Method for preparing 3-cyclohexyl propionic acid through solvent-free hydrogenation

Abstract

The invention provides a method for preparing 3-cyclohexyl propionic acid through solvent-free hydrogenation, and belongs to the technical field of organic synthesis. The method for preparing 3-cyclohexylpropionic acid through solvent-free hydrogenation provided by the invention comprises the following steps: mixing molten cinnamic acid with a catalyst, introducing hydrogen, and carrying out a hydrogenation reaction; and separating the catalyst in the hydrogenation reaction product to obtain the 3-cyclohexyl propionic acid. No solvent is used for reaction, so that the solvent consumption is reduced, and the production cost is reduced; the post-treatment process of acidification layering is reduced, the whole process is few, the production efficiency is improved, the loss of the intermediate process is reduced, and the actual yield is higher than that of a solvent method; and no solvent and no post-treatment by-product exist, so that the method accords with the green production development trend.

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, and in particular to a method for preparing 3-cyclohexylpropionic acid by hydrogenation without solvent. Background Art

[0002] 3-Cyclohexanepropionic acid allyl ester, also known as pineapple ester, has the aroma of pineapple and is often used as a flavoring agent. 3-Cyclohexanepropionic acid (3-CyclohexanepropionicAcid) is the main precursor for the synthesis of pineapple ester.

[0003] There are two main methods for synthesizing 3-cyclohexylpropionic acid: one is to use methyl acrylate and cyclohexanol as raw materials, synthesize γ,γ-cyclopentylbutyrolactone through ester exchange reaction, and then obtain 3-cyclohexylpropionic acid through hydrogenation reaction; the second is to add silver carbon catalyst to alkaline solution, then add cinnamic acid, then pass hydrogen, heat and hydrogenate to obtain 3-cyclohexylpropionic acid. The second method is a one-step method to directly synthesize 3-cyclohexylpropionic acid, optimize the synthesis process, improve efficiency and reduce cost, and is currently the most widely used method.

[0004] However, this method also has its shortcomings, such as: the process is cumbersome, alkaline solution is needed to dissolve the raw materials in the early stage, hydrochloric acid is needed for post-treatment, and oil-water separation is required to obtain the product, which affects the overall yield; the use and removal of solvents increase the synthesis cost, which is not conducive to the market competitiveness of the product; the use of solvents will have a certain impact on the environment, which is not conducive to the development requirements of green chemistry. Therefore, developing a hydrogenation method that is simpler to operate and does not use solvents is conducive to the healthy development of products. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing 3-cyclohexylpropionic acid by solvent-free hydrogenation. The method provided by the present invention does not use a solvent, reduces production costs and environmental pressure, reduces intermediate processes and post-processing steps, and greatly improves production efficiency.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing 3-cyclohexylpropionic acid by solvent-free hydrogenation, comprising:

[0008] The molten cinnamic acid is mixed with a catalyst and then hydrogen is introduced to carry out a hydrogenation reaction;

[0009] The catalyst in the product of the hydrogenation reaction is separated to obtain 3-cyclohexylpropionic acid.

[0010] Preferably, the catalyst comprises a ruthenium, gold, platinum or palladium catalyst, or a nickel-based nanocatalyst.

[0011] Preferably, the amount of the catalyst used is 2-10% of the mass of the cinnamic acid.

[0012] Preferably, the hydrogenation reaction is carried out under stirring conditions.

[0013] Preferably, the temperature of the hydrogenation reaction is 110-150°C.

[0014] Preferably, the pressure of the hydrogenation reaction is maintained at 0.5-5 MPa.

[0015] Preferably, the pressure of the hydrogenation reaction is maintained at 2-5 MPa.

[0016] Preferably, after the separation, the obtained liquid is distilled under reduced pressure to obtain 3-cyclohexylpropionic acid.

[0017] Preferably, the pressure of the reduced pressure distillation is -(0.05-0.1) MPa, the liquid phase temperature is 160-180°C, and the gas phase temperature is 140-160°C.

[0018] Preferably, the yield of the 3-cyclohexylpropionic acid is greater than 95%, and the purity is greater than 99%.

[0019] The present invention provides a method for preparing 3-cyclohexylpropionic acid by solvent-free hydrogenation, comprising: mixing molten cinnamic acid with a catalyst, introducing hydrogen, and performing a hydrogenation reaction; separating the catalyst from the product of the hydrogenation reaction to obtain 3-cyclohexylpropionic acid. The melting point of cinnamic acid is 133°C, which is close to the reaction temperature of solvent hydrogenation, and the hydrogenation reaction can be carried out in a molten state; the melting point of the product 3-cyclohexylpropionic acid is 15°C, and it is in a liquid state after the reaction is completed. The catalyst can be separated at room temperature to obtain a high-purity product; in the present invention, no solvent is used for the reaction, which reduces solvent consumption and reduces production costs; the post-processing steps of acidification and stratification are reduced, the overall process is less, the production efficiency is improved, and the intermediate process loss is reduced, and the actual yield is higher than that of the solvent method; there is no solvent and no post-processing by-products, which conforms to the development trend of green production. The results of the examples show that the production process for preparing 3-cyclohexylpropionic acid by solvent-free hydrogenation provided by the present invention has a product yield of 99%, which is higher than the 98.04% of the solvent method; compared with the solvent method, the solvent cost per ton of product can be reduced by 15,000 yuan, and the production efficiency is improved by 464%. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 GC spectrum of 3-cyclohexylpropionic acid prepared in Example 1;

[0021] Figure 2 GC spectrum of 3-cyclohexylpropionic acid prepared in Comparative Example 2;

[0022] Figure 3GC spectrum of 3-cyclohexylpropionic acid prepared in Comparative Example 1;

[0023] Figure 4 This is the GC spectrum of 3-cyclohexylpropionic acid prepared in Comparative Example 2. DETAILED DESCRIPTION

[0024] All raw materials of the present invention have no particular limitation on their sources and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0025] There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses analytically pure materials or materials with conventional purity in the field of 3-cyclohexylpropionic acid synthesis.

[0026] The present invention provides a method for preparing 3-cyclohexylpropionic acid by solvent-free hydrogenation, comprising:

[0027] The molten cinnamic acid is mixed with a catalyst and then hydrogen is introduced to carry out a hydrogenation reaction;

[0028] The catalyst in the product of the hydrogenation reaction is separated to obtain 3-cyclohexylpropionic acid.

[0029] In the present invention, the solvent-free hydrogenation process for preparing 3-cyclohexylpropionic acid is preferably carried out in a sealable pressure vessel, preferably a hydrogenation reactor.

[0030] The invention mixes molten cinnamic acid with a catalyst and then introduces hydrogen to carry out a hydrogenation reaction.

[0031] In the present invention, the cinnamic acid is preferably heated to a melting point of 133° C. or higher, preferably 140 to 150° C., to obtain molten cinnamic acid.

[0032] In the present invention, the catalyst is a catalyst for cinnamic acid hydrogenation, preferably including a ruthenium, gold, platinum or palladium-based catalyst, or a nickel-based nanocatalyst. As an embodiment of the present invention, the catalyst is a ruthenium carbon catalyst. In an embodiment of the present invention, the ruthenium carbon catalyst has a ruthenium content of 5% and a water content of 50% by mass.

[0033] In the present invention, the amount of the catalyst is preferably 2-10% of the mass of the molten cinnamic acid. As an embodiment of the present invention, the amount of the catalyst can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% of the mass of the molten cinnamic acid. The amount of the catalyst affects the rate of the hydrogenation reaction. If the amount is too small, the reaction is slow and the efficiency is affected; if the amount is too large, the reaction is too fast, the reaction system is disordered, and the normal operation of the reaction is affected; the present invention limits the amount of the catalyst to the above range, which can increase the rate of the hydrogenation reaction under a stable state.

[0034] The present invention has no special requirements for the mixing, as long as the catalyst can be evenly dispersed in the molten cinnamic acid. In the embodiment of the present invention, the catalyst is preferably evenly dispersed in the molten cinnamic acid by stirring.

[0035] After the mixing is completed, the present invention preferably seals the reaction vessel for nitrogen replacement, and then introduces hydrogen. In the present invention, nitrogen replacement can reduce the oxygen content in the reaction system, prevent oxygen from participating in the reaction and generating by-products; or react with the catalyst to reduce the activity and service life of the catalyst.

[0036] The present invention has no particular limitation on the method of introducing hydrogen, as long as the hydrogen can contact the molten cinnamic acid. The present invention preferably uses a conduit to introduce hydrogen into the bottom of the reaction system.

[0037] In the present invention, the hydrogenation reaction is preferably carried out under stirring conditions. Hydrogen has limited solubility in cinnamic acid, and stirring can make cinnamic acid fully contact with hydrogen, thereby promoting the hydrogenation reaction.

[0038] In the present invention, the temperature of the hydrogenation reaction is preferably 110-150°C, more preferably 120-150°C, and further preferably 130-150°C. The temperature of the hydrogenation reaction affects the reaction rate and the equilibrium conversion rate. A too low reaction temperature has a low hydrogenation reaction rate and a very low conversion rate; although a too high reaction temperature can increase the reaction rate, it will reduce the equilibrium conversion rate. The temperature of the hydrogenation reaction is within the above range, with a higher reaction rate and equilibrium conversion rate.

[0039] In the present invention, the pressure of the hydrogenation reaction is preferably maintained at 0.5 to 5 MPa, more preferably 2 to 5 MPa. The hydrogenation method of the present invention is to introduce hydrogen to the upper limit pressure at one time. As the reaction proceeds, the system pressure will gradually decrease. When the system pressure drops to the lower limit pressure, hydrogen is introduced again to the upper limit pressure, and then the reaction is carried out; repeat this operation until the pressure of the system drops slowly or no longer drops or even rises slightly, indicating that the reaction stops. In the present invention, the slow drop in pressure means that the pressure drop is less than 0.02 MPa in 10 minutes. The upper limit pressure is the maximum limit of the pressure of the hydrogenation reaction in the present invention. As an embodiment of the present invention, the upper limit pressure can be 2MPa, 2.5MPa, 3MPa, 3.5MPa, 4MPa, 4.5MPa, 5MPa. The lower limit pressure is the minimum limit of the pressure of the hydrogenation reaction in the present invention. As an embodiment of the present invention, the lower limit pressure can be 2MPa, 1.5MPa, 1MPa, 0.5MPa. The pressure of the hydrogenation reaction affects the rate and equilibrium conversion rate of the hydrogenation reaction. If the pressure is too low, the hydrogenation reaction rate is low and the conversion rate is very low. Although too high a pressure can increase the reaction rate, it has high requirements for equipment, and the reaction is too fast to generate a lot of heat, which poses a great safety hazard. The hydrogenation reaction pressure within the above range has a higher reaction rate, equilibrium conversion rate and safety.

[0040] The present invention preferably cools the reaction system, releases the pressure and replaces the reaction system with nitrogen after the hydrogenation reaction stops. The present invention has no particular requirements for the cooling method, as long as the temperature of the reaction system can be reduced. The present invention preferably reduces the temperature of the system to room temperature by passing cooling water into the coil disposed in the device.

[0041] After the hydrogenation reaction is completed, the present invention separates the catalyst from the reaction product to obtain 3-cyclohexylpropionic acid.

[0042] The present invention has no particular requirements for the separation method, as long as the catalyst can be separated from the reaction product. In the embodiment of the present invention, filter element filtration is preferably used.

[0043] After separation, the present invention preferably performs vacuum distillation on the separated liquid to obtain 3-cyclohexylpropionic acid. In the present invention, the pressure of the vacuum distillation is preferably -(0.05-0.1)MPa, the liquid phase temperature is preferably 160-180°C, and the gas phase temperature is preferably 140-160°C. Using the above parameters for vacuum distillation can better purify 3-cyclohexylpropionic acid while avoiding decomposition or polymerization of 3-cyclohexylpropionic acid caused by excessive temperature.

[0044] In the present invention, the yield of 3-cyclohexylpropionic acid is preferably greater than 95%, and the purity of 3-cyclohexylpropionic acid is preferably greater than 99%.

[0045] The method for preparing 3-cyclohexylpropionic acid provided by the present invention does not use a solvent for reaction, thus reducing solvent consumption and production costs; the post-processing step of acidification and stratification is reduced, the overall process is reduced, production efficiency is improved, and intermediate process losses are reduced, and the actual yield is higher than that of a solvent method; there is no solvent and no post-processing by-products, which conforms to the development trend of green production.

[0046] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] Example 1

[0048] A method for preparing 3-cyclohexylpropionic acid by solvent-free hydrogenation is as follows:

[0049] 300g of cinnamic acid was added to a hydrogenation reactor, heated to 140°C, and 6g of ruthenium carbon catalyst (5% ruthenium content, 50% water content) was added after the cinnamic acid was completely dissolved. The hydrogenation reactor was sealed, replaced with nitrogen, and hydrogen was introduced to 3MPa. The hydrogenation reaction was carried out at 140°C. When the hydrogen pressure was lower than 2MPa, hydrogen was introduced again to make the pressure reach 3MPa. After the pressure drop was less than 0.02MPa in 10 minutes, the reaction was stopped, and the reaction time was 5 hours. The cooling water was turned on to cool down, and after cooling to room temperature, the hydrogen was released and replaced with nitrogen, and then the hydrogenation reactor was turned on. After filtering (50μm filter element) the catalyst, the crude cyclohexylpropionic acid was obtained.

[0050] The crude cyclohexylpropionic acid was subjected to vacuum distillation at a pressure of -0.1 MPa, a liquid phase temperature of 150°C, and a gas phase temperature of 170°C to obtain 313.2 g of cyclohexylpropionic acid (colorless transparent liquid) with a yield of 99.0%. The product was subjected to GC detection by the following method. The detection results are as follows: Figure 1 As shown, the content of 3-cyclohexylpropionic acid is 99.860%.

[0051] Yield calculation:

[0052] Yield = actual yield / theoretical yield

[0053] Theoretical yield = 156.2 (3-cyclohexylpropionic acid molecular weight) * 300g / 148.1 (cinnamic acid molecular weight)

[0054] GC analysis method

[0055] Preparation method: Dissolve 3 drops of 3-cyclohexylpropionic acid sample in 2 mL of acetonitrile and inject 0.5 μL with a microinjector.

[0056]

[0057] Note: Qualified 3-cyclohexylpropionic acid requires a GC content greater than 99.0%.

[0058] Example 2

[0059] A method for preparing 3-cyclohexylpropionic acid by solvent-free hydrogenation is as follows:

[0060] 300g of cinnamic acid was added to a hydrogenation reactor, heated to 140°C, and 15g of ruthenium carbon catalyst (5% ruthenium content, 50% water content) was added after the cinnamic acid was completely dissolved. The hydrogenation reactor was sealed, replaced with nitrogen, and hydrogen was introduced to 3MPa. The hydrogenation reaction was carried out at 140°C. When the hydrogen pressure was lower than 2MPa, hydrogen was introduced again to make the pressure reach 3MPa. This operation was repeated until the pressure drop was less than 0.02MPa in 10 minutes, and the reaction was stopped. The reaction time was 5 hours. The cooling water was turned on to cool down. After cooling to room temperature, the hydrogen was released and replaced with nitrogen. The hydrogenation reactor was turned on, and the catalyst was filtered (50μm filter element) to obtain the crude cyclohexylpropionic acid.

[0061] The crude cyclohexylpropionic acid was subjected to vacuum distillation at a pressure of -0.1 MPa, a liquid phase temperature of 150°C, and a gas phase temperature of 170°C to obtain 313.9 g of cyclohexylpropionic acid (colorless transparent liquid) with a yield of 99.2%. The product was tested by GC, and the test results were as follows: Figure 2 As shown, the content of 3-cyclohexylpropionic acid is 99.720%.

[0062] Comparative Example 1

[0063] 50g of cinnamic acid, 14.7g of sodium hydroxide, and 300g of water were added to the hydrogenation kettle, and 6g of ruthenium carbon catalyst (5% ruthenium content, 50% water content) was added after dissolution. The hydrogenation reactor was sealed, and hydrogen was introduced to 3MPa through nitrogen replacement. The temperature was raised to 140°C for hydrogenation reaction. When the hydrogen pressure was lower than 2MPa, hydrogen was introduced again to make the pressure reach 3MPa. This operation was repeated until the pressure drop was less than 0.02MPa in 10 minutes, and the reaction stopped. The reaction time was 5 hours. The cooling water was turned on to cool down. After cooling to room temperature, the hydrogen was released and nitrogen replacement was performed. The hydrogenation kettle was turned on. After filtering (50μm filter element) the catalyst, it was neutralized with hydrochloric acid with a mass fraction of 31% to a pH of 2 in the water layer. After standing and stratification, the upper layer was taken to obtain a crude cyclohexylpropionic acid.

[0064] The crude cyclohexylpropionic acid was subjected to vacuum distillation at a pressure of -0.1 MPa, a liquid phase temperature of 150°C, and a gas phase temperature of 170°C to obtain 51.7 g of cyclohexylpropionic acid (colorless transparent liquid) with a yield of 98.04%. The product was tested by GC, and the test results were as follows: Figure 3 As shown, the 3-cyclohexylpropionic acid content is 99.776%.

[0065] Comparative Example 2

[0066] 50g of cinnamic acid, 14.7g of sodium hydroxide, and 300g of water were added to the hydrogenation kettle, and 15g of ruthenium carbon catalyst (5% ruthenium content, 50% water content) was added after dissolution. The hydrogenation reactor was sealed, and hydrogen was introduced to 3MPa through nitrogen replacement. The temperature was raised to 140°C for hydrogenation reaction. When the hydrogen pressure was lower than 2MPa, hydrogen was introduced again to make the pressure reach 3MPa. This operation was repeated until the pressure drop was less than 0.02MPa in 10 minutes, and the reaction stopped. The reaction time was 5 hours. The cooling water was turned on to cool down. After cooling to room temperature, the hydrogen was released and nitrogen was replaced. The hydrogenation kettle was turned on. After filtering (50μm filter element) the catalyst, it was neutralized with hydrochloric acid with a mass fraction of 31% to a pH of 2 in the water layer. After standing and stratifying, the upper layer was taken to obtain a crude cyclohexylpropionic acid.

[0067] The crude cyclohexylpropionic acid was subjected to vacuum distillation at a pressure of -0.1 MPa, a liquid phase temperature of 150°C, and a gas phase temperature of 170°C to obtain 50.9 g of cyclohexylpropionic acid (colorless transparent liquid) with a yield of 96.52%. The product was tested by GC, and the test results were as follows: Figure 4 As shown, the content of 3-cyclohexylpropionic acid is 99.585%.

[0068] From the above examples and comparative examples, it can be seen that the solvent-free method for preparing 3-cyclohexylpropionic acid provided by the present invention does not use solvents, and saves 0.32 tons of flake caustic soda, 0.95 tons of 31% hydrochloric acid, and about 1,536.6 yuan in raw material costs per ton of 3-cyclohexylpropionic acid product. Moreover, because the oil-water separation step is reduced, the product yield is higher, and the product yield reaches 99%, which is higher than 96.52-98.04% of the solvent method.

[0069] Production efficiency: Because no solvent is added, more cinnamic acid can be put into the reactor. To produce 100 tons of 3-cyclohexylpropionic acid, the reactor is 2m 3 According to calculation, the solvent method needs to produce 474 batches, while the solvent-free method needs to produce 84 batches, and the production efficiency is improved by 464%.

[0070] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing 3-cyclohexylpropionic acid by solvent-free hydrogenation, include: The molten cinnamic acid is mixed with a catalyst and then hydrogen is introduced to carry out a hydrogenation reaction; The catalyst in the product of the hydrogenation reaction is separated to obtain 3-cyclohexylpropionic acid.

2. The method according to claim 1, It is characterized in that The catalyst includes ruthenium, gold, platinum or palladium catalyst, or nickel-based nanocatalyst.

3. The method according to claim 2, It is characterized in that The amount of the catalyst used is 2-10% of the mass of the molten cinnamic acid.

4. The method according to claim 1, It is characterized in that The hydrogenation reaction is carried out under stirring conditions.

5. The method according to claim 1, It is characterized in that The temperature of the hydrogenation reaction is 110-150°C.

6. The method according to claim 1, It is characterized in that The pressure of the hydrogenation reaction is maintained at 0.5-5 MPa.

7. The method according to claim 6, It is characterized in that The pressure of the hydrogenation reaction is maintained at 2-5 MPa.

8. The method according to claim 1, It is characterized in that After the separation, the obtained liquid is subjected to reduced pressure distillation to obtain 3-cyclohexylpropionic acid.

9. The method according to claim 8, It is characterized in that The pressure of the reduced pressure distillation is -(0.05-0.1)MPa, the liquid phase temperature is 160-180°C, and the gas phase temperature is 140-160°C.

10. The method according to claim 9, It is characterized in that The yield of the 3-cyclohexylpropionic acid is greater than 95%, and the purity is greater than 99%.

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