A method for the atom-economical preparation of 1,4-dioxane-2-one

Abstract

This invention belongs to the field of chemical engineering and discloses an atom-economical method for preparing 1,4-dioxane-2-one. The method involves mixing ethylene oxide and glycolic acid in a certain proportion and reacting at 50-100 °C for 2-12 hours. After post-treatment, high-purity 1,4-dioxane-2-one is obtained. This method can be achieved through the autocatalytic action of glycolic acid, without the need for an external catalyst; alternatively, an acidic catalyst can be added to improve the reaction rate and yield. The only byproduct of the reaction is water, and the theoretical atom economy is over 85%. Post-treatment employs gradient vacuum distillation or extraction, and the purity of the obtained product is not less than 99.0%. This invention provides a novel technical solution for the green and efficient preparation of pDO.

Description

Technical Field

[0001] This invention belongs to the field of chemical engineering, and specifically relates to an atom-economical method for preparing 1,4-dioxane-2-one (pDO), and more particularly to a green synthesis process using glycolic acid and ethylene oxide as raw materials and water as the only byproduct. Background Technology

[0002] Atom economy is a core indicator for measuring the greenness of chemical synthesis routes, referring to the percentage of atomic masses of reactant molecules converted into the target product. High atom economy in synthesis means less raw material waste, lower byproduct emissions, and higher resource utilization efficiency. In the synthesis of fine chemicals and pharmaceutical intermediates, pursuing atom economy has become one of the core directions of green chemistry development.

[0003] 1,4-Dioxane-2-one (pDO) is a key monomer in the synthesis of biodegradable polyester poly(p-dioxane-2-one) (PPDO), and is also an important fungicide and fine chemical intermediate. However, existing methods for synthesizing pDO all have significant inherent defects in terms of atom economy. The traditional route using ethylene glycol and chloroacetic acid as raw materials is clearly uneconomical and environmentally unfriendly. This route involves a multi-step reaction between ethylene glycol and chloroacetic acid, producing one molecule of sodium chloride as a byproduct for every molecule of pDO generated. Neither chlorine nor sodium atoms enter the target product, resulting in complete waste. This route also generates a large amount of saline wastewater, leading not only to poor atom economy (theoretically less than 60%) but also a severe environmental burden. The catalytic dehydrogenation route using diethylene glycol as a raw material is carried out at high temperatures of 240–360 °C, with an actual yield of only about 25%, meaning that more than 75% of the carbon atoms in the raw material are converted into various unknown byproducts, resulting in extremely low atom economy.

[0004] The route using glycolate esters as raw materials is a novel method for the synthesis of pDO. This route involves the reaction of methyl glycolate, ethyl glycolate, etc., with ethylene oxide in the presence of a catalyst to generate pDO. The reaction equation is: glycolate ester + ethylene oxide → pDO + alcohol. Although this route is concise, from an atom economy perspective, for every molecule of pDO produced, one molecule of alcohol (methanol, ethanol, etc.) is generated as a stoichiometric byproduct.

[0005] The above analysis reveals a key fact: existing pDO synthesis technologies inevitably produce stoichiometric byproducts (alcohols, salts, or thermal cracking byproducts), naturally limiting atom economy. This invention, for the first time, uses glycolic acid (rather than its ester derivatives) to directly react with ethylene oxide, with the reaction equation: glycolic acid + ethylene oxide → pDO + water. The only byproduct of this reaction is water, and over 90% of the atoms in the glycolic acid molecule are retained in the target product, achieving a theoretical atom economy exceeding 85%, without generating any waste stream containing organic byproducts. This difference in pathway is not an improvement at the process parameter level, but a fundamental transformation in reaction type and stoichiometric relationship, opening up a new direction for green pDO synthesis. Summary of the Invention

[0006] The purpose of this invention is to overcome the fundamental problems of poor atom economy and numerous byproducts in existing pDO synthesis technologies, and to provide an atom-economical method for preparing 1,4-dioxane-2-one. The invention adopts the following technical solution: A method for the atom-economical preparation of 1,4-dioxane-2-one involves mixing ethylene oxide and glycolic acid in a specific ratio, reacting the mixture at a certain temperature for a period of time, and then post-processing to obtain 1,4-dioxane-2-one. The reaction pathway of this invention differs fundamentally from existing technologies. Existing glycolate routes inevitably generate alcohol byproducts, while this invention uses glycolic acid as a raw material, with water being the only byproduct during the reaction. This difference in pathway results in a substantial improvement in atom economy—the atom economy of this invention reaches over 85%, while existing glycolate routes only achieve 70%–75%.

[0007] In this invention, the reaction can be carried out without an external catalyst, achieved by the autocatalytic action of glycolic acid. The mechanism is as follows: the carboxyl group in the glycolic acid molecule provides an acidic site to activate ethylene oxide, while its hydroxyl group acts as a nucleophile to attack the activated ethylene oxide, resulting in a ring-opening addition-cyclization tandem reaction to generate the target product. The conditions for the autocatalytic reaction are: a molar ratio of glycolic acid to ethylene oxide of 1:(1~5), a reaction temperature of 50~100 °C, and a reaction time of 2~12 hours. Preferably, the molar ratio of glycolic acid to ethylene oxide is 1:2, the reaction temperature is 80 °C, and the reaction time is 6 hours.

[0008] In another preferred embodiment of the present invention, the reaction can be further improved by adding an acidic catalyst under the same conditions as the autocatalytic reaction, thereby increasing the reaction rate and yield. The molar ratio of the catalyst to ethylene oxide is 1:(100~1000). The acidic catalyst is selected from one or more of sulfuric acid, phosphoric acid, p-toluenesulfonic acid, methanesulfonic acid, and trifluoromethanesulfonic acid.

[0009] In this invention, the post-treatment includes gradient vacuum distillation or extraction. The gradient vacuum distillation involves first distilling away the water generated in the reaction at 50-60 °C and 50-300 Pa, then continuing distillation at 100-120 °C and 50-300 Pa to obtain the 1,4-dioxane-2-one product. The extraction method involves using organic solvents such as ethyl acetate, diethyl ether, dichloromethane, or chloroform to extract the product from the reaction solution, followed by drying and concentration to obtain 1,4-dioxane-2-one. The purity of the post-treated product is not less than 99.0%. Beneficial effects

[0010] Compared with the prior art, the present invention has at least the following significant advantages: (1) Fundamental improvement in atom economy. This invention is the first to use glycolic acid (rather than its ester derivatives) to directly react with ethylene oxide to prepare pDO, representing a fundamental shift in the reaction pathway from "ester exchange-cyclization" to "direct dehydration cyclization". The theoretical atom economy of existing glycolate routes is only about 70%~75%, while the theoretical atom economy of the method of this invention is close to 85%. The carbon and hydrogen atoms of the raw materials are retained in the target product to the greatest extent, reducing resource waste at the source.

[0011] (2) The only byproduct is water. The only byproduct of the reaction in this invention is water, which contains no organic matter or salts and causes no environmental pollution. Compared with the large amount of sodium chloride byproducts of the existing chloroacetic acid route and the alcohol byproducts of the ester route, this invention achieves a qualitative leap in the types and properties of byproducts.

[0012] (3) The reaction can proceed without the addition of an external catalyst. The glycolic acid molecule itself has a dual function—the carboxyl group provides acidic activation for ethylene oxide, and the hydroxyl group provides nucleophilicity to participate in the ring-opening reaction. This self-catalytic property is the first discovery and report in this field, which simplifies the use of catalysts and subsequent separation steps.

[0013] (4) High product purity. Since the byproduct is only water, the crude product contains few types and low content of impurities. Only one step of gradient vacuum distillation or simple extraction is needed to obtain high-quality pDO products with a purity of ≥99.0%, which can be directly used for the high molecular weight polymerization of PPDO. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1This is a high-purity 1,4-dioxane-2-one NMR spectrum provided in Example 4 of the present invention; Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0017] To more clearly illustrate the technical solution and advantages of the present invention, the following examples provide a detailed description of a low-cost method for preparing high-purity 1,4-dioxane-2-one.

[0018] Example 1 76 g (1.0 mol) of glycolic acid and 88 g (2.0 mol) of ethylene oxide (molar ratio of ethylene oxide:glycolic acid = 2:1) were added to a pressure-resistant reactor at 0 °C. After sealing, the reactor was stirred in an oil bath at 80 °C for 6 hours. After the reaction was completed, the reaction solution was cooled to room temperature. First, the water generated in the reaction was removed by vacuum distillation at 50–60 °C and 200 Pa. Then, the 1,4-dioxane-2-one fraction was collected by distillation at 110 °C and 200 Pa, yielding 68 g of product with a yield of 67% and a purity of 99%.

[0019] Example 2 76 g (1.0 mol) of glycolic acid, 44 g (1.0 mol) of ethylene oxide (molar ratio 1:1), and 1.9 g (10.0 mmol, catalyst to ethylene oxide molar ratio 1:100) of p-toluenesulfonic acid were added to a pressure-resistant reactor at 0 °C. The reactor was sealed and stirred in an oil bath at 70 °C for 2 hours. After the reaction was completed, the reaction solution was cooled to room temperature and subjected to gradient vacuum distillation: water was first distilled off at 55 °C and 200 Pa, and then the product was collected by distillation at 110 °C and 200 Pa to obtain 79 g of 1,4-dioxane-2-one, with a yield of 77% and a purity of 99%.

[0020] Example 3 76.05 g (1.0 mol) of glycolic acid, 66 g (1.5 mol) of ethylene oxide (molar ratio of ethylene oxide to glycolic acid = 1.5:1), and 16.7 mg (0.17 mmol, molar ratio of catalyst to ethylene oxide 1:1000) of 98% concentrated sulfuric acid were added to a pressure-resistant reactor at 0 °C. The reactor was sealed and stirred in a 50 °C oil bath for 4 hours. After the reaction was complete, the reaction solution was cooled to room temperature, and the pH was adjusted to neutral by adding 1 mol / L sodium hydroxide solution. Gradient vacuum distillation was performed: water was first distilled off at 55 °C and 200 Pa, then the temperature was raised to 110 °C and 200 Pa to collect the product, yielding 67.2 g of 1,4-dioxane-2-one, with a yield of 65.8% and a purity of 99%.

[0021] Example 4 152.10 g (2.0 mol) of glycolic acid, 176.20 g (4.0 mol) of ethylene oxide (molar ratio of ethylene oxide to glycolic acid = 2:1), and 0.73 g (2.0 mmol, molar ratio of catalyst to ethylene oxide 1:1000) of trifluoromethanesulfonic acid were added to a 2 L stainless steel high-pressure reactor at 0 °C. After sealing, the reactor was stirred in an 80 °C oil bath for 2 hours. After the reaction was completed, the reaction solution was cooled to room temperature. Gradient vacuum distillation was used: first, the water (approximately 36 g) generated in the reaction was distilled off at 55 °C and 250 Pa; then, the temperature was further increased to 110 °C and 200 Pa to collect the main fraction of 1,4-dioxane-2-one, yielding 169.5 g of product, with a yield of 83.0% and a purity of 98%.

[0022] pass Figure 1 The 1H NMR spectrum analysis assigned all the chemical shift signals, and the integrated area ratio of the three peaks was 2:2:2, corresponding to the three methylene structures respectively.

[0023] Finally, it should be noted that the examples are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An atom-economical method for preparing 1,4-dioxane-2-one, characterized in that, The method includes: mixing ethylene oxide and glycolic acid in a certain proportion, reacting them at a certain temperature for a period of time, and then post-processing to obtain 1,4-dioxane-2-one.

2. The method according to claim 1, characterized in that, The molar ratio of glycolic acid to ethylene oxide is 1:(1~5); preferably, the molar ratio of glycolic acid to ethylene oxide is 1:2; the reaction temperature is 50~100 °C, and the reaction time is 2~12 hours; preferably, the reaction temperature is 80 °C, and the reaction time is 6 hours.

3. The method according to claims 1 and 2, characterized in that, The reaction is achieved by the autocatalysis of glycolic acid without the addition of an external catalyst.

4. The method according to claims 1 and 2, characterized in that, The reaction is carried out in the presence of an acidic catalyst to improve the reaction rate and yield.

5. The method according to claim 4, characterized in that, The acidic catalyst is selected from one or more of sulfuric acid, phosphoric acid, p-toluenesulfonic acid, methanesulfonic acid, and trifluoromethanesulfonic acid; the molar ratio of the catalyst to ethylene oxide is 1:(100~1000).

6. The method according to claims 1 to 5, characterized in that, The post-processing includes gradient vacuum distillation and extraction. The gradient vacuum distillation involves distilling water at 50-60 °C and 50-300 Pa, followed by distillation at 100-120 °C and 50-300 Pa to obtain 1,4-dioxane-2-one. The extraction method involves using ethyl acetate, diethyl ether, dichloromethane, or chloroform as organic solvents to extract the product from the reaction solution, followed by drying to obtain 1,4-dioxane-2-one. The post-processing yields a 1,4-dioxane-2-one product with a purity of not less than 99.0%.

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