A method for preparing high optical purity (s)-ethyl lactate

Abstract

The application provides a preparation method of high-optical-purity (S)-ethyl lactate, comprising the following steps: performing esterification reaction on L-lactide and ethanol under the action of a catalyst to obtain an esterification liquid containing the ethyl lactate, wherein the catalyst is a chiral ionic liquid catalyst. The product obtained by the method has high optical purity and high conversion rate, the process is simple, environment-friendly and safe, energy consumption is low, the catalyst can be repeatedly used, and the method can be applied to industrial production.

Description

Technical Field

[0001] This invention relates to the field of chemical engineering, and specifically to a method for preparing high optical purity (S)-ethyl lactate. Background Technology

[0002] Ethyl lactate has the molecular formula C5H 10 O3 is a colorless, transparent liquid with a slight odor at room temperature and pressure. Its melting point is -26℃, boiling point is 154℃, and relative density is 1.03 g / cm³. 3 It has a flash point of 46.1℃ and an ignition temperature of 400℃, making it flammable. Ethyl lactate is volatile, miscible with water, and also soluble in alcohols, esters, ketones, hydrocarbons, and oils. It possesses excellent solvent properties, capable of dissolving a variety of organic, inorganic, and gaseous substances. It is a typical electronic-grade organic green cleaning agent, a polyimide (PI) film and coating adhesive, and also an important chiral synthetic intermediate.

[0003] Ethyl lactate is a permitted food flavoring widely used in alcoholic beverages, baked goods, candies, and drinks. It is also used as a non-toxic, green solvent in cellulose esters, coatings, and resins. In particular, as a cleaning agent for electronic products, ethyl lactate is a wet electronic chemical used in LCD and OLED display panels. Its demand as an intermediate in TMAH developer and photoresist is also gradually increasing, indicating broad development prospects.

[0004] Chiral ethyl lactate is widely used in pharmaceuticals, pharmaceutical intermediates, and resolving agents. It can also be used to synthesize room-temperature ionic liquids containing chiral centers, such as L-1-methyl-3-(2-benzyloxypropyl). The resulting chiral ionic liquids exhibit all the properties of ordinary ionic liquids, making it an excellent route for synthesizing chiral ionic liquids. It also has significant potential applications in the synthesis of naturally occurring chiral drugs.

[0005] However, the pharmaceutical and pesticide industries require high optical purity ethyl lactate as an intermediate raw material, and the cleaning process of electronic products also requires high optical purity ethyl lactate as a solvent. At present, the research and development of high content and high optical purity lactate production technology has not made any breakthrough progress. Due to its low content and low optical purity, domestically produced ethyl lactate can only be used as an additive in the food and other industries.

[0006] Existing technologies typically use lactic acid and ethanol as reaction substrates to prepare ethyl lactate through esterification under the action of an acidic catalyst such as concentrated sulfuric acid. However, in order to improve the conversion rate of the reaction, toxic organic solvents such as benzene and toluene are usually used as dehydrating agents to remove the water generated in the reaction and promote the reaction in the forward direction. The ethyl lactate produced often has limited use as a green solvent due to the presence of these substances. In addition, the use of concentrated sulfuric acid promotes side reactions such as intermolecular and intramolecular dehydration, condensation, and cyclization of lactic acid. These reactions are time-consuming and have low yields, which is not conducive to large-scale industrial applications.

[0007] Therefore, there is a need for a method to prepare ethyl lactate with short reaction time, high conversion rate and high optical purity of product. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing high optical purity ethyl lactate. This method uses L-lactide and ethanol as reaction substrates, and an esterification reaction occurs under the action of a chiral ionic liquid catalyst to obtain ethyl lactate. This method is simple, has a short reaction time, can completely eliminate the generation of alkylation byproducts in traditional preparation methods, has a high product conversion rate, and the obtained product has high optical purity, making it suitable for industrial production applications.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing high optical purity (S)-ethyl lactate, comprising the following steps: subjecting L-lactide and ethanol to an esterification reaction under the action of a catalyst to obtain an esterification liquid containing the ethyl lactate, wherein the catalyst is a chiral ionic liquid catalyst.

[0011] According to some embodiments of the present invention, the chiral ionic liquid catalyst is selected from alkylimidazolium lactate.

[0012] Preferably, the chiral ionic liquid catalyst is selected from 1-butyl-3-methylimidazolium lactate, such as sodium 1-butyl-3-methylimidazolium lactate, potassium 1-butyl-3-methylimidazolium lactate, calcium 1-butyl-3-methylimidazolium lactate, magnesium 1-butyl-3-methylimidazolium lactate, zinc 1-butyl-3-methylimidazolium lactate, or ammonium 1-butyl-3-methylimidazolium lactate.

[0013] According to some embodiments of the present invention, the molar ratio of L-lactide to ethanol is 1:(1-6), preferably 1:(2-4), and more preferably 1:(2.2-2.8).

[0014] In some embodiments, the molar ratio of the L-lactide to ethanol is 1:1, 1:1.5, 1:2, 1:2.2, 1:2.4, 1:2.5, 1:2.6, 1:2.8, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, or 1:6.

[0015] According to some embodiments of the present invention, the amount of catalyst used is 0.5-15% of the mass of the L-lactide, for example 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 11%, 12%, 13%, 14% or 15%; preferably 2-10%, more preferably 4-7%, and even more preferably 5-5.5%.

[0016] According to some embodiments of the present invention, the temperature of the esterification reaction is 70-100°C, preferably 80-95°C, and more preferably 85-90°C.

[0017] According to some embodiments of the present invention, the esterification reaction time is 1-5 h, preferably 1.5-4 h, and more preferably 2-2.5 h.

[0018] According to some embodiments of the present invention, the preparation further includes the step of vacuum distilling the esterification liquid to obtain high-purity ethyl lactate.

[0019] In some embodiments, the distillation temperature is 95-135°C, preferably 105-125°C, and more preferably 115-120°C.

[0020] In some embodiments, the vacuum degree of the distillation is 1-8 kPa, preferably 1.5-3.5 kPa, and more preferably 2.0-2.5 kPa.

[0021] According to some embodiments of the present invention, the ionic liquid catalyst 1-butyl-3-methylimidazolium lactate can be prepared by the following steps:

[0022] (1) N-methylimidazolium was mixed with bromobutane and reacted to obtain 1-butyl-3-methylimidazolium bromide;

[0023] (2) The 1-butyl-3-methylimidazolium bromide obtained in step (1) is mixed and reacted with 2-hydroxypropionate to obtain 1-butyl-3-methylimidazolium lactate.

[0024] Specifically, the 1-butyl-3-methylimidazolium lactate is prepared by the following steps:

[0025] (1) 1-Butyl-3-methylimidazolium bromide ([bmim]Br) was prepared by nucleophilic substitution reaction of N-methylimidazolium in a nitrogen atmosphere with toluene solvent and bromobutane.

[0026] (2) The 1-butyl-3-methylimidazolium bromide ([bmim]Br) obtained in step (1) is mixed with 2-hydroxypropionate, and acetone solvent is added to carry out metathesis reaction to prepare 1-butyl-3-methylimidazolium lactate [bmim][lactate]. After the reaction is completed, the reaction solution is filtered, and the acetone in the reaction filtrate is distilled under reduced pressure.

[0027] (3) The reaction solution after acetone distillation in step (2) was washed and purified with dichloromethane, and the dichloromethane was distilled under reduced pressure. The substrate was dried under vacuum to obtain 1-butyl-3-methylimidazolium lactate [bmim][lactate].

[0028] In the above preparation, toluene is used as a solvent to remove unreacted starting materials from the nucleophilic substitution reaction of N-methylimidazolium with bromobutane. Acetone is used as both a solvent for [bmim]Br in the metathesis reaction and a precipitant for hydrobromates such as sodium bromide. Dichloromethane is used as a solvent and a purifying agent for 1-butyl-3-methylimidazolium lactate [bmim][lactate].

[0029] According to some embodiments of the present invention, in step (1), the molar ratio of N-methylimidazolium to bromobutane is 1:(1-3), preferably 1:(1-2), and more preferably 1:(1-1.5).

[0030] In some embodiments, in step (1), the molar ratio of N-methylimidazole to bromobutane is 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2, 1:2.5 or 1:3.

[0031] According to some embodiments of the present invention, in step (1), the temperature for the nucleophilic substitution reaction of N-methylimidazolium with bromobutane is 60-120°C, preferably 65-85°C, and more preferably 65-75°C.

[0032] According to some embodiments of the present invention, in step (1), the time for the nucleophilic substitution reaction of N-methylimidazolium with bromobutane is 3-10 h, preferably 5-8 h, and more preferably 5-6 h.

[0033] According to some embodiments of the present invention, in step (1), the temperature of the vacuum drying is 60-80°C, preferably 60-75°C, and more preferably 68-73°C.

[0034] According to some embodiments of the present invention, in step (1), the vacuum drying time is 4-10h, preferably 6-9h, and more preferably 7-8.5h.

[0035] According to some embodiments of the present invention, in step (2), the molar ratio of 1-butyl-3-methylimidazolium bromide to 2-hydroxypropionate is 1:(0.5-2), preferably 1:(0.8-1.2).

[0036] In some embodiments, in step (2), the molar ratio of 1-butyl-3-methylimidazolium bromide to 2-hydroxypropionate is 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.5, 1:1.8 or 1:2.

[0037] According to some embodiments of the present invention, in step (2), the temperature of the metathesis reaction between 1-butyl-3-methylimidazolium bromide and 2-hydroxypropionate is 0-70°C, preferably 10-50°C, and more preferably 20-25°C.

[0038] According to some embodiments of the present invention, in step (2), the reaction time of the 1-butyl-3-methylimidazolium bromide with metathesis is 10-30 h, preferably 15-25 h, and more preferably 22-24 h.

[0039] According to some embodiments of the present invention, in step (3), the temperature of the vacuum drying is 30-70°C, preferably 35-50°C, and more preferably 40-45°C.

[0040] According to some embodiments of the present invention, in step (3), the vacuum drying time is 2-8 hours, preferably 3-6 hours, and more preferably 3-4 hours.

[0041] In a second aspect, the present invention provides the application of a chiral ionic liquid catalyst in the preparation of high optical purity (S)-ethyl lactate, wherein the ethyl lactate is prepared using L-lactide and ethanol as reaction substrates.

[0042] According to some embodiments of the present invention, the ionic liquid catalyst is selected from alkylimidazolium lactate.

[0043] Preferably, the ionic liquid catalyst is selected from 1-butyl-3-methylimidazolium lactate, such as sodium 1-butyl-3-methylimidazolium lactate, potassium 1-butyl-3-methylimidazolium lactate, calcium 1-butyl-3-methylimidazolium lactate, magnesium 1-butyl-3-methylimidazolium lactate, zinc 1-butyl-3-methylimidazolium lactate, or ammonium 1-butyl-3-methylimidazolium lactate.

[0044] According to some embodiments of the present invention, the molar ratio of L-lactide to ethanol is 1:(1-6), preferably 1:(2-4), and more preferably 1:(2.2-2.8).

[0045] According to some embodiments of the present invention, the amount of catalyst used is 0.5-15% of the mass of the L-lactide, preferably 4-10%, more preferably 4-7%, and even more preferably 5-5.5%.

[0046] According to some embodiments of the present invention, the reaction temperature of the L-lactide and ethanol is 70-100°C, preferably 80-95°C, and more preferably 85-90°C.

[0047] According to some embodiments of the present invention, the reaction time of the L-lactide and ethanol is 1-5 h, preferably 1.5-4 h, and more preferably 2-2.5 h.

[0048] The beneficial effects of this invention are as follows: Using L-lactide and ethanol as reaction substrates, and under the action of an ionic liquid catalyst, this invention yields high-optical-purity ethyl lactate. The preparation method of this invention is simple to operate, requires no dehydrating agent, and is environmentally friendly and pollution-free. Compared with inorganic acid catalysts such as concentrated sulfuric acid, the ionic liquid catalyst used in this invention results in higher product conversion rates, shorter reaction times, and the catalyst can be reused. It also eliminates the generation of alkylation byproducts in traditional methods, and the product has high optical purity. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention in any way. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this disclosure.

[0050] Example 1

[0051] This embodiment provides a method for preparing high optical purity (S)-ethyl lactate, the specific steps of which are as follows:

[0052] (1) 29.52 g of N-methylimidazolium and 50 ml of toluene solvent were added to a 250 ml four-necked flask equipped with a stirrer, reflux condenser, thermometer and nitrogen delivery tube. Nitrogen gas was purged and 61.65 g of bromobutane was slowly titrated with stirring at 70 °C. The addition of bromobutane was completed in 1 h. The reaction was continued for 5 h. After standing for 1 h, the upper toluene solution was separated and discarded. The lower colorless liquid was dried under vacuum at 5 kPa and 70 °C for 8 h. After cooling to room temperature, 71.39 g of 1-butyl-3-methylimidazolium bromide ([bmim]Br) was obtained, with a yield of 90.55%.

[0053] (2) Take 21.90g of 1-butyl-3-methylimidazolium bromide ([bmim]Br) and 11.21g of sodium 2-hydroxypropionate and add them to a 250ml single-necked flask. Add 50ml of acetone solution and stir at 25℃ for 24h. Filter the reaction solution. Evaporate the acetone solution in the filtered reaction solution at 40℃ and 7.0kPa. Add 50ml of dichloromethane solution to the remaining solution and stir at 25℃ for 10min. Filter the solution under vacuum. Evaporate the dichloromethane in the filtered filtrate at 40℃ and 7.0kPa. Dry the residue under vacuum at 40℃ for 3h to obtain 20.71g of light yellow viscous liquid sodium 1-butyl-3-methylimidazolium lactate [bmim][lactate], with a yield of 90.83%.

[0054] (3) In a 250 ml four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen delivery tube, 14.40 g of L-lactide, 11.50 g of anhydrous ethanol, and 0.72 g of sodium 1-butyl-3-methylimidazolium lactate [bmim][lactate] ionic liquid catalyst were added. Nitrogen gas was introduced for protection, and the mixture was heated to reflux at 85 °C for 2 h to complete the esterification reaction. 26.53 g of ethyl lactate esterified solution was obtained, with an ethyl lactate purity of 88.23% and an esterification rate of 99.18%.

[0055] (4) The ethyl lactate esterification solution from step (3) was subjected to vacuum distillation at 2.5 kPa and 115 °C to collect 22.69 g of ethyl lactate fraction at 61-62 °C. The purity of ethyl lactate was 99.999%, and the distillation yield of ethyl lactate was 96.94%.

[0056] Example 2

[0057] This embodiment provides a method for preparing high optical purity (S)-ethyl lactate, which differs from Example 1 only in that the mass of L-lactide in step (3) is 14.4 g, the mass of anhydrous ethanol is 9.2 g, and the mass of 1-butyl-3-methylimidazolium lactate [bmim][lactate] ionic liquid catalyst is 0.72 g.

[0058] 24.30 g of ethyl lactate esterification solution was obtained, with an ethyl lactate purity of 93.64% and an esterification rate of 96.42%. The ethyl lactate esterification solution was then subjected to vacuum distillation at 2.5 kPa and 115 °C, yielding 21.93 g of ethyl lactate in the 61-62 °C fraction. The ethyl lactate purity was 99.999%, and the distillation yield was 96.38%.

[0059] Example 3

[0060] This embodiment provides a method for preparing high optical purity (S)-ethyl lactate, which differs from Example 1 only in that the mass of the 1-butyl-3-methylimidazolium lactate sodium [bmim][lactate] ionic liquid catalyst in step (3) is 1.44 g. 27.30 g of ethyl lactate esterification solution was obtained, with an ethyl lactate purity of 85.71% and an esterification rate of 99.15%. The ethyl lactate esterification solution was subjected to vacuum distillation at 2.5 kPa and 115 °C, and 22.63 g of ethyl lactate was collected as the fraction distilled at 61-62 °C, with an ethyl lactate purity of 99.999% and an ethyl lactate distillation yield of 96.71%.

[0061] Example 4

[0062] This embodiment provides a method for preparing high optical purity (S)-ethyl lactate, which differs from Example 1 only in that the mass of the 1-butyl-3-methylimidazolium lactate sodium [bmim][lactate] ionic liquid catalyst in step (3) is 1.01 g. 26.89 g of ethyl lactate esterification solution was obtained, with an ethyl lactate purity of 87.02% and an esterification rate of 99.15%. The ethyl lactate esterification solution was subjected to vacuum distillation at 2.5 kPa and 115 °C, and 22.68 g of ethyl lactate was collected as the fraction distilled at 61-62 °C, with an ethyl lactate purity of 99.999% and a distillation yield of 96.92%.

[0063] Example 5

[0064] This embodiment provides a method for preparing high optical purity (S)-ethyl lactate, which differs from Example 1 only in that the mass of the 1-butyl-3-methylimidazolium lactate sodium [bmim][lactate] ionic liquid catalyst in step (3) is 0.87 g. 26.70 g of ethyl lactate esterification solution was obtained, with an ethyl lactate purity of 87.53% and an esterification rate of 99.03%. The ethyl lactate esterification solution was subjected to vacuum distillation at 2.5 kPa and 115 °C, and 22.60 g of the 61-62 °C fraction of ethyl lactate was collected. The ethyl lactate purity was 99.999%, and the ethyl lactate distillation yield was 96.70%.

[0065] Example 6

[0066] This embodiment provides a method for preparing high optical purity (S)-ethyl lactate, which differs from Example 1 only in that the mass of the 1-butyl-3-methylimidazolium lactate sodium [bmim][lactate] ionic liquid catalyst in step (3) is 0.58 g. 26.40 g of ethyl lactate esterification solution was obtained, with an ethyl lactate purity of 88.02% and an esterification rate of 98.46%. The ethyl lactate esterification solution was subjected to vacuum distillation at 2.5 kPa and 115 °C, and 22.49 g of ethyl lactate was collected as the fraction distilled at 61-62 °C, with an ethyl lactate purity of 99.999% and a distillation yield of 96.78%.

[0067] Example 7

[0068] This embodiment provides a method for preparing high optical purity (S)-ethyl lactate, which differs from Example 1 only in that the mass of the 1-butyl-3-methylimidazolium lactate sodium [bmim][lactate] ionic liquid catalyst in step (3) is 0.29 g. 26.13 g of ethyl lactate esterification solution was obtained, with an ethyl lactate purity of 88.10% and an esterification rate of 97.54%. The ethyl lactate esterification solution was subjected to vacuum distillation at 2.5 kPa and 115 °C, and 22.09 g of ethyl lactate was collected as the fraction distilled at 61-62 °C, with an ethyl lactate purity of 99.999% and a distillation yield of 95.96%.

[0069] Example 8

[0070] This embodiment provides a method for preparing high optical purity (S)-ethyl lactate, which differs from Example 1 only in that the mass of the 1-butyl-3-methylimidazolium lactate sodium [bmim][lactate] ionic liquid catalyst in step (3) is 0.07 g. 25.95 g of ethyl lactate esterification solution was obtained, with an ethyl lactate purity of 74.16% and an esterification rate of 81.54%. The ethyl lactate esterification solution was subjected to vacuum distillation at 2.5 kPa and 115 °C, and 18.26 g of ethyl lactate was collected as the fraction distilled at 61-62 °C, with an ethyl lactate purity of 99.999% and an ethyl lactate distillation yield of 94.88%.

[0071] Example 9

[0072] This embodiment provides a method for preparing high optical purity (S)-ethyl lactate, the specific steps of which are as follows:

[0073] (1) 29.52 g of N-methylimidazolium and 50 ml of toluene solvent were added to a 250 ml four-necked flask equipped with a stirrer, reflux condenser, thermometer and nitrogen delivery tube. Nitrogen gas was purged and 61.65 g of bromobutane was slowly titrated with stirring at 70 °C. The addition of bromobutane was completed in 1 h. The reaction was continued for 5 h. After standing for 1 h, the upper toluene solution was separated and discarded. The lower colorless liquid was dried under vacuum at 5 kPa and 70 °C for 8 h. After cooling to room temperature, 71.39 g of 1-butyl-3-methylimidazolium bromide ([bmim]Br) was obtained, with a yield of 90.56%.

[0074] (2) Take 21.90g of 1-butyl-3-methylimidazolium bromide ([bmim]Br) and 11.21g of sodium 2-hydroxypropionate and add them to a 250ml single-necked flask. Add 50ml of acetone solution and stir at 25℃ for 24h. Filter the reaction solution. Evaporate the acetone solution in the filtered reaction solution at 40℃ and 7.0kPa. Add 50ml of dichloromethane solution to the remaining solution and stir at 25℃ for 10min. Filter the solution under vacuum. Evaporate the dichloromethane in the filtered filtrate at 40℃ and 7.0kPa. Dry the residue under vacuum at 40℃ for 3h to obtain 20.71g of pale yellow viscous liquid 1-butyl-3-methylimidazolium lactate [bmim][lactate], with a yield of 90.83%.

[0075] (3) In a 250 ml four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen delivery tube, 14.42 g of L-lactide, 11.51 g of anhydrous ethanol, and 0.73 g of 1-butyl-3-methylimidazolium lactate [bmim][lactate] ion catalyst were added. Nitrogen gas was introduced for protection, and the mixture was heated to reflux at 95 °C for 2 h to complete the esterification reaction. 26.57 g of ethyl lactate esterified solution was obtained, with an ethyl lactate purity of 87.89% and an esterification rate of 98.83%.

[0076] (4) The ethyl lactate esterification solution from step (3) was subjected to vacuum distillation at 2.5 kPa and 115 °C to collect 22.51 g of ethyl lactate fraction at 61-62 °C. The purity of ethyl lactate was 99.999%, and the distillation yield of ethyl lactate was 96.38%.

[0077] Example 10

[0078] This embodiment provides a method for preparing high optical purity (S)-ethyl lactate, the specific steps of which are as follows:

[0079] (1) 29.55 g of N-methylimidazolium and 50 ml of toluene solvent were added to a 250 ml four-necked flask equipped with a stirrer, reflux condenser, thermometer and nitrogen delivery tube. Nitrogen gas was purged and 59.18 g of bromobutane was slowly titrated with stirring at 70 °C. The addition of bromobutane was completed in 1 h 10 min. The reaction was continued for 5 h. After standing for 1 h, the upper toluene solution was separated. The lower colorless liquid was dried under vacuum at 5 kPa and 70 °C for 8 h. After cooling to room temperature, 71.52 g of 1-butyl-3-methylimidazolium bromide ([bmim]Br) was obtained, with a yield of 90.62%.

[0080] (2) Take 21.95g of 1-butyl-3-methylimidazolium bromide ([bmim]Br) and 11.23g of sodium 2-hydroxypropionate and add them to a 250ml single-necked flask. Add 50ml of acetone solution and stir at 25℃ for 24h. Filter the reaction solution. Evaporate the acetone solution in the filtered reaction solution at 40℃ and 7.0kPa. Add 50ml of dichloromethane solution to the remaining solution and stir at 25℃ for 10min. Filter the solution under vacuum. Evaporate the dichloromethane in the filtered filtrate at 40℃ and 7.0kPa. Dry the residue under vacuum at 40℃ for 3h to obtain 20.81g of pale yellow viscous liquid 1-butyl-3-methylimidazolium lactate [bmim][lactate], with a yield of 91.07%.

[0081] (3) In a 250 ml four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen delivery tube, 14.43 g of L-lactide, 11.53 g of anhydrous ethanol, and 0.75 g of 1-butyl-3-methylimidazolium lactate [bmim][lactate] ion catalyst were added. Nitrogen gas was introduced for protection, and the mixture was heated to reflux at 85 °C for 4 h to complete the esterification reaction. 26.57 g of ethyl lactate esterified solution was obtained, with an ethyl lactate purity of 87.84% and an esterification rate of 98.69%.

[0082] (4) The ethyl lactate esterification liquid from step (3) was subjected to vacuum distillation at 2.5 kPa and 115 °C to collect 22.38 g of ethyl lactate fraction at 61-62 °C. The purity of ethyl lactate was 99.999%, and the distillation yield of ethyl lactate was 95.88%.

[0083] Comparative Example 1

[0084] This comparative example provides a method for preparing high optical purity (S)-ethyl lactate, specifically as follows:

[0085] (1) In a 250 ml four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen delivery tube, 14.40 g of L-lactide, 11.50 g of anhydrous ethanol, and 0.72 g of concentrated sulfuric acid catalyst were added. Nitrogen gas was introduced for protection, and the mixture was heated to reflux at 85 °C for 2 h to complete the esterification reaction. 26.57 g of ethyl lactate esterified solution was obtained, with an ethyl lactate purity of 77.20% and an esterification rate of 86.92%.

[0086] (2) The ethyl lactate esterification liquid from step (1) was subjected to vacuum distillation at 2.5 kPa and 115 °C to collect 19.58 g of ethyl lactate fraction at 61-62 °C. The purity of ethyl lactate was 99.992%, and the distillation yield of ethyl lactate was 95.46%.

[0087] Comparative Example 2

[0088] This comparative example provides a method for preparing high optical purity (S)-ethyl lactate, specifically as follows:

[0089] (1) In a 250 ml four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen delivery tube, 14.40 g of L-lactide, 11.50 g of anhydrous ethanol, and 0.72 g of p-toluenesulfonic acid catalyst were added. Nitrogen gas was introduced for protection, and the mixture was heated to reflux at 85 °C for 2 h to complete the esterification reaction. 25.96 g of ethyl lactate esterified solution was obtained, with an ethyl lactate purity of 75.17% and an esterification rate of 82.69%.

[0090] (2) The ethyl lactate esterification liquid from step (1) was subjected to vacuum distillation at 2.5 kPa and 115 °C to collect 18.37 g of ethyl lactate fraction at 61-62 °C. The purity of ethyl lactate was 99.993%, and the distillation yield of ethyl lactate was 94.14%.

[0091] Comparative Example 3

[0092] This comparative example provides a method for preparing high optical purity (S)-ethyl lactate, specifically as follows:

[0093] (1) In a 250 ml four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen delivery tube, 14.40 g of L-lactide, 11.50 g of anhydrous ethanol, and 0.15 g of p-toluenesulfonic acid catalyst were added. Nitrogen gas was introduced for protection, and the mixture was heated to reflux at 85 °C for 2 h to complete the esterification reaction. 25.97 g of ethyl lactate esterified solution was obtained, with an ethyl lactate purity of 72.99% and an esterification rate of 80.32%.

[0094] (2) The ethyl lactate esterification liquid from step (1) was subjected to vacuum distillation at 2.5 kPa and 115 °C to collect 17.81 g of ethyl lactate fraction at 61-62 °C. The purity of ethyl lactate was 99.992%, and the distillation yield of ethyl lactate was 93.96%.

[0095] Although the present invention has been described in detail above with general descriptions, specific embodiments, and experiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing high optical purity (S)-ethyl lactate, comprising the following steps: reacting L-lactide and ethanol in the presence of a catalyst to obtain an esterification solution containing the (S)-ethyl lactate, wherein... The catalyst is 1-butyl-3-methylimidazolium lactate; The molar ratio of L-lactide to ethanol is 1:(1-6). The amount of catalyst used is 1.5-12% of the mass of the L-lactide; The esterification reaction is carried out at a temperature of 70-100℃; The esterification reaction takes 1-5 hours.

2. The preparation method according to claim 1, characterized in that, The molar ratio of L-lactide to ethanol is 1:(2-4).

3. The preparation method according to claim 1, characterized in that, The amount of catalyst used is 4-10% of the mass of the L-lactide.

4. The preparation method according to claim 1, characterized in that, The esterification reaction is carried out at a temperature of 80-95℃.

5. The preparation method according to claim 1, characterized in that, The esterification reaction takes 2-4 hours.

6. The preparation method according to claim 1, characterized in that, It also includes the step of vacuum distilling the esterified liquid to obtain high-purity (S)-ethyl lactate.

7. The preparation method according to claim 6, characterized in that, The distillation temperature is 95-135℃.

8. The preparation method according to claim 6, characterized in that, The distillation temperature is 105-125℃.

9. The preparation method according to claim 6, characterized in that, The vacuum degree of the distillation is 1-8 kPa.

10. The preparation method according to claim 6, characterized in that, The vacuum degree of the distillation is 1.5-3.5 kPa.

11. The preparation method according to claim 1, characterized in that, The 1-butyl-3-methylimidazolium lactate is prepared by the following steps: (1) N-methylimidazolium is mixed with bromobutane and reacted at 60-120℃ for 3-10h to obtain 1-butyl-3-methylimidazolium bromide; (2) The 1-butyl-3-methylimidazolium bromide obtained in step (1) is mixed with 2-hydroxypropionate and reacted at 20-70℃ for 10-30h to obtain 1-butyl-3-methylimidazolium lactate.

12. The preparation method according to claim 11, characterized in that, The molar ratio of N-methylimidazolium to bromobutane is 1:(1-3).

13. The preparation method according to claim 11, characterized in that, The molar ratio of N-methylimidazole to bromobutane is 1:(1-2).

14. The preparation method according to claim 11, characterized in that, The molar ratio of 1-butyl-3-methylimidazolium bromide to 2-hydroxypropionate is 1:(0.5-2).

15. The preparation method according to claim 11, characterized in that, The molar ratio of 1-butyl-3-methylimidazolium bromide to 2-hydroxypropionate is 1:(0.8-1.2).

16. Application of chiral ionic liquid catalysts in the preparation of high optical purity (S)-ethyl lactate, wherein, The (S)-ethyl lactate was prepared using L-lactide and ethanol as reaction substrates; The chiral ionic liquid catalyst is selected from 1-butyl-3-methylimidazolium lactate; The molar ratio of L-lactide to ethanol is 1:(1-6). The amount of catalyst used is 1.5-12% of the mass of the L-lactide; The reaction temperature is 70-100℃; The reaction time is 1-5 hours.