RU2349578C1 - Method of producing perfluorocarboxylic acids - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: present invention pertains to the method of obtaining perfluorocarboxylic acids, which, like their derivatives, are used for polymerisation of perfluoro olefins, for producing perfluorinated surface active substances with high surface activity, as well as water and oil proofing agents for processing fabrics, paper and leather. The method of producing perfluorocarboxylic acids involves electrochemical fluorination in hydrogen fluoride of telomeric alkanols with general formula H(CF₂CF₂)_nCH₂OH, where n=3 and 4. The obtained perfluoroanhydrides subsequently undergo hydrolysis. Electrochemical fluorination of telomeric alkanols takes place in the presence of an aliphatic or aromatic amine as an electrolytic additive. Hydrolysis is achieved using water, adding it directly into the reaction crude mixture, obtained after electrochemical fluorination.

EFFECT: simplification of the process and increased output of target perfluorocarboxylic acids with high degree of purity.

3 cl, 3 ex

Description

The invention relates to a method for producing perfluorocarboxylic acids by hydrolysis of their fluorohydrides obtained by electrochemical fluorination (ECP) in hydrogen fluoride. Perfluorocarboxylic acids and their derivatives have very high thermal and chemical resistance and are used for the polymerization of perfluoroolefins, for the production of perfluorinated surfactants (perfluorinated surfactants) with high surface activity, and also serve as water and oil repellent agents for the treatment of fabrics, paper and leather.

Known chemical and electrochemical (ECP) methods for producing perfluorocarboxylic acids.

Chemical methods for producing perfluorocarboxylic acids include, for example, a method for the interaction of perfluoroalkyl halides with carbon dioxide and a pair of ZnM ₂ , where M is a more electropositive metal compared to zinc in a dialkyl sulfoxide medium [vyl. application of Germany 2756169, IPC S07C 51/15, S07C 53/21, op. 06/22/1978]. The disadvantage of this process is the high toxicity of dialkyl sulfofluorides and their unpleasant odor.

Perfluorocarboxylic acids can also be obtained by oxidation of perfluoroolefins [US Pat. UK No. 1473807, IPC S07C 51/32, op. 1977 g]. This patent describes a two-stage process for the preparation of perfluorocarboxylic acids, including the interaction of perfluoroolefin with ozone to form perfluoroalkylzonides and perfluoroalkylaldehydes and their subsequent conversion to perfluorocarboxylic acids using an oxidizing agent, for example hydrogen peroxide. However, this method requires the use of expensive feedstock and highly toxic and unstable ozone.

In all methods, big problems arise at the stage of purification of the target acid.

To reduce the fluoride ion content in the target product to 5 ppm, it was proposed to carry out hydrolysis in a medium of 15% sulfuric acid [PCT application 2004 29008, op. 04/08/2004]. However, due to the high corrosivity of 15% sulfuric acid, special equipment is required for hydrolysis.

Methods have been developed for producing perfluorocarboxylic acids by hydrolysis of their fluorohydrides obtained by electrochemical fluorination of hydrocarbon acids or their halides in hydrogen fluoride.

Thus, electrochemical methods for producing perfluorocarboxylic acid fluorides are known.

The known method [US Pat. Germany No. 2442106, IPC. C07C 143/70, 1978] for the preparation of perfluorooctanoic acid fluoride by electrochemical fluorination of octanoic acid fluoride in liquid hydrogen fluoride at 30 ° C, a voltage of 10 V, at a current density of 0.037 A / cm ² and a nitrogen pressure of 1 at. The content of perfluorinated products in the raw material is 87%, the yield of perfluorooctanoic acid fluoride is 37% of the theoretical. Examples of the production of perfluorocarboxylic acid fluorides with a large number of carbon atoms in a chain are not given.

The known method [US Pat. RF №2221765, С07С 19/08, op. 01/20/04], the preparation of perfluorinated organic compounds by ECP of their precursors — alkyl ethers and partially fluorinated compounds — using an aliphatic or aromatic amine as an electrolytic additive, but there is no information on the possibility of ECF of telomeric alkanols in the presence of aliphatic or aromatic amines.

According to the method [US Pat. RF 2107751, IPC С25В 3/08, С07С 53/21, op. 1998 - prototype] perfluorocarboxylic acid fluorides with 5-11 carbon atoms in the chain were obtained by ECF mixtures of fluorine-containing alkanols of the general formula H (CF ₂ -CF ₂ ) n CH ₂ OH, where n = 2-5 and the content of the fraction with n = 2 and 3 is 60-75%. In this way, perfluoroheptanoic acid fluoride was obtained with a maximum yield of 53.2% at an electrolyte temperature of 10-15 ° C, a current density of 0.01 A / cm ² , a voltage of 5.5-6 V. Under these conditions, the maximum yield of perfluorononanoic acid fluoride amounted to 12.79%.

The resulting perfluorohydrides were fractionated and hydrolyzed with 10% NaOH. As a result of hydrolysis, the sodium salt of the corresponding acid was obtained, which was decomposed with sulfuric acid. The yield of target acids is 95-96%.

In this way, it is practically possible to obtain in high yield only perfluoroheptanoic acid fluoride. In this method, corrosive substances — alkali and sulfuric acid — are used at the hydrolysis stage, the processing of which obtained products complicates and increases the cost of hydrolysis.

The authors were faced with the task of simplifying the process of producing perfluorocarboxylic acids, for example perfluoroheptanoic and perfluorononanoic acids, including the hydrolysis of their perfluorohydrides obtained by ECP of the initial telomeric alkanols, and increasing the yield of target acids with a high degree of purity.

The essence of the invention lies in the fact that a method for producing perfluorocarboxylic acids has been developed, including electrochemical fluorination of telomeric alkanols of the general formula H (CF ₂ CF ₂ ) n CH ₂ OH, where n = 3 and 4, followed by hydrolysis of the obtained perfluorohydrides. The electrochemical fluorination of telomeric alkanols is carried out in the presence of an electrolytic additive, hydrolysis is carried out with water, adding it to the raw reaction mass obtained after electrochemical fluorination. As an electrolytic additive, a tertiary aliphatic or aromatic amine is used, wherein the amine is taken in an amount of 5-10% by weight of the electrolyte.

One of the embodiments of the method consists in the fact that electrochemical fluorination of an individual fraction of telomeric alkanol with n = 3 or with n = 4 is carried out.

In particular, the method consists in the fact that perfluorocarboxylic acids are perfluoroheptanoic and perfluorononanoic acids.

The method according to the invention is carried out by exposing to ECF individual fractions of the starting alkanols with n = 3 or n = 4 and fluorination of alkanols of the general formula H (CF ₂ CF ₂ ) ₃ CH ₂ OH, where n = 3 or 4, is carried out in the presence of an electrolytic additive - tertiary aliphatic or aromatic amine. The obtained perfluorohydrides are subjected to hydrolysis, while the water necessary for hydrolysis is added directly to the reaction mass (crude) obtained after ECP. The aqueous phase containing hydrogen fluoride is separated from the hydrolysis products, and the perfluorinated amine and by-products are distilled off from the organic phase containing perfluoroheptanoic acid or perfluorononanoic acid, and by-products, and the target acid soluble in them precipitates as white or yellow flakes. The distilled products are rectified and perfluorinated amines are isolated.

Although the method for producing perfluorinated organic compounds by ECP of their precursors — alkyl ethers and partially fluorinated compounds — using an aliphatic or aromatic amine as an electrolytic additive is known [cited above. RF №2221765, IPC С07С 19/08, op. 01/20/04], there is no evidence of the possibility of ECP of telomeric alkanols in the presence of aliphatic or aromatic amines.

Moreover, in addition to the well-known advantages obtained when using a tertiary amine as an electrolytic additive (increasing the duration of electrolysis, reducing the gumming of the feedstock, the ability to obtain the perfluorinated amine that is currently required), the presence of the perfluorinated tertiary amine in the raw material provides a smooth hydrolysis without formation of undesirable side effects. products, as well as the quantitative yield of perfluoroheptanoic or perfluorononanoic acid at this stage. Adding directly to the raw mass of water also simplifies the purification of the target products from hydrogen fluoride.

The following examples illustrate the invention, but do not limit its essence.

Stage of ECF of telomeric alkanols

Example 1

Fluoridation of telomeric alkanol n = 3

A) Fluorination of telomeric alkanol H (CF ₂ —CF ₂ ) ₃ CH ₂ OH in the presence of pyridine.

560 g of anhydrous hydrogen fluoride, 50 g of pyridine and 50 g of the indicated alkanol are loaded into the electrolyzer. As the starting organic compounds are consumed, alkanol and pyridine are added to the electrolyte. The electrolysis duration was 61 hours, with 902.5 ampere hours (Ah) skipped, 1367 Ah / L. The fluorination products as they accumulate in the separator-collector are separated from hydrogen fluoride and the raw material is analyzed by GLC. Received 718 g of crude perfluoroheptanoic acid; current efficiency 56%.

Process parameters: current strength 15 A / cm ² ; current density 0.03 A / cm ² ; voltage 4.5-6.3 V;

B) fluorination in the presence of triethylamine

The experiment is carried out in the same cell where 560 g of anhydrous hydrogen fluoride, 50 g of triethylamine, 50 g of the same alkanol are loaded.

With the process parameters specified in example 1 (A), the electrolysis duration was 73 hours, electricity was missed 1095 Ah, 1533.5 Ah / l, 870 g of raw material were obtained, the current efficiency was 58%.

Example 2

Fluoridation of telomeric alkanol n = 4

A) In the presence of pyridine

Fluorination is carried out in the electrolyzer according to example 1 A) with the same current process parameters. 560 g of anhydrous hydrogen fluoride, 50 g of pyridine and 50 g of alkanol are loaded into the electrolyzer. At the end of the process, the raw material is analyzed by GLC.

The duration of electrolysis is 71 hours; electricity passed 1062 Ah, 1610 Ah / l.

Received 690 g of raw, current efficiency 21%.

B) in the presence of triethylamine

The experiment is carried out in the electrolyzer according to example 1 A), where 560 g of anhydrous hydrogen fluoride, 50 g of triethylamine, 50 g of alkanol are loaded.

With the process parameters indicated in example 1, the electrolysis duration was 64 hours, electricity was passed 962.5 Ah, 2139 Ah / l, 750 g of crude perfluorononanoic acid was obtained, the current efficiency was 33.5%.

The step of hydrolysis of raw ECF

Example 3

A) Hydrolysis of raw ECF alkanol n = 3

The hydrolysis of raw ECF is carried out in a sealed 1 liter Teflon reactor with a stirrer. To the raw material in an amount of 1.5 kg containing 50% heptanoic acid perfluorohydride, water is added in portions with continuous stirring, making sure that the temperature of the reaction mixture does not rise above 100 ° C. After applying the calculated amount of water, the contents of the reactor are heated to 25-30 ° C and stirred until hydrolysis is complete (according to the results of GLC analysis). As a result of hydrolysis, a solution of perfluoroheptanoic acid in organofluorine by-products is formed. The latter is distilled off at a residual pressure of 7-10 mm Hg. and collected in a cooled receiver. Perfluoroheptanoic acid remains in the reactor in the form of white or pale yellow flakes, which are dried at a temperature of 40-50 ° C and a residual pressure of 5-10 mm Hg. 730 g of 97.3% of theory are obtained.

Organofluorine by-products collected in the receiver are purified and rectified and the second target product, perfluoropentane and perfluoropiperidine, is isolated in an amount of 510 g (when using pyridine as an electrolytic additive), 689 g of perfluorodimethylethylamine and perfluorotriethylamine (when triethyl is used as an electrolytic )

B) Hydrolysis of raw ECF alkanol n = 4

Hydrolysis is carried out under conditions and on equipment according to example 3 A).

Raw material is charged in an amount of 1.4 kg containing 50% perfluorononanoic acid, after distillation of by-products, perfluorononanoic acid in an amount of 680 g (97.1%) is obtained.

As can be seen from the above examples, perfluoroheptanoic acid and perfluorononanoic acid are prepared using typical equipment and reagents for ECP processes. Due to the presence of a perfluorinated amine in the hydrolyzable mass, a raw material with a high content of the target product is obtained, since this hydrolysis proceeds in the automatic thermal control mode and is practically not accompanied by the decomposition of the target products, which simplifies their isolation and purification. Thus, the problem of simplifying the process of producing perfluorocarboxylic acids, including the hydrolysis of their perfluorohydrides obtained by ECP of the initial telomeric alkanols, was solved, and the yield of target acids of high purity was increased.

Claims (3)

1. A method of producing perfluorocarboxylic acids, including electrochemical fluorination of telomeric alkanols of the general formula H (-CF ₂ CF ₂ -) _n CH ₂ OH, where n = 3 and 4, and subsequent hydrolysis of the obtained perfluoroanhydrides, characterized in that the electrochemical fluorination of telomeric alkanols is carried out in the presence of an electrolytic additive, an aliphatic or aromatic amine, and hydrolysis is carried out with water, which is added to the reaction mass obtained after electrochemical fluorination. 2. The method of producing perfluorocarboxylic acids according to claim 1, characterized in that the electrochemical fluorination of the individual telomeric alkanol fraction with n = 3 or n = 4 is carried out. 3. The method of producing perfluorocarboxylic acids according to claim 1, characterized in that the aliphatic or aromatic amine is taken in an amount of 5-10 wt.% By weight of the electrolyte.