A method for synthesizing geranialdehyde

Abstract

This invention discloses a method for synthesizing geranialdehyde, comprising the following steps: Citral undergoes an isomerization reaction under the action of a catalyst; after the reaction, a post-treatment is performed to obtain a product rich in geranialdehyde; the catalyst includes a noble metal catalyst and an organophosphorus ligand; the noble metal catalyst is a palladium salt. This preparation method can effectively realize the conversion of nerol to geranialdehyde, and the reaction process generates relatively little waste, is environmentally friendly, fully utilizes the raw materials, and produces no waste gas.

Description

Technical Field

[0001] This invention discloses a method for synthesizing geranialdehyde, an isomer of citral, belonging to the field of fine chemical synthesis. Background Technology

[0002] Citral is an important synthetic fragrance and a raw material for the synthesis of ionones and vitamin A. It mainly comes from two sources: one is isolated from natural products, and the other is prepared through artificial synthesis. It has two isomers: neraldehyde ((Z)-3,7-dimethyl-2,6-octadienal) and geranialdehyde ((E)-3,7-dimethyl-2,6-octadienal), and most of these exist in a mixture of the two. Therefore, separation is necessary for its use. Thus, efficient methods for obtaining neraldehyde or geranialdehyde are an important research direction.

[0003] Patent CN112142583A discloses a method for preparing nerol from geranialdehyde. The method uses a bis(diarylphenol)aluminum compound as a catalyst to catalyze the conversion of geranialdehyde to nerol under carbon monoxide conditions. This method can convert geranialdehyde in waste materials into nerol and improve the separation yield of nerol. However, this method uses a bis(diarylphenol)aluminum compound, which has high safety requirements and high cost.

[0004] Patent CN101687751 discloses a continuous method for preparing neraldehyde by distilling citral to separate neraldehyde. This method solves the problem of separating geranialdehyde and neraldehyde on an industrial scale by continuously distilling in a partitioned wall column or a thermally coupled distillation column, achieving high-purity and high-yield preparation of neraldehyde and reducing side reactions and energy consumption. However, the use of distillation reduces the utilization rate of citral, resulting in a significant increase in cost. The aforementioned method is limited in its application due to its low safety and high cost. Therefore, there is a need to find a method that is both safe and relatively low-cost. Summary of the Invention

[0005] The problem this invention aims to solve is to provide a safe, reliable, mild, and relatively low-cost process for converting nerol into geraniol, addressing the above-mentioned shortcomings.

[0006] To solve the above problems, the present invention adopts the following technical solution: a method for synthesizing geranialdehyde, comprising the following steps:

[0007] Citral undergoes an isomerization reaction under the action of a catalyst, and after the reaction is completed, a product rich in geranialdehyde is obtained through post-treatment.

[0008] The catalyst includes a noble metal catalyst and an organophosphorus ligand, which can better catalyze the reaction.

[0009] The noble metal catalyst is a palladium salt, which exhibits excellent catalytic activity and high conversion rate in this reaction. The palladium salt can be Pd(CH3COO)2, Pd(acac)2, or PdCl2, with Pd(acac)2 being preferred.

[0010] The organophosphine ligand can be one or two of the following ligands (structures 1-4), preferably one or two of ligands with structure formula 3 and structure formula 4. Compared with other ligands, the complexes formed by structure formula 3 and structure formula 4 with metal coordination have a larger cone angle or bite angle, and the resulting complex skeleton also has greater rigidity, which makes the reaction more selective.

[0011]

[0012] The molar ratio of the noble metal catalyst to the organophosphorus ligand can be 1:(5-20), preferably 1:(10-15).

[0013] The reaction can be carried out using a solvent, which may be toluene, cyclohexane, petroleum ether, dichloroethane, or a mixture thereof.

[0014] The ratio of nerol to geraniol in the raw material citral is (35%-60%):(39%-64%), preferably (40%-45%):(54%-59%).

[0015] The mass ratio of citral to palladium salt can be (30-45):1.

[0016] The temperature of the isomerization reaction is 30-60℃, preferably 40-60℃.

[0017] The isomerization reaction takes 1-50 hours, preferably 4-24 hours.

[0018] The pressure of nitrogen gas is 0.5-1.5 MPa, preferably 0.8-1.2 MPa.

[0019] The post-processing involves removing the solvent from the reaction solution by de-evaporation after the isomerization reaction is completed. The remaining de-evaporated solution is then distilled to obtain geranialdehyde as a finished product. The catalyst in the bottom of the distillation column is reused in the next batch without any further treatment.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] (1) The precious metal catalyst used can be recycled, the operation process is simple, the requirements for instruments and equipment are low, the production cost is low, and the catalyst used has better catalytic performance, making the reaction more efficient.

[0022] (2) A novel ligand is used, which can form a complex with a larger cone angle or bite angle with the metal, so that the reaction has higher selectivity.

[0023] (3) The reaction process produces less waste, is environmentally friendly, utilizes all raw materials, and does not generate waste gas. Attached Figure Description

[0024] Figure 1 The image shows the gas chromatogram of citral, the raw material in Example 1.

[0025] Figure 2 This is the gas chromatogram after the reaction in Example 1. Detailed Implementation

[0026] The preferred embodiments of the present invention are described below. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0027] Testing conditions:

[0028] Gas chromatograph: Fuli 9790; Column: DB-17 cross-linked or coated quartz capillary column, 30m×0.25mm×0.25µm; Column oven temperature 130℃, vaporization chamber temperature 260℃, detection chamber temperature 280℃.

[0029] Example 1:

[0030] 200g of toluene and 10g of catalyst (in which the molar ratio of Pd(acac)2 to structure 4 ligand is 1:15) were added to a high-pressure reactor. The reactor was closed, and the air inside the reactor was replaced with nitrogen three times. The mixture was stirred to ensure that the palladium salt and ligand were fully dissolved.

[0031] 300g of citral (43% nerol and geranialdehyde in a ratio of 43%:56%) was drawn into the reactor under negative pressure. The air inside the reactor was replaced with nitrogen three times. The temperature was raised to the set temperature, and the nitrogen was pressurized to 1.0 MPa. The reaction was stopped after 24 hours at 60°C. The product was sampled and tested. The geranialdehyde content was 98.5%. The reaction solution was then desolventized by evaporation. The remaining desolventized solution was distilled to obtain geranialdehyde product with a purity of ≥95%. The catalyst in the bottom of the reactor was reused in the next batch without any treatment.

[0032] Catalyst application test

[0033] The separated catalyst was replenished with solvent and then reintroduced into the high-pressure reactor. The reaction and operating conditions remained unchanged. The experimental results are shown in Table 1.

[0034] Table 1. Catalyst Application Data

[0035]

[0036] As shown in Table 1, after 10 reuses of the catalyst provided by this invention, the geranialdehyde content in the product decreased by 1%. The reason is speculated to be that as the number of reuses increases, the amount of waste material also increases. The catalyst is coated by the waste material, which covers the active sites and leads to a decrease in catalyst activity.

[0037] Comparative Example 1:

[0038] Add 200g of toluene to the high-pressure reactor, close the reactor, and replace the air inside the reactor three times with nitrogen.

[0039] 300g of citral (43% nerol and 56% geranialdehyde) was drawn into the reactor under negative pressure. The air inside the reactor was replaced with nitrogen three times. The temperature was raised to the set temperature and the nitrogen was pressurized to 1.0 MPa. The reaction was stopped after 24 hours at 60°C. The product was sampled and tested. The geranialdehyde content was 61%.

[0040] Comparative Example 2:

[0041] Add 200g of toluene and 10g of structure 4 ligand to a high-pressure reactor, close the reactor, replace the air in the reactor with nitrogen three times, and stir to ensure that the ligand is fully dissolved;

[0042] 300g of citral (43% nerol and 56% geranialdehyde) was drawn into the reactor under negative pressure. The air in the reactor was replaced with nitrogen three times. The temperature was raised to the set temperature and the nitrogen was pressurized to 1.0 MPa. The reaction was stopped after 24 hours at 60°C. The product was sampled and tested. The geranialdehyde content was 65%.

[0043] Example 2:

[0044] 200g of toluene and 10g of catalyst (in which the molar ratio of Pd(acac)2 to structure 4 ligand is 1:8) were added to a high-pressure reactor. The reactor was closed, and the air inside the reactor was replaced with nitrogen three times. The mixture was stirred to ensure that the palladium salt and ligand were fully dissolved.

[0045] 300g of citral (43% neraldehyde and geranialdehyde: 56%) was drawn into the reactor under negative pressure. The air inside the reactor was replaced three times with nitrogen. The temperature was raised to the set temperature, and the nitrogen was pressurized to 1.0 MPa. The reaction was stopped after 24 hours at 60°C. The product was sampled and tested. The geranialdehyde content was 93%. The reaction solution was then desolventized by evaporation. The remaining desolventized solution was distilled to obtain geranialdehyde product with a purity of ≥99.5%. The catalyst in the bottom of the reactor was reused in the next batch without any treatment.

[0046] Example 3:

[0047] 200g of toluene and 10g of catalyst (in which the molar ratio of Pd(acac)2 to structure 4 ligand is 1:17) were added to a high-pressure reactor. The reactor was closed, and the air inside the reactor was replaced with nitrogen three times. The mixture was stirred to ensure that the palladium salt and ligand were fully dissolved.

[0048] 300g of citral (43% nerol and 56% geranialdehyde) was drawn into the reactor under negative pressure. The air inside the reactor was replaced three times with nitrogen. The temperature was raised to the set temperature, and the nitrogen was pressurized to 1.0 MPa. The reaction was stopped after 24 hours at 60°C. The product was sampled and tested. The geranialdehyde content was 71%. The reaction solution was then desolventized by evaporation. The remaining desolventized solution was distilled to obtain geranialdehyde product with a purity of ≥99.5%. The catalyst in the bottom of the reactor was reused in the next batch without any treatment.

[0049] Example 4:

[0050] 200g of toluene and 10g of catalyst (in which the molar ratio of Pd(acac)2 to structure 2 ligand is 1:15) were added to a high-pressure reactor. The reactor was then closed, and the air inside the reactor was replaced three times with nitrogen. The mixture was stirred to ensure that the palladium salt and ligand were fully dissolved.

[0051] 300g of citral (43% neraldehyde and geranialdehyde: 56%) was drawn into the reactor under negative pressure. The air inside the reactor was replaced three times with nitrogen. The temperature was raised to the set temperature, and the nitrogen was pressurized to 1.0 MPa. The reaction was stopped after 24 hours at 60°C. The product was sampled and tested. The geranialdehyde content was 72%. The reaction solution was then desolventized by evaporation. The remaining desolventized solution was purified by distillation to obtain geranialdehyde product with a purity of ≥99.5%. The catalyst in the bottom of the reactor was reused in the next batch without any treatment.

[0052] Example 5:

[0053] 200g of toluene and 10g of catalyst (in which the molar ratio of Pd(acac)2 to structure 4 ligand is 1:15) were added to a high-pressure reactor. The reactor was closed, and the air inside the reactor was replaced with nitrogen three times. The mixture was stirred to ensure that the palladium salt and ligand were fully dissolved.

[0054] 450g of citral (43% neraldehyde and geranialdehyde: 56%) was drawn into the reactor under negative pressure. The air inside the reactor was replaced with nitrogen three times. The temperature was raised to the set temperature, and the nitrogen was pressurized to 1.0 MPa. The reaction was stopped after 24 hours at 60°C. The product was sampled and tested. The geranialdehyde content was 81%. The reaction solution was then desolventized by evaporation. The remaining desolventized solution was distilled to obtain geranialdehyde product with a purity of ≥99.5%. The catalyst in the bottom of the reactor was reused in the next batch without any treatment.

[0055] Example 6:

[0056] 200g of toluene and 10g of catalyst (in which the molar ratio of Pd(acac)2 to structure 4 ligand is 1:15) were added to a high-pressure reactor. The reactor was closed, and the air inside the reactor was replaced with nitrogen three times. The mixture was stirred to ensure that the palladium salt and ligand were fully dissolved.

[0057] 300g of citral (43% neraldehyde and geranialdehyde: 56%) was drawn into the reactor under negative pressure. The air inside the reactor was replaced three times with nitrogen. The temperature was raised to the set temperature, and the nitrogen was pressurized to 1.0 MPa. The reaction was stopped after 24 hours at 50°C. The product was sampled and tested. The geranialdehyde content was 92%. The reaction solution was then desolventized by evaporation. The remaining desolventized solution was distilled to obtain geranialdehyde product with a purity of ≥99.5%. The catalyst in the bottom of the reactor was reused in the next batch without any treatment.

[0058] Example 7:

[0059] 200g of toluene and 10g of catalyst (in which the molar ratio of Pd(acac)2 to structure 4 ligand is 1:15) were added to a high-pressure reactor. The reactor was closed, and the air inside the reactor was replaced with nitrogen three times. The mixture was stirred to ensure that the palladium salt and ligand were fully dissolved.

[0060] 300g of citral (43% neraldehyde and geranialdehyde: 56%) was drawn into the reactor under negative pressure. The air inside the reactor was replaced with nitrogen three times. The temperature was raised to the set temperature, and the nitrogen was pressurized to 1.0 MPa. The reaction was stopped after 24 hours at 35°C. The product was sampled and tested. The geranialdehyde content was 81%. The reaction solution was then desolventized by evaporation. The remaining desolventized solution was purified by distillation to obtain geranialdehyde product with a purity of ≥99.5%. The catalyst in the bottom of the reactor was reused in the next batch without any treatment.

[0061] Example 8:

[0062] 200g of toluene and 10g of catalyst (in which the molar ratio of Pd(acac)2 to structure 4 ligand is 1:15) were added to a high-pressure reactor. The reactor was closed, and the air inside the reactor was replaced with nitrogen three times. The mixture was stirred to ensure that the palladium salt and ligand were fully dissolved.

[0063] 300g of citral (43% nerol and geranialdehyde: 56%) was drawn into the reactor under negative pressure. The air inside the reactor was replaced with nitrogen three times. The temperature was raised to the set temperature, and the nitrogen was pressurized to 1.0 MPa. The reaction was stopped after 40 hours at 60℃. The product was sampled and tested. The geranialdehyde content was 90%. The reaction solution was then desolventized by evaporation. The remaining desolventized solution was distilled to obtain geranialdehyde product with a purity of ≥99.5%. The catalyst in the bottom of the reactor was reused in the next batch without any treatment.

[0064] Example 9:

[0065] 200g of toluene and 10g of catalyst (in which the molar ratio of Pd(acac)2 to structure 4 ligand is 1:15) were added to a high-pressure reactor. The reactor was closed, and the air inside the reactor was replaced with nitrogen three times. The mixture was stirred to ensure that the palladium salt and ligand were fully dissolved.

[0066] 300g of citral (43% neraldehyde and geranialdehyde: 56%) was drawn into the reactor under negative pressure. The air inside the reactor was replaced three times with nitrogen. The temperature was raised to the set temperature, and the nitrogen was pressurized to 1.0 MPa. The reaction was stopped after 2 hours at 60°C. The product was sampled and tested. The geranialdehyde content was 85%. The reaction solution was then desolventized by evaporation. The remaining desolventized solution was distilled to obtain geranialdehyde product with a purity of ≥99.5%. The catalyst in the bottom of the reactor was reused in the next batch without any treatment.

[0067] Example 10:

[0068] 200g of toluene and 10g of catalyst (in which the molar ratio of Pd(acac)2 to structure 4 ligand is 1:15) were added to a high-pressure reactor. The reactor was closed, and the air inside the reactor was replaced with nitrogen three times. The mixture was stirred to ensure that the palladium salt and ligand were fully dissolved.

[0069] 300g of citral (43% neraldehyde and geranialdehyde: 56%) was drawn into the reactor under negative pressure. The air inside the reactor was replaced three times with nitrogen. The temperature was raised to the set temperature, and the nitrogen was pressurized to 0.6 MPa. The reaction was stopped after 24 hours at 60℃. The product was sampled and tested. The geranialdehyde content was 91%. The reaction solution was then desolventized by evaporation. The remaining desolventized liquid was purified by distillation to obtain geranialdehyde product with a purity of ≥99.5%. The catalyst in the bottom of the reactor was reused in the next batch without any treatment.

[0070] Example 11:

[0071] 200g of toluene and 10g of catalyst (in which the molar ratio of Pd(acac)2 to structure 4 ligand is 1:15) were added to a high-pressure reactor. The reactor was closed, and the air inside the reactor was replaced with nitrogen three times. The mixture was stirred to ensure that the palladium salt and ligand were fully dissolved.

[0072] 300g of citral (43% neraldehyde and geranialdehyde: 56%) was drawn into the reactor under negative pressure. The air inside the reactor was replaced three times with nitrogen. The temperature was raised to the set temperature, and the nitrogen was pressurized to 1.3 MPa. The reaction was stopped after 24 hours at 60°C. The product was sampled and tested. The geranialdehyde content was 93%. The reaction solution was then desolventized by evaporation. The remaining desolventized solution was distilled to obtain geranialdehyde product with a purity of ≥99.5%. The catalyst in the bottom of the reactor was reused in the next batch without any treatment.

[0073] Example 12:

[0074] 200g of toluene and 10g of catalyst (in which the molar ratio of Pd(acac)2 to structure 4 ligand is 1:15) were added to a high-pressure reactor. The reactor was closed, and the air inside the reactor was replaced with nitrogen three times. The mixture was stirred to ensure that the palladium salt and ligand were fully dissolved.

[0075] 300g of citral (a 50%:40% ratio of nerol to geranialdehyde) was drawn into the reactor under negative pressure. The air inside the reactor was replaced three times with nitrogen. The temperature was raised to the set temperature, and the nitrogen was pressurized to 1.0 MPa. The reaction was stopped after 24 hours at 60°C. The product was sampled and tested. The geranialdehyde content was 88%. The reaction solution was then desolventized by evaporation. The remaining desolventized solution was distilled to obtain geranialdehyde product with a purity of ≥99.5%. The catalyst in the bottom of the reactor was reused in the next batch without any treatment.

[0076] Example 13:

[0077] Add 200g of cyclohexane and 10g of catalyst (where the molar ratio of Pd(acac)2 to structure 4 ligand is 1:15) to a high-pressure reactor, close the reactor, replace the air in the reactor with nitrogen three times, and stir to fully dissolve the palladium salt and ligand.

[0078] 300g of citral (43% nerol and geranialdehyde in a ratio of 43%:56%) was drawn into the reactor under negative pressure. The air inside the reactor was replaced with nitrogen three times. The temperature was raised to the set temperature, and the nitrogen was pressurized to 1.0 MPa. The reaction was stopped after 24 hours at 60°C. The product was sampled and tested. The geranialdehyde content was 90%. The reaction solution was then desolventized by evaporation. The remaining desolventized solution was distilled to obtain geranialdehyde product with a purity of ≥99.5%. The catalyst in the bottom of the reactor was reused in the next batch without any treatment.

[0079] Example 14:

[0080] 200g of toluene and 10g of catalyst (in which the molar ratio of Pd(CH3COO)2 to structure 4 ligand is 1:15) were added to a high-pressure reactor. The reactor was closed, and the air inside the reactor was replaced with nitrogen three times. The mixture was stirred to ensure that the palladium salt and ligand were fully dissolved.

[0081] 300g of citral (43% nerol and geranialdehyde in a ratio of 43%:56%) was drawn into the reactor under negative pressure. The air inside the reactor was replaced three times with nitrogen. The temperature was raised to the set temperature, and the nitrogen was pressurized to 1.0 MPa. The reaction was stopped after 24 hours at 60°C. The product was sampled and tested. The geranialdehyde content was 93%. The reaction solution was then desolventized by evaporation. The remaining desolventized solution was distilled to obtain geranialdehyde product with a purity of ≥99.5%. The catalyst in the bottom of the reactor was reused in the next batch without any treatment.

[0082] The specific embodiments described above illustrate the technical solution and beneficial effects of the present invention in detail. It should be understood that the above description is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for synthesizing geranialdehyde, characterized in that, Includes the following steps: Citral undergoes an isomerization reaction under the action of a catalyst, and after the reaction is completed, a product rich in geranialdehyde is obtained through post-treatment. The catalyst includes a noble metal catalyst and an organophosphorus ligand; The noble metal catalyst is a palladium salt.

2. The method for synthesizing geranialdehyde according to claim 1, characterized in that, The palladium salt is one or more of Pd(CH3COO)2, Pd(acac)2, and PdCl2.

3. The method for synthesizing geranialdehyde according to claim 1, characterized in that, The structural formula of the organophosphine ligand is as follows: ； R1 and R2 are independently selected from C1 to C4 alkyl groups, or R1 and R2 form a five- or six-membered nitrogen-containing heterocyclic group with the N group that connects them.

4. The method for synthesizing geranialdehyde according to claim 1, characterized in that, The organophosphine ligand is one of the following structural formulas: 。 5. The method for synthesizing geranialdehyde according to claim 1, characterized in that, The molar ratio of the noble metal catalyst to the organophosphine ligand is 1:(5-20). The mass ratio of citral to catalyst is (30-45):

1.

6. The method for synthesizing geranialdehyde according to claim 1, characterized in that, The reaction is carried out in a solvent, which is toluene, cyclohexane, petroleum ether, dichloroethane, or a mixture thereof.

7. The method for synthesizing geranialdehyde according to claim 1, characterized in that, The ratio of nerol to geraniol in the raw material citral is (35%-60%):(39%-64%).

8. The method for synthesizing geranialdehyde according to claim 1, characterized in that, The isomerization reaction is carried out at a temperature of 30-60℃ for 1-50 hours.

9. The method for synthesizing geranialdehyde according to claim 1 or 8, characterized in that, The reaction is carried out in a nitrogen atmosphere at a pressure of 0.5-1.5 MPa, preferably 0.8-1.2 MPa.

10. The method for synthesizing geranialdehyde according to claim 1, characterized in that, The post-processing involves removing the solvent from the reaction solution by de-evaporation after the isomerization reaction is completed. The remaining de-evaporated solution is then distilled to obtain geranialdehyde as a finished product. The catalyst in the bottom of the distillation column is reused in the next batch without any further treatment.

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