The present invention relates to a novel process for the preparation of a suspension concentrate formulation of a herbicidal combination. More particularly, the present invention relates to a process for the preparation of a suspension concentrate formulation comprising glyphosate, metolachlor and mesotrione.
BACKGROUND OF THE INVENTION
For the purpose of application by the end user, herbicide compounds may be formulated in solid forms, such as wettable powders and granules, as well as in liquid forms, such as emulsifiable concentrates (EC) or suspension concentrates (SC) etc. The liquid formulations usually provide an easy-to-handle way of application. Herbicides in the form of suspension concentrates, that is, in the form of spray liquors are preferred due to its relative lower occupational toxicity in comparison to emulsifiable concentrates.
Suspension concentrates (SCs) are formulations, wherein the active ingredient is present in the form of finely divided solid particles, which are suspended (dispersed) in a liquid dispersing medium. Suspension concentrates usually contain surface-active compounds (surfactants), such as dispersants and wetting agents for stabilizing the active ingredient particles in the dispersing medium.
Despite the aforementioned advantages associated with the usage of SCs, there are a number of problems known to a skilled person which are sometimes encountered with SCs, as a result of settling during prolonged storage or storage at elevated temperatures, the resistance of settled particles to re-suspension and the formation of crystalline material upon storage. As a consequence, the formulations may be difficult to handle and the bio-efficacy may be inconsistent. These factors might result in a reduced chemical and physical stability of the formulations, an effect that is particularly pronounced when the formulations are stored over prolonged periods of time and/or at elevated temperatures. Said factors may also lead to poor dilution properties as the coarse active particles are prone to separate from the diluted formulation.

The U.S. Patent Application No. 10/560,097 discloses a method for the season-long control of unwanted vegetation, said method comprising a single application of a herbicidal combination comprising a 2-(substituted benzoyl)-1,3-cyclohexanedione or metal chelate thereof, glyphosate or a salt thereof and an acetamide. Further, the patent application also mentions in paragraph (0043) that the herbicidal composition comprises a 2-(substituted benzoyl)-1,3-cyclohexanedione or metal chelate thereof, glyphosate or a salt thereof and an acetamide, provided when the 2-(substituted benzoyl)-1,3-cyclohexanedione is mesotrione, then the acetamide is not metolachlor, acetochlor, alachlor or dimethenamide. Additionally, the patent does not disclose any process of preparation of herbicidal combination comprising 2-(substituted benzoyl)-1,3-cyclohexanedione, glyphosate and an acetamide.
The U.S. Patent 9,468,213 discloses a herbicide formulation comprising: (a) an aqueous phase; (b) an 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor in suspension in the aqueous phase, wherein the 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor is a triketone; (c) an encapsulated chloroacetamide and/or an isoxazoline herbicide in suspension in the aqueous phase; (d) glyphosate and/or glufosinate, or an agrochemically acceptable salt thereof, in solution in the aqueous phase; and (e) toluene sulfonic acid. In the formulation of the invention as disclosed in this patent, chloroacetamide or isoxazoline component is encapsulated and provided as a microcapsule suspension in the aqueous phase. This step of encapsulation not only adds to the cost but also makes the process time consuming and cumbersome.
Thus, there is a need to develop a process for preparing a suspension concentrate formulation which is simple, cost effective, industrially feasible and provides a stable formulation.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a process for the preparation of a herbicidal formulation comprising glyphosate, metolachlor and mesotrione, said process comprising: a) obtain a first aqueous solution comprising glyphosate and optionally alkali metal hydroxide, b) obtain a second solution comprising metolachlor, an organic solvent and optionally at least one of an emulsifier and a dispersing agent, c) obtain a first mixture comprising mesotrione, an emulsifier, a wetting agent, an anti-freezing agent, a biocide, an anti-foaming agent, a binder, water, and d) mixing the first solution, the second solution, the first mixture and a thickener to obtain the herbicidal formulation.

The process further comprising adding acid to step d), wherein the acid is hydrochloric acid, citric acid, or a combination thereof.
In an embodiment, the alkali metal oxide used in the process of the present invention is selected from sodium hydroxide and potassium hydroxide.
In another embodiment, the emulsifier and dispersing agent used in the process of the present invention is an emulsifier cum dispersing agent and is ethoxylated tristyryl phenol.
In one another embodiment, the organic solvent of step b) is selected from methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, t-butanol and mixtures thereof.
In another embodiment, the emulsifier and the wetting agent used in the process of present invention may be an emulsifier cum wetting agent and is sodium dioctyl sulphosuccinate.
In yet another embodiment the process of the present invention comprises anti-freezing agent and is selected from the group consisting of propylene glycol, diethylene glycol, monoethylene glycol and combinations thereof.
In still another embodiment the process of the present invention comprises biocide and is selected from the group consisting of 20% aqueous dipropylene glycol solution of 1,2-benzisothiazolin-3-one, formaldehyde and combinations thereof.
In an embodiment the process of the present invention uses dimethyl polysiloxane emulsion as antifoaming agent.
In another embodiment the process of the present invention uses silica as a binder and xanthan gum as a thickener.
DESCRIPTION OF THE INVENTION
Discussed below are some representative embodiments of the present invention. The invention in its broader aspects is not limited to the specific details and representative methods. The illustrative examples are described in this section in connection with the embodiments and methods provided. The invention according to its various aspects is particularly pointed out and distinctly claimed in the appended claims read in view of this specification and appropriate equivalents.

It is to be noted that, as used in the specification and the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a composition containing "a compound" includes a mixture of two or more compounds. It should also be noted that the term "or" is generally employed in its sense including "and/or" unless the content clearly dictates otherwise.
The expression of various quantities in terms of "% w/w" or "%" means the percentage by weight, relative to the weight of the total solution or composition unless otherwise specified.
The term "active ingredient" (A.I.) or "active agent" used herein refers to that component of the composition responsible for control of pest/weed.
As used herein, the expressions "SL formulation", "SC formulation" "WDG or WG formulation" "GR formulation", "DF formulation", "CG formulation", "EC formulation", "EW formulation", "ME formulation", "WP formulation" are the international denominations adopted by the FAO (Food and Agricultural Organization of the United Nations) to designate "soluble liquid", "aqueous suspension concentrate", "water dispersible granules", "granular", "dry flowable", "capsulated granules", "emulsion concentrate", "emulsion", "micro-emulsion" and "wettable powder" respectively.
In accordance with an embodiment of the invention, there is provided a process for the preparation of an herbicidal formulation comprising glyphosate, metolachlor and mesotrione. The process comprises a) obtain a first aqueous solution comprising glyphosate and optionally alkali metal hydroxide, b) obtain a second solution comprising metolachlor, an organic solvent and optionally at least one of an emulsifier and a dispersing agent, c) obtain a first mixture comprising mesotrione, an emulsifier, a wetting agent, an anti-freezing agent, a biocide, an anti-foaming agent, a binder, water, and d) mixing the first solution, the second solution, the first mixture and a thickener to obtain the herbicidal formulation. The process further comprising adding acid to step d), wherein the acid is hydrochloric acid, citric acid, or a combination thereof.
Glyphosate (IUPAC name: N-(phosphonomethyl)glycine) belongs to the class of organophosphorous herbicide and is represented by following structure-

0 0
II H |
HO | ^^ x/ T)H HO
Glyphosate inhibits 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), an enzyme of the aromatic acid biosynthetic pathway. This prevents synthesis of essential aromatic amino acids needed for protein biosynthesis. Glyphosate is a non-selective systemic herbicide, absorbed by the foliage, with rapid translocation throughout the plant. It provides control of annual and perennial grasses and broad-leaved weeds, pre-harvest in cereals, peas, beans, oilseed rape, flax and mustard. It also provides control of annual and perennial grasses and broad-leaved weeds in stubble and post-planting/pre-emergence of many crops. It is mostly used as a directed spray in vines and olives, in orchards, pasture, forestry and industrial weed control.
The present invention encompasses within its scope all known salts and esters of glyphosate. Non limiting examples include N-(phosphonomethyl)glycine-ammonium, N-(phosphonomethyl)glycine-diammonium, N-(phosphonomethyl)glycine-dimethyl ammonium, N-(phosphonomethyl)glycine-isopropyl ammonium, N-(phosphonomethyl)glycine-potassium, N-(phosphonomethyl)glycine-sesquisodium, N-(phosphonomethyl)glycine-trimesium.
In an embodiment, glyphosate is in the form of a soluble liquid and is obtained by mixing water, N-(phosphonomethyl)glycine and alkali metal hydroxide.
Metolachlor (IUPAC Name: 2-chloro-6a2-ethyl-N-[(lRS)-2-methoxy-l-methylethyl]acet-o-toluidide; 2-chloro-N-(6-ethyl-o-tolyl)-N-[(lRS)-2-methoxy-l-methylethyl]acetamide) belongs to the class of chloroacetamide herbicide and is represented by following structure-


It works by inhibiting cell division and also inhibits synthesis of very long chain fatty acids. Maize tolerance is attributed to rapid detoxification by glutathione transferases. Metolachlor is a selective herbicide, absorbed predominantly by the hypocotyls and shoots. It inhibits germination and provides control of annual grasses and some broad-leaved weeds in maize, sorghum, cotton, sugar beet, fodder beet, sugarcane, potatoes, peanuts, soybeans, safflowers, sunflowers, various vegetables, fruit and nut trees, and woody ornamentals.
Mesotrione (IUPAC name: 2-(4-mesyl-2-nitrobenzoyl) cyclohexane-l,3-dione) belongs to the class of triketone herbicide and is represented by following structure-

0

c

NO,

c

., -.

It works by inhibiting enzyme 4-hydroxyphenyl pyruvate dioxygenase (HPPD inhibitor). 2-(4-mesyl-2-nitrobenzoyl) cyclohexane-1, 3-dione is a selective herbicide for use in maize. The selectivity in maize is derived from differential metabolism (to the 4-hydroxy derivative) and also possibly from slower foliar uptake. 2-(4-mesyl-2-nitrobenzoyl) cyclohexane-1,3-dione is used for pre-emergence and post-emergence control of broad-leaved weeds such as Xanthium strumarium, Ambrosia trifida, Abutilon theophrasti, Chenopodium, Amaranthus, Polygonum spp. and some grass weeds in maize.
The alkali metal oxide used in the present invention is selected from sodium hydroxide and potassium hydroxide.
Emulsifiers are generally added to the formulation as they make it possible for water and oil to become finely dispersed in each other, creating a stable, homogenous, smooth emulsion. Emulsifiers are molecules with one water-loving (hydrophilic) and one oil-loving (hydrophobic) end.
It is generally observed that solid particles in a liquid undergo spontaneous aggregation to form lumps. Hence it is recommended to add a dispersing agent which prevents aggregation of solid

particles and keep them suspended in fluid. The dispersing agents such as amine salt of
phosphate tristyryl phenol ethoxylated, acrylic copolymer, naphthalene sulphonate of
formaldehyde condensate, lignin based sulphonate or combinations thereof may be used in the
process of the present invention. One or more dispersing agents may be used in the present
invention.
In a preferred embodiment, the emulsifier and dispersing agent used in the process of the present
invention is an emulsifier cum dispersing agent and is ethoxylated tristyryl phenol.
Wetting is the first stage of dispersion, in which air surrounding the granular composition is substituted with water. Wetting of the composition with water cannot occur if the surface tension of the liquid is very high. Hence, wetting agent is added to facilitate the process of dispersion of the granules in the liquid. Non-limiting examples of wetting agents that can be used in the present invention include ethoxylated polyarylphenol phosphate ester, dioctyl sulphosuccinate, non-ionic ethoxylate, each of which can be used individually or in combination. In another preferred embodiment, the emulsifier and the wetting agent used in the process of present invention may be an emulsifier cum wetting agent and is sodium dioctyl sulphosuccinate.
The organic solvent used in the present invention may be selected from methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, t-butanol and mixtures thereof.
An anti-freezing agent is generally added to the composition, to prevent the aqueous compositions from freezing. Suitable anti-freezing agents useful herein, but not limited to, include propylene glycol, diethylene glycol, monoethylene glycol and combinations thereof. A defoamer, also called as anti-foaming agent, is generally added to a composition, as foam formation prevents the efficient filling of a container. Preferably, the anti-foaming agent is polydimethyl siloxane emulsion and is commercially available as SAG®-1572. A biocide is added to the formulation for its preservation against spoilage from bacteria, yeasts and fungi, the process of the present invention comprises biocide and is selected from the group consisting of 20% aqueous dipropylene glycol solution of l,2-benzisothiazolin-3-one, formaldehyde and combinations thereof. The 20% aqueous dipropylene glycol solution of 1,2-benzisothiazolin-3-one is commercially available as Proxel® GXL.
In a preferred embodiment the process of the present invention uses silica as a binder.

In an embodiment, the step of mixing involves adding a thickener. The thickener is generally added to the formulation in order to maintain the physical stability. Suitable thickening agents are well known to the skilled person, for example xanthan gum.
The herbicidal formulation prepared by the process of the present invention exhibit good physical and chemical stability over prolonged storage times.
It is an advantage of the present invention that the herbicidal formulations are prepared efficiently and effectively with reduced time, labour and energy resources.
The process as disclosed in the present invention leading to the formation of a stable suspension concentrates having a pH value in the range of from 3 to 4.
A pH value within the stated range in coaction with the specific surfactants unexpectedly imparts a good to excellent overall stability to the formulation of the invention. That is, over prolonged storage periods, the highly active but degradation-prone 2-(4-mesyl-2-nitrobenzoyl) cyclohexane-l,3-dione remains intact and the formulation remains bio efficient while affording stable dispersions on dilution. Without being bound to theory, it is believed that the neutral to slightly acidic pH value on one hand stabilizes 2-(4-mesyl-2-nitrobenzoyl) cyclohexane-1,3-dione while still allowing the anionic surfactant to be fully effective. Thus, by employing the combination of surfactants and adjusting the pH value in the range given above, it is surprisingly possible to balance the chemical stability of 2-(4-mesyl-2-nitrobenzoyl) cyclohexane-1, 3-dione with the physical stability of the formulation.
The embodiments of the present invention are more particularly described in the following examples that are intended as illustrations only, since numerous modifications and variations within the scope of the present invention will be apparent to those of skill in the art. Unless otherwise noted, all parts, percentages and ratios reported in the following examples are on a weight basis and all reagents used in the examples were obtained or are available from the chemical suppliers.
EXAMPLES
Example 1: Process for the preparation of herbicidal formulation

In a vessel, 30% of demineralised water (DM) of total water of formulation was added to glyphosate (20.5% w/w) while stirring. Potassium hydroxide was then slowly added while maintaining the temperature at 20 to 25°C and a clear solution was obtained. The solution was stirred for 15 minutes (hereinafter referred as first solution).
In another vessel, n-butanol (5% w/w), Ethoxylated tristyrylphenol (2.6% w/w), and metolachlor (20.5%) w/w) were mixed under stirring for 15 minutes (hereinafter referred as second solution)
30%) DM water of total water of formulation, sodium dioctyl sulphosuccinate in glycol water solution (2%> w/w), propylene glycol (4% w/w), Proxel GXL (0.10% w/w), mesotrione (2.05 % w/w), dimethyl polysiloxane (0.2% w/w) and precipitated silica (1% w/w) were mixed to obtain a homogeneous mixture. After mixing homogeneously, grinding of the homogeneous mass is performed by using bead-mill until the required particle size is achieved (less than 10 micron); after milling the material is kept under stirring for approximately 15 minutes (hereinafter referred as first mixture).
2%> xanthan gum in demineralised water was prepared and Proxel GXL was added and mixed homogeneously and kept for 24 hours.
The first solution was added to second solution under stirring and mixed homogeneously for 15 minutes. The first mixture was then added under stirring and mixed homogeneously for 15 minutes and xanthan gum solution was then added slowly under stirring until material becomes homogeneous. The final pH was adjusted via using a combination of citric acid and hydrochloric acid to obtain a pH in the range of 3-4.From the foregoing it will be observed that numerous modifications and variations can be effectuated without departing from the true spirit and scope of the novel concepts of the present invention. It is to be understood that no limitations with respect to the specific embodiments illustrated is intended or should be inferred. It should be understood that all such modifications and improvements have been deleted herein for the sake of conciseness and readability but are properly within the scope of the following claims.

We Claim:

1.A process for the preparation of an herbicidal formulation comprising glyphosate,
metolachlor and mesotrione, said process comprising:
a) obtain a first aqueous solution comprising glyphosate and optionally alkali metal hydroxide,
b) obtain a second solution comprising metolachlor, an organic solvent and optionally at least one of an emulsifier and a dispersing agent,
c) obtain a first mixture comprising mesotrione, an emulsifier, a wetting agent, an anti-freezing agent, a biocide, an anti-foaming agent, a binder, water, and
d) mixing the first aqueous solution, the second solution, the first mixture and a thickener to obtain the herbicidal formulation.

2. The process as claimed in claim 1, further comprising adding acid to step d), wherein the acid is hydrochloric acid, citric acid, or a combination thereof.
3. The process as claimed in claim 1, wherein the alkali metal oxide is selected from sodium hydroxide and potassium hydroxide.
4. The process as claimed in claim 1, wherein in step b) the emulsifier and dispersing agent is an emulsifier cum dispersing agent.
5. The process as claimed in claim 4, wherein the emulsifier cum dispersing agent is ethoxylated tristyryl phenol.
6. The process as claimed in claim 1, wherein the organic solvent is selected from methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, t-butanol and mixtures thereof.
7. The process as claimed in claim 1, wherein the emulsifier and the wetting agent is an emulsifier cum wetting agent.

8. The process as claimed in claim 7, wherein the emulsifier cum wetting agent is sodium dioctyl sulphosuccinate.
9. The process as claimed in claim 1, wherein the anti-freezing agent is selected from the group consisting of propylene glycol, diethylene glycol, monoethylene glycol and combinations thereof.
10. The process as claimed in claim 1, wherein the biocide is selected from the group consisting of 20% aqueous dipropylene glycol solution of l,2-benzisothiazolin-3-one, formaldehyde and combinations thereof.
11. The process as claimed in claim 1, wherein the antifoaming agent is dimethyl polysiloxane emulsion.
12. The process as claimed in claim 1, wherein the binder is silica.
13. The process as claimed in claim 1, wherein the thickener is xanthan gum.