FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2006
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)
SYNTHESIS OF IMAZETHAPYR
GHARDA CHEMICALS LTD.
an Indian Company
of B-27/29, MIDC, Dombivli (E) Thane-421203, Maharashtra, India
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF DISCLOSURE
The present disclosure relates to imidazolinone herbicides.
More particularly, the present disclosure relates to a process for preparing
imidazoline herbicide , preferably 2-[4,5-Dihydro-4-methyl-4-(l-methylethyl)-5-
oxo-lH-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid, also known as
Imazethapyr.
BACKGROUND
2-[4,5-Dihydro-4-methyl-4-(l-methylethyl)-5-oxo-lH-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid also known as Imazethapyr is a herbicide used to control a variety of broad-leaf weeds and grasses in numerous crops. Imazethapyr is an imidazole compound used as a selective herbicide. It is applied pre-plant, pre-emergence, at cracking, and post-emergence. The compound controls weeds by reducing the levels of three branched-chain aliphatic amino acids, isoleucine, leucine and valine, through the inhibition of aceto-hydroxyacid synthase, an enzyme common to the biosynthetic pathway for these amino acids. This inhibition causes a disruption in protein synthesis which, in turn, leads to an interference in DNA synthesis and cell growth. The compound is used to control grasses and broadleaved weeds including barnyardgrass, crabgrass, cocklebur, panicums, pigweeds, nightshade, mustard, smartweed, velvetleaf, jimsonweed, foxtails, seedling johnsongrass, lambsquarters, morningglory and others. Tolerant crops include soybeans, peanuts, dry and edible beans, peas, alfalfa and imidazolinone resistant/tolerant corn.

Various methods for the preparation of 2-[4,5-dihydro-4-methyl-4-(l-methylethyl)-5-oxo-lH-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid are known in the prior art. 2-[4,5-dihydro-4-methyl-4-( 1-methylethyl)-5-oxo- lH-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid is prepared by the reaction of 5-ethyl-2,3-diethyl pyridine dicarboxylate with 2-aminoamide-3-methylbutane in the presence of a suitable base.
Pest. Sci. 1990, 293 describes preparation of 2-[4,5-dihydro-4-methyl-4-(l-methylethyl)-5-oxo-lH-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid by the reaction of 5-ethyl-2,3-diethyl pyridine dicarboxylate with 2-aminoamide-3-methylbutane in the presence of two equivalents of Potassium tert-butoxide , a costly raw material.
US 4758667, discloses a process that employs alkali metal alcoholate from C1-4 alkanol as a base during the condensation of 5-ethyl-2,3-diethyl pyridine dicarboxylate and 2,3-dimethyl-2-amino butyramide during the preparation of 2-[4,5-dihydro-4-methyl-4-( 1 -methylethyl)-5-oxo- lH-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid. Yield reported is only 74 %.
Molecules 2004, Vol-9, pp 535- describes the use of sodium Hydride as a base during the synthesis of 2-[4,5-dihydro-4-methyl-4-(l-methylethyl)-5-oxo-lH-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid. Sodium hydride is inherently expensive and its use entails in the slow addition to the reaction substrate which is hazardous, such a process combined with the cost of sodium hydride is commercially not tenable.

Thus, the methods as disclosed in the literature employ an expensive and hazardous base for the preparation of the imidazolinone herbicide making the process non-feasible for a large scale production. Therefore, there is a need for an industrially feasible process for the preparation of the imidazolinone herbicide.
OBJECTS
It is an object of the present disclosure is to provide a feasible process for the preparation of imazethapyr.
Another object of the present disclosure to provide a process for the preparation of imazethapyr with an improved yield.
SUMMARY
In accordance with the present disclosure, there is provided a process for the preparing an imidazolidone compound 2-[4,5-dihydro-4-methyl-4-(l-methylethyl)-5-oxo- lH-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid of formula I,


said process comprising , condensing 5-ethyI-2,3-diethyl pyridine dicarboxylate and 2,3-dimethyl-2-amino butyramide in the presence of alkali alcoholate in a solvent at temperatures ranging between 20 °C to 120 °C.
Typically, the alkali alcoholate is selected from the group consisting of sodium tertiary amy late.
Typically, the solvent is selected form the group consisting of tetrahydrofuran, dioxane, acetonitrile, N,N-dimethylformamide ,dimethyl sulfoxide, benzene, toluene, chlorobenzene and xylene.
Typically, the process is carried out at a temperature in the range of 25 to 100°C.
Typically, the amount of 5-ethyl-2,3-diethyl pyridine dicarboxylate and 2,3-dimethyl-2-arnino butyramide is in the ratio 1:1.
DETAILED DESCRIPTION OF THE DISCLOSURE
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the

embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The description herein after, of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
In accordance with the present invention there is provided a process for the preparation of 2-[4,5-dihydro-4-methyl-4-(l-methylethyl)-5-oxo-lii7-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid of formula I. The process involves a step of condensing 5-ethyl-2,3-diethyl pyridine dicarboxylate and 2,3-dimethyl-2-amino butyramide in the presence of alkali alcoholate in a solvent at temperatures ranging between 20 °C to 120 °C to obtain a compound of formula I


The alkali alcoholate used in the used in the process of the present disclosure is typically selected from the group that includes but is not limited to sodium tert-amylate (sodium salt of 2-methyl-2-butanol) and potassium tert-amylate (potassium salt of 2-methyl-2-butanol).
The solvent is selected from the group of solvents such as tetrahydrofuran, dioxane, acetonitrile, N,N-dimethylformamide ,dimethyl sulfoxide, benzene, toluene, chlorobenzene and xylene.
Typically, the yield of the compound of Formula I in accordance with the process of the present invention is more than 90%.
Schematic representation of the process in accordance with the present disclosure is illustrated as follows:


The disclosure is further illustrated with the help of the following working examples which should not be construed to limit the disclosure.
Examples
Example 1:
100 ml of xylene, 27.3 g (0.1m) of 5-ethyl-pyridine-2,3-diethyl carboxylate and 13 g ( 0.1m) of 2-amino-2,3-dimethyl butyramide was taken in a flask under nitrogen atmosphere. A solution of 0.3 molar of sodium-tert-amylate in xylene at 30°C was slowly added over a period of 30 minutes to the above mixture under constant stirring and the temperature was raised up to 52°C. The reaction mixture was then further heated to 80°C and maintained for 4 hr at 80°C. The yield of 2-[4,5-dihydro-4-methyl-4-( 1 -methylethyl)-5-oxo- 177-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid was 90 mole% after work up.

Example 2:
100 ml of Toluene, 27.3 g (0.1m) of 5-ethyl-pyridine-2,3-diethyl carboxylate and 13 g ( 0.1m) of 2-amino-2,3-dimethyl butyramide was taken in a flask under nitrogen atmosphere. A solution of 0.25 molar of potassium-tert-amylate in Toluene at 30°Cwas slowly added over a period of 30 minutes to the above mixture under constant stirring and the temperature was raised up to 52°C. The reaction mixture was then further heated to 80°C and maintained for 4 hr at 80°C. The yield of 2-[4,5-dihydro-4-methyl-4-(l-methylethyl)-5-oxo-lH-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid was 85 mole% after work up.
Example 3:
50 ml of Toluene, 50ml of Chlorobenzene, 27.3 g (0.1m) of 5-ethyl-pyridine-2,3-diethyl carboxylate and 13 g (0.1m) of 2-amino-2,3-dimethyl butyramide was taken in a flask under nitrogen atmosphere. A solution of 0.25 m of potassium-tert-amylate in Toluene & Chlorobenzene at 30°C was slowly added over a period of 30 minutes to the above mixture under constant stirring and the temperature was raised up to 52°C. The reaction mixture was then further heated to 80°C and maintained for 4 hr at 80°C. The yield of 2-[4,5-dihydro-4-methyl-4-(l-methylethyl)-5-oxo-lH-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid was 92 mole% after work up.

Example 4:
50 ml of o-Xylene, 50ml of Chlorobenzene, 27.3 g (0.1m) of 5-ethyl-pyridine-2,3-diethyl carboxylate and 13 g (0.1m ) of 2-amino-2,3-dimethyl butyramide was taken in a flask under nitrogen atmosphere. A solution of 0.25 m of potassium-tert-amylate in o-Xylene & Chlorobenzene at 30°C was slowly added over a period of 30 minutes to the above mixture under constant stirring and the temperature was raised up to 52°C. The reaction mixture was then further heated to 80°C and maintained for 4 hr at 80°C. The yield of 2-[4,5-dihydro-4-methyl-4-(l-methylethyl)-5-oxo-lH-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid was 91 mole% after work up.
Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression "at least" or "at least one" suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the

field relevant to the invention as it existed anywhere before the priority date of this application.
While considerable emphasis has been placed herein on the specific embodiments of the preferred process, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

We Claim:
1. A process for the preparing an imidazolidone compound 2-[4,5-dihydro-4-methyl-4-( 1-methylethyl)-5-oxo-lH-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid of formula I,

said process comprising, condensing 5-ethyl-2,3-diethyl pyridine dicarboxylate and 2,3-dimethyl-2-amino butyramide in the presence of alkali alcoholate in a solvent at a temperature in the range of 20 °C to 120 °C.
2. The process as claimed in claim 1, wherein the alkali alcoholate is sodium tertiary amylate.
3. The process as claimed in claim 1, wherein the solvent is selected from the group consisting of tetrahydrofuran, dioxane, acetonitrile, N,N-dimethylformamide ,dimethyl sulfoxide, benzene, toluene, chlorobenzene and xylene.
4. The process as claimed in claim 1, wherein the process is carried out at a temperature in the range of 25°C to 100°C.

5. The process as claimed in claim 1, wherein the amount of 5-ethyl-2,3-diethyl pyridine dicarboxylate and 2,3-dimethyl-2-amino butyramide is in the ratio 1:1.