WO1999012880A1

WO1999012880A1 - Process for the preparation of carvone

Info

Publication number: WO1999012880A1
Application number: PCT/NL1998/000505
Authority: WO
Inventors: Patricius Petrus Johannes Mulder; Jacco Van Haveren; Herman Henk Nijhuis
Original assignee: Nationale Aan- En Verkoopcoöperatie Voor Land -En Tuinbouw Cebeco-Handelsraad B.A.
Priority date: 1997-09-05
Filing date: 1998-09-04
Publication date: 1999-03-18
Also published as: AU9007598A; NL1006959C2; WO1999012880A9

Abstract

Carvone can be prepared by catalytic oxidation of limonene with 0.001-0.2 equivalent palladium or a salt thereof in the presence of a reoxidising agent such as a copper salt and a salt of a non-transition metal, for example sodium carbonate, in an organic solvent, the yield being improved if the oxidation is carried out in one step in the presence of oxygen and water. The presence of an acid results in a further improvement.

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 re-oxidising agent.

D-Carvone (2-methyl-5-isopropenyl-2-cyclohexenone) can be used as an anti- sprouting agent for potatoes and as a fungicide. It is a natural substance which occurs in dill and caraway seeds. However, these natural sources are inadequate for economically justifiable production of carvone. D-limonene (l-methyl-4-isopropenyl-cyclohexene) is available in larger quantities from natural sources and can be oxidised by a biochemical or chemical route to produce carvone. However, the known methods for the oxidation of olefins such as limonene to give the corresponding α,β-unsaturated ketones give a low yield of ketone, which, moreover, is impure.

The work by El Firdoussi et al (J. Molecular Catalysis, 72 (1992) L1-L5) discloses the reaction of limonene with a Pd(II) salt as catalyst (0.03-0.05 eq.) and benzoquinone or a copper salt as oxidising agent (1.8-2.7 eq.) in acetic acid or methanol, a mixture of isomeric allyl esters (including carveyl acetate) and allyl ethers being obtained; yields are not reported.

The reaction of limonene with cobalt acetate (0.01 eq.) in acetic anhydride under an oxygen pressure of 3 and 10 bar has been studied by Taher and Ubiergo (Essenze Deriv. Agrum. 54 (1984) 122-127). Up to degrees of conversion of about 33 and about 50 % respectively, the selectivity of carvone formation was about 20 %, in addition to the formation of carveol and other products. At these degrees of conversion, which are still low, the yield of carvone was about 6 % and 8 %, respectively, and this did not increase any further on further conversion.

According to Kurata and Matsubara (Yukagaka 22 (1983) 724) the oxidation of limonene with 0.1 eq. cobalt acetate in acetic acid under 1 bar oxygen gives a maximum yield of carvone of 31 %; other transition metals are less active. The inventors of the present invention were, however, unable to prepare carvone in a yield of more than 10 % under the conditions indicated by Kurata and Matsubara.

The known methods described above are variants of the so-called Wacker process as described in US Patent 3 076 032. According to this process, simple straight- chain olefins can be converted in good yield (50 %) to carbonyl compounds, the olefinic bond itself being oxidised. It is known that the yield of ,β-unsaturated carbonyl compounds according to this process is particularly 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 process has now been found which meets this need. The process is defined in the appended claims. This process leads to a yield of carvone of more than 60 %, with a degree of conversion of more than 98 %. The selectivity is also high. The characterising feature is that the allyl position next to the most highly substituted olefinic bond is oxidised whilst the less highly substituted olefinic bond displays no reactivity. The expected Wacker oxidation products, such as, for example, 2,3-dihydrocarvone or p-menth-l-en-9-one (8,9-dihydrolimonene-9-aldehyde), are not formed at all. In the case of the oxidation of limonene, the selectivity for carvone formation is higher than

60 %. This process is found to give an appreciably less good result with other olefins.

The starting concentration of limonene used in the oxidation reaction can be OJ-2 mol/1. The oxygen to be used can be present in the form of air, an adequate concentration of oxygen in the reaction mixture being ensured by stirring, shaking or blowing in. Preferably, enriched oxygen or even pure oxygen is used, preferably under a pressure of 0.5-10 bar. The presence of water is also important according to the invention. The quantity of water in the reaction mixture is in general 0.01-50 % V/V, preferably 2-40 and in particular 4-20 % V/V.

The primary oxidation takes place with palladium or a divalent salt thereof. Suitable palladium salts are, for example, the chloride, acetate or other carboxylate, haloacetate or other halocarboxylate, sulphate, nitrate, tetraborate, acetylacetonate or other beta-diketonate. Only a catalytic amount of the palladium is needed, i.e. in general 0.001-0.2 equivalent with respect to the olefin to be oxidised, in particular 0.01-OJ equivalent. The oxidation can be carried out at room temperature or elevated temperature, preferably at 25-120 °C, in particular at 40-80 °C.

The palladium or salt thereof used is oxidised in situ by a re-oxidising agent. Suitable re-oxidising agents are, for example, salts and oxides of copper, iron(III), manganese(IV), lead(IV), tantalum(III) and other transition metals. It is also possible to use other re-oxidising agents that are known as such, including heteropolyacids and corresponding anions, such as phosphomolybdovanadic, phosphotungstomolybdic and zodanig bekende reoxidatoren waaronder heteropolyzuren en overeenkomstige anionen zoals fosformolybdeenvanadium-, fosforwolfraammolybdeen- en fosforwolfraam- vanadium-zuren en organische oxidatoren zoals eventueel gesubstitueerde chinonen en benzochinonen komen in aanmerking. Ook van de reoxidator kan met een minder dan equivalente hoeveelheid worden volstaan. In het algemeen past men 0,005-2,0 equivalent ten opzichte van het olefine toe, in het bijzonder 0,2-0,6 equivalent. Koperzouten zoals koper(I)- en koper(II)-chloride hebben de voorkeur, vooral koper(II)zouten.

Het organische oplosmiddel is in het algemeen een polair oplosmiddel dat bestand is tegen de oxidatieomstandigheden. In aanmerking komen vooral vloeibare carbonzuren zoals mierenzuur, azijnzuur, chloorazijnzuur, propionzuur, boterzuur en isoboterzuur. Naast de genoemde oplosmiddelen mogen tot 75 vol.%, maar liever niet meer dan 50 vol.%, andere polaire of apolaire oplosmiddelen aanwezig zijn. Voorbeelden daarvan zijn water, aromaten (benzeen, tolueen, xyleen), esters (ethylacetaat, butylacetaat), ethers (THF, dioxaan, dimethoxyethaan), acetonitril, DMSO en amiden (DMF, DMA, NMP) en mengsels daarvan. De meeste voorkeur hebben azijnzuur en propionzuur. Gebleken is dat de opbrengst van de oxidatie verder kan worden verhoogd wanneer in het reactiemedium een sterk zuur wordt opgenomen. Voorbeelden zijn fosforzuur, zwavelzuur, zoutzuur, eventueel gesubstitueerde alkaan- en areen-sulfonzuren (bij voorbeeld trifluormethaan- sulfonzuur of p-tolueensulfonzuur) en in het bijzonder α-halogeenalkaanzuren, zoals dichloor-, trichloor- en trifluorazijnzuur en dichloorpropionzuur. De meeste voorkeur hebben trichloorazijnzuur en vooral trifluorazijnzuur. De toe te passen hoeveelheid bedraagt bij voorkeur 0,01-20 vol.% ten opzichte van het totale oplosmiddel, in het bijzonder OJ-2 vol.%. De pH is bij voorkeur lager dan 3, liefst tussen 1 en 2.

Als zout van een niet-overgangsmetaal kan bij voorbeeld een zout van een alkali-, aardalkali- of aardmetaal, en bij voorkeur een hydroxide of een zout van een carbonzuur, in het bijzonder een alkalimetaalhydroxide, -acetaat of -propionaat, worden toegepast. De reagentia, zoals de reoxidator (koperzout) of het niet-overgangsmetaalzout, kunnen vooraf worden toegevoegd, dan wel geleidelijk gedurende de oxidatie worden toegevoegd. Voorbeeld 1 In een glazen reactor werd een oplossing van palladium(II)chloride (0,50 mmol) in azijnzuur (45 ml) en water (5 ml) gebracht. Achtereenvolgens werden toegevoegd: natriumacetaat (5 mmol), koper(II)chloride (3 mmol), trifluorazijnzuur (6 mmol) en limoneen (10 mmol). Het reactiemengsel werd bij 50°C 20 uur krachtig geroerd limonene (10 mmol). The reaction mixture was stirred vigorously (magnetic stirrer, 500 revolutions per min.) at 50 °C for 20 hours under an oxygen atmosphere (1.1 bar). At the end of the reaction the reaction mixture was analysed with the aid of gas chromatography.

The limonene conversion was 99.5 % and the selectivity for carvone was 61 %. Carveol and carveyl acetate were formed as by-products. It was found that no significant oxidation of carveol to carvone takes place under the reaction conditions (see also comparative example D).

Example 2

Example 1 was repeated except that no trifluoroacetic acid was added. The limonene conversion was 98.5 %. The selectivity for carvone was 44 %.

Example 3

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

Example 4 Example 1 was repeated except that the reaction was carried out under 1J bar air instead of oxygen. The limonene conversion was 99 % and the selectivity for carvone was 38 %.

Comparative Example A

Example 1 was repeated except that no palladium(II) chloride was added. The limonene conversion was 18 %. The selectivity for carvone was less than 1 %.

Comparative Example B

Example 1 was repeated except that no water was added. The limonene conversion was 99 % and the selectivity for carvone was 6 %.

Comparative Example C Example 1 was repeated except that the reaction was carried out under 1J bar nitrogen instead of oxygen. 18 mmol copper(II) chloride was used instead of 3 mmol and

22 mmol sodium acetate was added instead of 5 mmol. The limonene conversion was

97 % and the selectivity for carvone 2 %.

Comparative Example D Example 1 was repeated except that carveol was used instead of limonene. The carvone yield was 5 %.

Claims

1. A 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 re-oxidising agent and a salt of a non-transition metal in an organic solvent, characterised in that the oxidation is carried out in one step in the presence of oxygen and water.

2. A process according to Claim 1, wherein a molecular oxygen pressure of 0.5-10 bar is used.

3. A process according to Claim 1 or 2, wherein 2-40 % V/V water, based on the total solvent, is used.

4. A process according to one of Claims 1-3, wherein 0.2-0.6 equivalent of the reoxidising agent is used.

5. A process according to one of Claims 1-4, wherein copper(I) chloride or copper(II) chloride is used as re-oxidising agent.

6. A process according to one of Claims 1-5, wherein the oxidation is carried out at a temperature of 40-80 ┬░C.

7. A process according to one of Claims 1-6, wherein an organic carboxylic acid and/or carboxylic acid anhydride, in particular acetic acid and/or propionic acid, is used as solvent.

8. A process according to one of Claims 1-7, wherein 0.01-10 % V/V of strong acid, based on the total amount of solvent, is also used.

9. A process according to Claim 8, wherein OJ-2 % V/V trifluoroacetic or trichloroacetic acid is used.

10. A process according to one of Claims 1-9, wherein the pH of the reaction mixture is kept between 1 and 3.