Preparation method of high-purity linalool

Abstract

The application provides a method for preparing high-purity linalool by homogeneous hydrogenation of dehydrolinalool. By controlling the content of substance A in the dehydrolinalool, preferably also controlling the molar concentration of a palladium catalyst in the reaction solution, the reaction temperature and the reaction residence time, the reaction conversion rate is greater than or equal to 99.8%, the reaction selectivity is greater than or equal to 99.5%, and the purity of the product linalool is greater than or equal to 99.5%, and the product has good aroma, the catalyst consumption is small, the operation is simple, and the operation time is short. The structure of the substance A is:

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a method for preparing high-purity linalool by homogeneous hydrogenation of dehydrolinalool. Background Technology

[0002] Linalool is an important fragrance product, with global annual consumption exceeding 30,000 tons, making it one of the most widely used fragrances. The purity of linalool significantly affects its aroma. Currently, the industrial process commonly uses dehydrolinalool to produce linalool via heterogeneous hydrogenation in the presence of a Lindlar catalyst (Pb-poisoned Pd-CaCO3). To improve the selectivity of the reaction, auxiliaries such as quinoline and pyridine are added to the system. However, the introduction of organic amine auxiliaries such as quinoline and pyridine has a certain impact on the aroma of the product linalool.

[0003] Patent CN 201910449643 reports the use of metals such as iron, zinc, and cobalt to poison Pd-CaCO3 catalyze the hydrogenation of alkynols to prepare enols. This method is applied to the hydrogenation of dehydrolinalool under a syngas atmosphere, achieving a selectivity of up to 97.5%.

[0004] Many patents and literature reports have also described the selective hydrogenation of other alkynols to prepare enols. For example, patent CN101869845 reports the use of Lindlar catalysts doped with metals such as Mn, Bi, and Zn for the selective hydrogenation of dehydroisophytols, with selectivity of the target product isophytol exceeding 98%. However, the catalyst preparation process is cumbersome. Literature Journal of Catalysis 251 (2007) 213–222 reports the use of ZnO-coated sintered metal fibers as a support to load Pd nanoparticles for catalytic hydrogenation to prepare 2-methyl-3-buten-2-ol, with a maximum target product yield of only 95%. Literature Reaction Chemistry Engineering, 2016, 1, 445-453 reports the use of a Pd / ZnO catalyst for the catalytic hydrogenation to prepare 2-methyl-3-buten-2-ol, but the catalyst was only reused 6 times, and the target product selectivity was only around 95%.

[0005] Existing methods for preparing linalool based on Lindlar catalysts have the following shortcomings:

[0006] (1) The reaction selectivity is generally around 96%, and the main byproduct is dihydrolinalool, which is difficult to separate from linalool, resulting in low purity of linalool product (around 98%).

[0007] (2) The reaction catalyst is used in large quantities at a time and needs to be recycled multiple times to reduce costs; the catalyst will lead to a significant increase in filtration time and operation time as the number of times it is recycled increases.

[0008] (3) The catalyst has a limited lifespan and the palladium is gradually lost as it is used, resulting in a decrease in reaction activity. It is necessary to activate or replenish the catalyst regularly. Summary of the Invention

[0009] To address the problems of low linalool purity, long catalyst recycling time, and limited catalyst life in existing Lindlar catalyst preparation methods, this invention provides a method for homogeneous hydrogenation of dehydrolinalool to prepare high-purity linalool. By controlling the content of key impurity A in the raw materials, a reaction conversion rate of ≥99.8%, a reaction selectivity of ≥99.5%, and a product linalool purity of ≥99.5% can be achieved.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A method for preparing high-purity linalool includes: a homogeneous hydrogenation reaction of dehydrolinalool in the presence of a palladium catalyst and hydrogen to produce linalool with a purity ≥99.5%, as shown in the following reaction formula:

[0012]

[0013] The content (C1) of the key impurity A in dehydrolinalool is controlled within 5–1000 ppm, based on the mass of dehydrolinalool; the structure of A is:

[0014]

[0015] Impurity A is produced by the thermal cyclization of dehydrolinalool. Since it is an isomer of dehydrolinalool and has a similar boiling point, it cannot be completely removed. Reducing the content of impurity A typically requires a very high theoretical plate number or a large reflux ratio, which significantly increases energy consumption. Through our study of the formation pattern of impurity A, we found that controlling the operating temperature and residence time of dehydrolinalool distillation can control the content of A within a certain range.

[0016] In this invention, the molar concentration (C2) of palladium catalyst in the reaction solution is 10-100 ppm, the reaction temperature (T) is 20-60℃, and the reaction residence time (t) is 3-5 h.

[0017] In this invention, more preferably, C1, C2, T, and t numerically satisfy the following relationship:

[0018]

[0019] In one specific embodiment, the palladium catalyst is one or more of bis(acetonitrile)palladium(II), bis(ethylenediamine)palladium(II), and (ethylenediamine)palladium(II), preferably bis(ethylenediamine)palladium(II).

[0020] In one specific embodiment, the hydrogen pressure of the homogeneous hydrogenation reaction is 1 to 10 MPaG, preferably 4 to 6 MPaG.

[0021] In one specific embodiment, the homogeneous hydrogenation reaction has a conversion rate of ≥99.8% and a selectivity of ≥99.5%.

[0022] In one specific embodiment, the homogeneous hydrogenation reaction is carried out under solvent-free or solvent-containing conditions, and the solvent may be selected from one or more of methanol, ethanol, acetone, and ethyl acetate.

[0023] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0024] 1) By controlling the content of key impurity A in the raw materials, and by simultaneously controlling the catalyst concentration, reaction residence time and reaction temperature, this invention can achieve a reaction conversion rate of ≥99.8%, a reaction selectivity of ≥99.5%, and a linalool purity of ≥99.5% in the product, with less waste and a good aroma in the product.

[0025] 2) The present invention uses less catalyst, does not require catalyst recycling, and has a significantly lower cost than the traditional process of preparing linalool using Lindlar catalyst. The operation process is simple and the operation time is short. Detailed Implementation

[0026] To better understand the technical solution of the present invention, the following embodiments will further illustrate the method provided by the present invention. However, the present invention is not limited to the listed embodiments, but should also include any other known modifications within the scope of the claims of the present invention.

[0027] The main reagent sources for each embodiment and comparative example are as follows:

[0028] Dehydrolinalool, purity ≥98%; bis(acetonitrile)palladium(II), bis(ethylenediamine)palladium(II), (ethylenediamine)palladium(II), purity ≥99%, Aladdin reagent.

[0029] NMR characterization data of impurity A: 1 H-NMR (500MHz, CDCl3): δ1.41(s,3H), 1.57-1.65(m,1H), 1.66(s,3H), 1.77-1.8 4(m,3H), 1.86-1.91(m,1H), 3.22(m,1H), 4.82(m,2H), 4.86(m,1H), 5.21(m,1H);

[0030] GC-MS:C 10 H 16O, MW = 152.23.

[0031] In the examples, by controlling the temperature of the dehydrolinalool distillation column to not exceed 85°C and the residence time to 2-6 hours, dehydrolinalool with an impurity A content of 5-1000 ppm can be obtained.

[0032] Methanol, ethanol, acetone, AR, Xilong Chemical.

[0033] The gas chromatography testing conditions used in this invention are as follows:

[0034] Instrument model: Agilent 7890B;

[0035] Injection volume: 0.5 μL;

[0036] Inlet temperature: 250℃;

[0037] Flow split ratio: 30 / 1;

[0038] Column: Agilent INNOWax, 30m × 250μm × 0.25μm;

[0039] Column flow rate: 1.5 mL / min;

[0040] Temperature program: Start at 80℃, increase to 250℃ at 10℃ / min, hold for 10min;

[0041] Detector temperature: 250℃; air flow rate: 400mL / min; hydrogen flow rate: 40mL / min; nitrogen flow rate: 25mL / min.

[0042] Example 1

[0043] 152.23 g of dehydrolinalool (purity 99.49%, impurity A content 5.1 ppm) and 3.0 mg of bis(ethylenediamine)palladium chloride (molar concentration 10 ppm) were added to a 0.5 L high-pressure reactor. The reactor was purged three times with nitrogen, followed by three purgings with hydrogen. The reactor temperature was maintained at 20 °C using a cooling water coil. Hydrogen gas was introduced into the reactor at 10 MPaG, and the hydrogen pressure was maintained at 10 MPaG throughout the reaction. After 3 hours of reaction, a sample was taken for GC analysis, showing a dehydrolinalool conversion of 99.8% and a linalool selectivity of 99.7%. The reactor was depressurized and purged with nitrogen. The reaction liquid was discharged and distilled under reduced pressure (controlled pressure 1 kPaG, collecting the 80 °C fraction) to obtain the linalool product with a purity of 99.8%.

[0044] Example 2

[0045] 152.23 g of dehydrolinalool (purity 99.51%, impurity A content 915.5 ppm) and 29.8 mg of bis(ethylenediamine)palladium chloride (molar concentration 100 ppm) were added to a 0.5 L high-pressure reactor. The reactor was purged three times with nitrogen, followed by three purgings with hydrogen. The reactor was heated, and the internal temperature was controlled at 40 °C using a cooling water coil. 1 MPaG of hydrogen was introduced into the reactor, and the hydrogen pressure was maintained at 1 MPaG throughout the reaction. After 4 hours of reaction, a sample was taken for GC analysis, showing a 100% conversion of dehydrolinalool and a linalool selectivity of 99.5%. The reactor was depressurized and purged with nitrogen. The reaction liquid was discharged, and the product was obtained by vacuum distillation (controlled pressure 1 kPaG, collecting the 80 °C fraction) to obtain linalool product with a purity of 99.6%.

[0046] Example 3

[0047] 152.23 g of dehydrolinalool (purity 99.48%, impurity A content 107.4 ppm) and 4.7 mg of palladium chloride (molar concentration 20 ppm) (ethylenediamine) were added to a 0.5 L high-pressure reactor. The reactor was purged three times with nitrogen, followed by three purgings with hydrogen. The reactor was heated, and the internal temperature was controlled at 60 °C using a cooling water coil. 6 MPaG of hydrogen was introduced into the reactor, and the hydrogen pressure was maintained at 6 MPaG throughout the reaction. After 3 hours of reaction, a sample was taken for GC analysis, showing a dehydrolinalool conversion of 99.9% and a linalool selectivity of 99.6%. The reactor was depressurized and purged with nitrogen. The reaction liquid was discharged, and the product was obtained by vacuum distillation (controlled pressure 1 kPaG, collecting the 80 °C fraction) to obtain linalool product with a purity of 99.5%.

[0048] Example 4

[0049] 152.23 g of dehydrolinalool (purity 99.47%, impurity A content 528.3 ppm) and 13 mg of bis(acetonitrile)palladium chloride (molar concentration 50 ppm) were added to a 0.5 L high-pressure reactor. The reactor was purged three times with nitrogen, followed by three purgings with hydrogen. The reactor was heated, and the internal temperature was controlled at 50 °C using a cooling water coil. 4 MPaG of hydrogen was introduced into the reactor, and the hydrogen pressure was maintained at 4 MPaG throughout the reaction. After 3.5 h of reaction, a sample was taken for GC analysis, showing a dehydrolinalool conversion of 99.9% and a linalool selectivity of 99.5%. The reactor was depressurized and purged with nitrogen. The reaction liquid was discharged, and the product was obtained by vacuum distillation (controlled pressure 1 kPaG, collecting the 80 °C fraction) to obtain linalool product with a purity of 99.6%.

[0050] Example 5

[0051] 152.23 g of dehydrolinalool (purity 99.53%, impurity A content 533.6 ppm) and 6.0 mg of bis(ethylenediamine)palladium chloride (molar concentration 20 ppm) were added to a 0.5 L high-pressure reactor. The reactor was purged three times with nitrogen, followed by three purgings with hydrogen. The reactor was heated, and the internal temperature was controlled at 60 °C using a cooling water coil. 6 MPaG of hydrogen was introduced into the reactor, and the hydrogen pressure was maintained at 6 MPaG throughout the reaction. After 3 hours of reaction, a sample was taken for GC analysis, showing a dehydrolinalool conversion of 99.9% and a linalool selectivity of 99.8%. The reactor was depressurized and purged with nitrogen. The reaction liquid was discharged, and the product was obtained by vacuum distillation (controlled pressure 1 kPaG, collecting the 80 °C fraction) to obtain linalool product with a purity of 99.9%.

[0052] Comparative Example 1

[0053] 152.23 g of dehydrolinalool (purity 99.61%, impurity A content 2000.3 ppm) and 6.0 mg of bis(ethylenediamine)palladium chloride (molar concentration 20 ppm) were added to a 0.5 L high-pressure reactor. The reactor was purged three times with nitrogen, followed by three purgings with hydrogen. The reactor was heated, and the internal temperature was controlled at 60 °C using a cooling water coil. 6 MPaG of hydrogen was introduced into the reactor, and the hydrogen pressure was maintained at 6 MPaG throughout the reaction. After 3 hours of reaction, a sample was taken for GC analysis. The conversion rate of dehydrolinalool was 99.9%, the selectivity of linalool was 98.3%, and the selectivity of dihydrolinalool was 1.4%. The reactor was depressurized and purged with nitrogen. The reaction liquid was discharged, and the product was obtained by vacuum distillation (controlled pressure 1 kPaG, collecting the 80 °C fraction) to obtain linalool product with a purity of 98.1%.

[0054] Comparative Example 2

[0055] 152.23 g of dehydrolinalool (purity 99.75%, impurity A content 537.2 ppm) and 6.0 mg of bis(ethylenediamine)palladium chloride (molar concentration 20 ppm) were added to a 0.5 L high-pressure reactor. The reactor was purged three times with nitrogen, followed by three purgings with hydrogen. The reactor was heated, and the internal temperature was controlled at 70 °C using a cooling water coil. 6 MPaG of hydrogen was introduced into the reactor, and the hydrogen pressure was maintained at 6 MPaG throughout the reaction. After 4 hours of reaction, a sample was taken for GC analysis. The conversion rate of dehydrolinalool was 99.8%, the selectivity of linalool was 97.9%, and the selectivity of dihydrolinalool was 1.8%. The reactor was depressurized and purged with nitrogen. The reaction liquid was discharged, and the product was obtained by vacuum distillation (controlled pressure 1 kPaG, collecting the 80 °C fraction) with a purity of 98.0%.

Claims

1. A method for preparing high purity linalool, characterized by, The application relates to a method for preparing linalool by homogeneous hydrogenation reaction of dehydro-linalool in the presence of a palladium catalyst and hydrogen. The dehydro-linalool contains 5-1000 ppm of substance A, and the structure of the substance A is as follows: The molar concentration of the palladium catalyst in the reaction solution is 10-100 ppm, the reaction temperature is 20-60 DEG C, and the reaction residence time is 3-5 h. The content C1 of the substance A in the dehydro-linalool, the molar concentration C2 of the palladium catalyst in the reaction solution, the reaction temperature T and the reaction residence time t satisfy the following relation: The palladium catalyst is one or more of bis(acetonitrile) palladium (II) chloride, bis(ethylenediamine) palladium (II) chloride and (ethylenediamine) palladium (II) chloride.

2. The method of claim 1, wherein, The hydrogen pressure of the homogeneous hydrogenation reaction is 1-10 MPaG.

3. The method according to any of claims 1-2, characterized in that, The hydrogen pressure of the homogeneous hydrogenation reaction is 4-6 MPaG.

4. The method of claim 3, wherein, The homogeneous hydrogenation reaction is carried out in the absence of a solvent or in the presence of a solvent, and the solvent is one or more of methanol, ethanol and acetone.

5. The method according to any of claims 1-2, characterized by, The homogeneous hydrogenation reaction is carried out in the absence of a solvent.

6. The method according to any one of claims 1-2, characterized in that, ​

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