DE3244890A1 - Process for the preparation of 3,4-dihydro- alpha -pyrones - Google Patents

Abstract

The present invention deals with the preparation of 3,4-dihydro- alpha -pyrones, which can optionally also be alkyl-substituted in the 3- and/or 4-position. These pyrones are prepared according to the invention by thermolysis of 4,5-epoxypentanecarboxylic acid esters which are optionally alkyl-substituted in the 2- and/or 3-position, or of 4-formylbutyric acid derivatives which are optionally alkyl-substituted in the 2- and/or 3-position. These 4-formylbutyric acid derivatives are formed as isolable intermediates when 4,5-epoxypentanecarboxylic acid or its esters are employed as starting materials and the thermolysis is preferably carried out at 350 to 450 DEG C. The formylbutyric acid derivatives isolable as intermediates are compounds unknown hitherto. The thermolysis for the preparation of the alpha -pyrones is preferably carried out in a temperature range between 250 and 350 DEG C and in the presence of high-surface area silicate materials, such as montmorillonite or zeolite, or of alumina. When the formylbutyric acids are employed as starting materials, the formation of the dihydropyrones takes place even at temperatures from 30 DEG C, particularly if acidic compounds are employed as catalysts.

Description

Process for the production of 3'4-I) hydropyrones

The present invention relates to a process for the production of -pyrones of the formula in which R1, R2 and R3 stand for identical or different alkyl radicals with 1 to 10 carbon atoms or for hydrogen.

The preparation of α-pyrones of the above formula is e.g. described in DE-OS 29 52 068. The starting products are the 5-hydroxymethyl-2 (3H) -furanones correspondingly substituted in the 3- and 4-positions used, a thermal treatment at temperatures between 200 and subjected to 500 ° C. The disadvantage of this procedure is that that these furanones in an additional process step from the corresponding 4,5-Epoxipentancarbonsäureestern must be obtained, whereby this procedure becomes very time-consuming.

The object was therefore to find a process for the preparation of 3,4-dihydro- «pyrones from 4,5-epoxypentanecarboxylic acid esters, in which the neat pyrone is obtained directly in one step. A process for the preparation has now been achieved found of 3,4-dihydro-a-pyrones of the above formula, which is characterized in that compounds of the general formula in which R1, R2 and R3 represent hydrogen and / or identical or different alkyl radicals with 1 to 10 carbon atoms and R represents hydrogen or an alkyl group with 1 to 4 carbon atoms and Z represents the grouping stands, heated to temperatures between 30 and 600 ° C. When using 4,5-epoxipentanecarboxylic acid derivatives as starting materials, ie if in the above formula Z for stands - arise in this procedure as intermediates 4-formylbutyric acid derivatives, ie compounds against the above formula II, in which Z is stands. These compounds can optionally be isolated and then processed into those insecticides which are mentioned in DE-OS 28 10 031. For the preparation of these formylbutyric acid derivatives, only the procedure described in DE-OS 28 10 031 was previously known, so that a new method for the preparation of 4-formylbutyric acid derivatives was found in fulfillment of the above-mentioned object, which is characterized in that one epoxypentane carboxylic acid derivatives formula in which R1, R2, R3 and R4 have the meaning given above, 0 heated to temperatures between 200 and 60000, preferably between 350 and 450 oC.

The yields of this intermediate product depend on the temperature chosen and the time of heating. In general, good yields of formylbutyric acid derivatives are obtained, when the temperatures are in the range between 350 and 450 OC.

If the compounds of the general formula II are heated in the presence of silicate materials or aluminum oxide, then both classes of compounds react of formula II, as the aldehyde and the epoxide directly to dihydropyrones of the general Formula 1.

As substances which thermolysis to form the 3,4-dihydro- d-pyrones have a positive effect, surface-rich, silicate materials such as e.g.

hydrous alkali or alkaline earth aluminosilicates. Of; these own particularly good the natural and synthetic zeolites and Montmorillonite. The latter can also be post-treated with hydrochloric acid, for example Temperatures between 400 and 800 oC must be heated before they are used according to the invention will. Such post-treated montmorillonite is predominantly (i.e. more than 90 ° O made of SiO2 and contains only small amounts of aluminum, which in the are generally less than 1% by weight. However, it still contains bound water, its Share can vary between 1 and 5 wt .-%. Its porosity is between 55 and 65% by volume (determined by water absorption and buoyancy weighing in accordance with DIN 51 056).

Dried, porous silica gels or aluminum oxide can also be used be used as reaction accelerating substances.

If the starting compounds for thermolysis are substances of the formula II are taken, in which R4 = II and Z = -CH2 - - OH = 0, thermolysis can be used can be carried out from 30 ° C. In principle, the reaction runs without additives from catalysts. However, the addition of catalytic amounts is recommended a Lewis and / or Brönsted acid. This addition enables a low temperature control. The above-mentioned silicate materials or aluminum oxide can also be used as Catalysts are used. This embodiment is the preferred one Temperature range between 50 and 150 00. The starting product is expediently optionally after addition of the catalysts, with drilling in a distillation apparatus heated and the resulting reaction products immediately separated off by distillation. the Thermolysis according to the invention is used in all other cases if no aldehydic acid is used as a starting material, both for the production of the 3,4-dihydropyrones as well as for the preparation of the formylbutyric acid derivatives way carried out in such a way that the compounds to be converted are passed through a pipe lets drip, which is heated to the desired thermolysis temperature. The pipe is filled with temperature-stable inert material that does not affect the reaction, such as porcelain saddles or glass balls 0 The residence time of the reaction mixture in the tube can be largely varied by filling level, shape and volume of this body will.

If, according to the invention, predominantly the production of 3,4-dihydro-ct-pyrones is desired, the temperature-stable, inert materials can partially or completely by molded bodies made from the above-mentioned reaction-accelerating substances be replaced. In this case, the reaction is preferred in the temperature range carried out between 200 and 350 ° C.

In the context of the present invention, it is also possible to use thermolysis carry out the respective starting materials in solution, using as a solvent such compounds come into question, which are stable at the temperatures to be used and do not react with any of the reaction components. Examples of such solvents are benzene, toluene and the xylenes. These solvents can also boil that are below the selected thermolysis temperature: One then drips E.g. a solution of the starting products in this solvent through a vertical standing, above-described reaction tube, wherein the solvent evaporates and is condensed in a collecting vessel together with the reaction products.

The thermolysis can be both at atmospheric pressure and at carry out a negative pressure down to about 10 3 bar.

The 3,4-dihydro-α-pyrones which can be prepared according to the invention are valuable Intermediate products used, among other things, for the production of insecticides based on cyclopropanecarboxylic acid derivatives Use, Example 1, 20 g of 4,5-epoxy-3,3-dimethylpentanecarboxylic acid methyl ester were through a vertically arranged glass tube (length 30 cm, diameter 2.2 cm) dripped within 160 min.

The glass tube was filled with balls made of a montmorillonite, the previously treated with 10 of the above hydrochloric acid for 8 hours, then with water washed out and then heated to 500 ° C for one hour. The internal temperature of the tube was 300 ° C. The thermolysate was collected in a cooled receiver and distilled. There were 15.3 g (97.5 0 3,4-dihydro-4,4-dimethyl - «- pyrone (boiling point: 76-79 OC / 16.10-3 bar).

Example 2 37.6 g of methyl 4-formyl-3,3-dimethylbutyrate were obtained through a vertically arranged glass tube (length 30 cm, diameter 2.2 cm), which was filled with the montmorillonite balls mentioned in Example 1, within 240 min dripped. The internal temperature of the tube was 300 ° C.

The thermolysate was collected in a cooled receiver and distilled. 28.8 g (97.6%) of 3,4-dihydro-4,4-dimethylqd-pyrone were obtained.

Example 3 Analogously to Example 2, 20 g of 4-Rormyl-3,3-dimethylbutyric acid are obtained brought to implementation. There were 15 g (87.1%) of 3,4-dihydro-4,4-dimethyl-pyrone obtain.

Example 4 70 g of 4,5-epoxy-3,3-dimethylpentanecarboxylic acid methyl ester became through a vertically arranged quartz tube (length 30 cm, diameter 2.2 cm), which was filled with porcelain saddles, dripped within 560 min. The internal tempera The temperature of the quartz tube was 400 ° C. The thermolysate was in a cooled template collected and distilled at a pressure of 16 bar. There were 57.7 g of 4-formyl-3,3-dimethylbutyrate (Bp 84-88 oO / 16.10 bar).

NMR Spectrum (100 MHz, CCl4): # # = 1.13 (6H); 2.37 (2H); 2.47 (2K); 3.63 (3H); 9.78 (1H).

Example 5 100.8 g of 3,3-dimethyl-5-oxo-pentanecarboxylic acid were in a distillation apparatus under vacuum (12 mm / Hg) to a temperature of 120 0 heated. H20 and 4,4-dimethyl-3, 4-dihydro-pyrone distilled already at 100 ° C After 11 hours of heating at 120 ° C, no further formation of H2O and 4,4-dimethyl-3,4-dihydro-α-pyrone was observed. Separates in the distillation receiver the water separates from the organic phase. Lie after separating the water 81.0 g of 4,4-dimethyl-3,4-dihydro-α-pyrone before Example 6 Analogously to Example 1, 100.8 g of 3,3-dimethyl-5-oxo-pentanecarboxylic acid are added in the presence of 0.25 g of H 2 SO 4 (conc.) Heated to 80 ° C for 9 hours. 78.2 g of 4,4-dimethyl-3,4-dihydro-α-pyrone are obtained.

Claims (8)

Claims: 1 J process for the preparation of 3,4-dihydro-4-pyrone of the formula in which Rl, R2 and R3 represent hydrogen and / or alkyl groups with 1 to 10 carbon atoms, since you rchgekisiert that one compounds of the formula in which R11, R2 and R3 have the abovementioned meaning, R4 for hydrogen and / or alkyl groups with 1 to 4 carbon atoms and Z for the radicals is heated to temperatures between 30 and 600 ° C. 2. The method according to claim 1, characterized in that in the case of the starting compounds heated to temperatures between 250 and 350 OG. 3. The method according to claim 1, characterized in that in the case of and R4 = H the starting compound is heated to temperatures between 30 and 50,000. 4. The method according to any one of claims 1 to 3, characterized in that indicates that heating in the presence of surface-rich silicate materials or Aluminum oxide is carried out. 5. The method according to claim 3, characterized. that heating is carried out in the presence of catalytic amounts of Lewis or Brönsted acids. 6. The method according to claim 4, characterized in that as surface-rich silicate material zeolite or montmorillonite is used. 7. The method according to claim 6, characterized in that one Montmorillonite is used, which is washed out with hydrochloric acid and then a thermal Has been subjected to treatment between 400 and 800 oC. 8. A process for the preparation of the formylbutyric acid derivatives of the formula which can be used as starting materials according to claim 1 in which R1, R2, R3 and R4 have the abovementioned meaning, characterized in that an epoxide of the formula in which R1, R, R3 and R44 have the abovementioned meaning, heated to temperatures between 200 and 600 ° C., preferably between 350 and 450 ° C.