JPS63196542A - Racemization of optically active chrysanthemum monocarboxylic acids - Google Patents

Abstract

PURPOSE:To directly obtain the titled racemized compound rich in trans-isomer, in high efficiency on an industrial scale at a low cost, by using a brominated phosphorus compound as a racemization catalyst and racemizing optically active chrysanthemum monocarboxylic acids in the presence of an azo compound. CONSTITUTION:Optically active chrysanthemum monocarboxylic acids of formula (R is H, 1-20C alkyl, cycloalkyl or aralkyl; * represents asymmetric carbon atom) which are raw materials for pyrethroidal insecticides such as pyrethrin, allethrin, etc., useful as a low-toxic rapid-acting insecticide is racemized by reacting in the presence of a brominated phosphorus compound (e.g. phosphorus tribromide, phosphorus pentabromide, phosphorus oxybromide, etc.) and an azo compound (preferably azobisisobutyronitrile, etc.) preferably in an inert solvent such as benzene usually at 0-100 deg.C for several min-7hr. The process gives racemized optically active chrysanthemum monocarboxylic acids rich in trans-isomer and useful for the production of an insecticidal compound having higher activity.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a racemization method of the Chrysanthemum group, and more specifically, to a racemization method of the Chrysanthemum group, and more specifically to a compound represented by the general formula (I) (wherein R is a hydrogen atom and has 1 to 20 carbon atoms) an alkyl group,
It represents a cycloalkyl group or an aralkyl group, and * represents an asymmetric carbon. ) This relates to a characteristic racemization method of optically active salts-chrysanthemum acids.

<Prior art and problems to be solved by the invention> The first dilute acid is a compound of esters which are well-known as so-called pyrethroid insecticides such as pyrethrin, allethrin, and phthalthrin, which are useful as low-toxicity and fast-acting insecticides. The cupric acids represented by the general formula (I), which constitute the acid component, are useful as raw materials for these pyrethroid insecticides.

The cupric acids represented by the general formula (I) have cis and trans geometric isomers, and each of them has ←) and (
Since there are optical isomers of ), there are a total of 4 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 (he)isomer esters.

The dilute acid is usually produced as a racemic mixture of the cis form and the trans form, that is, the (t) form, which is optically resolved using an optically active organic base to obtain the ← form;
Used to produce more active insecticidal compounds. The remaining (he) isomer optically resolved here has almost no activity as a pyrethroid ester, and therefore this useless H isomer is efficiently racemized and the raw material for the optical resolution described above. It is a big problem to be able to use it as a liquid, especially when producing (g) bodies on an industrial scale.

However, as mentioned above, the cyclopropanecarboxylic acid represented by the general formula (1) has two asymmetric carbon atoms at the C1 and 08 positions, so its racemization is accompanied by various difficulties. .

Up until now, the racemization method for cupric acids has been to oxidize the isobutenyl group at the Cs position of the H-trans-dilute acid to form a keto alcohol group, and then esterify the carboxylic acid at the C1 position. A method of thermally reacting an alkali metal alcoholate with a solvent in the presence of a solvent (Japanese Patent Publication No. 89-15977), or a method of irradiating a (he)-trans-dilute acid with ultraviolet rays in the presence of a photosensitizer ( Special Public Service 1978-806
However, the former requires many reaction steps, and the latter has an inferior reaction rate, high power consumption of the light source, and a relatively short lifespan of the light source. There are various problems in implementing this method.

The present inventors previously proposed a racemization method (Japanese Patent Publication No. 58-87858, JP-A-52-144651) in which optically active cupric acid is used as an acid halide and a Lewis acid is made to act on this as a catalyst. ), a racemization method based on the action of iodine on the anhydride of optically active cyclopropanecarboxylic acid (Japanese Patent Application Laid-Open No. 168841/1984), and a special catalyst called boron bromide on the dilute acid derivative. Racemization reaction by
No. 744).

As a result of further various studies, the present inventors found that brominated phosphorus compounds, which are more common as industrial raw materials, have optically active properties.
They discovered that the racemization reaction of chrysanthemum acids proceeded surprisingly efficiently, and also discovered that by using this in combination with an azo compound, the racemization reaction could proceed more efficiently and smoothly with a small amount of catalyst. The present invention was completed after various studies.

Means for Solving the Problems> That is, the present invention has the general formula (I) (wherein R is a hydrogen atom, an alkyl group having 1 to 20 carbon atoms,
It represents a cycloalkyl group or an aralkyl group, and * represents an asymmetric carbon. ) is treated with a brominated phosphorus compound in the presence or absence of an azo compound. It provides law.

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

Examples of the optically active chrysanthemum acids represented by the general formula (1), which are raw materials of the present invention, include di-dilute acids, di-dilute methyl acids,
Ethyl dilute acid, brobyl cuprate, butyl dilute acid,
Examples include optically active substances such as cyclohexyl-dilute acid, cyclohexylmethyl di-dilute acid, and benzyl di-dilute acid.

There are four isomers of each cupric acid, and 1m of these can be used alone or a mixture of these in any proportion, and any degree of optical purity can be used. Considering the purpose of the present invention, it goes without saying that the use of carboxylic acids rich in the (he)-isomer or (c)-isomer exhibits its significance.

Examples of the brominated phosphorus compound used in the method of the present invention include compounds of bromine and phosphorus such as tribromide, tribromide, oxytribromide, etc., or mixtures thereof. The amount used is usually 1/1o per mole of chrysanthemum acid to be treated.
The range is from oo to 1/4 mole, preferably from 1/20 to 1/4 mole when the brominated phosphorus compound is used alone.
1/200 to 1/1 when used in the presence of an azo compound
It is in the range of 0 mol.

Examples of azo compounds include azobisisobutylnitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), t,t'-azobis(cyclohexane-1-carbonitrile), 4°4'-azobis-4 -Cyanopentanoic acid, 2-phenylazo-2,4-dimethyl-4-methoxyvaleronitrile, 2-cyano-2-
7zonitriles such as propylazoform, azobisisobutanol diacetate, methyl azobisisobutyrate,
Azoesters such as ethyl azobisisobutyrate, azo-
Examples include alkylazos such as t-butane. Preferably, azonitriles and azo esters are used.

The amount used is generally 1/2 to 5 moles, preferably 1/2 to 2 moles, per mole of the brominated phosphorus compound.

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 reaction temperature is arbitrary within the range of -20"C to the boiling point of the -chrysanthemum acid ester (if a solvent is used, the boiling point of the solvent used), but is usually in the range of 0" to 100C.

The time required for the reaction may vary depending on the amounts of the brominated phosphorus compound and azo compound used and the reaction temperature, but usually several minutes to 7 hours is sufficient to achieve the purpose.

When carrying out the method of the present invention, usually, the to-be-treated tertiary chrysanthemum acids and an azo compound are mixed in the presence of a solvent, and then the brominated phosphorus compound is added thereto; is dissolved in a solvent, and then an azo compound and the brominated phosphorus compound are co-produced therein.

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.

<Effects of the Invention> The method of the present invention is extremely advantageous because it allows racemization of optically active cupric acid itself or its ester without leading to other derivatives. Cuprates separated and removed by optical resolution methods, such as ineffective H-cuprous acids separated by physicochemical resolution methods using optical resolution agents, or H separated and removed by biochemical resolution methods using enzymes, etc. -It becomes possible to directly, efficiently and effectively utilize primary chrysanthemum acid esters, etc.

Furthermore, according to the present invention, a more common phosphorus bromide compound can be used as an industrial raw material, and the azo compound that is commonly used is also easy to use because it does not have induced decomposition, so it is particularly suitable for industrial implementation. be advantageous at times.

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

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

Example 1 Levorotatory cupric acid ((t)-cis form 1.8%, (he)-cis form 17.6%, (e)-trans form 10.1%, (he)-trans form 70 1.79F (consisting of .5%) was dissolved in benzene 10-, azobisisobutyronitrile 2-4
Add 8'IP and add 144 tribromide while stirring at 80℃.
A benzene solution of 1119 was added dropwise over 16 minutes.

After the reaction, dilute hydrochloric acid was added and stirred to deactivate and remove the catalyst. After separation, 4.8g of 1O% caustic soda water was added to the organic layer. ! !
Extraction was performed twice with JPfL, and the resulting aqueous layer was acidified with hydrochloric acid and extracted twice with toluene. The toluene layer was washed with water, dried over sodium sulfate, the solvent was distilled off under reduced pressure, and the residual liquid was distilled to a boiling point of 110-119°C/2.5 mail.
A fraction of 1.51F was obtained. This substance was confirmed to be M based on the infrared absorption spectrum, and a part of it was sampled and converted into an ester with -2-octatool, and its optical isomer ratio was determined by gas chromatography. , (T) cis form 2.5%, H cis form
2.5%, (g)trans form 47.896, θtra2
1 body was rare at 47.2%.

Example 2 1.26F of the same levorotatory tertiary acid used in Example 1 was dissolved in 10-benzene, 50JlF of azobisisobutylnitrile was added, and 22F of phosphorus pentabromide was dissolved while stirring at 70°C.
A benzene solution of G+9 was added dropwise over 15 minutes.

Thereafter, the same operations as in Example 1 were performed.1. Olf's first dilute acid was obtained.

The optical isomer ratio is (t)-cis form 4.1%, H-cis form 4.
．． 1%, (t)-trans form 48.9%, and (c)-trans form 47.9%.

Example 8 The same levorotatory dilute acid 2,12 f as used in Example 1
was dissolved in benzene 10-, and methyl azobisisobutyrate 9
2M9 was added and heated to 70°C. Next, phosphorus tribromide 171
A benzene solution of MII was added dropwise over 16 minutes.

Thereafter, the same operation as in Example 1 was carried out to obtain a 1.78f dilute acid.

The optical isomer ratio is (t)-cis form 8.6%, (c)-cis form 865%, (t)-trans form 46.2%, (c)-
The trans isomer content was 4767%.

Example 4 Levorotatory ethyl chrysanthemum acid ((+)-cis form 265% H-cis form 14.8% (+) -) lance form 11.9968
-) lance body 70.9%) 8.48F benzene 20-
Azobisisobutyronitrile 10051P was added thereto, and a benzene solution of pentabrominated hydroxide 540MIP was added dropwise over 80 minutes while stirring at 80°C.

After the reaction, ice water was added to the reaction solution and stirred to deactivate the catalyst. After separating the aqueous layer, the organic layer was evaporated under reduced pressure. The residual liquid was diluted with 10% sodium hydroxide water fdH20f.
After heating under reflux with / for 8 hours, toluene was added to separate the layers, and neutral substances were removed to form a toluene layer. The aqueous layer was acidified with hydrochloric acid, extracted with toluene, the organic layer was washed with water, dried with anhydrous sodium sulfate, and the solvent was distilled off under reduced pressure.
The residual liquid was then distilled to give a boiling point of 110-b min 2.491. This substance was confirmed to be a dilute acid based on its infrared absorption spectrum.

The optical isomer ratio of this product is (t)cis isomer 8.9%, (
f) cis form 8.2%, (e) trans form 48.8%,
The H trans form was 49.6%.

Example 6 In a 26-volume flask under a nitrogen atmosphere, (t)-cis
Dilute acid 1. Ff,) 9 f of toluene was added, and 0.24 f of phosphorus tribromide was added dropwise while stirring at 20°C. After stirring at the same temperature for 1 hour, the optical isomer ratio of the reaction solution was measured: (a)-cis isomer 6.9%, H-cis isomer 4.8%, (g)
-trans form 44.6%, (to)-trans form 48.7%
It was %.

Claims (1)

[Claims] General formula ▲ Numerical formula, chemical formula, table, etc. ▼ (In the formula, R is a hydrogen atom, an alkyl group having 1 to 20 carbon atoms,
It represents a cycloalkyl group or an aralkyl group, and * represents an asymmetric carbon. ) in the presence of an azo compound,
Alternatively, a method for racemizing optically active chrysanthemum acids, which comprises reacting with a brominated phosphorus compound in its absence.