GB2548342A

GB2548342A - A novel form of amicarbazone, a process for its preparation and use of the same

Info

Publication number: GB2548342A
Application number: GB1604126.1A
Authority: GB
Inventors: Timothy Bristow James
Original assignee: Rotam Agrochem International Co Ltd
Current assignee: Rotam Agrochem International Co Ltd
Priority date: 2016-03-10
Filing date: 2016-03-10
Publication date: 2017-09-20
Anticipated expiration: 2036-03-10
Also published as: GB2548342B; GB201604126D0; TW201736353A; TWI778954B; CN108699010A; BR112017021866A2; WO2017152712A1

Abstract

A crystalline form (referred to as crystalline modification I) of the herbicide 4-amino-N-tert-butyl-4,5-dihydro-3-isopropyl-5-oxo-1H-1,2,4-triazole-1-carboxamide (amicarbazone): exhibiting at least three of the reflexes, in any combination, as 2θ ±0.2 degrees in an X-ray powder diffractogram (X-RPD) recorded using Cu-Kα radiation at 25 ºC: 11.0, 12.2, 13.1, 18.2, 19.4, 20.5, 21.5, 22.2, 23.5, 24.0, 27.4, 28.2, 29.2 and 31.3. Crystalline modification I also exhibits an infrared (IR) spectrum with peaks at wavenumbers (cm-1, ±0.2%) of 3315.4, 3209.4 and 2970.4 cm-1, and a melting point of 127-131 ºC. This crystalline form of amicarbazole may be prepared by recrystallisation for example of amorphous amicarbazone from methyl ethyl ketone or nitrobenzene. Water dispersible granules, aqueous suspension concentrates and oil-based suspension concentrates made with this crystalline form are also described.

Description

A NOVEL FORM OF AMICARBAZONE, A PROCESS FOR ITS PREPARATION AND

USE OF THE SAME

Technical Field

The present disclosure relates to a crystalline form of 4-amino-N-tert-butyl-4,5-dihydro-3-isopropyl-5-oxo-lH-l,2,4-triazole-l-carboxamide (amicarbazone), to its preparation processes and to its use in agrochemical preparations.

Background

Amicarbazone (4-amino-N-tert-butyl-4,5-dihydro-3-isopropyl-5-oxo-lH-l,2,4-triazole-l-carboxamide) is a new triazolinone related herbicide having a broad spectrum of weed control with good selectivity and high potency. The activity of this new triazolinone type herbicide is similar to the triazines and triazinones classes of herbicides in such a way that it provides potent inhibition of photosynthetic electron transport, inducing chlorophyll fluorescence and interrupting of oxygen evolution via binding to the Qb domain of photosystem Π (PSII) with a burn-down activity. Amicarbazone is absorbed through the roots of weeds and transported to the growing tips and leaves where inhibition of photosynthesis causes chlorosis, stunted growth, tissue necrosis and death. It can applied both pre- and post-emergences on crops, such as sugar cane and corn, against a variety of weeds

Amicarbazone has molecular formula of C10H19N5O2. Its chemical structure is

(I)

The commercially available amicarbazone, which is usually manufactured by the process described in U.S. PATENT NO. 5,194,085, is present in an amorphous state having a melting point of about 108°C. It has been found that amorphous amicarbazone is not suitable for being prepared as compositions or formulations because of residues formed after diluting the formulated products, which can block the spraying filters easily. Therefore, there is a high demand to develop a new and stable crystalline form of amicarbazone which is suitable for being prepared as a commercial formulation.

Statements of Invention

In attempt to resolve some or all of the problems with existing amorphous form of amicarbazone, a new and stable crystalline form of amicarbazone has been prepared.

In a first aspect, the invention provides a novel crystalline form of 4-amino-N-tert-butyl-4,5-dihydro-3 -isopropyl-5-oxo-lH-l,2,4-triazole-l -carboxamide (amicarbazone), termed “crystalline modification I”, exhibiting at least 3 of the following reflexes, in any combination, as 2Θ±0.2 degree in an X-ray powder diffractogram (X-RPD) recorded using Cu—^Ka radiation at25°C: 20 = 11.0±0.2 (1) 20 = 12.2 ±0.2 (2) 20 = 13.1 ±0.2 (3) 20 = 18.2 ±0.2 (4) 20 = 19.4 ±0.2 (5) 20 = 20.5 ±0.2 (6) 20 = 21.5 ±0.2 (7) 20 = 22.2 ±0.2 (8) 20 = 23.5 ±0.2 (9) 20 = 24.0 ±0.2 (10) 20 = 27.4 ±0.2 (11) 20 = 28.2 ±0.2 (12) 20 = 29.2 ±0.2 (13) 20 = 31.3±0.2 (14)

In an embodiment, the crystalline modification I of amicarbazone according to the first aspect of the invention, exhibiting at least 3 of the following reflexes, in any combination, as 20±O.2 degree in an X-ray powder difffactogram recorded using Cu—Ka radiation at 25°C: 20 = 11.0±0.2 (1) 20 = 13.1 ±0.2 (3) 20 = 18.2 ±0.2 (4) 20 = 19.4 ±0.2 (5) 20 = 20.5 ±0.2 (6) 20 = 27.4 ±0.2 (11) 20 = 28.2 ±0.2 (12)

In a second aspect, the present invention provides a crystalline modification I of amicarbazone, optionally according to the first aspect of the invention, exhibiting an infrared (IR) spectrum with characteristic functional group vibration peaks at wavenumbers (cm~\ ±0.2%) of 3315.4, 3209.4 and 2970.4 cm‘‘

In a third aspect, the present invention provides a crystalline modification I of amicarbazone, optionally according to the first or second aspect of the invention, exhibiting a melting point of I27-131°C, optionally I28-130°C, further optionally 129°C. In a fourth aspect, the present invention provides a crystalline modification I of amicarbazone, optionally according to any one of the first to third aspects of the invention, exhibiting a differential scanning calorimetry (DSC) profile exhibiting an endothermic melting peak with onset at 124°C and peak maximum at 129°C, further optionally with a melting enthalpy of 77J/g.

In a fifth aspect, the present invention provides a crystalline modification I of amicarbazone, optionally according to any one of the first to fourth aspects of the invention, characterized by powder X-ray diffraction pattern as substantially shown in Figure 2, and/or characterized by an IR spectrum as substantially shown in Figure I, and/or characterized by a DSC thermogram as substantially shown in Figure 3.

In a sixth aspect, the present invention provides a crystalline modification I of amicarbazone, optionally according to any one of the first to fifth aspects of the invention, obtainable by the process as substantially described in Example 2 or 3.

In a seventh aspect, the present invention provides a crystalline modification I of amicarbazone, optionally according to any one of the first to sixth aspects of the invention, obtainable by the process of the eighth aspect of the invention.

It has been found that the crystalline modification I of amicarbazone has a significant improvement in its stability, i.e. without residues after dilution. Furthermore, it has been found that the crystalline modification I is easier to comminute or grind compared to the amorphous amicarbazone prepared in accordance with the disclosure of U.S. PATENT NO. 5,194,085 and that formulations prepared using this crystalline modification I is stable even after prolonged storage. This allows the preparation of suspension concentrates (SC), oil-based suspension concentrates (OD) and water-dispersible granules (WG) and water-soluble granules (SG). In addition, the crystalline modification I has a lower tendency to aggregate and/or form residues after dilution compared to the amorphous phase described in U.S. Pat. No. 5,194,085. For these reasons, the crystalline modification I is more suitable for preparing commercial formulations. By virtue of its stability, the crystalline modification I gives the desired long storage period to its formulations. Hence, it is possible to prepare formulations of amicarbazone with excellent solution stability using the crystalline modification I, as will be disclosed hereinafter.

In an eighth aspect, the present invention provides a process for preparing a crystalline modification I of amicarbazone comprising steps of: i) dissolving amicarbazone into a solvent, or mixture of solvents; ii) precipitating the dissolved compound into crystalline modification I of amicarbazone; and iii) isolating the precipitated crystalline modification I.

In an embodiment of the eighth aspect of the invention, the amicarbazone in step i) is amorphous amicarbazone.

Methods for preparing amorphous amicarbazone are known in the art. Amorphous amicarbazone is manufactured and available on a commercial scale. A particularly suitable method for preparing amorphous amicarbazone is described in U.S. Pat. No. 5,194,085.

In an embodiment of the eighth aspect of the invention, the solvent is selected from the group consisting of halogenated hydrocarbons (for example, chlorobenzene, bromobenzene, dichlorobenzene, chlorotoluene, trifluoro methyl benzene and trichlorobenzene), ethers (for example, diethyl ether, ethyl propyl ether, n-butyl ether, anisole, phenetole, cyclohexyl methyl ether, dimethyl 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-tetrahydrofiiran, polyethers of ethylene oxide and/or propylene oxide), nitrated hydrocarbons (for example, nitromethane, nitroethane, nitropropane, nitrobenzene, chloronitrobenzene, ethyl benzene 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), esters (for example, malonates, acetic acid n-butyl ester (n-butyl acetate), isobutyl acetate, dimethyl carbonate, diethyl carbonate, dibutyl carbonate and ethylene carbonate), mesitylene, methyl ether ketone and mixtures thereof

In an embodiment of the eighth aspect of the invention, the solvent is selected from the group consisting of methyl ethyl ketone, benzene, chlorobenzene, dichlorobenzene, ethyl benzene, trifluoro methyl benzene, mesitylene, nitrobenzene, mixture of THF-hexane, ethyl acetate-hexane, dichloromethane-hexane, dichloromethane-methanol, THF-water and methanol-water. In an embodiment of the eighth aspect of the present invention, the solvent is selected from the group consisting of methyl ethyl ketone, nitrobenzene or a mixture thereof

According to an embodiment of the eighth aspect of the present invention, step ii) is effected by concentration of the solvent and/or by cooling and/or by the addition of a solubility reducing solvent and/or by adding a seed crystal of the crystalline modification I of amicarbazone.

According to an embodiment of the eighth aspect of the present invention, crystalline modification I of amicarbazone is prepared by dissolving the amorphous amicarbazone in a solvent or a solvent mixture as a concentrated solution by heating from ambient temperature to a temperature at or below the reflux temperature of the solvent or the solvent mixture. Optionally, the concentrated solutions can be prepared at the reflux temperature of the solvents. The concentration of the solution depends on the solubility of amicarbazone in the corresponding solvent or solvent mixture.

In an embodiment of the eighth aspect of the invention, the concentrated homogeneous solution thus prepared as in step (i) is then cooled to ambient temperature or cooled to about 0 to 20°C to crystallize the desired crystalline form from the solvent. The crystalline modification I of amicarbazone can also be crystallized out by concentrating the homogeneous solution by 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 an embodiment of the eighth aspect of the invention, crystallization of crystalline modification I of amicarbazone can also be obtained by adding seed crystals of the desired crystalline form during crystallization into the 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, more particularly in the range of 0.005% to 0.5% by weight, based on the weight of amicarbazone used for the preparation of concentrated solution in step (i). Optionally, the seed crystals are added to the concentrated solution at a temperature below the boiling point of the corresponding solvent or the solvent mixture.

In an embodiment of the eighth aspect of the invention, the precipitated crystalline modification I of amicarbazone 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 will be washed with solvent one or more times. Optionally, the solvent employed in the washing stage consists of one or more components of the solvent or solvent mixture employed for the preparation of concentrated solution in step (i), as described hereinbefore. 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 avoid the loss of crystal as minimum as possible in the corresponding washing solvent. In an embodiment of the eighth aspect of the invention, crystalline modification I of amicarbazone is dissolved and recrystallized. The washings and/or the solvent of crystallization in any of the methods may be concentrated to obtain solid amicarbazone which may be recycled.

In a ninth aspect, the present invention provides a crystalline modification I of amicarbazone obtained according to the eighth aspect of the invention, having a crystalline modification I of amicarbazone content of at least 98% by weight.

In a tenth aspect, the present invention provides a composition comprising the crystalline modification I of amicarbazone according to any one of the first to seventh and ninth aspects of the invention, and at least one auxiliary.

In an eleventh aspect, the present invention provides a use of the crystalline modification I of amicarbazone according to any one of the first to seventh and ninth aspects of the invention, or a composition according to the tenth aspect of the invention, for weed control.

In an embodiment of the tenth aspect of the invention, the amount of the crystalline modification I of amicarbazone is less than 90% by weight of the composition, optionally less than 80% by weight of the composition, further optionally less than 75% hy weight of the composition, still further optionally about 70% by weight of the composition.

The use of amorphous amicarbazone as a herbicide is known in the art and is used on a commercial scale. It has been found that the crystalline modification I of amicarbazone is also active in controlling undesirable plant growth, such as weeds. As a result, the techniques of formulating and applying amicarbazone known in the art with respect to amorphous amicarbazone, for example as disclosed in the prior art documents discussed hereinbefore, can also be applied in an analogous manner to amicarbazone in the crystalline modification I of the invention.

Accordingly, the invention provides a herbicidal composition comprising amicarbazone in the crystalline modification I as defined hereinbefore.

The invention additionally provides processes for preparing compositions for controlling weeds using the crystalline modification I of amicarbazone.

In an embodiment of the tenth aspect of the invention, the composition is in the form of a suspension concentrate (SC), oil-based suspension concentrate (OD), water-soluble granule (SG), dispersible concentrate (DC), emulsifiable concentrate (EC), emulsion seed dressing, suspension seed dressing, a granule (GR), a microgranule (MG), a suspoemulsion (SE) or water-dispersible granules (WG). Crystalline modification I of amicarbazone can be included into these customary formulations in a known manner using suitable auxiliaries, carriers and solvents and the like.

In an embodiment of the tenth aspect of the invention, the composition is in the form of a water-dispersible granules (WG).

In an embodiment of the tenth aspect of the invention, the crystalline modification I of amicarbazone may be present in a concentration sufficient to achieve the required dosage when applied to plants or the loci thereof, desirably in a concentration of about 70% by weight of the total mixture. The formulations are prepared, for example, by extending the crystalline modification I of amicarbazone 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 amicarbazone with customary additives, for example, one or more of wetting agents, dispersants, antifoaming agents and other formulation ingredients.

Wetting agents include, but are not limited to, sodium dodecyl sulfate, alkyl sulfosuccinates, laureates, alkyl sulfates, phosphate esters, acetylenic diols, ethoxyfluornated alcohols, ethoxylated silicones, alkyl phenol ethyoxylates, 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 mixtures thereof Sodium dodecyl sulfate is 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. Ligninsulfonates such as sodium ligninsulfonates are particularly useful for the composition of the invention.

Other formulation ingredients can also be used in the present invention such as filler, carrier, antifoaming agents, dyes, drying agents, and the like. These ingredients are known to one skilled in the art.

In an embodiment of the tenth aspect of the invention, the crystalline modification I of amicarbazone can be present in formulations and in other forms that are prepared from these formulations, and as a mixture with 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.

In an embodiment of the tenth aspect of the invention, when used as herbicide, the crystalline modification I of amicarbazone can furthermore be present in formulations and in other 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 and plant parts can be treated with the crystalline modification I of amicarbazone in accordance with any aspect or embodiment of 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 shoots, leaves, needles, stalks, stems, flowers, fruit bodies, fruits, seeds, roots, tubers and rhizomes. Harvested materials, and vegetative and generative propagation materials, for example, cuttings, tubers, meristem tissues, rhizomes, offsets, seeds, single and multiple plant cells, and any other plant tissues, are also included.

Treatment of the plants and plant parts with the compositions or formulations of the inventions can be 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 compositions of the invention can be used, for example, in control of one or more of following plants (weeds):

Monocotyledonous weeds include the genera: Aegilops, Agropyron, Agrostis, Alopecurus,

Apera, Avena, Brachiaria, Bromus, Cenchms, Commelina, Cynodon, Cyperus, Dactyloctenium, Digitaria, Echinochloa, Eleocharis, Eleusine, Eragrostis, Eriochloa, Eestuca, Eimbristylis, Heteranthera, Imperata, Ischaemum, Leptochloa, Lolium, Monochoria, Panicum, Paspalum, Phalaris, Phleum, Poa, Rottboellia, Sagittaria, Scirpus, Setaria, Sorghum. Dicotyledonous weeds include the genera: Abutilon, Amaranthus, Ambrosia, Anoda, Anthemis, Aphanes, Atnplex, Beilis, Bidens, Capsella, Carduus, Cassia, Centaurea, Chenopodium, Cirsium, Convolvulus, Croton, Datura, Desmodium, Emex, Erysimum, Euphorbia, Galeopsis, Galinsoga, Galium, Hibiscus, Ipomoea, Kochia, Lamium, Lepidium, Lindemia, Matricaria, Mentha, Mercurialis, Merremia, Momordica, Mullugo, Myosotis, Papaver, Pharbitis, Plantago, Polygonum, Portulaca, Ranunculus, Raphanus, Ricinus, Rorippa, Rotala, Rumex, Salsola, Senecio, Sesbania, Sida, Sinapis, Solanum, Sonchus, Sphenoclea, Stellaria, Stizolobium, Taraxacum, Thlaspi, Trifolium, Urtica, Veronica, Viola, Xanthium.

The benefits of the invention are seen most when the herbicidal composition is applied to kill weeds in growing crops of useful plants; such as sugarcane, corn, cereals, rice, maize, sorghum, cotton, canola, turf, barley, potato, sweet potato, sunflower, rye, oats, wheat, soybean, soya, sugar beet, tobacco, safflower, tomato, alfalfa, pineapple, cucurbits cassava and pastures. In an embodiment of the invention, sugar cane and corn are particularly suitable for treatment.

Throughout the description and claims of this specification, the words “comprise” and variations of the words, for example “comprising” and “comprises”, mean “including but not limited to”, and do not exclude other moieties, additives, components, integers or steps. Moreover the singular encompasses the plural unless the context otherwise requires: in particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Preferred features of each aspect of the invention may be as described in connection with any of the other aspects. Other features of the invention will become apparent from the following examples. Generally speaking the invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings). Thus features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. Moreover unless stated otherwise, any feature disclosed herein may be replaced by an alternative feature serving the same or a similar purpose.

Where upper and lower limits are quoted for a property then a range of values defined by a combination of any of the upper limits with any of the lower limits may also be implied.

In this specification, references to properties are - unless stated otherwise - to properties measured under ambient conditions, i.e. at atmospheric pressure and at a temperature of about 20°C.

As used herein, the term “about” or "around" when used in connection with a numerical amount or range, means somewhat more or somewhat less than the stated numerical amount or range, and for example 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 or the place on which the plant propagation materials of the plants will be sown. "Precipitation" as used herein, refers to the sedimentation of a solid material (a precipitate), including the sedimentation of a crystalline material, from a liquid solution in which the solid material is present in amounts greater than its solubility in the amount of liquid solution.

All percentages are given in weight % unless otherwise indicated.

Brief Description of the Drawings

The invention can be more clearly understood by reference to the drawings, which are described below, and are intended to exemplify and illustrate, but not to limit, the scope of the invention, wherein: FIG. 1 is a an infrared (IR) spectrograph of crystalline modification I of amicarbazone; FIG. 2 is a X-ray powder diffractogram of crystalline modification I of amicarbazone; FIG. 3 is a Differential Scanning Calorimetry (DSC) thermogram of crystal modification I of amicarbazone; FIG. 4 is a X-ray powder diffractogram of amorphous amicarbazone.

Detailed Description

The present invention will now be described by the following examples, and in which the following measurement techniques have been employed, and which the examples are provided for illustrative purposes only, and not intended to limit the scope of the disclosure.

All X-ray diffractograms were determined using powder diffractometer in reflection geometry at 25° C, using the following acquisition parameters:

The IR spectrum was measured with the resolution of 4 cm'* and with the number of scans of 16 for the crystallized samples. The crystalline modification I of amicarbazone can be identified by its characteristic functional group vibration peaks at wavenumbers (cm“\ ±0.2%) of 3315.38, 3209.42 and 2970.40cm'^ as shown in Figure 1.

All IR spectra were obtained using the following acquisition parameters:

All DSC thermograms were obtained using the following acquisition parameters:

Examples

Example 1: Preparation of amorphous amicarbazone in accordance with the disclosure of in the example 2 of U.S. Pat. No. U.S. PATENT NO. 5,194,085 with modification 3.6 g (0.036 mol) of t-butyl isocyanate and 0.05 g to 0.1 g of 1,8-diazabicycloundecene (DBU) were added to 3.52 g (0.03 mol) of 4-amino-3-isopropyl-lH-l,2,4-triazol-5-(4H)-one in 80 ml of absolute acetonitrile, the mixture was stirred for 2 hours at 20° C, concentrated in vacuo and the residue taken up in dichloromethane, the solution was washed with water, dried over sodium sulphate and concentrated in vacuo and the residue was precipitated as an amorphous solid by trituration with diethyl ether, having a melting point of 108°C in accordance with US 5,194,085.

Scheme 1. Synthesis of Amicarbazone

As shown in Figure 4, the X-ray powder diffraction pattern of the resulting amicarbazone product has no significant signals, which indicates the amicarbazone product prepared in accordance with the disclosure of in U.S. Pat. No. 5,194,085 is amorphous.

Preparation of crystalline modification I of amicarbazone Example 2 - Crystallization from methyl ethyl ketone

Amorphous amicarbazone sample (10 g) as prepared in Example 1 was taken in a 3-neck round bottom flask along with methyl ethyl ketone (60 ml) and the resulting slurry was heated to 35°C to get a homogeneous solution. The homogeneous solution was stirred at 35°C for 2h and the insoluble particles, if any, were filtered and the solution was slowly cooled to 20-25°C. Upon cooling, fine crystals were formed and the resulting heterogeneous mixture was stirred at 20°C for 2h. Then, the slurry was filtered and washed with methyl ethyl ketone at 20°C (3 ml). The filtered crystals were dried under vacuum at 20°C. The crystalline product, obtained had a purity of 98%.

The obtained crystal was analyzed by IR, X-RPD and DSC and found out to be crystalline modification I of amicarbazone as shown in Figure 1, 2 and 3respectively.

The IR spectrum of amicarbazone exhibited the functional group characteristic vibrations at wavenumbers (cm~\ ±0.2%) of 3315.38, 3209.42 and 2970.40cm'^ as shown in Figure 1.

The DSC thermogram of amicarbazone crystals exhibited an endothermic melting peak with onset at 123.8°C, a peak maximum at 129.2°C, and a melting enthalpy of 76.91 J/g as shown in Figure 3. The X-ray powder diffractogram of crystals exhibited the reflexes as shown in Figure 2 and the values are summarized in Table 1.

Table 1. X-ray Powder diffractogram reflexes of crystalline modification I of amicarbazone

Example 3 - Crystallization from nitrobenzene

Amorphous amicarbazone (5 g) sample as prepared in Example 1 was taken in a 3-neck round bottom flask along with nitrobenzene (35 ml) and the resulting slurry was heated to 60°C to get a homogeneous solution. The resultant hot solution was stirred at 60°C for 2h and the insoluble particles, if any, were filtered and the solution was slowly cooled to 20°C. Upon cooling, fine crystals were formed and the resulting heterogeneous mixture was stirred at 20°C for 2h. Then, the slurry was filtered, washed with nitrobenzene at 20°C (3 ml; and dried under vacuum at 45°C. The crystal thus obtained was having a purity of 98%.

The crystals were characterized as being amicarbazone crystalline modification I using infra-red spectrometry and x-ray diffraction, as described in Example 2.

Example 4: Preparation of water dispersible granules (WG)

All the components listed in Table 2 below were mixed, blended and milled in a highspeed 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 2 - WG formulations

Example 5: Preparation of suspension concentrates (SC)

An aqueous suspension concentrate (SC) was prepared by mixing finely ground active ingredients with auxiliaries as listed in Table 3: Table 3 - SC formulations

Example 6: oil-based suspension concentrates (OD)

All the components listed in Table 4 below were mixed uniformly and ground with a Dyno-Mill (manufactured by Willy A. Bachofen AG) to obtain an oil based suspension concentrate.

Table 4 - OD formulations

Example 7: Comparison of the stability of formulation - Wet sieve test WG samples prepared in Example 4-7 were diluted with water and their residues were compared by passing through a wet sieve of 325 mesh (44 pm openings). The amount of the material retained on the sieve is determined by drying and weighing. The results are tabulated in Table 5.

Table 5 - Wet sieve results

It is surprisingly found that the crystalline modification I of amicarbazone is extremely stable after dilution. It has a reduced tendency to produce aggregates and resides after dilution compared to the amorphous form. The retained residue in these tests for crystalline modification I of amicarbazone was 0.5% or less, 0.3% or less, and 0.2% or less. By comparison, the corresponding retained residues when amorphous amicarbazone was used was no less than 8%. When the dilution factor was 1000, there was up to about 25 times less residue, up to about 35 times less residue, up to about 50 times less residue produced when the crystalline modification I of amicarbazone was used when compared to the amorphous amicarbazone; this covering a range of about 25 to 50 times less relative residue formed. For these reasons, it is highly suitable for preparing commercial formulations where such aggregates/residues can block the spraying filters leading to a loss of productivity.

Claims

1. A crystalline modification I of 4-amino-N-tert-butyl-4,5-dihydro-3-isopropyl-5-oxo-lH-1,2,4-triazole-l-carboxamide (amicarbazone) exhibiting at least 3 of the following reflexes, in any combination, as 2Θ±0.2 degree in X-ray powder diffractogram (X-RPD) recorded using Cu—Ka radiation at 25°C: 20 = 11.0±0.2 (1) 20 = 12.2 ±0.2 (2) 20 = 13.1 ±0.2 (3) 20 = 18.2 ±0.2 (4) 20 = 19.4 ±0.2 (5) 20 = 20.5 ±0.2 (6) 20 = 21.5 ±0.2 (7) 20 = 22.2 ±0.2 (8) 20 = 23.5 ±0.2 (9) 20 = 24.0 ±0.2 (10) 20 = 27.4 ±0.2 (11) 20 = 28.2 ±0.2 (12) 20 = 29.2 ±0.2 (13) 20 = 31.3±0.2 (14)

2. The crystalline modification I of amicarbazone according to claim 1, exhibiting at least 3 of the following reflexes, in any combination, as 20±O.2 degree in an X-ray powder diffractogram recorded using Cu—^Ka radiation at 25°C: 20 = 11.0±0.2 (1) 20 = 13.1 ±0.2 (3) 20 = 18.2 ±0.2 (4) 20 = 19.4 ±0.2 (5) 20 = 20.5 ±0.2 (6) 20 = 27.4 ±0.2 (11) 20 = 28.2 ±0.2 (12)

3. The crystalline modification I of amicarbazone, optionally according to claim 1 or 2, exhibiting an infrared (IR) spectrum with characteristic functional group vibration peaks at wavenumbers (cm~\ ±0.2%) of 3315.4, 3209.4 and 2970.4 cm'\

4. A crystalline modification I of amicarbazone, optionally according to any one of claims 1 to 3, exhibiting a melting point of 127-131°C, optionally 128-130°C, further optionally 129°C.

5. A crystalline modification I of amicarbazone, optionally according to any one of claims 1 to 4, exhibiting a differential scanning calorimetry (DSC) profile exhibiting an endothermic melting peak with onset at 124°C and peak maximum at 129°C, further optionally with a melting enthalpy of 77 J/g.

6. A crystalline modification I of amicarbazone, optionally according to any one of claims 1 to 5, characterized by X-ray powder diffraction pattern as substantially shown in Figure 2, and/or characterized by an IR spectrum as substantially shown in Figure 1, and/or characterized by a DSC as substantially shown in Figure 3.

7. A crystalline modification I of amicarbazone, optionally according to any one of claims 1 to 6, obtainable by the process as substantially as described in Example 2 or 3.

8. A crystalline modification I of amicarbazone, optionally according to any one of claims 1 to 7, obtainable by the process of anyone of claims 9 to 14.

9. A process of preparing crystalline modification I of amicarbazone according to any one of claims 1 to 5, comprising; i) dissolving amicarbazone into a solvent, or mixture of solvents; ii) precipitating of the dissolved compound into the crystalline modification I of amicarbazone; and iii) isolating of the precipitated crystalline modification I.

10. The process according to claim 9, where the amicarbazone in step i) is amorphous amicarbazone.

11. The process according to claim 9 or 10, where the solvent is selected from the group consisting of methyl ethyl ketone, benzene, chlorobenzene, dichlorobenzene, ethyl benzene, trifluoro methyl benzene, mesitylene, nitrobenzene, or mixture of THF-hexane, ethyl acetate-hexane, dichloromethane-hexane, dichloromethane-methanol, THF-water and methanol-water.

12. The process according to any one of claims 9 to 11, where the solvent is methyl ethyl ketone, nitrobenzene or a mixture thereof

13. The process according to any one of claims 9 to 12, wherein step ii) is effected by concentration of the solvent and/or by cooling and/or by the addition of a solubility reducing solvent and/or by adding a seed crystal of the crystalline modification I of amicarbazone.

14. The process according to claim 13, wherein step ii) is effected by cooling to about 0 to 20°C.

15. A crystalline modification I of amicarbazone obtained according to any one of process claims 9 to 14 and having a crystalline modification I of amicarbazone content of at least 98% by weight.

16. A composition comprising the crystalline modification I of amicarbazone according to any one of claims 1 to 8 and 15 and at least one auxiliary.

17. The composition according to claim 16, wherein the auxiliary is selected from the group consisting of wetting agents, dispersants, antifoaming agents and other formulation ingredients.

18. The composition according to claim 17, wherein the other formulation ingredients can be filler, dyes and drying agents.

19. The composition according to any one of claims 16 to 18, which is in the form of a suspension concentrate (SG), an oil-based suspension concentrate (OD), water-soluble granules (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).

20. The composition according to claim 19, in the form of a water-dispersible granule (WG).

21. Use of the crystalline modification I of amicarbazone according to any one of the claims 1 to 8, and 15 or a composition according to any one of claims 16 to 20, for weed control.

22. A crystalline modification I of amicarbazone according to any one of claims 1 to 8 claim substantially as hereinbefore described with reference to any one of the examples, figures or the description.