Preparation method of 2-ethyl butyric acid

Abstract

The invention discloses a preparation method of 2-ethyl butyric acid. The preparation method comprises the following steps: S1, preparing diethyl diethyl malonate; s2, preparing preparation materials which comprise 32% sodium hydroxide solution, 95% ethanol and 31% hydrochloric acid, and S3, putting the diethyl diethyl malonate prepared in the S1 and the 32% sodium hydroxide solution and the 95% ethanol in the S2 into a reaction kettle; s4, dropwise adding the 31% hydrochloric acid in the S2 into the reaction kettle in the S3, adjusting to be strongly acidic, discharging the reaction kettle after a first index is reached, and performing centrifugal operation to obtain a diethyl malonic acid crude product. According to the preparation method, diethyl diethyl malonate is used as a main preparation material, is obtained by adopting a preparation mode, and reacts with 32% sodium hydroxide solution, 95% ethanol and 31% hydrochloric acid, so that the acquisition cost of the main raw material for preparing 2-ethyl butyric acid is reduced, and the yield of 2-ethyl butyric acid is increased. Meanwhile, the main content and the yield of the 2-ethyl butyric acid can be conveniently improved.

Description

Technical Field

[0001] The invention relates to the field of 2-ethylbutyric acid preparation, and in particular to a method for preparing 2-ethylbutyric acid. Background Art

[0002] 2-Ethylbutyric acid is usually an organic compound. 2-Ethylbutyric acid is a transparent liquid with low toxicity. It has a light smell of cheese and mold at room temperature and pressure. The physical properties of 2-ethylbutyric acid include specific gravity 0.923, melting point -14°C, boiling point 195°C and flash point 87°C. 2-Ethylbutyric acid is mainly used as an intermediate in organic synthesis and pharmaceutical chemistry, and is often used in the synthesis of drug molecules and organic functional molecules.

[0003] 2-Ethylbutyric acid usually needs to be prepared and produced, and thus 2-ethylbutyric acid needs to have a preparation process. The prior art preparation method of 2-ethylbutyric acid usually includes a 2-ethylbutanol oxidation method, which usually uses 2-ethylbutanol as the main raw material, and then cooperates with an oxidant and a catalyst to carry out an oxidation reaction. During the oxidation reaction, it is necessary to carry out the reaction under appropriate temperature, pressure and stirring conditions, and then allow the reaction to proceed. During the reaction, the hydroxyl group of the 2-ethylbutanol is oxidized to a carboxyl group to obtain 2-ethylbutyric acid.

[0004] However, this method has the characteristics of high cost of obtaining 2-ethylbutanol and low main content and yield of 2-ethylbutyric acid, resulting in high production cost. At the same time, harmful by-products or wastes may be produced in the preparation process, which is not environmentally friendly. Therefore, a preparation method of 2-ethylbutyric acid is proposed to reduce the production cost of 2-ethylbutyric acid and increase the main content and yield of 2-ethylbutyric acid. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing 2-ethylbutyric acid to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for preparing 2-ethylbutyric acid, comprising:

[0007] S1: Preparation of diethyl diethylmalonate;

[0008] S2: preparing materials, the materials comprising 32% sodium hydroxide solution, 95% ethanol and 31% hydrochloric acid, and specifying a first feed amount;

[0009] S3: Add the diethyl diethyl malonate prepared in S1, the 32% sodium hydroxide solution and 95% ethanol in S2 into a reaction kettle, slowly heat the mixture to reflux under stirring, and then cool it down;

[0010] S4: adding 31% hydrochloric acid in S2 dropwise to the reactor in S3, adjusting to strong acidity, discharging the reactor after reaching the first index, and performing centrifugal operation to obtain crude diethylmalonic acid, and treating the mother liquor at the same time;

[0011] S5: decarboxylation treatment, the crude diethylmalonic acid obtained in S4 is put into a reactor to carry out a decarboxylation reaction at normal pressure, and the decarboxylation is completed after reaching the second index;

[0012] S6: distillation operation, after the decarboxylation in S5 is completed, the temperature is lowered and reduced pressure distillation is started, and then fractionation treatment is performed under certain conditions to obtain the product 2-ethylbutyric acid.

[0013] Preferably, the preparation of diethyl diethyl malonate in S1 comprises the following specific steps:

[0014] S11: preparing materials, the materials comprising toluene, 60% sodium hydride, diethyl malonate and diethyl sulfate, and specifying a second feed amount;

[0015] S12: Toluene is added into a reaction kettle and filled with nitrogen to make the oxygen content less than 3%, and then the temperature inside the reaction kettle is raised. After the temperature reaches below 35° C., sodium hydride is added in batches;

[0016] S13: The temperature inside the reactor is raised again to 70° C., diethyl malonate is added dropwise to the reactor during the first dropping time, and then the reaction is kept warm for 1 hour;

[0017] S14: After the heat preservation reaction, diethyl sulfate is added dropwise to the reactor, and the addition is completed within the second dropping time, and then the heat preservation reaction is carried out for 5 hours;

[0018] S15: After the reaction is completed, the temperature is lowered to below 35° C., and then water is added dropwise to quench the excess sodium hydride. After the water is added, the reaction is stirred. After the reaction is completed, the reaction is allowed to stand for separation;

[0019] S16: vacuum distillation, subjecting the result of standing and separating to vacuum distillation to obtain the product diethyl diethyl malonate.

[0020] Preferably, the second feed amounts in S11 are 400 g toluene, 100 g 60% sodium hydride, 160 g diethyl malonate and 300 g diethyl sulfate, respectively, and the first dropping time in S13 is 2 hours.

[0021] Preferably, the second dropping time in S14 is 4 hours, the stirring reaction time in S15 is 1 hour, and the static separation result in S15 is an upper oil phase and a lower water phase, the lower water phase contains sodium ethyl sulfate, and the concentration by-product is used for other purposes. The upper oil phase is concentrated at normal pressure to recover toluene, and the water is dried for repeated use.

[0022] Preferably, the product diethyl malonate obtained in S16 is a colorless transparent liquid, the weight of the product diethyl malonate is 212 g, and the main content and yield of the product diethyl malonate are 99.6% and 98.15%, respectively.

[0023] Preferably, the chemical reaction equations generated in the reactor in S1, the reactor in S3, the reactor in S4, and the reactors in S5 and S6 are respectively as follows:

[0024]

[0025] Preferably, the first input amounts in S2 are 300 g of 32% sodium hydroxide solution, 80 g of 95% ethanol and 300 g of 31% hydrochloric acid, respectively; the reflux time in S4 is 3-5 hours, and the temperature is lowered to below 40°C; and the first indicator in S4 is lowering the temperature to below 30°C.

[0026] Preferably, the crude diethylmalonic acid obtained in S4 weighs 170 g and contains 7-8% water. The mother liquor in S4 is treated by adjusting the mother liquor to neutrality and then discharging it into a sewage treatment system.

[0027] Preferably, the second indicator in S5 is to increase the temperature to 130-150°C and keep the reaction at 130-150°C for 6-8 hours, the cooling temperature in S6 is below 100°C, and the certain condition of the reduced pressure distillation in S6 is to collect the fraction at -0.09MPa and between 130-140°C.

[0028] Preferably, the product 2-ethylbutyric acid obtained in S6 is a colorless transparent liquid, and the main content and yield of the product 2-ethylbutyric acid are 99.9% and 96.62% respectively.

[0029] Technical effects and advantages of the present invention:

[0030] (1) The present invention uses diethyl diethyl malonate as a main preparation material, obtains diethyl diethyl malonate in a preparation method, and reacts with 32% sodium hydroxide solution, 95% ethanol and 31% hydrochloric acid. After obtaining a crude diethyl malonate product, the crude diethyl malonate product is subjected to decarboxylation treatment and distillation operations to obtain a 2-ethylbutyric acid product, thereby reducing the acquisition cost of the main raw material for preparing 2-ethylbutyric acid and facilitating the improvement of the main content and yield of 2-ethylbutyric acid.

[0031] (2) The present invention utilizes the sodium ethyl sulfate obtained after standing and separating the liquid during the preparation of diethyl diethyl malonate, and uses the concentrated byproduct for other purposes, and recovers toluene by concentrating the upper oil phase under normal pressure, and dries the water for repeated use, thereby improving the environmental friendliness of the preparation of 2-ethylbutyric acid, and facilitating the recovery and use of toluene, thereby reducing production costs;

[0032] (3) The present invention utilizes the process of obtaining crude diethylmalonic acid, in which the mother liquor can be adjusted to neutrality and then discharged into a sewage treatment system, thereby facilitating environmentally friendly treatment of the preparation of 2-ethylbutyric acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The figure is a schematic diagram of the preparation process of 2-ethylbutyric acid of the present invention.

[0034] Figure 2 The present invention is a schematic diagram of the preparation process of diethyl diethyl malonate. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0036] Embodiment 1

[0037] The present invention provides Figure 1-2 A method for preparing 2-ethylbutyric acid is shown, comprising the following specific steps:

[0038] S1: Preparation of diethyl diethyl malonate. The preparation of diethyl diethyl malonate comprises the following specific steps:

[0039] S11: preparing materials, the materials comprising toluene, 60% sodium hydride, diethyl malonate and diethyl sulfate, and specifying a second feed amount, the second feed amounts being 400 g toluene, 100 g 60% sodium hydride, 160 g diethyl malonate and 300 g diethyl sulfate;

[0040] S12: Toluene is added into a reaction kettle and filled with nitrogen to make the oxygen content less than 3%, and then the temperature inside the reaction kettle is raised. After the temperature reaches below 35° C., sodium hydride is added in batches;

[0041] S13: heating the reactor again to 70° C., adding diethyl malonate dropwise to the reactor during the first dropping time of 2 hours, and then keeping the temperature for reaction for 1 hour;

[0042] S14: After the heat preservation reaction, diethyl sulfate is added dropwise to the reactor, and the addition is completed within a second dropping time, the second dropping time is 4 hours, and then the heat preservation reaction is carried out for 5 hours;

[0043] S15: After the reaction is completed, the temperature is lowered to below 35°C, and then water is added dropwise to quench the excess sodium hydride. After the water is added, the reaction is stirred for 1 hour. After the reaction is completed, the reaction is allowed to stand for separation. The result of the separation is an upper oil phase and a lower water phase. The lower water phase contains sodium ethyl sulfate, and the concentration byproduct is used for other purposes. The upper oil phase is concentrated at normal pressure to recover toluene, and the water is dried for repeated use.

[0044] S16: distilling under reduced pressure, distilling the static separation result under reduced pressure to obtain diethyl diethyl malonate, which is a colorless transparent liquid. The weight of the diethyl diethyl malonate is 212 g, and the main content and yield of the diethyl diethyl malonate are 99.6% and 98.15%, respectively.

[0045] S2: preparing materials, the materials comprising 32% sodium hydroxide solution, 95% ethanol and 31% hydrochloric acid, and specifying a first feeding amount, the first feeding amounts being 300 g of 32% sodium hydroxide solution, 80 g of 95% ethanol and 300 g of 31% hydrochloric acid;

[0046] S3: putting the diethyl diethyl malonate prepared in S1, the 32% sodium hydroxide solution and the 95% ethanol in S2 into a reaction kettle, slowly heating to reflux under stirring, the reflux time is 3-5 hours, and cooling to below 40°C;

[0047] S4: adding 31% hydrochloric acid in S2 to the reactor in S3, adjusting to strong acidity, and after reaching the first index, the first index is cooling to below 30°C, discharging the reactor, and centrifuging to obtain crude diethyl malonic acid, and treating the mother liquor at the same time to obtain a crude diethyl malonic acid product weighing 170g, which contains 7-8% water, and the mother liquor is treated to adjust the mother liquor to neutrality and then discharged to the sewage treatment system;

[0048] S5: Decarboxylation treatment, the crude diethylmalonic acid obtained in S4 is put into a reactor for decarboxylation reaction at normal pressure, and after reaching the second index, the second index is to increase the temperature to 130-150° C., and keep the temperature at 130-150° C. for 6-8 hours, and the decarboxylation is completed;

[0049] S6: distillation operation, after the decarboxylation in S5 is completed, the temperature is lowered to below 100°C, and reduced pressure distillation is started, and then under certain conditions, the certain conditions are collected at -0.09MPa and between 130-140°C, fractionation is carried out to obtain the product 2-ethylbutyric acid, the obtained product 2-ethylbutyric acid is a colorless transparent liquid, and the main content and yield of the product 2-ethylbutyric acid are 99.9% and 96.62% respectively.

[0050] The chemical reaction equations generated in the reactor in S1, the reactor in S3, the reactor in S4, and the reactors in S5 and S6 are as follows:

[0051]

[0052] Embodiment 2

[0053] A method for preparing 2-ethylbutyric acid comprises the following specific steps:

[0054] S1: Preparation of diethyl diethylmalonate;

[0055] S2: preparing materials, the materials comprising 32% sodium hydroxide solution, 95% ethanol and 31% hydrochloric acid, and specifying a first feeding amount, the first feeding amounts being 300 g of 32% sodium hydroxide solution, 80 g of 95% ethanol and 300 g of 31% hydrochloric acid;

[0056] S3: putting the diethyl diethyl malonate prepared in S1, the 32% sodium hydroxide solution and the 95% ethanol in S2 into a reaction kettle, slowly heating to reflux under stirring, the reflux time is 3-5 hours, and cooling to below 40°C;

[0057] S4: adding 31% hydrochloric acid in S2 to the reactor in S3, adjusting to strong acidity, and after reaching the first index, the first index is cooling to below 30°C, discharging the reactor, and centrifuging to obtain crude diethyl malonic acid, and treating the mother liquor at the same time to obtain a crude diethyl malonic acid product weighing 170g, which contains 7-8% water, and the mother liquor is treated to adjust the mother liquor to neutrality and then discharged to the sewage treatment system;

[0058] S5: Decarboxylation treatment, the crude diethylmalonic acid obtained in S4 is put into a reactor for decarboxylation reaction at normal pressure, and after reaching the second index, the second index is to increase the temperature to 120-140° C., and keep the temperature at 120-140° C. for 6-8 hours, and the decarboxylation is completed;

[0059] S6: distillation operation, after the decarboxylation in S5 is completed, the temperature is lowered to below 100°C, and reduced pressure distillation is started, and then under certain conditions, the certain conditions are collected at -0.09MPa and between 130-140°C, fractionation treatment is performed to obtain the product 2-ethylbutyric acid.

[0060] The 2-ethylbutyric acid prepared by the above method is a colorless transparent liquid, with a main content of 97.5% and a yield of 94.73%.

[0061] Embodiment 3

[0062] A method for preparing 2-ethylbutyric acid comprises the following specific steps:

[0063] S1: Preparation of diethyl diethylmalonate;

[0064] S2: preparing materials, the materials comprising 32% sodium hydroxide solution, 95% ethanol and 31% hydrochloric acid, and specifying a first feeding amount, the first feeding amounts being 300 g of 32% sodium hydroxide solution, 80 g of 95% ethanol and 300 g of 31% hydrochloric acid;

[0065] S3: putting the diethyl diethyl malonate prepared in S1, the 32% sodium hydroxide solution and the 95% ethanol in S2 into a reaction kettle, slowly heating to reflux under stirring, the reflux time is 3-5 hours, and cooling to below 40°C;

[0066] S4: adding 31% hydrochloric acid in S2 to the reactor in S3, adjusting to strong acidity, and after reaching the first index, the first index is cooling to below 30°C, discharging the reactor, and centrifuging to obtain crude diethyl malonic acid, and treating the mother liquor at the same time to obtain a crude diethyl malonic acid product weighing 170g, which contains 7-8% water, and the mother liquor is treated to adjust the mother liquor to neutrality and then discharged to the sewage treatment system;

[0067] S5: Decarboxylation treatment, the crude diethylmalonic acid obtained in S4 is put into a reactor for decarboxylation reaction at normal pressure, and after reaching the second index, the second index is to increase the temperature to 130-150° C., and keep the temperature at 130-150° C. for 4-6 hours, and the decarboxylation is completed;

[0068] S6: distillation operation, after the decarboxylation in S5 is completed, the temperature is lowered to below 100°C, and reduced pressure distillation is started, and then under certain conditions, the certain conditions are collected at -0.09MPa and between 130-140°C, fractionation treatment is performed to obtain the product 2-ethylbutyric acid.

[0069] The 2-ethylbutyric acid prepared by the above method is a colorless transparent liquid, the main content is 87.73%, and the yield reaches 85.24%.

[0070] Embodiment 4

[0071] A method for preparing 2-ethylbutyric acid comprises the following specific steps:

[0072] S1: Preparation of diethyl diethylmalonate;

[0073] S2: preparing materials, the materials comprising 32% sodium hydroxide solution, 95% ethanol and 31% hydrochloric acid, and specifying a first feeding amount, the first feeding amounts being 300 g of 32% sodium hydroxide solution, 80 g of 95% ethanol and 300 g of 31% hydrochloric acid;

[0074] S3: putting the diethyl diethyl malonate prepared in S1, the 32% sodium hydroxide solution and the 95% ethanol in S2 into a reaction kettle, slowly heating to reflux under stirring, the reflux time is 3-5 hours, and cooling to below 40°C;

[0075] S4: adding 31% hydrochloric acid in S2 to the reactor in S3, adjusting to strong acidity, and after reaching the first index, the first index is cooling to below 30°C, discharging the reactor, and centrifuging to obtain crude diethyl malonic acid, and treating the mother liquor at the same time to obtain a crude diethyl malonic acid product weighing 170g, which contains 7-8% water, and the mother liquor is treated to adjust the mother liquor to neutrality and then discharged to the sewage treatment system;

[0076] S5: Decarboxylation treatment, the crude diethylmalonic acid obtained in S4 is put into a reactor for decarboxylation reaction at normal pressure, and after reaching the second index, the second index is to increase the temperature to 140-160° C., and keep the temperature at 140-160° C. for 8-10 hours, and the decarboxylation is completed;

[0077] S6: distillation operation, after the decarboxylation in S5 is completed, the temperature is lowered to below 100°C, and reduced pressure distillation is started, and then under certain conditions, the certain conditions are collected at -0.09MPa and between 130-140°C, fractionation treatment is performed to obtain the product 2-ethylbutyric acid.

[0078] The 2-ethylbutyric acid prepared by the above method is a colorless transparent liquid, the main content of which is 98.12%, and the yield reaches 85.56%.

[0079] It can be seen that the decarboxylation reaction temperature and the insulation reaction time for preparing 2-ethylbutyric acid are preferably controlled at 130-150°C and 6-8 hours, which can obtain a higher yield and a high content of 2-ethylbutyric acid. The effects of the decarboxylation reaction temperature and the insulation reaction time are shown in the following table:

[0080]

[0081] Embodiment 5

[0082] A method for preparing 2-ethylbutyric acid comprises the following specific steps:

[0083] S1: Preparation of diethyl diethylmalonate;

[0084] S2: preparing materials, the materials comprising 32% sodium hydroxide solution, 95% ethanol and 31% hydrochloric acid, and specifying a first feed amount, the first feed amounts being 250 g of 32% sodium hydroxide solution, 80 g of 95% ethanol and 300 g of 31% hydrochloric acid;

[0085] S3: putting the diethyl diethyl malonate prepared in S1, the 32% sodium hydroxide solution and the 95% ethanol in S2 into a reaction kettle, slowly heating to reflux under stirring, the reflux time is 3-5 hours, and cooling to below 40°C;

[0086] S4: adding 31% hydrochloric acid in S2 to the reactor in S3, adjusting to strong acidity, and after reaching the first index, the first index is cooling to below 30°C, discharging the reactor, and centrifuging to obtain crude diethyl malonic acid, and treating the mother liquor at the same time to obtain a crude diethyl malonic acid product weighing 170g, which contains 7-8% water, and the mother liquor is treated to adjust the mother liquor to neutrality and then discharged to the sewage treatment system;

[0087] S5: Decarboxylation treatment, the crude diethylmalonic acid obtained in S4 is put into a reactor for decarboxylation reaction at normal pressure, and after reaching the second index, the second index is to increase the temperature to 130-150° C., and keep the temperature at 130-150° C. for 6-8 hours, and the decarboxylation is completed;

[0088] S6: distillation operation, after the decarboxylation in S5 is completed, the temperature is lowered to below 100°C, and reduced pressure distillation is started, and then under certain conditions, the certain conditions are collected at -0.09MPa and between 130-140°C, fractionation treatment is performed to obtain the product 2-ethylbutyric acid.

[0089] The 2-ethylbutyric acid prepared by the above method is a colorless transparent liquid, the main content is 84.5%, and the yield reaches 82.45%.

[0090] It can be seen that the weight of the prepared 32% sodium hydroxide solution of 2-ethylbutyric acid is preferably controlled at 300 g. As the 32% sodium hydroxide solution is used as an alkaline catalyst, a reduction in the amount thereof will lead to a decrease in the reaction rate, and a decrease in the main content and yield.

[0091] Working principle of the present invention:

[0092] First, diethyl diethyl malonate is prepared, and the preparation process is divided into preparing materials, the preparation materials include toluene, 60% sodium hydride, diethyl malonate and diethyl sulfate, toluene is put into a reactor, and nitrogen is filled to make the oxygen content less than 3%, then the temperature inside the reactor is raised, and after the temperature reaches below 35°C, sodium hydride is added in batches, and the temperature inside the reactor is raised again, and the temperature rises to 70°C, diethyl malonate is dripped into the reactor within a first dropping time, and then insulation reaction is carried out for 1 hour, after insulation reaction, diethyl sulfate is dripped into the reactor, and the dripping is completed within a second dropping time, and then insulation reaction is carried out for 5 hours, after the reaction is completed, the temperature is lowered to below 35°C, and then water is dripped and excess sodium hydride is quenched, after the water is added, stirring reaction is carried out, after the end, standing operation is carried out, liquid separation is carried out, and reduced pressure distillation is carried out, and the result of standing liquid separation is subjected to reduced pressure distillation to obtain the product diethyl diethyl malonate;

[0093] Then, materials for preparing 2-ethylbutyric acid are prepared, the materials comprising 32% sodium hydroxide solution, 95% ethanol and 31% hydrochloric acid, the prepared diethyl diethyl malonate and the 32% sodium hydroxide solution and 95% ethanol in S2 are put into a reaction kettle, the temperature is slowly raised to reflux under stirring, and the temperature is lowered;

[0094] 31% hydrochloric acid is added dropwise to the reactor in S3 and adjusted to strong acidity. After reaching the first index, the reactor is discharged and centrifuged to obtain crude diethylmalonic acid, and the mother liquor is treated at the same time;

[0095] Then, decarboxylation treatment is carried out, and the obtained crude diethylmalonic acid is put into a reactor for decarboxylation reaction at normal pressure. After the decarboxylation is completed, distillation operation is carried out, the temperature is lowered, and reduced pressure distillation is started. Then, under certain conditions, fractionation treatment is carried out to obtain the product 2-ethylbutyric acid, and the preparation is completed.

[0096] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing 2-ethylbutyric acid, characterized in that: The specific steps include: S1: Preparation of diethyl diethylmalonate; S2: preparing materials, the materials comprising 32% sodium hydroxide solution, 95% ethanol and 31% hydrochloric acid, and specifying a first feeding amount; S3: Add the diethyl diethyl malonate prepared in S1, the 32% sodium hydroxide solution and 95% ethanol in S2 into a reaction kettle, slowly heat the mixture to reflux under stirring, and then cool it down; S4: adding 31% hydrochloric acid in S2 dropwise to the reactor in S3, adjusting to strong acidity, discharging the reactor after reaching the first index, and performing centrifugal operation to obtain crude diethylmalonic acid, and treating the mother liquor at the same time; S5: decarboxylation treatment, the crude diethylmalonic acid obtained in S4 is put into a reactor to carry out a decarboxylation reaction at normal pressure, and the decarboxylation is completed after reaching the second index; S6: distillation operation, after the decarboxylation in S5 is completed, the temperature is lowered and reduced pressure distillation is started, and then fractionation treatment is performed under certain conditions to obtain the product 2-ethylbutyric acid.

2. The method for preparing 2-ethylbutyric acid according to claim 1, characterized in that: The preparation of diethyl diethyl malonate in S1 comprises the following specific steps: S11: preparing materials, the materials comprising toluene, 60% sodium hydride, diethyl malonate and diethyl sulfate, and specifying a second feed amount; S12: Toluene is added into a reaction kettle and filled with nitrogen to make the oxygen content less than 3%, and then the temperature inside the reaction kettle is raised. After the temperature reaches below 35° C., sodium hydride is added in batches; S13: The temperature inside the reactor is raised again to 70° C., diethyl malonate is added dropwise to the reactor during the first dropping time, and then the reaction is kept warm for 1 hour; S14: After the heat preservation reaction, diethyl sulfate is added dropwise to the reactor, and the addition is completed within the second dropping time, and then the heat preservation reaction is carried out for 5 hours; S15: After the reaction is completed, the temperature is lowered to below 35° C., and then water is added dropwise to quench the excess sodium hydride. After the addition of water is completed, the reaction is stirred. After the reaction is completed, the reaction is allowed to stand for separation; S16: vacuum distillation, subjecting the result of standing and separating to vacuum distillation to obtain the product diethyl diethyl malonate.

3. The method for preparing 2-ethylbutyric acid according to claim 2, characterized in that: The second feed amounts in S11 are 400 g toluene, 100 g 60% sodium hydride, 160 g diethyl malonate and 300 g diethyl sulfate, respectively, and the first dropping time in S13 is 2 hours.

4. The method for preparing 2-ethylbutyric acid according to claim 2, characterized in that: The second dropping time in S14 is 4 hours, the stirring reaction time in S15 is 1 hour, and the static separation result in S15 is an upper oil phase and a lower water phase. The lower water phase contains sodium ethyl sulfate, and the concentration by-product is used for other purposes. The upper oil phase is concentrated at normal pressure to recover toluene, and the water is dried for repeated use.

5. The method for preparing 2-ethylbutyric acid according to claim 2, characterized in that: The product diethyl malonate obtained in S16 is a colorless transparent liquid, the weight of the product diethyl malonate is 212 g, and the main content and yield of the product diethyl malonate are 99.6% and 98.15% respectively.

6. The method for preparing 2-ethylbutyric acid according to claim 1, characterized in that: The chemical reaction equations generated in the reactor in S1, the reactor in S3, the reactor in S4, and the reactors in S5 and S6 are respectively as follows:

7. The method for preparing 2-ethylbutyric acid according to claim 1, characterized in that: The first input amounts in S2 are 300 g of 32% sodium hydroxide solution, 80 g of 95% ethanol and 300 g of 31% hydrochloric acid, respectively. The reflux time in S4 is 3-5 hours, and the temperature is lowered to below 40°C. The first indicator in S4 is to cool to below 30°C.

8. The method for preparing 2-ethylbutyric acid according to claim 1, characterized in that: The crude diethylmalonic acid obtained in S4 weighs 170 g and contains 7-8% water. The mother liquor in S4 is treated by adjusting the mother liquor to neutrality and then discharging it into a sewage treatment system.

9. The method for preparing 2-ethylbutyric acid according to claim 1, characterized in that: The second indicator in S5 is to increase the temperature to 130-150°C and keep the temperature at 130-150°C for 6-8 hours. The cooling temperature in S6 is below 100°C. The certain condition of the reduced pressure distillation in S6 is to collect the fraction at -0.09MPa and between 130-140°C.

10. The method for preparing 2-ethylbutyric acid according to claim 1, characterized in that: The product 2-ethylbutyric acid obtained in S6 is a colorless transparent liquid, and the main content and yield of the product 2-ethylbutyric acid are 99.9% and 96.62% respectively.

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