DESC:FIELD

The present disclosure relates to a process for preparing an insecticidal compound.

BACKGROUND

Deltamethric acid is a vital intermediate used for diverse applications, one of which includes the synthesis of the insecticide deltamethrin. Deltamethrin is a pyrethroid ester and is a popular and widely used insecticide as they are less toxic to mammals as compared to insects. Deltamethrin is effective for eliminating and preventing the infestation of a wide variety of domestic pests such as spiders, fleas, ticks, carpenter ants, carpenter bees, cockroaches and bed bugs.
Deltamethric acid has a molecular weight of 297.97 and a structure as illustrated below

Deltamethric acid

Conventionally, deltamethric acid is prepared from deltamethric acid ester by alkali or alcoholic alkali hydrolysis, to yield a salt of the acid. The salt is acidified and then extracted in a solvent. However, the process of alkali-based hydrolysis results in the degradation of the product. Also the product obtained from the conventional processes has less yield and purity, require high processing time and release aqueous effluents.

Therefore, there is felt a need for a simple and economic process for the preparation of deltamethric acid. Accordingly, the present disclosure provides a process for the preparation of deltamethric acid using inexpensive reagents that can be recovered and reused.
OBJECTS

Some of the objects of the present disclosure, which at least one embodiment is adapted to provide, are described herein below:

It is an object of the present disclosure to provide a process for the preparation of a deltamethric acid.

It is another object of the present disclosure to provide a process for the preparation of deltamethric acid, which is rapid, economic and environment friendly.

It is still another object of the present disclosure to provide a high yielding process for the preparation of deltamethric acid.

It is yet another object of the present disclosure to provide a process for preparing deltamethric acid with high purity.

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

In accordance with the present disclosure there is provided a process for preparing a deltamethric acid having a structure of Formula 1, said process comprising the following steps: dissolving at least one sulfur containing acid in water at a temperature ranging from 50 to 90°C to obtain an acidic solution; and hydrolyzing a compound of Formula 2 in the presence of said acidic solution at a temperature ranging from 80 to 110°C to obtain the deltamethric acid having a structure of Formula 1.

Formula 1
wherein R2 and R3 are independently selected from the group consisting of linear or branched C1-C5 alkyl groups and R1 is a fragment selected from the group consisting of
and
wherein R4, R5, R6, R7, and R8 are independently selected from the group consisting of H, Cl, Br and I and * indicates the point of attachment.

Formula 2

wherein R is selected from the group consisting of C1-C5 alkyl groups, R2 and R3 are independently selected from the group consisting of linear or branched C1-C5 alkyl groups and R1 is a fragment selected from the group consisting of
and ,
wherein R4, R5, R6, R7, and R8 are independently selected from the group consisting of H, Cl, Br and I and * indicates the point of attachment.

DETAILED DESCRIPTION

Deltamethric acid is conventionally prepared from deltamethric acid ester by alkali or alcoholic alkali hydrolysis yielding a salt of the acid. The salt is further acidified and then extracted using a solvent, however, the product obtained has low yield and low purity. Also, these processes require comparatively high processing time and discharge aqueous effluents.

Accordingly, the present disclosure provides a process for the preparation of deltamethric acid that employs inexpensive, easy to handle reagents that can be recovered and reused.

In accordance with one aspect of the present disclosure there is provided a process for the preparation of a deltamethric acid.

In the first step, a sulfur containing acid is dissolved in water at a temperature ranging from 30 to 90oC to obtain an acidic solution. The use of the acidic solution for hydrolysis in accordance with the present disclosure prevents the degradation of the final product (deltamethric acid) and thus overcomes the problem associated with alkali or alcoholic alkali hydrolysis as well as eliminates effluent generation and is more economic.

In an embodiment of the present disclosure, the concentration of the sulfur containing acid in the acidic solution ranges from 50 to 80 % w/w.

The sulfur containing acid used in the process of the present disclosure includes but is not limited to sulfonic acid, methane sulfonic acid, benzene sulfonic acid, p-chloro benzene sulfonic acid, p-toluene sulfonic acid, sulfuric acid and mixtures thereof.

In the second step, a compound of Formula 2 is hydrolyzed using acidic solution at a temperature ranging from 80 to 110°C resulting in the compound of Formula 1.

In an embodiment of the present disclosure, the concentration of the acid solution ranges from 55 to 80 % w/w.

Formula 2
In an embodiment of the present disclosure the compound of Formula 2 is cypermethric acid ester as represented hereinabove, wherein R is selected from the group consisting of C1-C5 alkyl groups, R2 and R3 are independently selected from the group consisting of linear or branched C1-C5 alkyl groups and R1 is a fragment selected from the group consisting of
and ,
wherein R4, R5, R6, R7, and R8 are independently selected from the group consisting of H, Cl, Br and I and * indicates the point of attachment.

Formula 1
The structure of the compound of Formula 1 is represented hereinabove wherein, R2 and R3 are independently selected from the group consisting of linear or branched C1-C5 alkyl groups and R1 is a fragment selected from the group consisting of
and ,
wherein R4, R5, R6, R7, and R8 are independently selected from the group consisting of H, Cl, Br and I and * indicates the point of attachment.

In an exemplary embodiment of the present disclosure, the compound represented by Formula 1 is deltamethric acid.

During the hydrolysis of the ester in the presence of sulfur containing acid solution, alcohol formed is removed along with water by distillation. The loss of water is compensated by adding additional water to the hydrolysis reaction to maintain the concentration of sulfur containing acid in the acidic solution at a range of 50 to 80% w/w.

The acid hydrolysis is carried out for a time period sufficient to achieve complete hydrolysis of ester. The completion of hydrolysis is monitored by Gas Chromatography (GC) or High Performance Liquid Chromatography (HPLC). The hydrolysis reaction is terminated when the concentration of the ester is 0.5% or below.

After the complete hydrolysis of ester, the obtained compound of Formula 1 is extracted with at least one solvent, followed by quantification of the product.

The solvent may be an aromatic or an aliphatic solvent which includes but is not limited to xylene, benzene, ethylbenzene, hexane, cyclohexane, toluene and combinations thereof.

The compound of Formula 1 is present in the solvent layer, which is recovered by separating it from the sulfur containing acidic solution. The sulfur containing acid used for the hydrolysis of the ester is present in the aqueous layer and can be recovered and reused in the next batch.

The process of the present disclosure results in about 99.00% recovery of the sulfur containing acid. Further, the compound of Formula 1 prepared in accordance with the process of the present disclosure may be used as an intermediate and/ or a precursor for the synthesis of many products that includes but are not limited to deltamethrin, cypermethrin, alphamethrin and permethrin.

The process of the present disclosure provides 100% conversion of the ester to the acid. Further, the sulfur containing acid used during the process of the present disclosure is capable of being recycled after the completion of the reaction. Advantageously, it is found that there is no aqueous effluent discharge resulting from the process of the present disclosure. Thus, the process in accordance with the present disclosure is efficient, economical and environment friendly.

The present disclosure is further described in the light of the following non-limiting example which is set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure.

Example 1
Preparation of dibromocypermethric acid
400g of 70.0% w/w aqueous p-toluene sulfonic acid (PTSA) solution was added to 1.0 g mole of dibromocypermethric acid (DBCMA) ester (312g) to obtain a reaction mixture. The reaction mixture was maintained at a temperature of 75oC to keep the ester in molten stage. The reaction mixture was then heated to a temperature of 104 to 106oC for a time period of 10 to 12 hours. Methanol and water formed as result of the hydrolysis of the ester was removed by reflux. Additional water was supplied to the hydrolysis reaction to maintain the concentration of p-toluene sulfonic acid in the range of 55 to 75% w/w.

The termination of the reaction was monitored either by gas chromatography (GC) or by high performance liquid chromatography (HPLC) (the termination limit of dibromocypermethric acid ester was taken to be <0.5 %). A reaction mass was obtained after the completion of the reaction. The reaction mass was cooled to a temperature of 70oC. 400ml toluene was added to the reaction mass to extract the dibromocypermethric acid.

From the reaction mass, the toluene layer was separated to recover the dibromocypermethric acid (the over all yield of dibromocypermethric acid = 99.0%, and recovery of PTSA = 98.0%). The aqueous phase of p-toluene sulfonic acid was recycled in the next batch.

The recycle data of p-toluene sulfonic acid (PTSA) is depicted in Table-1 below.

Table-1: Experimental Data of p-Toluene Sulfonic Acid Recycle
Expt. No.
Batch Size PTSA solution wt/volume and purity Water added to get total hydrolysis Yield of DBCMA and analysis Recovered Dibromoester
#2
312 g 1st recycle of PTSA solution (Purity= 56%)
410 ml/ 472 g 600 ml/mole Wt of DBCMA= 288 g
Yield= 96.64%,
Sp rotation= 25.7°,
Purity= 99.0%, Wt= 10 g

#3
312 g 2nd recycle of PTSA solution (Purity= 53%)
455 ml/ 516 g 500 ml/mole Wt of DBCMA= 291 g
Yield= 97.65%,
Sp rotation= 24.6°,
Purity= 99.2%, Wt =10 g
#4
312 g 3rd recycle of PTSA solution (Purity= 48%)
492 ml/ 550.5 g 600 ml/mole Wt of DBCMA= 290 g
Yield= 97.3%,
Sp rotation= 24.5°,
Purity= 99.3%, Wt= 14.5 g

#5

312 g 4th recycle of PTSA solution (Purity= 53%)
430ml/ 488 g 600 ml/mole Wt of DBCMA= 288 g
Yield= 96.64%,
Sp rotation= 25.7°,
Purity= 99.8%, Wt= 10.0 g

#6

312 g 5th recycle of PTSA solution (Purity= 50%)
450 ml/ 509 g 600 ml/mole Wt of DBCMA= 283 g
Yield= 94.96%,
Sp rotation= 24.6°,
Purity= 99.8%, Wt= 13.0 g

#7

312 g 6th recycle of PTSA solution (Purity= 37%)
505 ml/ 551 g 650 ml/mole Wt of DBCMA= 285 g
Yield= 95.63%,
Sp rotation= 25.0°,
Purity= 99.9%, Wt= 14.5 g

#8

312 g 7th recycle of PTSA solution (Purity= 49%)
420 ml/ 473 g 650 ml/mole Wt of DBCMA= 290 g
Yield= 97.3%,
Sp rotation= 25.0°
Purity= 99.1%, Wt= 8.0 g

#9

312 g 8th recycle of PTSA solution (Purity= 50%)
375 ml/ 424 g 600 ml/mole Wt of DBCMA= 286 g
Yield= 95.97%,
Sp rotation= 20.7°,
Purity= 99.3%, Wt= 13 g

From the above experimental data it is clear that the continuous recycling of p-toluene sulfonic acid (PTSA) is possible. The process in accordance with the present disclosure therefore, is an environment friendly and cost effective process without any effluent generation.

The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the 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 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.

Any discussion of documents, acts, materials, devices, articles and 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.

While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications 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 modifications in the nature of the disclosure or the preferred embodiments 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 a compound of Formula 1,

Formula 1
wherein,
R2 and R3 are independently selected from the group consisting of linear and branched C1-C5 alkyl groups; and

R1 is a fragment selected from the group consisting of
and ,
wherein
R4, R5, R6, R7, and R8 are independently selected from the group consisting H, Cl, Br and I; and
* indicates the point of attachment,

said process comprising the following steps:

a. dissolving at least one sulfur containing acid in water at a temperature ranging from 50 to 90°C to obtain an acidic solution; and

b. hydrolyzing a compound of Formula 2,

Formula 2
wherein,
R is selected from the group consisting of C1-C5 alkyl groups;
R2 and R3 are independently selected from the group consisting of linear and branched C1-C5 alkyl groups; and
R1 is a fragment selected from the group consisting of
and ,
wherein,
R4, R5, R6, R7, and R8 are independently selected from the group consisting of H, Cl, Br and I; and
* indicates the point of attachment,

in the presence of said acidic solution at a temperature ranging from 80 to 110°C to obtain the compound of Formula 1.

2. The process as claimed in claim 1, wherein the compound of Formula 1 is a deltamethric acid.

3. The process as claimed in claim 1, wherein said sulfur containing acid is at least one selected from the group consisting of sulfonic acid, methane sulfonic acid, benzene sulfonic acid, p-chloro benzene sulfonic acid, p-toluene sulfonic acid and sulfuric acid.

4. The process as claimed in claim 1, wherein said compound of Formula 2 is at least one cypermethric acid ester.

5. The process as claimed in claim 1, wherein the process step (b) further comprises a step of extracting deltamethric acid using at least one solvent.

6. The process as claimed in claim 5, wherein said solvent is at least one selected from the group consisting of xylene, benzene, ethylbenzene, hexane, cyclohexane and toluene.

7. The process as claimed in claim 1 comprises the following steps:
a. dissolving p-toluene sulfonic acid (PTSA) in water to obtain an aqueous solution of PTSA; and
b. hydrolyzing dibromocypermethric acid in the presence of said aqueous solution of PTSA at a temperature ranging from 80 to 110°C to obtain a compound of Formula 1 (dibromocypermethric acid).

8. The process as claimed in claim 1 further comprises the steps of recovering the sulfur containing acid and recycling said recovered sulfur containing acid.