CS265189B1 - Method for the pH of 2,6-difluorobenzamide - Google Patents

Abstract

2,6-Difluorobenzamide is prepared by hydrolysis of 2,6-difluorobenzonitrile with concentrated sulfuric acid and a small amount of water at a temperature of 30 to 70 °C. The main part of the product is separated by filtration and/or centrifugation from the dilute, cold reaction mixture, and a small part of the product is obtained by additional extraction of the acidic filtrate with a polyhalogenated hydrocarbon, exclusively tetrachloroethane.

Description

The invention relates to a process for the preparation of 2,6-difluorobenzamide of the formula by acid hydrolysis of 2,6-difluorobenzonitrile.

2,6-difluorobenzamide is an important intermediate for the preparation of insecticidal agents (eg Diflubenzuron, etc.). The conditions for the preparation of 2,6-difluorobenzamide are not specified in more detail in the available literature, as they are generally overshadowed by the broader patent interests of the respective insecticidal agent and its application. An exception is U.S. Pat. No. 4,117,009 (1978) which discloses the preparation of the final insecticide Diflubenzuron from 2,6-difluorobenzamide obtained by hydrolysis of 2,6-difluorobenzonitrile in concentrated sulfuric acid and subsequent extraction of the resulting 2,6-difluorobenzamide from solution with a suitable polyhalogenated solvent. It will further be appreciated that 2,6-difluorobenzamide can be prepared from the corresponding 2,6-difluorobenzoic acid derivatives (e.g., by ammonolysis of an acyl chloride or ester).

It is apparent from the above overview that the above general principles for the preparation of 2,6-difluorobenzamides are either not properly specified or are technologically and economically demanding.

It has now been found that 2,6-difluorobenzamide is preferably prepared by the process of this invention by reacting 2,6-difluorobenzonitrile with concentrated sulfuric acid and water at a temperature of 30 to 70 ° C, wherein 2,6-difluorobenzamide is separated by filtration from dilute, cold of the reaction mixture and a small portion of the product is obtained by extraction of the dilute acid filtrate with tetrachloroethane.

The actual hydrolysis of 2,6-difluorobenzonitrile is preferably carried out by dissolving 2,6-difluorobenzonitrile in the present amount of 98% H 2 SO 4 and water while stirring, and then maintaining the mixture for 3 1/2 h at a temperature of about 60 ° C until complete. conversion of 2,6-difluorobenzonitrile. The mixture is then cooled and poured onto crushed ice and, after dissolving the ice, separated by filtration or centrifugation of the 2,6-difluorobenzamide suspension, which is washed repeatedly with cold water and then dried in a vacuum oven at 80 to 90 ° C. A smaller portion of the desired product is obtained from the aqueous acid filtrate by additional extraction with carbon tetrachloride and evaporation of the extract.

The reaction is rapid, the desired product is obtained in about 77% yield in high purity without the need for a complicated extraction device which will be required in the cited US patent.

The advantage of this process is simple and quick preparation, without complicated and expensive technological equipment. The disadvantage is that the dilute sulfuric acid used cannot be recirculated without concentration back to the hydrolysis, although the consumption standard I2SO4 can be reduced by a further min. 1/3.

The example below illustrates an embodiment of the invention.

Example

A 3/4 liter reactor was charged with 200 mL of 98% H 2 SO 4, 5 mL of distilled water and then, at a temperature of about 30 ° C, successively introduced from a measuring cup of 71 g of distilled 2,6-difluorobenzonitrile. Deň: 32 ° C. After the 2,6-difluorobenzonitrile feed is complete, the batch is heated to 60 ° C in the reactor and stirred at this temperature for 1/2 hour until 2,6-difluorobenzonitrile is totally reacted (TLC control).

The reaction mixture is then cooled and poured onto about 450 g of crushed ice and stirred for 1/2 hour after the ice has melted, then the precipitated 2,6-difluorobenzamide suspension is filtered on a vacuum suction through a POP cloth and washed with 4x100 ml of distilled water. . 101.2 g of wet paste are obtained, which are dried in a vacuum oven at 80 to 90 ° C to obtain

1. part 57 g of dried 2,6-difluorobenzamide, m.p. Melting point = 139.5-143 ° C.

The second share, respectively. 3 g of 2,6-difluorobenzamide are obtained by extracting the filtrates twice with 200 ml of tetrachloroethane each time, evaporating the tetrachloroethane under a vacuum of 26 to 35 kPa, washing the obtained residue with 50 ml of distilled water and drying.

A total of 60 g of 2,6-difluorobenzamide was obtained, i.e. 77.2% of theory. The product was pure by 2,6-difluorobenzoic acid according to TLC and NMR.

Claims (2)

1 ·. Process for preparing 2,6-difluorobenzamide of formula conh ₂ F F acid hydrolysis of 2,6-difluorobenzonitrile with concentrated H 2 SO 4, characterized in that the reaction is carried out at 30 to 70 ° C, the major product solid obtained is separated by filtration or centrifugation from the diluted, cold reaction mixture and from the remaining acid filtrate. yields a further smaller proportion of 2,6-difluorobenzamide by extraction with a polyhalogenated solvent. Process according to claim 1, characterized in that the extraction is preferably carried out with carbon tetrachloride.