CS199725B2 - Process for the separation of stereoisomere vinylcyclopropancarboxylic acids - Google Patents

Abstract

A process for the separation of the cis- and trans-stereoisomers of a mixture of cis- and trans-substituted vinylcyclopropanecarboxylic acids of the formula <IMG> in which R each independently is alkyl with 1 to 4 carbon atoms or halogen, comprising subjecting the mixture to distillation to obtain a distillate enriched in cis-isomer and a residue, dissolving the residue in a solvent, and selectively crystallizing at least one of the stereoisomers from the solvent. Crystallization of the distillation residue results in first crystallizing that one of the isomers which is present in larger amount.

Description

The present invention relates to a novel process for separating mixtures of known substituted vinyl cyclopropanecarboxylic acids and their stereoisomers.

It is already known that mixtures of stereoisomeric cis- or trans-substituted cyclopropanecarboxylic acids can be separated by traction crystallization [Coli. Czech. Chem. Commun. 24, 2230 (1959) Fist. Sci. 1971, 245; Pestic. Sci. 1974, 791; DOS No. 2,439,177]. However, this procedure is difficult and lossy. This process is not suitable for obtaining larger amounts of pure trans or cis isomers.

It has now been found that a mixture of stereoisomers of substituted vinyl cyclopropanecarboxylic acids of formula I

halogen, and the position of the substituents on the ring relative to each other is cis- or trans-, whereby the molecules are optionally also present in optically active form, can be separated in a simple manner by subjecting the mixture of stereoisomers of said acids to traction distillation at 100 to 200 ° C and at pressures of 0.133 to 267 Pa and the individual fractions are purified by recrystallization.

This process is preferably carried out continuously.

It can be described as surprising that the process according to the invention succeeds in separating the cis-isomers of the acid from the trans-isomers of the acid, since the more easily boiling fraction of the cis-isomer of the acid passes enriched first, and the more difficultly soluble compound, although it is always emphasized in the literature cited above that the more readily soluble isomer is the cis-isomer of the acid.

It is also surprising that the separation of cis-trans isomers is possible in a simple manner by distillation, although it has been known in the art that substituted vinyl cyclopropanecarboxylic acids are thermally unstable.

The process according to the invention has a number of advantages

Thus, it is possible to separate the cis-isomers which are occasionally present only in inferior amounts, based on the cis-transiso199725 mixture in which

R represents a methyl group and / or mer, from a major amount of other isomers, which can be used both for purification and for enrichment purposes. Furthermore, the process according to the invention is also suitable for obtaining larger quantities of the respective isomers and can be carried out continuously.

Formula (I) generally defines substituted vinyl cyclopropanecarboxylic acids which are separable into their isomers by the process of the invention. Preferably R is methyl, chloro and / or bromo.

As an example of compounds that. stereoisomers can be separated according to the process according to the invention:

2- j 2,2-dichlorvinyl-3,3-dimethylcyclopropanecarboxylic acid,

2- (2,2-3-dimethylamino) - S, 3-dimethylcyclopropanecarboxylic acid and

2- (2-methylbuten-1-yl) -3,3-3,4-dimethyl-propanecarboxylic acid.

Mixtures of the substituted vinylcyclopropylcarbonyloxycarboxylic acid isomers of formula (I) which are used as starting materials are known [see Coll. Czech. Chem. Commun. 24, 2230 (1959); DOS No. 2,615,159;

J. Agr. Chem. Food Chem. 21, 767 (1973); British Patent No. 1,446,304; Pestic. Sci. 1971, 245; Pestic. Sci. 1974, 537; British Patent No. 1413,491; J. Chem. Soc. 1945, 285; DOS No. 2,432,951; J. Org. Chem. 17, 381 (1952), DOS 2,439,177],

When implementing. The purification according to the invention is firstly distilled according to customary practice to a mixture of isomers under vacuum over a high separation column to obtain a front fraction containing a high proportion of cis -omer. This front fraction was taken up with solvent. Upon cooling, the excess pure cis-isomer crystallizes while the trans-isomer together with the equimolar proportion of its isomer remains in solution. . This finding contradicts the teachings of DOS No. 2,439,177, where it is claimed that the cis compound is more soluble in a solvent such as hexane, while the trans compound is more difficult to dissolve. According to the inventor ' s finding, the acid which is present in excess is first crystallized out of solution, as the more easily soluble fraction then remains in the solution. solution. in each case a 1: 1 mixture of cis and trans isomers.

The cis-acid, which crystallizes as described, is separated. The filtrate is concentrated and re-distilled, again distilling only the front fraction, which is strongly cis-isomer-enriched. The residue can be obtained by partial distillation after recrystallization. pure trans-acid.

According to a particular embodiment, the whole process can be arranged continuously by adding the solvent immediately to the optionally removed fraction of the vacuum distillation, the cis-isomer is separated in the cooling part, the mother liquor is concentrated and new distillate is fed to the distillate solvent and the remaining residue is returned. for distillation. This cycle is repeated until complete separation of the his-cis isomer. The trans-isomer is then distilled for purification. In this way, a complete separation of isomers without loss is achieved even on an industrial scale.

The distillation is carried out at temperatures in the range of 100 to 200 ° C, preferably 120 to 160 ° C.

The distillation is carried out at pressures of 0.133 to 1332 Pa, preferably 1.3 to 267 ° C. For distillation, a column having a good separation effect, such as a rotating column, a cap column, a Vigreux column, is used. and a packed column, preferably a packed column or a packed column.

The distillation is carried out at a rate such that the distilled substituted vinyl cyclopropanecarboxylic acids are not exposed to the temperature prevailing at the bottom of the distillation column for more than 10-15 hours, preferably 12-13 hours.

As. solvents for the recrystallization of the distillate are suitable non-polar solvents, such as alkanes of up to 8 carbon atoms, petroleum or cyclohexane, further alkaloalkanes, such as tetracloromethanes, trifluoromethanes, but also strongly polar solvents such as aqueous alcohol, ketones or ethers.

Stereoisomeric substituted vinyl cyclopropanecarboxylic acids of formula I obtained by the process. according to the invention are used for. production of highly effective insecticides.

The following examples illustrate the process of the invention without limiting its scope.

Example 1 A 1-mixture of the isomers of 2- (2, -dk: hydrvinyl) -3,3-dimethylcyclopropanecarboxylic acid (ratio cis / trans = 40/60) was fractionated through a 2 m high packed column At 142 ^° C, the preceding fractions solidify and represent pure cis-acid. The fraction between 143 ° C and 152 ° C yields after removal of the petroleum fraction. The pure mother liquor is again returned to distillation, so that all the fraction of the residue can be separated from the distillation residue which is not carried out in a simple manner. Up to the end, pure trans-acid was found to be obtained by recrystallization from the petvolether as found by the NM-R-spectrum.

The cis configuration isomer passes predominantly into a fraction having a temperature of 110 to 120 µ / 400 Pa. In doing so, distillation. It is carried out until the NMR-s-spectrum continuously carried out shows no more cis-isomer content in the distillate (cis-isomer in chloroform: s 11 ppm (1); d 6.2 ppm (1); m 2 ppm (2), s 1.4 ppm (6) NMR spectrum of the isomer: s 11 ppm (1), d 5.6 ppm (1), m 1.6 to 2.3 ppm (2); d 1.3 ppm (1) Pure distillate can then be distilled off from the distillation residue without further fractionation without the need for recrystallization, but it is also possible to simply crystallize the distillation residue without first distilling off the trans-distillation. Recrystallization is carried out from petroleum ether, and the isomer is crystallized between 0 ° C and room temperature.

Example 2 mol of a mixture of isomers of 2- (2,2-dibromvinyl) -3,3-dimethylcyclopropanecarboxylic acid (cis / trans ratio = 15/85) is distilled at 1.3 Pa as described above. Fractions up to. 150 ° C is recrystallized as above to obtain cis-acid from petroleum ether.

In this case too, after the distillation of the cis-isomer portion, the trans-isomer remains in the form of a distillation residue and this residue can be crystallized from petroleum ether or distilled off without further fractionation. NMR spectrum of trans-dibromoacid in chloroform:

with 11 ppm (1); d 6.1 ppm (1); m 1.5-2.3 ppm (2); d 1.2 ppm (6).

NMR spectrum of cis-dibromoacids:

s (11 ppm), d 6.8 ppm (1); m 2 ppm (2); d 1.3 ppm (6).

Claims (2)

A process for separating mixtures of stereoisomeric vinyl cyclopropanecarboxylic acids of the general formula I in which R represents a methyl group and / or halogen, and the relative position of the substituents on the cyclopropane ring is cis- or trans-, and the molecules are optionally also present in optically active form, characterized in that the mixture of stereoisomers of said acids is fractionally distilled at 100 to 200 ^C and at pressures of 0.133 to 267 Pa and the individual fractions are purified by recrystallization. 2. The process of claim 1 wherein the process is carried out continuously.