RU2757739C1 - Method for synthesising 2,4-dichlorophenoxyacetic acid - Google Patents

Abstract

FIELD: organic chemistry.

SUBSTANCE: invention relates to the field of organic chemistry, specifically to synthesis of the chemical compound 2,4-dichlorophenoxyacetic acid, organic and inorganic salts, esters and mixed preparations whereof which are well-known herbicides. The invention relates to a method for producing 2,4-dichlorophenoxyacetic acid, including a stage of synthesising a calcium salt of phenoxyacetic acid by condensation of phenol with monochloroacetic acid and calcium oxide at elevated temperature while mixing, a stage of chlorination of the calcium salt of phenoxyacetic acid with a chlorinating agent and isolation of the target product by a known method, wherein the calcium salt of phenoxyacetic acid is synthesised in the melt of the initial reagents at the temperature of self-heating of the reaction mixture.

EFFECT: technical result is an improved non-waste technology for obtaining the target product, wherein chlorine-substituted phenols and, therefore, dioxins, are not formed.

1 cl, 4 dwg, 1 tbl, 7 ex

Description

The invention relates to the field of organic chemistry, specifically to the synthesis of the chemical compound 2,4-dichlorophenoxyacetic acid (2,4-D), a well-known herbicide, which in the form of organic and inorganic salts, esters and mixtures is widely used to combat dicotyledonous and broadleaf weeds in cereal crops.

Of the large number of known methods for the preparation of 2,4-dichlorophenoxyacetic acid, only two are of practical importance for industrial production. The first method is based on the condensation of sodium salts of monochloroacetic acid with 2,4-dichlorophenolates in an aqueous solution or anhydrous media:

In turn, sodium 2,4-dichlorophenolate is obtained by direct chlorination of phenol with chlorine in organic solvents or in a melt, followed by interaction with sodium hydroxide:

2,4-Dichlorophenoxyacetic acid obtained by this method almost always contains a certain amount of 2,4-dichlorophenol, which gives a specific unpleasant odor. In addition, in an alkaline environment, especially at elevated temperatures, highly toxic compounds - chlorine-substituted dioxins - are formed from 2,4-dichlorophenol as impurities.

The second method for the preparation of 2,4-dichlorophenoxyacetic acid is based on the chlorination of phenoxyacetic acid:

Phenoxyacetic acid is obtained by the reaction of sodium phenolate with monochloroacetate in an aqueous solution at a temperature of 105-107 ° C:

During the condensation reaction, alkaline hydrolysis of monochloroacetic acid occurs with the formation of a significant amount of glycolic acid, which reduces the yield of phenoxyacetic acid and increases the amount of unreacted sodium phenolate in the target product. (NN Melnikov "Pesticides" Chemistry, technology and application, Moscow, Chemistry, 1987, pp. 229-232).

A known method of producing phenoxyacetic acid and its substituted (USSR Inventor's Certificate No. 84982, С07С 59/70, declared in 1949) by condensation, under pressure and without pressure of an alkali metal phenolate with an alkaline salt of chloroacetic acid, taken in equimolecular amounts, with the addition of the reaction mixture of sodium chloride to obtain its concentration of 10% and higher, followed by the isolation of the reaction product in a known manner. To obtain 2,4-dichlorophenoxyacetic acid, 2,4-dichlorophenol is dissolved in sodium hydroxide solution and sodium chloride is added. A solution of sodium chloroacetic acid is quickly added to the mixture with stirring. The reaction mixture is heated for 2 hours at a temperature of 150-155 ° C and a pressure of 3.4-3.7 atm. After that, the mixture is cooled to a temperature of 15-20 ° C and the precipitated crystals of sodium 2,4-dichlorophenoxyacetic acid are filtered off, squeezed out and washed with alcohol. When neutralizing the reaction mass with a mineral acid, free acid is obtained with a yield of 86-89% of the theoretically possible.

The disadvantages of this method are:

- low yield of the target product (86-89%);

- the need for effective separation of sodium chloride and the target product;

- a large amount of generated wastewater, causing environmental pollution.

A known method of producing 2,4-dichlorophenoxyacetic acid (USSR author's certificate No. 97724, С07С 59/70, 1954) by condensation of sodium 2,4-dichlorophenolate with an aqueous solution of sodium salt of monochloroacetic acid in a direct-flow condenser at a temperature of 150-180 ° C under a pressure of 10-15 atm. After condensation, the reaction mass is sent to a spray dryer for drying. The yield of the target product is 88-92%.

The disadvantages of this method are:

- insufficiently high yield of the target product (88-92%);

high condensation temperature (150-180 ° C) promotes the formation of highly toxic compounds - chlorine-substituted dioxins;

- high pressure 10-15 atm., which complicates the production technology.

A known method of producing 2,4-dichlorophenoxyacetic acid (USSR author's certificate No. 118508, С07С 59/70, 1959) by the action of a 40% sodium hydroxide solution on an alloy of 2,4-dichlorophenol with chloroacetic acid at a reaction mixture temperature of 40-60 ° C, after which heating is continued at 60-65 ° C for 2 hours, and to complete the reaction, the mixture is heated for another 3-4 hours at a temperature of 100 ° C.

Hot water is added to the hot semi-solid mass and the mixture is thoroughly stirred while heating in a water bath for 1 hour. After cooling to room temperature, the reaction mass is filtered off and for final washing from 2,4-dichlorophenol, washed with dilute alkali, filtered, washed twice on the filter with a small amount of water. The obtained sodium salt of 2,4-dichlorophenoxyacetic acid is dried in a steam dryer.

Next, the salt is dissolved in boiling water (for 1 weight part of the salt 15 weight parts of water), filtered, to the filtrate heated to 50-60 ° C, 15% hydrochloric acid is gradually added with stirring until the acid reaction. After a precipitate has formed, the mixture is cooled to room temperature, the precipitate is thoroughly washed with water until hydrochloric acid is removed and dried in a steam dryer (70-90 ° C). The expected product is obtained in 78% yield (based on 2,4-dichlorophenol). For final purification, the product is recrystallized from 35% acetic acid.

The disadvantages of this method are:

- low yield of the target product (78%);

- large volumes of waste water;

- quite a lot of physical stages for the isolation and purification of the target product: cooling, filtration, washing, settling, drying, recrystallization, which increases the cost of maintaining equipment and complicates the process.

A known method of producing aryloxyalkyl carboxylic acids (USSR Inventor's Certificate No. 187766, С07С 59/70, 1966) by condensation of phenol or orthocresol or their derivatives with chloralkyl carboxylic acids in ratios from 1.2: 1 to 2: 1 in ethylene glycol at pH 8- 11 and a temperature of 105-120 ° C.

To obtain 2,4-dichlorophenoxyacetic acid, crystalline monochloroacetic acid (molar ratio 1.2: 1), ethylene glycol, sodium hydroxide in the form of a 42% solution are loaded to molten dichlorophenol, while maintaining the temperature not higher than 20 ° C and stirring thoroughly; The pH of the medium is 10. The mass is heated by conducting a condensation reaction at 110 ° C for 4 hours. The condensed mass is acidified to pH 6-6.5 and subjected to vacuum distillation of ethylene glycol with unreacted dichlorophenol (residual pressure 30-40 mm Hg). The product is acidified, the free acid is isolated and dried. The yield of 2,4-dichlorophenoxyacetic acid is 90.5-96%, the content of the basic substance is 96-96.5%), dichlorophenol 0.9-1%, sodium chloride 1.1%, moisture 1.9%.

The disadvantages of this method are:

- insufficiently high yield and quality of the target product;

- significant contamination of the target product with dichlorophenol (up to 1%);

- the need for additional technological operations to separate unreacted dichlorophenol and ethylene glycol.

A known method of producing 2,4-dichlorophenoxyacetic acid (USSR author's certificate No. 220978, S07C 59/70, 1968) by chlorination of a thin suspension of phenoxyacetic acid with chlorine at a temperature of 60-65 ° C in an aqueous or hydrochloric acid medium for 3 hours and pressure from normal to 5-10 mm of water. Art. The reaction mixture is stirred, cooled to room temperature, filtered on a drum vacuum filter and washed with water. The target product is obtained in the form of a paste with a yield of up to 80%.

The disadvantages of this method are:

- low yield of the target product (up to 80%);

- the product in the form of a paste is inconvenient for further work with it.

A known method of producing chlorine-substituted aryloxyalkylcarboxylic acids (USSR author's certificate No. 256750, S07C 59/70, 1970). To obtain 2,4-dichlorophenoxyacetic acid, phenol is condensed with monochloroacetic acid, taken in a ratio of 1.2: 1, in a hexachlorobutadiene medium in the presence of a 30-42% aqueous solution of sodium hydroxide at a temperature of 110-115 ° C for 2 hours ... Then the reaction mass is cooled to 80 ° C, acidified with concentrated hydrochloric acid to pH 2-2.5, hot water is added, stirred, settled and the layers are separated. The organic (lower) layer is evaporated (pressure 30 mm Hg) to approximately half of the original volume and a suspension is obtained containing phenoxyacetic acid present in the remainder of hexachlorobutadiene. Chlorine is passed through the resulting suspension at a temperature of 125-130 ° C and vigorous stirring. The yield of 2,4-dichlorophenoxyacetic acid is 89.5%.

The disadvantages of this method are:

- low yield of the target product;

- the use of an organochlorine solvent, high chlorination temperatures, the need to use a vacuum complicate the process technology.

A known method of producing 4-chlorophenoxyacetic or 2,4-dichlorophenoxyacetic acids (RU 2082711, С07С 59/70, С07С 51/363, 1997) by chlorination of phenoxyacetic acid with gaseous chlorine in an environment of glacial acetic acid and acetic anhydride or a mixture of acetic anhydride carbon (methyl chloroform, tetrachloroethane, perchlorethylene, carbon tetrachloride) in the presence of sodium chloride at a temperature of 60-65 ° C. Isolation is carried out by crystallization at 8-13 ° C. The yield of the target product is 85-89%; the content of the basic substance is 97-99%, the content of dichlorophenol is 0.08-0.2%.

The disadvantages of this method are:

- low yield of the target product (85-89%);

- the presence of toxic dichlorophenol in the product, which is prone to the formation of dioxins;

- the use of an organochlorine solvent leads to stress corrosion cracking, which imposes increased requirements on structural materials and increases the cost of the process.

A known method of producing purified 2,4-dichlorophenoxyacetic acid (RU 2149157, С07С 59/70, С07С 51/347, 2000) by condensation of technical 2,4-dichlorophenol with monochloroacetic acid in an alkaline medium at 100-110 ° С, followed by acidification the reaction mass to pH 1-2 in the presence of an organic solvent such as perchlorethylene or toluene and the isolation of the target product by crystallization from the organic solvent with cooling to 5-30 ° C, filtration and drying of the resulting product. As a result, dry 2,4-dichloro-phenoxyacetic acid is obtained with a yield of 80-87% and a content of the 2,4-D isomer of 96.28-99.8%.

The disadvantages of this method are:

- low yield of the target product (80-87%);

- the presence of 0.02-0.41% chlorophenol, 0.15-0.82% trichloro-substituted phenoxyacetic acid in the product;

- the use of a large amount of solvent.

A known method of producing aryloxycarboxylic acids (RU 2345978, S07C 51/02, S07C 59/70, 2009), including the stage of obtaining phenolates of alkali metals by the interaction of phenol with an alkali metal hydroxide; the stage of obtaining salts of aryloxycarboxylic acids by the interaction of the salt of monochloroacetic acid with the phenolates of alkali metals obtained in the first stage upon heating, and these processes are carried out in the solid phase with simultaneous fine grinding and vigorous stirring, followed by acidification of the salt and the isolation of the final product.

To obtain the sodium salt of phenoxyacetic acid, 1.01-1.04 mol of solid alkali NaOH is ground to obtain a finely ground powder, 1 mol of phenol is added and at a temperature not exceeding the melting point of the reaction mixture, the mixture is stirred and ground to obtain a finely ground powdery mass. Then to sodium phenate (1 mol) add powdered sodium salt of monochloroacetic acid (1.05-1.15 mol) and stir vigorously for 0.5-2 hours. at a temperature of 80-95 ° C and the sodium salt of phenoxyacetic acid is obtained, which can be processed into an acid by a known method, for example, acidification followed by extraction.

The conversion of phenol to sodium phenolate is 99.1-99.5; conversion of sodium phenolate to sodium salt of phenoxyacetic acid is 99.3-99.6%; the content of free phenol in the reaction mass is 0.4-0.8%.

For the formation of phenolate 2,4-dichlorophenol take solid alkali NaOH, grind and mix in a mixer with 2,4-dichlorophenol. The resulting product, containing 0.5 mol of sodium 2,4-dichlorophenolate, is contacted in a mixer with powdered Na-salt of monochloroacetic acid under conditions similar to example 1 and at a temperature of 95 ° C for 2 hours.

Conversion of 2,4-dichlorophenol to sodium 2,4-dichlorophenolate - 99.9%; conversion of sodium 2,4-dichlorophenolate to sodium salt of 2,4-dichlorophenoxyacetic acid - 99.7%; the content of free 2,4-dichlorophenol in the reaction mass is 0.3%.

The disadvantages of this method are:

- sodium hydroxide is very hygroscopic and therefore it is difficult to obtain it in the form of a finely ground powdery mass;

- the reaction of interaction of 2,4-dichlorophenol and sodium salt of monochloroacetic acid in the presence of sodium hydroxide proceeds with a large evolution of heat. Therefore, in large-scale production, it is very difficult to maintain a stable temperature below the melting point of the reaction mixture under conditions of poor heat transfer of the powders. In addition, an additional step is required for the synthesis of the sodium salt of monochloroacetic acid and its drying;

- an additional stage of obtaining 2,4-dichlorophenol is required;

- the presence of free phenol (0.4-0.8%) and highly toxic 2,4-dichlorophenol (0.3%) impairs the consumer characteristics of the product.

A known method for producing chlorine-substituted aryloxycarboxylic acids (RU 2380350, С07С 51/363, С07С 51/02, С07С 59/68, С07С 59/70, 2010) by solid-phase chlorination of acids of the general formula

where R ₁ is hydrogen, halogen, C ₁ -C ₄ -alkyl, n is an integer from 1 to 3, or their salts with calcium hypochlorite in the absence of solvents with the activation of the process by mechanical action in the form of shock or shock-shear load on a mixture of solid reagents in the presence of a catalyst, which is Lewis acid, for 10-30 minutes at ambient temperature and atmospheric pressure. Mechanical action is carried out using a ball, vibroball or planetary mill. To obtain 2,4-dichloro-phenoxyacetic acid, a mixture of sodium salt of phenoxyacetic acid, calcium hypochlorite in the form of a dibasic salt of calcium hypochlorite with an active chlorine content of 60% and ferric chloride hexahydrate is mechanically processed for 10 minutes to obtain a finely ground powder. The resulting mass is dissolved with vigorous stirring in 15% hydrochloric acid and incubated for 15 minutes. The formed precipitate is filtered off, washed and dried. The precipitate contains 98.1% 2,4-dichlorophenoxyacetic acid.

The disadvantage of this method is the use in the process of additional equipment (mill) and catalyst, which in industrial production will lead to additional material costs. In addition, a significant amount of difficult-to-use wastewater is generated.

Known solid-phase synthesis of phenoxyacetic acid under conditions of mechanochemical activation. (Bashkir Chemical Journal, 2008. Volume 15. No. 1. P. 11-13. Yu. E. Sapozhnikov, V. V. Maslennikova, L. I. Buslaeva, Z.B. Galieva, N. A. Sapozhnikova, R B. Valitov Solid-phase synthesis of phenoxyacetic acid under conditions of mechanochemical activation).

The synthesis of the sodium salt of phenoxyacetic acid is carried out in two stages. Initially, sodium phenolate monohydrate is obtained by dosing phenol for 30-60 minutes into finely dispersed (modal size X50 = 3 microns) sodium hydroxide, providing intensive stirring and a temperature of 20-50 ° C. The authors note that the rate of the process depends significantly on the degree of grinding of sodium hydroxide and the intensity of stirring and depends only slightly on temperature. After the completion of the process, the reaction mass is a free-flowing powder. At the first stage, it is possible to achieve a residual concentration of unreacted phenol of less than 0.4%.

At the second stage, after adding sodium monochloroacetate to the reaction mass, the crushed mixture is subjected to preliminary mechanical activation in a vibratory or planetary mill and subsequent heating to 60-95 ° C with or without mechanical action, giving the target product - sodium salt of phenoxyacetic acid.

Since in some experiments the effect of water content at the condensation stage was investigated, the initial reagents were preliminarily dried in a vacuum drying oven at a temperature of 90 ° C and a residual pressure of 10 mm Hg. within 10-12 hours.

The disadvantages of this method are as follows:

- the target product contains initial phenol in an amount of up to 0.4% and its presence will affect the consumer characteristics of the product, since when this product is chlorinated to obtain 2,4-dichlorophenoxyacetic acid, phenol will also be chlorinated to form chlorophenols - sources of supertoxicants - dioxins. But even if the product is purified, toxic waste water is formed (MPC in the water of chlorophenols should be no more than 0, 0001 mg / l);

- due to the high hygroscopicity of sodium hydroxide, it is very difficult to obtain it in a finely dispersed form up to a size of 3 microns. In industrial production, it will be very difficult to keep the temperature in the range of 20-50 ° C due to the high exothermicity of the process and poor thermal conductivity of dispersed powders;

- ready-made sodium salt of monochloroacetic acid (sodium chloroacetate) is used in the synthesis. An additional stage is required for its preparation and purification, since monochloroacetic acid is prone to hydrolysis;

- sodium phenolate monohydrate is used in the synthesis. This is one more additional technological operation for its production from phenol and water;

- the need for preliminary long-term drying (10-12 hours) of the initial reagents under high vacuum (10 mm Hg), which is very difficult to create in industrial conditions.

In patent application CN 106397176 (A) (C07C 51/367, C07C 59/70, 2017), a method for producing sodium phenoxyacetate is proposed, including the following steps: 1) chloroacetic acid is dissolved in water and cooled to 0 ° C; 2) a saturated sodium carbonate solution is added to the chloroacetic acid solution with stirring at 0 ° C until the pH of the solution is 7-8; 3) phenol, water, 35% sodium hydroxide solution are added to the mixed solution to pH 12 and the reaction mixture is heated to 92 ° C, subjecting it to reaction for 0.5 hour; 4) the reaction mass is filtered, the solid obtained by filtration is washed, dried and sodium phenoxyacetate is obtained with a yield of 80-85%. The disadvantages of this method are:

- low yield of the target product;

- the formation of significant amounts of polluting wastewater, since the sodium salt of phenoxyacetate is quite well soluble in water.

In patent application CN 106397177 (A) (C07C 51/41, C07C 51/47, C07C 59/70, 2017), a full-cycle method for the preparation of sodium phenoxyacetate is proposed, including the following steps: 1) synthesis of sodium chloroacetate by the interaction of chloroacetic acid with sodium carbonate in an aqueous solution at a temperature not higher than 35 ° C and stirring; 2) synthesis of sodium phenoxyacetate by the interaction of a saturated solution of sodium chloroacetate obtained in stage 1), phenol and 40% sodium hydroxide at a weight ratio of components 1: 1.2: 1.2, pH 12, temperature 92 ° C and stirring for for 0.5 hours, adding concentrated hydrochloric acid to pH 7 and cooling to room temperature; 3) purification of sodium phenoxyacetate; 4) processing of the organic phase and reuse; 5) processing of the aqueous phase and reuse.

In the description of the application examples of obtaining sodium salt of phenoxyacetic acid, quantitative and qualitative indicators of the target product are not given.

The disadvantages of this method are:

- multistage process;

- the need to use two types of alkali: sodium carbonate and sodium hydroxide;

- the formation of significant amounts of polluting wastewater, since the sodium salt of phenoxyacetate is quite well soluble in water.

In patent application CN 104151152 (A) (C07C 51/02, C07C 51/367, C07C 51/42, C07C 59/70, 2014), a cyclic method for producing phenoxyacetic acid is proposed, which includes the following stages: 1) condensation of sodium phenolate with sodium chloroacetate to form sodium phenoxyacetate at a temperature of 90-95 ° C in the presence of a catalyst (ferric chloride, EDTA, sodium iodide at a ratio of 1: 1: 1); 2) dissolving excess phenol in a solvent (chlorobenzene, dichlorobenzene, toluene, xylene, dichloroethane or tetrachlorethylene) to return to the cycle; 3) washing sodium phenoxyacetate in a solvent to remove phenol; 4) acidification of sodium phenoxyacetate, cooling and crystallization to isolate phenoxyacetic acid.

The product is obtained with a yield of 95-98% and a purity of 98%.

The disadvantages of this method are:

- multistage process;

- the use of a catalyst of complex composition, the preparation of which itself requires additional technological equipment;

- the use of an organochlorine solvent complicates the process technology.

Patent application CN 101921188 (A) (C07C 51/363, C07C 59/70, 2010) proposes a method for producing 2,4-dichlorophenoxyacetic acid by chlorination of phenoxyacetic acid with chlorine at 10-100 ° C in a mixed solvent in the presence of phenothiazan catalysts and dimethylaminopyridine. A mixed solvent composed of two or more solvents such as water, dioxane, tetrahydrofuran, dimethyl or diethyl ether, diethylene glycol dimethyl or diethyl ether, acetone, butanone, acetic acid, acetonitrile, dimethylformamide, dimethylsulfoxide, monohydric C ₁ -C ₇ -alcohol ... The mass ratio of phenoxyacetic acid to the mixed solvent = 1: 1-100, the molar ratio of phenoxyacetic acid to the total amount of introduced chlorinating gas = 1: 2-2.2. The yield of 2,4-dichlorophenoxyacetic acid is 95.0-95.3% in terms of phenoxyacetic acid, the content of the active ingredient is 97.8-98.4%).

The disadvantages of this method are:

- the use of mixed solvents in the process will lead to the loss of the target product during the separation of solvents;

- cleaning and regeneration of solvents and catalysts will require additional material and energy costs;

- an additional stage of obtaining phenoxyacetic acid is required and the total yield of 2,4-dichlorophenoxyacetic acid in terms of phenol will be lower.

In patent application CN 102336654 (A) (C07C 51/363, C07C 59/70, 2012), a method is proposed for the chlorination of phenoxyacetic acid and its derivatives with a chlorinating agent (chlorine gas, sodium hypochlorite, calcium hypochlorite, sulfuryl chloride) at a temperature of 40-100 ° C for 1-10 hours in organic solvents (dichloromethane, dichloroethane, trichloromethane, carbon tetrachloride, formic acid, ethyl acetate, benzene, toluene, dimethylbenzene, chlorobenzene, o-dichlorobenzene) in the presence of catalysts (ferric chloride, tin chloride, aluminum chloride , trifluorobromo, trifluoromethylsulfonate, concentrated sulfuric acid, persulfuric acid, sulfuronic acid). The yield of 2,4-dichlorophenoxyacetic acid is 90.5% with a purity of 98.05%.

The disadvantages of this method are:

- insufficient yield of the target product;

- the use of an organochlorine solvent complicates the process technology;

- the use of solvents in the process will lead to the loss of the target product during the separation of the solvent;

- an additional stage of obtaining phenoxyacetic acid is required and the total yield of 2,4-dichlorophenoxyacetic acid in terms of phenol will be less;

- cleaning and regeneration of solvents and catalysts will require additional material and energy costs.

In patent application CN 103058855 (A) (C07C 51/363, C07C 59/70, 2013), a method for the synthesis of a phenoxyacetic acid derivative is proposed. The method includes the following stages: 1) mixing a salt of phenol or methyl phenol (sodium, potassium, methylamino, ethylamino) with a salt of chloroacetic acid (sodium, potassium, methylamino, ethylamino) when heated (50-150 ° C) in a solvent medium (water, methyl alcohol, ethyl alcohol, propyl alcohol, dimethylformamide, dimethylacetamide, dimethylsulfide oxide); 2) acidification of the reaction mixture with inorganic acid (hydrochloric, sulfuric, nitric, phosphoric) to pH 0-3 to obtain phenoxyacetic acid; 3) chlorination of phenoxyacetic acid with chlorine to obtain 2-chlorophenoxyacetic or 4-chlorophenoxyacetic acid by heating (10-100 ° C, mainly 30-80 ° C) for 1 minute - 10 hours in a solvent (dichloromethane, chloroform, dichloroethane, tetrachlorethylene , chlorobenzene, dichlorobenzene, acetic acid, propionic acid, butanoic acid, ethylene glycol dimethyl ether, dioxane, tetrahydrofuran) with the addition of a catalyst (oxide or chloride of iron, chromium); cooling and crystallization to obtain a chlorinated phenoxyacetic acid derivative. The yield of phenoxyacetic acid is 95-96%, the content is more than 98%.

The disadvantages of this method are:

- the use of an organochlorine solvent complicates the process technology;

- the use of solvents in the process will lead to the loss of the target product during the separation of the solvent;

- cleaning and regeneration of solvents and catalysts will require additional material and energy costs.

In patent application CN 103145549 (A) (C07C 51/363, C07C 59/70, 2013), a method for preparing 2,4-dichlorophenoxyacetic acid by condensation of o-chlorophenol with chloroacetic acid at a temperature of 95-110 ° C for 3- 5 hours in an alkaline (NaOH, KOH) or aqueous medium, acidification with hydrochloric or sulfuric acid, cooling and crystallization of the obtained o-chlorophenoxyacetic acid (yield 97.1-97.23%, content 98.6-98.4%); then the interaction of o-chlorophenoxyacetic acid with chlorine at a temperature of 10-60 ° C (mainly 30-50 ° C) in a mixed solvent, which is a mixture of dimethylformamide, water and dichloroethane. The target product is obtained with a content of 97.1-98.1% and a yield of 96.8-97.9%) in terms of o-chlorophenoxyacetic acid.

The disadvantages of this method are:

- o-chlorophenol is a more expensive reagent in comparison with phenol used in similar methods for producing 2,4-dichlorophenoxyacetic acid;

- two stages of chlorination are required: the stage of obtaining o-chlorophenol and the stage of chlorination of o-chlorophenoxyacetic acid;

- the yield of 2,4-dichlorophenoxyacetic acid in terms of o-chlorophenol will be less;

- the use of a mixed solvent complicates the process technology;

- the use of solvents in the process will lead to the loss of the target product during the separation of the solvent;

- regeneration and purification of solvents will require additional material and energy costs.

In patent application CN 103274925 (A) (C07C 51/363, C07C 59/70, 2013), a method for preparing 2,4-dichlorophenoxyacetic acid is proposed, which includes the following stages: dissolving phenoxyacetic acid in an organic solvent (tetrachlorethylene, dichloroethane, tetrachloride carbon); carrying out the chlorination reaction of phenoxyacetic acid with chlorine at a temperature of 25-100 ° C in the presence of a catalyst; removing the generated hydrogen chloride and residual chlorine after completion of the reaction; catalyst recovery at high temperature; filtration, cooling, crystallization of the filtrate, drying of the finished product. The weight ratio of phenoxyacetic acid and organic solvent is 1: 2-100, the molar ratio of phenoxyacetic acid and chlorine is 1: 2-2.3. The yield of 2,4-dichlorophenoxyacetic acid is 91.6-96.0%, the content is 96.7-98.7%.

The disadvantages of this method are:

- the use of an organochlorine solvent complicates the process technology;

- when using low-boiling dichloroethane ( _boiling point = 83.47 ° C) and carbon tetrachloride ( _boiling point = 76.75 ° C) as solvents, pressure is required to maintain the reaction temperature of 100 ° C, which complicates the process technology;

- a stage of synthesis of phenoxyacetic acid is required;

- the use of solvents in the process will lead to the loss of the target product during the separation of the solvent;

- cleaning and regeneration of solvents and catalysts will require additional material and energy costs.

In patent application CN 104447290 (A) (C07C 51/363, C07C 59/70, 2015), a method for producing 2,4-dichlorophenoxyacetic acid is proposed, which includes the following stages: obtaining sodium chloroacetate by adding chloroacetic acid to a sodium hydroxide solution with stirring within 15-20 minutes; obtaining sodium phenoxyacetate by reacting sodium chloroacetate with phenol at a temperature of 100 ° C for 40 minutes while adjusting to pH = 11 with sodium bicarbonate; obtaining phenoxyacetic acid by adding hydrochloric acid to pH = 4, cooling in an ice bath, washing the resulting solid and drying; obtaining 2,4-dichlorophenoxyacetic acid by chlorination of phenoxyacetic acid with chlorine at a temperature of 75 ° C in a solution of acetic acid and water in the presence of an iron phthalocyanine catalyst with stirring for 35-50 minutes, cooling to 18 ° C and filtering the reaction mixture, drying the solid at 60 ° C. The target product is obtained with a yield of 97.0-98.9% and a content of 97.9-99.8%). The disadvantages of this method are:

- multistage process;

- cooling to low temperatures (ice bath) on an industrial scale will require the use of refrigeration units, which significantly complicates and increases the cost of the process;

- the use of a solvent in the process will lead to the loss of the target product during the separation of the solvent;

- catalyst regeneration will require additional material and energy costs.

A similar method for the preparation of 2,4-dichlorophenoxyacetic acid is proposed in patent application CN 104402707 (A) (C07C 51/363, C07C 59/70, 2015), except that the chlorination of phenoxyacetic acid is carried out at a temperature of 65 ° C and as the catalyst uses a composite oxide Ni-Al-Mg. The target product is obtained with a yield of 97.9-99.1%) in terms of phenoxyacetic acid and a content of 97.2-99.9%.

The disadvantages of this method are:

- multistage process;

- cooling to low temperatures (ice bath) on an industrial scale will require the use of refrigeration units, which significantly complicates and increases the cost of the process;

- the use of a solvent in the process will lead to the loss of the target product during the separation of the solvent;

- catalyst regeneration will require additional material and energy costs;

- the product yield in terms of the initial phenol will be less.

In patent application CN 105001079 (A) (C07C 51/363, C07C 59/70, 2015), a method for preparing 2,4-dichlorophenoxyacetic acid is proposed, including the following steps: 1) obtaining phenoxyacetic acid by the reaction of chloroacetic acid with phenol and 32% sodium hydroxide in saturated sodium chloride at a temperature of 106 ° C and stirring for 30 minutes; then the reaction mass is cooled to 80 ° C, acidified with hydrochloric acid, cooled to 20 ° C, filtered to obtain a powder of phenoxyacetic acid with a content of 90.2%; 2) chlorination of phenoxyacetic acid with chlorine in a solution of lower carboxylic acid and water at a temperature of 45-85 ° C (mainly 55-65 ° C) and stirring for 0.5-1 hour; then the reaction mass is cooled to 18 ° C, filtered, the resulting precipitate is dried at 80 ° C. Acetic, propionic, butanoic, isobutanoic acids are proposed as the lower carboxylic acid. Mass ratio of lower carboxylic acid to water = (1: 9) - (9: 1), ratio of phenoxyacetic acid: lower carboxylic acid: water = (0.9-1) mol: 560 g: 240 g.

The yield of the target product is 84.1-98.5% in terms of phenoxyacetic acid, the content is 96.4-99.1%).

The disadvantages of this method are:

- the yield is calculated for the intermediate formed phenoxyacetic acid, based on the initial chloroacetic acid, the yield will be much less;

- the need to separate sodium chloride and the target product;

- a large amount of generated wastewater, causing environmental pollution.

In patent application CN 102180788 (A) (C07C 51/363, C07C 59/70, 2011), a method for producing 2,4-dichlorophenoxyacetic acid is proposed, including the steps: obtaining phenoxyacetic acid from phenol and epoxyethane by esterification, dehydrogenation at a temperature of 65- 70 ° C and stirring for 2-3 hours in the presence of an oxidation catalyst CuO / ZrO ₂ ; dissolving phenoxyacetic acid in a mixed solvent (water, benzene, toluene, C ₁ -C ₇ -alkanol or a composition of two or more solvents in diethyl ether); the reaction of a solution of phenoxyacetic acid with chlorine at a temperature of 75-80 ° C in the presence of a chlorination catalyst (sulfuric / benzenesulfonic acid, sulfuric / parachlorobenzenesulfonic acid, sulfuric / paratoluenesulfonic acid, sulfuric / orthotoluenesulfonic acid); cooling, crystallization, filtration and drying. The target product is obtained with a yield of 97.6-98.5% and an active ingredient content of 98.7-99.3%.

The disadvantages of this method are:

- the use of mixed solvents in the process will lead to the loss of the target product during the separation of the solvent;

- the need to use an oxidation catalyst and a chlorination catalyst at different stages of the process;

- purification and regeneration of mixed solvents and catalysts will require significant additional material and energy costs.

In patent application CN105622396 (A) (C07C 51/363, C07C 59/70, 2016), a method for preparing 2,4-dichlorophenoxyacetic acid is proposed, including the following steps: 1) obtaining phenoxyacetic acid by the reaction of phenol with chloroacetic acid and a liquid base in aqueous medium at pH 12 in the presence of an esterification catalyst (quaternary ammonium salts, polyester, cyclic branched ether and quaternary phosphonium salts) at a temperature of 35-120 ° C and stirring for 3-5 hours; adding chloroacetic acid to pH 2, cooling to 10-30 ° C, crystallization for 1-3 hours, filtration, washing and drying at 90 ° C for 2 hours; 2) chlorination of the obtained phenoxyacetic acid with a chlorinating agent (30% hydrochloric acid and 30% hydrogen peroxide, 36% hydrochloric acid and oxygen, 33% hydrochloric acid and ozone) in a solvent (ethyl acetate, acetonitrile) in the presence of a chlorination catalyst (Lewis acid (one or more chloride of iron, zinc, tin, aluminum, titanium, magnesium and barium) and / or solid acid) at a temperature of 40-70 ° C and stirring for 2-6 hours, cooling to room temperature, crystallization within 3 hours, filtration , washing (water, methanol) and drying at 130 ° C for 2 hours. Get 2,4-dichlorophenoxyacetic acid with a purity of 92.0-98.6%) and a yield of 73.38-95.2% in terms of phenol.

The disadvantages of this method are:

- multistage process;

- the use of organic solvents in the process will lead to the loss of the target product during the separation of the solvent;

- purification and regeneration of solvents and purification of the target product from catalysts will require additional material and energy costs.

In patent application CN 106892808 (A) (C07C 51/02, C07C 59/70, 2017), a method for producing 2,4-dichlorophenoxyacetic acid is proposed, including the following steps: 1) obtaining sodium haloacetate by the reaction of haloacetic acid (chloroacetic, bromoacetic, iodoacetic) with an alkali metal alkoxide (sodium methoxide, sodium ethoxide) in an alcohol solution; 2) obtaining phenolate by reaction of phenol with 10-80% (most preferably 20-50%) aqueous base solution (NaOH, KOH, Ca (OH) ₂ , Mg (OH) ₂ , Al (OH) ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , NaHCO ₃ , KHCO ₃ ) with stirring, followed by an increase in temperature to 110 ° C to distill off water and obtain dry phenolate; 3) obtaining sodium phenoxyacetate by adding the obtained dry phenolate to an alcoholic solution of haloacetate (sodium chloroacetate) at a temperature of 50-200 ° C (most preferably 100 ° C) and vigorous stirring for 2-6 hours (most preferably 4-5 hours); 4) obtaining 2,4-dichlorophenoxyacetate sodium by chlorination of sodium phenoxyacetate with gaseous chlorine or sulfuryl chloride in an alcohol solution with stirring in the presence of a metal chloride catalyst (titanium, aluminum, iron) at a temperature of 10-80 ° C (most preferably 20-70 ° C) in within 2-10 hours (most preferably 5 hours); 5) obtaining 2,4-dichlorophenoxyacetic acid by acidification of sodium 2,4-dichlorophenoxyacetate with 10-60% mineral acid (preferably hydrochloric acid) and its crystallization at 5-20 ° C for 1-1.5 hours. The target product is obtained with a yield of 99.0-99.2% and a purity of 99.2-99.6%).

The disadvantages of this method are as follows:

1) Multi-stage process (5 stages).

2) The complexity of the technology of the 1st stage of the process:

Sodium methylate is formed by the action of sodium metal on methyl alcohol:

2CH ₃ OH + 2Na → 2CH ₃ ONa + H ₂

In addition, the specified most preferred temperature (100 ° C) for carrying out the reaction requires conducting the process under pressure, since the boiling point of methanol is 64.7 ° C. This significantly complicates the technology.

Sodium and potassium alcoholates are stable in anhydrous alcohol, but hydrolyzed with water:

(L. Fizer, M. Fizer "Organic Chemistry", ed. "Chemistry", M. 1969, p. 336).

3) Formation of by-products - chlorinated ethers and aldehydes at the chlorination stage.

When sodium phenoxyacetate is chlorinated in an alcoholic medium, by-products are formed. So chlorination in methanol leads to the receipt of a by-product - dichloromethyl ether:

("Brief Chemical Encyclopedia", Moscow, 1961, vol. 1, p. 1181), and chlorination in ethanol leads to the formation of a by-product - chloral and hydrogen chloride:

(P. Carrer "Course of organic chemistry", Goskhimizdat, 1963, p. 313.).

4) High explosion and fire hazard of the process when using methyl and ethyl alcohol as a solvent.

5) Using toxic methyl alcohol as a solvent.

6) The use of a metal chloride catalyst (iron, aluminum, titanium) at the chlorination stage, the purification of the target product from which presents certain difficulties.

7) Ferric chloride with phenols gives color to the reaction mass, which will negatively affect the consumer characteristics of the product.

8) To acidify the reaction mass with mineral acid, additional equipment (measuring tanks, pumps) is required, which complicates the process technology.

9) Difficulty in the disposal of wastewater containing sodium chloride solutions.

In this application, an intermediate product - a salt of phenoxyacetic acid - is obtained by the reaction of a phenolate with sodium chloroacetate in an alcohol solution, and the phenolate of sodium, potassium, calcium, magnesium, zinc and aluminum can be used as the phenolate. As a result of such a reaction, regardless of which phenolate is taken, an alkaline salt of phenoxyacetic acid is formed.

It is known that the solubility of salts in water (hydration) and non-aqueous solvents (solvation) is determined by the difference between the energies of the crystal lattice and the energy of hydration (solvation).

This is consistent with the solubility of these salts in water, methanol and ethanol.

Solubility of chlorides

According to the description of CN 106892808, NaCl, KCl, CaCl ₂ , MgCl ₂ , ZnCl ₂ , AlCl ₃ can be formed as salts. Therefore, it is obvious that Ca ⁺² , Mg ⁺² , Zn ⁺² , Al ⁺³ salts will prevail in the solution, while phenoxyacetic acid, which will subsequently be chlorinated, is only in the form of a sodium salt, which is confirmed by the examples of the description.

In patent application CN 108947838 (A) (C07C 51/09, 2018), a method for preparing 2,4-dichlorophenoxyacetic acid and its salt is proposed, where the method of preparation includes the following steps: 1) carrying out the reaction of phenol with an ester of chloroacetic acid in an alkaline medium (NaOH, KOH, NaHCO ₃ , KHCO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , NH (CH ₃ ) ₂ ) in the presence of an organic solvent (benzene, toluene, xylene or their mixtures) at a temperature of 60-120 ° C within 0.2-1 hours to obtain a phenoxyacetic acid ester; 2) carrying out the reaction of selective chlorination of phenoxyacetic acid ester with a chlorinating agent (chlorine gas, thionyl chloride, sulfuryl chloride) under the action of catalyst A (Lewis acid) and catalyst B (C ₅ -C ₂₂ thioesters, thiazoles, isothiazoles and thiophenes or their halogenated derivatives) at a temperature of 20-100 ° C for 0.2-1 hours to obtain 2,4-dichlorophenoxyacetic ether; 3) carrying out the hydrolysis reaction of the ester of 2,4-dichlorophenoxyacetic acid in acidic conditions at a temperature of 60-120 ° C for 2-4 hours to obtain 2,4-dichlorophenoxyacetic acid; or after obtaining 2,4-dichlorophenoxyacetic ester, carrying out an alkaline hydrolysis reaction with an alkaline compound to give 2,4-dichlorophenoxyacetate.

The yield of 2,4-dichlorophenoxyacetic acid in terms of the starting phenol is 98.07-98.62% and the content is 98.5-98.9%.

The disadvantages of this method are:

- multistage process;

- an additional stage of synthesis of monochloroacetic acid ester is required;

- the use of organic solvents in the process will lead to losses of the target product during the separation of the solvent and enhance the flammable and toxic characteristics of the process;

- the use of complex catalysts at the chlorination stage;

- cleaning and regeneration of solvents and catalysts will require significant additional material and energy costs.

In patent application CN 108424366 (A) (C07C 51/363, C07C 59/70, 2018), a method for producing 2,4-dichlorophenoxyacetic acid is proposed, including the following steps: 1) obtaining halogenated acetate by the interaction of halogenated (chlorine, bromine, iodine ) acetic acid with alcohol (C ₂ -C ₁₀ ) in the presence of concentrated sulfuric acid at a temperature of 50-200 ° C for 4-5 hours; 2) obtaining a phenolate solution by the interaction of phenol with alkali (NaOH, KOH, Ca (OH) ₂ , Mg (OH) ₂ , Zn (OH) ₂ ) at a temperature of 50-120 ° C; 3) obtaining phenoxyacetate by the interaction of halogenated acetate with phenolate at a temperature of 50-200 ° C for 0.5-1 hour; 4) obtaining phenoxyacetic acid by hydrolysis of phenoxyacetate in an alkaline medium with mineral acid (sulfuric, hydrochloric, nitric) at a temperature of 70-200 ° C for 2-4 hours; 5) crystallization of phenoxyacetic acid at a temperature of 10-20 ° C for 1-1.5 hours; 6) obtaining 2,4-dichlorophenoxyacetic acid by chlorination of phenoxyacetic acid in a solvent medium in the presence of a catalyst at a temperature of 0-100 ° C for 3-7 hours. The chlorinating agent is chlorine gas, sulfonyl chloride. The solvent used is dimethyl disulfide, carbon tetrachloride, dichloroethane. The catalyst is one or more compounds consisting of iron trichloride, aluminum trichloride, boron trifluoride, niobium pentachloride, aluminum trifluoromethanesulfonate, alumina, iron oxide, boron trioxide, niobium pentoxide, diphenyl ether, diphenyl sulfide, diphenyl disulfide and dimethyl sulfide, dimethyl sulfide.

Upon completion of the reaction, the solvent is distilled off, the product is crystallized at a temperature of 10-20 ° C for 1-1.5 hours, filtered, dried. Get 2,4-dichlorophenoxyacetic acid with a yield of 99.0-99.4% and a purity of 99.3-99.4%

The disadvantages of this method are:

- multistage process;

- use in the process of 2 stages of halogenation;

- utilization of halogenated (bromide, iodide) waste;

- the use of organic solvents in the process, which, when the solvent is distilled off, leads to the loss of the target product;

- cleaning and regeneration of solvents and catalysts will require significant additional material and energy costs.

In patent application CN 108947822 (A) (C07C 51/09, C07C 59/68, C07C 59/70, 2018), a method for producing phenoxycarboxylic acid is proposed, including the following steps: 1) obtaining an ester of phenoxycarboxylic acid by condensation of phenol or ortho-cresol with a chlorocarboxylic acid ester of the general formula ClR ₁ COOR, where R _{1 is} selected from an alkylene group having 1-3 carbon atoms, R is selected from an alkyl group having 1-10 carbon atoms, or C ₃ -C ₁₀ -cycloalkyl, in the presence of a base (NaOH, KOH, Ca (OH) ₂ , Mg (OH) ₂ , Na ₂ CO ₃ , K ₂ CO ₃ , NaHCO ₃ , KHCO ₃ ) in an organic solvent such as benzene, toluene, xylene, at a temperature of 60- 120 ° C for 1-5 hours. The resulting liquid condensate is filtered at a temperature of 30-50 ° C, washed with water and dried until a solid product is obtained; 2) obtaining chlorophenoxycarboxylic acid ester by selective chlorination of phenoxycarboxylic acid ester with a chlorinating agent (chlorine gas, thionyl chloride, sulfuryl chloride) in the presence of one or two catalysts selected from Lewis acid, C ₅ -C ₂₂ thioester, C ₅ -C ₂₂ thiazole, C ₅ -C ₂₂ -isothiazole, C ₅ -C ₂₂ -thiophene, at a temperature from -20 ° C to 100 ° C; 3) obtaining chlorophenoxycarboxylic acid by the reaction of acid hydrolysis of chlorophenoxycarboxylic acid ester at a temperature of 60-120 ° C, for 2-4 hours. For hydrolysis, sulfonic, hydrochloric, phosphoric, sulfuric acids are used. At the end of the reaction, the formed alcohol is separated, the reaction mass is cooled to room temperature, filtered, the precipitate is washed with water and dried. Get 2,4-dichlorophenoxyacetic acid with a content of 98.8% and a yield of 98.0-98.12% in terms of phenol.

The disadvantages of this method are:

- the stage of obtaining an ester of chlorocarboxylic acid in an organic solvent;

- drying of the obtained chlorophenoisacetic acid ester to a solid state, which significantly complicates further technological operations;

- the use of an organic solvent at the condensation stage;

- the use of catalysts at the chlorination stage and the need for their regeneration;

- cleaning and regeneration of solvents and catalysts will require significant additional material and energy costs.

In patent application CN 108424360 (A) (C07C 51/09, C07C 59/70, 2018), a method for preparing 2,4-dichlorophenoxyacetic acid is proposed, including the following steps: 1) obtaining a halogenated acetate by the reaction of halogenated (Cl, Br, J ) acetic acid with alcohol having from 2 to 20 carbon atoms, in the presence of a catalyst (concentrated sulfonic acid, toluene, butyl titanate) at a temperature of 50-200 ° C and stirring for 1-10 hours; 2) obtaining phenolate by the interaction of phenol with alkali (NaOH, KOH, Ca (OH) ₂ , Mg (OH) ₂ , Zn (OH) ₂ ) at a temperature of 50-120 ° C; 3) obtaining phenoxyacetate by the interaction of halogenated acetate with phenolate at a temperature of 50-200 ° C and stirring for 0.5-1 hour; 4) obtaining 2,4-dichlorophenoxyacetate by chlorination of phenoxyacetate with gaseous chlorine or sulfonyl chloride in a solvent medium (dimethyl disulfide, carbon tetrachloride, dichloroethane) at a temperature of 0-100 ° C for 3-7 hours under the action of one or more catalysts. The catalyst is selected from the group consisting of iron trichloride, aluminum trichloride, boron trifluoride, niobium pentachloride, trifluoromethanesulfonate, alumina, iron oxide, boron trioxide, niobium pentoxide, diphenyl ether, diphenyl sulfide, diphenyl disulfide and dimethyl disulfide; 5) obtaining 2,4-dichlorophenoxyacetic acid by hydrolysis of 2,4-dichlorophenoxyacetate by the action of an alkaline solution (NaOH or KOH) at a temperature of 70-200 ° C for 2-4 hours, and then with an acid solution (sulfuric, hydrochloric, nitric, para- toluenesulfonic, formic, acetic) at a temperature of 70-200 ° C for 2-4 hours. After that, the solvent is distilled off, filtered, crystallized at a temperature of 10-20 ° C for 1-1.5 hours, dried and 2,4-dichlorophenoxyacetic acid is obtained with a yield of 99.3-99.5% and a purity of 99.3-99 ,5%).

The disadvantages of the process are:

- multistage process (5 stages);

- additional stage of obtaining halogenated (Cl, Br, J) acetic acid;

- the need to dispose of bromine and iodine-containing waste;

- the complexity of the technology: first, a halogenated acetate ester is obtained, which, after chlorination, is subjected to hydrolysis. This leads to the need for alcohol recovery and purification. Chlorination at elevated temperatures up to 100 ° C will require work under pressure, since the proposed solvents boil at a lower temperature (boiling point of carbon tetrachloride 76.7 ° C, boiling point of dichloroethane 83.47 ° C, boiling point of dimethyl sulfide 37.34 ° WITH);

- the need to regenerate the catalysts used at the chlorination stage;

- cleaning of solvents and regeneration of catalysts will require significant additional material and energy costs.

There is a known method of producing 2,4-dichlorophenoxyacetic acid (RU 2684114, С07С 59/70, 2019), including the stage of synthesis of an alkaline earth salt of phenoxyacetic acid by condensation of phenol with monochloroacetic acid and alkaline earth metal oxide in an aqueous medium at a temperature of 90-100 ° C and stirring, the stage of chlorination of the alkaline earth salt of phenoxyacetic acid with a chlorinating agent and the isolation of the target product in a known manner.

The synthesis of the alkaline earth salt of phenoxyacetic acid is carried out in three cycles for a more complete extraction of the product.

A suspension of alkaline earth metal in water is prepared by stirring for 0.5-1.5 hours at room temperature. Phenol is dosed to the resulting suspension, then monochloroacetic acid, maintaining the temperature at 20-25 ° C. At the end of dosing, the temperature in the reaction zone is raised to 90-100 ° C and kept at the specified temperature for 0.5-1 hour. with constant stirring. The reaction mass is cooled to room temperature, the phenoxyacetic acid salt (precipitate) is filtered off, the filtrate is returned to the next synthesis cycle of the phenoxyacetic acid salt, using instead of water. The precipitates obtained as a result of 3-cycle synthesis are combined, washed with water, filtered off and dried.

Three cycles of synthesis of the salt of phenoxyacetic acid on the return filtrate is due to the avoidance of product losses with the filtrate and additional operations with a more complete product recovery, that is, evaporation, cooling.

Chlorination of the alkaline earth salt of phenoxyacetic acid with gaseous chlorine is carried out in an aqueous medium at a temperature of 20-25 ° C and stirring for 2-3 hours. Upon completion of the reaction, chlorine is purged with air or an inert gas. The precipitate is filtered off, washed with water, and dried. The dry product, if necessary, is washed with toluene and dried.

In the case of using sodium and calcium hypochlorites as chlorinating agents, as well as hydrogen chloride in the presence of hydrogen peroxide or hydrochloric acid and hydrogen peroxide, chlorination is carried out in an aqueous medium at a temperature of 90-100 ° C and stirring for 3-3.5 hours. The target product is isolated by known methods: the reaction mass is cooled, filtered, washed, dried.

This technical solution was chosen as a prototype, the disadvantages of which are:

- to carry out the stage of condensation of phenol with monochloroacetic acid and alkaline earth metal oxide, it is necessary to heat the aqueous solution of the reaction mixture to a temperature of 90-100 ° C, which requires high energy costs;

- for a more complete separation of the intermediate product from the filtrate, a 3-cycle synthesis is carried out, which complicates the technological process and increases its duration;

- the intended disposal of the calcium chloride solution into the usually formed calcium sulfate requires an additional stage of interaction with sulfuric acid and high-temperature (more than 1200 ° C) calcination of calcium sulfate, so that it can be used as a building material. Such a high temperature is required for the thermal destruction of dioxins, which are inevitably formed during the combustion of organochlorine compounds. Energy costs for firing will significantly increase the cost of the target product.

In the cited patent sources, the authors developed a technology for obtaining the target product with a minimum content of chlorophenols in it, since their presence in the herbicidal preparation reduces the biological effect, worsens the stability of the preparation during storage, and imparts an unpleasant persistent odor to the commercial product. In addition, highly toxic hazardous compounds, dioxins, can be formed from chlorophenols.

Dioxins and dioxin-like polychlorinated biphenyls (PCBs) are environmental pollutants, persistent organic pollutants. They are industrial by-products that are generated, for example, from the production of pesticides and waste incineration. Due to their high chemical stability and good solubility in animal fats, they accumulate in the environment, plants and living organisms. A person can be exposed to dioxins as a result of eating meat, dairy and fish products. Dioxins are neurotoxic, can cause damage to the immune system, hormonal disorders, cancer, reproductive health problems, etc. Therefore, in many countries at the state level, it is prohibited to use raw materials, as well as finished products and feeds with their increased content.

The technical objective of the invention is to simplify and increase the productivity of the technological process for producing 2,4-dichlorophenoxyacetic acid, which does not form chlorine-substituted phenols and, as a consequence, toxicants - dioxins.

The problem is solved by the developed method for producing 2,4-dichlorophenoxyacetic acid, which consists in the fact that the intermediate product - the calcium salt of phenoxyacetic acid - is obtained by condensation of phenol with monochloroacetic acid and calcium oxide or hydroxide in the melt. The synthesis takes place under conditions of self-heating of the reaction mass and the temperature in the reaction zone is kept in the range of 80-160 ° C for 10-30 minutes with constant stirring. As a result, the monohydrate of the calcium salt of phenoxyacetic acid is obtained.

To obtain monohydrate of calcium salt of phenoxyacetic acid, three options have been proposed.

Option 1. Calcium oxide (CaO) or calcium hydroxide (CaOH) _{2 are} dosed into the phenol melt, then monochloroacetic acid.

Option 2. Calcium oxide (CaO) or calcium hydroxide (CaOH) ₂ is dosed into the monochloroacetic acid melt, then phenol is dosed.

Option 3. Calcium oxide (CaO) or calcium hydroxide (CaOH) _{2 is} dosed into the phenol melt with monochloroacetic acid.

The obtained monohydrate of the calcium salt of phenoxyacetic acid is chlorinated with gaseous chlorine in an aqueous medium at a temperature of 20-25 ° C and stirring for 1.5-2.5 hours. Upon completion of the reaction, chlorine is purged with air or nitrogen. The precipitate is filtered off, washed with water, and dried. The dry product, if necessary, is washed with toluene and dried.

It is known that at a normal chlorine pressure of 1 atm. at temperatures below 9.5 ° C, crystals of chlorine gas hydrate with an approximate composition of C1 ₂ ⋅ 6H ₂ O and C1 ₂ ⋅ 8H ₂ O are formed in water. Therefore, chlorination of an aqueous solution of a salt of phenoxyacetic acid with chlorine at temperatures below 20 ° C is undesirable, since at At elevated pressures, solid chlorine hydrates exist at higher temperatures.

Increasing the temperature during chlorination with gaseous chlorine of an aqueous solution of a salt of phenoxyacetic acid above 30 ° C is impractical. This leads to a decrease in the solubility of chlorine in water, which adversely affects the rate of the chlorination reaction and increases the energy consumption for heating the reaction mass. In addition, when chlorine is dissolved in water, hypochlorous acid is formed.

Cl ₂ + H ₂ O → HClO + HCl,

which, when heated, decomposes to chloric acid

6HClO → 4HCl + 2HClO ₃ .

Chloric acid is a strong oxidizing agent and can lead to undesirable oxidative processes that reduce the yield of 2,4-dichlorophenoxyacetic acid and contaminate it with oxidation products.

Chlorination is not limited to chlorine gas or any chlorine gas. Chlorination can be carried out with chlorine formed in chemical or electrochemical processes, for example, when peroxides react with aqueous solutions of hydrogen chloride. Chlorination can also be carried out by other reagents containing active chlorine, for example, but not limited to hypochlorites. All hypochlorites are very unstable and are good oxidizing agents (F. Cotton, J. Wilkinson "Modern inorganic chemistry". Publishing house "Mir", Moscow, 1969, p. 430). In order to avoid the occurrence of oxidative processes during the chlorination of the calcium salt of phenoxyacetic acid, in some cases it is advisable to introduce additives into the reaction zone that neutralize the effect of hypochlorite ions.

A distinctive feature of the proposed method is that the synthesis of the calcium salt of phenoxyacetic acid is carried out not in an aqueous solution, but in a melt of phenol, monochloroacetic acid or their mixture with oxide or calcium hydroxide.

It turned out unexpectedly that the condensation reaction can proceed in the melt of the reagents without the participation of a solvent at temperatures up to 170 ° C with the formation of monohydrate of the calcium salt of phenoxyacetic acid, which was impossible to predict in advance.

The essence of the invention is as follows.

The chemistry of the formation of the calcium salt of phenoxyacetic acid:

The overall process looks like this:

In the case of using calcium hydroxide, the total chemistry of the process is described as follows:

The chlorination chemistry of the calcium salt of phenoxyacetic acid:

The advantages of the proposed technical solution are:

- when dosing the initial components of calcium oxide or calcium hydroxide into the melts, the reaction mass self-heating occurs, which saves electricity on an industrial scale, allows to drastically reduce the dimensions of the reactors, which reduces material costs;

- carrying out the condensation reaction in the melt of the initial reagents increases the rate of the chemical process, which will have a positive effect on the productivity of the reactor equipment for the synthesis of the calcium salt of phenoxyacetic acid and will lead to a reduction in the cost of the process;

- the process is waste-free, carrying out the condensation reaction in the melt eliminates the formation of waste water, thanks to the reverse osmosis system, clean water is returned to the production cycle, which improves the environmental friendliness of the process.

Brief description of the drawings.

FIG. 1 is a derivative of the calcium phenoxyacetic acid salt prepared according to the present invention.

FIG. 2 is a ¹ H nuclear magnetic resonance spectrum of phenoxyacetic acid prepared according to the present invention.

FIG. 3 is a ¹ H nuclear magnetic resonance spectrum of 2,4-dichlorophenoxyacetic acid prepared according to the present invention.

FIG. 4 is a block diagram of a waste-free process for producing 2,4-dichlorophenoxyacetic acid according to the present invention, the production process of which includes:

1. Operating chlorine production.

2. Reactor for the synthesis of calcium salt of phenoxyacetic acid (FCA).

3. Unit of filtration and washing of calcium salt of phenoxyacetic acid (FUA).

4. Reactor for chlorination of calcium salt of phenoxyacetic acid (FUA).

5. Filtration unit 2,4-D.

6. Reactor for hydrolysis of calcium chloride.

7. Unit for filtration of calcium hydroxide.

8. Dryer for calcium chloride.

9. Reactor for photolytic filtrate purification.

10. Gas distributor.

11. Block of thermocatalytic filtration of ozone in the gas phase.

12. Unit for catalytic destruction of liquid phase ozone.

13. Reverse osmosis apparatus.

Threads designation:

A - Phenol.

B - Monochloroacetic acid.

C - Calcium oxide or hydroxide.

D1 - Water for washing the calcium salt of phenoxyacetic acid.

D2 - Water for rinsing 2,4-D.

E - Chlorine.

G - Sodium hydroxide.

H - Ozone.

F1 - Filtrate after washing with calcium salt of phenoxyacetic acid.

F2 - Filtrate after washing with 2,4-D. F3 - Calcium hydroxide precipitate.

F4 (D) - Water (permeate) after osmotic treatment of an aqueous solution of sodium chloride.

F5 (in 1) - Sodium chloride solution, return to chlorine production.

F6 (C) (in 2) - Calcium hydroxide or oxide, return to the reactor (2) for the synthesis of the calcium salt of phenoxyacetic acid.

The invention is illustrated by the following examples.

Example 1.

A suitable reactor is charged with 18.82 g (0.20 mol) of phenol, 18.90 g (0.20 mol) of monochloroacetic acid, the mixture is heated to melting and 11.21 g (0.20 mol) of calcium oxide are dosed with vigorous stirring CaO. In this case, spontaneous heating of the reaction mass is observed. At a temperature of 95-100 ° C, the reaction mass is kept for 10 minutes and after cooling, 76 ml of water is dosed to wash the formed calcium salt of phenoxyacetic acid from calcium chloride. The reaction mass is filtered off. Then the reaction mass is cooled to room temperature and additionally filtered off 2.01 g of solid product. The precipitate is dried and 35.03 g of the product is obtained, which is the monohydrate of the calcium salt of phenoxyacetic acid:

FIG. 1 shows the derivatogram of the calcium salt of phenoxyacetic acid. Derivatographic measurements were performed using a Q-derivatograph with a heating rate of 57 min.

The DTA curve exhibits an endothermic peak with a maximum process temperature of 150 ° C, at which a loss of sample mass is observed, corresponding to the removal of 1 molecule of crystalline hydrate water.

Using ¹ H-NMR spectroscopy of the solution of the calcium salt of phenoxyacetic acid chemical shifts detected signals and constants of spin-spin interaction characteristic of phenoxyacetic acid.

The ¹ H nuclear magnetic resonance spectrum recorded on a Brooker Avance-400 NMR spectrometer, shown in FIG. 2, confirms the formation of phenoxyacetic acid.

The spectrum characterizes the structure containing a phenoxy group with chemical shifts δ, ppm: 6.91-6.93 (2H, d, C ² H, C ⁶ H), 6.998 (1H, t, C ⁴ H), 7.302 (2H, t, C ³ H, C ⁵ H) and carboxymethyl fragment δ = 4.664 ppm. (2H, O-C H ₂ -COOH), which uniquely identifies the compound as phenoxyacetic acid.

Thus, the product was obtained in the amount of 35.03 g in the form of monohydrate of the calcium salt of phenoxyacetic acid with a yield of 97.2% in terms of phenol.

Example 2.

A phenol melt in the amount of 47.06 g (0.50 mol) is poured into a reaction device equipped with a suitable stirring device, a cooling system. Through a dosing device load 28.60 g (0.51 mol) of calcium oxide (CaO) and a melt of 48.19 g (0.51 mol) of monochloroacetic acid. The reaction mixture is self-heating and the temperature in the reaction zone is kept in the range of 80-100 ° C for 30 minutes with constant stirring. To remove the formed calcium chloride, 120 ml of water are added to the reaction mass and stirred to complete the removal of calcium chloride. After filtration of the reaction mixture and drying of the precipitate, 86.59 g of monohydrate of the calcium salt of phenoxyacetic acid are obtained with a yield of 96.1% in terms of phenol.

Example 3.

In a reactor with a stirring and dosing device, equipped with a cooling system, the monochloroacetic acid melt is charged in an amount of 48.19 g (0.51 mol). Then, 28.60 g (0.51 mol) of calcium oxide CaO are charged into the melt with vigorous stirring. Thereafter, phenol is metered in in the amount of 47.06 g (0.5 mol). When dosing, the temperature of the reaction mixture spontaneously rises to 150 ° C. The reaction mass is stirred for 10-20 minutes and after cooling, 140 ml of water is added to purify the formed calcium salt of phenoxyacetic acid. The precipitate is filtered off and after drying, 87.49 g of monohydrate of the calcium salt of phenoxyacetic acid are obtained with a yield of 97.1% in terms of phenol.

Example 4.

A suitable reactor is charged with 68.04 g (0.72 mol) of monochloroacetic acid, 65.88 g (0.70 mol) of phenol, the mixture is heated to melting and 53.35 g (0.72 mol) of calcium hydroxide is dosed with vigorous stirring Ca (OH) ₂ . In this case, spontaneous heating of the reaction mass is observed. At a temperature of 95 ° C, the reaction mass is kept for 30 minutes and after cooling, 200 ml of water is dosed to wash the formed calcium salt of phenoxyacetic acid from calcium chloride. The reaction mass is filtered off. Then the reaction mass is cooled to room temperature and additionally filtered. The precipitate is dried to obtain 121.09 g of monohydrate of the calcium salt of phenoxyacetic acid with a yield of 96.0% in terms of phenol.

Example 5.

In a reactor with a stirring and dosing device, equipped with a cooling system, the monochloroacetic acid melt is charged in the amount of 95.44 g (1.01 mol). Then, 74.83 g (1.01 mol) of calcium hydroxide Ca (OH) ₂ is loaded into the melt with vigorous stirring. Thereafter, phenol is dosed in an amount of 94.11 g (1.00 mol). When dosing, the temperature of the reaction mixture spontaneously rises to 160 ° C. The reaction mixture is stirred for 10-20 minutes and after cooling, 290 ml of water is added to purify the formed calcium salt of phenoxyacetic acid. The precipitate is filtered off and after drying, 174.06 g of monohydrate of the calcium salt of phenoxyacetic acid are obtained with a yield of 96.6% in terms of phenol.

After purification of the calcium salt of phenoxyacetic acid, the aqueous filtrate is directed to the stage of hydrolysis of calcium chloride, and then, after its separation, the clarified filtrate is directed to the stage of photochemical ozonation.

Completely mineralized filtrate, after photochemical ozonation, enters the brine purification unit of the existing production of electrochemical chlorine production.

This method of obtaining 2,4-dichlorophenoxyacetic acid is most expediently combined with the production of chlorine or in the immediate vicinity of the existing chlorine production. In this case, the technological process can be organized as waste-free.

Example 6.

Synthesis of 2,4-dichlorophenoxyacetic acid from monohydrate of calcium salt of phenoxyacetic acid.

In a round bottom flask equipped with a stirrer, bubbler and thermostat, load 330 ml of water and 28.83 g (0.08 mol) of monohydrate of calcium salt of phenoxyacetic acid obtained in examples 1-5. With the stirrer turned on, chlorine gas is fed through the bubbler. Taking into account the fact that the calcium salt of phenoxyacetic acid does not exist in the form of a hydrate in an aqueous medium, the reaction proceeds as follows:

The temperature in the reaction zone is maintained in the range of 20-25 ° C. Chlorination is carried out for 1.5 hours. After the completion of the reaction, chlorine dissolved in the reaction mass is blown off with a stream of air.

The formed precipitate is filtered off and washed with 65 ml of water and dried. After drying, 35.63 g of dry product is obtained, which, if necessary, is washed with 60 ml of an organic solvent, mainly toluene, and after drying, 33.94 g of a product is obtained containing 99.4% of 2,4-dichlorophenoxyacetic acid and 0.6% of monochloro- phenoxyacetic acid. The yield of 2,4-dichlorophenoxyacetic acid is 95.4% of theoretical in terms of monohydrate of the calcium salt of phenoxyacetic acid.

The ¹ H nuclear magnetic resonance spectrum of 2,4-dichlorophenoxyacetic acid, recorded on a Bruker Avance-400 NMR spectrometer, is shown in FIG. 3.

The spectrum corresponds to 2,4-dichlorophenoxyacetic acid with resonance signals δ, ppm: 6.869-6.886 (1H, dm, Ar (C ⁶ H)), 6.7227-7.245 (1H, dd, Ar (C ⁵ H)), 7.461 (1H, d, Ar (C ³ H)), 4.633-4.641 (2H, d, O — C H ₂ —COOH).

The spectrum presented unambiguously proves the formation of 2,4-dichlorophenoxyacetic acid.

Example 7.

Synthesis of 2,4-dichlorophenoxyacetic acid from the calcium salt of phenoxyacetic acid.

If necessary, it is possible to chlorinate not the monohydrate of the calcium salt of phenoxyacetic acid, but the calcium salt of phenoxyacetic acid.

Dried at 160 ° C monohydrate of the calcium salt of phenoxyacetic acid loses the water molecule and becomes the calcium salt of phenoxyacetic acid.

A round bottom flask equipped with a stirrer, bubbler and thermostat is charged with 1000 ml of water and 205.42 g (0.60 mol) of the calcium salt of phenoxyacetic acid. With the stirrer turned on, chlorine gas is fed through the bubbler at 20-25 ° C for 2.5 hours.

After the completion of the reaction, chlorine dissolved in the reaction mass is blown off with a stream of nitrogen.

The precipitate formed is centrifuged and washed with 120 ml of water, and after drying, 258.05 g of a product containing 99.5% 2,4-dichlorophenoxyacetic acid and 0.5% monochlorophenoxyacetic acids are obtained. The yield of 2,4-dichlorophenoxyacetic acid is 96.8% of theoretical in terms of the calcium salt of phenoxyacetic acid.

In order to dispose of production wastes, the calcium chloride formed as a result of the reaction can be returned to the technological process. For this, after filtration of the monohydrate of the calcium salt of phenoxyacetic acid, the filtrate is made alkaline with sodium hydroxide. This forms calcium hydroxide and sodium chloride:

CaCl ₂ + 2NaOH → Ca (OH) ₂ + 2NaCl

However, the filtrate after the synthesis of the calcium salt of phenoxyacetic acid contains organic impurities - calcium salts of phenoxyacetic acid, phenol, oxyacetic acid.

When processing the filtrate from the stage of synthesis of the calcium salt of phenoxyacetic acid with sodium hydroxide, the sodium salt of phenol is formed

and sodium salt of phenoxyacetic acid

CaCl ₂ + 2NaOH → Ca (OH) ₂ + 2NaCl

The formed calcium hydroxide is filtered off and returned to the stage of synthesis of the calcium salt of phenoxyacetic acid, and the filtrate is subjected to photochemical ozonation in a suitable photochemical reactor.

After filtration of calcium hydroxide, a certain amount of unreacted calcium chloride remains in the concentrate, which can be sent to the existing brine purification system, which is returned to the chlorine production plant. Calcium ions are removed in the usual way - a solution of soda ash is introduced into the brine:

CaCl ₂ + Na ₂ CO ₃ → CaCO ₃ + 2NaCl

At the same time, the solubility of CaCO ₃ at 40-50 ° C is about 4-5 mg / l, which meets the requirements for brines in the production of chlorine by the diaphragm method.

(https://chem21.info/page/177210234199166151151213102198236065169123199134).

As a result of mutual amplification of ozone and ultraviolet light, a complete mineralization of organic matter occurs. Proceeding chemical reactions:

The filtrate after chlorination of the calcium salt of phenoxyacetic acid, containing some 2,4-dichlorophenoxyacetic acid, is also treated with sodium hydroxide and subjected to photochemical ozonation.

Requirements for brine sent to chlorine production using diaphragm production:

NaCl concentration, g / l not less than 310 Ca ⁺² , mg / l no more than 5.0 NaOH, g / l 0.05-0.1 Na ₂ CO ₃ , g / l 0.3-0.4

(https://chem21.info/page/101128055038148249171089085009219147148076209048/).

The aqueous solutions formed during the synthesis of the calcium salt of phenoxyacetic acid and the chlorination of the calcium salt of phenoxyacetic acid are sent to the photolytic ozonation reactor after separation of calcium hydroxide. Reactors produced by the industry, operating on an ozone-oxygen or ozone-air mixture with UV irradiation with a wavelength in the range of 170-280 mm, can be used. Ozone under the action of UV irradiation forms active OH • radicals that destroy organic compounds. The time of passage of the treated solution through the irradiation zone should be sufficient for the complete mineralization of organic compounds (Rein Munter "Advanced Oxidution Processe-Current Status and Prospects" - Proc. Estonian Acid. Sci. Chem., 2001, 50, 2, 59-80).

After photocatalytic ozonation, the solution enters the gas separation system. The gas phase, which contains unreacted ozone, enters the thermocatalytic ozone decomposition unit for its destruction to the level of maximum permissible values when discharged into the atmosphere. The role of the catalyst can be played, for example, by Goptalum, or another suitable catalyst. The liquid phase passes through a catalytic filter, such as but not limited to manganese hydroxide, to remove dissolved ozone.

After photocatalytic ozonation in an aqueous solution of sodium chloride, hydrogen peroxide is formed in small amounts

О ₃ + Н ₂ О → Н ₂ О ₂ + О ₂

(M. Tozihi, M. Vahedpouz, F. Nazan, Journal of the Iranian Chemical Society, 7, 3, 585-596 (2010).

Peroxide decomposes rather slowly. Therefore, before feeding an aqueous solution of sodium chloride to the reverse osmosis system, hydrogen peroxide is catalytically destroyed

2H ₂ O ₂ → 2H ₂ O + O ₂

in a contact apparatus containing, for example, manganese hydroxide or other suitable catalyst.

During ozonation, organic molecules are completely oxidized, and ozone does not react with sodium chloride (Doklady Akademii Nauk, 2010, vol. 434, no. 4, pp. 493-495. Physical chemistry).

When analyzing waste water after photochemical ozonation using HPLC HITACHI "Chromaster" on a chromatographic column with a reversed phase and a UV detector, organic substances were not detected.

The resulting aqueous solution of sodium chloride, having a corresponding osmotic pressure, is subjected to reverse osmosis at the pressure required to obtain a solution of sodium chloride with a concentration of about 100 g / liter.

After the reverse osmosis system, the permeate (pure water) returns to the technological process to the stage of washing the calcium salt of phenoxyacetic acid or washing 2,4-dichlorophenoxyacetic acid, and the concentrate (10% aqueous solution of sodium chloride) returns to the department for preparing an aqueous solution of sodium chloride required concentration and further to the chlorine production workshop:

For a reverse osmosis system, any suitable units and devices can be used, for example, high pressure plunger pumps, for example, PRATISSOLI, but not limited to them.

In the industrial production of chlorine, the main cost items are electricity and raw materials - sodium chloride.

In addition, in the process of electrolysis, the consumption of water is also significant, which is due to its electrolytic decomposition, as well as the production of a sodium hydroxide solution. Therefore, for resource conservation, it is important to return the sodium chloride solution to the chlorine production.

The aqueous solution of sodium chloride after photolytic ozonation and the reverse osmosis unit can be returned to the existing system of purification of the feed brine of the chlorine production.

According to Van't Hoff's law, osmotic pressure, kPa:

where

i - Van't Hoff coefficient (for sodium chloride = 2)

R - universal gas constant equal to 8.31 J / mol ⋅ K

T is the temperature of the solute, K

С - concentration of solute, g / dm ³

M is the mass of one mole of a solute

(for sodium chloride = 58.5)

To obtain a concentration of an aqueous solution of sodium chloride 100 g / dm ³

In this case, suitable high-pressure diaphragms can be used, for example FILMTECCW30XLE - 440C with an operating pressure of up to 83 bar and a selectivity of 99.7% for sodium chloride.

The scheme of the most energy efficient reverse osmosis plant can be equipped with any suitable water pump, for example, PRATISSOLI KT series with operating pressures of 80 bar and above.

The main method for determining the content of organic impurities in wastewater is chemical oxygen demand (COD) using potassium dichromate as an oxidizing agent.

However, sodium chloride present in the aqueous solution during the analysis with the participation of sulfuric acid (GOST 31859-2012) will release hydrogen chloride, which is oxidized under the action of potassium dichromate:

14HCl + K ₂ Cr ₂ O ₇ → 3Cl ₂ + 2CrCl ₃ + 2KCl + 7H ₂ O

In this case, there will be a false-positive analysis even in the absence of organic impurities.

The analysis of the content of organic impurities in water after photolytic ozonation of filtrates and catalytic destruction of ozone was carried out using HPLC HITACHI "Chromaster" on a chromatographic column with a reversed phase and UV detector. The residual content of organic impurities in the treated water was 420-630 μG / liter in terms of phenol.

Thus, the technological process for producing 2,4-dichlorophenoxyacetic acid is waste-free.

The waste-free technological process for producing 2,4-dichlorophenoxyacetic acid is illustrated by the block diagram shown in FIG. 4.

Claims (1)

A method for producing 2,4-dichlorophenoxyacetic acid, comprising the step of synthesizing the calcium salt of phenoxyacetic acid by condensation of phenol with monochloroacetic acid and calcium oxide at elevated temperature and stirring, the step of chlorination of the calcium salt of phenoxyacetic acid with a chlorinating agent and isolation of the target product in a known manner, characterized in that the synthesis the calcium salt of phenoxyacetic acid is carried out in the melt of the starting reagents at the self-heating temperature of the reaction mixture.

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