A green synthetic process of 4,6-dimethyl-2-oxo-2h-pyran-5-carboxylic acid ethyl ester

Abstract

The application discloses a green synthesis process of 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylic acid ethyl ester, which comprises the following steps: (a) condensation reaction of ethyl acetoacetate under the action of a heterogeneous catalyst to generate a first mixture; (b) solid-liquid separation of the first mixture to obtain filtrate and residue; (c) first flash evaporation of the filtrate to obtain a first gaseous product and a first liquid product; (d) second flash evaporation of the first liquid product to obtain a second gaseous product and a second liquid product; (e) third flash evaporation of the second liquid product after impurity removal by water washing to obtain 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylic acid ethyl ester product and a third gaseous product. By adopting a heterogeneous catalyst and cooperating with a multi-flash evaporation process, a double-molecule condensation reaction can occur to generate 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylic acid ethyl ester.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fine chemical synthesis, and relates to a green synthesis process of 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylic acid ethyl ester. BACKGROUND

[0002] 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylic acid ethyl ester (also known as ethyl isodehydroacetic acid) is an important intermediate for synthesizing pyranone compounds, and has been widely applied in the fields of fine chemicals, chemical raw materials, daily chemicals and functional chemicals in recent years.

[0003] 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylic acid ethyl ester is mainly generated by bimolecular condensation of ethyl acetoacetate under the catalysis of hydrogen chloride gas or concentrated sulfuric acid, and the by-products are ethanol and water in equimolar ratio. The existing technical route has many defects: (1) for the hydrogen chloride gas catalytic system: a large amount of ethanol and water is contained in the by-products, thereby generating a water-hydrogen chloride-ethanol azeotropic system, leading to great difficulty in separation and purification, and poor economic efficiency of recycling the by-products and unreacted raw materials; (2) for the concentrated sulfuric acid catalytic system: a large amount of ethanol and water is contained in the by-products, leading to a decrease in the concentration of sulfuric acid and loss of catalytic performance, and the sulfuric acid is easy to react with ethanol to generate ethyl hydrogen sulfate and diethyl sulfate, and the product is easy to be entrained with sulfuric acid organic ester, thereby affecting the application of the downstream product, and the by-products and unreacted raw materials are difficult to recycle; (3) a large amount of catalyst (hydrogen chloride gas or concentrated sulfuric acid) is added, and the catalyst cannot be directly reused, but can only be discharged as waste acid, and the high-concentration waste acid per ton of product (i.e. per ton of product) is as high as 12-15 tons; (4) the single-pass conversion rate is low (40%-55%), and the unreacted ethyl acetoacetate raw material is difficult to recycle and reuse, thereby causing waste of resources. SUMMARY

[0004] The application aims at overcoming the defects of the prior art and providing a green synthesis process of 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylic acid ethyl ester.

[0005] To achieve the above object, the technical scheme adopted by the application is as follows: a green synthesis process of 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylic acid ethyl ester, comprising the following steps:

[0006] (a) condensation reaction of ethyl acetoacetate under the action of a heterogeneous catalyst to generate a first mixture; the condensation reaction is carried out at a temperature of 0-100 DEG C for 12 hours to 6 days;

[0007] (b) solid-liquid separation of the first mixture to obtain a filtrate and a residue;

[0008] (c) the filtrate is subjected to a first flash evaporation to obtain a first gas product and a first liquid product; the first flash evaporation is performed at a temperature of 50-60°C and a pressure of 0.03-0.04 MPa;

[0009] (d) the first liquid product is subjected to a second flash evaporation to obtain a second gas product and a second liquid product; the second flash evaporation is performed at a temperature of 100-110°C and a pressure of 0.005-0.01 MPa;

[0010] (e) the second liquid product is subjected to a third flash evaporation to obtain 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylic acid ethyl ester product and a third gas product after water washing to remove impurities; the third flash evaporation is performed at a temperature of 50-60°C and a pressure of 0.01-0.02 MPa.

[0011] Optimally, in step (a), the amount of the heterogeneous catalyst added is 5-30% of the mass of the ethyl acetoacetate.

[0012] Further, in step (a), the amount of the heterogeneous catalyst added is 10-20% of the mass of the ethyl acetoacetate.

[0013] Further, in step (a), the heterogeneous catalyst is a sulfonic acid resin.

[0014] Optimally, in step (a), the condensation reaction is performed at a temperature of 30-50°C for 24-36 hours.

[0015] Optimally, in step (b), the filter residue is dried and then used in step (a).

[0016] Optimally, in step (c), the first gas product is subjected to rectification to separate industrial-grade ethanol and first wastewater; the rectification is performed under the following conditions: top temperature 75-80°C, bottom temperature 90-100°C, pressure normal pressure, and mass reflux ratio 1:1.

[0017] Optimally, in step (d), the second gas product is recycled as a reaction raw material.

[0018] Optimally, in step (e), the washing is three-stage countercurrent washing, and the process parameters are as follows: temperature 20-80°C, mass flow ratio of water phase to organic phase (0.9-1.2):1; the temperature is preferably 55-65°C.

[0019] The washing obtains second wastewater.

[0020] Further, in step (e), the third gas product is condensed and used for washing and removing impurities from the second liquid product.

[0021] Due to the application of the above technical solutions, the present invention has the following advantages compared with the prior art: The green synthesis process of ethyl 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylate of the present invention, by using a heterogeneous catalyst and a multi-flash evaporation process, can generate ethyl 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylate through a bimolecular condensation reaction. After the reaction, solid-liquid separation is performed directly, the solid catalyst is recovered and recycled; the first flash evaporation removes ethanol, water, and low-boiling-point impurities, and the unreacted ethyl acetoacetate raw material is recovered; after the third flash evaporation removes residual water, the product ethyl 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylate is obtained (the single-pass yield of the product is 73%, and the yield after recycling the raw material is 92%).

[0022] The ethanol, water, and low-boiling-point impurities removed by the first flash evaporation are separated into industrial-grade ethanol (95% ethanol) by distillation and sold externally. The first wastewater has good biochemical indicators (pH=6-7, COD 360,000~420,000 mg / L, main components are ethanol, small molecule carboxylic acid impurities, etc.) and is used as a carbon source nutrient for wastewater treatment. The ethyl acetoacetate recovered by the second flash evaporation is reused as a reaction raw material. The washing process is a three-stage countercurrent washing process, and the resulting second wastewater has good biochemical indicators (pH=6-7, COD 120,000~170,000 mg / L, main components are small molecule carboxylic acid impurities and a small amount of unreacted ethyl acetoacetate, etc.) and is used as a carbon source nutrient for wastewater treatment. The first wastewater production is 0.11-0.15 tons / ton of product, and the second wastewater production is 1-1.2 tons / ton of product. The wastewater volume is reduced from 12-15 tons / ton of product in the existing process to 1.1-1.35 tons / ton of product. Moreover, the wastewater has good biochemical indicators and can be used as a carbon source nutrient for sewage treatment. The pollutant emission reduction reaches more than 90%. Attached Figure Description

[0023] Figure 1 The reaction equation is the green synthesis process of ethyl 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylate of the present invention;

[0024] Figure 2 This is a process flow diagram of the green synthesis process of ethyl 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylate according to the present invention. Detailed Implementation

[0025] The present invention discloses a green synthesis process for ethyl 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylate, comprising the following steps: (a) subjecting ethyl acetoacetate to a condensation reaction under the action of a heterogeneous catalyst to generate a first mixture; the condensation reaction is carried out at a temperature of 0°C to 100°C and a time of 12 hours to 6 days; (b) subjecting the first mixture to solid-liquid separation to obtain a filtrate and a filter residue; (c) subjecting the filtrate to a first flash evaporation to obtain a first gaseous product and a first liquid product; the first flash evaporation is carried out at a temperature of 50°C to 60°C and a pressure of 0.03 M. (d) The first liquid product is subjected to a second flash evaporation to obtain a second gaseous product and a second liquid product; the temperature of the second flash evaporation is 100℃~110℃ and the pressure is 0.005MPa-0.01MPa; (e) The second liquid product is washed with water to remove impurities and then subjected to a third flash evaporation to obtain ethyl 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylate product and a third gaseous product; the temperature of the third flash evaporation is 50℃~60℃ and the pressure is 0.01MPa-0.02MPa. By employing a heterogeneous catalyst and a multi-flash evaporation process, a bimolecular condensation reaction can occur to generate ethyl 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylate. After the reaction, solid-liquid separation is performed directly, and the solid catalyst is recovered and recycled. The first flash evaporation removes ethanol, water, and low-boiling-point impurities, and recovers unreacted ethyl acetoacetate feedstock. After the third flash evaporation removes residual moisture, the product ethyl 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylate is obtained (the single-pass yield of the product is 73%, and the yield after feedstock recovery and reuse is 92%).

[0026] In step (a), the amount of heterogeneous catalyst added is 5% to 30% of the mass of ethyl acetoacetate, preferably 10% to 20%; the amount of heterogeneous catalyst added can be any value within the above range, such as 5%, 6%, 8%, 10%, 15%, 20%, 25%, 30%.

[0027] In step (a), the heterogeneous catalyst is sulfonic acid resin, which minimizes the byproducts of the condensation reaction. In step (a), the preferred temperature for the condensation reaction is 30℃~50℃, and the preferred time is 24h-36h. In step (b), the dried filter residue is reused in step (a). In step (c), the first gaseous product is further subjected to distillation to separate industrial-grade ethanol and the first wastewater; the distillation process conditions are: top temperature 75~80℃, bottom temperature 90~100℃, atmospheric pressure, and a reflux ratio of 1:1. In step (d), the second gaseous product is also recovered and reused as a reaction feedstock. In step (e), the washing is a three-stage countercurrent washing process with the following parameters: temperature 20℃-80℃, and a mass flow ratio of aqueous phase to organic phase of (0.9-1.2):1; the preferred temperature is 55℃-65℃; the washing yields the second wastewater. In step (e), the third gaseous product is condensed and used for washing and removing impurities from the second liquid product. The ethanol, water, and low-boiling-point impurities removed by the first flash evaporation are separated by distillation to obtain industrial-grade ethanol (95% ethanol) for sale. The first wastewater has good biochemical indicators (pH=6-7, COD 360,000~420,000 mg / L, main components are ethanol, small molecule carboxylic acid impurities, etc.) and is used as a carbon source nutrient for wastewater treatment. The ethyl acetoacetate recovered by the second flash evaporation is reused as a reaction raw material. The washing process is a three-stage countercurrent washing process, and the resulting second wastewater has good biochemical indicators (pH=6-7, COD 120,000~170,000 mg / L, main components are small molecule carboxylic acid impurities and a small amount of unreacted ethyl acetoacetate, etc.) and is used as a carbon source nutrient for wastewater treatment. The first wastewater production is 0.11-0.15 tons / ton of product, and the second wastewater production is 1-1.2 tons / ton of product. The wastewater volume is reduced from 12-15 tons / ton of product in the existing process to 1.1-1.35 tons / ton of product. Moreover, the wastewater has good biochemical indicators and can be used as a carbon source nutrient for sewage treatment. The pollutant emission reduction reaches more than 90%.

[0028] The preferred embodiments of the present invention will now be described in detail. Example 1

[0029] This embodiment provides a green synthesis process for ethyl 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylate, such as... Figure 1 and Figure 2 As shown, the details are as follows:

[0030] (a) Add ethyl acetoacetate (2600 kg) and heterogeneous catalyst (390 kg, i.e. 15% of the mass of ethyl acetoacetate; the catalyst is sulfonic acid resin) to the reactor, and control the temperature inside the reactor at 30°C~50°C (this temperature range has a great impact on the quality of the product) to carry out the condensation reaction (the reaction time is 24h-36h; this reaction time has a great impact on the quality of the product. If energy consumption is taken into consideration, the reaction time can be shortened according to actual needs) to generate the first mixture;

[0031] (b) The first mixture is subjected to solid-liquid separation to obtain filtrate and filter residue (i.e. heterogeneous catalyst); the filter residue is dried and reused in step (a) for recycling;

[0032] (c) The filtrate is subjected to a first flash evaporation (the temperature of the first flash evaporation is controlled at 50℃~60℃, and the pressure is controlled at 0.03Mpa~0.04Mpa; the actual process conditions may fluctuate, but are usually within the aforementioned temperature range, the same below) to obtain the first gaseous product and the first liquid product; the first gaseous product (ethanol, water and other low-boiling-point impurities) is also subjected to rectification treatment (the rectification process conditions are: top temperature 78℃, bottom temperature 95℃, pressure at atmospheric pressure, and mass reflux ratio of 1:1; when When the top temperature of the tower is 75~80℃ and the bottom temperature is 90~100℃, the difference between the top and bottom products is not significant. This allows for the separation of industrial-grade ethanol and primary wastewater (the primary wastewater has good biochemical indicators: pH=6~7, COD is 360000-420000mg / L, and its main components are ethanol, small molecule carboxylic acid impurities, etc., which can be used as a carbon source nutrient for wastewater treatment; the yield is 0.11 tons~0.15 tons / ton of product, and the yield may fluctuate slightly due to the fluctuation of various control conditions, the same below).

[0033] (d) The first liquid product is subjected to a second flash evaporation (the temperature of the second flash evaporation is 100℃~110℃ and the pressure is 0.005MPa-0.01MPa) to obtain a second gaseous product (the second gaseous product (i.e. ethyl acetoacetate) is condensed or directly used as a reaction raw material in step (a) for recycling) and a second liquid product;

[0034] (e) The second liquid product is washed with water to remove impurities (the washing is a three-stage countercurrent washing, and the process parameters are: temperature control at 55℃~65℃, and the mass flow ratio of water phase to organic phase at 1:1; the flow ratio can be reasonably selected within the range of 0.9-1.2:1 according to actual needs) and then subjected to a third flash evaporation (the temperature of the third flash evaporation is 50℃~60℃, and the pressure is 0.01MPa-0.02MPa) to obtain ethyl 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylate product (1807 kg, yield of about 92%, purity of 99.2%) and a third gaseous product (mainly water, which is used for washing and removing impurities from the second liquid product after condensation). In this step, the three-stage countercurrent washing will generate a second wastewater. The biochemical indicators of the second wastewater are good: pH=6-7, COD is 120000-170000 mg / L, and the main components are small molecule carboxylic acid impurities and a small amount of unreacted ethyl acetoacetate, etc. It can be used as a carbon source nutrient for wastewater treatment (yield is 1 ton to 1.2 tons / ton of product). Example 2

[0035] This embodiment provides a green synthesis process for ethyl 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylate, which is basically the same as that in Example 1, except that in steps (d) and (e), the recycled gaseous products are not recovered, and the yield of ethyl 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylate is about 73%, with a purity of 99.6%. Example 3

[0036] This embodiment provides a green synthesis process for ethyl 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylate, which is basically the same as that in Example 1, except that in step (a), the temperature inside the reactor is controlled at 5°C to 10°C, the yield is about 70%, and the purity is 99.5%. Example 4

[0037] This embodiment provides a green synthesis process for ethyl 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylate, which is basically the same as that in Example 1, except that in step (a), the temperature inside the reactor is controlled at 90℃~100℃, the yield is about 86%, and the purity is 92.5%. Example 5

[0038] This embodiment provides a green synthesis process for ethyl 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylate, which is basically the same as that in Example 1, except that in step (e), the process parameters for the three-stage countercurrent washing are: temperature control at 20℃~30℃, yield of approximately 94.1%, and purity of 96.6%. Example 6

[0039] This embodiment provides a green synthesis process for ethyl 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylate, which is basically the same as that in Example 1, except that in step (e), the process parameters for the three-stage countercurrent washing are: temperature control at 70℃~80℃, yield of approximately 90.4%, and purity of 99.3%.

[0040] Comparative Example 1

[0041] This example provides a synthesis process for ethyl 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylate using sulfuric acid (98%) as a catalyst. Ethyl acetoacetate (1300 kg) and sulfuric acid (1550 kg) are added to a reactor, and the temperature inside the reactor is controlled at 10°C~15°C to carry out the condensation reaction for 72 h. After the reaction was completed, the material was discharged into a washing vessel and cooled to 10°C. 3200 kg of low-temperature water (5°C) was added, and the mixture was stirred evenly. Then, it was extracted with 1950 kg of ethyl acetate (three-stage countercurrent extraction). The aqueous phase was discharged as wastewater. The organic phase obtained from the extraction was deacidified with 1200 kg of 10% Na2CO3 aqueous solution (three-stage countercurrent deacidification). The deacidified aqueous phase was discharged as wastewater. The deacidified organic phase was washed with 1200 kg of water to remove salt (three-stage countercurrent extraction). The desalted aqueous phase was discharged as wastewater. The desalted organic phase was evaporated and concentrated to remove the organic solvent, yielding 472 kg of product with a yield of approximately 48% and a purity of 99.3%. The total wastewater generated is approximately 7950 kg, which is equivalent to 16.5 tons of wastewater per ton of product. The wastewater has poor biodegradability, with the following indicators: waste sulfuric acid content of approximately 16%-18%, COD of approximately 70000-90000 mg / L, and salt content of 15000-17000 mg / L.

[0042] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A green synthesis process of 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylic acid ethyl ester, characterized in that, The method comprises the following steps: (a) condensation of ethyl acetoacetate in the presence of a heterogeneous catalyst to form a first mixture; the condensation reaction is carried out at a temperature of 30-50℃ for 24-36 hours; the heterogeneous catalyst is a sulfonic acid resin; the amount of the heterogeneous catalyst added is 10-20% of the mass of the ethyl acetoacetate; (b) solid-liquid separation of the first mixture to obtain a filtrate and a residue; the residue is dried and used in step (a); (c) first flash evaporation of the filtrate to obtain a first gaseous product and a first liquid product; the first flash evaporation is carried out at a temperature of 50-60℃ and a pressure of 0.03-0.04 MPa; the first gaseous product is further subjected to rectification to separate industrial-grade ethanol and a first waste water; the rectification is carried out under the following conditions: a top temperature of 75-80℃, a bottom temperature of 90-100℃, normal pressure, and a mass reflux ratio of 1:1; (d) second flash evaporation of the first liquid product to obtain a second gaseous product and a second liquid product; the second flash evaporation is carried out at a temperature of 100-110℃ and a pressure of 0.005-0.01 MPa; the second gaseous product is recovered and used as a reaction raw material; (e) third flash evaporation of the second liquid product after water washing to remove impurities to obtain 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylic acid ethyl ester and a third gaseous product; the third flash evaporation is carried out at a temperature of 50-60℃ and a pressure of 0.01-0.02 MPa; the washing is three-stage countercurrent washing, and the process parameters are as follows: a temperature of 20-80℃, a mass flow ratio of water phase to organic phase of (0.9-1.2):1, and a second waste water is obtained; the third gaseous product is condensed and used for washing and removing impurities of the second liquid product.

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