DESC:This is an application for a patent of addition to Indian Patent Application No. 1297/MUM/2011 filed on 25th April 2011, the entire contents of which are specifically incorporated herein by reference.
FIELD
The present disclosure relates to a process for preparing dicyanopropionic acid ester and derivatives thereof.
BACKGROUND
Dicyanopropionic acid ester (Dicyanopropionate) is used for the preparation of pesticides. Many processes/methods are known for the preparation of dicyanopropionate.
Indian Application No.129/MUM/2010 discloses a process for the preparation of ethyl-2, 3-dicyano-propionate, which involves reacting an alkali metal cyanide and para-formaldehyde in the presence of a solvent to obtain glycolonitrile and reacting the glycolonitrile in-situ with an alkali ethoxide and cyanoacetate to obtain ethyl-2, 3-dicyanopropionate.
However, the synthesis of cyanoalkylpropionate by the aforestated method has a disadvantage that the extraction and isolation of the intermediate formaldehyde cyanohydrin (glycolonitrile), which is highly water soluble, is difficult. Further, formaldehyde cyanohydrin gets decomposed aggressively due to its unstable nature and forms dimeric side-products.
In order to overcome the above mentioned drawback, Indian Patent Application No.1297/MUM/2011 suggests a simple and economic process for preparing 2, 3-dicyanopropionic acid ester. Indian Patent Application No.1297/MUM/2011 discloses a method for synthesis of 2, 3-dicyanopropionic acid ester by reacting alkali metal cyanide with2-cyano-2 propenoic acid ester, resulting in better yield.
The present disclosure particularly focuses on providing a process of preparation for dicyanopropionic acid methyl ester from various starting compounds like methyl 2-cyano acrylate and polymers thereof and ethyl 2-cyano acrylate and polymers thereof.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows.
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide a process for preparing dicyanopropionic acid ester.
Another object of the present disclosure is to provide a process for preparing dicyanopropionic acid ester with high yield.
Still another object of the present disclosure is to provide a process for preparing dicyanopropionic acid methyl ester which is simple and economic
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

SUMMARY
The present disclosure relates to a process for preparing dicyanopropionic acid ester of formula (I) from 2-cyano 2-propionic acid ester of formula (II) and/ or polymer of 2-cyano 2-propionic acid ester of formula (III)

wherein, R is selected from the group consisting of C1-C20 straight or branched chain alkyl substituents, substituted or unsubstituted aromatic substituents and aliphatic substituents; and R1 and R2 are independently selected from the group consisting of hydrogen, C1-C20 straight or branched chain alkyl substituents, substituted or unsubstituted aromatic substituents and aliphatic substituents, and R3 is hydrogen.
In the process of the present disclosure, in the first step, at least one alkali metal cyanide and at least one fluid medium is stirred at a temperature in the range of 10 oC to 35 oC for a time period ranging from 1 hour to 3 hours to obtain a slurry. In the second step, the slurry obtained in the first step is treated with2-cyano-2-propenoic acid ester and/ or polymer of 2-cyano-2-propenoic acid ester, at a temperature in the range from 10 oC to 30 oC for a time period ranging from 2 hours to 6 hours to obtain a first reaction mixture comprising alkali salts of dicyanopropionic acid ester of formula (I). 2-cyano-2-propenoic acid ester of formula (II) and/or polymer of 2-cyano-2-propenoic acid ester of formula (III) may optionally stabilize by using at least one stabilizing agent prior to treating it with the slurry
The so obtained first reaction mixture is allowed to cool to a temperature ranging from 4 oC to 15oC and neutralized by using at least one neutralizing agent to obtain a second reaction mixture comprising dicyanopropionic acid ester of formula (I). The fluid medium used in the process of the present disclosure is distilled off from the second reaction mixture or carried forward for further step.
In the so obtained second reaction mixture, a medium containing at least one organic fluid and water is added to obtain a biphasic system comprising an organic phase and an aqueous phase. The organic phase contains dicyanopropionic acid ester. The organic phase is extracted from the biphasic system and is concentrated under vacuum to obtain crude dicyanopropionic acid ester of formula (I).
The crude dicyanopropionic acid ester of formula (I) is distilled under vacuum at a pressure in the range of 735-740 mm of Hg at a temperature in the range of 140 oC to 160 oC to obtain pure dicyanopropionic acid ester of formula (I).
DETAILED DESCRIPTION
The disclosure will now be described with reference to the accompanying embodiments which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.
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 following description 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 has 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.
Methyl 2-Cyano acrylate (2-cyano-2-propenoic acid methyl ester) is used in adhesives for manufacturing plastics, electronics, scientific instruments, jewelry, sports equipment, cable joining, manicuring, dentistry, mortuaries, and fingerprint development. Methyl 2-cyano acrylate (monomer) reacts with atmospheric moisture to form a polymer. However, poly(methyl 2-cyanoacrylate) is not reported for any commercial use. Further, poly(methyl 2-cyanoacrylate) can be converted into the monomer (Methyl 2-cyano acrylate) by heating it to a high temperature which is a very tedious and costly process.
Therefore, the inventors of the present disclosure utilized the polymers of (Methyl 2-cyano acrylate)and envisaged a process for the preparation of 2,3-dicyanopropionic acid ester with 90-94% yield from various starting compounds like (methyl 2-cyanoacrylate), poly(methyl 2-cyano acrylate), (ethyl-2-cyanoacrylate), poly(ethyl 2-cyano acrylate), 2-cyano acrylate and derivatives thereof. The preparation of 2,3-dicyanopropionic acid methyl ester from (methyl 2-cyanoacrylate), poly(methyl 2-cyano acrylate) and the like, can replace the use of existing 2,3-dicyanopropionate ethyl ester as aminopyrazole intermediate of Fipronil process.
In accordance with the present disclosure there is provided a process for preparing dicyanopropionic acid ester of formula (I).

wherein, R is selected from the group consisting of C1-C20 straight or branched chain alkyl substituents, substituted or unsubstituted aromatic substituents and aliphatic substituents; and R1 and R2 are independently selected from the group consisting of hydrogen, C1-C20 straight or branched chain alkyl substituents, substituted or unsubstituted aromatic substituents and aliphatic substituents, and R3 is hydrogen.
The process of the present disclosure is described in detail, herein below:
In step a) at least one alkali metal cyanide and at least one fluid medium is stirred at a temperature in the range of 10 oC to 35 oC for a time period ranging from 1 hour to 3 hours to obtain slurry.
The alkali metal cyanide used in the process of the present disclosure includes, but is not limited to, sodium cyanide, potassium cyanide, and lithium cyanide. Typically, alkali metal cyanide is sodium cyanide.
The fluid medium can be at least one selected from the group consisting of C1-C14 aliphatic alcohols, aromatic alcohols, acetonitrile, acetone, benzene, toluene dimethylsulfoxide(DMSO), sulfolane, dimethylformamide(DMF), ethylenedichloride(EDC), methylenedichloride, N-methylpyrrolidone, monoglyme, diglyme, methyl cello solve, ethyl cellosolve, butyl cellosolve and N,N-dimethylimidazolidone and combinations thereof. In one embodiment the fluid medium is methanol. The use of methanol in the process is economical as moisture can be easily removed from methanol and it can be easily recovered.
In step b) of the process of the present disclosure, the slurry obtained in step a) is treated with 2-cyano-2-propenoic acid ester and/or polymer of 2-cyano-2-propenoic acid ester under stirring at a temperature ranging from 10 oC to 30 oC for a time period ranging from 2 hours to 6 hours to obtain a first reaction mixture.
The 2-cyano-2-propenoic acid ester of formula (II)/ poly (methyl 2-cycano acrylate) of formula III used for the preparation of 2,3-dicyanopropionic acid ester may be used as such or it may be first stabilized using a stabilizing agent.
The 2-cyano-2-propenoic acid ester of formula (II) and its polymer of 2-cyano-2-propenoic acid ester of formula (III) is represented below:

wherein, R is selected from the group consisting of C1-C20 straight or branched chain alkyl substituents, substituted or unsubstituted aromatic substituents and aliphatic substituents; and R1 and R2 are independently selected from the group consisting of hydrogen, C1-C20 straight or branched chain alkyl substituents, substituted or unsubstituted aromatic substituents and aliphatic substituents.
The 2-cyano-2-propenoic acid ester of formula (II) includes, but is not limited to 2-cyano-2-propenoic acid methyl ester, 2-cyano-2-propenoic acid ethyl ester, 2-cyano-2-propenoic acid isopropyl ester, and 2-cyano-2-propenoic acid propyl ester. Formula (III) of the present disclosure includes, but is not limited to Poly (methyl 2-cyano acrylate) Poly (ethyl 2-cyano acrylate), Poly (propyl 2-cyano acrylate), and Poly (isopropyl 2-cyano acrylate).
In the process of the present disclosure, the proportion of the fluid medium is maintained between 300 ml to 1000 ml per mole of 2-cyano-2-propenoic acid ester of formula (II) and poly (2-cyano-2-propenoic acid ester) of formula (III). In an embodiment of the present disclosure, the proportion of the fluid media ranges between 300 ml and 700 ml per mole of 2-cyano-2-propenoic acid ester of formula (II) and poly (2-cyano-2-propenoic acid ester) of formula (III).
The stabilizing agent includes but is not limited to methanesulfonic acid, methanesulfonic anhydride, trifluoromethane sulfonic acid, trifluoromethane sulfonic anhydride, trichloromethane sulfonic acid, trichloromethane sulfonic anhydride, tribromomethane sulfonic acid, tribromomethane sulfonic anhydride, substituted or unsubstituted aromatic sulfonic acids, substituted or unsubstituted aromatic sulfonic anhydrides, hydroquinone, H2SO4, alkyl substituted hydroquinone, phosphorous pentoxide and C1-C14 aliphatic carboxylic acids. In an exemplary embodiment, stabilizing agent is methanesulfonic acid for the stabilization of 2-cyano-2-propenoic acid ester of formula (II)/ poly (methyl 2cycano acrylate) of formula III.
The amount of stabilizing agent used may be about 0.1 to 15% of the mass of 2-cyano-2-propenoic acid ester. Preferably, the amount of stabilizing agent used is about 1.0 to 10% of the mass of 2-cyano-2-propenoic acid ester. The stabilization is carried out to avoid sudden polymerization of the 2-cyano-2-propenoic acid ester during the reaction.
In an exemplary embodiment, a solution of 2-cyano-2-propenoic acid ester of formula (II) is injected into the slurry. The injection is carried out at a temperature ranging from 10 °C to 30 °C for 2 hours to 6 hours to obtain the first reaction mixture comprising alkaline salt of 2,3-dicyanopropionic acid ester of formula (I).
In step c) the so obtained first reaction mixture is cooled to a temperature in the range of 4 oC to 15°C and then neutralized to pH in the range of 3-4, by using at least one neutralizing agent to obtain a second reaction mixture comprising 2,3-dicyanopropionic acid ester of formula (I).
The neutralizing agent used in the process of the present disclosure includes, but is not limited to, hydrogen chloride, C1-C14 aliphatic acids and aromatic acids, H2SO4, phosphoric acid, SO2, aqueous HCl, dry HCl and acetic acid. In an embodiment, neutralizing agent of the present disclosure can be dry HCl gas, aqueous HCl and dry SO2 gas.
The fluid medium used in step (a) of the process of the present disclosure may be recovered by distilling it from the second reaction mixture or it will be carried forward to further step. The distilled/recovered medium can be reused further.
In step d) of the process of the present disclosure, a medium containing at least one organic fluid and water is added to the second reaction mixture to obtain a biphasic system comprising an organic phase and an aqueous phase. The organic phase may comprises dicyanopropionic acid ester and the aqueous phase may comprises other water soluble impurities.
The organic fluid can be at least one selected from the group consisting of methylene dichloride (dichloromethane), ethylene dichloride (dichloroethane), toluene and the like. Typically, the organic fluid is dichloromethane. The ratio of the amount of organic phase and water can be in the range of 50:50 to 60:40.
In step e), the organic phase is extracted from the biphasic system. The aqueous phase is further washed with an organic phase for 2-3 times and said organic phase is concentrated to obtain crude dicyanopropionic acid ester of formula (I).
In step f), the crude dicyanopropionic acid ester of formula (I) is distilled under vacuum at a pressure in the range of 735-740 mm of Hg at a temperature in the range of 140 oC to 160 oC to obtain pure dicyanopropionic acid ester of formula (I).
In an exemplary embodiment, 2,3-dicyanopropionic acid ester of formula (I) is 2,3-dicyanopropionic acid methyl ester.
The 2,3-dicyanopropionic acid ester of formula (I) obtained by the process of the present disclosure can be used for the preparation of Fipronil and hence the 2,3-dicyanopropionic acid methyl ester can be replaced by 2,3-dicyanopropionic acid ethyl ester.
The present disclosure is further illustrated herein below with the help of the following experiments. The experiments 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 embodiments herein. These laboratory scale experiments can be scaled up to an industrial/commercial scale.
EXPERIMENTAL DETAILS
Experiment 1: Process of preparation of 2,3-dicyanopropionic acid methyl ester in accordance with the present disclosure
0.6 liter of methanol (Moisture content= <0.1%) and 51.46 gm of sodium cyanide (1.05 mole) were charged in a glass reactor equipped with central vertical stirrer followed by stirring at 25°C till slurry obtained. Separately, 111 gm of 2-cyano-2-propenoic acid methyl ester (1 mole) was stabilized with methane sulfonic acid (3% W/W). Stabilized 2-cyano-2-propenoic acid methyl ester was added into slurry of sodium cyanide and methanol over 2 hours at 15- 22 °C. The reaction mixture was stirred for 3 hours at 25°C to obtain a clear solution of reaction mixture containing sodium salt of 2,3-dicyanopropionic acid methyl ester. The obtained clear solution was cooled to a temperature ranging from 5-10°C and neutralized by bubbling dry hydrogen chloride gas. The neutralized reaction mixture of 2,3 dicyanopropionic acid methyl ester was subjected to vacuum distillation to distill methanol. The residual mass obtained after methanol recovery, 300 ml of methylene dichloride and 300 ml of water is added to extract the product in methylene dichloride solvent. The organic layer (methylene dichloride) was washed with water and then concentrated to obtain crude 2,3-dicyanopropionic acid methyl ester in 94% yield (on purity basis).
Crude 2,3-dicyanopropenoic acid methyl ester was distilled under vacuum at a pressure 735-740 mm of Hg and at a temperature 145-155°C yields 88% (on purity basis).
Experiment 2-10: Process of preparation of 2,3-dicyanopropionic acid ester in accordance with the present disclosure
Similar experiments, as described in experiment 1, were carried out (expt 2-10) by varying the 2-cyano-2-propenoic acid ester, fluid medium, time period and other reaction conditions. The results obtained from the process of the present disclosure for the examples 1-10 are summarized in table 1.
Table 1:
Expt no Dicyanopropenoic acid ester Fluid medium Yield crude Distilled Yield
1 2-cyano-2-propenoic acid methyl ester Methanol 94% of crude 2,3 dicyanopropionic acid methyl ester 88% of pure 2,3 dicyanopropionicacid methyl ester
2 Solid polymer of 2-cyano-2- propenoic acid methyl ester Methanol 89% of crude 2,3 dicyanopropionicacid methyl ester 87% of pure 2,3 dicyanopropionic acid methyl ester
3 2-cyano2-propenoic acid ethyl ester Methanol 90.0 % of crude 2,3 dicyanopropionic acid methyl ester &
6% 2,3 -dicyanopropionic acid ethyl ester 90.0 %
4 Solid polymer of 2-cyano-2-propenoic acid ethyl ester Methanol 95.0 % crude mixture 87% of 2,3 dicyanopropionic acid methyl ester and
3% of 2,3 - dicyanopropionicacid ethyl ester
5 Solid polymer of 2-cyano-2-propenoic acid methyl ester Acetonitrile 87% of crude 2,3 dicyanopropionic acid methyl ester 87% of pure 2,3 dicyanopropionic acid methyl ester
6 Solid polymer of 2-cyano-2- propenoic acid methyl ester monoglyme 76% of crude 2,3 dicyanopropionic acid methyl ester 73% of pure 2,3 dicyanopropionic acid methyl ester
7 Solid polymer of 2-cyano-2- propenoic acid ethyl ester Methanol + dichloroethane 95.0 % crude yield having dicyanopropionic acid methyl ester and
5% of 2,3 -dicyano propionic acid ethyl ester
90.0 %
8 Solid polymer of 2-cyano-2- propenoic acid ethyl ester Methanol 93.0 % crude yield having dicyanopropionic acid methyl ester and
5% of 2,3 -dicyano propionic acid ethyl ester
90.0 %
9 2-cyano-2- propenoic acid ethyl ester Methanol 82% of crude 2,3 dicyanopropionicacid methyl ester 80.0 %
10 2-cyano-2- propenoic acid methyl ester Methanol+ dichloroethane 85% of crude 2,3 dicyanopropionicacid methyl ester 83.0 %

Experiment 11: Process of preparation of 2,3-dicyanopropionic acid ester using stabilized in accordance with the present disclosure-
200 ml, 1,2-dichloro ethane, 51.46 gm of sodium cyanide (1.05 mole) and 50 ml of methanol at 25 oC was charged in a glass reaction set up equipped with central vertical stirrer to obtain a mixture. 111 gm of 2-cyano-2-propeonic acid methyl ester (1.0mole) was stabilized with methane sulfonic acid (2% W/W) over 1 hour at 25°C. Stabilized 2-cyano-2-propeonic acid methyl ester was added to the mixture. The mixture was then stirred for 10 hours at 25°C to 30°C to obtain reaction mixture containing sodium salt of 2,3-dicyano propionic acid methyl ester. The reaction mixture was cooled to 5-10 oC and neutralized with 100 ml of 10 N HCl to pH 3.0-4.0 to obtain reaction mass. To this mass, 200 ml of a water and 200ml of dichloroethane was added to obtain biphasic system. Organic phase (dichloroethane extract) was separated. The aqueous phase (water) was again extracted with 100 ml of 1,2-dichloro ethane. The both organic phases (dichloroethane extract) mixed together and then concentrated to obtain crude 2,3-dicyano propionic acid methyl ester in 96 % yield. The crude 2,3-dicyano propionic acid methyl ester was distilled under vacuum of 735-740 mm of Hg at temperature 145 °C to 155 °C to obtain distilled yield of 94%.
Example-12: Process of preparation of 2,3-dicyanopropionic acid ester using stabilized in accordance with the present disclosure-
200 ml 1,2-dichloroethane, 50 ml methanol & 111 gm (1.0 mole) of pre stabilized 2-cyano-2-propeonic acid methyl ester was charged in a glass reaction set up equipped with central vertical stirrer. To this mixture, 51.46 gm of sodium cyanide (1.05 mole) was added over 2 hours at 15-25 oC to obtain mixture. The mixture was stirred for 10 hours at 25 °C to 30 °C to obtain reaction mixture containing sodium salt of 2,3-dicyano propionic acid methyl ester. The reaction mixture was cooled to 5-10 oC and neutralized with 100 ml of 10 N HCl to pH 3.0-4.0 pH to obtain reaction mass. To this mass, 200 ml water and 200 ml of organic phase (1,2-dichloro ethane) was added to obtain biphasic system. The organic phase (1,2-dichloro ethane) was separated and the aqueous phase was again extracted with 100 ml of 1,2-dichloro ethane and organic phase (1,2-dichloro ethane) was separated. The separated organic phases were mixed together and concentrated to obtain crude 2,3-dicyano propionic acid methyl ester in 95 % yield. The crude 2,3-dicyano propionic acid methyl ester was distilled under vacuum of 735-740 mm of Hg at temperature 145-155°C to obtain 2,3-dicyano propionic acid methyl ester with a yield of 93%.

Example-13: Process of preparation of 2,3-dicyanopropionic acid ester using stabilized in accordance with the present disclosure-
200 ml 1,2-dichloro ethane, 51.46 gm of sodium cyanide (1.05 mole) and 50 ml of methanol was charged in a glass reaction set up equipped with central vertical stirrer at a temperature of 15-25 oC. 111 gm of 2-cyano-2-propeonic acid methyl ester (1 mole) was stabilized with methane sulfonic acid (2% W/W) was over 1 hour at 15°C to 25°C. Stabilized 2-cyano-2-propenoic acid methyl ester was added into the mixture and the mixture was stirred for 10 hours at 25°C to 30°C to obtain reaction mixture containing sodium salt of 2,3-dicyano propionic acid methyl ester. The reaction mixture was cooled to 5-10 oC, 300 ml 1,2-dichloro ethane was added followed by neutralization. The neutralization was carried out by using 68 gms of dry SO2 gas to obtain the reaction mass having pH 3.0-4.0. To this mass, 500 ml of a mixture of water was added and organic phase (1,2-dichloro ethane) was added to obtain biphasic system. The organic phases (1,2-dichloro ethane) was separated. The aqueous phase was washed again with 100ml of 1,2-dichloro ethane and organic phase was separated. The separated organic phases were mixed together and concentrated to obtain crude 2,3-dicyano propionic acid methyl ester in 97 % yield. The crude 2,3-dicyano propionic acid methyl ester was distilled under vacuum of 735-740 mm of Hg at temperature 145-155 °C to obtain 2,3-dicyano propionic acid methyl ester having distilled yield of 94%.
The results obtained from experiments 11-13 of the process of the present disclosure by different variations are summarized in table 2.

Table 2:
Expt no Dicyanopropenoic acid ester Fluid medium Neutralizing agent Yield crude Distilled Yield
11 Stabilized 2-cyano- 2-propenoic acid methyl ester Methanol & 1,2-dichloroethane 10N HCl
96.0% 94.0%
12 Stabilized 2-cyano-2-propenoic acid methyl ester Methanol & 1,2-dichloroethane 10N HCl 95.0% 93.0%
13 Stabilized 2-cyano-2-propenoic acid methyl ester Methanol & 1,2-dichloroethane SO2 97.0 % 94.0%

Experiments 14-17 were carried out for preparing Fipronil i.e.5-amino-1-[2,6-dichloro-4-(trifluoromethyl) phenyl]-1H- pyrazole-3-carbonitrile, by using 2,3 dicyanopropionic acid methyl ester as an intermediate. The obtained product has better yield, which is calculated on purity base.
Experiment 14: Preparation of 5-amino-1- [2,6-dichloro-4- (trifluoro methyl) phenyl]-1H- pyrazole-3-carbonitrile using 2,3 dicyanopropionic acid methyl ester as an intermediate:
In one liter glass reactor equipped with central vertical stirrer was charged with 534.0 gm of 25%w/w nitrosyl sulfate solution and was cooled to 15 °C to 20 °C. A solution of 2,6-dichloro-4- (trifluoro) methyl aniline was separately prepared by dissolving 230 gm of 2,6-dichloro-4-(trifluoro)methyl aniline (1 mole) in 200 ml of 1,2-dichloro ethane. The solution of 2,6-dichloro-4-(trifluoro)methyl aniline was added into the nitrosyl sulfate solution for over 1 hour at 15 °C to 20°C. The obtained reaction mixture containing diazo mass was stirred for 3 hours at 15 oC to 20 °C. These obtained reaction mixture was added into 1200 gm of chilled ice water by controlling temperature below 20 °C. The diluted diazo mass was cooled to 5 °C and added 144.4 gm of 2,3-dicyano propionic acid ethyl ester (0.95 mole) over 30 minutes at a temperature ranging from 5 °C to 10 °C. The reaction mixture was stirred for 10 hours at 5 °C to10 °C to get a coupling product. From the obtained reaction mixture, the organic layer and aqueous layer were separated. The aqueous layer was again extracted with 100 ml of 1,2-dichloroethane. The organic layer containing the coupling product was added into 500 ml 8N ammonia solution (4 moles) at a temperature ranging from 5 °C to 10 °C and the reaction mixture was stirred for 4 hours at a temperature ranging from 5 °C to 10 °C. After stirring the reaction mixture was heated to 40-42 °C and equilibrated for 1 hour. Further, the organic layer containing product and the aqueous layer was separated. An organic layer containing product was washed with water and concentrated to obtain crude 5-amino-1-[2,6-dichloro-4-(trifluoro methyl) phenyl]-1H- pyrazole-3-carbonitrile in 86% yield (on purity basis).
Experiments 15 to 17: Preparation of 5-amino-1-[2,6-dichloro-4-(trifluoro methyl) phenyl]-1H- pyrazole-3-carbonitrile using 2,3 dicyanopropionic acid ester as an intermediate:
Similar experiments, as described in experiment 14, were carried out (expt 15-17) by varying the 2,3-dicyanopropenoic acid ester, and by varying the reaction conditions. The results obtained from experiments 14-17 of the process of the present disclosure by different variations are summarized in table 3.
Table 3:
Expt no Dicyanopropionic acid ester Yield of Crude 5-amino-1-[2,6-dichloro-4-(trifluoro methyl) phenyl]-1H- pyrazole-3-carbonitrile
14 2,3-dicyanopropionic acid ethyl ester 86%
15 2,3-dicyanopropionic acid methyl ester 88%
16 Mixture of 90% 2,3-dicyanopropionic acid ethyl ester+ 10% 2,3-dicyanopropionic acid methyl ester 84%
17 Mixture of 10% 2,3-dicyanopropionic acid ethyl ester + 90% 2,3-dicyanopropionic acid methyl ester 87%

From the above experimental data, it is observed that conversion of 2,3-dicyanopropionic acid methyl ester to Aminopyrazole i.e.5-amino-1-[2,6-dichloro-4-(trifluoro methyl) phenyl]-1H- pyrazole-3-carbonitrile is better than using 2,3-dicyano2- propionic acid ethyl ester to Aminopyrazole. Therefore 2,3-dicyanopropionic acid ethyl ester can be replaced by 2,3-dicyanopropionic acid methyl ester as an intermediate for preparing Aminopyrazole i.e.5-amino-1-[2,6-dichloro-4-(trifluoro methyl) phenyl]-1H- pyrazole-3-carbonitrile.
TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The present disclosure described herein above has several technical advantages including but not limited to the realization of:
? process provides 85-95% of yield;
? the 2,3-dicyanopropionate ester can be used as an intermediate in the process for preparing Fipronil; and
? simple and cost effective process.

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 disclosure 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 disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, 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 embodiment as well as other 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. ,CLAIMS:1. A process for preparing dicyanopropionic acid ester of formula (I) from 2-cyano-2-propenoic acid ester of formula (II) and/ or polymer of 2-cyano-2-propenoic acid ester of formula (III),

wherein, R is selected from the group consisting of C1-C20 straight or branched chain alkyl substituents, substituted or unsubstituted aromatic substituents and aliphatic substituents; and R1 and R2 are independently selected from the group consisting of hydrogen, C1-C20 straight or branched chain alkyl substituents, substituted or unsubstituted aromatic substituents and aliphatic substituents, and R3 is hydrogen,
said process comprising;
a) stirring at least one alkali metal cyanide in at least one fluid medium at a temperature in the range of 10 oC to 35 oC for a time period ranging from 1 hour to 3 hours to obtain a slurry;
b) treating said slurry with 2-cyano-2-propenoic acid ester of formula II and/ or polymer of 2-cyano-2-propenoic acid ester of formula III, at a temperature ranging from 10 oC to 30 oC for a time period ranging from 2 hours to 6 hours to obtain a first reaction mixture comprising alkali salts of dicyanopropionic acid ester of formula (I);
c) cooling said first reaction mixture to a temperature ranging from 5 oC to 15 oC and neutralizing it by at least one neutralizing agent to obtain a second reaction mixture comprising dicyanopropionic acid ester of formula (I);
d) adding a medium containing at least one organic fluid and water into said second reaction mixture to obtain a biphasic system comprising an organic phase containing dicyanopropionic acid ester and an aqueous phase;
e) extracting said organic phase from said biphasic system and concentrating said organic phase to obtain crude dicyanopropionic acid ester of formula (I); and
f) distilling said crude dicyanopropionic acid ester of formula (I) under vacuum at a pressure in the range of 735-740 mm of Hg at a temperature in the range of 140 oC to 160 oC to obtain dicyanopropionic acid ester of formula (I) having at least 95% purity.

2. The process as claimed in claim 1, wherein said 2-cyano-2-propenoic acid ester and/ or polymer of 2-cyano-2-propenoic acid ester is optionally stabilized by using at least one stabilizing agent prior to its treatment with said slurry in step (b).

3. The process as claimed in claim 2, wherein said stabilizing agent is at least one selected from the group consisting of methane sulfonic acid, H2SO4 and combinations thereof.

4. The process as claimed in claim 1, wherein said fluid medium is at least one selected from the group consisting of methanol, methylene dichloride, 1,2-dichloroethane, acetonitrile, monoglyme and mixtures thereof.

5. The process as claimed in claim 1, wherein said alkali metal cyanide salt is sodium cyanide.

6. The process as claimed in claim 1, wherein said neutralizing agent is at least one selected from the group consisting of dry HCl gas, aqueous HCl and dry SO2 gas.

7. The process as claimed in claim 1, wherein step c) further comprises the step of recovering said fluid medium from said second reaction mixture.

8. The process as claimed in claim 1, wherein said organic fluid is at least one selected from the group consisting of dichloromethane, dichloroethane, and toluene.