A method for selectively hydrogenating alkynols to prepare enols

Abstract

The present invention discloses a method for preparing enol by selective hydrogenation of alkynol. By adding an acidic substance to adjust the pH value of the reaction system and adding crown ether to inhibit the two main side reactions of self-coupling and over-hydrogenation of terminal alkyne, the purpose of improving low selectivity is achieved. The product has a pure odor and mild reaction conditions.

Description

Technical Field

[0001] The present invention relates to the field of selective catalytic hydrogenation, and particularly to a method for selectively hydrogenating alkynols to prepare enols. Background Art

[0002] As an important class of fine chemical products, enols can be used as intermediates for VE, pyrethroid intermediates, synthetic vitamins A, K1, carotenoid intermediates, synthetic rubber monomers, and fragrances. The synthesis method usually involves selectively hydrogenating alkynols to prepare the corresponding enols. The reaction general formula is:

[0003]

[0004] Wherein, R1 and R2 are hydrogen or hydrocarbon groups.

[0005] In addition, it is found that alkynols will also undergo self-coupling reactions of terminal alkynes during the selective hydrogenation process, reducing selectivity and resulting in a decrease in the final yield. According to the report in Organic Process Research & Development 2009, 13, 991–998, the self-coupling reaction of terminal alkynes occurs during the selective hydrogenation of 2-methyl-3-buten-2-ol. The reaction pathway is as follows:

[0006]

[0007] The self-coupling reaction of terminal alkynes is also known as the Glaser reaction. Glaser first used CuCl as a catalyst and air as an oxidant to successfully convert phenylacetylene into the corresponding conjugated diyne in ammonia water and ethanol. Conjugated diyne derivatives are also a very important class of substances and can be used as organic synthesis intermediates. However, the content of conjugated diynes is less than 3% during the process of selectively hydrogenating alkynols to prepare enols and is difficult to purify. Therefore, the self-coupling reaction of terminal alkynes is one of the main side reactions and needs to be inhibited. Summary of the Invention

[0008] The present invention provides a method for selectively hydrogenating alkynols to prepare enols.

[0009] To solve the above technical problems, the present invention adopts the following technical solutions:

[0010] A method for selectively hydrogenating alkynols to prepare enols, using alkynols as reaction raw materials, reacting under acidic conditions under the combined action of a selective hydrogenation catalyst and a crown ether to prepare enols.

[0011] In the present invention, the selective hydrogenation catalyst is a supported noble metal hydrogenation catalyst. The supported noble metal is preferably palladium, and the carrier is preferably calcium carbonate; the selective hydrogenation catalyst is preferably Lindlar catalyst.

[0012] Further preferably, the mass content of palladium metal supported in the Lindlar catalyst is 0.5% to 50%, preferably 5% to 25%. Lead acetate is usually used to poison the commercially available Lindlar catalyst in advance, and the lead content is preferably less than 15 wt%, more preferably less than 5 wt%. The usage amount of the catalyst for preparing enol by selective hydrogenation of alkynol is 0.1% to 10% of the mass of alkynol, preferably 0.5% to 2%.

[0013] In the present invention, an acidic substance is added to maintain the acidic reaction condition, and the pH value range of the reaction system is 4.0 to 6.0, preferably 4.5 to 5.5. The acidic substance selected to be added can be an inorganic acid or an organic acid, such as sulfuric acid, nitric acid, acetic acid, benzenesulfonic acid, etc., preferably acetic acid.

[0014] In the present invention, the pH value range after adjustment by adding an acidic substance is 4.0 to 6.0. Adjusting the system to an acidic state can reduce the occurrence probability of the self-coupling reaction of terminal alkynes and inhibit the formation of self-coupling products of terminal alkynes; secondly, since the catalyst for selective hydrogenation of alkynol uses calcium carbonate as a carrier, too low a pH value will damage the carrier, so the pH value range is selected to be 4.0 to 6.0.

[0015] In the present invention, the added crown ether can be 12-crown-4, 15-crown-5, 18-crown-6, 24-crown-8, benzo-12-crown-4, dibenzo-18-crown-6, etc., preferably 15-crown-5, 18-crown-6. The amount of crown ether added in the method for preparing enol by selective hydrogenation of alkynol is 1% to 10% of the mass of alkynol, preferably 2% to 5%.

[0016] The main function of adding crown ether in the present invention is that crown ether has special complexing ability for metal cations, and the change of the number of atoms and the size of the macrocyclic cavity has obvious selectivity for different metal ions. The preparation process of the catalyst for selective hydrogenation of alkynol is to deposit noble metal on the carrier and then reduce and immobilize it on the carrier. There are a small amount of unreduced metal ions in the preparation process, and trace metal ions may be introduced by the raw materials and solvents used in the reaction. Metal ions, especially free copper or palladium ions, can catalyze the side reaction of self-coupling of terminal alkynes. Therefore, it is necessary to reduce the interference of free metal ions on the selective hydrogenation of alkynol as the main reaction. Adding crown ether to the system can inhibit the formation of self-coupling products of terminal alkynes, and it is unexpectedly found that the addition of crown ether does not reduce the selectivity of selective hydrogenation of alkynol, but instead slightly improves the selectivity.

[0017] In some preferred embodiments of the present invention, the preparation method of the present invention comprises the following steps: First, under an inert gas atmosphere, a crown ether and a catalyst are mixed. Second, an acidic substance is added to the system to adjust the pH value to a target value, and after the system is heated, hydrogen is introduced to displace the system and reach a set pressure. Third, the reaction substrate alkynol is added to the reaction system, the temperature is maintained, and after the reaction is completed, the temperature is lowered, and the catalyst is separated from the reaction solution.

[0018] Specifically, first, a mixing device is started and under an inert gas atmosphere, the crown ether is mixed with a selective hydrogenation catalyst or a mixture of a selective hydrogenation catalyst and a solvent in the form of a solution or a pure substance. Second, an acidic substance is added to the system to adjust the pH value to a target value, and after the system is heated, hydrogen is introduced to displace the system and reach a set pressure. Third, the reaction substrate alkynol is added to the reaction system at a uniform rate, the temperature is maintained, and the change in gas flow rate is observed. Finally, after the reaction is completed, the temperature is lowered, and the catalyst is separated from the reaction solution by means of filtration, pressure filtration, suction filtration, etc.

[0019] The present invention provides a method for the selective hydrogenation of alkynol to prepare enol. Using an alkynol having the structural general formula I as a substrate, under the action of the catalyst system for the selective hydrogenation of alkynol to prepare enol, an enol having the structural general formula II is formed after a selective hydrogenation reaction:

[0020]

[0021] Wherein, R1 and R2 are hydrogen or hydrocarbon groups, preferably hydrogen or branched or straight-chain C6-C20 alkyl or alkenyl groups, R1 and R2 are the same or different, and more preferably, one of R1 or R2 is hydrogen and the other is a branched or straight-chain C6-C20 alkyl or alkenyl group.

[0022] In the method of the present invention, the alkynol is preferably selected from 2-methyl-3-butyn-2-ol, dehydro linalool, dihydro dehydro linalool, dehydro nerolidol, dihydro dehydro nerolidol, tetrahydro dehydro nerolidol, dehydro isophytol, etc., and their corresponding molecular structures are as follows:

[0023]

[0024] The corresponding selective hydrogenation enol product structure is:

[0025]

[0026] In the method of the present invention, for the selective hydrogenation reaction, the reaction temperature is 0-90°C, preferably 40-70°C, and the reaction time is 0.1-24 h, preferably 2-6 h.

[0027] In the method of the present invention, during the selective hydrogenation reaction, the introduced amount of hydrogen keeps the pressure in the system at 0.05 to 3 MPa (gauge pressure), preferably 0.1 to 2.0 MPa (gauge pressure).

[0028] In the method of the present invention, preferably, the alkynol can be diluted with a solvent, and the solvent is selected from one or more of pure water, inert aliphatic alkanes that do not react with the raw materials, aromatic hydrocarbons, ethers, and alcohols, such as one or more of pure water, n-heptane, toluene, and ethanol; preferably, the amount of the dilution solvent used is 0 to 3 times the mass of the alkynol, preferably 0.5 to 2.0 times.

[0029] The positive effect of the present invention is that by adding an acidic substance to adjust the pH value of the reaction system and adding a crown ether substance, the effects of inhibiting the two main side reactions of terminal alkyne self-coupling and over-hydrogenation are achieved, so that both the conversion rate of the alkynol and the selectivity of the product enol are improved. The goal of achieving an alkynol conversion rate ≥ 98.0% and an enol selectivity ≥ 98.0% is realized.

[0030] In the prior art, the Lindlar catalyst usually needs to be modified by adding other poison agents such as quinoline before it can be used. In this application, by adding a crown ether and adjusting the pH, it is not necessary to use poison agents such as quinoline for treatment to achieve excellent catalytic effects. The product has a pure odor, mild reaction conditions, and is suitable for industrial production. Specific embodiments

[0031] The following examples will further illustrate the process provided by the present invention, but the present invention is not limited to the listed examples, and should also include any other known changes within the scope of the rights required by the present invention.

[0032] I. Analysis method:

[0033] Gas chromatograph: Agilent 7820A, chromatographic column HP-5 (30 m × 320 μm × 0.25 μm), injection port temperature: 150 °C; split ratio 50:1; carrier gas flow rate: 1.5 ml / min; temperature programming: hold at 40 °C for 1 min, increase the temperature to 90 °C at a rate of 10 °C / min, hold for 0 min, then increase the temperature to 160 °C at a rate of 5 °C / min, hold for 0 min, and then increase the temperature to 280 °C at a rate of 30 °C / min, hold for 6 min. Detector temperature: 280 °C.

[0034] II. Sources of main raw materials

[0035] Lindlar catalyst, 5% Pd - 5% Pb palladium-calcium carbonate catalyst, Xinnuoke Technology Co., Ltd.;

[0036] 15-crown-5, 98 wt%, J&K Scientific Ltd.;

[0037] 18-Crown ether-6, 99wt%, Bailingwei Technology Co., Ltd.

[0038] Example 1

[0039] Under an inert gas atmosphere, 100.0 g of ethanol, 1.0 g of 15-crown ether-5 and 1.0 g of 5% Pd-5% Pb palladium-calcium carbonate catalyst were added to the autoclave. Stirring was started and the pH value was adjusted to 5.2 using acetic acid. The autoclave was sealed and replaced with hydrogen 6 times, and the hydrogen pressure was finally maintained at 2.0 MPa (gauge pressure).

[0040] Turn on the heating until the temperature in the autoclave is 60°C, use a horizontal flow pump to add 100.0g of dehydrolinalool to the autoclave, and control the addition time of dehydrolinalool to about 0.5h. After the addition of dehydrolinalool is completed, keep the temperature in the reactor at 60°C to continue the reaction. After continuing the reaction for 3.5h, the flow rate of the hydrogen flow meter in the reactor drops below 0.5mL / min, stop stirring and vent the hydrogen. GC analyzes the reaction solution, and the reaction solution composition: linalool content 98.666%, dihydrolinalool content 0.313%, 15-crown ether-5 content 0.977%, terminal alkyne self-coupling content 0.015%, and other components content 0.029%. Alkynol conversion rate>99.99%, enol selectivity 99.64%.

[0041] Example 2

[0042] Under an inert gas atmosphere, 100.0 g of toluene, 2.0 g of 18-crown ether-6 and 1.0 g of 5% Pd-5% Pb palladium-calcium carbonate catalyst were added to the autoclave. Stirring was started and the pH value was adjusted to 5.5 using acetic acid. The autoclave was sealed and replaced with hydrogen 6 times, and the hydrogen pressure was finally maintained at 2.0 MPa (gauge pressure).

[0043] Turn on the heating until the temperature in the autoclave is 70°C, use a horizontal flow pump to add 100.0g of dehydroisophytol to the autoclave, and control the addition time of dehydroisophytol to about 0.5h. After the addition of dehydroisophytol is completed, keep the temperature in the reactor at 70°C to continue the reaction. After continuing the reaction for 2.5h, the flow rate of the hydrogen flowmeter of the reactor drops below 0.5mL / min, stop stirring and vent the hydrogen. GC analyzes the reaction solution, and the reaction solution composition: dehydroisophytol 0.015%, isophytol content 97.730%, dihydroisophytol content 0.273%, 18-crown ether-6 content 1.948%, terminal alkyne self-coupling content 0.009%, and other components content 0.025%. Alkynol conversion rate 99.985%, enol selectivity 99.69%.

[0044] Example 3

[0045] Under an inert gas atmosphere, 100.0 g of toluene, 5.0 g of 18-crown ether-6 and 10.0 g of 5% Pd-5% Pb palladium-calcium carbonate catalyst were added to the autoclave. Stirring was started and the pH value was adjusted to 4.1 using acetic acid. The autoclave was sealed and replaced with hydrogen 6 times, and the hydrogen pressure was finally maintained at 0.5 MPa (gauge pressure).

[0046] Turn on the heating until the temperature in the autoclave is 40°C, use a horizontal flow pump to add 100.0g of dehydroisophytol to the autoclave, and control the addition time of dehydroisophytol to about 0.5h. After the addition of dehydroisophytol is completed, keep the temperature in the reactor at 40°C to continue the reaction. After continuing the reaction for 2.0h, the flow rate of the hydrogen flow meter of the reactor drops below 0.5mL / min, stop stirring and vent the hydrogen. GC analyzes the reaction solution, and the reaction solution composition: dehydroisophytol 0.031%, isophytol content 95.015%, dihydroisophytol content 0.199%, 18-crown ether-6 content 4.731%, terminal alkyne self-coupling content 0.003%, and other components content 0.021%. Alkynol conversion rate 99.97%, enol selectivity 99.77%.

[0047] Example 4

[0048] Under an inert gas atmosphere, 100.0 g of toluene, 9.0 g of 18-crown ether-6 and 5.0 g of 5% Pd-5% Pb palladium-calcium carbonate catalyst were added to the autoclave. Stirring was started and the pH value was adjusted to 4.5 with acetic acid. The autoclave was sealed and replaced with hydrogen 6 times, and the hydrogen pressure was finally maintained at 1.0 MPa (gauge pressure).

[0049] Turn on the heating until the temperature in the autoclave is 50°C, use a horizontal flow pump to add 100.0g of dehydrogenated nerolidol to the autoclave, and control the addition time of dehydrogenated nerolidol to about 0.5h. After the addition of dehydrogenated nerolidol, keep the temperature in the reactor at 50°C to continue the reaction. After continuing the reaction for 4.0h, the flow rate of the hydrogen flow meter of the reactor drops below 0.5mL / min, stop stirring and vent the hydrogen. GC analyzes the reaction solution, the reaction solution composition: nerolidol content 91.434%, dihydronerolidol content 0.355%, 18-crown ether-6 content 8.189%, terminal alkyne self-coupling content 0.002%, and other components content 0.020%. Alkynol conversion rate>99.99%, enol selectivity 99.59%.

[0050] Comparative Example 1

[0051] Under an inert gas atmosphere, 100.0 g of ethanol and 1.0 g of 5% Pd-5% Pb palladium-calcium carbonate catalyst were added to the autoclave, stirring was started, the autoclave was sealed, and hydrogen was replaced 6 times, and finally the hydrogen pressure was maintained at 2.0 MPa (gauge pressure).

[0052] Turn on the heating until the temperature in the autoclave is 60°C, use a horizontal flow pump to add 100.0g of dehydrolinalool to the autoclave, and control the addition time of dehydrolinalool to about 0.5h. After the addition of dehydrolinalool is completed, keep the temperature in the reactor at 60°C to continue the reaction. After continuing the reaction for 3.5h, the flow rate of the hydrogen flow meter of the reactor drops below 0.5mL / min, stop stirring and vent the hydrogen. GC analyzes the reaction solution, and the reaction solution composition: linalool content 95.788%, dihydrolinalool content 2.527%, 18-crown ether-6 content 0.986%, terminal alkyne self-coupling content 0.284%, and other components content 0.415%. Alkynol conversion rate>99.9%, enol selectivity 96.74%.

Claims

1. A method for preparing enol by selective hydrogenation of alkynol, characterized in that, Using an alkynol as a reaction raw material, under acidic conditions, reacting in the co - action of a Lindlar catalyst and a crown ether to prepare an enol; The Lindlar catalyst is a supported noble metal hydrogenation catalyst, the supported noble metal is palladium, and the carrier is calcium carbonate; the pH value range of the reaction system is 4.0 - 6.0; The general structural formula Ⅰ of the alkynol is as follows, The structural formula of the enol is as follows: Wherein, R1 and R2 are the same or different, and R1, R2 are hydrogen, branched or straight - chain C6 - C20 alkyl groups, branched or straight - chain C6 - C20 alkenyl groups.

2. The method according to claim 1, wherein The mass content of the supported palladium metal in the Lindlar catalyst is 0.5% - 50%.

3. The method according to claim 2, wherein The mass content of the supported palladium metal in the Lindlar catalyst is 5% - 25%.

4. The method according to claim 1, wherein The usage amount of the Lindlar catalyst is 0.1% - 10% of the mass of the alkynol.

5. The method according to claim 4, wherein The usage amount of the Lindlar catalyst is 0.5% - 2% of the mass of the alkynol.

6. The method according to claim 1, characterized in that, Maintaining the acidic condition of the reaction by adding an acidic substance, and the pH value range of the reaction system is 4.5 - 5.

5.

7. The method according to claim 6, characterized in that The acidic substance is an inorganic acid or an organic acid.

8. The method according to claim 7, wherein The acidic substance is sulfuric acid, nitric acid, acetic acid, benzenesulfonic acid.

9. The method according to claim 8, wherein The acidic substance is acetic acid.

10. The method according to claim 1, characterized in that, The crown ether is selected from 12 - crown - 4, 15 - crown - 5, 18 - crown - 6, 24 - crown - 8, benzo - 12 - crown - 4, dibenzo - 18 - crown - 6.

11. The method according to claim 1, wherein The crown ether is one or more of 15 - crown - 5 and 18 - crown - 6.

12. The method according to claim 1, characterized in that, The addition amount of the crown ether is 1% - 10% of the mass of the alkynol.

13. The method according to claim 12, wherein The addition amount of the crown ether is 2% - 5% of the mass of the alkynol.

14. The method according to claim 1, wherein Including: First, under an inert gas atmosphere, mixing the crown ether and the catalyst. Secondly, adding an acidic substance to the system to adjust the pH value to the target value, heating the system and then introducing hydrogen to displace the system to the set pressure. Adding the reaction substrate alkynol to the reaction system, keeping warm. After the reaction is completed, cooling down, and separating the catalyst from the reaction solution.

15. The method according to claim 1, characterized in that, One of R1 or R2 is hydrogen, and the other is a branched or straight - chain C6 - C20 alkyl group, a branched or straight - chain C6 - C20 alkenyl group.

16. The method according to claim 1, wherein The alkynol is selected from 2 - methyl - 3 - butyn - 2 - ol, dehydro - linalool, dihydro - dehydro - linalool, dehydro - nerolidol, dihydro - dehydro - nerolidol, tetrahydro - dehydro - nerolidol or dehydro - isophytol.

17. The method according to claim 1, characterized in that The reaction temperature is 0 - 90 °C, and the reaction time is 0.1 - 24 h.

18. The method according to claim 17, wherein The reaction temperature is 40 - 70 °C, and the reaction time is 2 - 6 h.

19. The method according to claim 1, wherein The introduction amount of hydrogen keeps the pressure in the system at 0.05 - 3 MPa.

20. The method according to claim 19, characterized in that, The introduction amount of hydrogen keeps the pressure in the system at 0.1 - 2.0 MPa.

21. The method according to claim 1, wherein In the said reaction, the alkynol is diluted with a solvent, and the solvent is selected from one or more of pure water, inert aliphatic alkanes that do not react with the raw materials, aromatic hydrocarbons, ethers, and alcohols.

22. The method according to claim 21, wherein The solvent is one or more of pure water, n - heptane, toluene, and ethanol.

23. The method according to claim 22, wherein The usage amount of the dilution solvent is 0 - 3 times the mass of the alkynol.

24. The method according to claim 23, wherein The usage amount of the dilution solvent is 0.5 - 2.0 times the mass of the alkynol.

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