DESC:FORM – 2

THE PATENTS ACT, 1970
(39 of 1970)

COMPLETE SPECIFICATION

“AN IMPROVED PROCESS FOR PREPARING 2, 4-DICHLOROPHENOXYACETIC ACID AND ITS SODIUM SALT”

MEGHMANI ORGANICS LTD.
A Company Incorporated under
The Indian Companies Act
Meghmani House, 10, Shreenivas Society,
Paldi, Ahmedabad-380007,
Gujarat State, INDIA

The following specification particularly describes the nature of this invention and manner in which it is to be performed:-

FIELD OF INVENTION:

The proposed invention relates to an improved process for preparation of 2, 4-dichlorophenoxyacetic acid and its Sodium salt. In particular the proposed invention relates to an improved process for preparing 2, 4-dichlorophenoxyacetic acid and its sodium salt which significantly removes the iron content in the traces, providing high quality of 2, 4-dichlorophenoxyacetic acid and its sodium salt with significantly increased yield of 2, 4-dichlorophenoxyacetic acid and its Sodium salt at significantly reduced cost.

BACKGROUND:

2, 4-Dichlorophenoxyacetic acid (usually referred to by its abbreviation, 2, 4-D) is a common systemic pesticide/herbicide used in the control of broadleaf weeds. It is one of the most widely used herbicide in the world, and the third most commonly used in North America. 2, 4-D is a synthetic auxin (plant hormone) and as such it is often used in laboratories for plant research and as a supplement in plant cell culture media.
The structure of 2, 4-Dichlorophenoxyacetic acid (2, 4-D) and it`s sodium salt is as under:

2, 4-D acid Na salt of 2, 4-D acid
The phenoxyalkanoic acids are usually made by the reaction of an alkali metal salt of the corresponding phenol with an alkali metal salt of the appropriate haloalkanoic acid. These salts are usually made by reaction of t corresponding phenol and the acid with alkali metal hydroxide, thus producing water as a by-product. Additionally, water is often used as a solvent for the reaction.

The said alkali metal salt of the corresponding phenol has the presence of iron content in traces (Particularly in catalytic process) as a result of which, the poor quality of 2, 4-dichlorophenoxyacetic acid and their sodium salt are produced. In order to get the acceptable quality of 2,4-dichlorophenoxyacetic acid , the alkali metal salt of the corresponding phenol are washed with excessive water which as a result increases the quantity of effluent and reduces the yield of 2, 4-dichlorophenoxyacetic acid and its sodium salt, making the process less viable.

PRIOR ART:

Various types of process for making 2, 4-dichlorophenoxyacetic acid are found in the prior art but they have several disadvantages as compared to the proposed invention, each of which are described below:

In the US4035416, titled as “Process for making Phenoxyalkanoic acids”, wherein Phenoxyalkanoic acids, e.g., 2, 4-dichlorophenoxyacetic acid, are made by simultaneously adding equivalent amounts of haloalkanoic acid and alkali metal hydroxide to a hot mixture of about equimolar amounts of the appropriate phenol and the alkali metal salt of the phenol while distilling water from the reaction mixture as formed. But use of 2, 4-dichlorophenol as starting raw material (in place of phenol) and azeotropic distillation to maintain anhydrous reaction conditions makes this process commercially costly and less lucrative.

In the US2656382, titled as “Preparation of 2,4-dichlorophenoxyacetic acid”, which involves Na –salt formation of 2, 4-dichlorophenol with aq. NaOH using Monochlorobenzene as solvent and carrying out azeotropic removal of water and condensation of 2, 4-DCP sodium salt with monochloroacetic acid at 135°C to give desired product in 94% yield. Since 2, 4-dichlorophenol is the starting raw material (instead of phenol) this process becomes commercially costly and less lucrative. Further use of Monochlorobenzene and azeotropic distillation to maintain anhydrous reaction condition makes this process less viable at commercial scale.

In the EP-0509518A1, titled as “Process for preparation of 2, 4-dichlorophenoxyacetic acid”, wherein a process is described for the preparation of 2, 4-dichlorophenoxyacetic acid by chlorination of Phenoxy acetic acid with chlorine at 50°C in a reaction mixture composed of acetic acid to give 78.5% yield of 2,4-D acid. Said invention uses costlier raw material such as Phenoxyacetic acid and also the yield of 2, 4-D acid is comparatively less, makes the said process commercially less lucrative.

DISADVANTAGES OF PRIOR ART:
The above mentioned inventions suffer from at least one of the following problems:
1. Most of them use pure 2,4-dichlorophenol as starting raw material which involves cost addition as it requires purification step i.e. fractionation using high efficient fractionation column and loss due to fractionation are also involved.
2. In case of catalytic halogenation of phenol with Iron chloride and biphenyl sulfide, presence of iron content in chlorinated phenol results in poor quality of 2, 4-dichlorophenoxyacetic acid and corresponding sodium salt.
3. In presence of Iron content it become mandatory to wash the alkali metal salt of the 2, 4-D acid with excessive water in order to get the acceptable quality of 2, 4-dichlorophenoxyacetic acid/Na salt. Excessive washing with water increases the quantity of effluent and reduces the yield of 2, 4-D acid and it`s sodium salt and thus making the process less viable.
4. Many of them uses costlier raw material like 2, 4 Dichlorophenol, organic solvents and maintain anhydrous reaction conditions by doing azeotropic distillation the entire process become expensive and less viable.
5. Most of them use organic solvent increasing the cost of manufacturing.
6. Many of them use organic solvents which are hazardous making the invention unsafe to handle.
7. They require recovery and recycling of solvents and unreacted 2,4- Dichlorophenol making the process complex and expensive.
To overcome the above mentioned problems, there is a need to come up with an improved process for preparation of 2, 4-dichlorophenoxyacetic acid which is free from the above mentioned problems.

OBJECTS OF INVENTION:
The main object of the proposed invention is to provide an improved process for preparing 2, 4-dichlorophenoxyacetic acid and it`s sodium salt which significantly removes the iron content from 2,4-dichloropenol, providing high quality of 2, 4-dichlorophenoxyacetic acid and its sodium salt with comparatively reduced quantity of effluent and significantly increased yield of 2, 4-dichlorophenoxyacetic acid.
Another object of the invention is to provide an improved process for preparing 2, 4-dichlorophenoxyacetic acid and its sodium salt which is economic, significantly viable and eco-friendly.
Another object of the invention is to provide an improved process for preparing 2, 4-dichlorophenoxyacetic acid and its sodium salt which uses economical and easily available raw material.
Yet another object of the invention is to provide an improved process for preparing 2, 4-dichlorophenoxyacetic acid and its sodium salt which uses the raw material which does not require purification and significantly reduces the cost involved in the process.
Yet another object of the invention is to provide an improved process for preparing 2, 4-dichlorophenoxyacetic acid and its sodium salt which does not involve use of organic solvent significantly reducing the cost of manufacturing.
Yet another object of the invention is to provide an improved process for preparing 2, 4-dichlorophenoxyacetic acid and its sodium salt which avoids the use of organic solvent eliminating health hazards.
Yet another object of the invention is to provide an improved process for preparing 2, 4-dichlorophenoxyacetic acid and its sodium salt which is carried out at comparatively low temperature.

DESCRIPTION OF INVENTION:

An improved process for preparation of 2, 4-dichlorophenoxyacetic acid and its sodium salt whereby the raw material used in the proposed invention is 93-95% crude 2, 4-dichlorophenol which is prepared by the conventional method which is explained as below:

Chlorination of Phenol: Phenol undergoes catalytic chlorination in presence of metal chlorides such as Iron Chloride and diphenylsulfide to give 93-95% crude 2, 4-dichlorophenol as major product along with small quantities of 2-chloro, 2, 6-dichloro and 2, 4, 6-Trichlorophenol as by products.

The said 93-95% crude 2, 4-dichlorophenol contains iron content in traces which results in poor quality of 2, 4-dichlorophenoxy acetic acid and their sodium salt.

An improved process for preparation of 2, 4-dichlorophenoxyacetic acid and its Sodium salt comprises of following steps:

Washing step: The 93-95% crude 2, 4-dichlorophenol is firstly washed with polar solvent to remove iron content present in traces. The said polar solvent is selected from methanol, ethanol, water, acidic water or combination of any of the said solvents. The quantity of polar solvent required to wash the said crude 2, 4-dichlorophenol to remove the iron content in traces is selected from the ratio of 2, 4-dichlorophenol to water in range of 1:0.5 to 1:1.

Condensation Step: 93-95% crude 2, 4-dichlorophenol is condensed with dilute sodium hydroxide (NaOH) and monochloroacetic acid to give Na salt of 2, 4-Dichlorophenoxyacetic acid along with sodium chloride and water as a by-product following the below steps:

Step 1: aqueous solution of sodium hydroxide is charged into a reaction flask and temperature is raised to 55 to 60°C;

Step 2: 93-95% crude 2,4-dichlorophenol is added to the said aqueous solution of sodium hydroxide in 30 minutes at temperature range of 55 to 60°C and the mixture is stirred for 30 minutes;

Step 3: aqueous solution of monochloroacetic acid and aqueous solution of sodium hydroxide are added simultaneously to the said mixture formed in step 2 in 1.0-1.5 hours at temperature range of 65 to 95°C by controlling pH preferably in range of 9.0 to 10 and

Step 4: the said reaction mixture is stirred additionally for 4.0 hours at temperature of 95±2°C and upon completion of reaction, reaction mass is cooled and filtered to get the white color wet cake of Na salt of 2, 4-Dichlorophenoxyacetic acid along with sodium chloride and water as a by-product.

In the said step 1, the quantity of aqueous solution of sodium hydroxide is taken in molar ratio of 2, 4-dichlorophenol to aqueous solution of sodium hydroxide in range of 1:1 to 1:2.

In the said step 3, the quantity of monochloroacetic acid is taken in molar ratio of 2, 4-dichlorophenol to monochloroacetic acid in range of 1:1 to 1:1.5.

In the said step 1, the quantity of aqueous solution of sodium hydroxide is taken in molar ratio of 2, 4-dichlorophenol to aqueous solution of sodium hydroxide in range of 1:1 to 1:2.

In the said step 3, the most preferable pH is in range of 9.0 to 9.5.

The said pH range of 9.0 to 10 is maintained while simultaneous addition of monochloroacetic acid and dilute sodium hydroxide (NaOH) in said step 3, as the reaction towards higher alkaline condition i.e. pH more than 10 results in conversion of monochloroacetic acid into glycolic acid (a by-product) and high alkaline condition also reduces the yield of sodium salt of 2, 4-dichlorophenoxyacetic acid.

The said sodium salt of 2, 4-Dichlorophenoxyacetic acid itself is used as selective weedicide as well as an intermediate for the synthesis of 2, 4-Dichlorophenoxyacetic acid.

Acidification step: The wet cake of Na salt of 2, 4-dichlorophenoxyacetic acid as obtained in the condensation step is dissolved in 500ml to 1 liter water at temperature in range of 90 to 95°C and acidified with 30-33% hydrochloric acid (HCl) solution at 90°C temperature. The reaction mass is cooled to 65°C temperature, filtered and wet cake is washed with water and dried at temperature of 100 ±5°C to get final white crystals of 2,4-dichlorophenoxyacetic acid having 84 to 88% molar yield and 98 to 99% purity.

Examples:
Example -1

Aqueous solution of sodium hydroxide (162 gm, 1.29 moles) is charged into a reaction flask and temperature is raised to 60°C and 200gm (1.153 mole, purity by GC:94%) of Crude 2,4-dichlorophenol (obtained from catalytic Chlorination using iron chloride and diphenylsulfide and treated with a polar solvent such as methanol, ethanol, water , acidic water or combination of any of said solvents to remove traces of iron contents) is added in 30 minutes at temperature in range of 55 to 60°C and the mixture is stirred for 30 minutes. Aqueous solution of monochloroacetic acid (191gm, 1.516 moles, purity: 75%) and aqueous solution of sodium hydroxide solution (193gm, 1.544moles) are added simultaneously in 1.0 to 1.5 hours at temperature in range of 65 to 95°C by controlling pH in range of 9.0 to 10. The reaction mixture is stirred additionally for 4 hours at temperature of 95±2°C. Upon completion of reaction, reaction mass is cooled, filtered to get the white color wet cake of Na salt of 2, 4-Dichlorophenoxyacetic acid along with sodium chloride and water as a by-product. The said wet cake of Na salt of 2,4-dichlorophenoxyacid (white colored, Weight:419g, LOD:39.59%, yield:90.31%) as obtained in the condensation step is dissolved in 1 liter water at temperature in range of 90 to 95°C and acidified with 33% hydrochloric acid (HCl) solution at 90°C temperature. The reaction mass is cooled to 65°C temperature, filtered and wet cake is washed with water and dried at temperature of 100 ±5°C to get final white crystals of 2,4-dichlorophenoxyacetic acid having 88.62 % molar yield and 98 to 99% purity.

Example -2

Aqueous solution of sodium hydroxide (81gm, 0.65 moles) is charged into a reaction flask and temperature is raised to 60°C and 100 gm (0.576 mole, Purity by GC: 94%) of crude 2,4-dichlorophenol (obtained from catalytic Chlorination using iron chloride and diphenylsulfide and treated with a polar solvent such as methanol, ethanol, water , acidic water or combination of any of said solvents to remove traces of iron contents) is added in 30 minutes at temperature in range of 55 to 60°C and the mixture is stirred for 30 minutes. Aqueous solution of monochloroacetic acid (95.5gm, 0.758 moles, Assay: 75%) and aqueous solution of sodium hydroxide solution (151gm, 1.20 moles) are added simultaneously in an hour at temperature in range of 65 to 95°C by controlling pH in range of 11.0 to 12.0. The reaction mixture is stirred additionally for 4 hours at temperature of 95±2°C. Upon completion of reaction, reaction mass is cooled, filtered to get the white color wet cake of Na salt of 2, 4-Dichlorophenoxyacetic acid along with sodium chloride and water as a by-product. The said wet cake of Na salt of 2,4-Dichlorophenoxyacetic acid (white colored, Weight:182.5gm, LOD:36.23%, yield:83.04%) as obtained in the condensation step is dissolved in 500 ml water at temperature in range of 90 to 95°C and acidified with 33% hydrochloric acid (HCl) solution at 90°C temperature. The reaction mass is cooled to 65°C temperature, filtered and wet cake is washed with water and dried at temperature of 100 ±5°C to get final white crystals of 2,4-Dichlorophenoxyacetic acid having 78.18% molar yield and 94.72% purity.

Example -3

Aqueous solution of sodium hydroxide (81gm, 0.65 moles) is charged into a reaction flask and temperature is raised to 60°C and 100gm (0.576 mole, purity by GC: 94%) of crude 2,4-dichlorophenol (obtained from catalytic Chlorination using iron chloride and diphenylsulfide and treated with a polar solvent such as methanol, ethanol, water , acidic water or combination of any of said solvents to remove traces of iron contents) is added in 30 minutes at temperature in range of 55 to 60°C and the mixture is stirred for 30 minutes. Aqueous solution of monochloroacetic acid (85.0, 0.674 moles, Assay: 75%) and aqueous solution of sodium hydroxide solution (75gm, 0.60 moles) are added simultaneously in an hour at temperature in range of 65 to 95°C by controlling pH in range of 9.0 to 10.0. The reaction mixture is stirred additionally for 4 hours at temperature of 95±2°C. Upon completion of reaction, reaction mass is cooled, filtered to get the white color wet cake of Na salt of 2, 4-Dichlorophenoxyacetic acid along with sodium chloride and water as a by-product. The said wet cake of Na salt of 2,4-Dichlorophenoxyacetic acid (white colored, weight:185gm, LOD:34.23%, yield:86.82%) as obtained in the condensation step is dissolved in 500 ml water at temperature in range of 90 to 95°C and acidified with 33% hydrochloric acid (HCl) solution at 90°C temperature. The reaction mass is cooled to 65°C temperature, filtered and wet cake is washed with water and dried at temperature of 100 ±5°C to get final white crystals of 2,4-Dichlorophenoxyacetic acid having 84.90% molar yield and 98.13% purity.

Example -4

Aqueous solution of sodium hydroxide (81gm, 0.65 moles) is charged into a reaction flask and temperature is raised to 60°C and 100 g (0.576 mole, Assay: 94%) of crude 2, 4-dichlorophenol (obtained from catalytic Chlorination using iron chloride and diphenylsulfide and without being washed with polar solvent) is added in 30 minutes at temperature in range of 55 to 60°C and the mixture is stirred for 30 minutes. Aqueous solution of monochloroacetic acid (95.5, 0.757 moles, Assay: 75%) and aqueous solution of sodium hydroxide solution (85 g, 0.68 moles ) are added simultaneously in an hour at temperature in range of 65 to 95°C by controlling pH in range of 9.0 to 10.0. The reaction mixture is stirred additionally for 4 hours at temperature of 95±2°C. Upon completion of reaction, reaction mass is cooled, filtered to get the white color wet cake of Na salt of 2, 4-Dichlorophenoxyacetic acid along with sodium chloride and water as a by-product. The said wet cake of Na salt of 2,4-Dichlorophenoxyacetic acid (brown colored, weight:190g, LOD:39.56%, yield:82.01%) as obtained in the condensation step is dissolved in 500 ml water at temperature in range of 90 to 95°C and acidified with 33% hydrochloric acid (HCl) solution at 90°C temperature. The reaction mass is cooled to 65°C temperature, filtered and wet cake is washed with water , dried at temperature of 100±5°C to get final light brown crystals of 2,4-Dichlorophenoxyacetic acid having 80.9% molar yield and 97.77% purity.

Having described what is considered the best form presently contemplated for embodying the present invention, various alterations, modifications, and/or alternative applications of the invention will be promptly apparent to those skilled in the art. Therefore, it is to be understood that the present invention is not limited to the practical aspects of the actual preferred embodiments hereby described and that any such modifications and variations must be considered as being within the spirit and the scope of the invention, as described in the attached claims.

Advantages of Proposed Invention:

- Provides high quality of 2, 4-dichlorophenoxyacetic acid and its sodium salt with comparatively reduced quantity of effluent and significantly increased yield of 2, 4-dichlorophenoxyacetic acid.
- Economic, significantly viable and eco-friendly.
- Uses economical and easily available raw material.
- Raw material which does not require purification by fractional distillation which significantly reduces the cost involved in the process.
- Does not involve use of organic solvent significantly reducing the cost of manufacturing.
- Does not involve use of organic solvent eliminating health hazards.
- Reaction is carried out at comparatively low temperature.
,CLAIMS:We Claim:

1. An improved process for preparation of 2, 4-dichlorophenoxy acetic acid and its sodium salt comprises of following steps:

Washing step: the 93-95% crude 2, 4-dichlorophenol is firstly washed with polar solvent to remove iron content in traces,

Condensation Step: 93-95% crude 2, 4-dichlorophenol is condensed with dilute sodium hydroxide (NaOH) and monochloroacetic acid to give Na salt of 2, 4-Dichlorophenoxyacetic acid along with sodium chloride and water as a by-product following the below steps:

Step 1: aqueous solution of sodium hydroxide is charged into a reaction flask and temperature is raised to 55 to 60°C;

Step 2: 93-95% crude 2,4-dichlorophenol is added to the said aqueous solution of sodium hydroxide in 30 minutes at temperature range of 55 to 60°C and the mixture is stirred for 30 minutes;

Step 3: aqueous solution of monochloroacetic acid and aqueous solution of sodium hydroxide solution are added simultaneously to the said mixture formed in step 2 in 1.0-1.5 hours at temperature range of 65 to 95°C by controlling pH preferably in range of 9.0 to 10 and

Step 4: the said reaction mixture is stirred additionally for 4.0 hours at temperature of 95±2°C and upon completion of reaction, reaction mass is cooled and filtered to get the white color wet cake of Na salt of 2, 4-Dichlorophenoxyacetic acid along with sodium chloride and water as a by-product,

acidification step: the wet cake of Na salt of 2, 4-dichlorophenoxyacid as obtained in the condensation step is dissolved in 500ml to 1 liter water at temperature in range of 90 to 95°C and acidified with 30-33% hydrochloric acid (HCl) solution at 90°C temperature followed by cooling the reaction mass to 65°C temperature, filtering, washing the wet cake with water and drying at temperature of 100 ±5°C to get final white crystals of 2,4-dichlorophenoxyacetic acid having molar yield in range of 84 to 88% and purity in range of 98 to 99%.

2. An improved process for preparation of 2, 4-dichlorophenoxy acetic acid and its sodium salt as claimed in claim 1, whereby polar solvent is selected from methanol, ethanol, water, acidic water or combination of any of the said solvents.

3. An improved process for preparation of 2, 4-dichlorophenoxy acetic acid and its sodium salt as claimed in claim 1, whereby the quantity of polar solvent required to wash the said crude 2, 4-dichlorophenol to remove the iron content in traces is selected from the ratio of 2, 4-dichlorophenol to polar solvent in range of 1:0.5 to 1:1.

4. An improved process for preparation of 2, 4-dichlorophenoxy acetic acid and its sodium salt as claimed in claim 1, whereby in the step 1 of condensation, the quantity of aqueous solution of sodium hydroxide is taken in molar ratio of 2, 4-dichlorophenol to aqueous solution of sodium hydroxide in range of 1:1 to 1:2.

5. An improved process for preparation of 2, 4-dichlorophenoxy acetic acid and its sodium salt as claimed in claim 1, whereby in the step 3 of condensation, the quantity of monochloroacetic acid is taken in molar ratio of 2, 4-dichlorophenol to monochloroacetic acid in range of 1:1 to 1:1.5.

6. An improved process for preparation of 2, 4-dichlorophenoxyacetic acid and its sodium salt as claimed in claim 1, whereby in the step 3 of condensation, the quantity of aqueous solution of sodium hydroxide is taken in molar ratio of 2, 4-dichlorophenol to aqueous solution of sodium hydroxide in range of 1:1 to 1:2.

7. An improved process for preparation of 2, 4-dichlorophenoxyacetic acid and its sodium salt as claimed in claim 1, whereby in the step 3 of condensation, the most preferable pH is in range of 9.0 to 9.5.

Dated this 24th day of September, 2013

________________________
GOPI J. TRIVEDI (Ms)
Patent Agent, CPVA
At Y. J. Trivedi & Co.
To, (Authorized Agent of the Applicant)
The Controller of Patents,
Patent Office, Mumbai