A method for synthesizing epsilon-caprolactone by 6-hydroxyhexanoic acid dehydrating cyclization
By employing a coupled reaction system of H-ZSM-5 catalyst and benzonitrile solvent in the synthesis of ε-caprolactone, the harsh conditions under vacuum were overcome, enabling the efficient and safe synthesis of ε-caprolactone, reducing production costs, and providing technical support for industrial production.
Patent Information
- Application Number
- CN202610568687.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-04-28
- Publication Date
- 2026-07-10
AI Technical Summary
Existing ε-caprolactone synthesis routes require harsh reaction conditions, necessitating a vacuum environment. This results in high equipment investment, high energy consumption, and complex catalyst structures, making industrial-scale production difficult.
A coupled reaction system was constructed using H-ZSM-5 catalyst and benzonitrile solvent. Utilizing the dual function of benzonitrile as both a solvent and a hydration reactant, the dehydration and cyclization of 6-hydroxyhexanoic acid was carried out under normal pressure. Water was consumed through chemical coupling, breaking the equilibrium and promoting the formation of ε-caprolactone.
The efficient synthesis of ε-caprolactone under normal pressure was achieved, improving conversion and yield while reducing equipment investment and energy consumption, providing a more practical and easily scalable technical solution for industrial production.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of green chemistry technology and mainly relates to a method for the dehydration and cyclization of 6-hydroxyhexanoic acid to synthesize ε-caprolactone. Background Technology
[0002] ε-caprolactone (ε-CL), as a novel polyester monomer, can be used to synthesize polycaprolactone (PCL) polymer materials. PCL combines excellent flexibility, shape memory, and biodegradability, and is widely used in the preparation of packaging materials, biodegradable bone scaffolds, artificial skin, and surgical sutures. As a result, the preparation of its precursor monomer ε-CL has attracted increasing attention.
[0003] Currently, there are few reports on the dehydration cyclization of 6-hydroxyhexanoic acid (6-HA) to synthesize ε-CL. Cheng et al. (Catalysis Letters, 2021, 151 (12): 3501-3508) investigated the synthesis of ε-CL by Co 2+ The TS-1 catalyzed 6-HA dehydration cyclization reaction achieved an ε-CL yield of 74.5% at 300 °C and 1.3 kPa. The results indicate that between 260-300 °C, higher temperatures facilitate the dehydration of 6-HA to ε-CL. Temperatures exceeding 300 °C exacerbate polymerization side reactions for both 6-HA and ε-CL. Higher pressure results in shorter 6-HA residence time and lower ε-CL yield. Therefore, this reaction requires maintenance under low-pressure conditions (1.3 kPa) to allow the generated product to vaporize and condense directly, thereby breaking the reaction equilibrium and promoting ε-CL formation. It is evident that current 6-HA dehydration cyclization processes for ε-CL synthesis generally suffer from stringent reaction conditions (vacuum environment). Summary of the Invention
[0004] The purpose of this invention is to address the problems existing in current ε-CL synthesis routes by providing a method for the preparation of ε-CL through the dehydration and cyclization of 6-HA using benzonitrile as a solvent. This method utilizes the solvent and hydration properties of benzonitrile to construct a coupled reaction system of 6-HA dehydration and cyclization with benzonitrile hydration without the need for vacuum conditions, achieving a safe and efficient synthesis of ε-CL. This invention solves the problem of demanding reaction conditions (vacuum environment) in current ε-CL synthesis routes, providing a more practical and easily scalable technical solution for the industrial production of ε-CL.
[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for synthesizing ε-CL by dehydration cyclization of 6-HA, the method comprising the following steps: 6-HA and H-ZSM-5 catalysts and benzonitrile solvent were added to a reactor, sealed, and reacted at 170-210 °C for 6-10 h under a nitrogen atmosphere and mechanical stirring to directly obtain ε-CL in one step. The mass ratio of 6-HA to H-ZSM-5 catalyst is 1:0.1~0.5; Add 10-50 mL of solvent for every 1 mmol of 6-HA; The preferred material ratio is 0.026-0.052 g of catalyst per 1 mmol (0.132 g) of 6-HA, with a mass ratio of 1:0.2-1:0.4. The preferred reaction temperature is 180-200 ℃; the preferred reaction time is 7-10 h.
[0006] The essential features of this invention are: This invention utilizes the dual function of benzonitrile (as both a reaction solvent and a hydration reactant) to construct a coupled reaction system of 6-HA dehydration cyclization and benzonitrile hydration, thereby achieving efficient synthesis of ε-CL under ambient pressure without the need for vacuum conditions.
[0007] The reaction mechanism is as follows: the acidic sites (Br) on the surface of the H-ZSM-5 molecular sieve Benzoic acid (both styrene and Lewis acid) can simultaneously activate the carboxyl group of 6-HA and the cyano group of benzonitrile. At the reaction temperature, benzonitrile undergoes a hydration reaction to generate benzamide. This process consumes the water generated from the dehydration cyclization of 6-HA, disrupting the chemical equilibrium of 6-HA dehydration cyclization and shifting the equilibrium to the right, promoting the formation of ε-CL. Simultaneously, benzonitrile, as a high-boiling-point polar solvent, can effectively dissolve 6-HA and ε-CL and provide a stable liquid-phase reaction environment. Therefore, this invention does not rely on vacuum vaporization to remove water as in existing technologies, but instead consumes water in situ through chemical coupling, achieving efficient conversion under atmospheric pressure. The H-ZSM-5 catalyst has tunable acidity and good thermal stability. Its microporous structure facilitates the adsorption of reactants and the diffusion of products, avoiding deactivation or swelling and achieving a stable coupled reaction.
[0008] The beneficial effects of this invention are as follows: A coupled reaction system of 6-HA dehydration cyclization and benzonitrile hydration was constructed, overcoming the problem of harsh reaction conditions (vacuum environment) in the current ε-CL synthesis route (Catalysis Letters, 2021, 151 (12): 3501-3508). This saved on equipment and energy investment, reduced costs, and provided a more practical and scalable technical solution for the industrial production of ε-CL. At 180 °C for 9 h, the conversion rate of 6-HA was 100%, and the yield of ε-CL was 89.5%, which is significantly higher than the ε-CL yield reported in the literature. Detailed Implementation
[0009] This invention addresses the problems of harsh reaction conditions (high temperature or vacuum environment), complex catalyst structure and preparation process in the current ε-CL synthesis route. It constructs a coupled reaction system with H-ZSM-5 as catalyst and 6-HA dehydration cyclization and benzonitrile hydration, realizing the safe, efficient and green synthesis of ε-CL and successfully solving the above problems.
[0010]
[0011] The essential features and significant effects of this invention can be seen from the following embodiments, but they do not limit the invention in any way. Those skilled in the art can make some non-essential improvements and adjustments based on the content of this invention. The invention is further described below through specific embodiments.
[0012] The H-ZSM-5 catalyst involved in this invention is a known material. The H-ZSM-5 catalyst with Si / Al=28 from the catalyst plant of Nankai University is used in the following examples. However, it is not limited to this.
[0013] Example 1: 6-HA (1 mmol, 0.132 g), H-ZSM-5 catalyst (0.052 g), and benzonitrile (20 mL) were added to a 50 mL polytetrafluoroethylene-lined high-pressure reactor. After sealing, the air was replaced with N2, and the temperature was raised to 180 °C. The reaction was carried out under mechanical stirring for 9 h. After the reaction was completed, the reaction solution was analyzed by gas chromatography. The conversion rate of 6-HA was 100%, and the yield of ε-CL was 89.5%.
[0014] Examples 2 to 13: Other conditions are the same as in Example 1. Different reaction conditions and results are shown in the summary table.
[0015]
[0016] The above descriptions are merely some specific examples of the present invention, but the scope of protection of the present invention is not limited thereto, nor does the order of the embodiments limit the present invention in any way. Any changes or substitutions made by those skilled in the art within the scope of the technology reported in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention is not limited to the above embodiments, and should be determined by the scope of the claims.
[0017] Matters not covered in this invention are common knowledge.
Claims
1. A method for synthesizing ε-CL by dehydration cyclization of 6-HA, characterized in that, The method includes the following steps: 6-HA and H-ZSM-5 catalysts and benzonitrile were added to a reactor, sealed, and reacted at 170-210 °C for 6-10 h under a nitrogen atmosphere and mechanical stirring to directly obtain ε-CL in one step. The mass ratio of 6-HA to H-ZSM-5 catalyst is 1:0.1~0.
5.
2. The method for synthesizing ε-CL by dehydration cyclization of 6-HA as described in claim 1, characterized in that, Add 10-50 mL of benzonitrile for every 1 mmol of 6-HA.
3. The method for synthesizing ε-CL by dehydration cyclization of 6-HA as described in claim 1, characterized in that, The mass ratio of 6-HA to the catalyst is 1:0.2-1:0.
4.
4. The method for synthesizing ε-CL by dehydration cyclization of 6-HA as described in claim 1, characterized in that, The reaction temperature is 180-200 ℃; the reaction time is 7-10 h.