DESC:FIELD OF THE INVENTION
The present invention relates to an improved process for the preparation of a herbicidal triketone compound. More particularly, the present invention relates to an improved process for preparation of Tembotrione of Formula (I). The improved process in relation to the present invention is a consistently reproducible process, which results in high yield, purity of Tembotrione apart from resulting in stable form of Tembotrione.
BACKGROUND OF THE INVENTION
Tembotrione (I) is one of the representative triketones with a chemical name 2-{2-chloro-4-(methylsulfonyl)-3-[(2,2,2-trifluoroethoxy)methyl]benzoyl}cyclohexane-1,3-dione and the structural formula is as follows:

Structure of Tembotrione of Formula (I)
The triketone compound has wide applications in the fields of organic synthesis, pesticides, and the like, wherein, this triketone compound has outstanding application in the field of herbicides, has good herbicidal activity, is mainly used as a p-hydroxy keto acid dioxygenase (HPPD) inhibitor.
Tembotrione (I) is a post-emergence herbicide for the control of a broad spectrum of broad-leaved and grassy weeds in corn and other crops. The triketone compound has flexible application period, can be compounded with various products. This compound effectively prevents and removes annual broadleaf weeds and some gramineous weeds, is safe to crops, is safe for the environment and succeeding crops, is mainly used for corn, and can also be used for lawn, sugarcane, rice, onion, sorghum, other small crops and the like. It has a control action against broad spectrum of weeds and it also possesses a long weeding suitability. Further, it mainly targets various broad-leaved weeds and gramineous weeds in their middle and late stages after germination in a corn field, and shows excellent control over weeds for instance, thistle, field bindweed, speedwell, pepper weed, weasel flower, cleavers and the like, shows no phytotoxicity even after the reap of crops.
Various synthesis routes and process for the preparation of triketone derivatives, mainly Tembotrione have been reported, for instance: Patent application no. CN1323292A of Bayer Cropscience AG reports that when 2, 6-dichlorotoluene is used as a starting material to synthesize 2-[2-chloro-4-mesyl-a-(2,2,2-trifluoroethoxy)-m-toluoyl]cyclohexane-1,3-dione, a large amount of solid waste is generated, and the yield of the resulting compound is low.
Reference can also be made with respect to patent application no. CN105601548A of University of Heilongjiang which reports that when 3-chloro-2-methylaniline is used as a starting material to synthesize 2-[2-chloro-4-mesyl-a-(2,2,2-trifluoroethoxy)-m-toluoyl]cyclohexane-1,3-dione, a large amount of solid waste is generated, and the yield is low, i.e., only 75.2%.
Thus, the prior art processes for preparing Tembotrione (I), are often complicated, and/or time- consuming preparation process resulting in lesser yield and purity of the final compound Tembotrione and which is also not stable in some of the cases. Further, many of the published processes do not produce high yields of the active ingredient.
Accordingly, there is an ongoing and long felt need for an improved process for preparing Tembotrione with an improved yield, purity and selectivity.
Thus, it is the objective of the present invention to provide a process for preparing Tembotrione under basic conditions in which the yield, purity and selectivity are improved. A need still remains for simple, cost effective, consistently reproducible and environmentally friendly process for preparing highly pure, stable Tembotrione.
Hence, there is a need for an improved process for preparation of Tembotrione which overcomes the drawbacks of prior arts, therefore, the present invention conceived a novel, inventive and industrially useful process for the preparation of Tembotrione of formula (I).
The present invention thus satisfies the existing needs, as well as others, and generally overcomes the deficiencies found in the prior arts.
OBJECTIVES AND ADVANTAGES OF THE INVENTION
The main objective of the present invention is to provide an improved, simple, economically advantageous and cost-effective process for the preparation of Tembotrione of formula (I), with high purity and yield on a commercial scale.
Another objective of the present invention is to provide a novel and effective process for preparation of Tembotrione of formula (I), with reduced or minimal waste generation.
Another objective of the present invention is to provide a process for the preparation of Tembotrione of formula (I), with an improved reaction rate and minimized side reaction and/or formation of by-products.
Another objective of the present invention is to provide a process for the preparation of Tembotrione of formula (I) that involves less expensive and readily available reagents and solvents.
Another objective of the present invention is to provide a process for the preparation of Tembotrione of formula (I), which is industrially and economically robust process with safe operations.
Another objective of the present invention is to provide a process for the preparation of Tembotrione of formula (I), which results in improved yield and purity of the final product.
Another objective of the present invention is to provide a process for the preparation of Tembotrione of formula (I) wherein, less effluent is generated.
Another object of this invention is to obtain a compound (2), i.e., 2-bromo-5-chloro-4-methylphenol, by reacting a compound-(1), i.e., 3-chloro-4-methylphenol with a halogenating agent, and a suitable solvent.
A further object of this invention is to obtain a compound-(3), i.e., 6-bromo-3-chloro-2-(chloromethyl)-4-methylphenol, by halomethylation of the compound-(2) i.e., 2-bromo-5-chloro-4-methylphenol, in the presence of a formylating agent and a Lewis acid.
A further object of this invention is to obtain a compound-(4), i.e., 6-bromo-3-chloro-4-methyl-2-[2,2,2-trifluoroethoxy)methyl]phenol, by reacting the compound-(3) i.e., 6-bromo-3-chloro-2-(chloromethyl)-4-methylphenol, with 2,2,2-trifluoroethan-1-ol in the presence of base.
A further object of this invention is to obtain a compound-(5), i.e., 3-chloro-4-methyl-2-[2,2,2-trifluoroethoxy) methyl] phenol, by debromination of the compound-(4) i.e., 6-bromo-3-chloro-4-methyl-2-[2,2,2-trifluoroethoxy)methyl]phenol, in the presence of a dehalogenating agent.
A further object of this invention is to obtain a compound-(6), i.e., 2-chloro-4-methanesulfonyl-3-[2,2,2-trifluoroethoxy) methyl]benzoic acid, by reacting the compound-(5) ), i.e., 3-chloro-4-methyl-2-[2,2,2-trifluoroethoxy) methyl] phenol, with tosyl chloride in the presence of a base and suitable solvent followed by reacting with methyl thiol and base or sodium thiomethoxide and subsequent oxidation to obtain a compound 2-chloro-4-methanesulfonyl-3-[2,2,2-trifluoroethoxy) methyl]benzoic acid (6).
A further object of this invention is to obtain a compound-(8), i.e., 2-[2-chloro-4-methylsulfonyl-3-(2,2,2-trifluoroethoxymethyl)benzoyl]resorcinol, by condensation reaction of the compound-(6) i.e., 2-chloro-4-methanesulfonyl-3-[2,2,2-trifluoroethoxy) methyl]benzoic acid, by converting the acid to the corresponding acid chloride and then condensing with a Resorcinol (7).
A further object of this invention is to reduce the compound-(8), i.e., 2-[2-chloro-4-methylsulfonyl-3-(2,2,2-trifluoroethoxymethyl)benzoyl]resorcinol, in the presence of hydrogen and catalyst to yield and produce a target compound, i.e., Tembotrione of formula (I).
ADVANTAGES:
1. The process of the present invention is simple to handle and economically viable as there is a large amount of reduction in solvent volume.
2. The reaction time in process of the present invention is reduced which in turn reduces the operational costs.
3. The process of the present invention is more environmentally friendly.
4. The process of the present invention provides final product in high yield and high purity.

SUMMARY OF THE INVENTION
Accordingly, the main aspect of the present invention is to provide an improved process for the preparation of Tembotrione of formula (I). Provided herein is simple, cost effective and consistently reproducible process for the preparation of highly pure and stable form of Tembotrione.
In an aspect, the present invention provides an improved process for the preparation of Tembotrione of formula (I), using cost effective and readily available reagents.
In another aspect, the present invention provides an improved process for the preparation of Tembotrione of formula (I), which comprises the steps of:
a) reacting a compound-(1), i.e., 3-chloro-4-methylphenol with a halogenating agent, and a suitable solvent, to obtain a compound-(2), i.e., 2-bromo-5-chloro-4-methylphenol;
b) halomethylation of the compound-(2) in the presence of a formylating agent and a Lewis acid, to obtain a compound-(3), i.e., 6-bromo-3-chloro-2-(chloromethyl)-4-methylphenol;
c) reacting the compound-(3) with 2,2,2-trifluoroethan-1-ol in the presence of base, to obtain a compound-(4), i.e., 6-bromo-3-chloro-4-methyl-2-[2,2,2-trifluoroethoxy)methyl]phenol;
d) dehalogenation of the compound-(4) in the presence of a dehalogenating agent, to obtain a compound-(5), i.e., 3-chloro-4-methyl-2-[2,2,2-trifluoroethoxy) methyl] phenol;
e) reacting the compound-(5) with protecting group in the presence of a base and suitable solvent followed by reacting with methyl thiol and base or sodium thiomethoxide and subsequent oxidation to obtain a compound 2-chloro-4-methanesulfonyl-3-[2,2,2-trifluoroethoxy) methyl]benzoic acid (6);
f) condensing the compound-(6) by carrying out the condensation reaction, by converting the acid to the corresponding acid chloride and then condensing with Resorcinol (7) to obtain a compound-(8), i.e., 2-[2-chloro-4-methylsulfonyl-3-(2,2,2-trifluoroethoxymethyl)benzoyl]resorcinol;
g) reducing the compound-(8) in the presence of reducing agent and catalyst to furnish a target compound, i.e., Tembotrione of formula (I).
In another aspect, the present invention provides an improved process for the preparation of Tembotrione (I), which comprises reacting the compound 3-chloro-4-methylphenol (1), i.e.,

with a brominating agent like but not limited to hydrogen bromide and hydrogen peroxide in absence or presence of radical initiator and ethylene dichloride (EDC) as a solvent, to obtain a compound 2-bromo-5-chloro-4-methylphenol (2), i.e.,

followed by chloromethylation of the compound(2), in the presence of formaldehyde and zinc chloride, to obtain a compound 6-bromo-3-chloro-2-(chloromethyl)-4-methylphenol (3), i.e.,

the compound (3), on reacting further with 2,2,2-trifluoroethan-1-ol in the presence of base, obtains a compound 6-bromo-3-chloro-4-methyl-2-[2,2,2-trifluoroethoxy)methyl]phenol (4), i.e.,

the compound (4) then undergoes debromination to obtain a compound 3-chloro-4-methyl-2-[2,2,2-trifluoroethoxy) methyl] phenol (5), i.e.,

the compound (5), on further reaction with tosyl chloride in the presence of a base and suitable solvent followed by methyl thiol and base or sodium thiomethoxide and subsequent oxidation to obtain a compound 2-chloro-4-methanesulfonyl-3-[2,2,2-trifluoroethoxy) methyl]benzoic acid (6), i.e.,

further, carrying out the condensation reaction of the compound (6), by converting the acid to the corresponding acid chloride and then condensing with Resorcinol (7) to furnish compound (8) i.e., 2-[2-chloro-4-methylsulfonyl-3-(2,2,2-trifluoroethoxymethyl)benzoyl]resorcinol


In the last step, the compound (8) is reduced in the presence of hydrogen and catalyst to furnish the target compound, Tembotrione of formula (I).

Formula (I).
The reaction scheme of the present invention is represented as:

Scheme 1:

DETAILED DESCRIPTION OF THE INVENTION
At the very outset of the detailed description, it may be understood that the ensuing description only illustrates a particular form of this invention. However, such a particular form is only exemplary embodiment, and without intending to imply any limitation on the scope of this invention. Accordingly, the description is to be understood as an exemplary embodiment and teaching of the invention and not intended to be taken restrictively.
It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present disclosure.
Certain ranges are presented herein with numerical values being preceded by the term “about”. The term “about” is used herein to provide literal support for the exact number that it precedes, as well as a number that is near to or approximately the number that the term precedes. In determining whether a number is near to or approximately a specifically recited number, the near or approximately unrecited number may be a number which in the context in which it is presented, provides the substantial equivalent of the specifically recited number. In an embodiment, “about” can mean within one or more standard deviations, or within ±30%, 25%, 20%, 15%, 10%, or 5% of the stated value.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skilled in the art to which the invention belongs. Although any process and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, preferred process is described. For the purposes of the present invention, the following terms are defined below:
The articles “a” and “an” are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element.
As used herein, the terms, “including”, “includes”, “comprising”, and comprises” mean “including without limitation” and shall not be construed to limit any general statement that it follows to the specific or similar items.
Each embodiment is provided by way of explanation of the invention and not by way of limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the process described herein without departing from the scope of the invention. For instance, features illustrated or described as part of one embodiment can be applied to another embodiment to yield a still further embodiment.
In an embodiment, the present invention provides an improved process for the preparation of Tembotrione of formula (I).
In one of the embodiments, the present invention provides a process for the preparation of Tembotrione of formula (I), using cost effective and readily available reagents.
In an aspect, the present invention provides an improved process for the preparation of Tembotrione of formula (I), which comprises the steps of
a) reacting a compound-(1), i.e., 3-chloro-4-methylphenol with a halogenating agent, and a suitable solvent, to obtain a compound-(2), i.e., 2-bromo-5-chloro-4-methylphenol;
b) halomethylation of the compound-(2) in the presence of a formylating agent and a Lewis acid, to obtain a compound-(3), i.e., 6-bromo-3-chloro-2-(chloromethyl)-4-methylphenol;
c) reacting the compound-(3) with 2,2,2-trifluoroethan-1-ol in the presence of base, to obtain a compound-(4), i.e., 6-bromo-3-chloro-4-methyl-2-[2,2,2-trifluoroethoxy)methyl]phenol;
d) dehalogenation of the compound-(4) in the presence of a dehalogenating agent, to obtain a compound-(5), i.e., 3-chloro-4-methyl-2-[2,2,2-trifluoroethoxy) methyl] phenol;
e) reacting the compound-(5) with protecting group in the presence of a base and suitable solvent followed by methyl thiol and base or sodium thiomethoxide and subsequent oxidation to obtain a compound 2-chloro-4-methanesulfonyl-3-[2,2,2-trifluoroethoxy) methyl]benzoic acid (6) i.e., 2-chloro-4-methanesulfonyl-3-[2,2,2-trifluoroethoxy) methyl]benzoic acid;
f) condensing the compound-(6) by carrying out the condensation reaction, by converting the acid to the corresponding acid chloride and then condensing with Resorcinol (7) to obtain a compound-(8);
g) reducing the compound-(8) in the presence of reducing agent and catalyst to furnish a target compound, i.e., Tembotrione of formula (I).
The process of the present invention is represented by way of Scheme 1:

In one of the embodiments, the halogenating agent is selected from the group comprising of Hydrogen bromide (HBr), bromine, chlorine, fluorine, iodine, N-bromosuccinimide (NBS), wherein the halogenating agent is combined with acetic acid, mandelic acid, water, and/or H2O2 or combination thereof. In a preferred embodiment, the halogenating agent is a brominating agent or bromine.
In one of the embodiments, the oxidizing agent in the reaction of the present invention is selected from the group comprising of hydrogen peroxide, urea-hydrogen peroxide complex, meta-chloroperbenzoic acid (m-CPBA), tert-butylhydroperoxide, potassium permanganate, potassium dichromate, chlorine, sodium dichromate, chromium trioxide, nitric acid, perchloric acid, osmium tetraoxide, iodine, fluorine etc or combination thereof with or without catalyst.
In one embodiment, the base in the reaction of the present invention is selected from the group comprising of diisopropylamine, diisopropylethylamine, triethylamine (Et3N), dimethylamine, trimethyl amine, pyridine, N-methylmorpholine, 3-picoline, 2-picoline, 4-picoline, sodium bicarbonate, potassium carbonate, calcium hydroxide or combination thereof.
In an embodiment, the protecting group in the reaction of the present invention is selected from the group comprising of tosyl chloride, benzyl chloride, mesyl chloride (methanesulfonyl chloride), or combination thereof.
In one of the embodiments, the suitable solvent in the reaction of the present invention is selected from the group comprising of N,N-dimethylformamide, benzene, dichloromethane, 1,2-dichloroethane, chloroform, 1, 4-dioxane, diethyl ether, acetic acid, hydrogen peroxide, o-dichlorobenzene ethylene dichloride, carbon tetrachloride, chlorobenzene, dichlorobenzene, tetrahydrofuran and acetonitrile, ethyl acetate, Acetone, dimethylsulfoxide, cyclohexane, hexane, heptane, toluene, xylene, etc or combination thereof.
In one of the embodiments, the formylating agent in the reaction of the present invention is selected from the group comprising of para-formaldehyde, formalin, formic acid, methyl formate, N,N-dimethylformamide, diazomethane, cyanogen bromide, hydrogen cyanide etc or combination thereof.
In one of the embodiments, the dehalogenating agent in the reaction of the present invention is selected from the group comprising of Zinc, Iron (Fe), sodium, hydrogen gas, Tin (II) chloride, NaH2PO2, sodium borohydride, sodium amalgam (Na/Hg) etc or combination thereof. In a preferred embodiment, the dehalogenating agent is debrominating agent.
In one of the embodiments, the Lewis acid in the reaction of the present invention is selected from the group comprising of Zinc chloride (ZnCl2), Aluminium Chloride (AlCl3), Ferric Chloride (FeCl3), Boron Trifluoride (BF3), Boron Trichloride (BCl3), Titanium tetrachloride (TiCl4), Antimony Pentafluoride (SbF5), Thionyl chloride (SOCl2), Copper Chloride (CuCl2), metal triflates for instance, Copper (II) triflate, etc or combination thereof.
In one of the embodiments, the reducing agent is selected from the group comprising of sodium formate, hydrogen, oxalic acid, ascorbic acid, phosphite or combination thereof.
In one of the embodiments, the catalyst in the reaction of the present invention is selected from Pd/C or Raney Nickel, or Na2WO4.2H2O, (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl or (2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl (TEMPO), Cobalt(II) acetate, Sodium tungstate, dihydrate, Co-napthenate, palladium (II) acetate, triphenyl phosphine, or combination thereof.
In an embodiment, the compound (5) i.e., 3-chloro-4-methyl-2-[2,2,2-trifluoroethoxy) methyl] phenol, after tosylation followed by treatment with MeSH/Base, is oxidized using a strong oxidising agent which will oxidize CH3 (Methyl) group to the corresponding -COOH group, furnishing compound (6), due to the regioselective organic transformations.
In one of the embodiments, a compound (2), i.e., 2-bromo-5-chloro-4-methylphenol, is obtained by reacting a compound-(1), i.e., 3-chloro-4-methylphenol with a halogenating agent, and a suitable solvent.
In one of the embodiments, a compound-(3), i.e., 6-bromo-3-chloro-2-(chloromethyl)-4-methylphenol, is obtained by halomethylation of the compound-(2) i.e., 2-bromo-5-chloro-4-methylphenol, in the presence of a formylating agent and a Lewis acid.
In one of the embodiments, a compound-(4), i.e., 6-bromo-3-chloro-4-methyl-2-[2,2,2-trifluoroethoxy)methyl]phenol, is obtained by reacting the compound-(3) i.e., 6-bromo-3-chloro-2-(chloromethyl)-4-methylphenol, with 2,2,2-trifluoroethan-1-ol in the presence of base.
In one of the embodiments, a compound-(5), i.e., 3-chloro-4-methyl-2-[2,2,2-trifluoroethoxy) methyl] phenol, is obtained by dehalogenation of the compound-(4) i.e., 6-bromo-3-chloro-4-methyl-2-[2,2,2-trifluoroethoxy)methyl]phenol, in the presence of a dehalogenating agent.
In one of the embodiments, a compound-(6), i.e., 2-chloro-4-methanesulfonyl-3-[2,2,2-trifluoroethoxy) methyl]benzoic acid, is obtained by reacting the compound-(5), i.e., 3-chloro-4-methyl-2-[2,2,2-trifluoroethoxy) methyl] phenol, ) with tosyl chloride in the presence of a base and suitable solvent followed by reacting with methyl thiol and base or sodium thiomethoxide and subsequent oxidation to obtain a compound 2-chloro-4-methanesulfonyl-3-[2,2,2-trifluoroethoxy) methyl]benzoic acid (6)..
In one of the embodiments, a compound-(8) is obtained by condensation reaction of the compound-(6) i.e., 2-chloro-4-methanesulfonyl-3-[2,2,2-trifluoroethoxy) methyl]benzoic acid, by converting the acid to the corresponding acid chloride and then condensing with a Resorcinol (7).
In one of the embodiments, a reduction of the compound-(8) in the presence of hydrogen and catalyst furnish a target compound, i.e., Tembotrione of formula (I).
In an embodiment, the reaction is carried at a temperature of from 0? to 200? for a period of about 1 hour to about 24 hours and at a pressure of from an atmospheric pressure to 50 bar.
In an embodiment, the reaction is carried at a pH range of 0-6, preferably at pH 3 wherein the pH may be regulated by acid. The acid used for regulating the pH is selected from but not limited to hydrochloric acid, sulfuric acid, nitric acid, acetic acid. In another embodiment, wherein the process of preparation of 2-Bromo-5-chloro-4-methylphenol (2) comprises two methods method A and method B.
In another embodiment, method A for the process of preparation of 2-Bromo-5-chloro-4-methylphenol (2) comprises charging the reactor with suitable solvent followed by addition of compound (1). Adding Lewis acid to this and stirring the mixture. Adding halogenating agent. The reaction mass is then slowly warmed. The reaction is monitored by different techniques for instance, TLC and HPLC. After completion, the reaction mass is filtered. The residue is washed with suitable solvent. The combined organic layer is washed with water, brine and dried over anhydrous Sodium salt, filtered, and concentrated to furnish compound (2), i.e., 2-Bromo-5-chloro-4-methylphenol. After purification, purity and yield are calculated.
In another embodiment, method B for the process of preparation of 2-Bromo-5-chloro-4-methylphenol (2) comprises charging the reactor with suitable solvent followed by 3-Chloro-4-methylphenol. Adding suitable solvent for instance, DMSO (dimethylsulfoxide). The mixture is stirred. Halogenating or brominating agent like HBr is added. The reaction is monitored by techniques like TLC and HPLC. After completion, the organic layer is separated. The Aqueous layer is washed with suitable solvent. The combined organic layer is washed with water, brine and dried over Sodium salt, filtered, and concentrated to furnish 2-Bromo-5-chloro-4-methylphenol. After purification, purity and yield are calculated.
In another embodiment, wherein the process of preparation of 6-Bromo-3-chloro-2-(chloromethyl)-4-methylphenol (3) comprises charging the reactor with concentrated acid for instance, conc. HCl. Compound (2) is suspended in the reactor followed by addition of Lewis acid. The reaction mixture is stirred. A formylating agent is added in one lot and then the reaction mass is saturated with acidic gas for instance, HCl gas. The reaction is stirred at room temperature and then warmed up. The reaction is monitored by techniques such as TLC and HPLC. After completion, the reaction mass is cooled and extracted with solvent. The combined organic layer is washed with water, brine and dried over Sodium salt, filtered, and concentrated to furnish crude product, 6-Bromo-3-chloro-2-chloromethyl-4-methylphenol. After purification, purity and yield are calculated.

In another embodiment, wherein the process of preparation of 6-Bromo-3-chloro-4-methyl-2-(2,2,2-trifluoro-ethoxymethyl)-phenol (4) comprises charging the reactor with solvent followed by trifluoroethanol. A base is charged in a single lot. The reaction mixture is stirred. Compounds such as Tetrabutyl ammonium bromide is added followed by 6-Bromo-3-chloro-2-(chloromethyl)-4-methylphenol in solvent is added. The reaction mass is refluxed. The reaction is monitored by techniques such as TLC and HPLC. After completion, the reaction mass is to RT and filtered using filtration aid. The solid cake is washed with solvent. The combined organic layer is washed with water, brine and dried over anhydrous Sodium salt, filtered, and concentrated to furnish crude product, 6-Bromo-3-chloro-4-methyl-2-(2,2,2-trifluoro-ethoxymethyl)-phenol, after purification, purity and yield are calculated.
In another embodiment, wherein the process of preparation of 3-Chloro-4-methyl-2-(2,2,2-trifluoro-ethoxymethyl)-phenol (5) comprises charging the reactor with freshly distilled alcohol, for instance methanol followed by 6-Bromo-3-chloro-4-methyl-2-(2,2,2-trifluoroethoxymethyl)-phenol. Catalyst such as Pd/C is added carefully to the reactor. A base is added. The reactor is subjected to three vacuum-fill cycles with gas such as Hydrogen. After this, the reaction is stirred vigorously. The reaction is monitored by techniques such as TLC and HPLC. After completion, the reaction mass is filtered using filtration aid. The solid cake is washed with compounds such as methanol. The combined organic layer is washed with water, brine and dried over anhydrous Sodium salt such as anhydrous sodium sulphate, filtered, and concentrated to furnish crude product, 3-Chloro-4-methyl-2-(2,2,2-trifluoroethoxymethyl)-phenol. After purification, purity and yield are calculated.
In another embodiment, wherein the process of preparation of 2-Chloro-4-methanesulfonyl-3 (2,2,2-trifluoro-ethoxymethyl)-benzoic acid (6) comprises charging the reactor with suitable solvent such as Ethylene dichloride followed by 3-chloro-4-methyl-2-(2,2,2-trifluoroethoxymethyl)-phenol. The reaction mixture is stirred and base such as triethylamine is added and the mixture is stirred, followed by addition of compound such as p-toluenesulfonyl chloride (or tosyl chloride). The reaction is monitored by techniques such as TLC and HPLC. After completion, the reaction mass is washed with water, brine and organic layer is dried over Sodium salt for instance, anhydrous Sodium sulphate. It is then filtered, and concentrated to furnish crude tosylate which is then checked for purity and yield.
After charging the reactor with solvent, tosylate is added followed by compounds such as Tetrabutyl ammonium bromide. The reaction mixture is then stirred. Compounds such as Sodium thiomethoxide is added. The reaction mixture is refluxed. The reaction is monitored using TLC and HPLC. After completion, the reaction mass is diluted with solvent such as Ethylene dichloride, then washed with water, brine and organic layer is dried over salt for instance, anhydrous Sodium sulphate, filtered, and concentrated to furnish crude product. After purification, purity and yield of the product is checked.
The product so formed is added after charging the reactor with methanol. Compounds such as sodium tungstate, dihydrate are added. The reaction mixture is stirred. Oxidizing agents such as hydrogen peroxide is added dropwise at room temperature. After complete addition of oxidizing agent, the reaction mass is stirred at room temperature. The reaction is monitored using techniques such as TLC and HPLC. After completion, the solid material is filtered and treated as first crop. The filtrate was concentrated in vacuo to obtain residue. The residue was dissolved in Ethyl acetate (300 mL), washed with water, brine, dried over anhydrous sodium sulfate, filtered and concentrated to furnish second crop. After purification, purity and yield are checked.
Further, an autoclave reactor is charged with acid such as acetic acid and the product formed in the above step is added. Compounds such as cobalt (II) acetate and Trimethylphenylammonium tribromide are added. The reactor is then subjected to cycles with gas such as Oxygen. After this, the reactor is closed and oxygen gas is filled till a certain pressure. The reaction mass is heated and the oxygen pressure is maintained by refilling the gas as per the consumption. The reaction is monitored by using techniques such as HPLC by taking out the samples at regular intervals. After completion, the reaction mass is cooled and poured over ice. The solid obtained is filtered and purified. After purification, purity and yield are checked.
In another embodiment, wherein the process of preparation of [2-Chloro-4-methanesulfonyl-3-(2,2,2-trifluoroethoxymethyl)-phenyl]-(2,6-dihydroxyphenyl)-methanone (8) comprises charging the reactor with solvent such as Ethylene dichloride (EDC) followed by 2-Chloro-4-methanesulfonyl-3-(2,2,2-trifluoroethoxymethyl)benzoic acid. Solvent such as N,N-Dimethyl formamide is added and the reaction mass is stirred. Lewis acid for instance, thionyl chloride is added dropwise at room temperature. After complete addition, the reaction mass is heated to till a certain point such as clear solution. After completion of the reaction, the suitable solvent and excess of Lewis acid is distilled out to provide the corresponding acyl chloride.
In another reactor, charged with solvent such as ethylene dichloride (EDC) and is followed by addition of the acyl chloride. The reaction mass is cooled. Lewis acid such as metal triflate is added. Further Lewis acid such as aluminium chloride is added. The reaction is stirred at the same temperature till the completion of the reaction. After completion, the reaction mass is poured on crushed ice with stirring. The organic layer is separated. The aqueous layer is washed with solvent. The combined organic layer is washed with water, brine, dried over salt such as anhydrous sodium salt, filtered and concentrated under reduced pressure to furnish [2-Chloro-4-methanesulfonyl-3-(2,2,2-trifluoroethoxymethyl)-phenyl]-(2,6-dihydroxyphenyl)-methanone (8). After purification, purity and yield are checked.
In another embodiment, wherein the process of preparation of 2-[2-chloro-4-methylsulfonyl-3-(2,2,2-trifluoroethoxymethyl) benzoyl]cyclohexane-1,3-dione, Tembotrione (I) comprises charging the reactor with water followed by [2-Chloro-4-methanesulfonyl-3-(2,2,2-trifluoroethoxymethyl)-phenyl]-(2,6-dihydroxyphenyl)-methanone (8) and compounds such as sodium formate is added. The reaction mixture is then heated. Along with heat, a slow stream of gas such as nitrogen is passed through the reaction mass. Catalyst for instance, Pd/C is added. After addition, the temperature is elevated and stirred till completion of the reaction. The hot reaction mass is then filtered to remove the catalyst for reuse. The filtrate was cooled and acidified to a lower pH value, preferably 3 with concentrated acids such as conc. HCl. The solid obtained is then filtered to furnish crude 2-[2-chloro-4-methylsulfonyl-3-(2,2,2-trifluoroethoxymethyl)benzoyl]cyclohexane-1,3-dione, Tembotrione (I). The material is then purified by crystallization. After purification, purity and yield are checked.
The process for preparing Tembotrione of formula (I) disclosed according to the present invention yields Tembotrione with purity of around 95% to 99% and a yield of around above 80%.
According to another aspect, there is provided a process for preparing agrochemical composition comprising highly pure and stable Tembotrione obtained as per the process disclosed herein. Yet in another embodiment, agrochemical compositions comprise at least a bio-active effective amount of highly pure and stable Tembotrione obtained by the processes disclosed herein. The agrochemical compositions further contain one or more agrochemically acceptable excipients. Suitable excipients and the amounts to use may be readily determined by the formulation scientist based upon experience and consideration of standard procedures and reference works in the field.
While preferred embodiments and examples have been shown and described, it is to be understood that various further modifications will be apparent to those skilled in the art.
EXAMPLES
Although the content of the present invention is further specifically explained using examples, the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded. The following examples are presented to further explain the invention with experimental conditions, which are purely illustrative and are not intended to limit the scope of the invention.
Tembotrione (Formula I) was synthesized by sequential reactions starting from compound with formula (1). The compound with formula (1) was subjected to bromination using brominating agents like but not limited to Bromine which is added in acetic acid or water, or combined with Hydrogen as HBr and H2O2, and alike with or without free radical initiators either neat or using solvents including but not limited to ethylene dichloride, acetonitrile, carbon tetrachloride, chlorobenzene, o-dichlorobenzene to furnish a compound with formula 2,wherein, the said bromination was carried out at a temperature range of 0oC to 180oC for a period of 1 hour to 24 hours. The preferred temperature range is from 25oC to 180oC and at pressure from atmospheric to 10 bar.
The compound with formula (2) was chloromethylated in the presence of formylating agent like para-formaldehyde or formalin or alike in presence of Lewis acid like but not limited to Zinc chloride, aluminium chloride or ferric chloride to furnish a compound (3), which was alkylated with Trifluoroethanol in the presence of bases known to the person skilled in the art to obtain a compound (4), wherein, the said reaction of chloromethylation was carried out at a temperature range of from 0oC to 200oC for a period of 1 hour to 24 hours. The more preferred temperature range is from 25oC to 200oC and at pressure from atmospheric to 10 bar. The compound (4) was debrominated to give a compound (5) at a temperature range of form 0oC to 200oC for a period of 1 hour to 24 hours. The more preferred temperature range was from 25oC to 200oC and at a pressure from atmospheric to 10 bar.
The compound (5) was subjected to tosylation, followed by nucleophilic substitution and oxidation using the reaction conditions known to the person skilled in the art to provide a compound (6). The compound (6) was converted to acyl chloride using reagent like sulfonyl chloride, sulfuryl chloride, phosphorous oxychloride, phosphorous pentachloride, phosphorous trichloride and alike followed by reacting with resorcinol to furnish a compound (7) which on reduction under the conditions known to the person skilled in the art to yield Tembotrione (Formula I).
The selected starting material is optimally substituted to get desired selectivity and improved yield and purity for the proposed scheme.
Example 1: Preparation of 2-Bromo-5-chloro-4-methylphenol (2)


Method A comprises: NBS, Mandelic acid, MeCN, H2O, room temperature, Overnight
Method B comprises: HBr (48%), DMSO, Ethyl acetate (EtOAc), 60oC, 8 hours
Method A:
A four necked glass reactor (2 Lit) fitted with condenser, thermometer pocket, thermometer, mechanical stirrer was charged with ethylene dichloride (EDC) (460 mL) followed by 3-Chloro-4-methylphenol (147.4 g). Mandelic acid (31.14 g) was added to this. The mixture was stirred for 30 mins. N-Bromosuccinimide (NBS) (210 g) was added portion-wise. The reaction mass was slowly warmed to 55oC to 60oC. The reaction was monitored by TLC and HPLC. After completion, the reaction mass was filtered. The residue was washed with EDC. The combined organic layer was washed with water, brine and dried over anhydrous Sodium sulfate, filtered, concentrated to furnish 2-Bromo-5-chloro-4-methylphenol. After purification, HPLC purity (area): 95%, Yield: 173 g, 78%
Method B:
A four necked glass reactor (2 Lit) fitted with condenser, thermometer pocket, thermometer, mechanical stirrer was charged with Ethyl acetate (EtOAc) (500 mL) followed by 3-Chloro-4-methylphenol (146 g). DMSO (dimethylsulfoxide) (40 g) was added to this. The mixture was stirred for 30 mins. HBr (48% Aqueous solution, 308 g) was added portion-wise at 60 oC. The reaction was monitored by TLC and HPLC. After completion, the organic layer was separated. The Aqueous layer was washed with ethyl acetate. The combined organic layer was washed with water, brine and dried over anhydrous Sodium sulfate, filtered, concentrated to furnish 2-Bromo-5-chloro-4-methylphenol. After purification, HPLC purity (Area): 98%, Yield: 168.8 g, 76%.
Example 2: Preparation of 6-Bromo-3-chloro-2-(chloromethyl)-4-methylphenol (3)

A four necked glass reactor (2 Lit) fitted with condenser, thermometer pocket, thermometer, mechanical stirrer was charged with Concentrated HCl (730 g). 2-Bromo-5-chloro-4-methylphenol (252.6 g) was suspended in the reactor followed by addition of ZnCl2 (45.2 g). The reaction mixture was stirred for 15-20 mins. Para-formaldehyde (44.5 g) was added in one lot and then the reaction mass was saturated with HCl gas. The reaction was stirred at room temperature and then warmed up to 55o C. The reaction was monitored by TLC and HPLC. After completion, the reaction mass was cooled to RT and extracted with Ethylene dichloride. The combined organic layer was washed with water, brine and dried over anhydrous Sodium sulphate, filtered, concentrated to furnish crude product, 6-Bromo-3-chloro-2-chloromethyl-4-methylphenol. After purification, HPLC purity (area): 98%, Yield: 222.4 g, 76%
Example 3: Preparation of 6-Bromo-3-chloro-4-methyl-2-(2,2,2-trifluoro-ethoxymethyl)-phenol (4)

A four necked glass reactor (2 Lit) fitted with condenser, thermometer pocket, thermometer, mechanical stirrer was charged with ethylene dichloride (EDC) (250 mL) followed by Trifluoroethanol (81.8g). Potassium carbonate (241 g) was charged in a single lot. The reaction mixture was stirred for 3-4 hrs. Tetrabutyl ammonium bromide (13.2 g) was added followed by 6-Bromo-3-chloro-2-(chloromethyl)-4-methylphenol (225.8 g) in EDC (500 mL) was added. The reaction mass was refluxed. The reaction was monitored by TLC and HPLC. After completion, the reaction mass was cooled to RT and filtered using filtration aid. The solid cake was washed with EDC (2 X 100 mL). The combined organic layer was washed with water, brine and dried over anhydrous Sodium sulphate, filtered, concentrated to furnish crude product, 6-Bromo-3-chloro-4-methyl-2-(2,2,2-trifluoro-ethoxymethyl)-phenol, After purification, HPLC purity (area): 93%, Yield: 223 g, 86%
Example 4: Preparation of 3-Chloro-4-methyl-2-(2,2,2-trifluoro-ethoxymethyl)-phenol (5)

A four necked glass reactor (2 Lit) fitted with condenser, thermometer pocket, thermometer, mechanical stirrer was charged with freshly distilled Methanol (820 mL) followed by 6-Bromo-3-chloro-4-methyl-2-(2,2,2-trifluoroethoxymethyl)-phenol (222.8 g) under Nitrogen atmosphere. Pd/C (5.36 g, 10 % W/W) was added carefully to the reactor. Sodium bicarbonate (337.2 g) was added. The reactor was subjected to three vacuum-fill cycles with Hydrogen. After this, the reaction was stirred vigorously. The reaction was monitored by TLC and HPLC. After completion, the reaction mass was filtered using filtration aid. The solid cake was washed with MeOH (2 X 75 mL). The combined organic layer was washed with water, brine and dried over anhydrous Sodium sulphate, filtered, concentrated to furnish crude product, 3-Chloro-4-methyl-2-(2,2,2-trifluoroethoxymethyl)-phenol. After purification, HPLC purity (area): 92%, Yield: 117.4 g, 75%
Example 5: Preparation of 2-Chloro-4-methanesulfonyl-3-(2,2,2-trifluoro-ethoxymethyl)-benzoic acid (6)

Step 5A:
A four necked glass reactor (2 Lit) fitted with condenser, thermometer pocket, thermometer, mechanical stirrer was charged with Ethylene dichloride (EDC) (510 mL) followed by 3-chloro-4-methyl-2-(2,2,2-trifluoroethoxymethyl)-phenol (115.8 g) under Nitrogen atmosphere. The reaction mixture was stirred for 20 mins. Triethylamine (98 g) was added and the mixture is stirred for 20 minutes, followed by addition of p-toluenesulfonyl chloride (tosyl chloride) (93.4 g). The reaction was monitored by TLC and HPLC. After completion, the reaction mass was washed with water, brine and organic layer was dried over anhydrous Sodium sulphate, filtered, concentrated to furnish crude tosylate. HPLC purity (area): 95%, Yield: 157.2 g, 89 %
Step 5B:
A four necked glass reactor (2 Lit) fitted with condenser, thermometer pocket, thermometer, mechanical stirrer was charged with Ethylene dichloride (EDC) (500 mL) followed by Tosylate obtained in Step 5A (152.6 g). Tetrabutyl ammonium bromide (5.84 g) was added. The reaction mixture was stirred for 20 mins. Sodium thiomethoxide (223.8 g, 20% Aqueous solution) was added. The reaction mixture was refluxed. The reaction was monitored by TLC and HPLC. After completion, the reaction mass was diluted with Ethylene dichloride (200 mL), washed with water, brine and organic layer was dried over anhydrous Sodium sulphate, filtered, concentrated to furnish crude product. After purification, HPLC purity (area): 97%, Yield: 72.7 g, 72 %
Step 5C:
A four necked glass reactor (1 Lit) fitted with condenser, thermometer pocket, thermometer, mechanical stirrer was charged with Methanol (450 mL) followed by the Step 5B product (72.2 g). Sodium tungstate, dihydrate (4.2 g) was added. The reaction mixture was stirred for 20 mins. Hydrogen peroxide (97.5 g, 30% Aqueous solution) was added dropwise at room temperature. After complete addition of hydrogen peroxide, the reaction mass was stirred at room temperature. The reaction was monitored by TLC and HPLC. After completion, the solid material was filtered and treated as first crop. The filtrate was concentrated in vacuo to obtain residue. The residue was dissolved in Ethyl acetate (300 mL), washed with water, brine, dried over anhydrous sodium sulfate, filtered and concentrated to furnish second crop. After purification, HPLC purity (Area): 96%, Yield: 70 g, 91 %
Step 5D:
Autoclave reactor (1 Lit) was charged with Acetic acid (150 mL) followed by the Step 5C product (68.5 g). Cobalt (II) acetate (5.1 g) and Trimethylphenylammonium tribromide (15.3 g) were added. The reactor was subjected to three vacuum-fill cycles with Oxygen. After this, the reactor was closed and oxygen gas was filled till 6 bar. The reaction mass is heated at 100 -110 o C. The oxygen pressure was maintained by refilling the gas as per the consumption. The reaction was monitored by HPLC by taking out the samples at regular intervals. After completion, the reaction mass was cooled to RT and poured over ice (200 g). The solid obtained was filtered and purified. After purification, HPLC purity (Area): 96%, Yield: 70 g, 91 %.
Example 6: Preparation of [2-Chloro-4-methanesulfonyl-3-(2,2,2-trifluoroethoxymethyl)-phenyl]-(2,6-dihydroxyphenyl)-methanone (8)

A three necked glass reactor (0.5 Lit) fitted with condenser, thermometer pocket, thermometer, mechanical stirrer was charged with Ethylene dichloride (EDC) (150 mL) followed by 2-Chloro-4-methanesulfonyl-3-(2,2,2-trifluoroethoxymethyl)benzoic acid (42.6 g). N,N-Dimethyl formamide ((0.17 g) was added and the reaction mass was stirred for 15-20 mins. Thionyl chloride (20.9 g) was added dropwise at room temperature. After complete addition, the reaction mass was heated to 70 oC till clear solution. After completion of the reaction, the suitable solvent and excess thionyl chloride was distilled out to provide the corresponding acyl chloride.
In another three necked glass reactor (1 Lit) fitted with condenser, thermometer pocket, thermometer, mechanical stirrer was charged with Ethylene dichloride (EDC) (150 mL) followed by the acyl chloride (in 100 mL of Ethylene dichloride) obtained. The reaction mass was cooled to 0 to 10 oC. Copper (II) triflate (2.2 mol%) was added. Aluminium chloride was added portion wise. The reaction was stirred at the same temperature till the completion of the reaction. After completion, the reaction mass was slowly poured on crushed ice (~250 g) with vigorous stirring. The organic layer was separated. The aqueous layer was washed with Ethylene dichloride (2 X 100 mL). The combined organic layer was washed with water, brine, dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure to furnish [2-Chloro-4-methanesulfonyl-3-(2,2,2-trifluoroethoxymethyl)-phenyl]-(2,6-dihydroxyphenyl)-methanone or (8). After purification, HPLC purity: 97%, Yield: 31.54 g, 75 %.
Example 7: Preparation of 2-[2-chloro-4-methylsulfonyl-3-(2,2,2-trifluoroethoxymethyl) benzoyl]cyclohexane-1,3-dione, Tembotrione (I)

A three necked glass reactor (0.5 Lit) fitted with condenser, thermometer pocket, thermometer, mechanical stirrer was charged with Water (125 mL) followed by [2-Chloro-4-methanesulfonyl-3-(2,2,2-trifluoroethoxymethyl)-phenyl]-(2,6-dihydroxyphenyl)-methanone (8) (24.7 g) and sodium formate (5.1 g). The reaction mixture was heated to 40 oC. At this temperature, a slow nitrogen stream is passed through the reaction mass for 30 minutes. Wet 10 % Pd/C (0.32 g) was added at this temperature. After addition, the temperature was elevated to 50 oC and stirred till completion of the reaction. The hot reaction mass was filtered to remove the catalyst for reuse. The filtrate was cooled to 0oC to 5oC and acidified to pH 3 with Conc HCl. The solid obtained was filtered to furnish crude 2-[2-chloro-4-methylsulfonyl-3-(2,2,2-trifluoroethoxymethyl)benzoyl]cyclohexane-1,3-dione, Tembotrione (I). The material is purified by crystallization. After purification, HPLC purity: 98 %, Yield: 21 g, 87 %.
It should be understood that the scope of the present invention is not limited by the examples in any manner. It will be appreciated by any person skilled in this art that the present invention includes the given examples and further can be modified and altered without departing from the novel teachings and advantages of the invention which are intended to be included within the scope of the invention.
,CLAIMS:I/We Claim:
1. An improved process for preparation of Tembotrione of formula (I), which comprises:
a) reacting a compound-(1), i.e., 3-chloro-4-methylphenol with a halogenating agent, and a suitable solvent, to obtain a compound-(2), i.e., 2-bromo-5-chloro-4-methylphenol;
b) halomethylating the compound-(2) in the presence of a formylating agent and a Lewis acid, to obtain a compound-(3), i.e., 6-bromo-3-chloro-2-(chloromethyl)-4-methylphenol;
c) reacting the compound-(3) with 2,2,2-trifluoroethan-1-ol in the presence of a base, to obtain a compound-(4), i.e., 6-bromo-3-chloro-4-methyl-2-[2,2,2-trifluoroethoxy)methyl]phenol;
d) dehalogenating the compound-(4) in the presence of a dehalogenating agent, to obtain a compound-(5), i.e., 3-chloro-4-methyl-2-[2,2,2-trifluoroethoxy) methyl] phenol;
e) reacting the compound-(5) with protecting group in the presence of the base and suitable solvent followed by addition of methyl thiol and base or sodium thiomethoxide.
f) oxidizing the compound formed in step (e) by an oxidizing agent to obtain a compound-(6), i.e., 2-chloro-4-methanesulfonyl-3-[2,2,2-trifluoroethoxy) methyl]benzoic acid;
g) condensing the compound-(6) by carrying out the condensation reaction, by converting the compound (6) to a corresponding acid chloride and then condensing with Resorcinol (7) to obtain a compound-(8);
h) reducing the compound-(8) in the presence of reducing agent and a catalyst to furnish a target compound, i.e., Tembotrione of formula (I).

2. The improved process as claimed in claim 1, wherein the halogenating agent is selected from the group comprising of Hydrogen bromide, bromine, chlorine, fluorine, iodine, N-Bromosuccinimide (NBS), of combination thereof.

3. The improved process as claimed in claims 1-2, wherein the halogenating agent is combined with an acetic acid, mandelic acid, water, and/or H2O2 or combination thereof.

4. The improved process as claimed in claim 1, wherein the suitable solvent is selected from the group comprising of N,N-dimethylformamide, benzene, dichloromethane, 1,2-dichloroethane, chloroform, 1, 4-dioxane, diethyl ether, acetic acid, , o-dichlorobenzene, ethylene dichloride, , carbon tetrachloride, chlorobenzene, dichlorobenzene, tetrahydrofuran and acetonitrile, ethyl acetate, Acetone, dimethylsulfoxide, cyclohexane, hexane, heptane, toluene, xylene, or combination thereof.

5. The improved process as claimed in claim 1, wherein the formylating agent is selected from the group comprising of para-formaldehyde, formalin, formic acid, methyl formate, N,N-dimethylformamide, diazomethane, cyanogen bromide, hydrogen cyanide etc or combination thereof.

6. The improved process as claimed in claim 1, wherein the Lewis acid is selected from the group comprising of Zinc chloride (ZnCl2), Aluminium Chloride (AlCl3), Ferric Chloride (FeCl3), Boron Trifluoride (BF3), Boron Trichloride (BCl3), Titanium tetrachloride (TiCl4), Antimony Pentafluoride (SbF5), metal triflates for instance Copper (II) triflate, or combination thereof.

7. The improved process as claimed in claim 1, wherein the protecting group is selected from the group comprising tosyl chloride, Benzyl chloride, mesyl chloride (Methanesulfonyl Chloride), or combination thereof

8. The improved process as claimed in claim 1, wherein the base is selected from the group comprising of diisopropylamine, diisopropylethylamine, triethylamine (Et3N), dimethylamine, trimethyl amine, pyridine, N-methylmorpholine, 3-picoline, 2-picoline, 4-picoline, sodium bicarbonate, potassium carbonate, calcium hydroxide or combination thereof.

9. The improved process as claimed in claim 1, wherein the dehalogenating agent is selected from the group comprising of Zinc, Iron (Fe), hydrogen gas, Tin (II) chloride, NaH2PO2, sodium borohydride, sodium amalgam (Na/Hg), or combination thereof.

10. The improved process as claimed in claim 1, wherein the reducing agent is selected from the group comprising of sodium formate, hydrogen, oxalic acid, ascorbic acid, phosphite or combination thereof.

11. The improved process as claimed in claim 1, wherein the catalyst is selected from Pd/C or Raney Nickel, Pt/C, PtO2/Cetc, Na2WO4.2H2O, (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl or (2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl (TEMPO), Sodium tungstate, dihydrate, Cobalt(II) acetate, Co-napthenate, palladium (II) acetate, triphenyl phosphine, or combination thereof.

12. The improved process as claimed in claim 1, wherein the oxidizing agent is selected from the group comprising of hydrogen peroxide, urea-hydrogen peroxide complex, meta-chloroperbenzoic acid (m-CPBA), tert-butylhydroperoxide, potassium permanganate, potassium dichromate, chlorine, sodium dichromate, chromium trioxide, nitric acid, perchloric acid, osmium tetraoxide, iodine, fluorine or combination thereof.

13. The improved process as claimed in claim 1, wherein the compound (6) is converted to acyl chloride using reagent like sulfonyl chloride, sulfuryl chloride, thionyl chloride, oxalyl chloride, phosphorous oxychloride, phosphorous pentachloride, phosphorous trichloride and alike, or combination thereof.

14. The improved process as claimed in claim 1, wherein the reaction is carried at a temperature of range from 0? to 200?.

15. The improved process as claimed in claim 1, wherein the reaction is carried out for a period of about 1 hour to about 24 hours and at a pressure of from an atmospheric pressure to 50 bar.

16. An agrochemical composition, wherein the composition comprises at least a bio-active effective amount of Tembotrione of formula (I) as obtained by the process claimed in claims 1-14.

17. The agrochemical composition as claimed in claim 16, wherein the composition further comprises one or more agrochemically acceptable excipients.

18. A process for preparing the agrochemical composition comprising Tembotrione of formula (I) as claimed in claims 16-17.