RO110698B1 - 2,4-dichlorinephenoxyacetic acid preparation process - Google Patents

Abstract

The invention relates to a a process for the preparation of 2,4- dichlorophenoxyacetic acid by condensation sodium phenolate, monochloracetic acid, in aqueous alkaline solution followed chlorination of phenoxyacetic acid and acidifying the reaction mass using a series of phase transfer catalysts.

Description

The invention relates to a process for obtaining 2,4-dichlorophenoxyacetic acid, with the chemical formula:

this being the most important representative of the class of aryloxy-alkanoic herbicides, widely used in agriculture, in order to combat the dicotyledonous weeds in cereal crops.

In order to obtain 2,4-dichlorophenoxyacetic acid, two main categories of processes are known:

1.-0 The first category of processes performs, in a first step, the chlorination of phenol in various media and conditions, in order to obtain dichlorophenol. and in the next step, it is etherified, in alkaline hydroxide medium, with monochloroacetic acid, resulting in the sodium (or potassium) salt of 2,4-dichlorophenoxyacetic acid, which is subsequently neutralized to 2,4-dichlorophenoxyacetic acid, according to the following reaction scheme. :

This category of procedures 4 presents a series of disadvantages, which make it extremely difficult and expensive to obtain the quality 2,4-dichlorophenoxyacetic acid, imposed by its use in the pesticide industry. 45

Thus, in the first stage, when the phenol is chlorinated, a mixture of mono-, dl ·, and irf-chlorinated phenols results (due to the high rate of phenol chlorination, which results in a 5o decrease in the selectivity of the chlorination process), in different proportions, these alkylating together in the next step, so that, finally, a mixture of phenoxyacetic acids mono-, md · and friclorurates. Also, the etherification of chlorophenols with monoloracetic acid, in alkaline medium, proceeds at a lower rate compared to the etherification of the non-chlorinated phenol, which favors the secondary hydrolysis reaction of monochloracetic acid, so that, although they work with relatively high excess of monochloracetic acid, it results in finally a 2,4-dichlorophenoxyacetic acid impurified with chlorophenols, phytotoxic substances prohibited in pesticide compositions;

2. the second category of processes performs, in a first step, the etherification of phenol with monochloroacetic acid, in the presence of alkalis, in the aqueous or organic phase, followed by chlorination in the subsequent step of the phenoxyacetic acid thus obtained, using various chlorination agents. (chlorine, sodium hypochlorite, sulfuryl chloride, etc.), this step taking place in the phenoxyacetic acid synthesis medium or in an extraction solvent and finally resulting in 2,4-dichlorophenoxyacetic acid, according to the following sequence of reactions:

OH O-CHj-COON

2NaOH fQ] + CI-CH, -COOH - [QJ + NaCl

O-CH ₂ -C0ONa O-CHj-COOH (Qj * HCI-- (q) + NaCl o-ch ₂ -cooh ° W ° ^oh xis chloride appendage kSi iQJ [cr] V

BUT

Within this category of processes, those of which involve the extraction of phenoxyacetic acid, resulting in the first step, in a suitable organic solvent and its subsequent chlorination in the extraction solvent, respectively, have, on the one hand, the disadvantage of a partial extraction of phenoxyacetic acid, due to its solubility in the aqueous phase, thus a low yield of 2,4-dichlorophenoxyacetic acid synthesis, and on the other hand, a generally low selectivity of chlorination in the respective organic solvents.

A series of processes achieves the chlorination of phenoxyacetic acid obtained by etherification in the aqueous phase, directly bubbling gas chlorine into the aqueous phenoxyacetic acid solution, without the need for isolation or separation of the reaction intermediates.

In this regard, in the patent PL 139896, the synthesis of phenoxyacetic acid in aqueous phase is described by alkylation of phenol with monochloracetic acid, in the presence of a 50% sodium hydroxide solution, at

95, .. 105 ° C, followed by dilution of the solution of sodium phenoxyacetate, up to a concentration of 10% and its chlorination with chlorine gas, bubbled in the reaction mass, maintaining the pH of the reaction mass in the range 3 ... 5, by adding sodium hydroxide solution, during the chlorination process.

Although it generally removes the disadvantages of the first category of 2,4-dichlorophenoxyacetic acid, the Polish process presented above has a number of disadvantages:

- relatively low yield of 2,4-dichlorophenoxyacetic acid synthesis (87 ... 90% relative to phenol):

- average purity of the finished product (92 ... 94%). due to the fact that the chlorination process takes place practically, in heterogeneous phase, the phenoxyacetic acid being only partially soluble in water, and partly, being in a melted state; on the other hand, the product of the first chlorination step, ie 4-chlorophenoxyacetic acid being insoluble in the reaction medium, the second chlorination step takes place, practically, also in the heterogeneous phase, thus resulting in a lower yield;

- the need to use a relatively large excess of monochloroacetic acid, in the etherification step (15% molar excess), due to the parallel hydrolysis reaction of the monochloroacetic acid and the low etherification yield, under working conditions, the reaction taking place partially in the heterogeneous phase (suspension) )

- the need to use a dilute solution of phenoxyacetic acid, at the chlorination stage, precisely to try to achieve a most homogeneous reaction medium;

- the need to use an excess of 15% chlorine compared to the necessary stoichiometric one in the chlorination process, precisely due to the heterogeneity of the reaction mass in the chlorination process;

- the need to use an excess of 15% chlorine compared to the necessary stoichiometric one in the chlorination process, precisely due to the heterogeneity of the reaction mass in the chlorination process.

The technical problem, which the present invention solves, is to determine the proportions between the raw materials and the optimal technical conditions for conducting the etherification and chlorination reactions so as to obtain acid.

2,4-dichlorophenoxyacetic of high purity and high efficiency, avoiding at the same time, its impurification with toxic products, prohibited.

The process according to the invention removes the disadvantages mentioned above, in that a very good contact of the reactants is carried out during the etherification and chlorination phases, greatly reducing the heterogeneity of the reaction mass, by introducing it into the reaction medium of some catalysts. phase transfer (substances with strong emulsifying and dispersing effect), these phase transfer catalysts being introduced into the reaction mass, in a proportion of 15 to 1 ... 8 g / mol of phenol.

The process according to the invention achieves 2,4-dichlorophenoxyacetic acid, following the next sequence of reactions; 2o

Stage I;

but

In the first step, phenol in aqueous alkaline solution and in the presence of a substance with a phase transfer catalyst effect, chosen from castor oil, ethoxylate or propoxylate. ethoxylated or propoxylated nonylphenol, ethoxylated or propoxylated 2-ethylhexanol, tertiary alkylamines 40, ethoxylated or propoxylated (to varying degrees of ethoxylation or propoxylation), sodium ligno sulphonate or sodium dibutylnaphthalinsulfonate, condensed to 45

90 .. .105 ° C, for 2 ... 4 h, with an aqueous solution of sodium monochloroacetate

25 .. .40%. at a molar ratio phenol sodium hydroxide: sodium monochloroacetate of 1: 1.01 ... 1.03: 1.1. 50 The phase transfer catalyst is introduced in a proportion of 1 ... 8 g / mol of phenol. The resulting sodium phenoxyacetate is acidified to pH = 3-5 with an aqueous hydrochloric acid solution.

In the second step, the phenoxyacetic acid thus obtained is chlorinated at temperatures between 3O ... 95 ° C with chlorine gas, barbotatt for 2 ... 4 h, under energetic stirring in the reaction mass, at a molar ratio of 2.1 ... 2,2: 1 relative to phenoxyacetic acid, maintaining the pH of the reaction mass in the range 3 ... 5%. by the addition of sodium hydroxide solution.

After completion of the chlorine dosage, the reaction mass is further stirred for □, 5 ... 1 h, after which it is cooled and acidified with hydrochloric acid solution, to pH 1 ... 1,5. The resulting 2,4-dichlorophenoxyacetic acid is filtered, washed on the water filter and dried, resulting in an advanced product of high purity.

The process according to the invention has the following advantages:

- ensures a product of high purity, free of phytotoxic impurities, such as chlorophenols;

- ensures the increase of the yield in useful product;

- ensures the reduction of specific consumption of raw materials and energy;

- ensures the reduction of production costs;

- it can be implemented on the existing installations in the chemical industry of profile, with minimal expenses of development. ,

Two examples of embodiments of the invention are given below.

Example 1. In a 1500 ml glass flask, fitted with propeller type stirrer, reflux refrigerant, dropper funnel and pH probe socket, 94 g (1 mol) of molten phenol and 165 g of hydroxide solution were introduced. of 25% sodium (1.03 mol NaOH), over which 2 g of polyethoxylated castor oil (UA 50) were added as a phase transfer catalyst.

The reaction was heated to 90 ° C, followed by dropwise addition of 427 g cold aqueous solution (below 20 ° C) of 30% sodium monochloroacetate (1.1 moles sodium monochloroacetate) for 3 hours, maintaining during this time the temperature of the reaction mass at

9O ... 97 ° C. The reaction mass remained homogeneous throughout the reaction.

After dosing the whole amount of sodium monochloracetate, the reaction mass was maintained for one hour at reflux. in order to perfect the reaction, permanently adjusting the pH so that it is in the range 8.5 ... 12.

Further, acidified table ^- the reaction to pH 3 using 25% hydrochloric acid solution, cooled to 35 ° C and started bubbling chlorine through a frit while agitating the reaction mixture vigorously. 155 g of chlorine were bubbled within 2 hours, permanently maintaining the pH of the reaction mass in the range of 3 ... 4, by dropping 353 g of 25% sodium hydroxide solution, the reaction mass increasing during the process of chlorination up to 95 ° C.

After the addition of chlorine, the reaction was further stirred for 0.5 h at 95 ° C, cooled to 35 ° C, and acidified with a 30% hydrochloric acid solution to pH = 1. Cooled in further at 20 ° C and the 2,4-dichlorophenoxyacetic acid was filtered through the vacuum tube. The acid precipitate

2,4-dichlorophenoxyacetic was washed on the filter with 500 ml of fresh water, dried, weighed and analyzed. 218 g of 2,4-dichlorophenoxyacetic acid of 97.5% purity was obtained, with a yield of 96.2%.

Example 2. In the installation shown in Example 1, 94 g (1 mol) of molten phenol and 163 g of 25% sodium hydroxide solution (1.02 mol of NaOH) were added, over which 5 g of polyethoxylated nonylphenol were added. (NF 10), as a phase transfer catalyst. The reaction mass was heated to 90 ° C, followed by the dropwise addition of 320 g of 40% aqueous sodium monochloroacetate (1.1 moles sodium monochloroacetate) over a period of 2.5 hours, maintaining the mass temperature. reaction at 9O ... 97 ° C, the reaction mass being kept fluid throughout the reaction.

After dosing the whole amount of sodium monochloroacetate, the reaction was held for another hour at reflux, in order to perfect the reaction, while maintaining the pH between 8.5 and 12, by correction with sodium hydroxide solution. 25%. Subsequently, the reaction mass was acidified to pH = 3 with a 25% hydrochloric acid solution, cooled to 60 ° C and the chlorine was bubbled under vigorous stirring by means of a brine. 152 g of chlorine gas were bubbled over 3 hours, maintaining the pH of the reaction mass in the range 3 ... 5, by dropping 347 g of 25% sodium hydroxide solution, the temperature of the reaction mass increasing during the process of chlorination up to 90 ° C. After adding the whole amount of chlorine, the reaction mass was stirred for 45 min. at 90 ° C, it was cooled to 40 ° C and acidified to pH = 1, with a 30% hydrochloric acid solution. It was further cooled to 20 ° C and the 2,4-dichlorophenoxyacetic acid was filtered through the vacuum tube. The 2,4-dichlorophenoxyacetic acid precipitate was washed on the filter with 500 ml of fresh water, dried, weighed and analyzed. 213 g of 2,4-dichlorophenoxyacetic acid of 98% purity with a yield of 94.3% over phenol were obtained.

Claim

Claims (2)

Process for obtaining the acid 2,4-dichlorophenoxyacetic, by condensation of sodium phenolate with monochloroacetic acid, in alkaline aqueous solution, at a molar ratio of sodium phenolate: sodium monochloroacetate 1: 1,1, at a temperature of 90 ... 105 ° C, followed by chlorination of the phenoxyacetic acid thus obtained with chlorine gas, for 2 ... 5 h, at temperatures of 30 ... 95 ° C, at a molar ratio of phenoxyacetic acid: chlorine of 1: 2,2, maintaining the pH in the chlorination time in the range 3 ... 5 with the aid of an alkaline aqueous solution, followed by acidification of the reaction mass to pH = 1, characterized in that both the condensation phase of sodium phenolate with monochloracetic acid and the phase for the chlorination of phenoxyacetic acid with chlorine gas a series of phase transfer catalysts are used, selected from: 9 10 ethoxylated or propoxylated ricin, ethoxylated or propoxylated nonylphenol. 2-ethylhexanol, ethoxylated or propoxylated, tertiary alkylamines, ethoxylated or propoxylated, sodium lignosulfonate or sodium dibutylnaphthalinsulphate, catalysts introducing the reaction mass at a rate of 1. g / mol of phenol.