阅读说明：本技术 一种光学活性的香茅醛的制备方法 (Preparation method of citronellal with optical activity ) 是由 董菁 于磊 张永振 黎源 于 2019-12-09 设计创作，主要内容包括：本发明提供一种光学活性的香茅醛的制备方法,采用该制备方法可以显著提高用于均相催化的不对称氢化的光学活性过渡金属催化剂的催化稳定性,从而实现更高的周转数。所述光学活性的香茅醛的制备方法中,底物在过渡金属催化剂存在下发生不对称氢化反应生成所述光学活性的香茅醛,所述过渡金属催化剂通过过渡金属化合物与包含两个磷原子的光学活性配体反应而获得,所述底物原料为橙花醛、香叶醛中的一种或两种的组合,控制用于所述不对称氢化反应的所述底物原料中的羟值≤6mgKOH/g和/或铁含量≤50ppm。(The invention provides a preparation method of citronellal with optical activity, which can remarkably improve the catalytic stability of an optically active transition metal catalyst for homogeneous catalytic asymmetric hydrogenation so as to realize higher revolution. In the preparation method of the citronellal with optical activity, a substrate is subjected to asymmetric hydrogenation reaction in the presence of a transition metal catalyst to generate the citronellal with optical activity, the transition metal catalyst is obtained by reacting a transition metal compound with an optical activity ligand containing two phosphorus atoms, the substrate raw material is one or the combination of two of neral and geranial, and the hydroxyl value in the substrate raw material for the asymmetric hydrogenation reaction is controlled to be less than or equal to 6mgKOH/g and/or the iron content is controlled to be less than or equal to 50 ppm.)

1. A process for producing optically active citronellal, wherein a substrate is subjected to asymmetric hydrogenation in the presence of a transition metal catalyst to produce the optically active citronellal, the transition metal catalyst being obtained by reacting a transition metal compound with an optically active ligand containing two phosphorus atoms, the substrate being selected from one or both of neral of formula (I) and geranial of formula (II), characterized in that the hydroxyl value in the substrate used for the asymmetric hydrogenation is controlled to 6mgKOH/g or less and/or the iron content in the substrate is controlled to 50ppm or less,

2. the method according to claim 1, wherein the optically active citronellal is an optically active R-citronellal represented by the following formula (III):

3. the production method according to claim 1 or 2, wherein the optically active ligand containing two phosphorus atoms is a ligand of the general formula (iv):

wherein the content of the first and second substances,

R¹and R²Each independently of the others being a hydrogen atom or an unbranched, branched or cyclic alkyl radical having from 1 to 20 carbon atoms and optionally bearing one or more olefinic double bonds and/or optionally bearing one or more identical or different radicals selected from halogen, C₆-C₁₀Aryl and C₃-C₉A substituent of heteroaryl; or R¹And R²May together form one or more 4-20 membered rings, preferably containing an unsaturated double bond in the ring and the ring-forming atoms on the ring being C atoms;

R³、R⁴、R⁵and R⁶Are identical or different from each other and are C₆-C₁₀Aryl, and each optionally carrying one or more substituents selected from C₁-C₄Alkyl radical, C₆-C₁₀Aryl radical, C₁-C₄Alkoxy and amino substituents.

4. The process according to claim 3, wherein the optically active ligand comprising two phosphorus atoms has structural formula (V), (VI), (VII) or (VIII) or is any one of enantiomers of structural formulae (V) to (VIII):

5. the production method according to any one of claims 1 to 4, wherein the transition metal compound is soluble in a reaction mixture of the asymmetric hydrogenation reaction; the transition metal compound is a compound of a metal of group VIII of the periodic table, preferably one or more of compounds of Ru, Rh, Pd, Ir and Pt, more preferably a compound of Rh.

6. The production method according to any one of claims 1 to 5, wherein the molar ratio of the transition metal atom in the transition metal compound to the optically active ligand is (0.5 to 10): 1, preferably (0.5-2): 1.

7. the method according to any one of claims 1 to 6, comprising the steps of:

dissolving the transition metal compound and the optically active ligand comprising two phosphorus atoms in the substrate under an inert gas atmosphere, thereby obtaining a mixed material containing the catalyst; before carrying out the asymmetric hydrogenation reaction, in the presence of CO/H₂Stirring the mixed material for 1-6h at 40-80 ℃ under the conditions that the volume ratio is 1/2-3/1 and the pressure is 0.5-5MPa, and then cooling to obtain a mixed material containing the pretreated catalyst;

and then placing the mixed material containing the pretreated catalyst under the reaction conditions required for carrying out the asymmetric hydrogenation reaction to carry out reaction so as to obtain the citronellal with optical activity.

8. The production method according to any one of claims 1 to 7, characterized in that the asymmetric hydrogenation is carried out in the presence of hydrogen containing 100-10000ppm of carbon monoxide.

9. The process according to any one of claims 1 to 8, wherein the asymmetric hydrogenation is carried out at an absolute pressure of 0.1 to 10MPa, preferably 5 to 8 MPa.

10. The process according to any one of claims 1 to 9, wherein the asymmetric hydrogenation is carried out at a reaction temperature of from 25 to 120 ℃, preferably from 50 to 90 ℃.

11. The production method according to any one of claims 1 to 10, wherein the number of revolutions of the transition metal catalyst is more than 50000.

12. The production method according to any one of claims 1 to 11, wherein the transition metal compound is used in an amount of 0.0001 to 0.1 mol% in terms of the molar amount of the transition metal atom, based on the amount of the substrate.

13. The production method according to any one of claims 1 to 12, wherein the hydroxyl value in the substrate is 6mgKOH/g or less and/or the iron content is 50ppm or less by subjecting the substrate for the asymmetric hydrogenation reaction to a rectification treatment in advance.

Technical Field

The invention relates to a method for preparing optically active citronellal, in particular to a method for preparing optically active citronellal, especially R-citronellal, by asymmetrically hydrogenating neral and/or geranial.

Background

Citronellal is an important fragrance ingredient and is widely used in the perfuming and formulating of beverages, candies, foods and the like. And is also an important intermediate compound, in particular to citronellal with optical activity which is an important intermediate for synthesizing L-menthol.

EP 0000315 discloses a process for preparing optically active R-citronellal by hydrogenating geranial or neral in the presence of a catalyst complex which is soluble in the reaction system and consists of rhodium and a chiral phosphine.

J.mol.Cat.16(1982)51-59 and Helv.Chim.acta.84(2001)230-242 report the homogeneous catalytic hydrogenation of α -unsaturated aldehydes and use this method for the preparation of optically active R-citronellal the catalysts used in this study were complexes of rhodium carbonyls and chiral phosphines.

CN 101039894 discloses the homogeneous catalytic hydrogenation of neral to prepare optically active R-citronellal by using a complex of rhodium carbonyl and chiral phosphine, the catalyst is firstly subjected to CO and H₂The mixture is prefabricated and reacted in H mixed with small amount of CO₂Is carried out in (1).

The reported method has the advantages of high chemoselectivity and stereoselectivity, but the homogeneous transition metal catalyst prepared by adopting the transition metal compound and the chiral ligand has the defect of low hydrogenation efficiency, particularly under the condition of a substrate/catalyst with a high molar ratio, the conversion frequency of the catalyst is obviously reduced, the catalyst needs to be recycled for many times, the process operation is complex, the catalyst is easy to have the problems of metal coupling inactivation and the like, the turnover number is low, and the catalyst is high in cost when being applied on an industrial scale.

Therefore, there is a need to find a method for preparing optically active citronellal by asymmetrically hydrogenating geranial and/or neral, which can realize high turnover number of the catalyst, thereby reducing the cost of the catalyst to the extent that the industrial scale production can be accepted.

Disclosure of Invention

The invention aims to provide a preparation method of optical active citronellal, which can remarkably improve the catalytic stability of an optical active transition metal catalyst for homogeneous catalytic asymmetric hydrogenation so as to realize higher revolution.

In order to achieve the purpose, the invention provides the following technical scheme:

a process for producing optically active citronellal, wherein a substrate is subjected to asymmetric hydrogenation in the presence of a transition metal catalyst to produce the optically active citronellal, the transition metal catalyst is obtained by reacting a transition metal compound with an optically active ligand containing two phosphorus atoms, the substrate is selected from one or a combination of two of neral of formula (I) and geranial of formula (II), the hydroxyl value in the substrate for the asymmetric hydrogenation is controlled to 6mgKOH/g or less and/or the iron content in the substrate is controlled to 50ppm (ppm by mass) or less,

the inventors of the present application have surprisingly found that by controlling the hydroxyl value in the substrate raw material (neral and/or geranial) to be less than or equal to 6mgKOH/g (e.g., 6mgKOH/g, 4mgKOH/g, 1mgKOH/g, etc.) (in this case, the iron content need not be considered, the iron content may be less than or equal to 50ppm or more than 50ppm, for example), or by controlling the iron (i.e., iron element) content in the substrate raw material (neral and/or geranial) to be less than or equal to 50ppm (e.g., 50ppm, 10ppm, 1ppm, etc.) (in this case, the hydroxyl value need not be considered, the hydroxyl value may be less than or equal to 6mgKOH/g or more than 6mgKOH/g), or by controlling the hydroxyl value in the substrate raw material (neral and/or geranial) to be less than or equal to 6mgKOH/g and the iron (i.e., iron element) content to be less than or equal to 50ppm, either of these means can be used to control the hydroxyl value and/or, the catalytic stability of an optically active transition metal catalyst for homogeneously catalyzed asymmetric hydrogenation, which is obtained by reacting a transition metal compound with an optically active ligand containing two phosphorus atoms, can be significantly improved, thereby achieving a higher turnover number.

In the present invention, the substrate raw material (neral and/or geranial) having an hydroxyl value of 6mgKOH/g or less and/or an iron content of 50ppm or less is obtained by rectification purification of the substrate raw material (neral and/or geranial), which rectification operation is known and has been fully described in the literature (e.g., CN 101687751B, etc.) or can be carried out by those skilled in the art using similar to known process conditions, and the hydroxyl value and iron content in neral and geranial can be controlled by controlling an appropriate reflux ratio and a ratio of light and heavy components to neral and geranial produced in the rectification (for example, as exemplified in examples 1 to 6 hereinafter). In some embodiments, the hydroxyl value in the substrate feedstock is less than or equal to 6mgKOH/g and/or the iron content is less than or equal to 50ppm by subjecting the substrate for the asymmetric hydrogenation reaction to a preliminary rectification treatment.

In the present invention, the substrate may be neral or geranial or a mixture of neral and geranial. The optically active citronellal is preferably prepared by asymmetrically hydrogenating a neral starting material having a neral/geranial molar ratio of at least 90:10 or a geranial starting material having a geranial/neral molar ratio of at least 90: 10.

In the present invention, the optical purity of the optically active citronellal is at least 70 ee%, preferably 80 ee% to 99.9 ee%, and those skilled in the art know that the optical purity obtained depends on the ratio of neral to geranial in the starting material, the type and purity of the chiral ligand, for example, the molar ratio of neral/geranial is higher than 90:10 and the purity of the chiral ligand is higher than 99 percent, so that the optical purity of the citronellal can reach 80ee percent to 99.9ee percent.

The optically active citronellal is optically active R-citronellal of the following formula (III):

the invention is carried out in the presence of at least one transition metal catalyst obtained by reacting a transition metal compound soluble in the reaction mixture of the asymmetric hydrogenation reaction with an optically active ligand comprising two phosphorus atoms. Such catalysts may in particular be those already disclosed in the art. In some embodiments, the molar ratio of transition metal atoms in the transition metal compound to the optically active ligand is (0.5 to 10): 1, preferably (0.5-2): 1.

in some embodiments, the optically active ligand comprising two phosphorus atoms is a ligand of formula (iv):

wherein the content of the first and second substances,

R¹and R²Each independently of the others, is a hydrogen atom or an unbranched alkyl group having from 1 to 20 carbon atoms, a branched alkyl group (in particular a branched alkyl group of from 3 to 20 carbon atoms) or a cyclic alkyl group (in particular a cyclic alkyl group of from 3 to 20 carbon atoms) and may optionally carry one or more, for example from 1 to 4, olefinic double bonds and/or optionally one or more, for example from 1 to 4, identical or different radicals selected from halogen, C₆-C₁₀Aryl and C₃-C₉A substituent of heteroaryl; or R¹And R²May together form one or more 4-20 membered rings, preferably containing an unsaturated double bond in the ring and the ring-forming atoms on the ring being C atoms;

R³、R⁴、R⁵and R⁶Are identical or different from each other and are C₆-C₁₀Aryl, and each optionally bearing one or more, usually 1 to 8, preferably 1 to 4, substituents selected from C₁-C₄Alkyl radical, C₆-C₁₀Aryl radical, C₁-C₄Alkoxy and amino substituents.

By way of illustration, the following compounds or their enantiomers are preferably used as optically active ligands comprising two phosphorus atoms:

wherein Ph denotes phenyl, Ph₂Refers to the two phenyl groups attached to P.

In some embodiments, the transition metal compounds are those of a metal from group VIII of the periodic table, especially one or more of compounds of Ru, Rh, Pd, Ir and Pt, more preferably Rh.

Suitable compounds of the transition metals are in particular those which are soluble in the reaction medium chosen (i.e.the substrate and optionally the solvent), for example salts or with suitable ligands such as carbonyl, acetylacetonate, hydroxy, cyclooctadieneAlkene, norbornadiene, cyclooctene, methoxy, acetyl or other aliphatic or aromatic carboxylate complexes. Preferred transition metal compounds in the process of the invention are Rh (I) and Rh (III) and Rh (0) compounds. Preference is given to those transition metal compounds which already have at least one CO ligand. Examples of transition metal compounds which can be used according to the invention are: RhCl₃、Rh(OAc)₃、[Rh(cod)Cl]₂、Rh(CO)₂acac、[Rh(cod)OH]₂、[Rh(cod)OMe]₂、Rh₄(CO)₁₂Or Rh₆(CO)₁₆Wherein "acac" is an acetylacetonate ligand and "cod" is a cyclooctadiene ligand. The described transition metal compounds and complexes and further examples thereof are known and are described in full in the literature or can be prepared by the person skilled in the art analogously to known compounds.

According to the invention, the transition metal compound is generally used in an amount of about 0.0001 to about 0.1 mol%, based on the amount of the substrate to be hydrogenated (i.e. the total amount of both neral and geranial), based on the molar amount of the transition metal atom. The catalyst can be recycled by methods known per se to the person skilled in the art, for example by removing the reaction product obtained from the reaction mixture by distillation, while the remaining catalyst is used in the further reaction process, in the process of the invention the number of revolutions of the transition metal catalyst is greater than 50000, for example a total number of revolutions of the catalyst of 100000-.

In the present invention, the choice of the solvent used in the asymmetric hydrogenation is not critical, and it is preferable to carry out the asymmetric hydrogenation in the absence of a solvent.

In the present invention, a transition metal compound and an optically active ligand are added to a substrate to be hydrogenated, and hydrogen is introduced to carry out asymmetric hydrogenation. The purity of the hydrogen used for asymmetric hydrogenation is 90-100% (v/v), the impurities comprise nitrogen, carbon monoxide, carbon dioxide and other gases, and the content of the impurities is 0-10% (v/v). The absolute pressure of the asymmetric hydrogenation reaction is 0.1-10MPa, preferably 5-8 MPa; the reaction temperature is from 0 to 120 deg.C, for example from 25 to 120 deg.C, preferably from 50 to 90 deg.C. In general, the reaction time of the asymmetric hydrogenation of the present invention is about 1 to about 150 hours, preferably about 2 to about 24 hours, but is not limited thereto.

In some embodiments, the asymmetric hydrogenation reaction is carried out in the presence of hydrogen containing 100-10000ppm (by volume) carbon monoxide.

In the invention, the chemical selectivity of the product of asymmetric hydrogenation can reach 99.8% at most, and the conversion rate can reach 99.9% at most.

Reactors suitable for carrying out the asymmetric hydrogenation of the invention are in principle all those vessels which allow reactions under the stated conditions, in particular pressure and temperature, and which are suitable for hydrogenation, for example autoclaves, tubular reactors, bubble columns, etc.

In some embodiments, the preparation method specifically comprises the following steps:

dissolving the transition metal compound and the optically active ligand comprising two phosphorus atoms in the substrate under an inert gas (e.g., argon) atmosphere, thereby obtaining a mixed material containing the catalyst; before carrying out the asymmetric hydrogenation reaction, in the presence of CO/H₂Stirring the mixture at a volume ratio of 1/2-3/1 (e.g., 1:1) and a pressure of 0.5-5MPa (e.g., 0.8MPa) for 1-6h (e.g., 3h) at 40-80 deg.C (e.g., 60 deg.C), and then cooling to room temperature to complete the pretreatment of the catalyst to obtain a pretreated catalyst-containing mixture;

and then placing the mixed material containing the pretreated catalyst under the reaction conditions required for carrying out the asymmetric hydrogenation reaction to carry out reaction so as to obtain the citronellal with optical activity. The reaction system may be supplemented with substrate feed as required for production. After the reaction is finished, the product can be distilled out, and the substrate is continuously supplemented for the next round of reaction.

The technical scheme provided by the invention has the following beneficial effects:

the commercially available artificially synthesized neral/geranial is mainly obtained by taking isoamylene alcohol and isoamylene aldehyde as raw materials, carrying out condensation reaction under the action of an acid catalyst to generate corresponding acetal, carrying out cracking reaction under the catalysis of the acid catalyst, and carrying out rearrangement reaction on the obtained product. In this process neral/geranial are susceptible to intramolecular ene reactions (ene reactions) to produce hydroxyl-containing compounds of the formula (IX); the prenol formula (X) is continuously generated in the cracking and rearrangement processes. Because of the corrosion problem of the acid catalyst to the device material, the neral/geranial contains iron-containing impurities which are easy to generate carbonyl iron compounds under the reaction condition. The present inventors have found that, in the preparation of citronellal using neral and/or geranial as a substrate raw material, such substrate raw material including, but not limited to, hydroxyl-containing impurities of formula (ix) and (x) and carbonyl iron compounds generated under reaction conditions, can compete with optically active ligands in the catalyst used for the preparation of citronellal to complex with transition metals, thereby destroying the structure of the catalyst, resulting in gradual deactivation of the catalyst. The inventor of the application finds that accumulated poisoning effect of trace impurities containing hydroxyl and carbonyl iron compounds in the raw materials on the catalyst at high revolution can be obviously reduced by controlling the hydroxyl value and/or the iron content in the neral and/or the geranial serving as the substrate raw materials, the catalytic stability of the optically active transition metal catalyst for the asymmetric hydrogenation of homogeneous catalysis is improved, on one hand, the catalytic activity of the catalyst is obviously improved, on the other hand, the service life of the catalyst is obviously improved, the reusability of the homogeneous catalyst is facilitated, and therefore higher revolution is realized.

The preparation process of the present invention can be operated batchwise, semicontinuously or continuously and is particularly suitable for industrial scale production.

Detailed Description

The process of the present invention is further illustrated by the following specific examples, but the invention is not limited to the examples listed, but also encompasses any other known modifications within the scope of the claims of the invention.

All references to pressure herein refer to absolute pressure.

Analytical instrument

Gas chromatograph: agilent7890, column DB-5 (for conversion determination), column Supelco β -DEX^TM225 (for optical purity determination), inlet temperature: 300 ℃; the split ratio is 50: 1; carrier gas flow: 52.8 ml/min; temperature rising procedure: at 95 ℃ for 40min, increasing to 180 ℃ at a rate of 10 ℃/min, for 40min, detector temperature: 280 ℃.

Hydroxyl value determination method: method a in GBT12008.3-2009, phthalic anhydride method.

The iron content determination method is described as follows:

nitric acid: the top grade is pure;

iron standard solution: is prepared by the research center of national standard substances of China, and the concentration is 1000 mg/L;

establishing a standard curve: accurately sucking 12.5mL of iron standard solution into a 1000mL volumetric flask, diluting the solution to 1000mL by using 2% HNO3, and preparing into 12.5ppm iron standard use solution. Accurately transferring 0, 1.00, 2.00, 3.00 and 4.00mL of the above 12.5ppm iron standard use solution, placing in 5 25mL volumetric flasks, respectively, adding 5mL of 1% HNO₃Diluting with water to scale, and shaking; the standard solution series with the iron concentrations of 0, 0.5, 1, 1.5 and 2.0ppm are obtained. The absorbance of the standard solution was measured using an atomic absorption spectrophotometer AA-6300 (shimadzu), and a standard curve was plotted with the iron concentration as ordinate and the absorbance as abscissa, and the standard curve was designated as Y ═ aX + b (Y: iron concentration, X: absorbance, a: slope of the standard curve, b: intercept of the standard curve).

Sample pretreatment: weigh the starting material to about 0.5g (to an accuracy of 0.0001g, denoted m₁) Adding 10-12mL of nitric acid into a polytetrafluoroethylene digestion tank (slowly adding the nitric acid to prevent violent reaction), covering a sealing cover after a system in the digestion tank is stable, putting the digestion tank into an Atonpaar Multiwave 3000 microwave digestion instrument to perform digestion for 30 minutes under the power of 1000W, taking out the polytetrafluoroethylene digestion tank after the system is completed, cooling the polytetrafluoroethylene digestion tank, transferring the polytetrafluoroethylene digestion tank into a 25mL volumetric flask, washing the digestion tank with ultrapure water for 3 times, transferring the digestion tank into the volumetric flask, weighing the ultrapure water, uniformly shaking to obtain a sample, and recording the total mass of the sample as m₂. Measuring the absorbance X of the sample by using an atomic absorption spectrophotometer₁Calculating the sample according to the standard curveIron content ═ aX₁+b)*m₂/m₁

Conversion rate:

conversion is 1- (neral peak area in gc + geranial peak area in gc)/total peak area in gc (removal of solvent).

Optical purity:

optical purity ee% (% of R-citronellal peak area in gas chromatography-S-citronellal peak area in gas chromatography)/(R-citronellal peak area in gas chromatography + S-citronellal peak area in gas chromatography)

Yield:

yield ═ citronellal peak area in gas chromatography/total peak area in gas chromatography (solvent removal)

Turnover number:

the number of revolutions per mole of citronellal obtained by the reaction/mole of rhodium in the catalyst used

Reagent:

raw material (neral): 99% of carbofuran.

Starting material (geranial): 99% of carbofuran.

Rh(CO)₂acac、[Rh(cod)OH]₂、[Rh(cod)OMe]₂、Rh₄(CO)₁₂、Rh₆(CO)₁₆98 wt%, Aldrich; the compound of formula (V) -formula (VIII) and the isomer of the compound of formula (V) (the compound of formula (V) is specifically (R, R) -chiralphos, the enantiomer of which is (S, S) -chiralphos), 99 wt%, carbofuran.