DESC:Field of the Invention
The present invention relates to an improved process for preparation of alkali metal salt of 2,4-dichlorophenoxy acetic acid.

Background of the Invention
2,4-dichlorophenoxy acetic acid and its sodium salt is a useful herbicide and is a known weed-killer, popularly accepted because of its effectiveness in low concentrations. It is a synthetic auxin, a class of plant growth regulator hormone that is often used as a supplement in plant cell culture media. It is also an active ingredient in herbicides that controls root elongation and cell production by disrupting the cytoskeleton.

EP0509518A1 patent application discloses a process of preparation of 2,4-dichlorophenoxyacetic acid is disclosed by chlorinating phenoxyacetic acid with chlorine in a reaction medium composed of acetic acid to give 75-80% yield of 2,4-acid. The raw material phenoxyacetic acid used is costly and the yield obtained is comparatively less, thus the process is less viable on commercial scale.

Further known preparation of 2,4-dichlorophenoxy acetic acid is disclosed in US4,035,416 patent by simultaneously adding equivalent amounts of chloroacetic acid and sodium hydroxide to a hot mixture of about equimolar amounts of 2,4-dichlorophenol and its sodium salt. However the process requires a continuous or intermittent removal of water from the reaction mixture during the reaction to maintain the water content of the mixture below 10% and involves distillation of 2,4-DCP along with water. Further need of continuous distillation of water for maintaining anhydrous conditions makes the process commercially costly. The pH is not adjusted (optimized) due to which the glycolic acid formation is variable and also it is clear that even though the number of moles are in the same range, the glycolic acid content is much higher.

US2,516,611 discloses a method of preparing sodium salt of 2,4-dichlorophenoxyacetic acid the process comprises reacting 1 mole dichlorophenol with 1 mole of chloroacetic acid, 2 moles of sodium hydroxide. The procedure in forming the mixture was to neutralize a mixture of the 2,4-dichlorophenol and water with an aqueous sodium hydroxide (1M equivalent) solution of 30 per cent concentration. Chloroacetic acid with the sodium hydroxide solution was separately neutralized in molar proportion. The resultant sodium dichlorophenate solution was heated to boiling under reflux and the sodium chloroacetate solution was added with stirring. The reaction mixture, which initially was of a pH value of 10-12, was maintained at the boiling temperature of about 106-108°C for 13 hours till completion of the reaction. The mixture was then cooled to 25°C, to crystallize the sodium 2,4-dichlorophenoxyacetate product and the latter was removed by filtration. The yield reported was 72% of theoretical.

CN102659571B patent application discloses a continuous preparation method of herbicide intermediate 2, 4-dichlorphenoxyacetic acid, which comprises the steps of subjecting 2,4-dichlorphenol with a chloroacetic acid with molar ratio of 1:(1.2-1.5). The reaction passes through a multistage condensation reaction tower. The reaction is carried out at a temperature of 80-110°C and at controlled pH 8-12.

CN107266310A patent application discloses preparation method for synthesizing 2,4-D through a chloroacetic acid acidifying technology. The method comprises reacting 2,4-dichlorophenol with sodium hydroxide to generate a sodium salt, and condensing sodium 2,4-dichlorophenate and sodium chloroacetate to obtain sodium 2,4-dichlorophenoxyacetate. Further sodium 2,4-dichlorophenoxyacetate is acidified by reacting chloroacetic acid to generate 2,4-D. Sodium chloroacetate solution which can be used in next-batch condensation. The method for producing the 2,4-D omits a liquid alkali used for neutralizing the chloroacetic acid and hydrochloric acid used during the acidification.

Furthermore it is known that there is incomplete conversion and higher reaction time required for reaction with more than 0.9 molar equivalent of monochloroacetic acid and sodium hydroxide. Further there is decomposition of monochloroacetic acid into sodium glycolate. The sodium glycolate formed is found to be greater than 5000 ppm. It is observed that if sodium glycolate content in the effluent is more i.e. around 3,000 - 8,000 ppm, the biological treatment of effluent is difficult. Particularly in a cited research paper it is stated that sodium glycolate contributes to soluble chemical oxygen demand (SCOD) of the waste water. If the total concentration of waste water is more than 30000 ppm, the physicochemical treatment such as distillation, incineration and filtration is supposed to be able to treat high concentration CMC wastewater. However it results in high operation costs. Hence biological treatment is not economical and practicable with high concentration of sodium glycolate in waste water along with the high salinity.

Summary of the Invention
In a general aspect, the present invention provides a process for preparing alkali metal salt of 2,4-dichlorophenoxy acetic acid of Formula (I)

wherein X = Na, K, or Ca.
The process comprises adding 2,4-Dichlorophenol (2,4-DCP) and alkali metal hydroxide forming an alkali metal salt of 2,4-Dichlorophenol. An alkali metal salt of monochloroacetic acid is formed in situ by adding 0.6 to 0.9 molar equivalent of monochloroacetic acid (MCA), and 0.6 to 0.9 molar equivalent of an alkali metal hydroxide to said alkali metal salt of 2,4-dichlorophenol. About 60% to 90% of said alkali metal salt of 2,4-dichlorophenol is converted to compound of Formula (I) in said in situ alkali metal salt of monochloroacetic acid at a temperature of 80-150°C and pH at 8.5 to 9.5. The process also produces significantly less amount of alkali metal glycolate, i.e. about 1 ppm to 10 ppm alkali metal glycolate.
In another aspect, the process comprises recycling 10% to 40% unreacted alkali metal salt of 2,4-Dichlorophenol, adding 0.6 to 0.9 molar equivalent of 2,4-dichlorophenol and 0.6 to 0.9 molar equivalent of alkali metal hydroxide forming said alkali metal salt of 2,4-dichlorophenol.
In another aspect, the process comprises recovering 2,4-Dichlorophenol by adjusting pH between 3 to 5 with an acid wherein the acid can be selected from hydrochloric acid, sulfuric acid, acetic acid and formic acid.
In a further aspect, the process comprises recycling said recovered 2,4-Dichlorophenol for forming said alkali metal salt of 2,4-dichlorophenol.
The process comprises adding 0.6V to 2.5V water for forming said alkali metal salt of 2,4-dichlorophenol and forming said alkali metal salt of monochloroacetic acid.
The alkali metal hydroxide can be selected from the group comprising of sodium hydroxide, potassium hydroxide or calcium hydroxide. The in situ alkali metal salt of monochloroacetic acid can be sodium monochloroacetate, potassium monochloroacetate or calcium monochloroacetate. The alkali metal glycolate can be sodium glycolate, potassium glycolate or calcium glycolate.
In another aspect, the process of the present invention is a continuous process.

Description of the invention
The present invention provides an improved process for preparation an alkali metal salt of 2,4-dichlorophenoxy acetic acid of Formula (I):

wherein X = Na, K, or Ca.

The present invention provides an accurate reaction stoichiometry giving optimum conversion of 2,4-dichlorophenol to alkali metal salt of 2,4-dichlorophenoxy acetic acid with negligible amount of alkali metal glycolate. Particularly, the present invention provides the process for preparation an alkali metal salt of 2,4-dichlorophenoxy acetic acid of Formula (I) where alkali metal glycolate content is less than 10 ppm, preferably 1 ppm to 10 ppm in final solid. Alkali metal glycolate can be less than 5000 ppm, preferably less than 1000 ppm in mother liquor (MLR).

In an embodiment, the process for preparation of alkali metal salt of 2,4-dichlorophenoxy acetic acid of Formula (I) has been provided. The process comprises adding 2,4-dichlorophenol (2,4-DCP) and alkali metal hydroxide forming an alkali metal salt of 2,4-dichlorophenol. An alkali metal salt of monochloroacetic acid can be formed in situ by adding monochloroacetic acid (MCA) and an alkali metal hydroxide to said alkali metal salt of 2,4-dichlorophenol. Preferably, 0.6 to 0.9 molar equivalent of monochloroacetic acid, and 0.6 to 0.9 molar equivalent of an alkali metal hydroxide is added to form the in situ alkali metal salt of MCA. About 60% to 90% of said alkali metal salt of 2,4-dichlorophenol is converted to compound of Formula (I) in said in situ alkali metal salt of monochloroacetic acid at a temperature of 80-150°C and pH at 8.5 to 9.5. The process also produces significantly less amount of alkali metal glycolate, i.e. about 1 ppm to 10 ppm.
Typically, while converting alkali metal salt of 2,4-Dichlorophenol to compound of Formula (I), the alkali metal salt of MCA and water undergoes a reaction which produces alkali metal glycolate and hydrochloric acid (HCl). HCl thus formed reacts with the alkali metal hydroxide present in the reaction mixture and neutralized to alkali metal chloride and water. Simultaneously, alkali metal salt of MCA reacts with alkali hydroxide to form alkali metal glycolate and water. The in situ formation of alkali metal salt of MCA reduces the amount of alkali metal glycolate by immediately converting the alkali metal salt of 2,4-Dichlorophenol to compound of Formula (I) avoiding the unwanted side reactions forming alkali metal glycolate. Further, the reaction conditions converting alkali metal salt of 2,4-Dichlorophenol in in situ alkali metal salt of MCA to compound of Formula (I) contributes to reduce the alkali metal glycolate formed in the reaction. About 60% to 90% conversion can be achieved with the controlled addition of the said reactants at a pH of about 8.5-9.5. The addition of reactants are preferably controlled to be equimolar addition of reactants, particularly MCA and the alkali metal hydroxide to the alkali metal salt of 2,4-dichlorophenol. The rate of conversion to Formula (I) can be achieved faster with the equimolar addition of reactants thereby reducing the formation of alkali metal glycolate. Equimolar addition of the reactants can achieve completion of the reaction in about 1 hour to 2 hours at a temperature of 80-150°C.
The alkali metal salt of 2,4-Dichlorophenol can be prepared by adding 2,4-Dichlorophenol and alkali metal hydroxide forming an alkali metal salt of 2,4-Dichlorophenol. Preferably, substantially equimolar quantity 2,4-Dichlorophenol (2,4-DCP) and alkali metal hydroxide can be added. In an aspect, about 1 molar equivalent of 2,4-DCP is added to 1.1 molar equivalent of alkali hydroxide. 2,4-DCP can be first converted to its alkali metal salt of 2,4-Dichlorophenol (2,4-DCP). The alkali metal salt formed depends on the alkali metal hydroxide used in the reaction. The alkali metal salt of 2,4-DCP according to the present invention can be sodium, potassium or calcium salt. The alkali metal hydroxide according to an aspect can be selected from the group comprising of sodium hydroxide, potassium hydroxide or calcium hydroxide, preferably sodium hydroxide. The alkali metal glycolate formed according to an aspect can be sodium glycolate, potassium glycolate or calcium glycolate, preferably sodium glycolate.
In an embodiment, 1 molar equivalent of 2,4-Dichlorophenol can be heated to a temperature of 60°C to 65°C, followed by drop-wise addition of 1.1 molar equivalent of alkali metal hydroxide to form alkali metal salt of 2,4-Dichlorophenol over a period of 15 to 20 minutes and raising temperature to 80°C-150°C. Preferably, the alkali metal is sodium hydroxide and the alkali metal salt of 2,4, Dichlorophenol is sodium salt of 2,4,dichlorophenol.
The use of separately synthesized alkali metal salt of MCA i.e. alkali monochloroacetate, for example sodium monochloroacetate (SMCA) as taught in prior art processes results in higher amount of alkali metal glycolate formation which is undesirable. The step of forming in situ alkali metal salt of monochloroacetic acid, number of molar equivalent of monochloroacetic acid, alkali metal hydroxide, and temperature contribute for the significant reduction in the formation of alkali metal glycolate. Thus, less than 1 molar equivalent of MCA, preferably, 0.6 to 0.9 molar equivalent of monochloroacetic acid, and 0.6 to 0.9 molar equivalent of an alkali metal hydroxide can be added to alkali metal salt of 2,4-Dichlorophenol at a temperature of about 100-110°C forming in situ alkali metal salt of MCA and to achieve 60% to 90% conversion to compound of Formula (I) with reduced alkali metal glycolate formation. Temperature of the reaction above 110°C to 125°C results in increased formation of alkali metal glycolate, over 10,000 ppm.
The in situ alkali metal salt of monochloroacetic acid in accordance with the present invention can be a salt of sodium, potassium or calcium. Preferably, the alkali metal salt is sodium monochloroacetate, potassium monochloroacetate or calcium monochloroacetate.
In an embodiment, 0.6 to 0.9 molar equivalent of monochloroacetic acid, and 0.6 to 0.9 molar equivalent of sodium hydroxide can be added to sodium salt of 2,4-Dichlorophenol at a temperature of about 100-110°C forming in situ sodium salt of MCA.
The present invention provides a controlled conversion of the alkali metal salt of 2,4-Dichlorophenol and in situ alkali metal salt of MCA to Formula (I) for reducing the formation of alkali metal glycolate. In an aspect, the conversion is controlled to be about 60% to about 90%. The controlled conversion can be achieved by adding an equimolar quantity of the MCA and alkali metal hydroxide for forming the in situ alkali metal salt of MCA such that the rate of conversion of the alkali metal salt of MCA in situ and alkali metal salt of 2,4-DCP to Formula (I) occurs faster and less alkali metal salt of MCA is decomposed to form alkali metal glycolate. The desirable rate of conversion of said alkali metal salt of MCA and alkali metal salt of 2,4-DCP to Formula (I) can be achieved at temperature of about 80-150°C and pH at 8.5 to 9.5. The 60% to 90% conversion of alkali metal salt of 2,4-DCP and alkali metal salt of MCA significantly reduced the formation of alkali metal glycolate from about 1 ppm to 10 ppm in final product. Preferably, 60% conversion of alkali metal salt of 2,4-Dichlorophenol in said in situ alkali metal salt of monochloroacetic acid to compound of Formula (I) results in the formation of alkali metal glycolate below 1000 ppm in MLR and/or less than 700 ppm in the MLR and 1 to 10 ppm in the final product.
In an aspect, the process of the present invention provides recycling unreacted alkali metal salt of 2,4-dichlorophenol for the preparing alkali metal salt of 2,4-dichlorophenol. The process of the present invention provides converting about 60% to 90% of the alkali metal salt of 2,4-Dichlorophenol to compound of Formula (I). 10% to 40% of unreacted alkali metal salt of 2,4-Dichlorophenol can be recycled. After the recovery of the compound of Formula (I), remaining 10% to 40% of unreacted alkali metal salt of 2,4-Dichlorophenol present in mother liquor (MLR) can be recycled to the step of forming alkali metal salt of 2,4-Dichlorophenol with addition of further 0.6 to 0.9 molar equivalent of fresh 2,4-Dichlorophenol and 0.6 to 0.9 molar equivalent of alkali metal hydroxide forming said alkali metal salt of 2,4-Dichlorophenol. The recycling process can be carried out with one or more recycle of the MLR containing the unreacted alkali metal salt of 2,4-Dichlorophenol. The process of recycling can be carried out in batch process or continuous process wherein one or more recycling can be performed by controlling the formation of alkali metal glycolate. The recycling step reduces alkali metal glycolate formation in MLR without altering the product yield and purity. With the reduced alkali metal glycolate content in the MLR, the alkali metal glycolate content can be maintained less than 10 ppm in final product. Thus, the process of the present invention can be economical and efficient reducing the cost of monochloroacetic acid and also reduces the effluent treatment.
In another aspect, the process of the present invention further provides recovering 2,4-dichlorophenol. The recovery can be carried out after recovering the product and/or after recycling step. The 2,4-Dichlorophenol can be recovered by adjusting pH of MLR to about 3 to 5 with an acid. The pH of the MLR can be adjusted to about 3 to 5 and heated to 40-45°C to recover 2,4-Dichlorophenol. The acid for recovering 2,4-Dichlorophenol can be selected from hydrochloric acid, sulfuric acid, acetic acid, and formic acid. In an embodiment, the recovered 2,4-Dichlorophenol can be recycled or reused for the preparation of the alkali metal salt of 2,4-Dichlorophenol.
The process of the present invention provides water content in the reaction between 0.6V to 2.5V for forming said alkali metal salt of 2,4-Dichlorophenol and forming said alkali metal salt of monochloroacetic acid. The reaction can proceed efficiently with quantity of water in the range between 0.6V to 2.5V. Apparently, water quantity less than 0.6V and more than 2.5V may cause reduction, which ultimately results in more alkali metal glycolate formation in the reaction.
In the process of preparing the compound of Formula (I), alkali metal glycolate formed in a quantity above 100 ppm is undesirable. The process of the present invention thus provides the improved process of preparing compound of Formula (I) with a significantly less amount of alkali metal glycolate by preparing the alkali metal salt of MCA in situ and controlled conversion of 60% to 90% of alkali metal salt of 2,4-dichlorophenol and formation of in situ alkali metal salt of MCA by carrying out the conversion at a temperature in the range of about 80°C to 150°C and pH of about 8.5 to 9.5.
Effluent from the reaction generally contains alkali metal glycolate. Alkali metal glycolate is known to kill bacteria, therefore biological treatment of the effluent may not be feasible. Hence effluent is generally treated with chemical or physicochemical methods such as distillation, incineration and filtration. Such chemical treatments are expensive and increases operational costs. The reduction in the amount of alkali metal glycolate formed in the present invention reduces the cost of effluent treatments. Further, recycling of alkali metal salt of 2,4-DCP and recovery and recycle of 2,4,DCP also makes the process of the present invention economical and efficient.
2,4-dichlorophenoxy acetic acid and its salt prepared by the present invention is useful as a systemic herbicide and known as a weed killer which selectively kills most terrestrial and aquatic broadleaf weeds by causing uncontrolled growth in them.

EXAMPLES
Example and implementation is provided herein below for illustration of the invention. Variations, modifications, and enhancements to the described examples and implementations and other implementations can be made based on what is disclosed.
Example is set forth herein below and is illustrative of different amounts and types of reactants and reaction conditions that can be utilized in practicing the disclosure. It will be apparent, however, that the disclosure can be practiced with other amounts and types of reactants and reaction conditions than those used in the examples, and the resulting devices various different properties and uses in accordance with the disclosure above and as pointed out hereinafter.

EXAMPLE 1-
Preparation of 2,4-dichlorophenoxy acetic acid (With optimized moles, pH, temperature and recycling of aqueous layer)
Solid 2,4-Dichlorophenol flakes (100 g, or 0.6135 moles, or 1 molar equivalent) were heated and melted at 60-65°C. 32 % w/w solution of sodium hydroxide (27 gm, or 0.675 moles, or 1.10 molar equivalent) (27 gm NaOH dissolved in 57.37 ml water) was added gradually and addition is completed in 15-20 minutes. The mass was maintained for 30 minutes at 60-65°C. The temperature of the mass was raised to 100-110°C. Addition of monochloroacetic acid (75% w/w) (35 gm or 0.3703 moles or 0.60 molar equivalent) (35 gm dissolved in 11.67 ml of water) and 32% w/w solution of Sodium hydroxide (32%) (14.8gm or 0.37 moles or 0.60 molar equivalent) (14.8 gm NaOH dissolved in 31.45 ml water) was charged gradually and simultaneously in equimolar proportion to the reaction mass over the period of 40-45 minutes at 100-110°C. The pH was maintained between 8.5-9.5 during course of the reaction. After complete addition the mass was maintained for 1 hour at 100-110°C. After completion of reaction sodium hydroxide (14.8 gm or 0.37 moles or 0.61 molar equivalent, 32% solution 14.8 gm NaOH and 31.45 gm water) was added. The mass was maintained at 100-110°C for 30 minutes. The mass was cooled gradually to 60-65°C, filtered and suck dried. Mother liquor (MLR) was recycled in the next batch. The suck dried material was slurried with water (2V) at 60-65°C and filtered. The washing MLR was distilled and recycled in the next reaction along with main MLR. The solid material obtained was dried at 60-65°C under vacuum for 6-7 hours.
Yield: 87.6 gm (98%), Glycolate content in solids is: Less than 10 ppm.
The reaction conversion is 60% and sodium glycolate is 650 ppm in MLR.
Total water used in reaction is 57.37+11.67+31.45 =100.50 gm = 1.0 V of DCP; 25 ml water remains with solid. Net water = 75.50 ml.

EXAMPLE 2-
PREPARATION OF 2,4-DICHLOROPHENOXY ACETIC ACID (1ST RECYCLE OF MLR)
Fresh Solid 2,4-dichlorophenol (60 gm, 0.3680 moles) was charged to MLR obtained from example 1 and heated to 60-65°C till 2,4-dichlorophenol melts. The MLR contains 40 gm (0.2453 moles) of 2,4-Dichlorophenol in the form of sodium salt of 2,4-DCP resulted in total 100 gm (0.6135 moles, 1.0 molar equivalent) 2,4-DCP. The mass was maintained under stirring for 30 minutes at 60-65°C. During this 2,4-DCP reacts with the NaOH available in MLR and forms sodium salt of 2,4-DCP. Raise the temperature of the mass to 100-110°C. Monochloroacetic acid (35 g, 75% solution, 0.3703 moles, 0.6 molar equivalent) and sodium hydroxide (14.8 gm, 32% solution, 0.37 moles, 0.60 molar equivalent) was gradually and simultaneously in equimolar proportion charged to the reaction mass within 40-45 minutes at 100-110°C. The pH of the reaction mass was maintained between 8.5-9.5. After completion of addition, the mass was maintained for 1 hour at 100-110°C. After completion of the reaction, sodium hydroxide (14.8 gm, 32% solution, 0.37 moles, 0.60 molar equivalent) was added to the reaction mass and maintained for 30 minutes at 100-110°C. The mass was cooled to 60-65°C, filtered and suck dried. MLR was recycled in the next batch. The suck dried material was slurried with water (2V) at 60-65°C and filtered. The washing MLR was distilled and recycled in the next reaction along with main MLR. The solid material obtained was dried at 60-65°C under vacuum for 6-7 hours.
Yield: 87.4 gm (98%), Glycolate content in final product: Less than 10 ppm.
The reaction conversion is 60% and sodium glycolate is 730 ppm in Reaction mass.
The water used in the reaction mass is 57.37+11.67+31.45+70.5 (from 1st batch) = 170.99 ml; 25 ml water remains with solids. Net water =146 ml.

EXAMPLE 3-
PREPARATION OF 2,4-DICHLOROPHENOXY ACETIC ACID (2ST RECYCLE OF MLR)
Fresh Solid 2,4-dichlorophenol (60 gm, 0.3680 moles) was charged to MLR obtained from example 2 and heated to 60-65°C till 2,4-dichlorophenol melts and reacts with the equivalent NaOH in MLR, the MLR contains 40 gm (0.2453 moles) 2,4-Dichlorophenol in the form of sodium salt of 2,4-DCP resulted in total 100 gm (0.6135 moles, 1.0 molar equivalent 2,4-DCP. Monochloroacetic acid (35 g, 75% solution, 0.3703 moles, 0.6 molar equivalent) and sodium hydroxide (14.8 gm, 32% solution, 0.37 moles, 0.60 molar equivalent) was gradually and simultaneously in equimolar proportion charged to the reaction mass within 40-45 minutes at 100-110°C. The pH of the reaction mass was maintained between 8.5-9.5. After completion of addition, the mass was maintained for 1 hour at 100-110°C. After completion of the reaction, sodium hydroxide (14.8 gm, 32% solution, 0.37 moles, 0.60 molar equivalent) was added to the reaction mass and maintained for 30 minutes at 100-110°C. The mass was cooled to 60-65°C, filtered and suck dried. The mass was cooled to 60-65°C, filtered and suck dried. The suck dried material was slurried with water (2V) at 60-65°C and filtered. The solid material obtained was dried at 60-65°C under vacuum for 6-7 hours.
Yield: 87.2 gm (98%), Glycolate content in final solid: Less than 10 ppm.
The reaction conversion is 60% and sodium glycolate is 810 ppm in Reaction mass.
The water used in the reaction mass is 57.37+11.67+31.45+146 (from 2nd batch) = 246.50 ml.

EXAMPLE 4-
RECOVERY OF 2,4-DICHLOROPHENOL
pH of the combined MLR from example 3 is 7-9. It was heated to 40-45°C and the pH was adjusted to 3-4 using 30% concentrated hydrochloric acid. The two layers obtained after pH adjustment were separated. The organic layer containing 2,4-DCP was taken in the next batch as a fresh material. The aqueous layer was sent for ETP treatment.
The reaction was repeated with 0.7, 0.75, 0.8, 085 and 0.9 molar equivalent of monochloroacetic acid and NaOH i.e. when the reaction conversion is 70%, 75%, 80%, 85% and 90% with the same reaction procedure described in Examples 1-4 at optimized temperature conditions. Below Table 1 is illustrative for showing the results.
TABLE 1
Moles Temperature % yield % Purity Sodium glycolate content in MLR (ppm) Sodium glycolate content in Compound (I)
0.7 110-115°C 98.11% 99.90% 720 3
0.7 (1st MLR recycle) 110-115°C 97.8% 99.85% 760 4
0.7 (2nd MLR recycle) 110-115°C 97.65% 99.80% 800 6
0.75 115-120°C 99.56% 99.75% 770 5
0.75 (1st MLR recycle) 115-120°C 98.75% 99.80% 805 6
0.75 (2nd MLR recycle) 115-120°C 97.85% 99.83% 840 7
0.8 125-130°C 98.98% 99.77% 810 6
0.8 (1st MLR recycle) 125-130°C 98.83% 99.79% 850 7
0.8 (2nd MLR recycle) 125-130°C 92.89% 99.82% 880 7
0.85 140-145°C 99.85% 99.84% 930 8
0.85 (1st MLR recycle) 140-145°C 99.72% 99.75% 940 8
0.85 (2nd MLR recycle) 140-145°C 97.35% 99.54% 960 9
0.9 145-150°C 98.81% 99.75% 960 8
0.9 (1st MLR recycle) 145-150°C 98.35% 99.62% 975 9
0.9 (2nd MLR recycle) 145-150°C 97.91% 99.71% 990 9

EXAMPLE 5-
COMPARATIVE EXAMPLE - PREPARATION OF SODIUM SALT OF 2,4-DICHLOROPHENOXY ACETIC ACID
Dichlorophenol (100 gm, 0.6135 moles, 1 molar equivalent) was heated to 55-60°C and 40% sodium hydroxide (27 gm, 0.675 moles, 1.1 molar equivalent) was charged dropwise to the molten mass. The reaction mass was maintained under stirring for 30 minutes at 55-60°C. The temperature was raised to 115-120°C. 40% solution of sodium monochloro acetate (78.62 gm, 0.6748 moles, 1.10 molar equivalent) was added dropwise at 115-120°C for 6-7 hours by maintaining pH 8.5-9.5. After complete addition, reaction mass was maintained for 3 hours. After completion of the reaction, the reaction mass was cooled up to 60-65°C. The mass was filtered in hot condition at 60-65°C and the solid was suck dried. 2V Water washing is given to the solids and then suck dried. The solid was further dried at 70°C for 6 hours under vacuum to yield sodium salt of 2,4-dichlorophenoxy acetic acid.
(Yield: 146 gm, 98%) Purity: 99.7%. Glycolate content in final solids: 385 ppm.
The reaction conversion is 98.8% and sodium glycolate is 13000 ppm in MLR.

EXAMPLE6-
COMPARISON OF IN SITU SODIUM MONOCHLOROACETATE (SMCA) PREPARED AND SEPARATELY PREPARED SMCA
Table 2 below, explains the impact of higher number of moles of sodium salt of monochloroacetic acid (SMCA) on conversion of 2,4-dichlorophenol (2,4-DCP) to 2,4-dichlorophenoxy acetic acid (2,4-DCPAA) and formation of sodium glycolate at 110-125°C.
Table 2 shows reaction results of SMCA separately prepared (For comparison of in situ SMCA prepared as shown in Table 2). Results with both SMCA prepared in house and SMCA outsourced are shown in separate tables.
TABLE 2
NaOH: 1.1M and 2,4 DCP: 1 M SMCA-IN HOUSE PREPARED
Reagent Molar ratio IC Result HPLC Result
SMCA (ppm) Sodium Glycolate in MLR (ppm) 2,4 DCPAA 2,4 DCP
SMCA 0.3 0 5498 28.12% 71.63%
SMCA 0.4 0 5556 39.60% 60.26%
SMCA 0.5 2242 6023 48.59% 49.97%
SMCA 0.6 3235 7381 56.97% 42.88%
SMCA 0.7 6449 8472 66.53% 33.31%
SMCA 0.8 9527 9711 75.47% 24.43%
SMCA 0.9 14333 11738 78.29% 21.55%
SMCA 1 27922 14829 83.53% 16.24%

NaOH: 1.1M and 2,4 DCP: 1 M SMCA-OUTSOURCED
Reagent Molar ratio IC Result HPLC Result
SMCA (ppm) Sodium Glycolate in MLR (ppm) 2,4 DCPAA 2,4 DCP
SMCA 0.3 21 3403.8 29.19% 70.83%
SMCA 0.4 2 4014.8 38.60% 61.56%
SMCA 0.5 1 4037.3 50.76% 49.11%
SMCA 0.6 1 5141.2 59.39% 39.47%
SMCA 0.7 10 5774.0 67.53% 31.78%
SMCA 0.8 75 6679.6 75.53% 23.47%
SMCA 0.9 223 8093.7 80.21% 18.68%
SMCA 1 1065 12069.4 84.18% 15.32%

It is clear from above Table 2 that, reaction proceeds smoothly up to 0.6-0.7 molar equivalent of monochloroacetic acid. As number of molar equivalent of sodium monochloroacetic acid (SMCA) increases, the conversion rate decreases due to low concentration of 2,4-DCP in MLR, which result in longer exposure of SMCA to higher temperature and end with formation of sodium glycolate. This is particularly observed because of formation of sodium glycolate as a side product reaction becomes slow. Sodium glycolate content in the MLR observed is >10000 PPM, when the molar equivalent of sodium monochloroacetic acid (SMCA) is more than 0.9. As the molar equivalent of sodium monochloroacetic acid increases, the Sodium glycolate content in the MLR analyzed is much higher than 10000 PPM. It is observed that due to presence of high product concentration and sodium glycolate content the reaction becomes sluggish.
Thus optimization can be done with 0.6-0.9 molar equivalent, preferably 0.6-0.8 molar equivalent of sodium monochloroacetic acid. 2,4-dichlorophenol is converted to its alkali metal salt such as sodium, potassium or calcium salt. One mole Equivalent of sodium, potassium or calcium salt of 2,4-dichlorophenol is treated with 0.6-0.9 molar equivalent of monochloroacetic acid in presence of suitable alkali in equimolar (0.6-0.9) proportion. The alkali can be selected from sodium hydroxide, potassium hydroxide and calcium hydroxide.
TABLE 3
NaOH: 1.1M. Equ and 2,4 DCP: 1 M. Eqv NaOH 1.0 M Eqv
Reagent Molar ratio IC Result HPLC Result
SMCA (ppm) Sodium glycolate in MLR (ppm) 2,4 DCPAA 2,4 DCP
MCA NaOH 0.4 768 419 39.01% 60.73%
MCA NaOH 0.5 860 585 49.7 49.7
MCA NaOH 0.6 522 650 59.8 40.1
MCA NaOH 0.7 1589 1028 65.1 34.5
MCA NaOH 0.8 1321 1062 70.8 28.9
MCA NaOH 0.9 1138 1124 77.9 22.0
MCA NaOH 1 1215 1259 83.4 16.22

From Table 2 and 3 it is clear that when separately prepared SMCA is used in the reaction, we cannot control its decomposition to sodium glycolate and sodium glycolate formation is much higher even at low molar equivalent. This can be controlled when the SMCA is prepared in situ.

EXAMPLE 7–
EFFECT OF IN SITU SMCA PREPARATION
It is observed that, when externally synthesized SMCA is used in the reaction, the sodium glycolate formation is comparatively higher than the reaction, in which the SMCA is prepared in situ. As shown in the above reaction sequence, a molecule of SMCA, when comes in contact with water or sodium hydroxide molecule, immediately gets converted to sodium glycolate. Thus separately prepared and stored SMCA contains sodium glycolate, which is carry forwarded in the reaction of preparation of sodium salt of 2,4-dichlorophenoxy acetic acid. To avoid this, SMCA is prepared in situ, which is immediately converted to sodium salt of 2,4-dichlorophenoxyacetic acid. Thus unwanted side reactions are avoided.

EXAMPLE 8-
EFFECT OF MOLE RATIO OF DICHLOROPHENOL TO MONOCHLOROACETICACID
When one mole of sodium 2,4-dichlorophenol is reacted with 1.05 molar equivalent of monochloroacetic acid (MCA) & NaOH is used it was observed that, after consumption of 0.6-0.7 molar equivalent of monochloroacetic acid and NaOH, the reaction becomes slow and takes longer time for completion of the reaction due to formation of sodium glycolate by decomposition of SMCA.
The study of effect molar equivalent of SMCA used in the reaction on the % conversion of reactants was carried out. The time required for reaction completion at different temperatures and with 1.05, 1.15, and 1.3 molar equivalent of MCA is studied. Table 4 below illustrates the effect of temperature and number of moles of SMCA on complete conversion of the reaction.
TABLE 4
Reagents Molar equivalents HPLC Analysis Time (complete conversion) Yield
Reaction Temperature = 80-85°C
2,4 DCP 1 2,4-DCPAA= 98.36% 8 hrs 97.5%
NaOH 1.1
MCA 1.3 2,4-DCP= 1.07%
NaOH 1.4
Sodium glycolate >10,000 ppm
2,4 DCP 1 2,4-DCPAA= 95.83% 16 hrs 95%
NaOH 1.10
MCA 1.15 2,4-DCP= 3.54%
NaOH 1.25
Sodium glycolate >10,000 ppm
2,4 DCP 1 2,4-DCPAA=92.48 % 18 hrs 92%
NaOH 1.10
MCA 1.05 2,4-DCP= 7.08%
NaOH 1.15 Sodium glycolate >10,000 ppm

The reaction is carried out with variable molar equivalent of MCA and NaOH at 80-85°C. It can be concluded from the above Table 4, that as number molar equivalent of MCA increases, reaction takes longer time and still does not show complete conversion. Hence the same reaction was tried at 100-110°C and the results obtained are stated in below Table 5.
TABLE 5

Reagents Molar equivalents HPLC Analysis Time (complete conversion) Yield
Reaction Temperature = 100-110°C
2,4 DCP 1 2,4 DCPAA=99.49% 2 hrs 98.5%
NaOH 1.10
MCA 1.3 2,4DCP= 0.29%
NaOH 1.4
Sodium glycolate >10,000 ppm
2,4 DCP 1 2,4 DCPAA=97.89% 4-5 hrs 97.5%
NaOH 1.10
MCA 1.15 2,4DCP= 1.56%
NaOH 1.25
Sodium glycolate >10,000 ppm
2,4 DCP 1 2,4 DCPAA=98.02 % 5-6 hrs ~98%
NaOH 1.10
MCA 1.05 2,4DCP= 0.68%
NaOH 1.15 Sodium glycolate >10,000 ppm

It can be concluded from the above Table 5, that the reaction shows almost complete conversion at 100-110°C even with less molar equivalents (1.05) of MCA and NaOH.
Further the same reaction of the present invention was also carried at 110-125°C with 1.05 molar equivalent of MCA and is illustrated in below Table 6.
TABLE 6
Reagents Molar equivalents Temp HPLC Analysis Time (complete conversion) Yield
2,4 DCP 1 110-125°C 2,4 DCPAA=98.68% 2-3 hrs 98%
NaOH 1.10
MCA 1.05 2,4DCP= 1.16%
NaOH 1.15
Sodium glycolate >10,000 ppm
The above Table 6 shows that the time required for complete conversion minimizes at higher temperature.

Thus from the above illustrations in Table 4, Table 5 and Table 6, it is concluded that reaction conversion observed is maximum using 1.05 molar equivalent of MCA at reaction temperature 110-125°C. However it is observed that the sodium glycolate content which is formed as a side product in the reaction is more than 10,000 ppm.

We can conclude from Table 2, 3, 4, 5, and 6 that less molar equivalent of MCA and NaOH or in situ SMCA at higher temperature will result in less sodium gylcolate formation compared to higher molar equivalent of MCA and NaOH or in situ SMCA at higher temperature due to increase in reaction rate and less decomposition of SMCA.

EXAMPLE 9-
STUDY OF REACTION CONDITIONS
The reaction conditions are studied to minimize the sodium glycolate formation and to obtain maximum conversion of the reactants. In this study, the reaction conditions are studied in which sodium glycolate is formed.
In the main course of reaction, one mole of sodium dichlorophenate (SDP) is reacted with one mole of Sodium monochloroacetate (SMCA) to form one mole of sodium-2,4-dichlorophenoxy acetate and a mole of sodium chloride.

It is observed that along with main reaction, the below side reactions (a) and (b) also occur.
(i) SMCA and water undergoes a reaction which produces sodium glycolate and one mole of hydrochloric acid.

Due to presence of sodium hydroxide in the reaction mixture, HCl formed in the reaction is neutralized to sodium chloride and water.
(ii) SMCA also reacts with sodium hydroxide to form sodium glycolate and water.

Thus stoichiometric ratio of monochloroacetic acid or SMCA and sodium hydroxide is to be controlled to avoid any side reactions, taking place due to free mole of sodium hydroxide and sodium monochloroacetate.
The reaction conditions are studied for formation of sodium glycolate and various factors contributing the same. It is observed that number of moles of monochloroacetic acid, sodium hydroxide and temperature also contribute for the purpose.
It is also observed that sodium glycolate formation, where separately synthesized SMCA is used, is higher than the reaction in which SMCA is prepared in situ. Mode of addition of SMCA or MCA also plays an important role in complete conversion and sodium glycolate formation.
It is observed that during reaction, rate of addition of reagents also plays an important role. If the addition of the reagents is faster, the reaction does not go to completion. This is due to decomposition of SMCA or MCA in the reaction and formation of sodium glycolate in the reaction.
It is also observed that reaction conversion is maximum and sodium glycolate formation is minimum at controlled pH between 8.5-9.5. Hence the rate of addition should be controlled such that pH of the reaction is constantly maintained between 8.5-9.5.
Hence mode of addition of reagents in the reaction, temperature, preparation of SMCA in situ, effect of water quantity present in the reaction was studied separately, which constitutes a part of different embodiments of the present invention.

EXAMPLE 10-
EFFECT OF TEMPERATURE
It is observed that temperature plays very important role in the reaction. The effect of temperature on similar reaction conditions is studied in the present invention. Table 1-3 above clearly states effect of temperature on the conversion rate and ultimately formation of sodium glycolate impurity. Thus it is observed that when the reaction is carried out at lower temperature for e.g. at 80-90°C, the rate of the reaction is less and hence more time and more molar equivalent of monochloroacetic acid and NaOH are required for completion of reaction. This ultimately results in more formation of sodium glycolate impurity. At 100-125°C, the molar equivalent of MCA is less and reaction rate is fast and hence sodium glycolate formation is comparatively lesser. So it can be concluded that if the molar equivalent of MCA is less (0.6 - 0.9) and temperature is high (100-150°C), the reaction completion will be much faster and sodium glycolate formation is lesser.

EXAMPLE 11-
EFFECT OF pH AND MODE OF ADDITION
As stated above, during preparation of SMCA, sodium glycolate is formed as a byproduct due to decomposition of SMCA. Thus mode of addition of SMCA should be controlled in such a manner, that decomposition of SMCA into sodium glycolate is least. However during preparation of SMCA, formation of sodium glycolate takes place, hence to avoid formation of sodium glycolate, SMCA is prepared in situ using MCA and NaOH solution. Thus the solution of sodium salt of 2,4-dichlorophanol is prepared separately. To this solution monochloroacetic acid and sodium hydroxide solution is added simultaneously and in controlled manner. The addition is done within 3-5 hours in such a manner that pH of the reaction mass was maintained between 8.5-9.5. At higher pH, presence of NaOH is more, which leads to more decomposition of SMCA and formation of sodium glycolate. At lower pH i.e. at acidic pH, the sodium salt of 2,4-DCP gets converted to 2,4-DCP, which results in termination of the reaction.

EXAMPLE 12-
EFFECT OF WATER CONTENT
It is observed during the reaction that if water content is more in reaction or dilution is more the reaction proceeds very slowly or sometimes stops at lower conversion due to decomposition of SMCA at higher temperature as shown in above reaction sequence. It is also observed that during reaction if water content is less, the reaction mass becomes very thick, which is not stirrable, which leads to incomplete conversion. Hence the optimum conditions were derived and concluded that minimum 0.6V with respect to 2,4-DCP of water is required with for forming said alkali metal salt of 2,4-dichlorophenol and forming said alkali metal salt of monochloroacetic acid to proceed reaction smoothly. It was observed that if maximum water for forming said alkali metal salt of 2,4-dichlorophenol, and forming said alkali metal salt of monochloroacetic acid is NMT 2.5V with respect to 2,4-DCP, the reaction proceeds smoothly with lesser alkali metal glycolate formation.
Thus from above study it is observed that maximum conversion and minimum alkali metal glycolate formation occurs at lower molar equivalent of MCA, at higher temperature by maintaining the conditions of pH, mode of addition and water content. Further it was observed that as molar equivalent of MCA is used is less, the conversion of 2,4-DCP is also less. The remaining unreacted alkali metal salt of 2,4-DCP is recycled in the next batch. pH of the reaction mass is adjusted to 8.5-9.5 and reaction is carried out at 90-150°C, preferably at 100-130°C, particularly at 100-125°C. 0.6-0.9 molar equivalent of MCA is used in the reaction for optimum results. The reaction shows quantitative 60-90% conversion and remaining 10-40% of unreacted alkali metal salt of 2,4-dichlorophenol is recycled in the next batch along with addition of fresh 2,4-dichlorophenol. This can be carried out in batch process or continuous process by controlling formation of sodium glycolate. The results from the batch processes can be specifically seen from illustrated examples above. After last recycle the unreacted alkali metal salt of 2,4-DCP is recovered by adjusting the pH to 3-4 with acid. The solid recovered 2,4-DCP is filtered and recycled in the next reaction batch.

The foregoing description of specific embodiments of the present invention has been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching.

The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others, skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated.

It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.

,CLAIMS:

1. A process for preparing alkali metal salt of 2,4-Dichlorophenoxy acetic acid of Formula (I)

wherein X = Na, K, or Ca comprising:
(i) adding 2,4-Dichlorophenol and alkali metal hydroxide forming an alkali metal salt of 2,4-Dichlorophenol;
(ii) forming in situ an alkali metal salt of monochloroacetic acid by adding 0.6 to 0.9 molar equivalent of monochloroacetic acid, and 0.6 to 0.9 molar equivalent of an alkali metal hydroxide to said alkali metal salt of 2,4-Dichlorophenol; and
(iii) converting 60% to 90% of said alkali metal salt of 2,4-Dichlorophenol and said in situ alkali metal salt of monochloroacetic acid to compound of Formula (I) and 1 ppm to 10 ppm alkali metal glycolate at a temperature of 80°C to 150°C and pH at 8.5 to 9.5.

2. The process as claimed in claims 1, wherein comprises recycling 10% to 40% unreacted alkali metal salt of 2,4-Dichlorophenol, adding 0.6 to 0.9 molar equivalent of 2,4-dichlorophenol and 0.6 to 0.9 molar equivalent of alkali metal hydroxide forming said alkali metal salt of 2,4-Dichlorophenol.

3. The process as claimed in claims 1 or 2, wherein further comprises recovering 2,4-Dichlorophenol by adjusting pH between 3 to 5 with an acid.

4. The process as claimed in claim 3, wherein the acid is selected from hydrochloric acid, sulfuric acid, acetic acid and formic acid.

5. The process as claimed in claims 3 to 4, further comprises recycling said recovered 2,4-Dichlorophenol for forming said alkali metal salt of 2,4-Dichlorophenol.

6. The process as claimed in claim 1 to 5, wherein comprises 0.6V to 2.5V water for forming said alkali metal salt of 2,4-Dichlorophenol, forming said alkali metal salt of monochloroacetic acid.

7. The process as claimed in claim 1, wherein the alkali metal hydroxide is selected from the group comprising of sodium hydroxide, potassium hydroxide or calcium hydroxide.

8. The process as claimed in claim 1, wherein the in situ alkali metal salt of monochloroacetic acid is sodium monochloroacetate, potassium monochloroacetate or calcium monochloroacetate.

9. The process as claimed in claims 1 to 8, wherein the alkali metal glycolate is sodium glycolate, potassium glycolate or calcium glycolate, preferably sodium glycolate.

10. The process as claimed in claims 1 to 9, wherein the process is a continuous process.