DESC:FIELD
The present disclosure relates to a process for preparation of Pyraclostrobin.
DEFINITION
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.
Partial reduction refers to the reduction of nitro functional group to hydroxylamine functional group.
Equilibrating refers to allowing a mixture or slurry to stand to attain equilibrium.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Pyraclostrobin (I) belongs to the class of strobilurin fungicide that displays broad fungicidal activity. Pyraclostrobin is used to curb diseases on a variety of plants such as wheat, rice, peanut, grape, vegetables, potato, banana, lemon, coffee, fruit, walnut, tea, tobacco, ornamental plants, lawn and other field crops. Pyraclostrobin (I) has the following structural formula:

Pyraclostrobin (CAS number : 175013-18-0)
IUPAC name: (methyl N-[2-[[1-(4-chlorophenyl)pyrazol-3-yl]oxymethyl]phenyl]-N-methoxycarbamate
Although several methods are known for the synthesis of pyraclostrobin, the large-scale production of pyraclostrobin is costly, tedious and requires highly toxic chemicals.
N-{2-[1-(4-chloro-phenyl)-1H-pyrazol-3-yl-oxymethyl]-phenyl}–hydroxylamine (PHABE) (III) is a key intermediate for synthesizing pyraclostrobin. The intermediate (III) is obtained by partial reduction of the corresponding nitro derivative, 1-(4-chlorophenyl)-3-[2-(nitrophenyl)-methoxy]-1H-pyrazole (PNBE) (II). Conventional methods for preparing PHABE (III) lack selectivity for partial reduction and result in the formation of some amount of completely reduced amino product. Moreover, the synthetic route of obtaining pyraclostrobin (I) from PNBE (II) often involves tedious isolation steps and employs reagents or catalysts that are expensive and toxic.
There is, therefore, felt a need for a process for preparing pyraclostrobin (I) that mitigates the drawbacks mentioned hereinabove.
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.
Another object of the present disclosure is to provide a process for preparation of pyraclostrobin (I).
Still another object of the present disclosure is to provide a process for partial reduction of PNBE (II) with high selectivity.
Still another object of the present disclosure is to provide a process for the preparation of pyraclostrobin (I) with comparatively high yields.
Yet another object of the present disclosure is to provide a process for the preparation of pyraclostrobin (I) that is simple, economical and eco-friendly.
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 provides a process for preparing pyraclostrobin (I). The process comprises a step of partially reducing 1-(4-Chlorophenyl)-3-[2-(nitrophenyl)-methoxy]-1H-pyrazole (II) using hydrazine hydrate with a metal catalyst and a phase transfer catalyst, in a first solvent at a temperature in the range of 12 °C to 18 °C, to obtain a first mixture comprising N-{2-[1-(4-chloro-phenyl)-1H-pyrazol-3-yl-oxymethyl]-phenyl}–hydroxylamine (PHABE) (III). The first mixture is filtered to obtain a first residue comprising the unreacted metal catalyst and a first filtrate containing the compound (III). Further, the compound (III) is methoxycarbonylated using a methoxycarbonylating agent and a first alkali in a second solvent at a temperature in the range of 10 °C to 15°C to obtain a second mixture comprising methyl N-hydroxy-N-2-[1-(4-Chloro-phenyl)-1H-pyrazol-3-yl-oxymethyl]-phenyl}-carbamate (PHABEC) (IV). The second mixture is filtered to obtain a second filtrate containing the compound (IV). The second solvent is separated from the second filtrate by distillation and a second residue comprising the compound (IV) is retained. Water is added to the second residue under stirring to form a slurry followed by equilibrating the slurry to precipitate the compound (IV). The precipitate is separated from the slurry to obtain a precipitate of compound (IV). The precipitate is dried and washed to obtain the compound (IV). The compound (IV) is methylated to obtain pyraclostrobin (I).
DETAILED DESCRIPTION
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details, are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
The broad fungicidal activity of pyraclostrobin (I) and its application to a wide variety of plants makes it a common choice as a fungicide. The conventional route for preparing pyraclostrobin (I) includes multiple steps that use expensive and toxic catalysts. Further, the selectivity for partial reduction of 1-(4-chlorophenyl)-3-[2-(nitrophenyl)-methoxy]-1H-pyrazole (PNBE) (II) is low and thus result in the formation of completely reduced amino product.
The present disclosure provides a process for synthesis of pyraclostrobin (I) that is simple, gives comparatively high yields and uses inexpensive catalysts and/or reagents having low toxicity. Further, the present disclosure provides a process for the partial reduction of PNBE (II) with high selectivity.
The present disclosure provides a process for preparation of pyraclostrobin (I), having the following structural formula.

The schematic representation of the process of the present disclosure is provided below.
Step 1: Partial reduction of PNBE (II) to obtain PHABE (III)

Step 2: Methoxycarbonylation of PHABE (III) to obtain PHABEC (IV)

Step 3: Methylation of PHABEC (IV) to obtain Pyraclostrobin (I)

The process for the preparation of pyraclostrobin (I) is described in detail.
In the first step, 1-(4-Chlorophenyl)-3-[2-(nitrophenyl)-methoxy]-1H-pyrazole (PNBE) (II) is partially reduced using hydrazine hydrate with a metal catalyst and a phase transfer catalyst, in a first solvent at a temperature in the range of 12 °C to 18 °C, to obtain a first mixture comprising N-{2-[1-(4-chloro-phenyl)-1H-pyrazol-3-yl-oxymethyl]-phenyl}–hydroxylamine (PHABE) (III).
The temperature range of 12 °C to 18 °C is important as below 12 °C, the rate of partial reduction is slow, whereas above 18 °C, the resulting hydroxylamine derivative gets further reduced to amines, which would be an impurity for the present reaction.
The first mixture is filtered to obtain a first residue comprising the unreacted metal catalyst and a first filtrate containing the compound (III).
The phase transfer catalyst is at least one selected from tetrabutylammonium bromide (TBAB) and tetrabutylammonium chloride (TEBACl). In an embodiment, the phase transfer catalyst is tetrabutylammonium bromide (TBAB).
The amount of the phase transfer catalyst is in the range of 0.3 mol% to 1 mol%. The amount of phase transfer catalyst less than 0.3 mol% reduces the rate of reaction, whereas use of catalyst more than 1 mol% would add to the cost. An amount upto 0.8 mol% is optimum for the partial reduction.
In an embodiment, the amount of the phase transfer catalyst is 0.5 mol%.
The phase transfer catalyst ensure better mixing between the various phases such as solvent phase, aqueous phase (aqueous solution of hydrazine hydrate) and solid phase (metal catalyst).
The first solvent is at least one selected from the group consisting of tetrahydrofuran, 2-propanol and methanol. In an embodiment, the first solvent is tetrahydrofuran.
The weight-volume ratio of the PNBE (II) to the first solvent is in the range of 1:6 to 1:8. In an embodiment, the weight-volume ratio of PNBE (II) to the first solvent is 1:7.
The first solvent ensures effective solubilization of the PNBE (II) during reaction. A weight-volume ratio of the PNBE (II) to the first solvent, lesser than 1:6 will lead to coating of the raw material (PNBE) on the metal catalyst due to less solvent which causes the active sites in the metal catalyst to be less available whereas a ratio higher than 1:8 would lead to wastage in the amount of the first solvent.
The metal catalyst is selected from the group consisting of raney nickel, palladium on carbon and platinum on carbon. In an exemplary embodiment, the metal catalyst is raney nickel.
The amount of the metal catalyst is in the range of 2 wt% to 3 wt% with respect to the PNBE (II). In an embodiment, the amount of the metal catalyst is 2.4 wt.% with respect to PNBE (II).
The metal catalyst provides a catalytic active surface for the in-situ generated hydrogen. The amount 2.4 wt.% is optimum for the effective partial reduction. The use of the metal catalyst less than 2 wt.% leads to lesser conversion of nitro group to hydroxylamine group, whereas use of the metal catalyst more than 3 wt.% leads to formation of more amino compound (impurity) due to complete reduction.
The hydrazine hydrate is used in the form of an aqueous solution having concentration in the range of 30 % to 40 %. In an embodiment, the concentration of the aqueous hydrazine hydrate is 32 %.
The concentration of less than 30% of the hydrazine hydrate leads to diluted system that result in lower conversion, and using hydrazine hydrate with concentration more than 40 %, leads to exothermic reaction, which is not preferred on a plant scale.
The molar ratio of the PNBE (II) to the hydrazine hydrate is in the range of 1:1 to 1:1.2.
The hydrazine hydrate is added slowly over a time period in the range of 1.5 to 2.5 hours. In an embodiment, the hydrazine hydrate is added over a period of 2 hours.
The hydrazine hydrate acts as a source of hydrogen and results in partial reduction of the nitro group in the PNBE (II) to hydroxylamine group as one mole of hydrazine hydrate gives 2 moles of hydrogen in presence of catalyst which helps in controlling the reduction at hydroxylamine stage thus yielding partially reduced hydroxylamine compound (PHABE) (III). The complete reduction to obtain amino group compound is thus avoided.
In an embodiment, the temperature during the first step of partial reduction is 15 °C.
The time for the completion of the partial reduction is in the range of 2 hours to 8 hours.
The time required for partial reduction of the PNBE (II) is monitored using High Pressure Liquid Chromatography (HPLC). In an embodiment, the reaction was stopped when the HPLC indicated consumption of more than 98% of the PNBE (II).
In an exemplary embodiment, the first solvent is cooled to a temperature in the range of 12 °C to 18 °C, followed by the addition of the PNBE (II), the metal catalyst and the phase transfer catalyst to the first solvent. The resultant mixture is stirred for time period in the range of 25 minutes to 35 minutes while adding the hydrazine hydrate slowly over a period of 1.5 hours to 2 hours. The product mixture so obtained is filtered to obtain a first residue comprising the unreacted metal catalyst and a first filtrate containing the PHABE (III). The first residue is sent for the recovery of the metal catalyst. The first filtrate is used directly in the next step.
In accordance with the present disclosure, the isolation of the PHABE (III) is not required. Thus, the cost and resources required for isolation of the PHABE (III) are saved.
In the second step, the first filtrate is methoxycarbonylated by using a methoxycarbonylating agent and a first alkali in a second solvent at a temperature in the range of 10 °C to 15°C to obtain a second mixture comprising methyl N-hydroxy-N-2-[1-(4-Chloro-phenyl)-1H-pyrazol-3-yl-oxymethyl]-phenyl}-carbamate (PHABEC) (IV).
The second mixture is filtered to obtain a second filtrate containing the compound (IV). The second solvent is separated from the second filtrate by distillation and a second residue comprising the compound (IV) is retained. Water is added to the second residue under stirring to form a slurry followed by equilibrating the slurry to precipitate the compound (IV). The precipitate is separated from the slurry to obtain a precipitate of compound (IV). The precipitate is dried and washed to obtain the compound (IV).
In an embodiment, the methoxycarbonylating agent is methyl chloroformate.
The first alkali is at least one selected from the group consisting of sodium bicarbonate, potassium bicarbonate, sodium carbonate and potassium carbonate. The first alkali is a carbonate or bicarbonate compound which is used to neutralize HCl liberated at the time of condensation during methoxycarbonylation reaction.
In one embodiment, the first alkali is sodium bicarbonate.
The molar ratio of the PHABE (III) to the first alkali is in the range of 1:1 to 1:2.5. The use of less than 1 mole of carbonate leads to corrosion of the reactor vessel due to the presence of in-situ generated hydrochloric acid which is not neutralized by carbonate, whereas use of more carbonate than the mentioned ratio leads to wastage.
In an embodiment, the molar ratio of the PHABE (III) to the first alkali is 1:1.5.
The molar ratio of the compound (III) to the methoxycarbonylating agent is in the range of 1:1 to 1:1.4. The use of less than 1 mole of the methoxycarbonylating agent leads to incomplete conversion whereas use of an amount higher than that mentioned leads to impurity formation.
In an embodiment, the molar ratio of the compound (III) to the methoxycarbonylating agent is 1:1.2.
The second solvent is at least one selected from the group consisting of chlorobenzene, o-dichlorobenzene and trichlorobenzene. In one embodiment, the second solvent is chlorobenzene.
The methoxycarbonylating agent is added slowly over a time period in the range of 1 to 5 hours. In one embodiment, the methoxycarbonylating agent is added over a time period of 1.5 hours.
In an exemplary embodiment, the first filtrate comprising the PHABE (III) is cooled under stirring to a temperature in the range of 10 °C to 15 °C, and first alkali is added to the cooled first filtrate followed by the addition of the methoxycarbonylating agent over a period of 1 hour to 2 hours. The mixture so obtained is stirred at a temperature in the range of 10 °C to 15 °C to obtain the second mixture. The second mixture is filtered to obtain the second filtrate containing the PHABEC (IV). The second solvent from the second filtrate is distilled out followed by addition and distillation of a high boiling solvent to obtain a residue. Water is added to the residue to obtain a mixture comprising precipitate of the compound (IV).
The time required for completion of the methoxycarbonylation step is monitored using High Pressure Liquid Chromatography (HPLC). In an embodiment, the reaction was stopped when the HPLC indicated consumption of more than 99% of the PHABE (III).
In the next step, the PHABEC (IV) is methylated to obtain pyraclostrobin (I).
The step of methylating the PHABEC (IV) is done by using a methylating agent selected from dimethylsulfate and methyl chloride, and an alkali selected from the group consisting of sodium hydroxide and potassium hydroxide, and a phase transfer catalyst at a temperature in the range of 20°C to 30°C.
The alkali used for methylation step is at least one selected from the group consisting of sodium hydroxide and potassium hydroxide. In one embodiment, the alkali is sodium hydroxide.
The concentration of the alkali used for methylation is in the range of 0.5N to 1.5N. In one embodiment, the concentration of the second alkali is 1N.
The molar ratio of the compound (IV) to the alkali is in the range of 1:1 to 1:1.5. In an embodiment, the molar ratio of the compound (IV) to the alkali is 1:1.1.
In one embodiment, the methylating agent is dimethylsulfate.
The molar ratio of the PHABEC (IV) to the methylating agent is in the range of 1:1 to 1:1.5. The use of less than 1 mole of the methylating agent leads to incomplete conversion whereas use of an amount higher than that mentioned leads to impurity formation.
In an embodiment, the molar ratio of the PHABEC (IV) to the methylating agent is 1:1.1.
The step of methylation is carried out in a solvent selected from the group consisting of toluene, xylene, chlorobenzene, o-dichlorobenzene, and trichlorobenzene. The solvent being water immiscible enables easy separation during extraction and also allows easy recovery by distillation due to its boiling point being higher than 110°C.
In an embodiment of the present disclosure, the solvent used in the methylation step is toluene.
The addition of alkali in methylation step is carried out over a time period in the range of 10 minutes to 30 minutes. In one embodiment, the slow addition of the alkali is carried out over 15 minutes.
In an embodiment, the temperature during methylation is 25 °C.
The phase transfer catalyst is at least one selected from the group consisting of tetrabutylammonium bromide (TBAB) and tetrabutylammonium chloride (TEBACl). In one embodiment, the phase transfer catalyst is tetrabutylammonium bromide (TBAB).
The amount of the phase transfer catalyst is in the range of 0.3 mol% to 5 mol%. In an embodiment, the amount of the phase transfer catalyst is 0.5 mol%.
In an exemplary embodiment, the PHABEC (IV) is mixed with toluene, followed by slow addition of sodium hydroxide under stirring for a time period of 15 minutes. To the mixture so obtained, dimethyl sulfate is slowly added under stirring followed by the addition of TBAB. The mixture so obtained is stirred to obtain a product mixture comprising the pyraclostrobin (I). The product mixture is extracted with a solvent. The organic layer comprising the pyraclostrobin (I) is collected, and the organic layer is further partitioned with water until water layer with a neutral pH was obtained. The organic layer, thus obtained, is concentrated to obtain pyraclostrobin (I).
The temperature during methylation is in the range of 20 °C to 30 °C.
The slow addition of the methylating agent is done over a time period in the range of 1 hour to 5 hours. In an embodiment, the slow addition of the methylating agent is done over a time period of 3 hours.
The time for completion of the methylation reaction of the PHABEC (IV) is monitored using High Pressure Liquid Chromatography (HPLC). The time for completion of the methylation reaction was determined by HPLC and the reaction was stopped when the HPLC indicated consumption of more than 99% of the PHABEC (IV).
In an embodiment, the pyraclostrobin (I) obtained after the methylation step is an oily mass. The oily mass is crystallized by using an alcohol selected from isopropyl alcohol and methanol to obtain solid form of the pyraclostrobin (I).
The present disclosure provides a simple process that gives comparatively high yields of pyraclostrobin (I). The process does not require the isolation of the PHABE (III) in the step of partial reduction of the PNBE (II), wherein the filtrate comprising the PHABE (III) is directly used in the step of methoxycarbonylation, thereby avoiding the need of tedious work-up, purification and use of additional solvent. Further, the process uses chemicals and fluid media which are inexpensive and less toxic. Hence, the process is economical and environment friendly.
The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
The present disclosure is further described in light of the following laboratory scale experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. These laboratory scale experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial/commercial scale.
Experimental Details
Experiment 1:
To a reactor, a mixture of 1-(4-chlorophenyl)-3-[2-(nitrophenyl)-methoxy]-1H-pyrazole (PNBE) (II) (330 gms, 1 mol) and tetrahydrofuran (2.4 litres) were charged, under stirring and cooled to 15°C. To the cooled mixture, raney nickel catalyst (8 gms) was added followed by the addition of tetrabutylammonium bromide (1.61 g) as a phase transfer (PTC) catalyst to obtain a slurry. The slurry so obtained was stirred for 30 minutes, followed by the slow addition of aqueous hydrazine hydrate solution (32% solution, 1.15 mole, 115 g) over 2 hours to obtain a resultant mixture. The resultant mixture so obtained was stirred at 15°C and the progress of the reaction was monitored by using HPLC. When HPLC indicated the consumption of 98.5 % PNBE (II) to be, the stirring was stopped to obtain first mixture comprising N-{2-[1-(4-Chloro-phenyl)-1H-pyrazol-3-yl-oxymethyl]-phenyl}–hydroxylamine (PHABE) (III). The first mixture was filtered to obtain a first residue comprising the unreacted raney nickel and a first filtrate containing the compound (III) was used for the next step.
Experiment 2:
The first filtrate from experiment 1 comprising PHABE (III) was charged into a reactor. The first filtrate was cooled to 12 °C under stirring followed by the addition of sodium bicarbonate NaHCO3 (1.5 mole) to obtain a thin slurry. To the slurry, methyl chloroformate (1.2 mole) was then slowly added over a period of 1.5 hrs maintaining the temperature at 12 °C under stirring to obtain a mixture. The mixture so obtained was stirred and the progress of the reaction was monitored by HPLC. When HPLC indicated the consumption of 99% PHABE (III), the stirring was stopped to obtain a second mixture comprising N-{2-[1-(4-chloro-phenyl)-1H-pyrazol-3-yl-oxymethyl]-phenyl}–hydroxylamine (PHABE) (III). The second mixture was subjected to filtration. The filtrate containing the compound (III)was distilled out to recover tetrahydrofuran (THF) followed by the addition of 700ml of chlorobenzene, and the mixture thus obtained was further distilled out till chlorobenzene started to distill out to obtain a second residue. Further, water (300ml) was added to the residue obtained after distillation and stirred which caused precipitation, and the precipitate so obtained was filtered, washed and dried to obtain methyl N-hydroxy-N-2-[1-(4-Chloro-phenyl)-1H-pyrazol-3-yl-oxymethyl]-phenyl}-carbamate (PHABEC) (IV) in 80% yield (300 g).

Experiment 3:
To a reactor, toluene (2.5 litres) was charged followed by addition of PHABEC (IV) (374 gms; 1mole) in lots/portions under stirring to get a resultant mixture in the form of a thick stirrable slurry. A solution of 1N NaOH solution (1.2 mole) was added under stirring over a time duration of 15 mins followed by addition of TBAB (1.61 g, 0.005 mole) to obtain a mixture. The mixture so obtained was stirred at room temperature for 1 hour, followed by addition of dimethyl sulphate (DMS; 1.1 mole) over 3 hrs under stirring to obtain a third reaction mixture which shows a transformation of thin slurry to an almost clear solution. The progress of the reaction was monitored by HPLC. When the reaction monitoring indicated the consumption of 98% PHABEC (IV), the stirring was stopped to obtain a resultant mixture which was subjected to separation by extraction. The organic and aqueous layers were separated and the aqueous layer was again extracted with toluene. The combined organic layer was washed with water till neutral pH was reached. The organic layer was concentrated under reduced pressure to obtain 378 g of oily mass comprising pyraclostrobin (I) with 98% purity by HPLC. The oily mass was crystallized from isopropyl alcohol to get 326 g of solid product pyraclostrobin (I) having 99% purity by HPLC.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for preparing pyraclostrobin, wherein the process:
- facilitates high selectivity towards partial reduction of PNBE (II);
- avoids isolation and purification of PHABE (III) after the step of partial reduction;
- results in comparatively high yield and purity of pyraclostrobin (I); and
- employs phase transfer catalyst which is inexpensive and less toxic.
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 foregoing description of the specific embodiments 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.
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:WE CLAIM:
1. A process for preparing pyraclostrobin (I), said process comprising the following steps:
(i) partially reducing 1-(4-Chlorophenyl)-3-[2-(nitrophenyl)-methoxy]-1H-pyrazole (PNBE) (II) using hydrazine hydrate with a metal catalyst and a phase transfer catalyst, in a first solvent at a temperature in the range of 12 °C to 18 °C, to obtain a first mixture comprising N-{2-[1-(4-chloro-phenyl)-1H-pyrazol-3-yl-oxymethyl]-phenyl}–hydroxylamine (PHABE) (III);
(ii) filtering said first mixture to obtain a first residue comprising the unreacted metal catalyst and a first filtrate containing the compound (III);
(iii) methoxycarbonylating said compound (III) by using a methoxycarbonylating agent and a first alkali in a second solvent at a temperature in the range of 10 °C to 15°C to obtain a second mixture comprising methyl N-hydroxy-N-2-[1-(4-Chloro-phenyl)-1H-pyrazol-3-yl-oxymethyl]-phenyl}-carbamate (PHABEC) (IV);
(iv) filtering said second mixture to obtain a second filtrate containing the compound (IV);
(v) separating the second solvent from said second filtrate by distillation and retaining a second residue comprising the compound (IV);
(vi) adding water to said second residue under stirring to form a slurry followed by equilibrating the slurry to precipitate the compound (IV);
(vii) separating the precipitate from said slurry by filtration to obtain precipitate of compound (IV);
(viii) washing and drying said precipitate to obtain the compound (IV); and
(ix) methylating the compound (IV) to obtain pyraclostrobin (I).

2. The process as claimed in claim 1, wherein the hydrazine hydrate used in the step (i) is in the form of an aqueous solution having concentration in the range of 30 % to 40 %, wherein the addition of hydrazine hydrate is done slowly over a time period in the range of 1.5 to 2.5 hours.
3. The process as claimed in claim 1, wherein the metal catalyst is selected from the group consisting of raney nickel, palladium on carbon and platinum on carbon, and wherein the amount of the metal catalyst is in the range of 2 wt% to 3 wt% with respect to the compound (II).
4. The process as claimed in claim 1, wherein the phase transfer catalyst in step (i) is at least one selected from tetrabutylammonium bromide (TBAB) and tetrabutylammonium chloride (TEBACl), and wherein the amount of the phase transfer catalyst is in the range of 0.3 mol% to 5 mol%.
5. The process as claimed in claim 1, wherein the first solvent in the step (i) is at least one selected from the group consisting of tetrahydrofuran, 2-propanol and methanol.
6. The process as claimed in claim 1, wherein the methoxycarbonylating agent in the step (iii) is methyl chloroformate.
7. The process as claimed in claim 1, wherein the molar ratio of the PHABE (III) to the first alkali in the step (iii) is in the range of 1:1 to 1:2.5.
8. The process as claimed in claim 1, wherein the molar ratio of the compound (III) to the methoxycarbonylating agent in the step (iii) is in the range of 1:1 to 1:1.4.
9. The process as claimed in claim 1, wherein the second solvent used in the step (iii) is at least one selected from the group consisting of chlorobenzene, o-dichlorobenzene and trichlorobenzene.
10. The process as claimed in claim 1, wherein the step (viii) of methylation is done by using a methylating agent selected from dimethylsulfate and methyl chloride, an alkali selected from sodium hydroxide and potassium hydroxide, and a phase transfer catalyst at a temperature in the range of 20 °C to 30 °C.