RU2368595C1 - Preparation of 1,1-difluoro-2-bromoethylene - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to method of obtaining 1,1-difluoro-2-bromoethylene through dehydrohalogenation of 1,1-difluoro-1,2-dibromoethane with an aqueous 15-30% solution of potassium hydroxide, which is added while stirring with simultaneous distillation of the formed 1,1-difluoro-2-bromoethylene in fractionation mode.

EFFECT: increased output of desired product from 83,2 to 96,3-98,5%.

1 cl, 3 ex

Description

The invention relates to chemical technology and is intended to produce 1,1-difluoro-2-bromoethylene-fluorine-containing olefin, which is used as an additive in the preparation of fluorine-containing elastomers.

A known method for producing 1,1-difluoro-2-bromoethylene by reacting 1,1-difluoro-1,2,2,2-tetrabromoethane with metallic zinc or magnesium in ethanol (US Pat. No. 3,554,516, IPC C07C 19/08 , С07С 21/14, С07С 21/18, NPK 260-653.3, publ. 04/07/1970). The disadvantage of this method is the use of a flammable solvent.

There is another method for producing bromine-containing alkenes, which eliminates the disadvantage of the previous one. This method consists in dehalogenation of the corresponding bromoalkane with zinc in water in the presence of a catalyst, which is used as dimethyl- or diethylalkylbenzylammonium chloride (ed. St. USSR No. 882990, IPC 3 C07C 21/04, C07C 17/24, publ. 11/25/1981). The disadvantage of this method is the use of highly toxic metallic zinc and no less toxic catalyst.

There is also known a method for producing bromine-containing alkenes, which allows you to partially eliminate the disadvantage of the previous one and, in its technical essence, is closest to the proposed one. This method consists in dehydrochlorinating the corresponding bromoalkane with an aqueous solution of alkali metal hydroxide at elevated temperature and in the presence of a catalyst, which is used dimethyl- or diethylalkylbenzylammonium chloride (ed. St. USSR No. 771081, IPC 3 С07С 21/04, С07С 21/14, С07С 17/24, publ. 10/15/1980). The method eliminates the use of toxic zinc.

The disadvantage of this method is the use of an expensive and toxic catalyst, the discharge of which into the hydrographic network is limited. When using this method on an industrial scale, there will be a need to create an additional installation for the disposal of spent aqueous-alkaline solutions contaminated with a catalyst.

The technical problem solved by the claimed invention is to simplify the method of producing 1,1-difluoro-2-bromoethylene, increasing its efficiency and environmental safety.

The stated technical problem is solved in that in the method for producing 1,1-difluoro-2-bromoethylene by dehydrohalogenation of the corresponding bromoalkane with an aqueous solution of alkali metal hydroxide at elevated temperature, 1,1-difluoro-1,2-dibromoethane is used as bromoalkane and dehydrohalogenation is carried out with a 15-30% solution of potassium hydroxide, which is introduced into 1,1-difluoro-1,2-dibromethane with stirring while distilling off the resulting 1,1-difluoro-2-bromoethylene in the rectification mode.

Potassium hydroxide is introduced in an amount of 1.00-1.05 mol per 1 mol of 1,1-difluoro-1,2-dibromoethane at a temperature of 50-75 ° C.

Distillation of 1,1-difluoro-2-bromoethylene is carried out on a distillation column with an efficiency of 5-10 theoretical plates.

The invention is illustrated by the following examples.

Example 1

Obtaining 1,1-difluoro-2-bromoethylene is carried out in a reactor of steel 12X18H10T with a volume of 15 dm ³ equipped with a thermostatic jacket. The reactor is equipped with a stirrer, siphons for loading 1,1-difluoro-1,2-dibromoethane and a dosage of potassium hydroxide solution. On the reactor lid there is a fitting on which a distillation column with an efficiency of 5 theoretical plates is installed, equipped with a reflux condenser cooled to a temperature of minus 5 ° С.

8,200 g (36.61 mol) of 1,1-difluoro-1,2-dibromoethane are charged into the reactor, heated to 60 ° C with stirring, and a 30% potassium hydroxide solution in the amount of 6950 g is gradually introduced into the reactor (37, 23 mol). The resulting vaporous 1,1-difluoro-2-bromethylene together with 1,1-difluoro-1,2-dibromethane vapor enters the distillation column, where 1,1-difluoro-2-bromethylene is separated from impurities, mainly from 1 , 1-difluoro-1,2-dibromethane. The purified 1,1-difluoro-2-bromoethylene is taken into the balloon as a light fraction of rectification from the reflux line. 5155 g (36.05 mol) of 1,1-difluoro-2-bromoethylene are obtained with a basic substance content of 99.9%. The product yield is 98.5%.

Example 2

The preparation of 1,1-difluoro-2-bromoethylene is carried out in the apparatus described in Example 1, but 6500 g (29.02 mol) of 1,1-difluoro-1,2-dibromethane are charged into the reactor. Heated to a temperature of 70 ° C 1,1-difluoro-1,2-dibromoethane is introduced a 15% solution of potassium hydroxide in an amount of 11300 g (30.27 mol). 3996 g (27.94 mol) of 1,1-difluoro-2-bromoethylene are obtained with a basic substance content of 99.9%. The product yield is 96.3%.

Example 3 (control)

Obtaining 1,1-difluoro-2-bromoethylene is carried out in a reactor similar to that described in example 1, but instead of a distillation column, a reflux condenser is installed on the reactor lid, cooled to a temperature of + 10 ° С, to remove raw 1,1-difluoro-2-bromoethylene which is condensed in a cylinder cooled by liquid nitrogen. The obtained raw 1,1-difluoro-2-bromoethylene is subjected to rectification on a column with an efficiency of 5 theoretical plates to isolate a fraction of the basic substance.

7500 g (33.48 mol) of 1,1-difluoro-1,2-dibromoethane are charged to the reactor. Heated 1,1-difluoro-1,2-dibromethane to a temperature of 60 ° C and gradually introduced a 30% solution of potassium hydroxide in an amount of 6560 g (35.14 mol). Raw materials of 1,1-difluoro-2-bromoethylene in the amount of 5217 g are condensed into the balloon, which is rectified to isolate the fraction of 1,1-difluoro-2-bromoethylene. 3983 g (27.85 mol) of 99% 1,1-difluoro-2-bromoethylene are isolated. The product yield is 83.2%.

As can be seen from the presented examples, the synthesis of 1,1-difluoro-2-bromoethylene by the proposed method is characterized by a higher yield of the target product, apparently due to the combination of the synthesis stage and the rectification stage. Self-rectification of raw 1,1-difluoro-2-bromoethene requires prolonged heating of 1,1-difluoro-2-bromoethene, which leads to its partial resinification and a decrease in the yield of the purified product. In addition, due to the use of an active base (potassium hydroxide), which itself is a catalyst for the dehydrobromination process, the proposed method does not require the use of a special catalyst, while the catalysts used in the prototype belong to highly toxic substances (hazard class 2), therefore, the implementation of the method in on an industrial scale would require the creation of a special installation for the disposal of waste solutions.

Thus, the proposed method is simpler in its implementation, characterized by higher economic and environmental indicators.

Claims (3)

1. The method of producing 1,1-difluoro-2-bromoethylene by dehydrohalogenation of the corresponding bromoalkane with an aqueous solution of alkali metal hydroxide at elevated temperature, characterized in that 1,1-difluoro-1,2-dibromoethane is used as bromoalkane and 15- 30% potassium hydroxide solution, which is introduced into 1,1-difluoro-1,2-dibromethane with stirring while distillation of the resulting 1,1-difluoro-2-bromoethylene in distillation mode. 2. The method according to claim 1, characterized in that the potassium hydroxide is introduced in an amount of 1.00-1.05 mol per 1 mol of 1,1-difluoro-1,2-dibromethane at a temperature of 50-75 ° C. 3. The method according to claim 1, characterized in that the distillation of 1,1-difluoro-2-bromoethylene is carried out on a distillation column with an efficiency of 5-10 theoretical plates.