Synthesis method of convallaria majalis pyrane

Abstract

The invention discloses a synthesis method of convallaria majalis pyrane. According to the synthesis method, 3-methyl-3-butene-1-alcohol (isopentenol) and isovaleraldehyde are used as raw materials and react in the presence of a catalyst to generate the lily pyran, the catalyst is a supported catalyst and comprises a carrier and a coating supported on the carrier, the coating comprises a Nafion polymer and an inorganic oxide, and the carrier is in a foam state. Preferably, the carrier is selected from one or a combination of more of silicon carbide foam, aluminum foam, nickel foam and iron foam. The preparation method comprises the following steps: mixing a Nafion polymer solution, water and an inorganic oxide precursor, stirring to form sol, coating the sol on a carrier, and drying to obtain the catalyst. The catalyst has the advantages of high raw material conversion rate, high product selectivity, less discharge of three wastes, excellent catalyst stability and the like when being used for synthesis of convallaria majalis pyrane.

Description

Technical Field

[0001] The invention relates to the technical field of synthetic chemistry, in particular to a method for synthesizing lily of the valley pyran. Background Art

[0002] Lily of the valley is one of the most popular aromas in the world. Traditional lily of the valley aldehyde and lyral are restricted in use due to their allergenicity. Lily of the valley pyran has a lily of the valley flower fragrance with a frankincense aroma. The floral scent is fresh, soft, and natural. It blends and enhances the floral characteristics of roses and lily of the valley very well, and the fragrance lasts for a long time. It is the most promising fragrance to replace lily of the valley aldehyde and lyral. The current market volume is increasing.

[0003] At present, the industry mainly uses 3-methyl-3-butene-1-ol (isopentenol) and isovaleraldehyde as raw materials, and uses an acidic catalyst. This method has the advantages of low raw material price, short synthesis route, and low cost. For example, patent CN105175372A uses solid superacid as catalyst and adopts continuous synthesis of lily of the valley pyran. The yield of lily of the valley pyran is 86% calculated by isovaleraldehyde. Patent CN104529969A, in which BASF is the applicant, uses macroporous acidic resin AmberlystTM131 as catalyst, and the yield is 79% calculated by isopentenol.

[0004] The molecular structure of lily of the valley pyran is relatively large, and it is greatly affected by the pore size of the catalyst during the reaction. After the reaction, lily of the valley pyran is not easy to diffuse away from the catalyst. In addition, lily of the valley pyran contains hydroxyl groups on the tertiary carbon, and it is easy to undergo dehydroxylation reaction to generate double bond-containing by-products under acidic catalyst conditions. Double bond by-products are easy to polymerize on acidic catalysts. The combined effect of these factors leads to reduced product selectivity and catalyst deactivation.

[0005] Silicon carbide has a large pore structure, which is conducive to the diffusion of macromolecular compounds. However, silicon carbide has a low specific surface area and is not easy to load acidic active components. In addition, the interaction between silicon carbide and acidic active components is weak, which makes the active components easy to peel off and cause catalyst deactivation.

[0006] The molecular structure of Nafion is composed of polytetrafluoroethylene (PTFE) and a polymer containing fluoride ions. It is a copolymer of polytetrafluoroethylene and perfluoro-3,6-diepoxy-4-methyl-7-decene-sulfuric acid. It has a stable structure and sulfuric acid is not easy to fall off. It is an excellent acid catalyst. However, pure Nafion is a solid with a very small specific surface area and is difficult to use as a catalyst. Therefore, Nafion is usually dissolved in isopropanol or ethanol as a catalyst. At this time, it is a homogeneous catalyst, which will cause the problem of difficult catalyst recovery and application, and the reaction selectivity needs to be further improved. Summary of the invention

[0007] In view of the shortcomings and deficiencies of the prior art, the present invention provides a method for synthesizing lily of the valley pyran, which can achieve a high conversion rate of isovaleraldehyde and a high reaction selectivity of the target product lily of the valley pyran, and the catalyst has high stability and is easy to recover.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] A method for synthesizing lily of the valley pyran comprises taking isopentenol (3-methyl-3-butene-1-ol) and isovaleraldehyde as raw materials, reacting in the presence of a catalyst to generate the lily of the valley pyran, wherein the catalyst is a supported catalyst and comprises a carrier and a coating supported on the carrier, wherein the coating comprises a Nafion polymer and an inorganic oxide, and the carrier is in a foam state.

[0010] In some embodiments, the specific surface area of ​​the catalyst is 50-120 m 2 / g, and the average pore size is 10-30nm. The catalyst of the present invention has a large specific surface area and average pore size. When the specific surface area is too low, the average pore size is large, but the catalytic active sites are small, which will reduce the conversion rate; when the specific surface area is too high, the coating will destroy the three-dimensional pore structure of the foam, the average pore size is small, and the diffusion is affected, resulting in reduced reaction selectivity and stability.

[0011] In some embodiments, the carrier is selected from a combination of one or more of silicon carbide foam, aluminum foam, nickel foam, and iron foam.

[0012] In some embodiments, the inorganic oxide is selected from a combination of one or more of silicon dioxide, aluminum oxide, titanium dioxide, and zinc oxide.

[0013] In some embodiments, the mass of the coating layer is 3% to 50% of the mass of the catalyst.

[0014] In some embodiments, the catalyst is prepared by a preparation method comprising the following steps: 1) mixing the Nafion polymer solution, water and the inorganic oxide precursor, forming a sol under stirring, and standing for aging; 2) coating the sol after standing for aging on the carrier, and obtaining the catalyst after drying. The inorganic oxide precursor undergoes an in-situ hydrolysis reaction in the Nafion system to form an inorganic oxide, and the sol contains the inorganic oxide. After drying, Nafion is attached to the inorganic oxide, and the inorganic oxide provides a transitional carrier between the catalyst carrier and the Nafion.

[0015] In some embodiments, the Nafion polymer solution is an alcohol solution; preferably, the alcohol in the alcohol solution is selected from ethanol or isopropanol. Nafion polymer is hydrophobic and difficult to dissolve in water, while alcohol is miscible with water.

[0016] In some embodiments, the mass percent concentration of the Nafion polymer solution is 10%-40%.

[0017] In some embodiments, the precursor of the inorganic oxide is selected from tetraethyl silicate, tetrabutyl silicate, tetraisopropyl silicate, trimethylaluminum, triethylaluminum, triisobutylaluminum, diethylaluminum chloride, aluminum isopropoxide, aluminum n-butoxide, aluminum acetate, aluminum propionate, tetrabutyl titanate, isopropyl titanate, zinc acetylacetonate, or one or more combinations thereof. All of these precursors can undergo a hydrolysis reaction.

[0018] In some embodiments, in step 1), the mass ratio of the Nafion polymer solution to the inorganic oxide precursor is 0.05 to 10:1.

[0019] In some embodiments, the mass ratio of water to the inorganic oxide precursor is 1:0.05-20.

[0020] In some embodiments, the temperature of the static aging is 20-60°C.

[0021] In some embodiments, the static aging time is 0.5 to 24 hours.

[0022] In some embodiments, in step 2), the coating and drying are repeated multiple times; preferably, the coating and drying are repeated 1-4 times. The coating and drying may not be repeated, and the coating is only performed once. The more times the coating is performed, the higher the content of active components in the catalyst.

[0023] In some embodiments, the drying temperature is 80-140°C.

[0024] In some embodiments, the drying time is 3 to 48 hours.

[0025] In some embodiments, the reaction is carried out in a solvent selected from the group consisting of water, a mixed solvent of ethanol and water, and a mixed solvent of isopropanol and water.

[0026] In some embodiments, the mass ratio of the solvent to isopentenol is 1:10-300.

[0027] In some embodiments, the molar ratio of isopentenol to isovaleraldehyde is 0.5-5:1.

[0028] In some embodiments, the mass ratio of the catalyst to isopentenol is 1:10-200.

[0029] In some embodiments, the reaction temperature is 40-100°C.

[0030] In some embodiments, the reaction time is 3 to 24 hours.

[0031] In some embodiments, the reaction is carried out at normal pressure.

[0032] In some embodiments, the synthesis method includes the following steps: 1) adding the isopentenol, isovaleraldehyde, solvent and the catalyst into a reaction kettle; 2) heating the reaction kettle to a reaction temperature so that the isopentenol and isovaleraldehyde react; 3) separating and recovering the catalyst after the reaction is completed to obtain the lily of the valley pyran.

[0033] The present invention also provides the above catalyst. The catalyst is used for the synthesis of lily of the valley pyran, which has the advantages of high raw material conversion rate, high product selectivity, less three wastes emission and excellent catalyst stability.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] The synthesis method of the invention can achieve a high conversion rate of isovaleraldehyde and a high reaction selectivity of the target product lily of the valley pyran, and the catalyst has high stability and is easy to recycle.

[0036] In the present invention, the supported catalyst used for the synthesis of lily of the valley pyran has the advantages of high catalytic efficiency, high product selectivity, multiple application batches, high catalytic stability and the like. DETAILED DESCRIPTION

[0037] In the prior art, the molecular structure of lily of the valley pyran is relatively large, and it is greatly affected by the pore size of the catalyst during the reaction. The lily of the valley pyran after the reaction is not easy to diffuse out from the catalyst, and the tertiary carbon of lily of the valley pyran contains a hydroxyl group, and it is easy to undergo a dehydroxylation reaction to generate a double-bond by-product under the condition of using an acidic catalyst, and the double-bond by-product is easy to polymerize on the acidic catalyst, and the combined effect of the two causes a decrease in product selectivity and catalyst deactivation. Although foam carriers such as silicon carbide have a large pore structure, they have a low specific surface area and are not easy to load acidic active components, and the interaction between silicon carbide and acidic active components is weak, causing the active components to easily peel off, causing catalyst deactivation. Although Nafion polymer is an excellent acid catalyst, its specific surface area is very small, and it is difficult to directly use it as a catalyst in a solid form, and homogeneous catalysts in solution form are difficult to recycle and apply.

[0038] Based on this, the inventor of the present application has found through research that by mixing the solution of Nafion polymer, water and the precursor of inorganic oxide to form sol, wherein the precursor of inorganic oxide is hydrolyzed in situ in the Nafion system to form inorganic oxide, so that Nafion is attached to the inorganic oxide formed (compared to silicon carbide, the specific surface area increases), the specific surface area of ​​Nafion is improved, and then the sol is applied to carriers such as silicon carbide foam, the interaction strength of Nafion, inorganic oxide and carrier increases, and the loading capacity of carriers such as silicon carbide to Nafion is also significantly improved, and Nafion is not easy to fall off at the same time. If inorganic oxide is not added, Nafion is directly coated on carriers such as silicon carbide foam, then the coating amount is very small, and it is easy to fall off, and the catalyst stability is poor. The present application is through the interaction of Nafion, inorganic oxide and carrier, and the coating containing Nafion and inorganic oxide is set on the carrier, which can improve the catalytic activity and stability of the catalyst.

[0039] The Nafion polymer in the catalyst coating is the catalytically active component, and the inorganic oxide therein does not act as an active component.

[0040] The catalyst of the present invention is a solid acid catalyst, which has suitable acidity and has the following characteristics:

[0041] 1. Using foam carriers with well-developed pores, such as silicon carbide foam, as carriers is conducive to the diffusion of substrates and products, improving substrate conversion, product selectivity and catalyst stability;

[0042] 2. In the process of preparing the catalyst, the inorganic oxide is introduced into the Nafion polymer by in-situ hydrolysis of the precursor, thereby increasing the specific surface area of ​​the catalyst and the number of active sites, so that when the catalyst is used in the synthesis method of the present invention, it is beneficial to improve the substrate conversion rate;

[0043] 3. The Nafion-inorganic oxide coating on the carrier has a strong interaction with the foam-type carrier, which prevents the active component Nafion from falling off, improves the stability of the catalyst, and allows the catalyst to be recycled and reused more than 40 times with the catalytic activity remaining basically unchanged.

[0044] The present invention is further described below in conjunction with the examples. However, the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to the different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in each embodiment of the present invention can be combined with each other as long as they do not conflict with each other.

[0045] Preparation Example 1

[0046] This preparation example provides a supported catalyst, and its preparation method is as follows:

[0047] 1) Add 100 g of Nafion solution (Nafion is commercially available, the mass percentage concentration of Nafion is 30%, and the solvent is isopropanol), 50 g of water and 1000 g of tetraethyl orthosilicate into a 2 L glass kettle, stir for 2 hours to form a uniform sol (in which tetraethyl orthosilicate will be hydrolyzed into silicon dioxide), and age at 40° C. for 24 hours;

[0048] 2) weighing 300 g of foamed silicon carbide, then evenly coating the sol prepared in step 1) on the foamed silicon carbide, and drying at 80° C. for 24 hours;

[0049] 3) Repeat step 2) three times to obtain a supported catalyst, which is recorded as Nafion-SiO2 / SiC-foam.

[0050] The weighing method shows that the Nafion-SiO2 coating on the Nafion-SiO2 / SiC-foam catalyst accounts for 32% of the total mass of the catalyst. The BET specific surface area test method shows that the specific surface area of ​​the Nafion-SiO2 / SiC-foam catalyst is 68 m 2 / g, and the average pore size is 17nm.

[0051] In this preparation example, the number of coating times in step 3) can be adjusted to obtain catalysts with different mass percentages of the above-mentioned Nafion-SiO2 coating.

[0052] In this preparation example, different Nafion-coatings can be obtained by adjusting the organic oxide precursor in step 1). For example, replacing tetraethyl orthosilicate with aluminum isopropoxide, tetrabutyl titanate, and zinc acetylacetonate can respectively obtain Nafion-Al2O3 / SiC-foam, Nafion-TiO2 / SiC-foam, and Nafion-ZnO / SiC-foam.

[0053] Comparative Preparation Example 1

[0054] This comparative preparation example provides a comparative supported catalyst, and its preparation method is as follows:

[0055] 1) Add 100 g of Nafion solution (Nafion is commercially available, the mass percentage concentration of Nafion is 30%, and the solvent is isopropanol) and 50 g of water into a 2 L glass kettle, stir for 2 hours (no sol can be formed at this time), and then stand and age at 40° C. for 24 hours;

[0056] 2) weighing 300 g of foamed silicon carbide, then coating the mixture prepared in step 1) on the foamed silicon carbide, and drying at 80° C. for 24 hours;

[0057] 3) Repeat step 2) three times to obtain a supported catalyst, which is recorded as Nafion / SiC-foam.

[0058] The specific surface area of ​​Nafion / SiC-foam catalyst was 5.4 m 2 / g, and the average pore size is 38nm.

[0059] Comparative Preparation Example 2

[0060] This comparative preparation example provides a comparative supported catalyst, and its preparation method is as follows:

[0061] 1) Add 50 g of water and 1000 g of tetraethyl orthosilicate into a 2 L glass kettle, stir for 2 hours to form a uniform sol, and then age at 40° C. for 24 hours;

[0062] 2) weighing 300 g of foamed silicon carbide, then evenly coating the sol prepared in step 1) on the foamed silicon carbide, and drying at 80° C. for 24 hours;

[0063] 3) Repeat step 2) for 3 times to obtain a supported catalyst, which is recorded as SiO2 / SiC-foam.

[0064] The specific surface area of ​​SiO2 / SiC-foam catalyst was determined by BET specific surface area test method to be 72 m 2 / g, and the average pore size is 15nm.

[0065] Comparative Preparation Example 3

[0066] This comparative preparation example provides a comparative supported catalyst, and its preparation method is as follows:

[0067] 1) Add 100 g of Nafion solution (Nafion is commercially available, the mass percentage concentration of Nafion is 30%, and the solvent is isopropanol), 50 g of water and 1000 g of tetraethyl orthosilicate into a 2 L glass kettle, stir for 2 hours to form a uniform sol, and then stand and age at 40° C. for 24 hours;

[0068] 2) The aged sample was dried at 80°C for 24 hours to obtain a supported catalyst, which was recorded as Nafion-SiO2;

[0069] The specific surface area of ​​Nafion-SiO2 catalyst was 197 m 2 / g, and the average pore size is 4nm.

[0070] Example 1

[0071] This embodiment provides a method for synthesizing lily of the valley pyran, which is as follows:

[0072] 1) Add 3.5 kg of isopentenol, 3 kg of isovaleraldehyde, 0.2 kg of water and 0.3 kg of each of the above-prepared catalysts into a 10 L reactor at room temperature;

[0073] 2) After starting stirring, heat the reactor to 60°C and react at normal pressure for 12 hours;

[0074] 3) After the reaction is completed, the temperature is lowered to room temperature, and then the catalyst is separated by filtration. The separated catalyst is used in the next batch of experiments.

[0075] The quantitative analysis of the reaction solution was carried out on an Agilent 7890 gas chromatograph using a chromatographic column HP-INNOWax and a FID detector.

[0076] Table 1 shows the reaction results of Nafion-SiO2 / SiC-foam prepared in Preparation Example 1, Nafion / SiC-foam, SiO2 / SiC-foam, Nafion-SiO2 catalyst prepared in Comparative Preparation Examples 1, 2, and 3, as well as commercial macroporous acidic resin AmberlystTM131 catalyst (used in patent CN104529969A), solid Nafion, and isopropanol solution of Nafion (the mass percentage concentration of Nafion is 30%, the solvent is isopropanol, the reaction system is homogeneous catalysis, and the catalyst cannot be separated from the reaction system and cannot be recovered for application).

[0077] As shown in Table 1, the Nafion-SiO2 / SiC-foam catalyst of Preparation Example 1 has the best reaction performance, isovaleraldehyde conversion rate 98%, lily of the valley pyran selectivity 97.6%. Compared with the Nafion / SiC-foam catalyst of Preparation Example 1, the activity and selectivity are greatly reduced, the isovaleraldehyde conversion rate is 28.4%, the lily of the valley pyran selectivity is 85.6%, and the dehydration byproducts are significantly increased. The comparison between the two shows that the addition of oxide effectively improves the isovaleraldehyde conversion rate. The SiO2 / SiC-foam catalyst has no catalytic activity, indicating that Nafion is its reactive active site, and the oxide has no catalytic activity and is not used as an active component. However, when solid Nafion is added as a catalyst, its conversion is only 2.3%, which is mainly because the specific surface area of ​​solid Nafion is too low and the catalytic sites are too few. The isopropanol solution of Nafion is used as a catalyst, the isovaleraldehyde conversion rate is 99%, but the lily of the valley pyran selectivity is 86%, which is because when the isopropanol solution of Nafion is used as a catalyst, the reaction system is a homogeneous reaction, and the generated lily of the valley pyran will continue to undergo dehydration reaction. Compared with the Nafion-SiO2 used as the catalyst in Preparation Example 3, the isovaleraldehyde conversion rate was 96.8% and the lily of the valley pyran selectivity was 87.4%, which were significantly lower than the Nafion-SiO2 / SiC-foam catalyst in Preparation Example 1. This is mainly because the Nafion-SiO2 catalyst has smaller pores than the Nafion-SiO2 / SiC-foam catalyst, resulting in more dehydration side reactions and reducing the reaction selectivity.

[0078] Table 1 Results of synthesizing lily of the valley pyran with different catalysts

[0079]

[0080]

[0081] Table 2 shows the catalysts prepared in Preparation Example 1 with different coating times and their catalytic results. As shown in Table 2, the conversion rate of isovaleraldehyde increases with the increase of coating times, first increases, and then slightly decreases. This is mainly because the number of active sites gradually increases with the increase of coating times, so the conversion rate increases. However, too many coating times lead to smaller pores, and the conversion rate slightly decreases. The selectivity of lily of the valley pyran gradually decreases with the increase of coating times, and the main reason is that too many coating times also lead to smaller pores.

[0082] Table 2 Performance of lily of the valley pyran synthesized by catalysts with different coating times

[0083] Coating times Isovaleraldehyde conversion rate (%) Lily of the valley pyran selectivity (%) Average pore size (nm) 1 90.2 98.3 28 2 93.4 97.9 24 3 98.0 97.6 17 4 98.8 97.4 16 5 97.2 91.4 12

[0084] Table 3 shows the catalysts of different oxides prepared in Preparation Example 1 and their catalytic results. As shown in Table 3, the catalysts prepared from various oxides have excellent yields of lily of the valley pyran.

[0085] Table 3 Performance of different oxide catalysts in synthesizing lily of the valley pyran

[0086] catalyst Isovaleraldehyde conversion rate (%) Lily of the valley pyran selectivity (%) <![CDATA[Nafion-SiO2 / SiC-foam]]> 98.0 97.6 <![CDATA[Nafion-Al2O3 / SiC-foam]]> 97.4 96.7 <![CDATA[Nafion-TiO2 / SiC-foam]]> 94.5 98.1 Nafion-ZnO / SiC-foam 94.2 96.9

[0087] Table 4 shows the application activity of the Nafion-SiO2 / SiC-foam catalyst prepared in Preparation Example 1. As shown in Table 4, after 40 batches of Nafion-SiO2 / SiC-foam catalyst were applied, the catalyst activity remained basically unchanged. Table 5 shows the application activity of the Nafion-SiO2 catalyst prepared in Comparative Preparation Example 3. As shown in Table 5, during the 14 applications, the conversion rate and selectivity of the Nafion-SiO2 catalyst decreased significantly. The comparison between the two shows that the developed pore structure of the Nafion-SiO2 / SiC-foam catalyst helps to increase the catalyst stability, and it can still maintain high reaction activity and selectivity after multiple applications.

[0088] Table 4. Nafion-SiO2 / SiC-foam catalyst application activity

[0089]

[0090] Table 5. Nafion-SiO2 catalyst application activity

[0091] Use times Isovaleraldehyde conversion rate (%) Lily of the valley pyran selectivity (%) 1 96.8 87.4 2 96.4 87.2 3 96.4 86.9 4 95.1 86.9 5 95.3 86.4 6 93.3 85.2 7 92.2 85.4 8 91.9 83.2 9 91.1 83.0 10 88.4 81.2 11 84.2 80.8 12 78.6 80.4 13 72.4 78.6 14 60.6 77.1

[0092] It can be seen that by adopting the catalyst of the present invention, a high conversion rate of the raw material isovaleraldehyde and a high reaction selectivity of the target product lily of the valley pyran can be achieved when synthesizing lily of the valley pyran, and the catalyst has high stability, and the catalytic activity remains basically unchanged after being used for more than 40 times. Moreover, the catalyst is a heterogeneous catalyst and can be easily recycled and used in the reaction system.

[0093] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

[0094] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

Claims

1. A method for synthesizing lily of the valley pyran, comprising taking isopentenol and isovaleraldehyde as raw materials, reacting in the presence of a catalyst to produce the lily of the valley pyran, characterized in that: The catalyst is a supported catalyst and comprises a support and a coating layer supported on the support, wherein the coating layer comprises a Nafion polymer and an inorganic oxide, and the support is in a foam state.

2. The method for synthesizing lily of the valley pyran according to claim 1, wherein: The specific surface area of ​​the catalyst is 50-120m 2 / g, and the average pore size is 10-30nm.

3. The method for synthesizing lily of the valley pyran according to claim 1, wherein: The carrier is selected from one or more combinations of silicon carbide foam, aluminum foam, nickel foam, and iron foam; and / or the inorganic oxide is selected from one or more combinations of silicon dioxide, aluminum oxide, titanium dioxide, and zinc oxide.

4. The method for synthesizing lily of the valley pyran according to claim 1, characterized in that: The mass of the coating layer is 3%-50% of the mass of the catalyst.

5. The method for synthesizing lily of the valley pyran according to claim 1, characterized in that: The catalyst is prepared by a preparation method comprising the following steps: 1) mixing the Nafion polymer solution, water and the inorganic oxide precursor to form a sol under stirring, and standing for aging; 2) coating the sol after standing for aging on the carrier, and obtaining the catalyst after drying.

6. The method for synthesizing lily of the valley pyran according to claim 5, characterized in that: The solution of the Nafion polymer is an alcohol solution; preferably, the alcohol in the alcohol solution is selected from ethanol or isopropanol; and / or, the mass percentage concentration of the Nafion polymer solution is 10%-40%; and / or, the precursor of the inorganic oxide is selected from a combination of one or more of tetraethyl silicate, tetrabutyl silicate, tetraisopropyl silicate, trimethylaluminum, triethylaluminum, triisobutylaluminum, diethylaluminum chloride, aluminum isopropoxide, aluminum n-butoxide, aluminum acetate, aluminum propionate, tetrabutyl titanate, isopropyl titanate, and zinc acetylacetonate.

7. The method for synthesizing lily of the valley pyran according to claim 5, characterized in that: In the step 1), the mass ratio of the Nafion polymer solution to the inorganic oxide precursor is 0.05-10:1; and / or the mass ratio of water to the inorganic oxide precursor is 1:0.05-20.

8. The method for synthesizing lily of the valley pyran according to claim 5, characterized in that: The temperature of the static aging is 20 to 60° C.; and / or, the time of the static aging is 0.5 to 24 hours; and / or, in the step 2), the coating and drying are repeated multiple times; preferably, the coating and drying are repeated 1-4 times; and / or, the drying temperature is 80 to 140° C., and / or, the drying time is 3 to 48 hours.

9. The method for synthesizing lily of the valley pyran according to claim 1, characterized in that: The reaction is carried out in a solvent, and the solvent is selected from one of water, a mixed solvent of ethanol and water, and a mixed solvent of isopropanol and water.

10. The method for synthesizing lily of the valley pyran according to claim 9, characterized in that: The mass ratio of the solvent to isopentenol is 1:10-300.

11. The method for synthesizing lily of the valley pyran according to claim 1, characterized in that: The molar ratio of isopentenol to isovaleraldehyde is 0.5-5:1; and / or the mass ratio of the catalyst to isopentenol is 1:10-200.

12. The method for synthesizing lily of the valley pyran according to claim 1, characterized in that: The reaction temperature is 40 to 100° C., and / or the reaction time is 3 to 24 hours, and / or the reaction is carried out under normal pressure.

13. The method for synthesizing lily of the valley pyran according to claim 1, characterized in that: The synthesis method comprises the following steps: 1) adding the isopentenol, isovaleraldehyde, a solvent and the catalyst into a reaction kettle; 2) heating the reaction kettle to a reaction temperature so that the isopentenol and isovaleraldehyde react; 3) separating and recovering the catalyst after the reaction is completed to obtain the lily of the valley pyran.

14. The catalyst as claimed in any one of claims 1 to 13.

Images