CN114292163B - Method for preparing isopulegol from citronellal - Google Patents
Method for preparing isopulegol from citronellal Download PDFInfo
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- CN114292163B CN114292163B CN202210024894.2A CN202210024894A CN114292163B CN 114292163 B CN114292163 B CN 114292163B CN 202210024894 A CN202210024894 A CN 202210024894A CN 114292163 B CN114292163 B CN 114292163B
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- Y02P20/584—Recycling of catalysts
Abstract
The invention provides a method for preparing isopulegol from citronellal. The method can greatly reduce the use amount of the catalyst by controlling the content of citronellyl acetaldehyde ether in the raw material citronellal to be 0.01-0.5wt%, and the mass ratio of citronellyl acetaldehyde ether to citronellic acid to be more than or equal to 10, and simultaneously ensures that the isopulegol product prepared from the citronellal has higher selectivity and industrial value.
Description
Technical Field
The invention belongs to the field of perfume, and particularly relates to a method for preparing isopulegol from citronellal.
Technical Field
Isopulegol, also known as menthol and isopulegol, exists in natural substances such as orange and peppermint, is an important intermediate for synthesizing L-menthol, and is widely applied to industries such as foods, essence, cosmetics and the like.
Currently, the most valuable commercial synthetic route to isopulegol sources other than extraction from natural products is to prepare it by cyclization of citronellal, after which menthol can be prepared by further hydrogenation.
CN 108484355 discloses a method for preparing isopulegol by catalytic cyclization reaction with a proper amount of calixarene as an auxiliary agent under the catalysis of anhydrous zinc bromide by using citronellal as a raw material, wherein the catalyst used in the method has low price but low catalytic selectivity, and a large amount of byproducts are generated.
CN 104211566 discloses a catalytic system using triethylaluminum as a catalyst and diaryl phenols as a ligand, and a method for preparing isopulegol by catalytic citronellal cyclization reaction, the method shows good catalytic activity and selectivity, but the catalyst dosage is large, only the recycling of the ligand in the catalyst can be realized, a large amount of aluminum-containing wastewater can be obtained by the reaction, and the recycled ligand still needs to be regenerated to obtain the catalyst. The operation is complex, and the continuous operation is difficult to realize.
Therefore, a practical and efficient method for preparing isopulegol is required to be developed, so that the catalyst dosage can be reduced while higher selectivity is realized in the catalytic process, the production cost is reduced, the economy of the reaction is improved, and the large-scale industrial production of isopulegol is realized.
Disclosure of Invention
In order to solve the technical problems, the invention provides a method for preparing isopulegol from citronellal, which can ensure that the catalyst is used in a reduced amount while realizing higher selectivity in the catalytic process, so as to reduce the production cost and improve the economy of the reaction.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a method for preparing isopulegol from citronellal controls the content of citronellyl acetaldehyde ether in raw material citronellal to be 0.01-0.5wt%, and the mass ratio of citronellyl acetaldehyde ether to citronellic acid is more than or equal to 10. Wherein, the citronellyl acetaldehyde ether structure is as follows:
in the invention, the preparation steps of the isopulegol prepared from citronellal are as follows: citronellal undergoes cyclization in the presence of a catalyst obtained by reacting triethylaluminum with a phenolic ligand to produce isopulegol. Carrying out cyclization reaction on citronellal in the presence of a catalyst to generate isopulegol in the formula (I);
the reaction process for preparing isopulegol by citronellal of the invention in the presence of a catalyst obtained by reacting triethylaluminum with a phenolic ligand is schematically as follows:
the product isopulegol generated in the reaction process can undergo substitution reaction with a catalyst, and the generated product can catalyze citronellal to generate a large amount of byproducts citronellyl citronellate. In order to ensure the selectivity of the main reaction, the method used in the prior report is to increase the dosage of the catalyst, and the catalyst only can realize the recycling of the ligand in the catalyst, so that a large amount of aluminum-containing wastewater can be obtained in the reaction and is difficult to treat, the recycled ligand still needs to be regenerated to obtain the catalyst, the operation is complex, and the method still faces the challenge of high cost. The inventor surprisingly found that the existence of a certain amount of citronellyl acetaldehyde ether in a reaction system can compete with isopulegol, so that the substitution reaction of isopulegol and a catalyst is greatly reduced, the generation of citronellyl citronellate byproducts is avoided, and the selectivity of the reaction is greatly improved. Therefore, under the condition of keeping the reaction selectivity unchanged, the catalyst dosage can be greatly reduced, the production cost is reduced, and the operation is simplified. The inventors have further found that the starting citronellal inevitably contains small amounts of citronellyl ether, but at lower levels (< 0.01 wt%) it is insufficient to compete adequately with isopulegol, and therefore additional additions to the indicated concentrations (0.01-0.5 wt%) are required to achieve the effects of the invention. In addition, the raw materials also contain a small amount of citronellal oxidation product citronellic acid, and under the reaction condition, the existence of the citronellic acid can catalyze the disproportionation reaction of the citronellyl acetaldehyde ether, so that the effective content of the citronellyl acetaldehyde ether is reduced. Therefore, the mass ratio of citronellyl acetaldehyde ether to citronellic acid is more than or equal to 10, so that the citronellyl acetaldehyde ether and isopulegol compete sufficiently in the reaction process, and side reactions are avoided.
In the invention, the preparation method of the catalyst comprises the following steps: preparing a phenol ligand solution and a triethylaluminum solution respectively; the formulated triethylaluminum solution was added to the ligand solution to form a catalyst solution.
In the present invention, the phenolic ligand is a bis-diarylphenol and/or a mono-diarylphenol; preferably, the molar amount ratio of the phenolic ligand to triethylaluminum is (1-5): 1.
The above-mentioned bis-diarylphenol structure is of the following formula (III):
wherein R is 1 、R 2 、R 3 、R 4 Independently of one another, from C6-C15 aryl, R 5 Selected from hydrogen, C1-C6 alkyl or C1-C6 perfluoroalkyl.
By way of example, the bis-diarylphenol may employ one or more of the compounds having the following structural formula:
the structure of the mono-diaryl phenol in the invention is as follows (IX):
wherein R is 1 、R 2 Independently of one another, from C6-C15 aryl.
By way of example, the monoaryl phenol may employ one or more of the following compounds having the structural formula:
the bis-diaryl phenols or mono-diaryl phenols described in the present invention are well-studied applications in the art and are described in detail in the literature and can be prepared by those skilled in the art by existing methods.
In the present invention, the solvent is one or more of alkane, arene, halohydrocarbon, ether and fat solvent, preferably one or more of n-hexane, toluene, tetrahydrofuran and dichloromethane.
In the present invention, the catalyst is used in an amount of 0.1 to 10%, preferably 0.1 to 5% by mole of citronellal based on the mole of aluminum atoms.
In the present invention, the reaction temperature of the cyclization reaction is-10 to 50 ℃, preferably 5 to 25 ℃, and the reaction time is 0.5 to 24 hours.
It is another object of the present invention to provide an isopulegol product.
The preparation method of isopulegol by using citronellal is characterized in that the isopulegol is prepared by using citronellal as a raw material.
The reactors required for the practice of the invention are in principle all those which allow the reaction under the stated conditions, in particular pressure and temperature, and are suitable for isomerisation reactions, such as autoclaves, tubular reactors and the like, without particular limitation.
The process of the invention can be operated batchwise, semicontinuously or continuously and is particularly suitable for industrial scale production.
Compared with the prior art, the invention has the following positive effects:
the method can ensure that the catalyst dosage (0.1% -5%) is reduced while realizing higher selectivity (98-99%) in the catalytic process, so as to reduce the production cost and improve the economy of the reaction.
Detailed Description
The invention is further illustrated below in connection with the examples, but the invention is not limited to the examples listed but also includes equivalent improvements and variants of the solution defined in the claims appended hereto.
Analytical instrument:
the gas chromatography analysis was performed as follows: 30m DB-WAX, ID: 0.32mm, FD: 0.25 μm; 80-230 ℃ and 3 ℃/min; rf (citronellal): 10.5; r is R f (neo-isopulegol): 13.24; r is R f (isopulegol): 13.58; r is R f (neoiso-isopulegol): 14.64; r is R f (iso-isopulegol): 15.28. the concentration of the reaction product obtained in the reaction solution (in each case in% by weight) was determined by GC analysis using an internal standard.
Device information:
and (3) a reaction kettle: 10L normal temperature and pressure reaction kettle, ledebouriella, atsen mechanical technology Co., ltd.
Ligands (IV), (V), (VI): 99wt%, of the carbofuran technologies limited;
ligands (VII), (VIII), (X), (XI): 98wt%, of the carbofuran technologies Co., ltd;
triethylaluminum: 98wt%, of the carbofuran technologies Co., ltd;
citronellal: 98wt%, ala Ding Shiji Co., ltd;
the pressures referred to in the examples below are absolute pressures.
Example 1
The isopulegol is prepared from citronellal under the protection of high-purity nitrogen and is prepared by the following steps:
1) Preparing a catalyst solution: into a dry flask were added 8.988g (12.5 mmoL) of ligand (IV) and 6.00mL of anhydrous n-hexane to give a transparent solution of the ligand. 5.00mL (5 mmol,1 mmol/L, n-hexane as solvent) of triethylaluminum solution was added dropwise to the clear solution at room temperature for 0.2h, followed by stirring at 25℃for 1h to obtain a bis (diarylphenol) aluminum binaphthol-based aluminum solution.
2) Pretreatment of citronellal: firstly, detecting the content of citronellic acid in the citronellal raw material by gas chromatography to be 0.001wt%, and adding citronellyl acetaldehyde ether into the citronellal raw material until the content of citronellyl acetaldehyde ether in the citronellal raw material is 0.25wt%. The mass ratio of citronellyl acetaldehyde ether to citronellic acid is 250.
3) 770g (5 mol) of citronellal after the pretreatment and 4000g of normal hexane are mixed, then the catalyst solution in the step 1) is added dropwise, and the mixture is stirred and kept at 0 ℃ for cyclization reaction for 5 hours, wherein the conversion rate is 99.9%, and the selectivity of isopulegol is 99%.
Example 2
The isopulegol is prepared from citronellal under the protection of high-purity nitrogen and is prepared by the following steps:
1) Preparing a catalyst solution: into a dry flask were added 30.25g (50 mmoL) of ligand (V) and 25.00mL of toluene to give a transparent solution of the ligand. 50.00mL (50 mmoL,1 mmoL/L, toluene as solvent) of triethylaluminum solution was added dropwise to the clear solution at room temperature for 0.2h, followed by stirring at 25℃for 1h to obtain a bis (diarylphenol) aluminum binaphthol-based aluminum solution.
2) Pretreatment of citronellal: firstly, detecting the content of citronellic acid in the citronellal raw material by gas chromatography to be 0.001wt%, and adding citronellyl acetaldehyde ether into the citronellal raw material until the content of citronellyl acetaldehyde ether in the citronellal raw material is 0.05wt%. The mass ratio of citronellyl acetaldehyde ether to citronellic acid is 50.
3) 770g (5 mol) of citronellal pretreated as described above and 4000g of toluene were mixed, and then the catalyst solution of step 1) was added dropwise thereto, and the mixture was stirred and kept at 25℃for cyclization reaction for 6 hours with a conversion of 99.7% and a isopulegol selectivity of 98%.
Example 3
The isopulegol is prepared from citronellal under the protection of high-purity nitrogen and is prepared by the following steps:
1) Preparing a catalyst solution: into a dry flask were added 309.5g (500 mmoL) of ligand (VI) and 250.00mL of tetrahydrofuran to give a clear solution of the ligand. 250.00mL (250 mmoL,1 mmoL/L, tetrahydrofuran as solvent) of triethylaluminum solution was added dropwise to the clear solution at room temperature for 0.2h, followed by stirring at 25℃for 1h to obtain a bis (diarylphenol) aluminum binaphthol-based aluminum solution.
2) Pretreatment of citronellal: firstly, detecting the content of citronellic acid in the raw material citronellal by gas chromatography to be 0.001wt%, and adding citronellyl acetaldehyde ether into the raw material citronellal until the content of citronellyl acetaldehyde ether in the raw material citronellal is 0.1wt%. The mass ratio of citronellyl acetaldehyde ether to citronellic acid is 100.
3) 770g (5 mol) of citronellal after the pretreatment and 4000g of tetrahydrofuran are mixed, then the catalyst solution in the step 1) is added dropwise, and the mixture is stirred and kept for cyclization reaction at 5 ℃ for 12 hours, wherein the conversion rate is 99.4%, and the selectivity of isopulegol is 98%.
Example 4
The isopulegol is prepared from citronellal under the protection of high-purity nitrogen and is prepared by the following steps:
1) Preparing a catalyst solution: 171.9g (300 mmoL) of ligand (VII) and 200.00mL of methylene chloride were added to a dry flask to obtain a transparent solution of the ligand. 100.00mL (100 mmoL,1 mmoL/L, dichloromethane as solvent) of triethylaluminum solution was added dropwise to the clear solution at room temperature for 0.2h, followed by stirring at 25℃for 1h to obtain a bis (diarylphenol) aluminum binaphthol-based aluminum solution.
2) Pretreatment of citronellal: firstly, detecting the content of citronellic acid in the citronellal raw material by gas chromatography to be 0.001wt%, and adding citronellyl acetaldehyde ether into the citronellal raw material until the content of citronellyl acetaldehyde ether in the citronellal raw material is 0.5wt%. The mass ratio of citronellyl acetaldehyde ether to citronellic acid is 500.
3) 770g (5 mol) of citronellal pretreated as described above and 4000g of methylene chloride were mixed, and then the catalyst solution of step 1) was added dropwise thereto, and the mixture was stirred and kept at-10℃for cyclization reaction for 8 hours, with a conversion of 99.6% and a isopulegol selectivity of 99%.
Example 5
The isopulegol is prepared from citronellal under the protection of high-purity nitrogen and is prepared by the following steps:
1) Preparing a catalyst solution: 504.75g (750 mmoL) of ligand (VIII) and 400.00mL of toluene were added to a dry flask to give a clear solution of ligand. 500.00mL (500 mmoL,1 mmoL/L, toluene as solvent) of triethylaluminum solution was added dropwise to the clear solution at room temperature for 0.2h, followed by stirring at 25℃for 1h to obtain a bis (diarylphenol) aluminum binaphthol-based aluminum solution.
2) Pretreatment of citronellal: firstly, detecting the content of citronellic acid in the raw material citronellal by gas chromatography to be 0.001wt%, and adding citronellyl acetaldehyde ether into the raw material citronellal until the content of citronellyl acetaldehyde ether in the raw material citronellal is 0.01wt%. The mass ratio of citronellyl acetaldehyde ether to citronellic acid is 10.
3) 770g (5 mol) of citronellal pretreated as described above and 4000g of toluene were mixed, and then the catalyst solution of step 1) was added dropwise thereto, and the mixture was stirred and kept at 50℃for cyclization reaction for 0.5 hours with a conversion of 99.5% and a isopulegol selectivity of 99%.
Example 6
The isopulegol is prepared from citronellal under the protection of high-purity nitrogen and is prepared by the following steps:
1) Preparing a catalyst solution: 43.25g (125 mmoL) of ligand (X) and 40.00mL of tetrahydrofuran were added to the dried flask to obtain a transparent solution of the ligand. 25.00mL (25 mmoL,1 mmoL/L, tetrahydrofuran as solvent) of triethylaluminum solution was added dropwise to the clear solution at room temperature for 0.2h, followed by stirring at 25℃for 1h to obtain a bis (diarylphenol) aluminum binaphthol-based aluminum solution.
2) Pretreatment of citronellal: firstly, detecting the content of citronellic acid in the citronellal raw material by gas chromatography to be 0.001wt%, and adding citronellyl acetaldehyde ether into the citronellal raw material until the content of citronellyl acetaldehyde ether in the citronellal raw material is 0.15wt%. The mass ratio of citronellyl acetaldehyde ether to citronellic acid is 150.
3) 770g (5 mol) of citronellal pretreated as described above and 4000g of methylene chloride were mixed, and then the catalyst solution of step 1) was added dropwise thereto, and the mixture was stirred and kept at 15℃for cyclization reaction for 24 hours, with a conversion of 99.8% and a isopulegol selectivity of 98%.
Example 7
The isopulegol is prepared from citronellal under the protection of high-purity nitrogen and is prepared by the following steps:
1) Preparing a catalyst solution: 49.2g (200 mmoL) of ligand (XI) and 40.00mL of n-hexane were added to the dried flask to obtain a transparent solution of the ligand. 100.00mL (100 mmoL,1 mmoL/L, n-hexane as solvent) of triethylaluminum solution was added dropwise to the clear solution at room temperature for 0.2h, followed by stirring at 25℃for 1h to obtain a bis (diarylphenol) aluminum binaphthol-based aluminum solution.
2) Pretreatment of citronellal: firstly, detecting the content of citronellic acid in the raw material citronellal by gas chromatography to be 0.001wt%, and adding citronellyl acetaldehyde ether into the raw material citronellal until the content of citronellyl acetaldehyde ether in the raw material citronellal is 0.2wt%. The mass ratio of citronellyl acetaldehyde ether to citronellic acid is 200.
3) 770g (5 mol) of citronellal pretreated as described above and 4000g of methylene chloride were mixed, and then the catalyst solution of step 1) was added dropwise thereto, and the mixture was stirred and kept at 30℃for cyclization reaction for 18 hours with a conversion of 99.8% and a selectivity of isopulegol of 99%.
Comparative example 1
The difference between this comparative example is that untreated citronellal was used.
770g (50 mol) of untreated citronellal (the content of citronellic acid in the raw material citronellal was 0.001wt%, and the content of citronellyl glyoxyl ether was 0.001 wt%) and 4000g of n-hexane were mixed, and then the catalyst solution prepared in step 1) of example 1 was added dropwise thereto, and the mixture was stirred and kept at 0℃for cyclization reaction for 5 hours with a conversion of 45.8% and a isopulegol selectivity of 26%.
Comparative example 2
The comparative example differs in that citronellal was used in an amount and ratio outside the scope of the present invention.
Pretreatment of citronellal: firstly, detecting the content of citronellic acid in the raw material citronellal by gas chromatography to be 0.001wt%, and adding citronellyl acetaldehyde ether into the raw material citronellal until the content of citronellyl acetaldehyde ether in the raw material citronellal is 0.005wt%. The mass ratio of citronellyl acetaldehyde ether to citronellic acid is 5.
770g (5 mol) of citronellal pretreated as described above and 4000g of n-hexane were mixed, and then the catalyst solution prepared in step 1) of example 1 was added dropwise thereto, and the mixture was stirred and kept at 0℃for cyclization reaction for 5 hours with a conversion of 68.8% and a selectivity to isopulegol of 67%.
Those skilled in the art will appreciate that certain modifications and adaptations of the invention are possible and can be made under the teaching of the present specification. Such modifications and adaptations are intended to be within the scope of the present invention as defined in the appended claims.
Claims (10)
1. A method for preparing isopulegol from citronellal is characterized in that the method controls the content of citronellyl acetaldehyde ether in raw material citronellal to be 0.01-0.5wt%, and the mass ratio of citronellyl acetaldehyde ether to citronellic acid is more than or equal to 10; the preparation method comprises the following steps: citronellal undergoes cyclization in the presence of a catalyst obtained by reacting triethylaluminum with a phenolic ligand to produce isopulegol.
2. The method for preparing isopulegol according to claim 1, wherein the method for preparing the catalyst comprises: preparing a phenol ligand solution and a triethylaluminum solution respectively; the formulated triethylaluminum solution was added to the ligand solution to form a catalyst solution.
3. The method for producing isopulegol according to claim 1 or 2, wherein the phenolic ligand is bis-diaryl phenol and/or mono-diaryl phenol.
4. The process for producing isopulegol according to claim 3, wherein the molar ratio of the phenol ligand to triethylaluminum is 1 to 5:1.
5. The method for producing isopulegol according to claim 2, wherein the solvent of the solution is one or more of an alkane, an aromatic hydrocarbon, a halogenated hydrocarbon, an ether and a lipid solvent.
6. The method for producing isopulegol according to claim 5, wherein the solvent of the solution is one or more of n-hexane, toluene, tetrahydrofuran and methylene chloride.
7. The method for preparing isopulegol according to claim 1, wherein the catalyst is used in an amount of 0.1 to 10% by mole of citronellal based on the mole of aluminum atoms.
8. The method for producing isopulegol according to claim 7, wherein the catalyst is used in an amount of 0.1 to 5% by mole based on the molar amount of the aluminum atom.
9. The process for producing isopulegol as claimed in claim 1, wherein the cyclization reaction is carried out at a reaction temperature of-10 to 50 ℃ for a reaction time of 0.5 to 24 hours.
10. The process for producing isopulegol as claimed in claim 9, wherein the cyclization reaction has a reaction temperature of 5 to 25 ℃.
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