Supported catalyst and method for preparing the same, and method for synthesizing l-menthone

Abstract

The present application relates to a kind of supported catalyst and its preparation method, the supported catalyst includes nano porous carrier and active component supported on the nano porous carrier, wherein, the active component is the complex formed by transition metal salt and pyrimidine compound.The present application also relates to a kind of synthesis method of L-menthone, including the following steps: L-isopulegol and the supported catalyst are mixed, and intramolecular hydrogen transfer reaction is carried out to obtain L-menthone.The supported catalyst of the present application has the advantages such as structural stability, excellent activity, etc., can catalyze intramolecular hydrogen transfer reaction of L-isopulegol under mild conditions, and L-menthone is obtained with high selectivity, and moreover, supported catalyst can be recycled, greatly reduce production cost, it is beneficial to the industrial production of L-menthone.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of menthone preparation, in particular to a supported catalyst, a preparation method thereof and a synthesis method of L-menthone. BACKGROUND

[0002] Menthone, also known as mone, has the cooling characteristic aroma of natural mint. As a naturally occurring L-menthone, it is one of the main components of Asian mint and American mint oil, and is an important raw material for aromatic and perfume chemicals. Due to its cooling and refreshing properties, it is widely used in essence blending and condiments. Therefore, the synthesis of menthone has attracted much attention.

[0003] At present, menthone products include natural menthone and synthetic menthone. Natural menthone is mainly obtained by rectification extraction of natural raw materials such as natural mint and old crane grass. Its price and supply are significantly affected by the raw materials. There are many methods for synthesizing menthone, mainly based on the oxidation of menthol. Stoichiometric oxidation systems such as chromate, permanganate and hypochlorite are used. Although this route is mature, the oxidizing agents involved in the process are toxic or hazardous, and a large amount of volatile organic solvents is required during use. Therefore, a large amount of waste liquid and by-product salt is generated during the production process.

[0004] Patent US9029605B2 discloses a method for preparing menthone and isomenthone mixture from isobornyl alcohol as raw material under the action of phosphine ligand-ruthenium homogeneous catalyst, with o-xylene as solvent and refluxing for 12 hours. The conversion rate of isobornyl alcohol is 60.5%, and the selectivity of menthone is 47.3%. In addition, 31.6% of menthol and 14.9% of isobornyl ketone are obtained. The selectivity is low, the yield of menthone is low, and the catalyst is expensive and difficult to recover, which has poor practicability.

[0005] Patent CN106061933B reports a method for preparing menthone by contacting isobornyl alcohol with activated oxidized copper catalyst in gas phase. Isobornyl alcohol is reacted at 170℃ for 5 hours, the conversion rate of isobornyl alcohol is 100%, the selectivity of menthone is 59.2%, the selectivity of isomenthone is 29.3%, and the selectivity of thymol is 6.3%. It can be seen that the reaction temperature of this method is relatively high, the selectivity of menthone is slightly low, and other impurities are also produced.

[0006] Patent CN106068160B discloses a method for preparing menthone from isoborneol, which uses a ruthenium precursor-phenol ligand catalyst to catalyze the intramolecular hydrogen transfer reaction of isoborneol to obtain menthone. The conversion rate of isoborneol is 100% after heating at 180℃ for 6 hours, the total selectivity of the reaction is 93.8%, and the yield of menthone is 80.3%. However, the specific selectivity of each product is not given in the document. In addition, the turn over number (TON) of this process is limited, the catalyst has a short service life, and a large amount of phenol derivatives are used, which is not conducive to the separation and treatment of the product in the later stage.

[0007] Patent CN112250556B discloses that isoborneol undergoes selective intramolecular hydrogen transfer reaction in the presence of a silver-based catalyst to obtain menthone. However, this method requires the use of a photocatalyst, which limits its application in industrial mass production.

[0008] Patent CN115784854A discloses a method for preparing menthone, which uses an amino acid Schiff base ruthenium complex as a catalyst and adds a pyrrolidone compound as an additive in an amount of 20wt%-200wt% of the Schiff base ruthenium complex. The method uses a homogeneous catalyst system, which has achieved good results. However, the use of a homogeneous catalyst and an additive increases the difficulty of post-treatment, and the use of a large amount of pyrrolidone additive is not conducive to environmental protection. In addition, the reuse of the catalyst and the additive is not given.

[0009] In summary, in the prior art, there are problems such as low conversion rate, poor selectivity, and high reaction temperature in the preparation of menthone from isoborneol, especially in the preparation of L-menthone from L-isoborneol, which is rarely reported. Therefore, it is of great significance to develop an efficient and economical method for preparing L-menthone from L-isoborneol. SUMMARY

[0010] Therefore, it is necessary to provide a supported catalyst and a preparation method thereof to solve the above problems. The supported catalyst has the advantages of structural stability and excellent activity, can catalyze the intramolecular hydrogen transfer reaction of L-isoborneol under mild conditions, and can obtain L-menthone with high selectivity and can be recycled.

[0011] To achieve the above-mentioned purposes, the technical scheme adopted by the present application is as follows: a supported catalyst for catalyzing the intramolecular hydrogen transfer of L-isoborneol to prepare L-menthone, the supported catalyst comprising a nano-sized porous carrier and an active component supported on the nano-sized porous carrier, wherein the active component is a complex formed by a transition metal salt and a pyrimidine compound.

[0012] In one embodiment, the transition metal salt is selected from at least one of iron salt, nickel salt, copper salt, bismuth salt or lead salt;

[0013] In one embodiment, the pyrimidine compound is selected from at least one of 2- aminopyrimidine, 2-mercaptopyrimidine, 2,2'-bipyrimidine, 4,6-dihydroxypyrimidine, 2- cyanopyrimidine;

[0014] In one embodiment, the nanoscale porous carrier is selected from at least one of nanoscale porous ZrO2 carrier, nanoscale porous SiO2 carrier, nanoscale porous SnO2 carrier, nanoscale porous TiO2 carrier, nanoscale porous Fe3O4 / SiO2 carrier.

[0015] In one embodiment, the transition metal salt is selected from at least two of iron salt, nickel salt, copper salt, bismuth salt or lead salt;

[0016] In one embodiment, the specific surface area of the nanoscale porous carrier is selected from 100 m 2 / g to 500 m 2 / g, and the pore size distribution is selected from 20 nm to 100 nm.

[0017] In one embodiment, the nanoscale porous carrier has a hollow structure.

[0018] In one embodiment, the mass ratio of transition metal ion in any of the transition metal salts to the nanoscale porous carrier is 0.01:1 to 0.09:1.

[0019] In one embodiment, the molar ratio of the pyrimidine compound to the transition metal ion in the transition metal salt is 6:1 to 20:1.

[0020] A preparation method of the supported catalyst, comprising the following steps:

[0021] Mixing the transition metal salt, the pyrimidine compound and the solvent to obtain a preparation;

[0022] Adding the nanoscale porous carrier to the preparation for adsorption, and separating to obtain the supported catalyst.

[0023] In one embodiment, in the step of mixing the transition metal salt, the pyrimidine compound and the solvent, the temperature is 40°C to 80°C, and the time is 4 h to 8 h.

[0024] In one embodiment, in the step of adding the nanoscale porous carrier to the preparation for adsorption, the temperature is 50°C to 100°C, and the time is 4 h to 8 h.

[0025] The application discloses a synthesis method of L-menthone, which comprises the following steps: mixing L-isopulegol and the supported catalyst, and performing intramolecular hydrogen transfer reaction to obtain L-menthone.

[0026] In one of the embodiments, the mass ratio of the supported catalyst to the L-isopulegol is 0.01:1-0.09:1.

[0027] In one of the embodiments, the temperature in the step of the intramolecular hydrogen transfer reaction is 120-160 DEG C, and the time is 4-8 hours.

[0028] In one of the embodiments, after the intramolecular hydrogen transfer reaction, the supported catalyst is separated and recycled to catalyze the intramolecular hydrogen transfer reaction of L-isopulegol.

[0029] In the supported catalyst, the active component is a stable complex formed by a transition metal salt and a pyrimidine compound, the complex can be stably supported in the nanoscale porous carrier, the loss of the active metal in the reaction process is reduced, the stability of the supported catalyst is enhanced, the recycling of the supported catalyst is realized, the nanoscale porous carrier has a large specific surface area, the active component is highly dispersed on the outer surface of the carrier and in the internal pores of the carrier, the distribution of the active component is facilitated, more active sites are exposed, and therefore, the supported catalyst has the advantages of structural stability and excellent activity; meanwhile, the steric hindrance of the complex makes the supported catalyst have excellent steric selectivity. DETAILED DESCRIPTION

[0030] In order to facilitate the understanding of the present application, the present application will be described in more detail below.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for the purpose of describing particular embodiments or examples only and is not intended to be limiting of the application. As used herein, the term "and / or," encompasses all possible combinations of one or more of the associated listed items and can be abbreviated as " / ". It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments or examples only and is not intended to be limiting.

[0032] The present application provides a supported catalyst for catalyzing intramolecular hydrogen transfer of L-isopulegol to prepare L-menthone, the supported catalyst comprising a nano-porous carrier and an active component supported on the nano-porous carrier, wherein the active component is a complex formed by a transition metal salt and a pyrimidine compound.

[0033] In the supported catalyst of the present application, the transition metal salt and the pyrimidine compound can form a stable complex as the active component, reducing the loss of active metal during the reaction and favoring the enhancement of the stability of the supported catalyst; and the nano-porous carrier has a large specific surface area and pores, allowing the active component to be highly dispersed on the outer surface of the carrier and inside the pores of the carrier, favoring the distribution of the active component and exposing more active sites, so that the supported catalyst has excellent activity and structural stability.

[0034] Meanwhile, the complex is highly dispersed in the nano-porous carrier, and the steric hindrance of the complex allows the supported catalyst to have excellent steric selectivity.

[0035] Therefore, the supported catalyst of the present application can catalyze the intramolecular hydrogen transfer of L-isopulegol under mild conditions, and L-menthone is obtained with high selectivity, and the supported catalyst can be recycled and reused, greatly reducing the production cost and favoring the industrial production of L-menthone.

[0036] Optionally, the nano-porous carrier is at least one selected from nano-porous ZrO2 carrier, nano-porous SiO2 carrier, nano-porous SnO2 carrier, nano-porous TiO2 carrier, and nano-porous Fe3O4 / SiO2 carrier.

[0037] As preferred, the nano-porous carrier has a hollow structure, which can further increase the specific surface area and pores of the nano-porous carrier, allowing the active component to be highly dispersed on the outer surface of the carrier, inside the pores and cavities of the carrier, and further exposing more active sites, so that the supported catalyst has more excellent activity and structural stability.

[0038] Preferably, the specific surface area of the nanoscale porous carrier is selected from 100 m 2 / g~500 m 2 / g, and the pore size distribution is selected from 20 nm~100 nm.

[0039] Optionally, the transition metal salt is selected from at least one of iron salt, nickel salt, copper salt, bismuth salt or lead salt, and the transition metal salt can be selected from at least one of nitrate, chloride, sulfate, acetate, acetylacetone salt, ammonium salt.

[0040] Preferably, the transition metal salt is selected from at least two of iron salt, nickel salt, copper salt, bismuth salt or lead salt, and more preferably the transition metal salt is a mixture of at least one of iron salt, nickel salt, copper salt, bismuth salt or lead salt and nickel salt, which can make the supported catalyst have more excellent catalytic activity and space selectivity.

[0041] Optionally, the pyrimidine compound is selected from at least one of 2-aminopyrimidine, 2-mercaptopyrimidine, 2,2'-bipyrimidine, 4,6-dihydroxypyrimidine and 2-cyanopyrimidine.

[0042] Optionally, the mass ratio of the transition metal ion in any of the transition metal salts to the nanoscale porous carrier is 0.01:1~0.09:1, further preferably 0.03:1~0.07:1, more preferably 0.03:1~0.05:1, and / or the molar ratio of the pyrimidine compound to the transition metal ion in the transition metal salt is 6:1~20:1, further preferably 6:1~18:1, more preferably 10:1~18:1.

[0043] Optionally, the mass ratio of the total transition metal ion in the supported catalyst to the nanoscale porous carrier is less than or equal to 0.5:1.

[0044] The application also provides a preparation method of the supported catalyst, comprising the following steps:

[0045] S11, mixing the transition metal salt, the pyrimidine compound and the solvent to obtain a preparation;

[0046] S12, adding the nanoscale porous carrier to the preparation for adsorption, and separating to obtain the supported catalyst.

[0047] In step S11, the solvent is preferably water which can disperse the transition metal salt and the pyrimidine compound.

[0048] Optionally, in the step of mixing the transition metal salt, the pyrimidine compound and the solvent, the temperature is 40-80℃ and the time is 4-8h, which can make the transition metal salt and the pyrimidine compound form a complex better.

[0049] In the step S12, in the step of adding the nanoscale porous carrier into the preparation to adsorb, the temperature is 50-100℃ and the time is 4-8h, which is beneficial to improve the adsorption rate and effect of the complex on the carrier.

[0050] The preparation method of the catalyst is simple, mild and environmentally friendly.

[0051] The application further provides a synthesis method of L-menthone, which comprises the following steps: mixing L-isopulegol and the supported catalyst to perform intramolecular hydrogen transfer reaction to obtain L-menthone, and the reaction equation is as follows:

[0052]

[0053] Optionally, the mass ratio of the supported catalyst to the L-isopulegol is 0.01:1-0.09:1, further preferably 0.01:1-0.05:1, and more preferably 0.02:1-0.05:1.

[0054] Optionally, in the step of the intramolecular hydrogen transfer reaction, the temperature is 120-160℃ and the time is 4-8h, and further preferably, the temperature is 120-140℃ and the time is 4-6h.

[0055] The application uses L-isopulegol as raw material and the supported catalyst to perform intramolecular hydrogen transfer reaction to prepare L-menthone, which can obtain optically pure L-menthone, does not need to use hydrogen and solvent, has high process safety and low energy consumption.

[0056] In addition, after the intramolecular hydrogen transfer reaction, the application further comprises the steps of separating the supported catalyst and recycling it to catalyze L-isopulegol to perform intramolecular hydrogen transfer reaction, which greatly reduces the production cost and is beneficial to the industrial production of L-menthone.

[0057] In the following, the supported catalyst, the preparation method thereof and the synthesis method of L-menthone will be further described through the following specific examples.

[0058]

Supported catalyst and preparation method thereof

[0059] Example 1

[0060] At room temperature, 1.49g of NiSO4·6H2O and 1.97g of CuSO 4˙5H₂O was added to 30.0g of purified water and stirred until completely dissolved. Then, 12.34g of 2-aminopyrimidine was added, the temperature was raised to 60℃, and the mixture was stirred at a constant temperature for 6 hours. Finally, 10.0g of nanoscale hollow porous ZrO₂ support (BET: 238m) was added. 2 / g; pore size: 30nm), then heated to 80℃ and stirred at a constant temperature for 6 hours for adsorption. The solvent was removed by rotary evaporation under reduced pressure to obtain the supported catalyst. The supported catalyst was placed in a 100℃ constant temperature drying oven and dried to constant weight, and denoted as CAT-1.

[0061] Example 2

[0062] At room temperature, 0.45 g of Ni(NO3)2 and 2.03 g of anhydrous FeCl3 were added to 40.0 g of purified water and stirred until completely dissolved. Then, 22.34 g of 4,6-dihydroxypyrimidine was added, the temperature was raised to 40 °C, and the mixture was stirred at a constant temperature for 8 hours. Finally, 10.0 g of nanoscale hollow porous SiO2 support (BET: 256m) was added. 2 / g; pore size: 20nm), then heated to 60℃ and stirred at a constant temperature for 6 hours for adsorption. The solvent was removed by rotary evaporation under reduced pressure to obtain the supported catalyst. The supported catalyst was placed in a 100℃ constant temperature drying oven and dried to constant weight, denoted as CAT-2.

[0063] Example 3

[0064] At room temperature, 2.19 g of Ni(acac)₂ and 1.28 g of Pb(OAc)₂·3H₂O were added to 20.0 g of purified water and stirred until completely dissolved. Then, 16.02 g of 2-mercaptopyrimidine was added, the temperature was raised to 60 °C, and the mixture was stirred at a constant temperature for 4 hours. Finally, 10.0 g of nanoscale hollow porous SnO₂ support (BET: 173m) was added. 2 / g; pore size: 100nm), then heated to 80℃ and stirred at a constant temperature for 6 hours for adsorption. The solvent was removed by rotary evaporation under reduced pressure to obtain the supported catalyst. The supported catalyst was placed in a 100℃ constant temperature drying oven and dried to constant weight, and designated as CAT-3.

[0065] Example 4

[0066] At room temperature, 2.83 g of NiCl2·6H2O and 2.09 g of Bi(NO3)2·5H2O were added to 60.0 g of purified water and stirred until completely dissolved. Then, 46.21 g of 2,2′-bipyrimidine was added, the temperature was raised to 60 °C, and the mixture was stirred at a constant temperature for 8 hours. Finally, 10.0 g of nanoscale hollow porous TiO2 support (BET: 301m) was added. 2(g; pore size: 30 nm), and then heated to 100°C, and stirred at constant temperature for 4 hours to adsorb. The solvent was removed by rotary evaporation under reduced pressure to obtain a supported catalyst. The supported catalyst was placed in a constant-temperature drying box at 100°C, and dried to constant weight, and recorded as CAT-4.

[0067] Example 5

[0068] At room temperature, 2.19 g of Ni(acac)2and 2.66 g of Cu(NO3)2·3H2O were added to 60.0 g of purified water, stirred until completely dissolved, then 41.06 g of 2,2'-bipyrimidine was added, heated to 60°C, and stirred at constant temperature for 6 hours. Then 10.0 g of nano-sized hollow porous Fe3O4 / SiO2support (BET: 465 m 2 / g; pore size: 20 nm) was added, and stirred at constant temperature for 4 hours at 60°C. The solvent was removed by rotary evaporation under reduced pressure to obtain a supported catalyst. The supported catalyst was placed in a constant-temperature drying box at 100°C, and dried to constant weight, and recorded as CAT-5.

[0069] Example 6

[0070] At room temperature, 2.19 g of Ni(acac)2and 2.66 g of Cu(NO3)2·3H2O were added to 60.0 g of purified water, stirred until completely dissolved, then 20.53 g of 2,2'-bipyrimidine was added, heated to 60°C, and stirred at constant temperature for 6 hours. Then 10.0 g of nano-sized hollow porous Fe3O4 / SiO2support (BET: 465 m 2 / g; pore size: 20 nm) was added, and stirred at constant temperature for 4 hours at 60°C. The solvent was removed by rotary evaporation under reduced pressure to obtain a supported catalyst. The supported catalyst was placed in a constant-temperature drying box at 100°C, and dried to constant weight, and recorded as CAT-6.

[0071] Example 7

[0072] At room temperature, 2.19 g of Ni(acac)2and 1.16 g of Bi(NO3)2·5H2O were added to 40.0 g of purified water, stirred until completely dissolved, then 19.57 g of 4,6-dihydroxypyrimidine was added, heated to 60°C, and stirred at constant temperature for 8 hours. Then 10.0 g of nano-sized hollow porous ZrO2support (BET: 238 m 2 / g; pore size: 30 nm) was added, and then heated to 100°C, and stirred at constant temperature for 4 hours to adsorb. The solvent was removed by rotary evaporation under reduced pressure to obtain a supported catalyst. The supported catalyst was placed in a constant-temperature drying box at 100°C, and dried to constant weight, and recorded as CAT-7.

[0073] Example 8

[0074] After stirring to complete dissolution at room temperature, 26.55 g of 2-cyanopyrimidine was added, and the temperature was raised to 60°C. After constant temperature stirring for 8 hours, 10.0 g of a nano-sized hollow porous TiO2 carrier (BET: 301 m 2 / g; pore size: 30 nm) was added, and the temperature was lowered to 50°C. After constant temperature stirring for 6 hours, the solvent was removed by rotary evaporation under reduced pressure to obtain a supported catalyst. The supported catalyst was placed in a constant temperature drying oven at 100°C, and dried to a constant weight. This was recorded as CAT-8.

[0075] Example 9

[0076] After stirring to complete dissolution at room temperature, 26.55 g of 2-cyanopyrimidine was added, and the temperature was raised to 60°C. After constant temperature stirring for 8 hours, 10.0 g of a nano-sized hollow porous TiO2 carrier (BET: 301 m 2 / g; pore size: 30 nm) was added, and the temperature was lowered to 50°C. After constant temperature stirring for 6 hours, the solvent was removed by rotary evaporation under reduced pressure to obtain a supported catalyst. The supported catalyst was placed in a constant temperature drying oven at 100°C, and dried to a constant weight. This was recorded as CAT-8.

[0077] Comparative Example 1

[0078] After stirring to complete dissolution at room temperature, 26.55 g of 2-cyanopyrimidine was added, and the temperature was raised to 60°C. After constant temperature stirring for 8 hours, 10.0 g of a nano-sized hollow porous TiO2 carrier (BET: 301 m 2 / g; pore size: 30 nm) was added, and the temperature was lowered to 50°C. After constant temperature stirring for 6 hours, the solvent was removed by rotary evaporation under reduced pressure to obtain a supported catalyst. The supported catalyst was placed in a constant temperature drying oven at 100°C, and dried to a constant weight. This was recorded as CAT-8.

[0079] Comparative Example 2

[0080] After stirring to complete dissolution at room temperature, 26.55 g of 2-cyanopyrimidine was added, and the temperature was raised to 60°C. After constant temperature stirring for 8 hours, 10.0 g of a nano-sized hollow porous TiO2 carrier (BET: 301 m 2 / g; pore size: 30 nm) was added, and the temperature was lowered to 50°C. After constant temperature stirring for 6 hours, the solvent was removed by rotary evaporation under reduced pressure to obtain a supported catalyst. The supported catalyst was placed in a constant temperature drying oven at 100°C, and dried to a constant weight. This was recorded as CAT-8.

[0081] Synthesis of L-menthone

[0082] Example 1

[0083] The autoclave was replaced with nitrogen for 3 times, 77.13 g (0.5 mol) of L- isopulegol, 3.86 g of catalyst CAT-1 were added, the stirring was started, the reaction temperature was set to 140 °C, the reaction was kept constant for 6 hours, the reaction was stopped, the reaction liquid was detected by gas chromatography, the conversion rate of L-isopulegol was 97.63%, the selectivity of L- menthone was 98.04%. After the reaction liquid was pressed out, the catalyst CAT-1 was separated by filtration and reused in the next batch.

[0084] Example 2

[0085] The autoclave was replaced with nitrogen for 3 times, 77.13 g (0.5 mol) of L- isopulegol, 6.94 g of catalyst CAT-2 were added, the stirring was started, the reaction temperature was set to 160 °C, the reaction was kept constant for 8 hours, the reaction was stopped, the reaction liquid was detected by gas chromatography, the conversion rate of L-isopulegol was 95.82%, the selectivity of L- menthone was 98.61%. After the reaction liquid was pressed out, the catalyst CAT-2 was separated by filtration and reused in the next batch.

[0086] Example 3

[0087] The autoclave was replaced with nitrogen for 3 times, 77.13 g (0.5 mol) of L- isopulegol, 5.40 g of catalyst CAT-3 were added, the stirring was started, the reaction temperature was set to 140 °C, the reaction was kept constant for 6 hours, the reaction was stopped, the reaction liquid was detected by gas chromatography, the conversion rate of L-isopulegol was 98.72%, the selectivity of L- menthone was 96.45%. After the reaction liquid was pressed out, the catalyst CAT-3 was separated by filtration and reused in the next batch.

[0088] Example 4

[0089] The autoclave was replaced with nitrogen for 3 times, 77.13 g (0.5 mol) of L- isopulegol, 2.31 g of catalyst CAT-4 were added, the stirring was started, the reaction temperature was set to 140 °C, the reaction was kept constant for 6 hours, the reaction was stopped, the reaction liquid was detected by gas chromatography, the conversion rate of L-isopulegol was 99.11%, the selectivity of L- menthone was 97.84%. After the reaction liquid was pressed out, the catalyst CAT-4 was separated by filtration and reused in the next batch.

[0090] Example 5

[0091] The autoclave was replaced with nitrogen for 3 times, 77.13 g (0.5 mol) of L-isopulegol, 3.86 g of catalyst CAT-5 were added, the stirring was started, the reaction temperature was set to 140 °C, the reaction was kept constant for 6 hours, the reaction was stopped, the reaction liquid was detected by gas chromatography, the conversion rate of L-isopulegol was 99.23%, the selectivity of L-menthone was 98.57%. After the reaction liquid was pressed out, the catalyst CAT-5 was separated by filtration and reused in the next batch.

[0092] Example 6

[0093] The autoclave was replaced with nitrogen for 3 times, 77.13 g (0.5 mol) of L-isopulegol, 3.86 g of catalyst CAT-5 were added, the stirring was started, the reaction temperature was set to 140 °C, the reaction was kept constant for 6 hours, the reaction was stopped, the reaction liquid was detected by gas chromatography, the conversion rate of L-isopulegol was 99.23%, the selectivity of L-menthone was 98.57%. After the reaction liquid was pressed out, the catalyst CAT-5 was separated by filtration and reused in the next batch.

[0094] Example 7

[0095] The autoclave was replaced with nitrogen for 3 times, 77.13 g (0.5 mol) of L-isopulegol, 3.86 g of catalyst CAT-5 were added, the stirring was started, the reaction temperature was set to 140 °C, the reaction was kept constant for 6 hours, the reaction was stopped, the reaction liquid was detected by gas chromatography, the conversion rate of L-isopulegol was 99.23%, the selectivity of L-menthone was 98.57%. After the reaction liquid was pressed out, the catalyst CAT-5 was separated by filtration and reused in the next batch.

[0096] Example 8

[0097] The autoclave was replaced with nitrogen for 3 times, 77.13 g (0.5 mol) of L-isopulegol, 3.86 g of catalyst CAT-5 were added, the stirring was started, the reaction temperature was set to 140 °C, the reaction was kept constant for 6 hours, the reaction was stopped, the reaction liquid was detected by gas chromatography, the conversion rate of L-isopulegol was 99.23%, the selectivity of L-menthone was 98.57%. After the reaction liquid was pressed out, the catalyst CAT-5 was separated by filtration and reused in the next batch.

[0098] Example 9

[0099] The autoclave was replaced with nitrogen for 3 times, 77.13 g (0.5 mol) of L-isopulegol, 3.86 g of catalyst CAT-5 were added, the stirring was started, the reaction temperature was set to 140 °C, the reaction was kept constant for 6 hours, the reaction was stopped, the reaction liquid was detected by gas chromatography, the conversion rate of L-isopulegol was 99.23%, the selectivity of L-menthone was 98.57%. After the reaction liquid was pressed out, the catalyst CAT-5 was separated by filtration and reused in the next batch.

[0100] Example 10

[0101] The autoclave was replaced with nitrogen for 3 times, 77.13 g (0.5 mol) of L- isomenthol, 2.31 g of catalyst CAT-9 were added, the stirring was started, the reaction temperature was set to 120°C, the reaction was carried out for 4 hours, the reaction was stopped, the reaction liquid was detected by gas chromatography, the conversion rate of L-isomenthol was 99.13%, and the selectivity of L-menthone was 99.50%. After the reaction liquid was pressed out, the catalyst CAT-9 was separated by filtration and used in the next batch.

[0102] Comparative Example 1

[0103] The autoclave was replaced with nitrogen for 3 times, 77.13 g (0.5 mol) of L- isomenthol, 6.94 g of catalyst CAT-10 were added, the stirring was started, the reaction temperature was set to 160°C, the reaction was carried out for 8 hours, the reaction was stopped, the reaction liquid was detected by gas chromatography, the conversion rate of L-isomenthol was 91.45%, and the selectivity of menthone was 87.32%, wherein the content of L-menthone was 69.37%.

[0104] Comparative Example 2

[0105] The autoclave was replaced with nitrogen for 3 times, 77.13 g (0.5 mol) of L- isomenthol, 6.94 g of catalyst CAT-11 were added, the stirring was started, the reaction temperature was set to 160°C, the reaction was carried out for 8 hours, the reaction was stopped, the reaction liquid was detected by gas chromatography, the conversion rate of L-isomenthol was 82.64%, and the selectivity of menthone was 74.29%, wherein the content of L-menthone was 56.82%.

[0106]

Loaded catalyst reuse experiment

[0107] The catalyst CAT-9 obtained by filtering the reaction liquid of the synthesis example 10 of L-menthone was directly used in the reuse experiment, and other reaction conditions and operations were the same as those of the synthesis example 10 of L-menthone. The experimental results are shown in the following table.

[0108] Table 1

[0109] Number of runs Temperature (°C) Time (h) Conversion Selectivity Fresh charge 140 4 98.50％ 99.43％ 1 140 4 98.61％ 99.42％ 2 140 4.5 98.41％ 99.38％ 3 150 4.5 98.48％ 99.24％ 4 150 5 98.25％ 99.16％ 5 160 5 98.31％ 99.08％ 6 160 5 98.02％ 98.85％

[0110] As can be seen from Table 1, the loaded catalyst of the present application has excellent stability, and when reused for the sixth time, the conversion rate and the selectivity can be maintained at more than 98%, and the activity of the loaded catalyst does not decrease obviously.

[0111] Any combination of the technical features in the above-described embodiments can be made, and for the sake of brevity, not all possible combinations are described, however, as long as the combination of the technical features does not exist in contradiction, it shall be considered within the scope of the present disclosure.

[0112] The above-described embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it shall not be understood as a limitation on the patent scope of the present application. It shall be pointed out that, for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and these shall be within the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A method of synthesizing L-menthone, characterized by, The method comprises the following steps: The L-menthone is prepared by mixing L-isopulegol and a supported catalyst to perform intramolecular hydrogen transfer reaction, wherein the supported catalyst comprises a nano-porous carrier and an active component supported on the nano-porous carrier, the active component is a complex formed by a metal salt and a pyrimidine compound, and the metal salt is selected from at least one of iron salt, nickel salt, copper salt, bismuth salt or lead salt.

2. The method of claim 1, wherein the L-menthone is synthesized by the process of claim 1, wherein the process is carried out in the presence of a base. The pyrimidine compound is selected from at least one of 2-aminopyrimidine, 2-mercaptopyrimidine, 2,2'-bipyrimidine, 4,6-dihydroxypyrimidine and 2-cyanopyrimidine; And / or, the nano-porous carrier is selected from at least one of nano-porous ZrO2 carrier, nano-porous SiO2 carrier, nano-porous SnO2 carrier, nano-porous TiO2 carrier and nano-porous Fe3O4 / SiO2 carrier.

3. The method for synthesizing L-menthol according to claim 1, characterized in that, The metal salt is selected from at least two of iron salt, nickel salt, copper salt, bismuth salt or lead salt; and / or, the specific surface area of the nanoscale porous support is 100 m 2 / g ~ 500 m 2 / g, with a pore size distribution of 20 nm ~ 100 nm; And / or, the nano-porous carrier has a hollow structure.

4. The method for synthesizing L-menthol according to claim 1, characterized in that, The mass ratio of metal ions in the metal salt to the nano-porous carrier is 0.01:1-0.09:

1. And / or, the molar ratio of the pyrimidine compound to metal ions in the metal salt is 6:1-20:

1.

5. The method for synthesizing L-menthol according to claim 1, characterized in that, The mass ratio of the supported catalyst to the L-isopulegol is 0.01:1-0.09:

1.

6. The method for synthesizing L-menthol according to claim 1, characterized in that, In the step of the intramolecular hydrogen transfer reaction, the temperature is 120-160 DEG C, and the time is 4-8 h.

7. The method of claim 1 to 6, wherein, After the intramolecular hydrogen transfer reaction, the supported catalyst is separated and recycled to catalyze the intramolecular hydrogen transfer reaction of L-isopulegol.

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