SU1699993A1 - Method of producing trifluoroacetic acid and its salts - Google Patents

Abstract

The invention relates to halo-substituted aliphatic acids, in particular trifluoroacetic acid or its salts, used in the organic synthesis of drugs and agricultural chemicals. The purpose of the invention is to simplify the process. The latter are carried out by electrolysis of a mixture of bromotrifluoromethane and carbon dioxide using an inert cathode, an electrolyte (based on a solution of a quaternary ammonium salt in an aprotic polar solvent) and an anode from a metal capable of anodic dissolution in this system, such as zinc, aluminum, cadmium. The process is carried out in a sealed cell with unseparated cathode and anode spaces with continuous introduction into the cell of a mixture of gaseous bromine trifluoromethane and carbon dioxide, taken in a molar ratio of 1: (1.5-5). The desired product is isolated in the form of a salt, which, if necessary, is converted to an acid. These conditions allow electrolysis to be performed with an unseparated cathode and anode space while reducing the consumption of violet electrolyte (50-100). С $ С / с

Description

The invention relates to the electrochemical synthesis of organic compounds, namely, the electrochemical method for producing trifluoroacetic acid or its salts from bromotrifluoromethane and carbon dioxide, which are used in organic synthesis, the synthesis of medicinal substances and agricultural chemicals.

The aim of the invention is to simplify the process.

The electrolysis of the mixture of bromotrifluoromethane and carbon dioxide is carried out in an inert cathode system, an electrolyte based on a solution of a quaternary ammonium salt in an aprotic polar solvent and an anode, using as the anode a metal capable of anodic dissolution in this system, for example, zinc, aluminum , cadmium, in a tight sealed with unseparated cathode and anode spaces with a continuous introduction into the cell of a mixture of gaseous bromotrifluoromethane and carbon dioxide, taken in a molar ratio of 1: 1.5-5s with the release of Vågå vlde product salt and then, if necessary, transfers in kislotu-.

and her her her

PRI me R 1.

a) Preparation of potassium trifluoroacetate; Place in a 150 ml well

60 ml of dimethylformamide containing 0.1 mol / l of 1-labutylammonium bromide. The cathode is a platinum foil with an area of 20 cm2, and the anode is a zinc cylinder with an area of 110 cm2. A saturated calomel electrode is used as a reference electrode. The gas tank is filled with 0.89 g (6.0 mmol) of bromotrifluoromethane and 0.43 g (9.8 mmol) of carbon dioxide (CF BriCC ratio). The electrolysis is carried out in potentiostatic mode at a cathode potential of 2.4 V, continuously bubbling. into the working solution mixture of reacting gases using a peristaltic pump. After electrolysis (total of 965 Cl is missed), the cell is opened, the solution is filtered from a small amount of zinc carbonate by-product, and then the dimethylformation is distilled off under reduced pressure (35 ° C / 5 mmHg, Art.) Dry residue decompose 10 ml of 36.5% hydrochloric acid and extracted with ether. An equal amount of water is added to the ether fraction and neutralized with potassium hydroxide to pH 10, after which the ether and water are distilled off on a rotary evaporator, and the dry residue is extracted with hot acetone. After distilling off the acetone and drying the extract under vacuum to constant weight, 0.50 g of potassium trifluoroacetate (3.8 mmol, substance yield (Vb) 55%, yield current l (W) 76%), 142-143 ° C are obtained. ,

: 6g -Found,%: C 15.25. Calculated for

b) Conversion of potassium trifluoroacetate to trifluoroacetic acid.

To the 0.50 g of potassium trifluoroacetate obtained in Example 1, 2 ml of 96% sulfuric acid are poured, heated to 140-150 ° C and the trifluoroacetic acid evaporating is distilled into a cooled receiver. 0.32 g of trichloroacetic acid (2.8 mmol, yield but potassium trifluoroacetate 85.5%) is obtained, b.p. 72 ° C.

Example 2. In the cell described in Example 1, 60 ml of dimethylformamide containing C, 05 mol of tetraethylammonium fluoroborate are placed. In ka

1C | NMR: 5 86 ppm

mp, rel,

 (singlet).

%: C 15.79

20

,

,

. JQ {5 ohm, 25 k th

/ l

699993

cathode

thirty

35

40

9,

45

50

55

use platinum foil with an area of "-. 20 cm2, and as the anode - an aluminum cylinder with an area of A 110 cm2. The gas tank is filled with 1.38 g (9.3 mmol) of bromotrifluoromethane and 1.15 g (26.1 mmol) of carbon dioxide (the ratio CPpBr: COЈ 1: 2.8). The reference electrode is silver chloride electrode. Electrolysis is carried out in galvanostatic mode at a current density of 2.5 mA / cm2, reducing it to the end of the synthesis to 0.5 mA / cm2. At the end of the electrolysis (a total of 1395 Cl is missed), the cell is opened and the product is isolated according to the procedure described in Example 1 (ammonium hydroxide is used to neutralize potassium hydroxide). Obtain 0.62 g of ammonium trifluoroacetate (4.7 mmol, VV 51%, W 65%), mp, 155-156 ° C.

Found: C: C 18.19; H 2.99; N 10.54.

Calculated for;%: C 18,32; H 3.05; N 10.69.

Example 3 60 ml of dimethyl sulfoxide containing 0.2 mol / l of tetrabutylammonium perchlorate is placed in the cell described in example 1. A platinum foil of 20 cm2 is used as a cathode, and a cadmium plate of 40 cm2 is used as an anode. The gas tank is filled with 1.56 g (10.5 mmol) of bromotrifluoromethane and 2.23 g (50.7 mmol) of carbon dioxide (Cr Br: CO ratio 1: 4.8). The reference electrode is a saturated calomel electrode. The electrolysis is carried out in the potentiostatic mode at a cathode potential of 2.2 V, continuously bubbling a mixture of bromotrifluoromethane and carbon dioxide into the working solution using a peristaltic pump. At the end of the electrolysis (a total of 1480 K are missed) and the product are isolated, (as described in Example 1a (hydrochloride hydroxide is used for neutralization), 0.94 g of barium trifluoroacetate (2.6 mmol, Vb 50%, W 68%) are obtained .

JC-spectrum (tablet KBV), 1670 och. 1442 wed; 1200 ops; 1140 s; 845 sr .; 800 cf.

Found,%: C 13.35.

Calculated for,%: C 13.58.

The invention allows to fundamentally simplify the process of echectrosynthesis,

since it can be carried out in an electrolyzer with unseparated cathode and anode spaces. This reduces the consumption of expensive pho-, new electrolyte in the process of electrosynthesis (50-100 times).

Claims (1)

Invention Formula The method of producing trifluoroacetic acid or its salts by electrolysis of a mixture of halo-trifluoromethane and carbon dioxide in the presence of a quaternary ammonium salt in an aprotic polar solvent in a cell with an inert material cathode, o t , o five In order to simplify the process, bromotrifluoromethane is used as halogenated fluoromethane, anode is a metal capable of anodic dissolution in this system, for example, zinc, aluminum, cadmium, and the process is carried out in a sealed cell with unseparated cathodic and anodic spaces with a continuous introduction into the cell of a mixture of gaseous bromotrifluoromethane and carbon dioxide, taken in a molar ratio of 1: 1.5–5, with the selection of the target product in the form of a salt and subsequent, if necessary, conversion to acid.