A kind of ethyl benzoate and preparation method thereof

Abstract

The invention discloses a kind of ethyl benzoate and its preparation method, belong to the field of fine chemical preparation. The preparation method of ethyl benzoate is, in the first step, acrolein and ethyl malonate are subjected to Kneuwengel condensation reaction to generate enester under triethylenediamine catalyst; In the second step, the diene ester and acrolein generated by the first step undergo Diels-Alder reaction to obtain cyclohexene carboxylate substituted with aldehyde group; In the third step, the cyclohexene carboxylate substituted with aldehyde group is subjected to decarbonylation and dehydrogenation reaction to generate ethyl benzoate under metal catalyst. The reaction conditions of the present invention are simple, the catalyst is simple and easy to obtain, and the cost is low. It is a method for synthesizing spices and flavors through a biomass route with great industrialization prospects.

Description

Technical Field

[0001] The invention belongs to the field of fine chemical preparation, and particularly relates to ethyl benzoate and a preparation method thereof. Background Art

[0002] Fossil energy (oil, coal, and natural gas) has always held an unshakable position in people's daily lives and production. On the one hand, traditional fossil energy can be used to synthesize the chemicals we need to meet our daily needs. However, due to the increasing depletion and non-renewable nature of fossil energy, the carbon dioxide emitted during its production process can contribute to environmental problems such as the greenhouse effect. Therefore, the development of new energy sources that can replace fossil resources holds great potential for application. Biomass energy, due to its abundant reserves, renewable nature, and the recycling of carbon dioxide during its utilization process, can achieve zero carbon dioxide emissions. Therefore, using biomass energy to synthesize various fine chemicals can fully utilize resources and achieve greater ecological and economic benefits.

[0003] Ethyl benzoate, also known as ethyl benzoate, has a strong wintergreen and fruity aroma and is naturally found in peaches and pineapples. It is commonly used in stronger floral fragrances, particularly ylang-ylang, as well as in flavors such as carnation and tuberose. It is also suitable for formulating non-floral fragrances such as freshly cut grass and fennel. It can be used with cistus products to create leather-scented fragrances. It is also used as a flavoring in fresh fruit, berry, and nut flavors, such as banana, cherry, plum, and grape flavors, as well as in tobacco and wine flavors. It is also used as a solvent for cellulose esters, cellulose ethers, and resins, and is in high market demand.

[0004] Currently, ethyl benzoate is synthesized through the esterification reaction of benzoic acid and ethanol via the petroleum route. Benzoyl chloride and ethanol are also used for esterification. However, as mentioned above, fossil energy is non-renewable and will cause environmental problems. Therefore, it is of great significance to explore a mild biomass route to synthesize ethyl benzoate.

[0005] Biomass can be fermented with microorganisms to produce lactic acid, which can then be converted to acrolein through simple esterification and dehydration reactions. Glucose from biomass hydrolysis can be oxidized, hydrogenated, and hydrogenolyzed to produce malonic acid, which can then be further esterified to produce monoethyl malonate. Cellulose can be directly hydrolyzed to produce ethylene glycol using tungsten carbide as a catalyst. Ethylene glycol dimethyl ether can then be obtained from biomass-derived ethylene glycol through a simple etherification reaction. The sources of these biomass raw materials have all been reported in the literature. Summary of the Invention

[0006] The present invention provides a novel method for preparing benzoic acid esters using acrolein and ethyl malonate as renewable raw materials. The raw materials and catalysts used are inexpensive and readily available, and the entire reaction process is simple. Compared to previous literature reports that used 4-dimethylaminopyridine as a catalyst and pyridine as a solvent for the diene esters produced by the reaction of acrolein and ethyl malonate, our method uses ethylene glycol dimethyl ether, which is more environmentally friendly and can be obtained from biomass, as a solvent. The reaction conditions are milder and have promising industrial application prospects.

[0007] The present invention is achieved through the following technical solutions:

[0008] A method for preparing ethyl benzoate comprises the following steps:

[0009]

[0010] (1) Acrolein and ethyl malonate undergo Knoevenagel condensation reaction in the presence of an alkali catalyst to produce a diene ester;

[0011] (2) The diene ester produced in the first step undergoes a Diels-Alder reaction with acrolein in the absence of a catalyst or solvent to produce an aldehyde-substituted cyclohexene carboxylate;

[0012] (3) Aldehyde-substituted cyclohexene carboxylate undergoes decarbonylation and dehydrogenation reaction in the presence of a metal catalyst to produce ethyl benzoate.

[0013] Based on the above scheme, preferably, the reaction medium in each step is as follows:

[0014] In step (1), the reaction medium is an organic solvent; the organic solvent includes one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DEF), water (H2O), γ-valerolactone (VL), ethylene glycol (EG), cyclohexane, methyl isobutyl ketone (MIBK), 1,4-dioxane, dimethyl sulfoxide (DMSO), toluene, 2-methyltetrahydrofuran (2-MeTHF), N-methylpyrrolidone (NMP), PEG-400, ethylene glycol dimethyl ether (EGDME) and diethylene glycol dimethyl ether (DEGDME), and the volume ratio of the added solvent to the acrolein is between 4.5 and 20;

[0015] In step (2), the reaction is carried out in the absence of a solvent;

[0016] In step (3), the solvent used includes ethyl acetate.

[0017] Based on the above scheme, preferably, the catalyst and conditions required for each step of the reaction are as follows:

[0018] In step (1), the base catalyst includes 4-dimethylaminopyridine (DMAP), diisopropylethylamine ( i One of Pr2NEt), 1,8-diazabicycloundec-7-ene (DBu), proline (Proline e), tetrahydropyrrole (Pyrrolidine), triethylamine (Et3N), and triethylenediamine (DABCO);

[0019] In step (2), the reaction is carried out in the absence of a catalyst;

[0020] In step (3), the metal catalyst used has a noble metal as an active component and a carbon material as a carrier; the metal catalyst used includes one of Pd / C, Pt / C, Rh / C, and Ru / C;

[0021] As a further preference of the above scheme, the catalyst and conditions required for each step of the reaction are as follows:

[0022] In step (1), the molar ratio of acrolein to monoethyl malonate is between 1:2 and 2:1; the reaction temperature is 30-80°C, the reaction time is between 12-48 hours, and the volume ratio of the added solvent to acrolein is preferably between 4.5-18;

[0023] In step (2), the molar ratio of acrolein to diene ester is between 1:2-3:1; the reaction temperature is between 80-140° C., and the reaction time is between 1-4 hours;

[0024] In step (3), the reaction temperature is between 180-260°C.

[0025] Based on the above scheme, preferably, the specific reaction conditions of each step are as follows:

[0026] In step (1), the molar ratio of acrolein to monoethyl malonate is 1:1-1:1.5; the reaction temperature is 40-70°C, the reaction time is between 24-36 hours, and the volume ratio of the added solvent to the acrolein is between 12-15;

[0027] In step (2), the molar ratio of acrolein to diene ester is between 2:1 and 3:1; the reaction temperature is between 100-120° C., and the reaction time is between 3-4 hours;

[0028] In step (3), the reaction temperature is between 200-240°C.

[0029] Based on the above scheme, preferably, the acrolein, ethyl malonate and ethylene glycol dimethyl ether are all prepared from biomass.

[0030] Ethyl benzoate prepared according to the above method.

[0031] The present invention has the following advantages:

[0032] Traditional synthetic routes use petroleum resources as raw materials, and fossil resources are increasingly depleted, and carbon dioxide is released during the production process, polluting the environment. The ethyl benzoate synthetic route provided by the present invention is environmentally friendly. It uses renewable biomass platform compounds as starting materials, has simple reaction conditions, and catalysts are readily available at low cost. Compared with the petroleum route, the biomass route can be reused, and literature reports show that the selected ethylene glycol dimethyl ether is greener than the pyridine in the literature and can be obtained from biomass. Therefore, the present invention is a method for synthesizing flavors and fragrances via a biomass route with great industrial prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is the GC spectrum of the enester prepared by the Knoevenagel condensation reaction of acrolein and monoethyl malonate catalyzed by triethylenediamine.

[0034] Figure 2 This is the GC spectrum of the aldehyde-substituted cyclohexene carboxylate prepared from the diene ester and acrolein generated in the present invention.

[0035] Figure 3 GC spectrum of ethyl benzoate prepared by decarbonylation and dehydrogenation of aldehyde-substituted cyclohexenecarboxylate.

[0036] Figure 4 The product of the Knoevenagel condensation reaction of acrolein and monoethyl malonate catalyzed by triethylenediamine is 1 H-NMR spectrum.

[0037] Figure 5 The product of the Knoevenagel condensation reaction of acrolein and monoethyl malonate catalyzed by triethylenediamine is 13 C-NMR spectrum.

[0038] Figure 6 Preparation of aldehyde-substituted cyclohexene carboxylate from diene ester and acrolein produced by the present invention 1 H-NMR spectrum.

[0039] Figure 7 Preparation of aldehyde-substituted cyclohexene carboxylate from diene ester and acrolein produced by the present invention 13 C-NMR spectrum.

[0040] Figure 8 Ethyl benzoate prepared by decarbonylation and dehydrogenation of aldehyde-substituted cyclohexene carboxylate 1 H-NMR spectrum.

[0041] Figure 9 Ethyl benzoate prepared by decarbonylation and dehydrogenation of aldehyde-substituted cyclohexene carboxylate13 C-NMR spectrum.

[0042] Figure 10 This is the reaction route for preparing ethyl benzoate from acrolein and ethyl malonate. DETAILED DESCRIPTION

[0043] The present invention will be described below with reference to specific embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0044] Comparative Example 1

[0045] Acrolein and ethyl malonate undergo Knoevenagel condensation reaction in the presence of an alkali catalyst to produce a diene ester.

[0046] In a 35 mL test tube, base catalyst 4-dimethylaminopyridine, acrolein and monoethyl malonate and pyridine solvent were added in sequence to react.

[0047]

[0048] Table 1. Effect of reaction conditions on the reaction

[0049]

[0050] As can be seen from the results in Table 1, when 10 mol% 4-dimethylaminopyridine is added as a catalyst and pyridine is used as a solvent, at 50°C, the molar ratio of acrolein to monoethyl malonate is 1:1.5, the volume ratio of solvent to acrolein is 4.5, and the reaction is carried out for 24 hours, the yield of diene ester can reach 60%.

[0051] Examples 1-40

[0052] Acrolein and ethyl malonate undergo Knoevenagel condensation reaction in the presence of an alkali catalyst to produce a diene ester.

[0053] In a 35 mL test tube, catalyst, acrolein and monoethyl malonate were added in sequence to react.

[0054]

[0055] Table 2. Effect of reaction conditions on the reaction

[0056]

[0057]

[0058] The results in Table 2 show that with the addition of 10 mol% triethylenediamine catalyst, ethylene glycol dimethyl ether as the solvent, a molar ratio of acrolein to ethyl malonate of 1:1.5 at 50°C, and a reaction time of 24 hours, the yield of diene ester reached 82%. Compared with Comparative Example 1, the present invention utilizes the biomass-derived, green solvent ethylene glycol dimethyl ether, achieving a higher yield and significant advantages.

[0059] Examples 41-50

[0060] The diene ester prepared in Example 39 and acrolein undergo a one-step dehydration and Diels-Alder reaction.

[0061] In a 15 mL reactor, diene ester 3 and acrolein 1 were added without adding a catalyst or solvent. The reaction was carried out at a certain temperature under a 2 MPa N2 atmosphere to obtain aldehyde-substituted cyclohexene carboxylate 4.

[0062]

[0063] Table 3. Effect of reaction conditions on the reaction

[0064]

[0065] The results in Table 3 show that, in the absence of a catalyst or solvent, under a nitrogen atmosphere of 2 MPa at 120°C, the molar ratio of diene ester to acrolein generated in the first step is 1:2, and the reaction is carried out for 4 hours. The yield of aldehyde-substituted cyclohexene carboxylate can reach 92%.

[0066] Examples 51-57

[0067] Example 50 Decarbonization and dehydrogenation of aldehyde-substituted cyclohexene carboxylate 4.

[0068] The fixed bed was used as a reactor, and an ethyl acetate solution (2 wt%) of cyclohexene carboxylate 4 substituted with aldehyde was added, followed by the addition of a catalyst, and the space velocity was 6.3 h -1 , nitrogen pressure is normal pressure, and the reaction is carried out at different temperatures to obtain ethyl benzoate 5.

[0069]

[0070] Table 4. Effect of reaction conditions on dehydrogenation reaction

[0071]

[0072] From the results in Table 4, it can be seen that with Pd / C as catalyst, ethyl acetate as reaction medium, normal pressure nitrogen, 220℃, and space velocity of 6.3h -1 Under the following reaction conditions, the yield of the target product ethyl benzoate can reach 97%.

Claims

1. A method for preparing ethyl benzoate, characterized in that: The steps include: (1) Acrolein and ethyl malonate react in the presence of an alkali catalyst to form a diene ester; (2) reacting the diene ester obtained in step (1) with acrolein in the absence of a catalyst and a solvent to produce an aldehyde-substituted cyclohexene carboxylate; (3) reacting the aldehyde-substituted cyclohexene carboxylate obtained in step (2) in the presence of a metal catalyst to produce ethyl benzoate; In step (1), the reaction medium is an organic solvent; the organic solvent is ethylene glycol dimethyl ether; The solvent used in step (3) is ethyl acetate; The base catalyst in step (1) is triethylenediamine; In step (2), the molar ratio of acrolein to diene ester is between 1:2 and 3:1; the reaction temperature is between 80 and 140° C., and the reaction time is between 1 and 4 hours; The metal catalyst in step (3) is one of Pd / C, Pt / C, Rh / C, and Ru / C.

2. The method for preparing ethyl benzoate according to claim 1, wherein: In step (1), the molar ratio of acrolein to monoethyl malonate is between 1:2 and 2:1; the reaction temperature is 30-80° C., the reaction time is between 12-48 hours, and the volume ratio of the added organic solvent to acrolein is between 4.5-20; The reaction temperature in step (3) is between 180-260°C.

3. The method for preparing ethyl benzoate according to claim 2, wherein: In step (1), the molar ratio of acrolein to monoethyl malonate is 1:2-2:1; the reaction temperature is 30-80° C., the reaction time is between 12-48 hours, and the volume ratio of the added organic solvent to acrolein is between 4.5-18; In step (2), the molar ratio of acrolein to diene ester is between 2:1 and 3:1; the reaction temperature is between 80-140° C., and the reaction time is between 1-4 hours; The reaction temperature in step (3) is between 180-260°C.

4. The method for preparing ethyl benzoate according to claim 2, wherein: In step (1), the molar ratio of acrolein to monoethyl malonate is 1:1-1:1.5; the reaction temperature is 40-70° C., the reaction time is between 24-36 hours, and the volume ratio of the added organic solvent to acrolein is between 12-15; in step (2), the molar ratio of acrolein to diene ester is between 2:1-3:1; the reaction temperature is between 100-120° C., and the reaction time is between 3-4 hours; The reaction temperature in step (3) is between 200-240°C.

5. The method for preparing ethyl benzoate according to claim 1, wherein: The acrolein, ethyl malonate and ethylene glycol dimethyl ether are all prepared from biomass.

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