A method for recovering R-citronellal

Abstract

The invention provides a method for recovering R-citronellal. The invention adds compound A to a heavy component of R-citronellal prepared from citral, thereby realizing competitive binding between compound A and rhodium in an asymmetric hydrogenation catalyst. The generated complex can catalyze a reverse aldol reaction, and the generated citronellal is continuously evaporated under low pressure, thereby promoting equilibrium shift. Finally, the heavy component is substantially completely converted into R-citronellal, thereby realizing recovery of R-citronellal from the heavy component byproduct.

Description

Background Art

[0001] Citronellal is an important flavor compound. Because of its effect of highlighting the grassy smell, it can be used in small quantities in low-grade lemon-type, cologne-type, magnolia-type, lily-of-the-valley-type, and frangipani-type flavors. At the same time, citronellal is also an important synthetic intermediate and can be used as a raw material for synthesizing citronellol, hydroxycitronellal, menthol, etc.

[0002] At present, there are two main ways to produce citronellal. It can be obtained from the oxidation or catalytic dehydrogenation of citronellol, or from the catalytic hydrogenation of citral. Since there is an asymmetric carbon atom in the citronellal molecule, the citronellal separated from natural essential oils is optically active, while the citronellal prepared by synthetic means is mostly not optically active.

[0003] CN 105254474 discloses a method for preparing single chiral citronellal from E or Z citral by asymmetric hydrogenation. The method achieves high conversion rate and high corresponding selectivity under the catalysis of a chiral rhodium complex, and the reaction conditions are mild, but the presence of heavy components during the reaction reduces the yield of citronellal.

[0004] CN 102093182 discloses a method for efficiently preparing citronellal by air oxidation of citronellol at room temperature. The method realizes the preparation of citronellal under mild conditions by using a variety of co-catalysts in combination. The catalyst is cheap and easy to obtain and the operation is simple. However, the prepared citronellal is in a racemic state, which reduces its application value.

[0005] Therefore, there is an urgent need for a method for efficiently preparing citronellal with a single optical activity, while achieving maximum raw material utilization and product recovery, so as to reduce costs and improve production efficiency. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a method for recovering citronellal from the reaction byproduct of preparing R-citronellal from citral, thereby achieving maximum recycling of the reaction product. The technical solution adopted by the present invention is as follows:

[0007] A method for recovering R-citronellal from a heavy component concentrate prepared from citral, wherein the heavy component concentrate contains 0.01 wt% to 10 wt% of R-citronellal and 0.01 wt% to 10 wt% of citral, 40 wt% to 60 wt% of a citronellal dimer (formula (II)), 20 wt% to 40 wt% of a citronellal trimer (formula (III)), and 10 wt% to 20 wt% of a citronellal tetramer (formula (IV)), and based on the total weight of the concentrate, the method comprises at least the following steps:

[0008] A), contacting the heavy component concentrate with at least one compound A to obtain a treated concentrate;

[0009] B), subjecting the treated concentrated solution to a temperature of 50°C to 200°C to obtain R-citronellal;

[0010] C), separating R-citronellal from the treated concentrated solution.

[0011]

[0012] The heavy component concentrated liquid is obtained by asymmetric hydrogenation of citral under the catalysis of a transition metal catalyst obtained by reacting a transition metal compound soluble in the reaction system with an optically active ligand containing two phosphorus atoms, to obtain a reaction liquid containing R-citronellal, and high-purity citronellal and a concentrated liquid rich in heavy components are separated.

[0013] In the present invention, the structure of the compound A is shown in formula (I):

[0014]

[0015] In the formula, X is N or P atom, Z is O or S atom, R1, R2 and R3 have one or two halogen atoms, and the others are the same or different aryl, alkyl or alkoxy groups with 1 to 10 carbon atoms.

[0016] Specifically, the compound A includes but is not limited to diisopropyl chlorophosphate, diethyl chlorothiophosphate, phenyl dichlorophosphate, dimethyl chlorophosphate, diphenylphosphinyl chloride, dicyclohexyl phosphoryl chloride, and methyl dichlorophosphate.

[0017] In the R-citronellal recovery method of the present invention, the heavy component concentrate contains 20 wt% to 70 wt% of R-citronellal oligomers based on the total weight of the concentrate.

[0018] In the present invention, the specific composition of the R-citronellal oligomer in the heavy component concentrate includes: 40wt% to 60wt% of citronellal dimer, 20wt% to 40wt% of citronellal trimer, and 10wt% to 20wt% of citronellal tetramer.

[0019] In the present invention, in the R-citronellal recovery method, based on the total weight of the concentrated solution, the added amount of compound A is 20ppm-500ppm.

[0020] In the present invention, in the R-citronellal recovery method, the reaction temperature in step B) is 80-150° C.; the reaction time is 1-10 hours, preferably 4-6 hours.

[0021] In the present invention, in the R-citronellal recovery method, the heavy component concentrate is obtained by a method comprising at least the following steps:

[0022] a) The substrate citral undergoes asymmetric hydrogenation under the catalysis of a transition metal catalyst to obtain citronellal.

[0023] b) After the reaction is completed, the reaction solution is subjected to reduced pressure distillation to obtain high-purity citronellal and a concentrated solution rich in heavy components.

[0024] In the present invention, the transition metal catalyst is preferably a homogeneous catalyst soluble in the reaction system, obtained by reacting a transition metal compound with an optically active ligand containing two phosphorus atoms; the molar ratio of the transition metal atom in the transition metal catalyst to the optically active ligand containing two phosphorus atoms is (0.5-10):1, preferably (0.5-1):1;

[0025] In the present invention, the transition metal element in the transition metal catalyst is selected from the metal elements of Group VIII in the periodic table, preferably rhodium; the transition metal compound is one or more of a transition metal halide, a transition metal carbonate and a transition metal complex;

[0026] In the present invention, the transition metal complex is selected from the complex formed by the transition metal and one or more of carbonyl compounds, acetylacetonate compounds, hydroxyl compounds, cyclooctadiene, norbornadiene, cyclooctene, methoxy compounds, acetyl compounds, aliphatic carboxylic acid compounds or aromatic carboxylic acid compounds;

[0027] Further preferably, the transition metal compound is selected from one or more of transition metal halides, complexes formed by the coordination of transition metals and carbonyl compounds, complexes formed by the coordination of transition metals and cyclooctadiene, and complexes formed by the coordination of transition metals and acetyl compounds;

[0028] More preferably, the transition metal compound is selected from RhCl3, Rh(OAc)3, Rh(cod)2BF4, [Rh(cod)Cl]2, Rh(CO)2acac, [Rh(cod)OH]2, [Rh(cod)OMe]2, Rh4(CO) 12 and Rh6(CO) 16 One or more of the following, wherein "acac" is an acetylacetone ligand and "cod" is a cyclooctadiene ligand.

[0029] In the present invention, the optically active ligands of the two phosphorus atoms are selected from one or more of the ligands represented by the following general formula (V) and general formula (VI):

[0030]

[0031] Among them, R 1 , R 2 Each is independently an unbranched alkyl group, a branched alkyl group or a cyclic alkyl group having 1 to 20 carbon atoms, and optionally has one or more olefinic double bonds, and / or, optionally has one or more identical or different selected from OR 9 NR 10 R 11 , halogen, C6-C 10 aryl and C3-C9 heteroaryl substituents; or R 1 and R 2 are joined together to form a ring having 4 to 20 ring carbon atoms, and

[0032] R 3 , R 4 are each independently hydrogen or a linear C1-C4 alkyl group or a branched C1-C4 alkyl group, and

[0033] R 5 , R 6 , R 7 , R 8 Each independently is C6-C 10 aryl, and each may optionally carry one or more selected from C1-C4 alkyl, C6-C 10 aryl, C1-C4 alkoxy and amino substituents, and

[0034] R 9 , R 10 , R 11 are independently hydrogen, C1-C4 alkyl, C6-C 10 Aryl, C7-C 12 Arylalkyl or C7-C 12 Alkyl aryl, or R 10 , R 11 They are joined together to form an alkylene chain having 2 to 5 carbon atoms and optionally have N atoms or O atoms inserted in the alkylene chain.

[0035] For example, the optically active ligand containing two phosphorus atoms may be one or more of a chiral bidentate diphosphine ligand and its enantiomers having the following structural formula:

[0036]

[0037] Among them, Ph refers to phenyl, and Ph2 refers to two phenyl groups connected to P.

[0038] In the present invention, the amount of transition metal catalyst used in the asymmetric hydrogenation reaction (calculated as the molar amount of transition metal) is 0.0001 mol% to 0.1 mol%, calculated as the total amount of substrate.

[0039] In the present invention, the asymmetric hydrogenation reaction is carried out at an absolute pressure of 10-100 bar, preferably 50-80 bar (the pressure is the hydrogen pressure); the reaction temperature of the asymmetric hydrogenation is 0-120°C, preferably 25-90°C, the contact reaction pressure is 1-5000Pa, preferably 100-1000Pa, and the reaction time is 1h to 150h, preferably 2h to 24h.

[0040] And / or, the asymmetric hydrogenation is carried out in the absence of solvent or with solvent, and the solvent is one or more of alkanes, aromatic hydrocarbons, halogenated hydrocarbons, and ether solvents, preferably the reaction is carried out in the absence of solvent.

[0041] In the present invention, in the R-citronellal recovery method, the method for separating R-citronellal from the treated concentrated liquid is distillation, preferably reduced pressure distillation.

[0042] In the present invention, the R-citronellal recovery method is described, and the recovered R-citronellal has a purity of ≥98.0% by weight.

[0043] The beneficial effects of the present invention are as follows:

[0044] In the present invention, after the asymmetric hydrogenation of citral to prepare citronellal is completed, high-purity R-citronellal and a concentrated solution rich in heavy components are obtained by reduced pressure distillation, and the main components of the concentrated solution of heavy components are di-, tri- and tetra-heavy heavy components generated by aldol between R-citronellal itself, and the generation of the di-, tri- and tetra-heavy heavy components is derived from the removal of α-H from one molecule of citronellal to generate an enolate anion, which then performs a nucleophilic attack on the carbonyl group of another aldehyde.

[0045] The present invention adds compound A to the heavy components to achieve competitive binding between the compound A and rhodium in the asymmetric hydrogenation catalyst. The generated complex can catalyze the reverse aldol reaction, so that the generated citronellal is continuously evaporated under low pressure, and the equilibrium shift is promoted. Finally, the heavy components are substantially completely converted into R-citronellal, thereby realizing the recovery of R-citronellal from the heavy component by-product. Specific implementation methods

[0046] In order to make the objectives, technical solutions and advantages of the present invention clearer, the embodiments described below will further illustrate the technical solutions in the embodiments of the present invention. It is obvious that the present invention includes but is not limited to the described embodiments, and any non-creative changes made by those skilled in the art based on the embodiments of the present invention belong to the protection scope of the present invention.

[0047] Analysis method: Gas chromatograph: Agilent7820A, chromatographic column DB-5 (30m×320μm×0.25μm), inlet temperature: 200℃, split ratio 80:1; carrier gas flow rate: 1.5ml / min; heating program: keep at 50℃ for 2min, increase the temperature to 120℃ at a rate of 10℃ / min, keep for 0min, then increase the temperature to 180℃ at 5℃ / min, keep for 0min, then increase the temperature to 280℃ at 20℃ / min, keep for 5min; detector temperature: 280℃.

[0048] Device information:

[0049] Reactor: 500mL high pressure reactor, Yantai Arteson Machinery Technology Co., Ltd.

[0050] Raw material (citral): 99%, Bailingwei.

[0051] RhCl3, Rh(OAc)3, Rh(cod)2BF4,, Rh(CO)2acac, [Rh(cod)OH]2, Rh6(CO) 16 , Aldrich;

[0052] Diisopropyl chlorophosphate: 97%, J&K;

[0053] Diethyl chlorothiophosphate: 98%, J&K;

[0054] Phenyl dichlorophosphate: 94%, J&K;

[0055] Dimethyl chlorophosphate: 98%, Bailingwei;

[0056] Diphenylphosphine chloride: 98%, J&K;

[0057] Biscyclohexylphosphoryl chloride: 98%, J&K;

[0058] Methyl dichlorophosphate: 95%, J&K.

[0059] Optical purity:

[0060] Optical purity ee% = (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);

[0061] Conversion rate:

[0062] Conversion rate = 100% - (peak area of ​​neral in gas chromatography + peak area of ​​geranal in gas chromatography) / total peak area in gas chromatography (excluding solvent).

[0063] Example 1

[0064] Preparation of R-citronellal

[0065] First, the catalyst was pre-prepared, and Rh(CO)2acac and the compound of formula (III) were uniformly mixed at a molar ratio of 0.5:1 at room temperature. Then, 3 mol of citral raw material was added to a 1L autoclave under a hydrogen atmosphere, followed by 0.00015 mol of the above-mentioned rhodium catalyst (based on the molar amount of the rhodium element), the autoclave was closed, the pressure in the autoclave was controlled to 50 bar with hydrogen, the reaction temperature was controlled to 80°C by heating, the reaction was carried out for 12 hours, and then the reaction conversion rate was measured by gas chromatography to be 99%, and the optical purity of citronellal was 98ee%.

[0066] Recovery of R-citronellal

[0067] The reaction solution was subjected to vacuum distillation to obtain 420 g of high-purity citronellal and 42 g of a concentrated solution rich in heavy components, wherein the concentrated solution contained 2 wt% of citronellal, 1.5 wt% of citral, 50.5 wt% of citronellal dimer, 33.5 wt% of citronellal trimer, and 12.5 wt% of citronellal tetramer. The concentrated solution was collected and added to a 500 mL reactor, 2.9 mg (20 ppm) of diisopropyl chlorophosphate was added, a vacuum distillation apparatus was installed, the temperature in the reactor was controlled to be 50 ° C, the pressure was 100 Pa, maintained for 2 hours, and the distillate was continuously collected. The output of citronellal was 36 g, and the optical purity was 98 ee% as measured by gas chromatography.

[0068] The recovery yield of citronellal was 85.7%.

[0069] Example 2

[0070] The reaction solution prepared in Example 1 was subjected to vacuum distillation to obtain 310 g of high-purity citronellal and 145 g of a concentrated solution rich in heavy components. The concentrated solution was collected and added to a 500 mL reactor, 72.5 mg (50 ppm) of diethyl chlorothiophosphate was added, a vacuum distillation device was installed, the temperature in the reactor was controlled to be 100° C., the pressure was 1000 Pa, and the reaction was maintained for 3 hours. The distillate was continuously collected, and the output of citronellal was 37 g. The optical purity was measured by gas chromatography to be 98 ee%.

[0071] The recovery yield of citronellal was 88.1%.

[0072] Example 3

[0073] The reaction solution prepared in Example 1 was subjected to vacuum distillation to obtain 310 g of high-purity citronellal and 145 g of a concentrated solution rich in heavy components. The concentrated solution was collected and added to a 500 mL reactor, 14.5 mg (100 ppm) of phenyl dichlorophosphate was added, a vacuum distillation device was installed, the temperature in the reactor was controlled to be 150° C., the pressure was 5000 Pa, maintained for 1 hour, and the distillate was continuously collected. The output of citronellal was 35 g, and the optical purity was measured by gas chromatography to be 98 ee%.

[0074] The recovery yield of citronellal was 83.3%.

[0075] Example 4

[0076] The reaction solution prepared in Example 1 was subjected to vacuum distillation to obtain 310 g of high-purity citronellal and 145 g of a concentrated solution rich in heavy components. The concentrated solution was collected and added to a 500 mL reactor, 7.25 mg (50 ppm) of dimethyl chlorophosphate was added, a vacuum distillation device was installed, the temperature in the reactor was controlled to be 80° C., the pressure was 500 Pa, and the temperature was maintained for 5 hours. The distillate was continuously collected, and the output of citronellal was 38 g. The optical purity was measured by gas chromatography to be 98 ee%.

[0077] The recovery yield of citronellal was 90.5%.

[0078] Example 5

[0079] The reaction solution prepared in Example 1 was subjected to vacuum distillation to obtain 310 g of high-purity citronellal and 145 g of a concentrated solution rich in heavy components. The concentrated solution was collected and added to a 500 mL reactor, 29 mg (200 ppm) of diphenylphosphinyl chloride was added, a vacuum distillation device was installed, the temperature in the reactor was controlled to be 200° C., the pressure was 1 Pa, and maintained for 3.5 hours, and the distillate was continuously collected. The output of citronellal was 38 g, and the optical purity was measured by gas chromatography to be 98 ee%.

[0080] The recovery yield of citronellal was 90.5%.

[0081] Example 6

[0082] The reaction solution prepared in Example 1 was subjected to vacuum distillation to obtain 310 g of high-purity citronellal and 145 g of a concentrated solution rich in heavy components. The concentrated solution was collected and added to a 500 mL reactor, 43.5 mg (300 ppm) of dicyclohexylphosphinoyl chloride was added, and a vacuum distillation device was installed. The temperature in the reactor was controlled to be 120° C. and the pressure was 50 Pa. The temperature was maintained for 2.5 hours, and the distillate was continuously collected. The output of citronellal was 35 g, and the optical purity was measured by gas chromatography to be 98 ee%.

[0083] The recovery yield of citronellal was 83.3%.

[0084] Example 7

[0085] The reaction solution prepared in Example 1 was subjected to vacuum distillation to obtain 310 g of high-purity citronellal and 145 g of a concentrated solution rich in heavy components. The concentrated solution was collected and added to a 500 mL reactor, 58 mg (400 ppm) of methyl dichlorophosphate was added, a vacuum distillation device was installed, the temperature in the reactor was controlled to be 180° C., the pressure was 200 Pa, and the temperature was maintained for 4 hours. The distillate was continuously collected, and the output of citronellal was 37 g. The optical purity was measured by gas chromatography to be 95 ee%.

[0086] The recovery yield of citronellal was 88.1%.

[0087] Example 8

[0088] The reaction solution prepared in Example 1 was subjected to vacuum distillation to obtain 310 g of high-purity citronellal and 145 g of a concentrated solution rich in heavy components. The concentrated solution was collected and added to a 500 mL reactor, 21.75 mg (150 ppm) of diisopropyl chlorophosphate was added, a vacuum distillation device was installed, the temperature in the reactor was controlled to be 90° C., the pressure was 2000 Pa, and the temperature was maintained for 1.5 hours. The distillate was continuously collected, and the output of citronellal was 36 g. The optical purity was measured by gas chromatography to be 95 ee%.

[0089] The recovery yield of citronellal was 85.7%.

[0090] Those skilled in the art should understand that any improvement to the present invention, equivalent replacement of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for recovering R-citronellal from a heavy component concentrate of R-citronellal prepared from citral, comprising at least the following steps: A), contacting the heavy component concentrate with at least one compound A to obtain a treated concentrate; B), subjecting the treated concentrated solution to a temperature of 50°C to 200°C to obtain R-citronellal; C), separating R-citronellal from the R-citronellal obtained in step B); The heavy component concentrate contains 0.01 wt% to 10 wt% of R-citronellal and 0.01 wt% to 10 wt% of citral, 40 wt% to 60 wt% of citronellal dimer, 20 wt% to 40 wt% of citronellal trimer, and 10 wt% to 20 wt% of citronellal tetramer, based on the total weight of the concentrate; The structure of the compound A is shown in formula (I): In the formula, X is a P atom, Z is an O or S atom, R1, R2 and R3 have one or two halogen atoms, and the others are the same or different aryl, alkyl or alkoxy groups with 1 to 10 carbon atoms.

2. The method according to claim 1, characterized in that The compound A includes, but is not limited to, diisopropyl chlorophosphate, diethyl chlorothiophosphate, phenyl dichlorophosphate, dimethyl chlorophosphate, diphenylphosphinyl chloride, dicyclohexyl phosphoryl chloride, and methyl dichlorophosphate.

3. The method according to claim 1, characterized in that Based on the total weight of the concentrate, the added amount of compound A is 20 ppm-500 ppm.

4. The method according to any one of claims 1 to 3, characterized in that: The reaction temperature in step B) is 80-150° C. and the reaction time is 1-10 hours.

5. The method according to claim 4, characterized in that The reaction time in step B) is 4-6 hours.

6. The method according to any one of claims 1 to 3, characterized in that: The heavy component concentrate is obtained by a method comprising at least the following steps: a) The substrate citral undergoes asymmetric hydrogenation under the catalysis of a transition metal catalyst to obtain citronellal; b) After the reaction is completed, the reaction solution is subjected to reduced pressure distillation to obtain high-purity citronellal and a concentrated solution rich in heavy components.

7. The method according to claim 6, characterized in that The transition metal catalyst is obtained by reacting a transition metal compound with an optically active ligand containing two phosphorus atoms; the molar ratio of the transition metal atom in the transition metal catalyst to the optically active ligand containing two phosphorus atoms is (0.5-10):

1.

8. The method according to claim 7, characterized in that The molar ratio of the transition metal atom in the transition metal catalyst to the optically active ligand containing two phosphorus atoms is (0.5-1):

1.

9. The method according to claim 7, characterized in that The amount of the transition metal catalyst used in the asymmetric hydrogenation reaction is 0.0001 mol% to 0.1 mol% of the total amount of the substrate based on the molar amount of the transition metal substrate.

10. The method according to any one of claims 1 to 3, characterized in that: The method for separating R-citronellal from the treated concentrated liquid is distillation.

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