A metal complex and its ligand, a catalyst composition and a preparation method of citronellol

Abstract

This invention discloses a metal complex and its ligands, a catalyst composition, and a method for preparing citronellol. The method for preparing citronellol uses citral as a raw material and employs a bimetallic catalyst containing two or more metal complexes M, namely palladium, copper, nickel, and cobalt. The selective hydrogenation of citral to citronellol significantly improves product selectivity, reduces the selectivity of the over-hydrogenation product tetrahydrogeraniol, and maintains a certain degree of inertness towards the terminal C=C.

Description

Technical Field

[0001] This invention relates to the field of catalysts, specifically to catalysts for the preparation of citronellol, and more specifically to a method for the selective hydrogenation of citral to prepare citronellol using a bimetallic catalyst. Background Technology

[0002] Citronellol is an important flavoring ingredient with a sweet floral aroma, similar to rose. It is widely used in perfume, soap, and cosmetic fragrance formulations, and can be used as a raw material for the manufacture of dihydrocitronellol and hydroxydihydrocitronellol. Citronellol can also be used in food flavorings, such as in soft drinks, baked goods, candies, and jellies / puddings.

[0003] Citral has two cis-trans isomers and is an important raw material for fragrances and pharmaceutical intermediates. The hydrogenation reaction of citral produces a variety of products, including nerol, geraniol, citronellol, citronellol, and dihydrocitronellol. Depending on the catalyst and reaction conditions, the hydrogenation reaction may occur at different sites, resulting in different products.

[0004] US Patent 4029709A discloses a method for selectively hydrogenating citral or citronellol to obtain citronellol. This method uses a chromium-modified Raney catalyst as the reaction catalyst and one or more saturated lower alcohols as the reaction solvent. The method claims a direct selectivity of up to 92%, and the catalyst used does not involve precious metals and is relatively inexpensive. However, this method also suffers from a relatively low selectivity.

[0005] Patent CN1247182A discloses a method for preparing citronellol by gas-phase catalytic hydrogenation using a cobalt-active catalyst supported on alumina. The problem with this method is its low conversion rate and selectivity (maximum 93%). Furthermore, the similar boiling points of the feedstock citral and the product citronellol make it difficult to separate citronellol by distillation.

[0006] Patent CN102295531B discloses a method for directly reducing citral to citronellol using intermittent hydrogenation. The reaction system uses citral as a raw material, an M2-type metallic framework alloy solid as a catalyst, and also includes an aqueous solution of amines and a non-polar solvent. The intermittent hydrogenation method selectively reduces citral to crude citronellol, which is then purified by vacuum distillation to obtain refined citronellol. This process involves a complex reaction system, including an aqueous phase, an oil phase, a solid phase (catalyst), and a gas phase (hydrogen). Many factors influence the reaction process, making it difficult to implement in industrial applications.

[0007] The aforementioned literature describes several catalysts and production methods with high selectivity, but it has not completely solved the problems of high cost and low operability. Summary of the Invention

[0008] To address the problems existing in the prior art, the present invention aims to provide a metal complex and its ligand, and a catalyst composition; the catalyst composition is used for the selective hydrogenation of citral to prepare citronellol.

[0009] A metal complex ligand has the following structural formula:

[0010] The method for preparing the ligand of the present invention includes the following steps: reacting 1,10-phenanthroline-4,7-dicarboxaldehyde with 2,2,2-trifluoroethanethiol.

[0011] The reaction formula is as follows:

[0012]

[0013] In the preparation method of the ligand, the reaction temperature is 100-150℃ and the reaction time is 5-12h, preferably the reaction temperature is 100-120℃ and the time is 6-8h.

[0014] In the preparation method of the ligand, the molar ratio of 1,10-phenanthroline-4,7-dicarboxaldehyde to 2,2,2-trifluoroethanethiol is 1:2 to 1:3, preferably 1:2 to 1:2.5.

[0015] Preferably, in the preparation method of the ligand, an initiator is also added. The initiator can be an azo initiator, and the amount of initiator added can be 0.01-0.05% of the molar amount of the raw material 1,10-phenanthroline-4,7-dicarboxaldehyde.

[0016] A metal complex with the following structural formula: M is one of palladium, copper, nickel, and cobalt.

[0017] The method for preparing the metal complex of the present invention includes the following steps: reacting the ligand with a salt solution of metal M.

[0018] The reaction formula is as follows:

[0019]

[0020] In the preparation method of the metal complex, the salt of the metal M is selected from palladium chloride, copper chloride, nickel chloride, and cobalt chloride.

[0021] In the preparation method of the metal complex, the reaction temperature is 70-100℃ and the reaction time is 2-10h, preferably 70-80℃ and 3-5h.

[0022] In the preparation method of the metal complex, the molar ratio of the ligand to the salt of metal M is 1:5 to 1:20, preferably 1:10 to 1:15.

[0023] A catalyst composition comprising two or more metal complexes as shown below.

[0024]

[0025] Preferably, in the catalyst composition, the molar ratio of the two metal complexes is 1:2 to 2:1.

[0026] In this invention, the catalyst composition can be prepared by adding two or more metal M salts simultaneously when preparing the metal complex, or by preparing a complex of one metal M alone and then mixing the two or more metal complexes.

[0027] A method for preparing citronellol by hydrogenating citral includes the following steps: using citral as a raw material, a hydrogenation reaction is carried out under the action of the above-mentioned catalyst composition.

[0028] As a preferred embodiment, in the method for preparing citronellol by hydrogenation of citral, the catalyst composition comprises a main catalyst. and co-catalyst The molar ratio of the two is 4:3. Pd is the active component of the diene-selective hydrogenation catalyst, but it still suffers from side reactions, is easily complexed by alkyne bonds, and has poor stability. Adding a second metal co-catalyst further improves the catalyst function. Pb-based bimetals show significantly improved selectivity, activity, stability, and lifetime for diene hydrogenation compared to single Pb catalysts. Co, as a co-catalyst, exhibits high selectivity for various C-C bond formations. Co catalysts also demonstrate good functional group tolerance, mild reaction conditions, and high chemoselectivity.

[0029] In the method for preparing citronellol by hydrogenation of citral, the amount of catalyst composition added is 0.1-2% of the mass of the substrate citral, preferably 0.5-2%.

[0030] In the method for preparing citronellol by hydrogenating citral, the reaction temperature is 60-80℃, the hydrogen pressure range is 1-5MPa, and the reaction time is 2-6h.

[0031] In the method for preparing citronellol by hydrogenating citral according to the present invention, the selectivity of citronellol is above 99%, and the selectivity of the over-hydrogenation product tetrahydrogeraniol is 0.1-0.3%.

[0032] In the method for preparing citronellol by hydrogenation of citral, the main catalyst has high activity and fast catalytic reaction rate, while the co-catalyst is used to regulate the activation energy and valence band structure, optimize the reaction pathway, and thus improve selectivity.

[0033] The technical solution provided by this invention has the following beneficial effects:

[0034] (1) The catalyst of this invention introduces fluorine and sulfur elements, which regulates the catalytic hydrogenation activity of the catalyst and effectively controls the selectivity of citral hydrogenation; moreover, fluorine has the strongest electronegativity, and its electron-withdrawing ability makes the conjugated C=C and C=O bonds in citral more likely to combine with the metal in the catalyst, thereby improving the product selectivity.

[0035] (2) In this invention, phenanthroline is used as a substrate for modification. The NM bond formed by nitrogen and metal is conducive to the dispersion of metal, thus exposing more active sites and improving catalytic performance.

[0036] (3) The addition of composite metal sites is beneficial to the enhancement of catalytic activity. In particular, the selected elements such as palladium, copper, nickel and cobalt enable the catalyst to have good binding activity for the conjugated C=C and C=O of citral, and maintain a certain inertness for the terminal C=C, thereby achieving selective hydrogenation of citral to prepare citronellol. Detailed Implementation

[0037] To better understand the technical solution of the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0038] Information on the main sources of raw materials used; unless otherwise specified, all other raw materials are ordinary commercially available:

[0039] 1,10-Phenanthroline-4,7-dicarboxaldehyde: 95wt%, Aladdin Reagent Co., Ltd.;

[0040] 2,2,2-Trifluoroethanethiol: 98wt%, Shanghai Jinjinle Industrial Co., Ltd.;

[0041] Azobisisobutyronitrile: 98wt%, Aladdin Reagent Co., Ltd.;

[0042] Palladium chloride: 99.9 wt%, Aladdin Reagent Co., Ltd.;

[0043] Copper chloride: 99.9 wt%, Aladdin Reagent Co., Ltd.

[0044] Nickel chloride: 99.9 wt%, Aladdin Reagent Co., Ltd.;

[0045] Cobalt chloride: 99.9 wt%, Aladdin Reagent Co., Ltd.

[0046] THF: 99wt%, Comio Reagent Co., Ltd.

[0047] Citral: purity ≥98%, Hubei Julongtang Pharmaceutical Chemical Co., Ltd., wherein neraldehyde: geranialdehyde (mass ratio) is 1:1;

[0048] Nuclear magnetic resonance spectrometer model: BRUKER AVANCE Ⅲ 400.

[0049] Gas chromatograph: Agilent 7890, column DB-5 (conversion determination), injection port temperature: 300℃; split ratio 50:1; carrier gas flow rate: 52.8 ml / min; temperature program: hold at 95℃ for 40 min, increase to 180℃ at a rate of 10℃ / min, hold for 40 min; detector temperature: 280℃.

[0050] Example 1

[0051] Step 1: Mix 1 mol of 1,10-phenanthroline-4,7-dicarboxaldehyde, 2 mol of 2,2,2-trifluoroethanethiol and 0.03 mol of azobisisobutyronitrile, and reflux at 110 °C for 6 h with 1000 ml of toluene as solvent. After the reaction is complete, wash with 2000 ml of ethanol and then remove volatile components by vacuum distillation to obtain 0.89 mol of ligand.

[0052] H-NMR (400MHz, CDCl3): δ8.69(2H), 7.37(2H), 7.98(2H), 3.67(2H), 2.96(2H).

[0053] Step 2: At 80℃, 0.5 mol palladium chloride and 0.7 mol copper chloride were dissolved in THF. While maintaining this temperature, 0.1 mol of the product from Step 1 was added and reacted for 3 hours. After rotary evaporation, the product was washed with 1000 ml of ethanol to obtain crude catalyst. Then, it was washed with 500 ml of deionized water and placed in a vacuum oven at 60℃ for 4 hours to obtain 0.087 mol of catalyst product.

[0054] 0.5 g of bimetallic catalyst and 100 g of citral were added sequentially to a 500 ml hydrogenation reactor. The reactor was sealed, and the mixture was purged three times each with nitrogen and hydrogen. Heating and stirring were then initiated. When the temperature reached 80 °C, hydrogen was introduced to a pressure of 3 MPa, which was maintained for 6 hours until the reaction was complete. The reaction results were analyzed by GC, and the results are shown in Table 1.

[0055] Example 2

[0056] Step 1: Mix 1 mol of 1,10-phenanthroline-4,7-dicarboxaldehyde, 2.3 mol of 2,2,2-trifluoroethanethiol and 0.05 mol of azobisisobutyronitrile, and reflux at 100°C for 8 h with 1000 ml of toluene as solvent. After the reaction is complete, wash with 2000 ml of ethanol and then remove volatile components by vacuum distillation to obtain 0.87 mol of ligand.

[0057] Step 2: At 70℃, 0.6 mol of copper chloride and 0.6 mol of nickel chloride were dissolved in THF. While maintaining this temperature, 0.1 mol of the product from Step 1 was added to the solution. The reaction was carried out for 5 hours. After rotary evaporation, the product was washed with 1000 ml of ethanol to obtain crude catalyst. Then, it was washed with 500 ml of deionized water and placed in a vacuum oven at 60℃ for 4 hours to obtain 0.091 mol of catalyst product.

[0058] 1 g of bimetallic catalyst and 100 g of citral were added sequentially to a 500 ml hydrogenation reactor. The reactor was sealed, and the mixture was purged three times each with nitrogen and hydrogen. Heating and stirring were then initiated. When the temperature reached 70 °C, hydrogen was introduced to a pressure of 2 MPa, which was maintained for 4 hours until the reaction was complete. The reaction results were analyzed by GC, and the results are shown in Table 1.

[0059] Example 3

[0060] Step 1: Mix 1 mol of 1,10-phenanthroline-4,7-dicarboxaldehyde, 2.2 mol of 2,2,2-trifluoroethanethiol and 0.03 mol of azobisisobutyronitrile, and reflux at 110 °C for 6 h with 1000 ml of toluene as solvent. After the reaction is complete, wash with 2000 ml of ethanol and then remove volatile components by vacuum distillation to obtain 0.91 mol of ligand.

[0061] Step 2: At 80℃, 0.5 mol of nickel chloride and 0.5 mol of cobalt chloride were dissolved in THF. While maintaining this temperature, 0.1 mol of the product from Step 1 was added to the solution. The reaction was carried out for 4 hours. After rotary evaporation, the product was washed with 1000 ml of ethanol to obtain crude catalyst. Then, it was washed with 500 ml of deionized water and placed in a vacuum oven at 60℃ for 4 hours to obtain 0.093 mol of catalyst product.

[0062] 1 g of bimetallic catalyst and 100 g of citral were added sequentially to a 500 ml hydrogenation reactor. The reactor was sealed, and the mixture was purged three times each with nitrogen and hydrogen. Heating and stirring were then initiated. When the temperature reached 70 °C, hydrogen was introduced to a pressure of 3 MPa, which was maintained for 4 hours until the reaction was complete. The reaction results were analyzed by GC, and the results are shown in Table 1.

[0063] Example 4

[0064] Step 1: Mix 1 mol of 1,10-phenanthroline-4,7-dicarboxaldehyde, 2.1 mol of 2,2,2-trifluoroethanethiol and 0.02 mol of azobisisobutyronitrile, and reflux at 110 °C for 7 h with 1000 ml of toluene as solvent. After the reaction is complete, wash with 2000 ml of ethanol and then remove volatile components by vacuum distillation to obtain 0.86 mol of ligand.

[0065] Step 2: At 70℃, 0.8 mol palladium chloride and 0.6 mol cobalt chloride were dissolved in THF. While maintaining this temperature, 0.1 mol of the product from Step 1 was added and reacted for 4 hours. After rotary evaporation, the product was washed with 1000 ml of ethanol to obtain crude catalyst, then washed with 500 ml of deionized water, and placed in a vacuum oven at 60℃ for 4 hours to obtain 0.092 mol of catalyst product.

[0066] 1 g of bimetallic catalyst and 100 g of citral were added sequentially to a 500 ml hydrogenation reactor. The reactor was sealed, and the mixture was purged three times each with nitrogen and hydrogen. Heating and stirring were then initiated. When the temperature reached 60 °C, hydrogen was introduced to a pressure of 5 MPa, which was maintained for 4 hours until the reaction was complete. The reaction results were analyzed by GC, and the results are shown in Table 1.

[0067] Example 5

[0068] Step 1: Mix 1 mol of 1,10-phenanthroline-4,7-dicarboxaldehyde, 2.5 mol of 2,2,2-trifluoroethanethiol and 0.01 mol of azobisisobutyronitrile, and reflux at 120 °C for 6 h with 1000 ml of toluene as solvent. After the reaction is complete, wash with 2000 ml of ethanol and then remove volatile components by vacuum distillation to obtain 0.85 mol of ligand.

[0069] Step 2: At 80℃, 0.5 mol of copper chloride and 0.5 mol of cobalt chloride were dissolved in THF. While maintaining this temperature, 0.1 mol of the product from Step 1 was added and reacted for 3 hours. After rotary evaporation, the product was washed with 1000 ml of ethanol to obtain crude catalyst. Then, it was washed with 500 ml of deionized water and placed in a vacuum oven at 60℃ for 4 hours to obtain 0.086 mol of catalyst product.

[0070] 2g of bimetallic catalyst and 100g of citral were added sequentially to a 500ml hydrogenation reactor. The reactor was sealed, and the mixture was purged three times each with nitrogen and hydrogen. Heating and stirring were then initiated. When the temperature reached 70℃, hydrogen was introduced to a pressure of 1MPa and maintained for 2 hours until the reaction was complete. The reaction results were analyzed by GC, and the results are shown in Table 1.

[0071] Comparative Example 1

[0072] Step 1: Mix 1 mol of 1,10-phenanthroline-4,7-dicarboxaldehyde, 2.2 mol of 2,2,2-trifluoroethanethiol and 0.03 mol of azobisisobutyronitrile, and reflux at 110 °C for 6 h with 1000 ml of toluene as solvent. After the reaction is complete, wash with 2000 ml of ethanol and then remove volatile components by vacuum distillation to obtain 0.91 mol of ligand.

[0073] Step 2: At 80℃, 1 mol of nickel chloride was dissolved in THF. While maintaining this temperature, 0.1 mol of the product from Step 1 was added and reacted for 4 hours. After rotary evaporation, the product was washed with 1000 ml of ethanol to obtain crude catalyst. Then, it was washed with 500 ml of deionized water and placed in a vacuum oven at 60℃ for 4 hours to obtain 0.089 mol of catalyst product.

[0074] 1 g of bimetallic catalyst and 100 g of citral were added sequentially to a 500 ml hydrogenation reactor. The reactor was sealed, and the mixture was purged three times each with nitrogen and hydrogen. Heating and stirring were then initiated. When the temperature reached 70 °C, hydrogen was introduced to a pressure of 3 MPa, which was maintained for 4 hours until the reaction was complete. The reaction results were analyzed by GC, and the results are shown in Table 1.

[0075] Comparative Example 2

[0076] Step 1: At 80℃, 0.8 mol palladium chloride and 0.6 mol cobalt chloride were dissolved in THF. While maintaining this temperature, 0.1 mol 1,10-phenanthroline-4,7-dicarboxaldehyde was added. The reaction was carried out for 4 hours. After rotary evaporation, the crude catalyst was washed with 1000 ml ethanol to obtain the crude catalyst product. Then, it was washed with 500 ml deionized water and placed in a vacuum oven at 60℃ for 4 hours to obtain 0.089 mol catalyst product.

[0077] 1 g of bimetallic catalyst and 100 g of citral were added sequentially to a 500 ml hydrogenation reactor. The reactor was sealed, and the mixture was purged three times each with nitrogen and hydrogen. Heating and stirring were then initiated. When the temperature reached 70 °C, hydrogen was introduced to a pressure of 3 MPa, which was maintained for 4 hours until the reaction was complete. The reaction results were analyzed by GC, and the results are shown in Table 1.

[0078] Table 1 Comparative results of the examples

[0079] Example Citronellol Selectivity % Tetrahydrogeraniol selective % Selectivity of other substances / % 1 99.6 0.2 0.2 2 99.4 0.3 0.3 3 99.5 0.3 0.2 4 99.7 0.2 0.1 5 99.5 0.2 0.3 Comparative Example 1 90.5 7.3 2.3 Comparative Example 2 87.6 9.7 2.7

Claims

1. A ligand for a metal complex, having the following structural formula: .

2. The ligand according to claim 1, characterized in that, The method for preparing the ligand includes the following steps: reacting 1,10-phenanthroline-4,7-dicarboxaldehyde with 2,2,2-trifluoroethanethiol.

3. A metal complex with the following structural formula: in, M is one of palladium, copper, nickel, or cobalt.

4. The metal complex according to claim 3, characterized in that, The method for preparing the metal complex includes the following steps: reacting the ligand described in claim 1 or 2 with a salt solution of metal M; wherein the salt of metal M is selected from palladium chloride, copper chloride, nickel chloride, and cobalt chloride.

5. A catalyst composition comprising two or more metal complexes as shown below, 。 6. The catalyst composition according to claim 5, characterized in that, The molar ratio of the two metal complexes is 1:2 to 2:

1.

7. A method for preparing citronellol by hydrogenating citral, comprising the following steps: Using citral as a raw material, a hydrogenation reaction is carried out under the action of the catalyst composition described in claim 5 or 6.

8. The method according to claim 7, characterized in that, The catalyst composition comprises a main catalyst. and co-catalyst The molar ratio of the two is 4:

3.

9. The method according to claim 7 or 8, characterized in that, The catalyst composition is added at an amount of 0.1-2% of the mass of the substrate citral.

10. The method according to claim 9, characterized in that, The catalyst composition is added at an amount of 0.5-2% of the mass of the substrate citral.

11. The method according to claim 9, characterized in that, The hydrogenation reaction temperature is 60~80℃, the hydrogen pressure range is 1~5MPa, and the reaction time is 2~6h.

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