NL1006959C2 - Process for the preparation of carvone. - Google Patents

Description

Process for the preparation of carvone

The invention relates to a process for the preparation of carvone by catalytic oxidation of limonene with a palladium (II) salt and a reoxidator.

D-Carvon (2-methyl-5-isopropenyl-2-cyclohexenone) is useful as an earth 5 chemical inhibitor and as a fungicide. It is a natural substance found in dill and caraway seeds. However, these natural resources are insufficient for economically sound production of carvone. D-Limonene (1-methyl-4-isopropenylcyclohexene) is available in larger amounts from natural sources and can be oxidized to carvone by biochemical or chemical means. However, the known methods for the oxidation of olefins such as limonene to the corresponding α, β-unsaturated ketones yield a low yield of ketone, which is additionally impure.

It is known from the work of El Firdoussi et al. (J. Molecular Catalysis, 72 (1992) L1-L5) to convert limonene with a Pd (II) salt as catalyst (0.03-0.05 cq.) 15 and benzoquinone or a copper salt as an oxidizer (1.8-2.7 eq.) in acetic acid or methanol, wherein a mixture of isomeric allyl esters (including carveyyl acetate), respectively. allylcs are obtained; yields are not reported.

Tahcr and Ubiergo (Essenze Deriv. Agrum. 54 (1984) 122-127) examined the conversion of limonene with cobalt acetate (0.01 eq.) Into acetic anhydride under an oxygen pressure of 3 and 10 bar. Up to conversion rates of approx. 33 resp. about 50%, the selectivity of can formation was about 20% in addition to the formation of caneol and other products. At those still low conversions, the yield of carvone was approx. 6% resp. 8% and upon further conversion it no longer increased.

According to Kurata and Matsubara (Yukagaka 22 (1973) 724), the oxidation of 25 limonene yields 0.1 eq. cobalt acetate in acetic acid under 1 bar oxygen, a maximum yield of carvone of 31%; other transition metals are less active. However, the inventors of the present invention were unable to prepare carvone in greater than 10% yield under the conditions indicated by Kurata and Matsubara.

The known methods described above are variants of the so-called Wackcr process, as described in US patent 3076032.

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According to this process, simple linear olefins can be converted in good yield (50%) to carbonyl compounds, oxidizing the olefin bond itself. It is known that the yield of α, β-unsaturated carbonyl compounds by this process is very low.

There is therefore a need for a process for the preparation of carvone by oxidation of limonene which has a higher selectivity and a higher yield.

A method has now been found that meets this need. The method is defined in the appended claims. This process leads to a yield of carvone of more than 60% at a conversion rate of more than 98%. The selectivity is also high. Typically, the allylic position adjacent to the highly substituted olefinic band is selectively oxidized, while the lower substituted olefinic band exhibits no reactivity. The expected Wacker oxidation products, such as, for example, 2,3-dihydrocarvone or p-menth-1-en-9-one (8,9-dihydroimonene-9-aldchyd) are not formed at all. In the oxidation of limonene, the selectivity for carbon formation is higher than 60%. With other olefins, this method has been found to produce a considerably less good result.

As the initial concentration of the limonene in the oxidation reaction, 0.1-2 mol / l can be used. The oxygen to be used can be in the form of air, whereby a sufficient concentration of oxygen is provided in the reaction mixture by stirring, shaking or blowing. Enriched oxygen or even pure oxygen is preferably used, preferably at a pressure of 0.5-10 bar. The presence of water is also important according to the invention. The amount of water in the reaction mixture is generally 0.01-50% by volume, preferably 2-40 and especially 4-20% by volume.

The primary oxidation takes place with palladium or a divalent salt thereof.

Suitable palladium salts are, for example, the chloride, acetate or other carboxylate, halo-acetate or other halo-carboxylate, sulfate, nitrate, tetraborate, acetylacetonate or other β-diketonate. Only a catalytic amount is required of the palladium, ie generally 0.001-0.2 equivalent to the olefin to be oxidized, in particular 0.01-0.1 equivalent. The oxidation can be carried out at room temperature or elevated temperature, preferably at 25-120 ° C, especially at 40-80 ° C.

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The used palladium or salt thereof is re-oxidized on site by a reoxidator. Suitable reoxidators are, for example, salts and oxides of copper, iron (III), manganese (IV), lead (IV), tantalum (III) and other transition metals. Other reoxidators known per se, including heteropolyacids and corresponding anions such as phosphorus-molybdenum vanadium, phosphorus tungsten molybdenum and phosphorus-tungsten vanadium acids and organic oxidizers such as optionally substituted quinones and benzoquinones are also suitable. A less than equivalent amount of the reoxidator is also sufficient. Generally 0.005-2.0 equivalent to the olefin is used, in particular 0.2-0.6 equivalent. Copper salts such as copper (I) and copper (II) chloride are preferred, especially copper (II) salts.

The organic solvent is generally a polar solvent that is resistant to the oxidation conditions. Particularly suitable are liquid carboxylic acids such as formic acid, acetic acid, chloroacetic acid, propionic acid, butyric acid and isobutyric acid. In addition to the mentioned solvents, up to 75% by volume, but preferably not more than 50% by volume, other polar or non-polar solvents may be present. Examples thereof are water, aromatics (benzene, toluene, xylene), esters (ethyl acetate, butyl acetate), ethers (THF, dioxane, dimethoxyethane), acetonitrile, DMSO and amides (DMF, DMA, NMP) and mixtures thereof. Most preferred are acetic acid and propionic acid. It has been found that the yield of the oxidation can be further increased if a strong acid is included in the reaction medium. Examples are phosphoric acid, sulfuric acid, hydrochloric acid, optionally substituted alkane and arene sulfonic acids (eg trifluoromethanesulfonic acid or p-toluenesulfonic acid) and in particular α-haloalkanoic acids, such as dichloro, trichloro and trifluoroacetic acid and dichloropropionic acid. Most preferred are trichloroacetic acid and especially trifluoroacetic acid. The amount to be used is preferably 0.01-20% by volume relative to the total solvent, in particular 0.1-2% by volume.

As a salt of a non-transition metal, for example, a salt of an alkali, alkaline earth or earth metal, and preferably a hydroxide or a salt of a carboxylic acid, in particular an alkali metal hydroxide, acetate or propionate, can be used. The reagents, such as the reoxidator (copper salt) or the non-transition metal salt, can be added beforehand or gradually added during the oxidation 1006959-4.

Example 1

A solution of palladium (II) chloride (0.50 mmol) in acetic acid (45 ml) and water (5 ml) was placed in a glass reactor. The following were added successively: 5 sodium acetate (5 mmol), copper (II) chloride (3 mmol), trifluoroacetic acid (6 mmol) and limonene (10 mmol). The reaction mixture was stirred vigorously (magnetic, 500 revolutions per minute) at 50 ° C for 20 hours under an oxygen atmosphere (1.1 bar). At the end of the reaction, the reaction mixture was analyzed by gas chromatography. The conversion of limonene was 99.5% and the selectivity to 10 carvone was 61%. Carveol and carveyl acetate were formed as by-products. It was found that no appreciable oxidation of carveol to carvone takes place under the reaction conditions (see also comparative example D).

Example 2

Example 1 was repeated with the difference that no trifluoroacetic acid was added. The limonene conversion was 98.5%. The selectivity to carvone was 44%.

Example 3

Example 1 was repeated with the difference that propionic acid was used instead of acetic acid. The limonene conversion was 98.5% and the selectivity to carvone was 68%.

Example 4

Example 1 was repeated with the difference that the reaction was carried out under 1.1 bar of air instead of oxygen. The limonene conversion was 99% and the selectivity to carvone was 38%.

Comparative example A

Example 1 was repeated with the difference that no palladium (II) chloride was added. The limonene conversion was 18%. The selectivity to carvone was less than 1%.

Comparative example B

Example 1 was repeated with the difference that no water was added.

The limonene conversion was 99% and the selectivity to carvone was 6%. Comparative example C

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Example 1 was repeated with the difference that the reaction was carried out under 1.1 bar of nitrogen instead of oxygen. Instead of 3, 18 mmol of copper (II) chloride and instead of 5 were added 22 mmol of sodium acetate. The conversion of limonene was 97%, the selectivity to carvone 2%.

5 Comparative example D

Example 1 was repeated with the difference that instead of limonene carveol was used. The yield of carvone was 5%.

1006959

Claims (9)

1. Process for the preparation of carvone by catalytic oxidation of limonene with 0.001-0.2 equivalent palladium or a salt thereof in the presence of a reoxidator and a salt of a non-transition metal in an organic solvent, characterized in that the one-step oxidation in the presence of oxygen and water. The method according to claim 1, wherein a molecular oxygen pressure of 0.5-10 bar is used. 3. Process according to claim 1 or 2, wherein 2-40% by volume of water relative to the total solvent is used. Process according to any one of claims 1-3, wherein 0.2-0.6 equivalent of the reoxidator is used. 5. Process according to any one of claims 1-4, wherein copper (I) chloride or copper (II) chloride is used as reoxidator. 6. Process according to any one of claims 1-5, wherein the oxidation is carried out at a temperature of 40-80 ° C. 7. Process according to any one of claims 1-6, wherein an organic carboxylic acid and / or carboxylic anhydride, in particular acetic acid and / or propionic acid, is used as a solvent. Process according to any one of claims 1-7, wherein 0.01-10% by volume of strong acid with respect to the total amount of solvent is also used. The process according to claim 8, wherein 0.1-2% by volume of trifluoro- or trichloroacetic acid is used. 1 0069 59 COOPERATION TREATY (PCT) REPORT ON CENTURY RESEARCH OF INTERNATIONAL TYPE IDENTIFICATION OF NATIONAL APPLICATION May Mar *, of Applicant or of Gemacnogcej N.O. 40737 EH j New Zealand application no. Filngsdaiim 1006959. September 5, 1997 _ - .. __ ___ -__ _ \ In 9th call priority priority Request (Name) I ί ATO-DLO I t _____ ____ _ 1 Date of reconciliation for «and unzoo * of mtemasonaai ryp« By the insanne for International Inquiry (ISA) to ne: reconcile for «and o na« f 20 «κ of interna do na aJ type ttegexend nr. I SN 30030 NL 'I I. CLASSIFICATION OF THE SUBJECT MATTER (for various dassilieaoes. csassrficaoesymboien)) According to the Inemaoonaie dassifiease (IPC) Int.Cl.6: C 07 C 45/30, C 07 C 45/28, C 07 C 49/647 II. FIELDS OF TECHNIQUE EXAMINED __Under minimum documentation___ Classification system _Classification class __ * __ j Int.Cl.6: C 07 C Onaeroenie documents other than the minimum battery menace insofar as such documents are included in the prayers examined III. NO INVESTIGATION FOR CERTAIN CONCLUSIONS (comments on supplemental Dlad) IV. LACK OF UNIT OF INVENTION (Notes on Supplementary Sheet) Form PC7 / ISA-20I (ai CS I99J