Synthesis method of citronellyl acetate

Abstract

The invention provides a synthesis method of citronellyl acetate, and relates to the technical field of citronellyl acetate preparation. According to the synthesis method of citronellyl acetate, solid superacid is used as a catalyst, under the action of SO2-4 / TiO2-Fe2O3 solid superacid catalysts with different Ti-Fe molar ratios, citronellol and acetic anhydride are heated and stirred to react for 3 h at the temperature of 65-75 DEG C, then esterification reaction can be completed, a thermodynamic equilibrium state can be achieved, and the content of the prepared citronellyl acetate is about 94-95%. As a novel catalyst, the solid superacid prepared by the preparation method has the advantages of high catalytic activity, good selectivity, easiness in separation from a product, small acid pollution, recyclability and the like, and citronellyl acetate with relatively high content can be prepared through purification of a rectifying tower section and reaches the standards of food additives and spice supplies. Compared with the prior art, the method has the advantages that the solid superacid is used as the catalyst, the reaction is rapid, the yield is high, a one-pot method is adopted for reaction, the operation is simple, the post-treatment is easy, the catalytic performance is better, and the economic benefit is higher.

Description

Technical Field

[0001] The invention relates to the technical field of citronellyl acetate preparation, in particular to a method for synthesizing citronellyl acetate. Background Art

[0002] Citronellyl acetate, chemical name 3,7-dimethyl-6-octenyl-1-acetate, is a colorless liquid with fresh fruit aroma, almost insoluble in water, easily soluble in methanol, ethanol and chloroform. Its aroma has the sweet fruity aroma of white lemon, bergamot, raw pear, plum, lychee, fresh rose, lemongrass, bellflower, lavender, with the background of green grass, and the taste of rose and fruit. Due to its obvious aroma characteristics, it is favored by perfumers and is used to mix rose, gardenia, lily of the valley, carnation, yew and other floral flavors and lemon, apricot, apple, banana, grape and other fruit flavors. It is an important spice ingredient and has been widely used in food and cosmetics.

[0003] The traditional production methods of citronella acetate include natural extraction and chemical synthesis. Since citronella acetate is naturally present in some vegetable oils such as citronella oil, citronella oil and rose oil, citronella acetate can be separated from some plant essential oils by distillation: however, due to the high cost of distillation and the scarcity of natural raw materials, it is not suitable for large-scale industrial production, so the application of natural extraction is limited. At present, the production of citronella acetate, except for a very small number of natural extraction methods, the rest are synthesized by traditional chemical methods. The disadvantages of the traditional chemical synthesis method are as follows: first, the method uses inorganic acid and organic acid as catalysts, the amount of catalyst is large, the corrosion rate of equipment in the production process is fast, a large amount of alkali is needed to neutralize the catalyst after the reaction, the catalyst cannot be recycled, and a large amount of waste water is easily generated, which seriously pollutes the environment. Secondly, during the reaction process, the high temperature and high pressure production conditions are prone to other side reactions and pollute the environment. Moreover, the synthetic method can be prepared by esterification of citronellol, acetic anhydride, sulfuric acid, etc. according to the usual method, but in fact its yield is about 85%, the yield is low, and the post-processing pollutants are large, thus hindering the application prospects of this method.

[0004] Therefore, we developed a new method for synthesizing citronellyl acetate. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] In view of the deficiencies in the prior art, the present invention provides a method for synthesizing citronellyl acetate. The preparation method uses a solid superacid as a catalyst. As a new type of catalyst, the solid superacid has the advantages of high catalytic activity, good selectivity, easy separation from the product, low acid pollution, and recyclability. The method solves the problem that the traditional production methods of citronellyl acetate in the prior art include natural extraction method and chemical synthesis method. However, due to the high distillation cost and the shortage of natural raw materials, it is not suitable for large-scale industrial production, so the application of the natural extraction method is limited. The chemical synthesis method cannot be recycled and is prone to generate a large amount of wastewater, which seriously pollutes the environment. Secondly, in the reaction process, the high temperature and high pressure production conditions are prone to generate other side reactions and pollute the environment. Both methods have major defects.

[0007] (II) Technical solution

[0008] To achieve the above objectives, the present invention is implemented by the following technical scheme: a method for synthesizing citronella acetate, the preparation method using citronellol and acetic anhydride as raw materials, in SO 2-4 / TiO2-Fe2O3 solid super acid catalyst to obtain citronella acetate. The specific operation steps of the synthesis method of citronella acetate containing solid super acid as catalyst are as follows:

[0009] Step 1: Catalyst preparation: First, the SO 2-4 / TiO2-Fe2O3 solid superacid catalyst, TiCl4 solution and FeCl3·6H2O aqueous solution were mixed according to a certain Ti-Fe molar ratio and then stirred with a magnetic stirrer;

[0010] Add 35% ammonia water by mass to the mixed solution until complete precipitation, filter the precipitate and wash it with distilled water, then dry it in an oven at 150°C, take it out and grind it with a mortar, soak it in sulfuric acid for 24 hours, filter it, dry it in an oven at 150°C and grind it again, and finally calcine it in a muffle furnace at 550-650°C for 10 hours to obtain the catalyst;

[0011] Step 2, catalyst synthesis reaction: add citronellol and acetic anhydride into a reactor, then add SO2-4 / TiO2-Fe2O3 solid superacid, stir and heat to react, and obtain a reaction solution, wherein the reaction temperature is 65-75°C and the reaction time is 3 hours;

[0012] Step 3: After the reaction is completed, filter to remove SO 2-4 / TiO2-Fe2O3 solid superacid catalyst, the obtained filtrate is crude citronellyl acetate, and further vacuum distillation is performed to obtain citronellyl acetate.

[0013] Preferably, the citronellol is synthetic citronellol with a purity of 98%, and the acetic anhydride is an industrial-grade raw material with a purity of more than 99%.

[0014] Preferably, in step 1, the concentrations of the TiCl4 solution and the FeCl3·6H2O aqueous solution are both 0.5 mol / L.

[0015] Preferably, in step 2, the mass ratio of citronellol to acetic anhydride is 1:1.1-1.5, and the SO 2-4 The added amount of / TiO2-Fe2O3 solid super acid is 1-5% of the total mass of citronellol and acetic anhydride.

[0016] Preferably, the reactor in step 2 is a round-bottom flask, and the heating method adopted is heating with an electromagnetic heating jacket.

[0017] Preferably, the reaction liquid in step 3 is transferred to a vacuum distillation device after recovering the catalyst and oil, and acetic acid and acetic anhydride are recovered by low vacuum, and further vacuum distilled to obtain citronella acetate.

[0018] Preferably, the temperature of the reduced pressure distillation of citronellyl acetate in step three is 100-135° C. and the vacuum degree is 50-100 Pa.

[0019] (III) Beneficial effects

[0020] The present invention provides a method for synthesizing citronellyl acetate, which has the following beneficial effects:

[0021] The synthesis method of citronellyl acetate uses a solid superacid as a catalyst, and SO 2-4 / Under the catalytic action of TiO2-Fe2O3 solid superacid, citronellol and acetic anhydride are heated and stirred at 65-75°C for 3 hours to complete the esterification reaction, and a thermodynamic equilibrium state can be reached. The content of the prepared citronellol acetate is about 94-95%, and the content of citronellol is about 0.2-0.5%. The solid superacid of the preparation method is a new type of catalyst with high catalytic activity, good selectivity, easy separation from the product, low acid pollution and recyclability, and has been widely used in industry. Citronellol acetate with a high content can be prepared by purification in a distillation tower section, meeting the standards of food additives and spice products. Compared with the prior art, the present invention uses a solid superacid as a catalyst, has a rapid reaction, a high yield, adopts a one-pot method for reaction, is simple to operate, and is easy to post-process. The present invention solves the problems that the traditional production methods of citronella acetate in the prior art include a natural extraction method and a chemical synthesis method, and the natural raw materials are scarce due to the high distillation cost, and are not suitable for large-scale industrial production, so the application of the natural extraction method is limited; the chemical synthesis agent cannot be recycled, and a large amount of waste water is easily generated, which seriously pollutes the environment. Secondly, during the reaction process, the high temperature and high pressure production conditions are easy to generate other side reactions and pollute the environment. The two methods each have major defects. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only 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.

[0023] The preparation method uses citronellol and acetic anhydride as raw materials, 2-4 Citronellyl acetate is obtained by reaction under the action of TiO2-Fe2O3 solid super acid catalyst, wherein citronellol is synthetic citronellol with a purity of 98%, and acetic anhydride is an industrial grade raw material with a purity of more than 99%.

[0024] The specific operation steps of the synthesis method of citronella acetate containing solid superacid as catalyst are as follows:

[0025] Step 1: Catalyst preparation: First, SO 2-4 / TiO2-Fe2O3 solid superacid catalyst, TiCl4 solution and FeCl3·6H2O aqueous solution are mixed according to a certain Ti-Fe molar ratio, and then stirred with a magnetic stirrer, wherein the concentrations of the TiCl4 solution and the FeCl3·6H2O aqueous solution are both 0.5 mol / L;

[0026] Add 35% ammonia water by mass to the mixed solution until complete precipitation, filter the precipitate and wash it with distilled water, then dry it in an oven at 150°C, take it out and grind it with a mortar, soak it in sulfuric acid for 24 hours, filter it, dry it in an oven at 150°C and grind it again, and finally calcine it in a muffle furnace at 550-650°C for 10 hours to obtain the catalyst;

[0027] Step 2: Catalyst synthesis reaction: Add citronellol and acetic anhydride into the reactor, then add SO 2-4 / TiO2-Fe2O3 solid super acid, stirring and heating to react, to obtain a reaction solution, wherein the reaction temperature is 65-75°C, the reaction time is 3 hours, the reactor in step 2 is a round-bottom flask, and the heating method used is electromagnetic heating jacket heating;

[0028] Wherein, in step 2, the mass ratio of citronellol to acetic anhydride is 1:1.1-1.5, SO 2-4 / The amount of TiO2-Fe2O3 solid superacid added is 1-5% of the total mass of citronellol and acetic anhydride;

[0029] Step 3: After the reaction is completed, filter to remove SO 2-4 / TiO2-Fe2O3 solid superacid catalyst, the obtained filtrate is crude citronellyl acetate, further vacuum distillation to obtain citronellyl acetate;

[0030] Specifically, the reaction liquid in step 2 is transferred to a vacuum distillation device after recovering the catalyst and oil, and acetic acid and acetic anhydride are recovered by low vacuum, and further vacuum distilled to obtain citronella acetate, wherein the temperature of the vacuum distillation of citronella acetate in step 3 is 100-135° C., and the vacuum degree is 50-100 Pa;

[0031] Reduced pressure distillation (also known as vacuum distillation) is an important method for separating and purifying compounds, mainly because reduced pressure distillation can reduce the boiling point of the reaction products, thereby avoiding decomposition, oxidation or polymerization during the distillation process. It is especially suitable for the separation and purification of high-boiling point substances and those compounds that have been thermally decomposed, oxidized or polymerized before reaching the boiling point during atmospheric distillation.

[0032] Corresponding to the present application, an esterification reaction occurs during the generation of citronella acetate in the present application, and the product of the esterification reaction usually has a high boiling point. If distillation is performed at normal pressure, the product may decompose due to excessively high temperature. Through reduced pressure distillation, distillation can be performed at a lower temperature, effectively protecting the product from damage. This method can effectively avoid the decomposition of the product at high temperature, reduce the occurrence of side reactions, and thus maintain the purity, quality and stability of citronella acetate.

[0033] Example 1

[0034] A method for synthesizing citronellyl acetate comprises the following specific steps:

[0035] Step 1, catalyst preparation: take a certain volume of 0.5 mol / L TiCl4 solution and a certain volume of 0.5 mol / L FeCl3·6H2O aqueous solution respectively, make the Ti-Fe molar ratio therein 1:2, and then stir with a magnetic stirrer;

[0036] Add 35% ammonia water by mass to each mixed solution in turn until complete precipitation occurs, turn off the magnetic stirrer, let stand for 5 hours, remove the supernatant, filter the precipitate, wash the precipitate with distilled water, dry it in a 150°C oven, take it out and grind it with a mortar, soak it in 0.5 mol / L sulfuric acid for 24 hours, filter it, dry it in a 150°C oven and grind it again, and finally roast it in a muffle furnace at 550-650°C for 10 hours to obtain the catalyst;

[0037] Step 2, catalyst synthesis reaction: 156 g citronellol (content 98.0%), SO 2-4 1.50 g of TiO2-Fe2O3 solid super acid and 102 g of acetic anhydride were added into the round-bottom flask in sequence, and heated with an electromagnetic heating jacket to a temperature of 65-75°C, and maintained at this temperature for 3 hours;

[0038] Step 3: After the reaction is completed, the machine is shut down to cool down, the catalyst is recovered, and the oil is transferred to a vacuum distillation device to recover acetic acid and acetic anhydride under low vacuum. Then, the vacuum degree is 50-100 Pa and the temperature is 100-135° C. to obtain about 190 g of citronella acetate (citronellol: 0.2-0.5%, citronella acetate: 94.0-95.0%).

[0039] Example 2

[0040] A method for synthesizing citronellyl acetate comprises the following specific steps:

[0041] Step 1, preparation of catalyst: taking a certain volume of 0.5 mol / L TiCl4 solution and a certain volume of 0.5 mol / L FeCl3·6H2O aqueous solution respectively, mixing them at a Ti-Fe molar ratio of 1:1, and then stirring with a magnetic stirrer;

[0042] Add 35% ammonia water by mass to each mixed solution in turn until complete precipitation occurs, turn off the magnetic stirrer, let stand for 5 hours, remove the supernatant, filter the precipitate, wash the precipitate with distilled water, dry it in a 150°C oven, take it out and grind it with a mortar, soak it in 0.5 mol / L sulfuric acid for 24 hours, filter it, dry it in a 150°C oven and grind it again, and finally roast it in a muffle furnace at 550-650°C for 10 hours to obtain the catalyst;

[0043] Step 2, catalyst synthesis reaction: 156 g citronellol (content 98.0%), SO 2-4 1.50 g of TiO2-Fe2O3 solid super acid and 102 g of acetic anhydride were added into the round-bottom flask in sequence, and heated with an electromagnetic heating jacket to a temperature of 65-75°C, and maintained at this temperature for 3 hours;

[0044] Step 3: After the reaction is completed, the machine is shut down to cool down, the catalyst is recovered, and the oil is transferred to a vacuum distillation device to recover acetic acid and acetic anhydride under low vacuum. Then, the vacuum degree is 50-100 Pa and the temperature is 100-135° C. to obtain about 190 g of citronella acetate (citronellol: 0.2-0.5%, citronella acetate: 94.7-95.2%).

[0045] Example 3

[0046] A method for synthesizing citronellyl acetate comprises the following specific steps:

[0047] Step 1, preparation of catalyst: taking a certain volume of 0.5 mol / L TiCl4 solution and a certain volume of 0.5 mol / L FeCl3·6H2O aqueous solution respectively, mixing them at a Ti-Fe molar ratio of 2:1, and then stirring with a magnetic stirrer;

[0048] Add 35% ammonia water by mass to each mixed solution in turn until complete precipitation occurs, turn off the magnetic stirrer, let stand for 5 hours, remove the supernatant, filter the precipitate, wash the precipitate with distilled water, dry it in a 150°C oven, take it out and grind it with a mortar, soak it in 0.5 mol / L sulfuric acid for 24 hours, filter it, dry it in a 150°C oven and grind it again, and finally roast it in a muffle furnace at 550-650°C for 10 hours to obtain the catalyst;

[0049] Step 2, catalyst synthesis reaction: 156 g citronellol (content 98.0%), SO 2-4 1.50 g of TiO2-Fe2O3 solid super acid and 102 g of acetic anhydride were added into the round-bottom flask in sequence, and heated with an electromagnetic heating jacket to a temperature of 65-75°C, and maintained at this temperature for 3 hours;

[0050] Step 3: After the reaction is completed, the machine is shut down to cool down, the catalyst is recovered, and the oil is transferred to a vacuum distillation device to recover acetic acid and acetic anhydride under low vacuum. Then, the vacuum degree is 50-100 Pa and the temperature is 100-135° C. to obtain about 190 g of citronella acetate (citronellol: 0.2-0.5%, citronella acetate: 94.2-95.2%).

[0051] Comparative Example 1

[0052] Compared with Example 1, this comparative example only changes the "prepared SO 2-4 / TiO2-Fe2O3 solid superacid catalyst" was replaced with "an equal amount of common Raney nickel catalyst on the market", and based on the characteristics of Raney nickel itself, the reaction temperature range was modified to 60-65°C, and the remaining steps and parameters were the same, and citronellyl acetate was finally obtained;

[0053] Among them, Raney nickel is also translated as Lanny nickel, which is a solid heterogeneous catalyst composed of fine grains of nickel-aluminum alloy with a porous structure. Raney nickel appears as a fine gray powder on the surface, but from a microscopic perspective, each tiny particle in the powder is a three-dimensional porous structure. This porous structure greatly increases its surface area. The extremely large surface area brings high catalytic activity, which makes Raney nickel widely used as a heterogeneous catalyst in hydrogenation reactions in organic synthesis and industrial production. It is usually used as a hydrogenation catalyst for organic compounds and can be used for hydrogenation reduction reactions of compounds containing unsaturated bonds such as aldehydes and ketones.

[0054] Furthermore, in conjunction with the limitation of the suitable temperature for the esterification reaction under mild conditions, Raney nickel has the best catalytic effect on citronellyl acetate at 60-65°C. Within this temperature range, the catalytic activity of Raney nickel is relatively high and can effectively promote the hydrogenation reaction of citronellyl acetate. Therefore, the reaction temperature range is modified to 60-65°C.

[0055] Specifically, a method for synthesizing citronellyl acetate comprises the following specific steps:

[0056] Step 1: Purchase the Raney nickel catalyst from a reagent company;

[0057] Step 2: 156 g citronellol (content 98.0%), 1.50 g Raney nickel catalyst and 102 g acetic anhydride were added into a round-bottom flask in sequence, and heated with an electromagnetic heating jacket to a temperature of 60-65° C., and maintained at this temperature for 3 hours;

[0058] Step 3: After the reaction is completed, the machine is shut down to cool down, the catalyst is recovered, and the oil is transferred to a vacuum distillation device to recover acetic acid and acetic anhydride under low vacuum. Then, the vacuum degree is 50-100 Pa and the temperature is 100-135° C. to obtain about 190 g of citronella acetate (citronellol: 0.2-0.5%, citronella acetate: 82.5-84.5%).

[0059] Comparative Example 2

[0060] Compared with Example 1, this comparative example only 2-4 / TiO2-Fe2O3 solid superacid catalyst" was replaced with "an equal amount of palladium carbon catalyst commonly found on the market", the reaction temperature range was modified to 60-65°C, and the remaining steps and parameters were the same, and citronellyl acetate was finally obtained;

[0061] Among them, palladium carbon is a chemical substance in the form of black powder particles, a catalyst, which is made by loading metal palladium powder on activated carbon. Its main function is to catalyze the hydrogenation of unsaturated hydrocarbons or CO. Palladium carbon has the characteristics of high hydrogenation reduction, good selectivity, stable performance, small feed ratio during use, repeated use, easy recycling, etc., so it is widely used in the hydrogenation reduction refining process of petrochemical industry, pharmaceutical industry, electronics industry, fragrance industry, dye industry and other fine chemicals;

[0062] Furthermore, when palladium carbon is used to catalyze citronellyl acetate, the optimal temperature range is 60°C to 70°C. Within this temperature range, the palladium carbon catalyst can exhibit the best catalytic efficiency and ensure that the reaction proceeds in a direction that is conducive to the formation of esters. Therefore, optionally, in combination with Comparative Example 1, the difference between the two comparative examples is reduced and the reaction temperature range is also modified to 60-65°C.

[0063] Specifically, a method for synthesizing citronellyl acetate comprises the following specific steps:

[0064] Step 1: Purchase palladium carbon catalyst from a reagent company;

[0065] Step 2: 156 g citronellol (content 98.0%), 1.50 g palladium carbon catalyst and 102 g acetic anhydride were added into a round-bottom flask in sequence, and heated with an electromagnetic heating mantle to a temperature of 60-65° C., and maintained at this temperature for 5 hours;

[0066] Step 3: After the reaction is completed, the machine is shut down to cool down, the catalyst is recovered, and the oil is transferred to a vacuum distillation device to recover acetic acid and acetic anhydride under low vacuum. Then, the vacuum degree is 50-100 Pa and the temperature is 100-135 ° C. to obtain about 190 g of citronella acetate (citronellol: 0.2-0.5%, citronella acetate: 85.3-91.5%);

[0067] Based on the data obtained from the above experiments, the following table is obtained.

[0068] Table 1 Summary of experimental data in Example 1-Example 3 and Comparative Example 1-Comparative Example 2

[0069] project Ti-Fe molar ratio Catalyst mass / g Reaction temperature / ℃ Yield / % Example 1 1∶2 1.50 65-75 94.0-95.0 Example 2 1∶1 1.50 65-75 94.7-95.2 Example 3 2∶1 1.50 65-75 94.2-95.2 Comparative Example 1 / 1.50 60-65 82.5-84.5 Comparative Example 2 / 1.50 60-65 85.3-91.5

[0070] Data Analysis:

[0071] It can be seen from Table 1 that the synthesis method prepared by the present invention: SO at different Ti-Fe molar ratios 2-4 / Under the catalytic action of TiO2-Fe2O3 solid superacid, citronellol and acetic anhydride can complete the esterification reaction by heating and stirring at 65-75℃ for 3h, and can reach thermodynamic equilibrium (citronellol acetate content: about 94-95%, citronellol content: about 0.2-0.5%). 2-4 / TiO2-Fe2O3 solid superacid has better catalytic performance and higher economic benefits.

[0072] Specifically, in Example 1, 0.5 mol / L TiCl4 solution and a certain volume of 0.5 mol / L FeCl3·6H2O aqueous solution were mixed at a Ti-Fe molar ratio of 1:2 to obtain the final SO 2-4 / TiO2-Fe2O3 solid superacid catalyst is then reacted with citronellol and acetic anhydride for esterification at a temperature range of 65-75°C to obtain about 190g of citronellyl acetate, with the proportion of citronellyl acetate being 94.0-95.0%.

[0073] Example 2: A 0.5 mol / L TiCl4 solution and a certain volume of a 0.5 mol / L FeCl3·6H2O aqueous solution were mixed at a Ti-Fe molar ratio of 1:1 to obtain the final SO 2-4 / TiO2-Fe2O3 solid superacid catalyst is then reacted with citronellol and acetic anhydride for esterification at a temperature range of 65-75°C to obtain about 190g of citronellyl acetate, with the proportion of citronellyl acetate being 94.7-95.2%.

[0074] Example 3: The final SO was prepared by mixing 0.5 mol / L TiCl4 solution and a certain volume of 0.5 mol / L FeCl3·6H2O aqueous solution with a Ti-Fe molar ratio of 2:1. 2-4 / TiO2-Fe2O3 solid superacid catalyst is then reacted with citronellol and acetic anhydride for esterification at a temperature range of 65-75°C to obtain about 190g of citronellyl acetate, with the proportion of citronellyl acetate being 94.2-95.2%.

[0075] Comparing Example 1, Example 2, and Example 3, under the same conditions of other parameters, the yield of Example 2 is the highest, the yield of Example 3 is the second, and the yield of Example 1 is the lowest. It is obvious that in the preparation of SO 2-4 / TiO2-Fe2O3 solid superacid catalyst, the different Ti-Fe molar ratios may affect the structure, acidity, active site distribution and catalytic performance of the catalyst, thus leading to differences in the yield of citronellyl acetate.

[0076] The following are some possible reasons why the catalyst with a Ti-Fe molar ratio of 2:1 produced less citronellyl acetate than the 1:1 catalyst:

[0077] 1. Effect of acidity: The acidity of solid superacids is crucial to their catalytic performance. Different Ti-Fe molar ratios may affect the acid strength and amount of the catalyst. At a 2:1 molar ratio, different acid centers may be formed, and the acidity of these acid centers is not as strong as that at a 1:1 molar ratio, thus affecting the catalytic efficiency.

[0078] 2. Number and distribution of active sites: At a molar ratio of 2:1, the relatively low Fe content in the catalyst may lead to a reduced number of active sites or an uneven distribution of active sites, which may reduce the catalytic efficiency of the catalyst.

[0079] 3. Changes in catalyst structure: Different Ti-Fe molar ratios may lead to changes in the microstructure of the catalyst, such as grain size, pore structure, specific surface area, etc. These structural differences may affect the adsorption capacity of the catalyst and the contact efficiency of the reactants.

[0080] 4. Interaction and synergistic effect: At a molar ratio of 1:1, the interaction between Ti and Fe may be stronger, resulting in a synergistic effect that helps to improve the activity of the catalyst. However, at a molar ratio of 2:1, this synergistic effect may be weakened, resulting in a decrease in catalytic activity.

[0081] 5. Increase of side reactions: Different molar ratios may result in different degrees of promotion of side reactions by the catalyst. At a molar ratio of 2:1, side reactions may occur more easily, consuming the reactants and thus reducing the yield of the target product.

[0082] 6. Thermal stability: Different molar ratios may affect the thermal stability of the catalyst. At higher Ti contents, the thermal stability of the catalyst may be poor, resulting in catalyst deactivation during the reaction. Similarly, higher Fe contents may affect the thermal stability of the catalyst, resulting in easy catalyst deactivation during the reaction.

[0083] In order to optimize the performance of the catalyst, it is usually necessary to conduct a detailed study of the catalyst preparation conditions, including the molar ratio of the raw materials, drying conditions, activation process, etc. By adjusting these parameters, the activity and selectivity of the catalyst can be improved, thereby increasing the yield of citronellyl acetate. Experimental studies and characterization techniques (such as XRD, BET, NH3-TPD, FTIR, etc.) can help understand the relationship between catalyst structure and performance.

[0084] The following are some reasons why the catalyst with a Ti-Fe molar ratio of 1:2 may have a lower yield than the catalyst with a Ti-Fe molar ratio of 1:1:

[0085] 1. Changes in acidic centers: The catalytic activity of solid superacids depends largely on the type and number of their acidic centers. In the case of a Ti-Fe molar ratio of 1:2, the relatively high Fe content may cause changes in the acidic centers of the catalyst, which may be detrimental to the esterification reaction.

[0086] 2. Coverage of active sites: Higher Fe content may cause the active sites on the TiO2 surface to be covered by Fe2O3, reducing the number of active sites available for catalytic reactions and thus reducing the catalytic efficiency.

[0087] Other factors are similar to the above analysis and will not be elaborated here. In summary, the solid superacid prepared with a relatively balanced Ti-Fe molar ratio has better catalytic performance, and Ti is more critical in the preparation of solid superacids. In order to improve the yield of the catalyst, the preparation and reaction conditions of the catalyst can be optimized in the following ways:

[0088] -Optimize preparation conditions: adjust parameters such as solution mixing ratio, drying temperature, activation temperature and time.

[0089] - Catalyst Characterization: The catalysts are characterized in detail using techniques such as X-ray diffraction (XRD), nitrogen adsorption (BET), Fourier transform infrared spectroscopy (FTIR) to understand their structure and properties.

[0090] - Optimization of reaction conditions: adjusting reaction parameters such as reaction temperature, reaction time, molar ratio of alcohol and acid, etc.

[0091] Through these methods, the relationship between catalyst activity and Ti-Fe molar ratio can be better understood, and the preparation of catalysts can be optimized accordingly to increase the yield of citronellyl acetate.

[0092] Comparative Example 1: Due to the "prepared SO 2-4 / TiO2-Fe2O3 solid superacid catalyst" was replaced with "an equal amount of common Raney nickel catalyst on the market", and, based on the characteristics of Raney nickel itself, the reaction temperature range was modified to 60-65°C to obtain about 190g of citronellyl acetate, and the proportion of citronellyl acetate was 82.5-84.5%;

[0093] In the reaction of catalyzing the synthesis of citronellyl acetate using Raney nickel and solid superacid as catalysts, the difference in yield may be caused by the following factors:

[0094] (1) Catalyst activity: Different catalysts have different activities. Solid superacids usually have higher acidity and catalytic activity, and can more effectively promote the esterification reaction; (2) Catalyst selectivity: The selectivity of the catalyst determines its efficiency in forming the target product. Solid superacids may have higher selectivity for the formation of citronellyl acetate, while Raney nickel may be more inclined to other side reactions; (3) Reaction conditions: Different catalysts may require different reaction conditions (such as temperature, pressure, solvent, etc.) to achieve optimal activity. If the reaction conditions are more suitable for solid superacids, then its yield will naturally be higher; (4) Surface area and structure of the catalyst: Solid superacids usually have a large specific surface area and a specific pore structure, which helps to increase the contact area with the reactants, thereby increasing the yield; (5) Side reactions: Raney nickel may cause more side reactions during the catalytic process, such as hydrogenation reactions or other reduction reactions. These side reactions will consume the raw materials and reduce the yield of the target product; (6) Stability of the catalyst: Solid superacids may be more stable under reaction conditions, while Raney nickel may be deactivated due to poisoning or sintering, resulting in a decrease in catalytic efficiency; (7) Differences in adsorption of raw materials: Solid superacids may have a stronger adsorption capacity for reactants, which helps to activate the reactant molecules, thereby increasing the yield.

[0095] Comparative Example 2: Due to the addition of "SO 2-4 / TiO2-Fe2O3 solid superacid catalyst" was replaced with "an equal amount of palladium-carbon catalyst commonly found on the market", and based on the characteristics of the palladium-carbon catalyst itself, the reaction temperature range was modified to 60-65°C to obtain about 190g of citronellyl acetate, and the proportion of citronellyl acetate was 85.3-91.5%;

[0096] The yields of palladium carbon and solid superacid as catalysts in the catalytic synthesis of citronellyl acetate are different. Possible reasons include the following:

[0097] (1) Different catalytic mechanisms: Palladium-carbon catalysts are usually used for hydrogenation reactions or coupling reactions, while solid superacid catalysts are more commonly used for esterification reactions. The synthesis of citronellal acetate is an esterification reaction, and solid superacids may be more suitable for the catalytic mechanism of this type of reaction; (2) Catalyst acidity: Solid superacids have high acidity and can effectively promote the protonation of carboxylic acids and alcohols in esterification reactions, thereby accelerating the formation of esters. Palladium-carbon catalysts do not have this strong acidity, so they may not be as good as solid superacids in promoting esterification reactions; (3) Active sites: The surface of solid superacids has abundant active sites, which can effectively adsorb reactant molecules and increase the collision frequency between reactants, thereby increasing the yield. The palladium-carbon catalyst may have fewer active sites, which is not conducive to the esterification reaction; (4) Selectivity: the palladium-carbon catalyst may promote the occurrence of side reactions during the catalytic process, such as hydrogenation or other reduction reactions. These side reactions will consume the raw materials and reduce the yield of citronellal acetate; (5) Catalyst stability: solid superacids may be more stable under reaction conditions, while palladium-carbon catalysts may be deactivated due to poisoning, sintering or agglomeration, resulting in a decrease in catalytic efficiency; (6) Reaction conditions: solid superacid catalysts may be more suitable for specific reaction conditions, such as temperature, pressure and solvent, which may be more conducive to the esterification reaction; (7) Interaction between raw materials and catalysts: the interaction between solid superacids and reactants may be stronger, which helps to activate the reactant molecules and thus increase the yield.

[0098] In summary: citronella acetate is a colorless liquid with a fresh fruit aroma, a strong rose aroma, and an apricot fruit aroma, quite similar to lemon oil, and has been widely used in the fields of food and cosmetics. Natural citronella acetate exists in more than 20 essential oils such as citronella oil and geranium oil. Due to the lack of natural raw materials, it is not suitable for large-scale industrial production. Synthetic preparation can be esterified by citronellol, acetic anhydride, sulfuric acid, etc. according to the usual method, with a yield of about 85%, a low yield, and a large number of post-processing pollutants.

[0099] The present invention provides a preparation method of citronellyl acetate. The preparation method uses a solid superacid as a catalyst. The solid superacid, as a new type of catalyst, has the advantages of high catalytic activity, good selectivity, easy separation from the product, low acid pollution, and recyclability, and has been widely used in industry. Citronellyl acetate with a high content can be prepared by purification in a distillation tower section, meeting the standards of food additives and spice products. Compared with the prior art, the present invention uses a solid superacid as a catalyst, has a rapid reaction, a high yield, adopts a one-pot method for reaction, is simple to operate, and is easy to post-process.

[0100] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for synthesizing citronellyl acetate, characterized in that: The preparation method uses citronellol and acetic anhydride as raw materials, 2-4 / TiO2-Fe2O3 solid super acid catalyst to obtain citronella acetate. The specific operation steps of the synthesis method of citronella acetate containing solid super acid as catalyst are as follows: Step 1: Catalyst preparation: First, the SO 2-4 / TiO2-Fe2O3 solid superacid catalyst, TiCl4 solution and FeCl3·6H2O aqueous solution were mixed according to a certain Ti-Fe molar ratio and then stirred with a magnetic stirrer; Add 35% ammonia water by mass to the mixed solution until complete precipitation, filter the precipitate and wash it with distilled water, then dry it in an oven at 150°C, take it out and grind it with a mortar, soak it in sulfuric acid for 24 hours, filter it, dry it in an oven at 150°C and grind it again, and finally calcine it in a muffle furnace at 550-650°C for 10 hours to obtain the catalyst; Step 2, catalyst synthesis reaction: add citronellol and acetic anhydride into a reactor, then add SO2-4 / TiO2-Fe2O3 solid superacid, stir and heat to react, and obtain a reaction solution, wherein the reaction temperature is 65-75°C and the reaction time is 3 hours; Step 3: After the reaction is completed, filter to remove SO 2-4 / TiO2-Fe2O3 solid superacid catalyst, the obtained filtrate is crude citronellyl acetate, and further vacuum distillation is performed to obtain citronellyl acetate.

2. The method for synthesizing citronellyl acetate according to claim 1, wherein The citronellol is synthetic citronellol with a purity of 98%, and the acetic anhydride is an industrial-grade raw material with a purity of more than 99%.

3. The method for synthesizing citronellyl acetate according to claim 1, wherein: In the step 1, the concentrations of the TiCl4 solution and the FeCl3·6H2O aqueous solution are both 0.5 mol / L.

4. The method for synthesizing citronellyl acetate according to claim 1, wherein: In the step 2, the mass ratio of citronellol to acetic anhydride is 1:1.1-1.5, and the SO 2-4 The added amount of the TiO2-Fe2O3 solid super acid is 1-5% of the total mass of citronellol and acetic anhydride.

5. The method for synthesizing citronellyl acetate according to claim 4, characterized in that: The reactor in step 2 is a round-bottom flask, and the heating method adopted is heating with an electromagnetic heating jacket.

6. The method for synthesizing citronellyl acetate according to claim 1, characterized in that: The reaction liquid in step 3 is transferred to a vacuum distillation device after recovering the catalyst and oil, and acetic acid and acetic anhydride are recovered by low vacuum, and further vacuum distilled to obtain citronella acetate.

7. The method for synthesizing citronellyl acetate according to claim 1, characterized in that: In the step 3, the temperature of the reduced pressure distillation of citronella acetate is 100-135° C., and the vacuum degree is 50-100 Pa.