DE2003548C - Process for stabilizing S-BenzylS-furyl-methyl-cyclopropanecarboxylic acid esters - Google Patents

Description

CH ₃

in which either R ₁ and R _{1 are} each a methyl group or R _{1 is} a hydrogen atom and R _{2 is} the isobutenyl group, characterized in that the crude ester of the general formula I is either dissolved in a solvent of low polarity and using silica gel or a mixture Silica gel and activated aluminum oxide treated as adsorbent, or that the crude ester is stirred with silica gel or a mixture of silica gel and activated aluminum oxide at a temperature between the melting point and the decomposition point of the compound and then stirred at this temperature Adsorbent filtered off, or that a reaction mixture obtained by reacting 5-benzyl-3-furylmethanol with a cyclopropanecarboxylic acid of the general formula II

CH ₁ -OC-CH-

"11 \ ο

H, C

R ₁

CH ₃ (1,

in which either R ₁ and R _{2 are} each a methyl group or R _{1 is} a hydrogen atom and R _{2 is} an isobutenyl group.

The 5-benzyl-3-furylmethylchrysanthemic acid ester is a valuable, known insecticide that is non-toxic to warm-blooded animals (cf. M. Elliott. AW Far η ha rn and coworkers, "Nature". Vol. 213, p.493 [1967]) . The ester of the general formula I. in which R ₁ and R each represent a methyl group, is also an excellent known insecticide (see French patent specification 1,541 OfS).

The esters of the general formula 1 can easily be obtained by reacting 5-benzyl-3-furylmethano! with one of the general cyclopropanecarboxylic acids Formula II

HOOC -CH H ₃ C C. -C \ ⁷ \
R ₂ ^X CH ₃

HOOC-CH - C (II)

H ₃ C CH ₃

in which R _{1 and R 2 have} the meaning given above, or has been obtained with a reactive derivative of this cyclopropanecarboxylic acid, first dehydrated with toluene and then stirred with silica gel or a mixture of silica gel and activated aluminum oxide and then the adsorbent is filtered off. 2. The method according to claim 1, characterized in that when using silica gel alone, at least 1 percent by weight, preferably about 10 percent by weight, or when using a mixture of silica gel and activated aluminum oxide, at least 1 percent by weight, preferably about 30 percent by weight, each based on the ester of the general formula I, is used, in the latter case the weight ratio of the silica gel to the activated aluminum oxide is about 1: 2.

The invention relates to a method for stabilizing S-benzyl-S-furyl-methylcyclopropancarin in which R ₁ and R _{2 have} the aforementioned meaning, or with a reactive derivative of this cyclopropanoic acid according to known condensation processes.

The esters of the general formula 1 are relatively stable in the pure state; they form white Crystals and change their color and other properties even if they are stored for several weeks not at room temperature. The corresponding industrially produced esters are, however, light yellow, cristal “'All substances that change color quickly and gradually are black-brown after about one week's storage at room temperature. They also form through touch with iron, copper or certain plastics made of graphitic material, rubber-like deposits on the product, which significantly reduce the quality and thus the sales value as an insecticide.

So far there is no method of stabilizing joints of the formula I known. One in the book "Heterocyclic Compounds", Vol. 1 (1950), p. 199, by The stabilization method explained in the following of furan-2-carboxylic acid, in which urea is used, is not satisfactory when it is is transferred to the compound of formula I.

A method for stabilizing 5 - benzyl - 3 - furyl - methylcyclopropanecarboxylic acid esters has now been found of the general formula I given, which prevents the time-related discoloration and deterioration in quality of these compounds.

The inventive method for stabilizing 5 - benzyl - 3 - furyl - methyleyclopropancarbon-

acid esters of the general formula I

CH ₃ -0-C-CH
Il \ C. -C
/ \ Ii \
O ' \
R ₂ H ₃ C ^X CH ₃ (I)

VCH /

in which either R ₁ and R _{2 are} each a methyl group or R _{1 is} a hydrogen atom and R _{2 is} the isobutenyl group, is characterized in that the crude ester of general formula 1 is either dissolved in a solvent of low polarity and with silica gel or with a mixture of silica gel and activated aluminum oxide as adsorbent, or that the crude ester is treated with silica gel or a mixture of silica gel and activated aluminum oxide at a temperature between the melting point and the decomposition point and then at this temperature the adsorbent is filtered off, or a reaction mixture obtained by reacting 5-benzyl-3-furylmethanol with a cyclopropanecarboxylic acid of the general formula II

HOCC-CH

H ₃ C

(II)

CH ₃

in which R ₁ and R _{2 have} the meaning given above, or has been obtained with a reactive derivative of this cyclopiopanecarboxylic acid, first dehydrated with toluene and then stirred with silica gel or a mixture of silica gel and activated aluminum oxide and then the adsorbent is filtered off.

All three embodiments of the method according to the invention can be easily carried out with good effect technically carried out.

Suitable solvents of low polarity are for example benzene, toluene, η-hexane, n-pentane, carbon tetrachloride and acetone.

The amount of silica gel to be used in the process according to the invention, if appropriate in a mixture with activated alumina is not critical as long as it is sufficient to adsorb the contaminants.

In general, an amount of silica gel of at least 1 percent by weight, preferably about 10 percent by weight, based on the ester of general formula I. When using a mixture from activated aluminum oxide and silica gel this is expedient in an amount of at least 1 percent by weight, preferably about 30 percent by weight, based on the ester of the general Formula I, used, the weight ratio of the silica gel to the activated aluminum oxide is about 1: 2.

The process according to the invention can also be applied to the optical isomers and stereonomers of the esters of the general formula I can be used.

Although it is already known, coloring substances or other impurities from z. B. organic solvents separated by treatment with an adsorbent such as silica gel.

According to the invention, however, it is a different technical problem, decomposition of the ester in question under the influence of catalytic to prevent active substances, which only occur during storage or in the presence of z. B.

ίο mead; Len unfold their effect, surprisingly it is possible to prevent this disruptive catalytic influence by the process according to the invention.

For example ρ iel 1

5-Benzyl-3-furylmethylchrysanthemate (m.p. 55 to 56 C). that by reacting 26.4 g of 5-Ber> 2yl-3-furylmethanol with 28.0 g of chrysanthemic acid chloride in the usual way. comes in 150 g

ίο Toluoy solved. 191 g of this solution becomes the Water is distilled off as an azeotropic mixture in vacuo, and then 5.3 g are added to the residue Silica gel and 10.5 g activated aluminum oxide were added. The whole is stirred at 20 ° C. for 30 minutes and the solids are filtered off under reduced pressure. After removing the solvent, one obtains 47.0 g of the stabilized ester.

In a corresponding comparison experiment, treatment with silica gel and activated aluminum oxide is used waived. The yield is then 47.5 g.

The table below shows the time-related discoloration of the treated according to the invention and of the untreated 5-benzyl-3-furylmethylchrysanthemic acid ester shown. For this experiment, both connections are exposed to air at 25 to 30 C in stored in an iron vessel.

40 According to example 1
treated ester Attempt
beginning To
10 days 2 To
30 days Untreated ester White White White 45 light yellow Brown black
Brown. rubber
good 50 example

98 g raw S-benzyl-S-furylmethylchrysanlhemat, which has been obtained as described in Example 1 is dissolved in 280 ml of toluene. The solution is with 11 g of silica gel are added and the mixture is stirred thoroughly, and then to separate the silica gel filtered under reduced pressure. After removal of the solvent, 97 g of the purified ester are obtained.

The purified ester is even after a 30-day storage at room temperatures of 25 to 30 ^carbon C after the described in Example 1 Method no discoloration and deterioration.

Example 3

98 g of crude S-benzyl-S-furylmethylchrysanthemic acid ester, obtained as described in Example 1

are melted by heating to 60 C with 22 g of activated aluminum oxide and 11 g of silica gel are added and the mixture is stirred at 60 ° C. for 30 minutes. The solids are reduced under Filtered off pressure. 97 g of the purified compound are obtained, which in the case of an example 1 does not show any discoloration or deterioration in quality.

A 5-benzyl-3-furylmethyl-tetramethylcyclopropanecarboxylic acid ester stabilized according to one of the above examples (F. = 34 to 36 ° C) behaves like the S-benzyl-S-furylmethylchrysanthemic acid ester obtained there. In the storage test according to Example 1, no discoloration or deterioration in quality occurs on. κ

Example 4

To a solution of 90 g of 5-benzyl-3-furylmethyllelramethylcyclopropanoic acid ester (F. = 34 to 36 C) in 270 ml of toluene is added to a mixture of 10 g of silica gel and 20 g of activated aluminum oxide. The mixture is stirred for 30 minutes at room temperature and then the solids are filtered off in vacuo. The The filtrate is concentrated, and 88 g of the stabilized ester, which has the same melting point, is isolated therefrom as the starting material has (34 to 36 C).

Even with storage of the stabilized ester in an iron kettle in air for 30 days and with Ambient temperature (10 to 20'C) there is no discoloration.

Claims (1)

Claims: acid esters of the general formula 1 1. Process for stabilizing 5-benzyl-3-furyl-methylcyclopropanecarboxylic acid esters of the general formula I. -CH ₁