JPS615045A - Racemization of chrysanthemum-monocarboxylic acid - Google Patents

Abstract

PURPOSE:To obtain racemic chrysanthemum-monocarboxylic acid useful as a raw material of pyrethroidal insecticides, from an optically active chrysanthemum-monocarboxylic acid without converting to other derivative, by racemizing the chrysanthemum-monocarboxylic acid with aluminum bromide. CONSTITUTION:An optically active chrysanthemum-monocarboxylic acid constituting the acid component of esters known as pyrethroidal insecticides such as pyrethrin, allethrin, phthalthrin, etc. useful as low-toxic rapid-acting insecticides is made to react with aluminum bromide at -30-+100 deg.C preferably in an inert solvent such as toluene, etc. to effect the racemization of the acid. Racemic chrysanthemum-monocarboxylic acid rich in transisomer having higher activity as an ester can be produced by this process. EFFECT:The process is effective in the case of using the (-)-isomer of chrysanthemum-monocarboxylic acid or carboxylic acid mixture rich in the (-)-isomer of chrysanthemum-monocarboxylic acid. The obtained chrysanthemum-monocarboxylic acid can be converted to a valuable (+)-isomer by combining various optical resolution processes.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for racemizing primary dilute acid, and more specifically to a racemization method for optically active primary chrysanthemum acid, which is characterized by reacting aluminum bromide with optically active primary acid. Regarding the method.

The dilute acid constitutes the acid component of esters that are well known as pyrethroid insecticides such as pyrethrin, allethrin, and phthalthrin, which are useful as slow-acting insecticides. It is useful as a raw material for agents.

By the way, the dilute acid has cis and trans geometric isomers, and each of them has (+) and ←) optical isomers, so there are a total of four isomers. Generally, among these isomers, pyrethroid esters derived from the trans isomer exhibit stronger insecticidal activity than the corresponding pyrethroid esters derived from the cis isomer; ←) It is known that it exhibits slightly higher activity than the esters in the body.

In the usual manufacturing method, the dilute acid No. 1 is synthesized as a racemic mixture of cis and trans forms, i.e., the (a) form, which is optically resolved using an optically active organic base←)
The body is obtained and used in the production of more highly active insecticidal compounds. Here, the remaining optically resolved (→-isomer has almost no activity as a pyrethroid ester and is therefore useless) can be efficiently racemized and used as a raw material for the above-mentioned optical resolution. To do so is
This is especially a big issue when producing products on an industrial scale.

However, as mentioned above, since the first 5PJW has two asymmetric carbon atoms, its racemization is accompanied by various difficulties.

Up until now, the racemization method for dilute acids has been to oxidize the isobutenyl group at position 03 of trans-dilute acid to form a ketoalcohol group, then esterify the carboxylic acid at position 31, A method of heating and reacting with an alkali metal alcoholate in the presence of a solvent (Japanese Patent Publication No. 89-1597
7), (→-method of irradiating -trans-dilute acid with ultraviolet rays in the presence of a photosensitizer (Japanese Patent Publication No. 47-8069)
No. 7), optically active chrysanthemum acid as acid halide,
A method in which a Lewis acid is applied to this (Special Publication No. 5B-878
No. 58, JP-A No. 52-144651], a method is known in which iodine is applied to an anhydride of a dilute acid (JP-A No. 57-168841) 5. The present inventors As a result of further research, they found that racemization unexpectedly progressed by allowing aluminum bromide to act on the optically active primary chrysanthemum acid itself, without introducing it into other derivatives. This discovery led to the present invention.

The method of the present invention will be explained in detail below.

The optically active primary chrysanthemum acid used as a raw material in the present invention is 4
One of the isomers of the species can be used alone or a mixture of these isomers in any proportion can be used, and any degree of optical purity can be used. (It goes without saying that its significance is demonstrated when using a carboxylic acid rich in 9 types.

In addition, it is preferable to use an inert solvent when carrying out the reaction, and such solvents include saturated hydrocarbons,
Examples include aromatic hydrocarbons, halides thereof, and ethers.

The amount of aluminum bromide used is 1/100 to 1/2 mole, preferably 1750 to 1/2 mole, per mole of chrysanthemum acid product to be treated.
The range is 4 moles.

Moreover, the reaction temperature is usually in the range of -80°C to 180°C.

The degree of progress of the reaction can be determined by sampling a portion of the reaction solution and measuring the optical rotation, or by analysis using gas chromatography or the like.

The racemized primary acid obtained as described above can be converted into an insecticidal ester through an esterification reaction with various pyrethroid alcohols. Acid←
) body, or dilute acid rich in it, can be converted into a useful racemic body, and by combining this with various optical resolution methods, a more useful (l-)
It is also possible to transform it into the body.

The racemate obtained by the method of the present invention is rich in the trans form, which is more effective as an ester, and the method of the present invention is advantageous in this respect as well.

Hereinafter, the present invention will be explained in detail using +m examples.

Example 1 50- flask number ζ Under nitrogen atmosphere, levorotatory - dilute acid (
())-cis form 8.0 嗟, ←)-cis form 22, Ol, ←
)-trans form 11.8, ←)-trans form 68.2
%) and 11.75 L of toluene were added, and then 0.12 F of aluminum bromide was added to this solution at 15 to 20°C and stirred. After 80 minutes, a part of the reaction solution was sampled to induce (+)-2-octyl ester, and the optical isomer ratio was measured using a gas chromatograph.
-cis isomer 4.6%, (+)-trans isomer 26.5%, (
→-Trans isomer content was 65.9%.

Procedural amendment (voluntary) July 1985! 6th Drama Patent Office Commissioner Michibe Uga 1, Indication of the case 1982 Patent Application No. 124846 2, Name of the invention <209) Representative of Sumitomo Chemical Co., Ltd. Sat.
Takeshi 4, Agent Address: 5-15-6 Kitahama, Higashi-ku, Osaka, Box 6 of "Detailed Description of the Invention" of the specification to be amended, and the following after the bottom line of page 6 of the specification of the contents of the amendment: join.

Example 2 To a 50 wt flask under a nitrogen atmosphere, 2.0 ? of (→-cis dilute acid) and 17.5 f of dioxane were added. Then, to this solution was added aluminum under the odor while stirring at 15-20°C. 0
．． A solution consisting of 068 F and 0.5 P of dioxane was added, and after 80 minutes, 0.5 F water was added and concentrated under reduced pressure.

After adding hexane to the concentrated solution and washing with diluted hydrochloric acid, 1o9F
Sodium dihydroxide aqueous solution7. IP was added and stirred at 40°C, and then the aqueous layer was separated.

Dilute sulfuric acid was added to the aqueous layer for acid precipitation, then toluene was added for extraction, and the toluene layer was then washed with water and concentrated.

Distill the concentrated liquid to a boiling point of 110-119℃ 72.611s
(ii) A distillate of 1.88 F was obtained. The infrared spectrum of this product matched that of primary chrysanthemum acid.

The optical isomer ratio of the distillate was measured in the same manner as in Example 1 (...-cis isomer 8.0%, (→-cis isomer 4.0%), (→-cis isomer 4.0%).
9%, (±-trans form 46.0%, (→-trans form 4661%).''

Claims (1)

[Claims] A method for racemizing optically active chrysanthemum acid, which comprises reacting optically active chrysanthemum acid with aluminum bromide.