JPS615047A - Racemization of chrysanthemum-monocarboxylic acid - Google Patents

Abstract

PURPOSE:To carry out the racemization of an optically active chrysanthemum- monocarboxylic acid, easily in high yield, and to obtain a racemic chrysanthemum-monocarboxylic acid useful as a raw material of phyrethroidal insecticides, by reacting the optically active acid in the presence of boron bromide and an organic hydroperoxide. CONSTITUTION:Chrysanthemum-monocarboxylic acid of formula which is an acid component of the esters of pyrethroidal insecticides such as pyrethrin useful as low-toxic rapid-acting insecticides, is racemized in the presence of boron bromide such as BBr3 and an organic hydroperoxide, preferably in an inert solvent at -30-+100 deg.C for 10min-10hr to obtain racemic chrysanthemum-monocarboxylic acid rich in the trans-isomer having higher insecticidal activity in the form of an ester. EFFECT:The process is suitable for the use in an industrial scale. The active (+)- isomer can be produced by combining with various optical resolution processes. Furthermore, the consumption of boron bromide can be decreased remarkably by the use of only a small amount of the organic hydroperoxide, and the racemization reaction time can be remarkably shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for racemizing dilute acids. More specifically, it is a compound represented by optically active chrysanthemum acid, which is characterized by reacting optically active chrysanthemum acid with boron bromide in the presence of an organic hydroperoxide, and is useful as a low-toxicity, fast-acting insecticide. It constitutes the acid component of esters that are well known as pyrethroid insecticides such as pyrethrin, allethrin, and phthalthrin.
It is useful as a raw material for these pyrethroid insecticides.

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 types of isomers. In general, 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 to exhibit much higher activity than the corresponding 9-ester esters.

In the usual manufacturing method, the dilute acid No. 1 is synthesized as a racemic form, a mixture of cis and trans forms, 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. The remaining (c) form optically resolved here has almost no activity as a pyrethroid ester,
Therefore, this usefulness (→Efficiently racemizes the body,
Making it usable as a raw material for the above-mentioned optical resolution is a major challenge, especially when producing the (+) isomer on an industrial scale.

However, as mentioned above, the dilute acid has C1 position and 0
Since it has two asymmetric carbon atoms at the 8-position, its racemization is accompanied by various difficulties.

Up until now, the racemization method for dilute acids has been to oxidize the isobutenyl group at the 08-position of the (-)trans-dilute acid to convert it into a keto alcohol group, and then esterify the carboxylic acid at the C1 position. A method of heating and reacting this with an alkali metal alcoholate in the presence of a solvent (Japanese Patent Publication No. 89-15977
(Japanese Patent Publication No. 47-80697), a method of irradiating H-1 lance-th dilute acid with ultraviolet rays in the presence of a photosensitizer (Japanese Patent Publication No. 47-80697), optical activity ratio - dilute acid as an acid halide; Method of acting with Lewis acid (Japanese Patent Publication No. 5B-87858, Japanese Patent Application Laid-Open No. 52-144651), optical activity ratio -
A racemization method is known in which an anhydride of a dilute acid is treated with gold iodine (Japanese Patent Laid-Open No. 168841/1984).

As a result of various studies, the present inventors have found that, in the presence of an organic hydroperoxide, boron bromide can be converted into optical activity ratio - dilute acid itself without leading the dilute acid to other derivatives. It was unexpectedly discovered that racemization progresses easily and in high yield by allowing the reaction to occur, and the present invention was completed by making various studies on this.

According to the method of the present invention, optically active chrysanthemum acid itself can be easily racemized in high yield without leading to other derivatives, which is extremely advantageous especially when carried out on an industrial scale. Furthermore, it becomes possible to directly and efficiently utilize the ineffective (→-th-kikusui acid) separated in various optical resolution methods.

Furthermore, in the method of the present invention, by making a small amount of organic hydroperoxide exist, not only can the amount of boron bromide used be greatly reduced, but also the time required for the racemization reaction can be greatly shortened. This makes it possible to achieve various rationalizations, especially during industrial implementation.

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

Optical activity ratio - dilute acid used as 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; however, considering the purpose of the present invention, (→It goes without saying that its significance is demonstrated when using dilute acids that are rich in the body.

The boron bromide used in the method of the present invention is typically boron tribromide, which may form a complex with a small amount of water, acid, alcohol, ether, etc.

The amount of boron bromide used is 1/2000 to 1/10 mol, preferably 1/100 mol, per 1 mol of dilute acid to be treated.
It is in the range of 0 to 1/20 mol.

Examples of organic hydroperoxides include the following.

(11 Aliphatic hydroperoxide Hydroperoxide produced by oxidation of ethers such as tetrahydrofuran and dioxane t-Butyl hydroperoxide 1.1,8.8-Tetramethylbutyl hydroperoxide etc. (2) Aromatic hydroperoxide oxide cumene hydroperoxide diisopropylbenzene hydroperoxide etc.

The amount used is usually 1 mol per mole of boron bromide.
/10 to 5 mol, preferably 1/4 to 2 mol.

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, their halides, and ethers.

Although the reaction temperature is not particularly limited, it is usually -
It is in the range of 80°C to 100°C.

The time required for the reaction may vary depending on the amounts of boron bromide and organic hydroperoxide used and the reaction temperature, but usually 10 minutes to 10 hours is sufficient to achieve the purpose.

When carrying out the method of the present invention, the dilute acid to be treated and the hydroperoxide are usually dissolved in a solvent, and then boron bromide is added thereto, or the dilute acid to be treated is dissolved in the solvent. This is followed by an operation that co-produces hydroperoxide and boron bromide.

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 dilute acids obtained as described above can be converted into insecticidal esters by esterification reactions with various pyrethroid alcohols.

As described above in detail, the method of the present invention can be used to efficiently and economically produce racemic forms of (→ bodies of dilute acids represented by the formula (force), or dilute acids enriched therein) which are more economically useful on an industrial scale. By combining this with various optical separation methods, it becomes possible to convert into a more effective (+) body, and this plays an extremely important role.

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

Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

Example 1 (+)-cis isomer 8.0 in a 50-flask under nitrogen atmosphere
Attack, (→-cis #22.0%, (+)-trans body 11
．． 8%, (→-trans isomer 5.02%, toluene 9.02% and tert-butyl hydroperoxide 0.0279%, 15-20%
While stirring at °C, a mixed solution of 0.159% of boron tribromide and 2.62% of toluene was added dropwise. After 80 minutes, a part of the reaction solution was sampled to induce the dilute acid into (+)-2-octyl ester, and the optical isomer ratio of the dilute acid was measured by gas chromatography. )-cis form 2.
1%, (→-cis form 2.1%, (+)-trans form 47
．． 3%, and the (-)-trans isomer was 48.5. After 1 hour, 5 parts of a dilute aqueous hydrochloric acid solution was added to the reaction mixture and stirred to separate the aqueous layer. Next, the organic layer was poured into 17.9 g of a 10% aqueous sodium hydroxide solution, stirred and separated while heating to about 40°C. After neutralizing the aqueous layer with dilute sulfuric acid and extracting with toluene,
The organic layer was washed with water. This toluene solution was concentrated and distilled,
A boiling point of 110-119"C/2.5 wrml (4.8 ml of distillate of 9) was obtained. The infrared absorption spectrum of this product matched that of the dilute acid, and a part of the distillate was (+) When induced to -2-octyl ester and measured the optical isomer ratio by gas chromatography (+)
-cis form 2.2%, (→-cis form 2.2%.

(÷)-trans form 47.8%, (→-trans form 48%
．． It was 8%.

Example 2 Under a nitrogen atmosphere, the same dilute acid 5.0% as used in Example 1 was placed in a 50rnl flask. , dioxane 17,0 y and te
Add 0.08F of rt-butyl hydroperoxide, stir for 15-20°C, then add 0.08F of boron tribromide.
A mixture of 2y and dioxane (8.07 g) was added dropwise.

After 80 minutes of dropping, a portion of the reaction solution was sampled and the optical isomer ratio of the dilute acid was measured in the same manner as in Example 1. As a result, the (+)-cis isomer ratio was 2.5%.

(→-cis form 2.6%, (+) -trans form 47.
0 yen.

(→-Trans form was 47.9%.

After 1 hour, the reaction solution was analyzed by gas chromatography, and the dilute acid content in the reaction solution was calculated to be 4.62.

Example 8 The dilute acid 5.0 used in Example 1 was placed in a 50 ml flask under a nitrogen atmosphere. Oy,) Add luene io, o y- and cumyl hydroperoxide 0.0462 to 15-2
A mixed solution of 0.099 y of boron tribromide and 1.7 y of toluene was added dropwise while stirring at 0°C.

After 30 minutes of dropping, a part of the reaction solution was sampled and the optical isomer ratio of the dilute acid was measured in the same manner as in Example 1. As a result, the (+)-cis isomer ratio was 8.0%.

(→-cis form 2.9%, (+)-trans form 45.8%.

The (-)-cis form was 48.4%.

After 1 hour, the reaction solution was analyzed by gas chromatography, and the dilute acid content in the reaction solution was calculated to be 4.9.

Claims (1)

[Claims] A method for racemizing optically active chrysanthemum acid, which comprises reacting optically active chrysanthemum acid with boron bromide in the presence of an organic hydroperoxide.