hydrocarbons (for example, pentane, n-hexane, n-heptane, n-octane, nonane), cymene, petroleum fractions having a boiling range of from 70° C. to 190° C., cyclohexane, methylcyclohexane, petroleum ether, ligroin, octane, benzene, toluene and xylene), esters (for example, malonates, acetic acid n-butyl ester (n-butyl acetate), methyl acetate, ethyl acetate, isobutyl acetate, dimethyl carbonate, diethyl carbonate, dibutyl carbonate and ethylene carbonate), and aliphatic alcohols (for example, methanol, ethanol, n-propanol, isopropanol, n-butanol and tert-amyl alcohol), and mixtures of these.
Preferred solvents includes ethers, aromatic hydrocarbons (such as benzene, toluene, xylene, chlorobenzene), esters and aliphatic alcohols and mixtures thereof. Particularly preferred solvents or solvent mixtures are isopropanol, toluene, methyl-tetrahydrofuran, diethyl carbonate, chlorobenzene, n-butyl acetate, isobutyl acetate, n-butanol, ethanol, ethyl malonate, methyl t-butyl ether, and mixtures of toluene and butanol, toluene and n-butyl acetate, ethyl malonate and methyl t-butyl ether, as well as mixtures of butyl acetate and methyl t-butyl ether. Solvent mixtures of more than 2 or 3 or 4 components are also envisaged by embodiment of the invention.
In an embodiment of the invention, it is preferred that the solvent comprises at least one alcohol, and more preferably comprises at least one straight or branched C1-C8 aliphatic alcohol, more preferably at least one straight or branched C1-C4 aliphatic alcohol, even more preferably at least one of isopropanol and n-butanol.
According to a preferred embodiment in step (i), amorphous thifensulfuron-methyl is dissolved in a solvent or a solvent mixture as a concentrated solution by heating from room temperature or ambient temperature to reflux temperature or below the reflux temperature of the solvent or the solvent mixture. Preferably, the concentrated solutions can be prepared at the reflux temperature of the solvents. The concentration of the solution depends on the solubility of thifensulfuron-methyl in the corresponding solvent or solvent mixture.
The concentrated homogeneous solution thus prepared as in step (i) is then cooled to room or ambient temperature, or to a temperature of around 0° C. to 20° C. to crystallize the desired crystalline form from the solvent. The crystalline modification I of thifensulfuron-methyl can also be crystallized out by concentrating the homogeneous solution through removing the solvent or solvent mixture to a certain volume with or without applying vacuum and cooling to below the reflux temperature of the solvent or the solvent mixture.
In another embodiment, crystalline modification I of thifensulfuron-methyl can also be effected by adding seed crystals of the desired crystalline form during crystallization into a solution prepared in step (i), which can promote or accelerate the crystallization.
The seed crystal amount added to the concentrated solution is typically in the range of 0.001 to 10% by weight, preferably 0.001 to 2.5% by weight, often 0.005 to 0.5% by weight based on the weight of thifensulfuron-methyl used for the preparation of concentrated solution in step (i). Preferably, the seed crystals are added to the concentrated solution at the temperature below the boiling point of the corresponding solvent or the solvent mixture.
Hence, the precipitation of the crystalline modification I of thifensulfuron-methyl can be effectively achieved from the concentrated solution by a person of ordinary skill in the art.
The precipitated crystalline modification I of thifensulfuron-methyl obtained from step (ii) is isolated by the usual solid component separating techniques from solutions, such as filtration, centrifugation or decantation. Then, the isolated solid is washed with solvent one or more times. Preferably, the solvent employed in washing stage consists of one or more components of the solvent or solvent mixture used for the preparation of concentrated solution in step (i). The washing is usually carried out using the corresponding solvent or solvent mixture between room temperature and 0° C. depending on the solubility of the crystal, in order to minimize or avoid the loss of crystalline material in the corresponding washing solvent as much as possible.
The invention, in an embodiment, also relates to a composition comprising the crystalline modification I of thifensulfuron-methyl. The amount of the crystalline modification I of thifensulfuron-methyl is less than 75% by weight of the composition, preferably less than 50% by weight of the composition, more preferably less than 30% by weight of the composition, still more preferably about 25% by weight of the composition.
The use of thifensulfuron-methyl as a herbicide is known in the art and is used on a commercial scale. The crystalline modification I of thifensulfuron-methyl is also active in controlling undesirable plant growth, such as weeds. Techniques of formulating and applying amorphous thifensulfuron-methyl are known in the art, for example as disclosed in the prior art documents described hereinbefore. Thifensulfuron-methyl in the crystalline modification I of the present invention may be formulated and applied in manner analogous to those described for amorphous thifensulfuron-methyl.
Accordingly, in a further aspect, an embodiment of the invention provides a herbicidal composition comprising thifensulfuron-methyl in the crystalline modification I as defined hereinbefore.
Accordingly, an embodiment of the invention furthermore provides processes for preparing compositions for controlling undesirable plant growth using the crystalline modification I of thifensulfuron-methyl.
Accordingly, the invention also provides a method for controlling undesirable plant growth, comprising applying to the plant, plant part, or surroundings of the plant, a herbicidally effective amount of crystalline modification I of thifensulfuron-methyl.
The crystalline modification I of thifensulfuron-methyl can be incorporated into the customary formulations, such as suspension concentrates (SC), oil-based suspension concentrates (OD), water-soluble granules (SG), dispersible concentrates (DC), emulsifiable concentrates (EC), emulsion seed dressings, suspension seed dressings, granules (GR), microgranules (MG), suspoemulsions (SE) and water-dispersible granules (WG) using suitable auxiliaries, carriers and solvents, in a manner analogous to that known for amorphous thifensulfuron-methyl.
In this context, the crystalline modification I of thifensulfuron-methyl should be present in a concentration of from about 0.1 to about 75% by weight of the total mixture, i.e., in amounts sufficient to achieve the required dosage. The formulations are prepared, for example, by extending the crystalline modification I of thifensulfuron-methyl with water, solvents and carriers, using, if appropriate, emulsifiers and/or dispersants, and/or other auxiliaries.
These formulations are prepared by mixing the crystalline modification I of thifensulfuron-methyl with customary additives, for example, surfactants, liquid diluents, solid diluents, wetting agents, dispersants, thickening agent, antifoaming agent and other formulation ingredients.
Liquid diluents include, but are not limited to, water, N,N-dimethylamide, dimethyl sulfoxide, N-alkylpyrrolidone, ethylene glycol, polypropylene glycol, propylene carbonate, dibasic esters, paraffines, alkylbenzenes, alkyl naphthalenes, glycerine, triacetin, oils of olive, castor, linseed, sesame, corn, peanut, cotton-seed, soybean, rape-seed and coconut, ketones such as cyclohexanone, 2-heptanone, isophorone and 4-hydroxy-4-methyl-2-pentanone, acetates such as hexyl acetate, heptyl acetate and octyl acetate, and alcohols such methanol, cyclohexanol, decanol, benzyl and tetrahydrofurfuryl alcohol, and mixtures thereof.
Solid diluents can be water-soluble or water-insoluble. Water-soluble solid diluents include, but are not limited to, salts such as alkali metal phosphates (e.g., sodium dihydrogen phosphate), alkaline earth phosphates, sulfates of sodium, potassium, magnesium and zinc, sodium and potassium chloride, sodium acetate, sodium carbonate and sodium benzoate, and sugars and sugar derivatives such as sorbitol, lactose, sucrose and mannitol. Examples of water-insoluble solid diluents include, but are not limited to clays, synthetic and diatomaceous silicas, calcium and magnesium silicates, titanium dioxide, aluminum, calcium and zinc oxide, and mixtures thereof.
Wetting agents include, but are not limited to, alkyl sulfosuccinates, laureates, alkyl sulfates, phosphate esters, acetylenic diols, ethoxyfluorinated alcohols, ethoxylated silicones, alkyl phenol ethoxylates, benzene sulfonates, alkyl-substituted benzene sulfonates, alkyl a-olefin sulfonates, naphthalene sulfonates, alkyl-substituted napthalene sulfonates, condensates of naphthalene sulfonates and alkyl-substituted naphthalene sulfonates with formaldehyde, and alcohol ethoxylates, and mixture thereof. Alkyl naphthalene sulphonates, sodium salts are particularly useful for the composition of the invention
Dispersants include, but are not limited to, sodium, calcium and ammonium salts of ligninsulfonates (optionally polyethoxylated); sodium and ammonium salts of maleic anhydride copolymers; sodium salts of condensed phenolsulfonic acid; and naphthalene sulfonate-formaldehyde condensates, and mixtures thereof. Ligninsulfonates such as sodium ligninsulfonates are particularly useful for the composition of the invention. Naphthalene sulfonate-formaldehyde condensates such as naphthalenesulfonic acid, polymers with formaldehyde, and sodium salts are particularly useful for the composition of the invention.
Thickening agents include, but are not limited to, guar gum, pectin, casein, carrageenan, xanthan gum, alginates, methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, and carboxymethylcellulose and mixtures thereof. Synthetic thickening agents include derivatives of the former categories, and also polyvinyl alcohols, polyacrylamides, polyvinylpyrrolidones, various polyethers, their copolymers as well as polyacrylic acids and their salts, and mixtures thereof. Alkylpolyvinylpyrrolidones are particularly useful for the composition of the invention
Other formulation ingredients can also be used in the present invention such as dyes, drying agents, and the like. These ingredients are known to one skilled in the art.
The crystalline modification I of thifensulfuron-methyl according to an embodiment of the invention can be present in formulations and in its use forms, prepared from these formulations, and as a mixture with one or more of other active compounds (such as insecticides, attractants, sterilizing agents, bactericides, acaricides, nematicides, fungicides, growth-regulating substances, herbicides, safeners, fertilizers and semiochemicals) or with agents for improving plant properties.
When used as herbicide, the crystalline modification I of thifensulfuron-methyl according to an embodiment of the invention can furthermore be present in formulations and its use forms, prepared from these formulations, and as a mixture with inhibitors which reduce degradation of the active compounds after their use in the environment of the plant, on the surface of plant parts or in plant tissues.
All plants, plant parts and their surroundings can be treated in accordance with the invention. In the present context, plants are to be understood as meaning all plants and plant populations such as desired and undesired wild plants or crop plants (including naturally occurring crop plants). Crop plants can be plants which can be obtained by conventional breeding and optimization methods, by biotechnological and genetic engineering methods, or by combinations of these methods, including the transgenic plants and the plant cultivars which can or cannot be protected by plant breeders' rights. Plant parts are to be understood as meaning all parts and organs of plants above and below the ground, such as shoot, leaves, needles, stalks, stems, flowers, fruit bodies, fruits, seeds, roots, tubers and rhizomes. Harvested materials, and vegetative and generative propagation materials, for example, cutting, tubers, meristem tissue, rhizomes, offsets, seeds, single and multiple plant cells and any other plant tissues, are also included.
As used herein, the term “about,” when used in connection with a numerical amount or range, means somewhat more or somewhat less than the stated numerical amount or range, to a deviation of ±10% of the stated numerical amount or endpoint of the range.
“Surrounding,” as used herein, refers to the place on which the plants are growing, the place on which the plant propagation materials of the plants are sown, the place on which the plant propagation materials of the plants will be sown or the environment near the plants.
The term “herbicidally effective amount” as used herein, refers to the quantity of such a compound or combination of such compounds that is capable of producing a controlling effect on the growth of plants. The controlling effects include all deviation from the natural development of the target plants, for example killing, retardation of one or more aspects of the development and growth of the plant, leaf burn, albinism, dwarfing and the like.
Treatment according to the invention of the plants, plant parts and/or their loci or surroundings the compositions or formulations of the inventions is carried out directly or by allowing the compositions or formulations to act on their surroundings, habitat or storage space by the customary treatment methods. Examples of these customary treatment methods include dipping, spraying, vaporizing, fogging, broadcasting, painting on in the case of propagation material, and applying one or more coats particularly in the case of seed.
The benefits of the present invention are seen most when the herbicidal composition is applied to kill weeds in growing crops of useful plants: such as maize (corn) including field corns, pop corns and sweet corns, cotton, sunflower, cereal, barley, wheat, rice, oats, potatoes, sugar beets, plantation crops (such as bananas, fruit trees, rubber trees, tree nurseries), vines, citrus, olive, amenity, asparagus, bushberries (such as blueberries), caneberries, cranberries, flax, grain sorghum, okra, peppermint, rhubarb, spearmint, turf grass, grapevine and sugarcane. In this invention, treatment of soybean and cereal are particularly beneficial.
All percentages are given in weight % unless otherwise indicated.
Embodiments of the present invention will now be described by the following examples which are provided for illustrative purposes only, and not intended to limit the scope of the disclosure.
EXAMPLES
Example 1: Preparation of Amorphous Thifensulfuron-Methyl in Accordance with the Disclosure of U.S. Pat. No. 4,481,029, Example 5 with Modification
To 2.3 g of 2-amino-4-methoxy-6-methyl-1,3,5-triazine in 30 ml of anhydrous methylene chloride was added with stirring 4.5 g of methyl 3-(N-(methoxycarbonyl)sulfamoyl)thiophene-2-carboxylate. The mixture was heated to the boiling point and allowed to cool and stirred at ambient temperature for sixteen hours. The solid thus obtained was removed by filtration to yield the crude desired product.
As shown in FIG. 4, the X-ray powder diffraction pattern of the resulting thifensulfuron-methyl product has no significant individual signals or peaks, which indicates the thifensulfuron-methyl product prepared in accordance with the disclosure of U.S. Pat. No. 4,481,029 is amorphous.




Preparation of Crystalline Modification I of thifensulfuron-methyl
Example 2—Crystallization from Isopropanol
Thifensulfuron-methyl sample prepared in Example 1 (10 g) was taken in a three-necked round bottom flask along with isopropanol (60 mL) and the resulting slurry was heated to 70° C. to get a homogeneous solution. The insoluble particles, if any, were filtered and the solution was slowly cooled to room temperature. Upon cooling, fine crystals were formed and the heterogeneous mixture was stirred at room temperature for 2 h. Then, the slurry was filtered and washed with isopropanol (3 mL). The filtered crystals were dried under vacuum at 60° C. in order to remove the isopropanol traces from the crystalline product. The crystalline product thus obtained had a purity of >98% and the recovered yield was not less than 80%.
The obtained crystal was analyzed by IR, X-ray powder diffraction and DSC, and found to be crystalline modification I of thifensulfuron-methyl as shown in FIGS. 1, 2 and 3, respectively.
Differential scanning calorimetry (DSC) (FIG. 3) shows an endothermic peak with onset at about 179.2° C. and peak maximum at about 181.05° C. as shown in FIG. 3.
IR spectrum of thifensulfuron-methyl shows the functional group characteristic vibrations at about 3293.22, 3075.76 and 1728.23 cm-1 as shown in FIG. 1.
Powder X-ray diffractogram of has the reflexes as shown in FIG. 2 with reflexes summarized are summarized in Table 1 below.







TABLE 1







X-ray powder diffractogram reflexes 


of crystalline modification I of 


thifensulfuron-methyl


crystalline modification I










2 θ (°)
d (Å)







 6.62 ± 0.2
13.67 ± 0.05 



11.11 ± 0.2
8.46 ± 0.05



12.84 ± 0.2
8.03 ± 0.05



13.30 ± 0.2
6.32 ± 0.05



15.48 ± 0.2
5.63 ± 0.05



20.04 ± 0.2
5.31 ± 0.05



22.34 ± 0.2
5.22 ± 0.05



24.62 ± 0.2
4.22 ± 0.05



24.92 ± 0.2
4.00 ± 0.05



27.83 ± 0.2
3.82 ± 0.05










Example 3—Crystallization from n-Butanol
Thifensulfuron-methyl (5 g) sample prepared in Example 1 was taken in a three-necked round bottom flask along with n-butanol (35 mL) and the resulting slurry was heated to 80° C. to get a homogeneous solution. The resultant hot solution was filtered to remove the insoluble (if any) and the solution was slowly cooled to ambient temperature. Product was precipitated out as fine crystal during cooling and the mixture was stirred at room temperature for 2 h. Then, the slurry was filtered, washed with n-butanol (3 mL) and dried under vacuum at room temperature in order to remove the n-butanol traces from the crystal. The crystal thus obtained was having a purity of >98% and the recovered yield was found to be not less than 80%.
The crystals were characterized as being thifensulfuron-methyl crystalline modification I using IR spectrometry, X-ray powder diffraction and DSC, as described in Example 2.
Example 4: Preparation of Oil Based Suspension Concentrate (OD) Formulation
All the components listed in Table 2 below were mixed uniformly and ground with a Dyno-Mill (manufactured by Willy A. Bachofen AG) to obtain an oil based suspension concentrate.









TABLE 2





Ingredients
Weights %
Function


















Thifensulfuron-methyl, crystalline
40.8
0
Active compound


modification I, 98% (prepared in





Example 2)





Amorphous thifensulfuron-methyl
0
40.8
Active compound


(prepared in Example 1)





Sodium lignosulfonate (REAX ®
22
22
Dispersing agent


88B)





Alkylpolyvinylpyrrolidone
20
20
Thickening agent


Corn oil
Balance 
Balance 
Carrier



to 100%
to 100%









Example 5: Preparation of Soluble Granules (SG)
All the components listed in Table 3 below were mixed, blended and milled in a high-speed rotary mill. Sufficient water was added to obtain an extrudable paste. The paste was extruded through a die or screen to form an extrudate. The wet extrudate was dried at 70° C. in a vacuum oven and then sifted through 0.71 mm-2 mm screens to obtain the product granules.









TABLE 3





Ingredients
Weights %
Function


















Thifensulfuron-methyl, crystalline
25.51
0
Active 


modification I, 98% (prepared in


compound


Example 2)





Amorphous thifensulfuron-methyl
0
25.51
Active 


(prepared in Example 1)


compound


Lignosulfonic acid, sodium salt,
15
15
Dispersing 


(REAX ® 88B)


agent


Naphthalenesulfonic acid, polymer
6
6
Dispersing 


with formaldehyde, sodium salt


agent


(TAMOL ® NN 8906)





Sodium acetate
4
4
Filler


Sodium carbonate
4
4
Filler


Non-ionic aqueous emulsion of
1
1
Antifoaming 


Polydimethylsiloxanes


agent


Mannitol
Balance 
Balance
Carrier



to 100%
to 100%









Example 6: Preparation of Water Dispersible Granules (WG)
All the components listed in Table 4 below were mixed, blended and milled in a high-speed rotary mill. Sufficient water was added to obtain an extrudable paste. The paste was extruded through a die or screen to form an extrudate. The wet extrudate was dried at 70° C. in a vacuum oven and then sifted through 0.71 mm-2 mm screens to obtain the product granules.









TABLE 4





Ingredients
Weights %
Function


















Thifensulfuron-methyl, crystalline
25.51
0
Active compound


modification I, 98% (prepared in





Example 2)





Amorphous thifensulfuron-methyl
0
25.51
Active compound


(prepared in Example 1)





Alkyl naphthalene sulphonate,
2
2
Wetting agent


sodium salt (Akzo Nobel)





Lignosulfonic acid, sodium salt,
15
15
Dispersing agent


REAX ® 88B)





Naphthalenesulfonic acid, polymer
6
6
Dispersing agent


with formaldehyde, sodium salt





(TAMOL ® NN8906)





Sucrose
10
10
Filler


Non-ionic aqueous emulsion of
1
1
Antifoaming agent


Polydimethylsiloxanes





Mannitol
Balance 
Balance 
Carrier



to 100%
to 100%









Example 7: Determining Water Solubility
A stock pH 7 buffer solution was prepared by adding aqueous sodium hydroxide solution (0.1 M, 145 mL) to aqueous potassium dihydrogen phosphate solution (0.1 M, 250 mL), and then adding sufficient distilled water to adjust the final volume to 500 mL. At least 1 time and up to about 5 times the amount of thifensulfuron-methyl needed for saturation was added to a mixing vessel containing stock buffer solution at the test temperature (e.g., 20° C.). The mixture was magnetically stirred in the dark while being maintained at the test temperature. Samples were periodically removed for analysis. The samples were centrifuged using a high speed, temperature-controlled centrifuge at the test temperature for about 20 minutes at ≧12000 G to remove suspended particles. An aliquot of each supernatant was taken for analysis.
The concentration of thifensulfuron-methyl in the supernatant was determined by a high pressure liquid chromatography (HPLC) with a reversed phase chromatography column and UV detection. The method should include development of best-fit calibration curves based on at least three standards using linear regression analysis Samples were successively withdrawn from the mixing vessel and analyzed until three successive samples show little or no variation in concentration. The test is preferably replicated to ensure accuracy.











TABLE 5







Original
Concentration





concen-
measured by




Formu-
tration,
HPLC after



Sample
lation
%
treatment, %
Solubility



















Thifensulfuron-methyl,
OD
40
35
88%


crystalline modification I,






98% (prepared in Example






2)






Amorphous
OD
40
14
35%


thifensulfuron-methyl






(prepared in Example 1)






Thifensulfuron-methyl,
SG
25
24.9
99.6%  


crystalline modification I,






98% (prepared in Example






2)






Amorphous
SG
25
15
60%


thifensulfuron-methyl






(prepared in Example 1)






Thifensulfuron-methyl,
WG
25
23
92%


crystalline modification I,






98% (prepared in Example






2)






Amorphous
WG
25
12
48%


thifensulfuron-methyl






(prepared in Example 1)









Example 8: Cleanout Test
The test was conducted by dispersing in water a sample to produce a concentration that is normally used when applying the herbicide: 25% thifensulfuron-methyl. The sample was added to tap water (300 mL) in a 400 mL beaker and magnetically stirred for 2 minutes. The mixture was then stirred for 2 minutes, whereupon the resulting dispersion was dispensed in three 100 mL aliquots to 4-oz (118 mL) polyethylene bottles. The bottles were capped, inverted twice and allowed to stand overnight.
After standing overnight, each individual bottle was inverted twice and the liquid contents were then poured out. Tap water (10 mL) was added and the bottle was inverted until all sediment was re-suspended, whereupon the contents were poured out. Tap water (100 mL) was added and the bottle was inverted twice and then allowed to stand undisturbed for 10 minutes. The bottle was inverted twice more and the contents were poured out. Acetonitrile (10 mL) was added to the bottle to extract any remaining material. The acetonitrile solution was analyzed by reversed-phase liquid chromatography with UV detection. The cleanout rating (the concentration of thifensulfuron-methyl herbicide in the acetonitrile solution) is reported in % in Table 6 below. Lower cleanout ratings indicate more effective cleanout compared to higher ratings.









TABLE 6






Formu-
Cleanout 


Sample
lation
rating, %

















Thifensulfuron-methyl, crystalline modification 
OD
5


I, 98% (prepared in Example 2)




Amorphous thifensulfuron-methyl, prepared in 
OD
26


Example 1




Thifensulfuron-methyl, crystalline modification 
SG
0.1


I, 98% (prepared in Example 2)




Amorphous thifensulfuron-methyl, prepared in 
SG
10


Example 1




Thifensulfuron-methyl, crystalline modification 
WG
2


I, 98% (prepared in Example 2)




Amorphous thifensulfuron-methyl (prepared in 
WG
13


Example 1)









The results in Table 6 demonstrate that the crystalline modification I of thifensulfuron-methyl exhibited markedly superior cleanout properties to those of the known amorphous thifensulfuron-methyl product.

## Claims

1. A crystalline modification I of (methyl 3-(4-methoxy-6-methyl-1,3,5-triazin-2-ylcarbamoylsulfamoyl)thiophene-2-carboxylate) (thifensulfuron-methyl) exhibiting each of the following reflexes as 2θ values in X-ray powder diffractogram recorded using Cu-Kα radiation at 25° C.:


2θ=6.62±0.2  (1)



2θ=11.11±0.2  (2)



2θ=12.84±0.2  (3)



2θ=13.30±0.2  (4)



2θ=15.48±0.2  (5)



2θ=20.04±0.2  (6)



2θ=22.34±0.2  (7)



2θ=24.62±0.2  (8)



2θ=24.92±0.2  (9)



2θ=27.83±0.2  (10).

2. The crystalline modification I of thifensulfuron-methyl according to claim 1, exhibiting an IR spectrum with characteristic bands at one or more of 3293.22, 3075.76 and 1728.23 cm−1.

3. The crystalline modification I of thifensulfuron-methyl according claim 1 exhibiting a Differential Scanning calorimeter (DSC) thermogram having a single predominant endotherm at about 179° C. to 183° C.

4. A process of preparing crystalline modification I of thifensulfuron-methyl according to claim 1, comprising:
i) dissolving an amorphous thifensulfuron-methyl in a solvent, wherein the solvent comprises at least one of isopropanol and n-butanol;
ii) precipitating the dissolved compound into crystalline modification I of thifensulfuron-methyl; and
iii) isolating the precipitated crystalline modification I.

5. The process according to claim 4, wherein step ii) comprises concentrating the solvent or cooling to ambient temperature of around 0 to 20° C., or adding seed of the crystalline modification I, or a combination thereof.

6. A crystalline modification I of thifensulfuron-methyl obtained according to the process of claim 4, wherein crystalline modification I of thifensulfuron-methyl has a purity of at least 98% by weight.

7. A composition comprising an herbicidally effective amount of the crystalline modification I of thifensulfuron-methyl according to claim 1 and at least one auxiliary.

8. The composition according to claim 7, wherein the auxiliary is selected from the group consisting of a surfactant, a diluent, a wetting agent, a dispersant, a thickening agent and an antifoaming agent.

9. The composition according to claim 7, wherein the composition is formulated as a suspension concentrate (SC), an oil-based suspension concentrate (OD), a water-soluble granule (SG), a dispersible concentrate (DC), an emulsifiable concentrate (EC), an emulsion seed dressing, a suspension seed dressing, a granule (GR), a microgranule (MG), a suspoemulsion (SE) or a water-dispersible granule (WG).

10. The composition according to claim 7, wherein the composition is formulated as an oil-based suspension concentrate (OD), a water-dispersible granule (WG) or a water-soluble granule (SG).

11. A method for controlling unwanted plant growth, comprising applying to the plant, plant part, or surroundings of the plant, a herbicidally effective amount of crystalline modification I of thifensulfuron-methyl according to claim 1.