EP1718589A2

EP1718589A2 - Method for producing astaxanthin and canthaxanthin intermediate products

Info

Publication number: EP1718589A2
Application number: EP04803760A
Authority: EP
Inventors: Bernd Rumpf; Petra Deckert; Thomas Müller; Johannes Grimmer
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2003-12-11
Filing date: 2004-12-10
Publication date: 2006-11-08
Also published as: DE10358003A1; WO2005056507A3; WO2005056507A2

Abstract

The invention relates to a method for producing cyclohexenone derivatives of general formula (I), wherein R<1> represents hydrogen or OH; R<2> represents (Ia), comprising the following steps: (a) hydrolyzing a cyclohexenol compound of formula (II), wherein R<3> represents hydrogen and R<4> represents C1-C6-alkoxy or R<3> and R<4> represent vicinal hydroxy groups, which carry a common acetal protective group or a ketone protective group, R<5> represents (IIa), and R<6> represents a protected hydroxy group, in the absence of an organic solvent and in the presence of an acid catalyst; and; (b) extracting the reaction mixture by using a polar extracting agent.

Description

Process for the preparation of astaxanthin and canthaxanthin precursors

description

The invention relates to a process for the preparation of certain cyclohexenone derivatives which serve as astaxanthin and canthaxanthin precursors.

The C ₄₀ carotinoids astaxanthin and canthaxanthin are very popular dyes in animal nutrition, for example for fish or egg yolk pigmentation. The possibilities for obtaining these carotenoids from natural sources such as algae, fungi or yeast on an industrial scale are very limited. The most productive access to astaxanthin or canthaxanthin is therefore in chemical synthesis.

Technical processes for the production of astaxanthin are u. a. in EP-A-0 005 748 and EP-A-0 633 258 and in Helv. Chim. Acta 64 (1981), 2436 ff. The synthesis of canthaxanthin is the subject of DE-A-26 25 259.

Common to these processes is the synthesis strategy: C ₉ + C ₆ = C ₁₅

C _n here stands for a molecular building block that has a basic structure of n C atoms. According to the above-mentioned prior art, the C ₁₅ intermediates are obtained by linking C ₈ with C _{6 building} blocks. The linkage takes place by means of an organometallic reaction in which an acetylene group on the C _{6 building} block is deprotonated either with the aid of a Grignard reagent in THF or a butyl lithium solution.

EP 0 633 258 discloses a process in which the linking of C ₉ and C ₆ building blocks for astaxanthin synthesis in an organic solvent in the presence of lithium amide succeeds. This is a C _{9 building} block of the general formula

wherein R ^{1 is} H or CC alkyl and R ^{2 is} CC alkyl, with a C _{6 building} block of the general formula

wherein R ^{3 is} a protected hydroxy group linked.

An important process step in this synthesis of the C-ι _{5 building} blocks is the protection of the OH functionalities of the components used. After the CC linkage, the protective groups are split off again, e.g. B. by acid catalyzed hydrolysis, as illustrated by the following reaction scheme of the acetal compound Ila:

(lla) (la)

In multi-stage syntheses, the aim is to carry out the individual steps as efficiently as possible and to achieve a high yield. In the above hydrolysis step, therefore, it is desirable to use the catalyst and the hydrolysis by-products as in the above case e.g. Acetaldehyde, acetaldehyde diacetal and ethanol, easily removed and avoiding the need to evaporate large amounts of solvent.

The fact that the acid catalyst required for acetal cleavage remains in the reaction mixture is associated with safety risks. The catalyst thus lowers the temperature at which the thermal decomposition of the reaction mixture begins. In addition, the adiabatic induction time is shortened, ie the time until the onset of a self-accelerating reaction without further energy supply at a given temperature. A synthesis of the C _{15 building} blocks used, which does not require the addition of an organic solvent, is the subject of application DE 102 31 590.6.

The invention is based on the object of providing a process for the preparation of C ₁₅ building blocks for the synthesis of astaxanthin or canthaxanthin suitable cyclohexenone derivatives of the general formula I below, which allows simple and uncomplicated implementation with high operational reliability and in which the C ₅ -Building blocks can be obtained in good yield and high purity.

This object is achieved by a process for the preparation of cyclohexenone derivatives of the general formula I,

wherein

R ^{1 represents} hydrogen or OH;

R ² for

stands,

comprising the steps:

(a) Hydrolysis of a cyclohexenol compound of the formula II

wherein R ^{3 represents} hydrogen and R ^{4 represents} d-Ce alkoxy, or

R ³ and R ^{4 represent} vicinal hydroxyl groups which carry a common acetal or ketal protective group,

R ⁵ for

R ^{6 represents} a protected hydroxy group in the absence of an organic solvent in the presence of an acid catalyst;

(b) Extracting the reaction mixture with a polar extractant.

In the present case, C 1 -C 4 -alkyl stands for a linear or branched aliphatic hydrocarbon radical with 1 to 6 C atoms, such as, for. B. methyl, ethyl, n-propyl, 1-methyl-ethyl, n-butyl, 1-methyl propyl, 2-methylpropyl or 1, 1-dimethylethyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl , 2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 1, 1-dimethylpropyi, 1, 2-dimethylpropyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1, 1-dimethylbutyl, 1, 2-dimethylbutyl, 1, 3-dimethylbutyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 3,3-dimethylbutyl, 1-ethylbutyl, 2-ethylbutyl, 1, 1, 2-trimethylpropyl, 1, 2,2-trimethylpropyl, 1-ethyl-1-methylpropyl, 1-ethyl-2-methylpropyl, 1-ethyl-3-methylpropyl.

The C ₆ -C ₆ -alkyl radicals mentioned can optionally have one or more, for. B. 1, 2, 3 or 4, Ci-Cs-alkoxy substituents, as in d-Cs-alkoxy-d-Ce-alkyl, for. B. 2-methoxyethyl.

Here and in the following, C -C alkoxy represents an alkyl radical, bonded via an oxygen atom, as defined above, having 1 to 6 C atoms, such as, for. B. methoxy, ethoxy, propoxy, 1-methylethoxy, butoxy, 1-methyl propoxy, 2-methylpropoxy or 1, 1-dimethylethoxy.

The C ₁ -C ₆ alkoxy radicals mentioned can optionally have one or more, for. B. 1, 2, 3 or 4, Ci-Cs-alkoxy substituents, as in -CC ₅ alkoxy -CC ₆ -alkoxy, z. B. 2-methoxyethoxy. A "common acetal or ketal protecting group" means the remainder of any protecting group that is commonly used to protect vicinal hydroxy groups. Typically, the common acetal or ketal protecting group comprises a methylene moiety between the oxygen atoms of the vicinal hydroxy groups which is substituted by one or two CC ₆ alkyl groups as defined above.

A "protected hydroxyl group" means a hydroxyl group which carries a customary protective group, ie a functional group which can be split off by hydrolysis under relatively mild conditions. Examples of protected hydroxy groups are ether groups such as benzoxy or tert-butoxy; Silyl ether groups, such as -O-Si (CH ₃ ) ₃ , -O-Si (CH ₂ CH ₃ ) ₃ , -O-Si (iso-propyl) ₃ , -O-Si (CH ₂ CH ₂ ) ₂ (iso -Propyl), -0-Si (CH ₃ ) ₂ (tert-butyl) and -O-Si (CH ₃ ) ₂ (n-hexyl); substituted methyl ether groups such as methoxymethoxy, 1-methoxyethoxy, 1-ethoxyethoxy, 2-methoxy-iso-propoxy, -benzoxyethoxy, 2-benzoxy-iso-propoxy; and suitable pyranyl ether groups such as tetrahydropyranyloxy or 4-methyl-5,6-dihydro-2H-pyranyloxy.

The corresponding reaction conditions for introducing and splitting off the above-mentioned protective groups are known to the person skilled in the art and can be found u. a. in T. Greene, "Protective Groups in Organic Cherriistry," John Wiley & Sons, 1981, Chapter 2.

The cyclohexenol compounds of the formula II which can be used as starting materials for the hydrolysis can be prepared by methods of organic synthesis known to the person skilled in the art, such as, for. B. described in EP 0 633 258.

In a preferred embodiment, in the above formula II, R ^{3 represents} hydrogen and R ^{4 represents} CC ₆ alkoxy, preferably CC ₄ alkoxy, particularly preferably methoxy, ethoxy or 2-methylpropoxy.

In a further preferred embodiment, R and R are

wherein

R ^{7 represents} hydrogen or -CC ₆ alkyl; and

R ^{8 represents} d-Cβ-Al yl. R ⁷ preferably represents hydrogen, methyl, ethyl, n-propyl or 1-methylethyl, and R ^{8 represents} methyl, ethyl, n-propyl or 1-methylethyl.

In a particularly preferred embodiment, R ^{7 is} H and R ⁸ is methyl, ethyl, n-propyl or 1-methylethyl.

In a very particularly preferred embodiment, R ^{7 is} H and R ^{8 is} methyl.

In a preferred embodiment, R ⁵ stands for

In a preferred embodiment, R ^{6 is} tetrahydropyranyloxy of the formula below

or 1-ethoxyethoxy, particularly preferably 1-ethoxyethoxy.

Thus, a cyclohexenol compound of the formula II which is preferably used has the formula IIa:

The term "in the absence of an organic solvent" means that the reaction mixture in step (a) contains essentially no external organic solvent, and it does not matter whether the organic solvent is separate is added or introduced into the reaction mixture as a mixture with the starting materials. The hydrolysis by-products such as aldehydes, ketones or alcohols are not external organic solvents. “Essentially no solvent” or “essentially absent solvent” (hereinafter “absent solvent”) means a content of one or more external organic solvents of less than 10% by weight, preferably less than 5% by weight. %, particularly preferably less than 3% by weight, very particularly preferably less than 0.5% by weight, based on the total weight of the reaction mixture, in particular those solvents which are immiscible with water are absent.

Typical organic solvents that are absent in the process according to the invention include a. aliphatic alcohols; aliphatic hydrocarbons, especially hexane and / or heptane; Alkyl esters of aliphatic carboxylic acids, such as methyl acetate and / or ethyl acetate; aromatic hydrocarbons such as toluene and / or xylene; Ethers such as diethyl ether, diisopropyl ether, methyl tert-butyl ether, dioxane and / or THF, halogenated aliphatic hydrocarbons such as dichloromethane, perchlorethylene and / or chloroform, especially dichloromethane.

As acidic catalysts are usually suitable for the cleavage of acetals used acidic catalysts, for. B. mineral acids, such as sulfuric acid, hydrochloric acid or hydrobromic acid; Sulfonic acids, such as methanesulfonic acid, trifluoromethanesulfonic acid, benzenesulfonic acid or para-toluenesulfonic acid; as well as other strong organic acids such as citric acid, trifluoroacetic acid or formic acid.

The acidic catalysts used are preferably sulfonic acids, selected from methanesulfonic acid, trifluoromethanesulfonic acid, benzenesulfonic acid or para-toluenesulfonic acid, particularly preferably para-toluenesulfonic acid. The abovementioned catalysts can either be mixed into one of the starting materials before the reaction or can be fed into the reactor as a separate stream.

The amount of catalyst is in the range from 0.05 to 100 mol%, preferably in the range from 0.1 to 1.0 mol%, based on the C ₅ -acetals / ketals of the general formula II.

Water is also added to the reactor in at least the stoichiometrically required amount. The proportion of water is generally 0.1 to 20% by weight, preferably 0.5 to 15% by weight, particularly preferably 1 to 12% by weight, based on the total weight of the reaction mixture.

In a particularly preferred embodiment, an aqueous solution of the acid catalyst is used in step (a) in order to introduce the acid catalyst and the water required for the hydrolysis simultaneously into the reactor. The concentration ration of the acid is preferably 0.01 to 90 wt .-%, preferably 0.01 to 2 wt .-%, based on the aqueous solution.

In preferred embodiments, the cyclohexenol compound of the formula II is introduced continuously into a reactor which has at least one backmixed region. There are conventional stirred tank reactors, stirred tank reactor cascades or combinations of stirred tank reactors and loop reactors in which the reaction mixture z. B. is passed over a mixing and control system, which may have addition and / or removal points.

A molar ratio of the cyclohexenone derivative of the formula I to the cyclohexenol compound of the formula II of at least 90:10, in particular at least 95: 5, is preferably maintained in the reactor. The person skilled in the art is familiar with the measures for setting the operating point of the reactor in such a way that the specified molar ratio is achieved. These measures include choosing an adequate one

Residence time of the reaction mixture in the reactor, a suitable reaction temperature and a suitable pressure, which in turn influence the reaction rate.

The residence time in the reactor is typically 5 to 60 minutes, preferably 10 to 30 minutes. The hydrolysis is preferably carried out at a temperature in the range from 20 ° C. to 100 ° C., particularly preferably from 40 ° C. to 60 ° C. It is also preferred to carry out the hydrolysis in the pressure range from 50 to 1000 mbar, particularly preferably in the pressure range from 900 to 1000 mbar. Operation at ambient pressure is particularly preferred. H. about 1000 mbar, since in this case the cost-intensive vacuum system can be omitted.

Alternatively, acidic ion exchange resins, in particular strongly acidic ion exchange resins containing sulfonic acid groups, can also be used as catalysts in the hydrolysis. In this case, it is advantageous to pump the compounds of the formula II together with the water required for the hydrolysis continuously through a tube reactor filled with ion exchange resin.

By the term "acidic ion exchange resins" available Har- are commercially ze or to understand detoxans such as Lewatit ^® S 100, Lewatit SP 112 or ^® 2631 (Bayer) or Amberlite ^® 18 and Amberlyst ^® IRA 120 or 15 or Duolite ^® C 20, C 26 and C 264 (Rohm & Haas) or Dowex ^® ion exchangers.

In addition to the above-mentioned acidic ion exchange resins, other heterogeneous acidic catalysts, for example zeolites, can also be used for the hydrolysis in step (a).

Zeolites are crystalline aluminosilicates that have a highly ordered structure with a rigid three-dimensional network of SiO ₄ or AIO tetrahedra are connected by common oxygen atoms. The ratio of the Si and Al atoms to oxygen is 1: 2. The electrovalence of the aluminum-containing tetrahedra is due to the inclusion of cations in the crystal, e.g. B. an alkali or hydrogen atom, balanced. A cation exchange is therefore possible. The spaces between the tetrahedra are occupied by drying or calcining water molecules before dehydration.

Suitable zeolites are e.g. B. those of the Pentasil type, especially aluminosilicate zeolites or borosilicate zeolites. By partial coking (pre-eoke) it is possible to adjust the activity of the catalyst for an optimal selectivity of the desired reaction product.

Heterogeneous catalysts are advantageously arranged fixed in the reactor.

The reaction mixture obtained after the hydrolysis is treated with a polar extractant. To do this, the reaction mixture is brought into intensive contact with the extractant and the extract phase is then separated off.

During the extraction, the by-products from the hydrolysis step (a) are largely separated off. Such by-products are in particular the protective groups split off during the hydrolysis (or secondary products formed therefrom) for the OH functionalities of the compounds of the formula I, such as, for. As ethanol, acetaldehyde or acetaldehyde diacetal. This relieves downstream processing stages and can be operated with lower separation performance and with smaller apparatus dimensions.

If, as in preferred embodiments, a water-soluble acid catalyst is used for the hydrolysis, the catalyst is extracted into the polar phase and effectively removed from the reaction product.

At least one and preferably a maximum of 20 theoretical plates which can be operated in countercurrent or crossflow are used for the extraction. It is conceivable to carry out the extraction in all the equipment usually used for this purpose, e.g. B. extraction columns (with or without energy input), mixer settlers or membrane-based extraction devices.

The extraction is preferably carried out in one stage in a mixer-settler unit. The two liquid phases are dispersed in the mixer. Stirring vessels are preferably used for this purpose in order to set the residence time to values between 1 to 30 min, preferably 5 to 15 min and particularly preferably about 10 min.

The organic phase is separated from the polar phase in the settler unit. The Settier can be equipped with coalescence-enhancing internals (e.g. packing, knitted fabric, plates or packing elements) for effective phase separation. be tested. It is also possible to improve the phase separation by using coalescing filters and thus to improve the product loss and / or the depletion of the acid catalyst. Suitable coalescing filters can be installed in the inlet to the settier as well as in both processes.

The polar extractant is a solvent which is not completely miscible with the reaction product from step (a), such as water, polar organic solvents, for example methanol, or mixtures thereof. An aqueous extracting agent, in particular water itself, is preferably used. If a water-soluble acid catalyst is used, its separation in the extraction step (b) can be intensified in that the polar extractant comprises a base. This base can e.g. B. under alkali, alkaline earth and ammonium hydroxides, carbonates and bicarbonates, such as NaOH, KOH, Na ₂ CO ₃ , NaHCO ₃ ; and / or NH _{3 may be} selected. The concentration of the base added is generally in the range from 0 to 40% by weight, preferably 0 to 15% by weight, based on the polar extractant.

The hydrolysis by-products, such as aldehydes, ketones or alcohols, act as solubilizers between the organic and polar phases, so that sufficient phase separation with minimal product loss is not achieved with all quantitative ratios of extractant to reaction mixture. The weight ratio of the polar extractant to the reaction mixture is therefore preferably in the range from 10: 1 to 0.3: 1, preferably from 5: 1 to 1: 1.

The extraction is advantageously carried out at a temperature of 5 to 90 ° C., preferably 30 to 50 ° C.

For further processing, the organic phase can be subjected to purification by distillation. In most cases, however, it is sufficient to evaporate only the compounds boiling lower than the cyclohexenone derivatives of the formula I and to use the evaporation residue as such for further reaction. Evaporators known to those skilled in the art are suitable for this purpose, such as thin-film evaporators, short-path evaporators, natural circulation evaporators, falling film evaporators, forced circulation evaporators, forced circulation relaxation evaporators, helical tube evaporators or flash evaporation.

The use of falling-film evaporators operated in circulation is particularly preferred, since these enable the mixture to be worked up gently with a simultaneously inexpensive apparatus concept. Advantageously, the reaction mixture is fed to the falling film evaporator in such a way that backmixing with the current flowing from the tubes of the falling film evaporator is prevented. For this purpose, the mixture of low-boiling components, e.g. B. Level control by means of an overflow or siphons, divided and partly discharged as a product stream from the falling film evaporator and partly returned to the vapor space.

Since the product, which is poor in low-boiling components, has a high viscosity, the heat transfer is limited by the heat transfer in the (viscous) trickle film. To effectively break down temperature gradients in falling film, the falling film evaporator in the pipes can therefore be equipped with turbulence generators. Such turbulence generators lead to an improved heat transfer and thus to a gentler evaporation. For example, wire mesh (e.g. the so-called HiTran ™ elements) can be used.

Degassing in the evaporator is preferably combined with flash evaporation. For this purpose, the reaction mixture obtained after the extraction is relaxed in a relaxation space, the reaction mixture breaking down into a liquid phase and a gas phase which contains part of the low-boiling components. Pressures of 1 to 600 mbar, preferably 10 to 100 mbar, are suitably maintained in the relaxation room. The vapor space of a falling film evaporator, for example, can serve as the relaxation space, into which the reaction mixture is expanded to the pressure prevailing in the vapor space via a pressure-maintaining valve. The mixture running out of the vapor space is fed onto the distributor or the upper tube plate of the falling film evaporator, from which the mixture reaches the heated tubes of the evaporator. The subsequent evaporation on the trickle film achieves effective material separation at moderate wall and product temperatures.

The process according to the invention is preferably carried out continuously.

The invention will now be illustrated with reference to the accompanying figure and the example below.

1 schematically shows a device suitable for carrying out the method according to the invention.

1, the cyclohexenol compound of the formula II and an aqueous solution of the acid catalyst are introduced into the stirred tank reactor 1 via lines 2 and 3 and the metering pumps 4a and 4b. Via the pump 5, the reaction mixture reaches the mixer 6, into which water is led for extraction via line 7. The two-phase organic-aqueous mixture passes via line 8 into the phase separation vessel 9, from which the aqueous phase is drawn off via line 10 and discarded. The organic phase is drawn off via the line 11 and expanded by means of the pump 12 and the valve 13 into the expansion space 14, which is designed as a vapor space of the falling film evaporator 15. The gas phase from the vapor space 14 is withdrawn via line 18. The bottom product from the vapor space 14 is brought to the distributor 17 of the falling film evaporator 15 by means of the pump 16. From the sump 19 of the falling film evaporator 15 is a part of The bottom product is withdrawn as a product stream via line 20, and part of the bottom product is fed via the overflow 21 into the vapor space 14.

Example: Preparation of 6-hydroxy-3- (3-hydroxy-3-methyl-4-penten-1-ynyl) -2,4,4-trimethyl-2-cyclohexen-1-one

A device according to FIG. 1 was used. About 6 kg / h of the compound (IIIa) and 0.6 kg / h of a 1% strength by weight aqueous solution of para-toluenesulfonic acid were introduced into the reactor 1. The reactor was thermostated to a temperature of 50 ° C. A gaseous stream of 0.71 kg / h was discharged from the reactor. In the mixer 6 below, about 12 kg / h of water were added to the organic phase, the outlet temperature was about 44 ° C. The organic phase running out of the phase separation vessel 9 had a residual para-toluenesulfonic acid content of 86 ppm. The organic phase was let down in the vapor space kept at 50 mbar in a falling film evaporator operated in circulation. The outlet temperature of the product in the pipes was about 53 ° C.

The concentration of the title compound in the outlet of the falling film evaporator was 95.78 GC area percent, the concentrations of acetaldehyde, acetaldehyde diacetal and ethanol 0.31 or 0 or 0.74 GC area percent.

The temperature of the onset of decomposition of the reaction mixture running out of the reactor was about 105 ° C., that of the organic phase running out of the phase separation vessel was about 160 ° C.

Claims

claims

1. Process for the preparation of cyclohexenonde derivatives of the general formula I,

wherein

R ^{1 represents} hydrogen or OH; R ² for

, includes the steps:

(a) Hydrolysis of a cyclohexenol compound of the formula II

wherein

R ^{3 represents} hydrogen and R ^{4 represents} C, -C ₆ alkoxy, or

R ⁵ for stands,

R ^{6 represents} a protected hydroxy group in the absence of an organic solvent in the presence of an acid catalyst; and

(b) Extracting the reaction mixture with a polar extractant.

Process according to Claim 1, characterized in that the cyclohexenol compound of the formula II is introduced continuously into a reactor which has at least one back-mixed region.

3. The method according to claim 2, characterized in that a molar ratio of the cyclohexenone derivative of the formula I to the cyclohexenol compound of the formula II of at least 90:10 is maintained in the reactor.

Method according to one of the preceding claims, characterized in that R ³ and R ⁴ for

stand in what

R ^{7 represents} hydrogen or dC ₆ alkyl; and

R ^{8 represents} -C ₆ alkyl.

A method according to claim 4, characterized in that R ^{7 is} hydrogen and R ^{8 is} methyl.

6. The method according to any one of the preceding claims, characterized in that one uses an aqueous solution of an acid catalyst in step (a).

7. The method according to any one of the preceding claims, characterized in that the polar extractant comprises a base.

8. The method according to any one of the preceding claims, characterized in that the weight ratio of the polar extractant to the reaction mixture is in the range from 10: 1 to 0.3: 1.

9. The method according to any one of the preceding claims, characterized in that the reaction mixture is relaxed after the extraction step (b) in a relaxation room and partially evaporated.

10. The method according to claim 9, characterized in that one maintains a pressure of 1 to 600 mbar in the relaxation room.

11. The method according to any one of the preceding claims, characterized in that the lower boiling than the cyclohexenone derivatives of the formula I compounds are evaporated from the reaction mixture after the extraction step (b).

12. The method according to claim 11, characterized in that the evaporator is selected from a thin-film evaporator, short-path evaporator, natural circulation evaporator, falling film evaporator, forced circulation evaporator, forced circulation flash evaporator, helical tube evaporator and / or flash evaporation.

13. The method according to claim 12, characterized in that the reaction mixture is fed to a falling film evaporator in such a way that backmixing with the current flowing from the tubes of the falling film evaporator is prevented.

14. The method according to any one of the preceding claims, characterized in that one carries out the hydrolysis according to step (a) at a temperature in the range from 20 to 100 ° C.

15. The method according to any one of the preceding claims, characterized in that one carries out the extraction according to step (b) at a temperature in the range of 5 to 90 ° C.