FR2500442A1 - PROCESS FOR THE PREPARATION OF A HIGH PURITY CHRYSANTHEMIC ACID - Google Patents

Abstract

The invention relates to a process for the preparation of chrysanthemum-monocarboxylic acid (I) in high purity by alkaline hydrolysis of the C1-C6-alkyl ester of I (II), in the absence of organic solvents and in the presence of a phase transfer catalyst, with 100-150% by weight of the equivalent amount of alkali metal hydroxide which corresponds to the ester (II) when II is to be hydrolysed completely while maintaining the isomer ratio, or with 70-110% by weight of the equivalent amount of alkali metal hydroxide corresponding to the trans-isomer of II if II is to be hydrolysed partially or selectively while changing the ratio of the isomers. I can be used as intermediate for the synthesis of insecticidal pyrethroids.

Description

 The present invention relates to a process for the preparation of a chrysanthemic acid of high purity.

par hydrolyse des esters correspondants. Selon un autre aspect de l'invention, il est prévu un procédé pour la séparation des isomères cis et trans de l'acide de formule (I) par hydrolyse sélective des cis- et trans-esters de la formule (II)

dans laquelle R est un groupe alcoyle ayant de 1 à 6 atomes de carbone.More particularly, it relates to a process for the preparation of a cyclopropanecarboxylic acid of formula (I)

by hydrolysis of the corresponding esters. According to another aspect of the invention, there is provided a process for the separation of the cis and trans isomers of the acid of formula (I) by selective hydrolysis of the cis- and trans-esters of formula (II)

wherein R is an alkyl group having from 1 to 6 carbon atoms.

 Pyrethroids possessing insecticidal activity, for example cinerin, allethrin, phthaltrin, permetrine, cypermetrine, decametrine, etc., are generally prepared by synthesis from a lower aliphatic ester of a corresponding cyclopropanecarboxylic acid . Pyrethroids can be conveniently prepared by hydrolyzing these esters so as to obtain the corresponding free acids and by combining the acids thus obtained with the alcohol portions of the active compounds desired by conventional esterification techniques.

 The hydrolysis methods used conventionally have many drawbacks which prohibit their use on a large scale. When hydrolysis is carried out in a solvent, large volumes are involved, the solvent must be removed from the reaction mixture when the hydrolysis is complete, cyclopropanecarboxylic acid must be isolated from the residual solution by means of a solvent which must be removed again to give the desired pure acid.

 By known methods, mixtures of cis- and trans-esters of cyclopropanecarboxylic acid are produced.

The activity of pyrethrols prepared from the two isomers is considerably different. It may therefore be desirable to separate the isomers. The methods known in the art generally relate to the separation of free cis and trans acids, preferably by recrystallization from suitable solvents (J. Chem.

Soc. 283, 1945).

 The object of the present invention is to provide a simple industrial process for the preparation of cyclopropanecarboxylic acids by total hydrolysis of the corresponding esters in the absence of solvents, and for the selective hydrolysis of the trans isomer in a mixture of cis- and cyclopropanecarboxylic acid trans-esters.

 It has been surprisingly found that esters of cyclopropanecarboxylic acid of formula (II) in which R is an alkyl group having from 1 to 6 carbon atoms, preferably an alkyl group having from 1 to 4 carbon atoms, can also be hydrolyzed in the absence of organic solvents, if a small amount of a catalyst is present to facilitate the heterogeneous reaction with the aqueous solutions of alkali metal hydroxides used for hydrolysis. As catalysts, quaternary amines or another phase transfer catalyst, an active anion, active cation and / or nonionic emulsifier can be used. In addition, the rate of hydrolysis of trans isomers has been found. is greater than that of the cis isomers, and therefore the two isomers can be separated with good selectivity when appropriate reaction conditions are used.

 The process can also be used for total hydrolysis and selective hydrolysis, for the preparation of pure acid from esters containing non-hydrolysable impurities, for the separation of impurities and for the recovery of chrysanthemic acids from byproducts of synthesis.

 The hydrolysis is carried out with an aqueous solution of alkali metal hydroxide. Generally, 4-30% by weight solutions of alkali metal hydroxides are used.

 As the alkali metal hydroxide, sodium hydroxide and / or potassium hydroxide are preferably used.

 The hydrolysis is carried out at a temperature between 200C and 1200C, preferably between 500C and 1000C. Lower alkali concentration, lower temperature, and portionwise addition of the alkali metal hydroxide solution improve the selectivity of hydrolysis.

In the case of partial hydrolysis, the alkali metal hydroxide solution is added in an amount of 70 to 110%, preferably in an amount of 80 to 95% by weight of the amount equivalent to the trans-ester isomer, in small portions.

 The catalyst must be resistant to alkalis. Its concentration in the reaction mixture is between 0.01 and 5%, preferably between 0.1 and 1%, calculated relative to the amount of the ester. Preferred phase transfer catalysts are anion or active cation or nonionic emulsifiers.

 After partial hydrolysis, the unreacted ester enriched in the cis isomer of non-hydrolyzable impurities can be separated from the aqueous phase by virtue of their different specific gravity, can be dissolved by an appropriate solvent, for example solvents chlorinated, aliphatic or aromatic hydrocarbons, or can be evaporated by steam distillation.

 From aqueous solutions containing salts of cyclopropanecarboxylic acid, the acid can be released by a mineral acid. Chrysanthemic acid which is insoluble in the aqueous phase can be separated in a melt from a solid crystalline substance, can be dissolved in an organic solvent and, if desired, can be recrystallized from a solvent, preferably an aliphatic hydrocarbon.

 The chrysanthemic acid obtained has a high purity and can be used for the preparation of pyre thyroid insecticides without further purification.

 Other details of the invention are illustrated by the following examples, which should not be considered as limiting the invention in any way.

Example 1
20 g of chrysanthemic acid methyl ester (2,2-dimethyl-3- (2,2-dimethylvinyl) -cyclo propane-1-carboxylic acid ethyl ester) (98% purity, cis ratio / trans 14:86), 20 g of a 25% aqueous solution of sodium hydroxide and 0.02 g of -nonylphenyl-polyglycol ether are stirred at 950C for 180 minutes. After about 30 to 40 minutes, a homogeneous mixture is obtained, after which total hydrolysis occurs and the ethanol formed in the reaction is distilled off. From the sodium chrysanthemate solution obtained, chrysanthemic acid is precipitated by adding 50 g of 10% aqueous hydrochloric acid solution at 50 ° C., with stirring. The upper oily phase becomes crystalline on cooling and can be separated in the form of a solid material. Production 16.2 g (yield 96%).

Example 2
20 g of ethyl ester of chrysanthemic acid (ethyl ester of 2,2-dimethyl-3- (2,2-dimdthylvinyl) -cyclo-propane-1-carboxylic acid) (purity: 98%, cis / trans ratio
3 38: 62) are stirred with 6 cm of water and 0.01 g of sodium dodecyl sulphate and then 4 g of a 20% aqueous solution of sodium hydroxide. By adding two 4 g portions of the sodium hydroxide solution every 40 minutes, the hydrolysis is carried out at a temperature of 70 "C for a total of 240 minutes. After the reaction mixture has cooled, the ester is separated unreacted Weight 8.3%, purity: 95%, cis / trans ratio: 78: 22.

 The aqueous phase is mixed with 0.4 g of a 35% aqueous hydrochloric acid solution and the chrysanthemic acid precipitated is isolated as described in Example 1.

Production: 9.6 g, cis / trans ratio: 10:90.

Claims (7)

 1. Process for the preparation of a cyclopropanecarboxylic acid of formula (I)

 by hydrolysis of the corresponding esters and for the selective hydrolysis of cis- and trans-esters of formula (II)

 in which R is an alkyl group having from 1 to 6 carbon atoms, in order to separate the cis and trans isomers, according to which the hydrolysis is carried out in the absence of organic solvents, in the event of conservation of the initial cis / trans ratio with an amount of 100 to 150% or in the event of modification of the initial cis / trans ratio with an amount of 70 to 110% of an aqueous solution at 2-50% of an alkali metal hydroxide, equivalent to the ester starting and trans-ester, respectively, in the presence of 0.01 to 5% of a catalyst by phase transfer, at a temperature of 200C to 12DOC, the hydrolysis product is transformed into a carboxylic acid of the formula (I) in a manner known per se, if desired, the cyclopropanecarboxylic acid obtained is purified by separating it from aliphatic hydrocarbons having 5 to 10 carbon atoms by recrystallization and optionally separating the non-hydrolysed ester enriched in l isomer cis and subjected to further purification in a manner known per se.  2. Method according to claim 1, characterized in that the alkali metal hydroxide is used in an amount corresponding to 102 to 130% of the amount equivalent to the starting ester or in an amount corresponding to 80 to 95% of the amount equivalent to the trans-ester.  3. Method according to claim 1 or claim 2, characterized in that a 4-30% aqueous solution of an alkali metal hydroxide is used.  4. Method according to any one of claims 1 to 3, characterized in that the reaction is carried out at a temperature of 500C to 1000C.  5. Method according to any one of claims 1 to 4, characterized in that 0.1 to 1% of a catalyst is used by phase transfer.  6. Method according to any one of claims 1 to 5, characterized in that as the alkali metal hydroxide is used sodium hydroxide and / or potassium hydroxide.  7. Method according to any one of claims 1 to 6, characterized in that as catalyst, a catalyst is used by phase transfer, an emulsifying agent with active anion or with active cation and / or non-ionic.