WO1992005299A1 - Process for producing halogenated acrylic acids - Google Patents

Abstract

A process is disclosed for producing by electrolytic reduction compounds having formula (I), in which R1 is a fluorine atom, a methyl or a deuteromethyl group; R?2 and R3¿ are the same or different and represent a fluorine, chlorine, hydrogen or deuterium atom; R4 is a group (a), in which R5 is -OH, -OD, C¿1?-C4-alkoxy or -OMe, whereas Me represents an alkaline, alkaline earth or NH4 ion. For this purpose, a compound having formula (II) or a compound having formula (III), in which R?1, R2, R3 and R4¿ have the above-mentioned meaning, whereas R6 is a chlorine atom, are subjected to an electrolytic process in a one-piece or subdivided cell filled with an electrolytic liquid, in the presence of an iron salt concentration of 1 to 500 ppm in the electrolyte.

Description

 description

Process for the production of halogenated acrylic acids

Acrylic acid derivatives have a very wide range of applications as organic intermediates. They allow access to a variety of useful compounds, but they are particularly suitable for the production of plastics.

Halogenated and deuterated acrylic and methacrylic acid derivatives have been of particular interest for some time, since such substances are suitable for the production of special plastics with special properties.

For example, α-Haloacrylic acid ester used for the production of radiation-sensitive protective layers in resist technology. For example, α-fluoroacrylic acid esters are suitable for the production of plastic glasses for aviation technology and are also suitable starting materials for polymer optical fibers, with deuterated derivatives being of particular interest because of their better optical properties.

3-chloro-2-fluoroacrylic acid and its derivatives are used, for example, to improve the

Pre-vulcanization process in the manufacture of

Elastomer mixtures (US-A 4254 013) or in the synthesis of fluorine-substituted pyrethroid esters with insecticides

Properties used (Australian patent application

004813).

For the synthesis of 3-chloro-2-fluoroacrylic acid and its

Various methods are available for derivatives.

3-chloro-2-fluoroacrylic acid is formed when 2-bromo 3-chloro-2-fluoropropionic acid or 2,3-dichloro-2-fluoropropionic acid esters with 40% potassium hydroxide solution at 60-70 ° C in yields of 73-76%. With quantitative yield, the pyrolysis of 2,3-dichloro-2-fluoropropionic acid chloride is achieved by passing it through a quartz tube heated to 440 ° C. and filled with activated carbon. The problem with this process is the complex synthesis of the selectively chlorinated or chlorinated and brominated 2-fluoropropionic acid derivatives, which are required as starting materials.

In the reaction of 1,2-dichloro-3,3-difluorocyclopropene with methanolic sodium methylate, the 3-chloro-2-fluoroacrylic acid methyl ester is formed only in a yield of 12% (J. Fluorine Chem. 10 (1977), 4, 261).

Also in the electrochemical dehalogenation of the easily accessible, fully halogenated 2-fluoropropionic acids to halogenated fluoroacrylic acids, 3-chloro-2-fluoroacrylic acid is only produced as a minor by-product. (EP A 0 308 838). Thus, in inventive example 7, when electrolyzing 2,3,3,3-tetrachloro-2-fluoropropionic acid on graphite electrodes in a catholyte, which, in addition to NaOH, also contains Pb (OOCCH3) 2 as the salt of a metal with a hydrogen overvoltage of at least 0.25 V. (based on a current density of 300 mA / cm ² ) contains dissolved, the yield of 3,3-dichloro-2-fluoroacrylic acid 97.2%; 3-Chloro-2-fluoroacrylic acid is formed as a by-product with a yield of only 2.1%.

The electrochemical exchange of halogen atoms for hydrogen or deuterium atoms on 3,3-dichloro-2-fluoroacrylic acid and its derivatives offers a basic access to 3-chloro-2-fluoroacrylic acid or to 3-chloro-3-deutero-2-fluoroacrylic acid and their derivatives. With this method, however, the reaction only incomplete at the level of

Stop 3-chloro-2-fluoroacrylic acid, and it mainly produces 2-fluoroacrylic acid or its derivatives. It can be seen from the inventive examples of EP-A-0 280 120 that 3-chloro-2-fluoroacrylic acid is used as an intermediate in the dehaiogenation of 3,3-dichloro-2-fluoroacrylic acid to 2-fluoroacrylic acid. However, 3-chloro-2-fluoroacrylic acid is formed at best with a yield of 62.8%, but is only in a purity of at most 78%, in addition to the two hard-to-separate acids 3,3-dichloro-2-fluoroacrylic acid and 2-fluoroacrylic acid , before (Example 3).

The production of 3-chloro-2-fluoroacrylic acid by this process is unselective and uneconomical, since complex cleaning of the electrolysis product is necessary.

The task therefore arose from the prior art of a process for the production of

2-fluoroacrylic acid derivatives, especially in the 3-position halogen or deuterium substituted

To find 2-fluoroacrylic acid derivatives, which enables a selective and economical synthesis of these compounds.

It has now surprisingly been found that the object can be achieved if the electrolysis in water or deuterium oxide is carried out, if appropriate with the addition of an organic solvent, on carbon electrodes in the presence of iron salts.

This finding is particularly surprising, since it is known from the prior art that the presence of iron salts during electrolysis is to be avoided, since even in very low concentrations (0.1 ppm) they can completely poison the cathode ( F. Beck, Electroorganic Chemistry, Weinheim, 1974, 95). As a result of such poisoning, the cathode loses its hydrogen overvoltage, ie the ability to reduce organic compounds in the presence of protons, ie under acidic conditions.

Then only the thermodynamically more favorable reduction of protons to hydrogen takes place at the cathode. Since this reaction drastically deteriorates the current efficiency of the process concerned, the process becomes uneconomical. For this reason, the presence of iron ions is carefully excluded in the prior art in the case of electrochemical reductions.

The invention thus relates to a process for the preparation of compounds of the formula (I)

wherein

R ^{1 represents} a fluorine atom, a methyl or deuteromethyl group, in particular a fluorine atom

R ^ and R ^{J are the} same or different and are a fluorine, chlorine, hydrogen or deuterium atom, preferably a chlorine, hydrogen or deuterium atom, and

R a group

O

- R "

is where R ⁵ -OH, -OD, C - ^ - C ^ -alkoxy or -OMe, with Me = alkali,

Alkaline earth metal or NH _A ion means by electrolytic reduction of compounds of the formula (II)

wherein R ¹ , R ² , R ³ and R ^{4 have} the meaning given above and R ° represents a chlorine atom or compounds of the formula (III)

where R, R ⁴ and R ° have the meaning given above, in a divided or undivided cell in an electrolysis liquid consisting of - in each case based on the total amount of the electrolyte in the undivided cell or of the catholyte in the divided cell - 0 to 100% by weight. -% deuterium oxide or water and 100 to 0 wt .-% of one or more organic solvents at a temperature in the range of -10 ° C to the boiling point of the electrolyte liquid, at a pH below 6 and current densities of 10 to 500 mA / cm , in the presence of iron salts, which are present in the electrolyte at a concentration of 1 to 5000 ppm, on a carbon cathode.

The method according to the invention is carried out in divided or undivided cells. To divide the cells into The anode and cathode compartments use the usual diaphragms made of polymers, preferably perfluorinated polymers, or other organic or inorganic materials, such as glass or ceramics, but preferably ion exchange membranes, which are stable in the electrolyte. Preferred ion exchange membranes are cation exchange membranes made of polymers, preferably perfluorinated polymers with carboxyl and / or sulfonic acid groups. The use of stable anion exchange membranes is also possible.

The electrolysis can be carried out in all customary electrolysis cells, for example in beaker or plate and frame cells or cells with a fixed bed or

Fluid bed electrodes. Both the monopolar and the bipolar circuit of the electrodes can be used.

Preferred anolyte liquids are aqueous mineral acids or solutions of their salts, such as, for example, dilute sulfuric acid, concentrated hydrochloric acid, sodium sulfate or sodium chloride solutions and solutions of hydrogen chloride in alcohol.

The catholyte fluid consists of or can contain water or deuterium oxide.

During electrolysis in the presence of deuterium oxide, all active protons and water contained in the anolyte and catholyte, including the water of crystallization, must be replaced by deuterium atoms or deuterium oxide.

The catholyte liquid can also consist of organic solvents, which can contain water or deuterium oxide. Examples of organic solvents are short-chain aliphatic alcohols such as methanol, ethanol, propanols or butanols, diols such as ethylene glycol, Propanediol but also polyethylene glycols and their ethers, ethers such as tetrahydrofuran, dioxane, amides such as diethylformamide, N-methyl-2-pyrrolidinone, nitriles such as acetonitrile, ketones such as acetone or other solvents.

The proportion of organic solvents in the catholyte liquid is 0% by weight in the case of electrolysis in water or in deuterium oxide, or 100% by weight if electrolysis is carried out without water. When working in mixtures of water or deuterium oxide and organic solvents, the proportion of organic solvents is 5 to 95% by weight, preferably 10 to 90% by weight, of the catholyte liquid.

The salts of iron contained in the electrolyte solutions according to the invention can be present in oxidation states 2+ and 3+, also side by side. The type of anion is unproblematic, but preference is given to using iron salts with the anions halide, S0 ₄ ² -, HS0 ₄ ^* , N0 ₃ ^" , BF ₄ " and CH ₃ C00 ~. The concentrations of the iron salts in the electrolysis solutions are 1 to 5000 ppm, preferably 10 to 3000 ppm, in particular 100 to 1000 ppm.

The electrolysis is carried out at pH values below 6, preferably below 5, in particular at pH values below 3.

To set the pH value which is favorable for the electrolysis and to increase the conductivity, dissociating compounds, for example inorganic or organic acids, preferably acids such as salt, boron or phosphorus, can be added to the catholyte in the divided cell or the electrolyte in the undivided cell -, Sulfuric or tetrafluoroboric acid and / or formic, acetic or citric acid and / or their salts.

Tetraalkylammonium salts, such as, for example, are also particularly suitable for increasing the conductivity Tetramethyl, tetraethyl, tetrapropyl and tetrabutylammonium salt with halide, sulfate, hydrogen sulfate, tetrafluoroborate, nitrate or acetate anions. The salts should be selected so that there is no formation of poorly soluble compounds.

The electrolysis is carried out at current densities of 10 to 500 A / cm, preferably at current densities of 20 to 400 mA / cm, in particular at 50 to 300 mA / cm.

Furthermore, salts of metals with a hydrogen overvoltage of at least 0.25 V (based on a current density of 300 mA / cm " ⁶ ) and, if appropriate, dehalogenating properties can be added to the electrolyte in the undivided cell or the catholyte in the divided cell mainly the soluble salts of Cu, Ag, Au, Zn, Cd, Hg, Sn, Pb, Tl, Ti, Zr, Bi, V, Ta, Cr or Ni, preferably the soluble Pb-, Zn-, Cd- , Cu and Sn salts, especially the soluble lead salts. The preferred anions of these salts are CI ^~ , S0 ₄ ^~~ , N0 ₃ "and CH ₃ C00 ~.

The salts can be added directly to the electrolysis solution or, e.g. by adding oxides, carbonates etc. - in some cases also the metals themselves (if soluble) - in the solution.

The salt concentration in the catholyte of the divided cell is expediently set to about 0.1 to 5000 ppm, preferably 10 to 1000 ppm.

In principle, all possible carbon electrode materials come into question as carbon cathodesή. e.g .: electrode graphites, impregnated graphite materials and also glassy carbon.

The same material as for the cathode or all materials on which can be used as anode material the anode reactions known per se take place. Examples are lead, lead oxide on lead or other carriers, platinum or titanium dioxide on titanium doped with noble metal oxides, for example platinum oxide or ruthenium dioxide, or other materials for developing chlorine from aqueous alkali metal chloride or aqueous or alcoholic hydrogen chloride solutions

The electrolysis temperature is in the range from -10 ° C to the boiling point of the electrolyte liquid, preferably from 10 to 90 ° C, in particular from 15 to 80 ° C.

It is possible to carry out the electrolysis both continuously and batchwise. A method of operation in divided electrolysis cells with a discontinuous execution of the cathode reaction and a continuous execution of the anode reaction is particularly expedient. If the anolyte contains hydrogen chloride, Cl ~ is constantly consumed by the anodic chlorine evolution, which can be compensated for by the continuous addition of gaseous HC1 or aqueous hydrochloric acid.

The electrolysis product is worked up in a known manner, e.g. by distillation or extraction of the products.

The compounds added to the catholyte can thus be returned to the process.

The process according to the invention can still be carried out even at high current densities and low pH values, without any appreciable development of hydrogen at the cathode being observable. The high selectivity of the reaction is retained even under these conditions. An increase in the current efficiency and the selectivity of the reaction and thus the economy of the process when carrying out the electrolysis in the presence of iron salts was in no way to be expected in the prior art.

Examples

The electrolysis was carried out in divided plates and frame cells (Sigri, Meitingen, Germany) electrode area: 1000 cm ² electrode distance: 4 mm cation exchange membrane: ®Nafion 423,

(Single layer membrane made of a copolymer of a perfuorsulfonylethoxy vinyl ether and

Tetrafluoroethylene) turbulence amplifier: polyethylene etze anolyte: 20% HC1 in water flow rate: 800 1 / h

Electrolytic cell 2:

Like electrolysis cell 1, with the exception of the following differences:

Electrode area: 200 cm ²

Anode: Titanium electrode coated with Ti0 and activated with Ru0 ₂ . Anolyte: 2% D ₂ S0 ₄ in 300 g D ₂ 0 or 5% H ₂ S0 ₄ in H ₂ 0 flow rate: 300 1 / h

The following table shows the catholyte composition, the electrolysis conditions and the electrolysis results. Examples

Deuterium [1] 14.6

Eq

Examples

Electrolysis resultJ

[g (yield)]

CHC1 = CFC00H 635.5 (89.4%) 388 (80.5)

CDC1 = CFC00D 18.8 (90.4%)

CDC1 = CFC00CH ₃

CC1 ₂ = CFC00H 64.2 21.1

CC1 ₂ = CFC00CH ₃

CH ₂ = CFC00H 14.3 (2.6 12.9 (3.7

CD ₂ = CFC00D 1.2 (7.2

CD ₂ = CFC00CH ₃

Electricity yield 75.5% 71.2% 61.4%

Claims

Claims: 1.

.

and

Alkaline earth or NH ₄ ion means, through electrolytic reduction, or a compound of formula (III)

where R, R and R have the meaning given above in an undivided or divided cell in an electrolysis liquid consisting of - based in each case on the total amount of the electrolyte in the undivided cell or of the catholyte in the divided cell - 0 to 100% by weight of water or deuterium oxide and 100 to 0 wt .-% of one or more organic solvents, at a temperature from -10 ° C to the boiling point of the electrolyte liquid, at a pH below 6 and current densities of 10 to 500 mA / cm ² in the presence of Iron salts, which are present in the electrolyte in a concentration of 1 to 5000 ppm, are subjected to electrolysis, the cathode consisting of carbon. 2. The method according to claim 1, characterized in that R is a fluorine atom and R ^ and R ^{J are} chlorine, hydrogen or deuterium. 3. The method according to claim 1, characterized in that the iron salts are present in the electrolyte of the undivided cell or the catholyte of the divided cell in the valence levels +2 or +3 or in both valence levels side by side. 4. The method according to claim 1, characterized in that the electrolysis is preferably carried out at a current density of 20 to 400 mA / cm, in particular at a current density of 50 to 300 mA / cπr. 5. The method according to claim 1, characterized in that the electrolysis is carried out in the presence of salts of metals with a hydrogen overvoltage of at least 0 to 25 V (based on a current density of 300 mA / cm ² ). 6. The method according to claim 5, characterized in that soluble salts of copper, zinc, cadmium, tin, lead or bismuth are used as metal salts in the electrolyte of the undivided cell or in the catholyte of the divided cell. 7. The method according to claim 6, characterized in that soluble lead salts are used as the metal salt in the electrolyte of the undivided cell or in the catholyte of the divided cell. 8. The method according to claim 5, characterized in that the concentration of the metal salts is in the range from 0.1 to 5000 ppm, preferably in the range from 10 to 3000 ppm. 9. The method according to claim 1, characterized in that the electrolysis is carried out at a temperature of 10 to 90, preferably 15 to 80 ° C. 10. The method according to claim 1, characterized in that the electrolysis is carried out in a divided cell with discontinuous cathode reaction and continuous anode reaction. Summary Process for the production of halogenated acrylic acids Process for the preparation of compounds of formula (I)

through electrolytic reduction. R ^{1 represents} a fluorine atom, a methyl or deuteromethyl group; R ^ and ^J are the same or different and represent a fluorine, chlorine, hydrogen or deuterium atom; R ⁴ is a group

in which R ⁵ denotes -OH, -OD, C ₁ -C ₄ -alkoxy or -OMe, with Me = alkali-earth alkali or NH ^ -ion. A compound of formula II

or a compound of formula (III) R ⁶ _.R ⁶ C = C (I I I) R - (R ¹ , R ² , R ³ and R ⁴ have the meaning given above; R is a chlorine atom) is in an undivided or divided cell in an electrolysis liquid in the presence of iron salts, which are present in the electrolyte in a concentration of 1 to 500 ppm are subjected to electrolysis.