CS270773B1 - Process for preparing 2,4,4-trichloro-5,5,5-trifluoropentanoic acid - Google Patents

Abstract

A method for producing 2,4,4-trichloro-5,5,5-trifluoropentanoic acid by transesterification reaction of esters of the general formula CF3CCI2CH2 CHC1C00R, where R is up to C4 alkyl in formic acid or acetic acid in the presence of a catalytic amount of a mineral acid such as sulfuric acid or an organic acid such as p-toluenesulfonic acid or an ion exchanger containing SOjH group in the presence of water by heating the mixture at 60 to 140 °C to boiling while simultaneously removing the resulting alkyl ester of formic acid or alkyl esters of acetic acid. 2,4,4-trichloro-5,5,5-trifluoropentanoic acid is an important intermediate for the production of top-quality fluorinated pyrethroids, which are highly effective insecticides.

Description

The present invention relates to a process for the preparation of 2,4,4-trichloro-5,5,5-trifluoropentanoic acid, which is an important intermediate in the production of synthetic pyrethroids.

Synthetic pyrethroids derived from cyclopropanecarboxylic acid derivatives are currently of interest as top insecticides, as they excel in a number of advantages, especially in terms of environmental friendliness. Pyrethroids are up to 30 times more effective than natural pyrethrins, 2 orders of magnitude more effective than organophosphates and 3 orders of magnitude more effective than 00T-type organic chlorine compounds. In addition, they have a broad spectrum and a relatively long duration of action, fast metabolism and easy degradability to harmless substances. Their properties are described in detail in the monograph of J.P. Leahey The Pyrethroid Insecticides, Taylor and Francis, London 1985.

One possibility for the synthesis of cyclopropanecarboxylic acid derivatives is the conversion of 2,4,4-trichloro-5,5,5-trifluoropentanoic acid via cyclobutane ring intermediates (Brit. Pat. Application No. GB 2,065,118 (1981)). 2,4,4-Trichloro-5,5,5-trifluoropentanoic acid can be prepared by radical addition of 1,1,1-trifluorotrichloroethane to acrylic acid by the action of copper chloride in acetonitrile. The disadvantage of this process is the need to operate at elevated temperatures and pressures with a long reaction time (120 ° C, 24 hours), while the product yield is low (34%) and insufficient for practical purposes (Europe, Pat. No. EP 50 777 (1982)).

Alternatively, 2,4,4-trichloro-5,5,5-trifluoropentanoic acid can be prepared by hydrolysis of their esters, which can be obtained by adding 1,1,1-trifluorotrichloroethane to acrylic acid esters by the action of copper complexes in high yields of 70 to 90% according to MS. copyright certificate 257 965 (1987). The preparation of 2,4,4-trichloro-5,5,5-trifluoropentanoic acid by acid hydrolysis of esters by prolonged boiling in dilute hydrochloric acid in a yield of 75% is described in Brit, Pat. login No. GB 2 065 118 (1981) and NSR Pat. login No. DE 3,045,768 (1981). Alkaline hydrolysis cannot be used in this case because of the side dehydrochlorination reactions.

A simpler industrially applicable and waste-free conversion method; of esters to 2,4,4-trichloro-5,5,5-trifluoropentanoic acid by a catalytic transesterification reaction describes the present invention.

The present invention provides a process for the preparation of 2,4,4-trichloro-5,5,5-trifluoropentanoic acid by the transesterification reaction of esters of the general formula CF of sulfuric acid or of a strong organic acid of p-toluenesulphonic acid or of an ion exchanger containing an SO 2 H group or mixtures thereof, preferably in the presence of water, the resulting reaction mixture being heated to boiling at 60 to 140 ° C, preferably at 100 ° C. to 120 ° C, while removing the resulting formic acid alkyl ester or acetic acid alkyl ester.

2,4,4-Trichloro-5,5,5-trifluoropentanoic acid is obtained by the transesterification reaction of its esters according to the invention in almost quantitative yield. The transesterification reaction catalyst, which is preferably a strong non-volatile inorganic or organic acid, does not need to be removed after completion of the reaction before isolation of the product by distillation, since 2,4,4-trichloro-5,5,5-trifluoropentanoic acid is stable to acids such as e.g. sulfuric acid. After isolation of the product by distillation, the catalyst remains as a distillation residue and is suitable for reuse. In the case of the volatile nature of the catalyst or in the case of its desired removal from the reaction mixture, it is suitable to neutralize the catalytic amount of acid with alkaline reagents. Particularly advantageous for carrying out the transesterification reaction industrially is the use of a catalyst in the form of an acidic ion exchanger, which can be easily separated from the reaction mixture by filtration and reused.

The catalyzed transesterification reaction is preferably carried out in the presence of water or water. dilute acetic acid or dilute formic acid, as the presence of water accelerates the reaction due to the facilitated removal of the resulting alkyl acetate or alkyl formate in the form of an azeotrope. A rectification column of 3 to 5 theoretical plates is sufficient to separate it from the reaction mixture. '

The conversion of esters to the free 2,4,4-trichloro-5,5,5-trifluoropentanoic acid catalyzed transesterification reaction according to the invention is much more advantageous than the known process by acidic hydroysis and is easily applicable on an industrial scale.

The following examples further describe the process for the preparation of 2,4,4-trichloro-5,5,5-trifluoropentanoic acid without limiting or limiting its scope.

Example 1

A mixture of 185.5 g of 2,4,4-trichloro-5,5,5-trifluoropentanoic acid methyl ester, 185 g of acetic acid, 32 g of water and 3.6 g of sulfuric acid is heated to reflux for 8 hours while removing the resulting of methyl acetate on a rectification column of 5 TP. 165.5 g of 2,4,4-trichloro-5,5,5-trifluoropentanoic acid with a melting point of 95 DEG C./0.1 mm Hg are isolated by distillation under reduced pressure after evaporation of the acetic acid, in a yield of 93.8%. The distillation residue is 3.9 g of sulfuric acid.

Example 2

A mixture of 54.7 g of 2,4,4-trichloro-5,5,5-trifluoropentanoic acid methyl ester, 70 g of acetic acid, 17 g of water and 2.2 g of p-toluenesulfonic acid monohydrate is heated to reflux for 6 hours. simultaneous removal of the methyl acetate formed. After neutralization of p-toluenesulfonic acid with sodium bicarbonate and evaporation of dilute acetic acid, 47.2 g of 2,4,4-trichloro-5,5,5-trifluoropentanoic acid are isolated by distillation under reduced pressure in a yield of 91%.

Example 3

(a) A mixture of 100 g of 2,4,4-trichloro-5,5,5-trifluoropentanoic acid methyl ester, 100 g of acetic acid, 25 ml of water and 50 g of Ostion KSC 1 ion exchanger in H form (dry matter content 17.5 g) was heat to reflux for 15 h while removing the methyl acetate formed. After the reaction mixture was cooled, the solid ion exchanger was separated by filtration, and 74.04 g of 2,4,4-trichloro-5,5,5-trifluoropentanoic acid was isolated by distillation of the filtrate in a yield of 78.0%.

b) The transesterification reaction is repeated in the same way for a reaction mixture containing 100 g of 2,4,4-trichloro-5,5,5-trifluoropentanoic acid methyl ester, 100 g of acetic acid, 18 ml of water and the unwashed ion exchanger from Example 3a used. 90.7 g of 2,4,4-trichloro-5,5,5-trifluoropentanoic acid are isolated in the same manner in a yield of 85.6%.

Example 4

A mixture of 54.7 g of 2,4,4-trichloro-5,5,5-trifluoropentanoic acid methyl ester, 54 g of 85% formic acid and 1 g of sulfuric acid is heated to reflux for 8 hours while removing the methyl acetate formed. Following the same procedure as described in Example 1, 49.3 g of 2,4,4-trichloro-5,5,5-trifluoropentanoic acid were isolated in a yield of 95.0%.

Example 5

A mixture of 57.5 g of 2,4,4-trichloro-5,5,5-trifluoropentanoic acid ethyl ester, 48 g of acetic acid, 9 g of water and 0.2 g of sulfuric acid is heated to reflux for 15 hours while removing the resulting ethyl acetate. By treating the reaction mixture as described in Example 1, 49.8 g of 2,4,4-trichloro-5,5,5-trifluoropentanoic acid are isolated in a yield of 96.0%.

Claims (5)

SUMMARY OF THE INVENTION A process for the preparation of 2,4,4-trichloro-5,5,5-trifluoropentanoic acid, characterized in that the 2,4,4-trichloro-5,5,5-trifluoropentanoic acid ester of the general formula CF 3 CHClCOOR, where R is up to alkyl, is subjected to a transesterification reaction in formic acid or acetic acid in the presence of a catalytic amount of a mineral acid of sulfuric acid type or a strong organic acid of p-toluenesulfonic acid type or an ion exchanger containing an SO-JH group or mixtures thereof, preferably in the presence of water, by heating the resulting reaction mixture to boiling at a temperature of 60 to 140 ° C, while removing the resulting formic acid alkyl ester or acetic acid alkyl ester. CS 270773 81 2. The process according to item 1, characterized in that 1 to 20 parts by mole of formic acid or acetic acid with a concentration of 50 to 100% are used per 1 molar part of 2,4,4-trichlorob-5,5,5-trifluoropentanoic acid ester. . 3. The process according to items 1 to 2, characterized in that concentrated formic acid or concentrated acetic acid is used and up to 0.5 parts by weight of water per 1 part by weight of formic acid or acetic acid is added to the reaction mixture. . 4. The process according to item 1, characterized in that 0.001 to 0.1 molar parts of sulfuric acid or phosphoric acid or perchloric acid are used per 1 molar part of 2,4,4-trichloro-5,5,5-trifluoropentanoic acid ester, or nitric acid or: p-toluenesulphonic acid or up to 3 parts by weight of an ion exchanger which is a sulphonated styrene-divinylbenzene copolymer containing at least 0.5% by weight of divinylbenzene. 5. The method of claim 1, wherein the temperature is 100 to 120 ° C.