A new method for synthesizing propylene glycol methyl ether acetate

Abstract

This invention belongs to the field of materials and chemical synthesis technology, and discloses a novel method for synthesizing propylene glycol methyl ether acetate. The synthesis method includes the following steps: Step 1: In a reactor, a hydrogen bond donor and a hydrogen bond acceptor are added, and the mixture is heated at 40–60 °C. A eutectic solvent system is formed by heating at ℃ for 0.5–3 hours, followed by the sequential addition of methanol and propylene oxide, and then heating at 40–60 °C. At ℃, the reaction is stirred for 0.1–12 hours. Water is added, and the reaction solution is extracted with an organic solvent. The aqueous phase is removed by separation, and the organic solvent is removed by rotary evaporation under reduced pressure to obtain a crude product. Purification by column chromatography yields 1-methoxy-2-propanol (intermediate II). Alternatively, after the reaction, 1-methoxy-2-propanol (intermediate II) is obtained by distillation under reduced pressure. Second step: In a reactor, 1-methoxy-2-propanol, acetic acid, a solid acid catalyst, and a solvent are added. The reaction is stirred at 50–100 ℃ for 1–24 hours. After the reaction, the mixture is cooled to room temperature, filtered, and the solvent is removed by rotary evaporation under reduced pressure to obtain a crude product. Purification by column chromatography yields propylene glycol methyl ether acetate. This invention's synthesis method is the first to achieve the selective synthesis of 1-methoxy-2-propanol (intermediate II) using a eutectic solvent, and utilizes a solid acid catalyst to achieve the esterification reaction of 1-methoxy-2-propanol (intermediate II) with acetic acid to synthesize propylene glycol methyl ether acetate I, demonstrating promising industrial application prospects.

Description

Technical Field

[0001] This invention belongs to the field of materials and chemical synthesis technology, and specifically relates to a new method for synthesizing propylene glycol methyl ether acetate. Background Technology

[0002] Propylene glycol methyl ether acetate I ( Figure 1 Also known as 1-methoxy-2-propyl acetate or propylene glycol monomethyl ether acetate, its molecular formula is C6H. 12 O3, a colorless, hygroscopic liquid with a characteristic odor, is a non-polluting solvent with multiple functional groups. It is mainly used as a solvent in inks, paints, textile dyes, and textile oils, and can also be used as a cleaning agent in the production of liquid crystal displays. Its traditional synthesis methods are as follows... Figure 1 As shown: The first step involves ring-opening propylene oxide with sodium methoxide under alkaline conditions to obtain 1-methoxy-2-propanol (intermediate II). The second step involves esterification of intermediate II with acetic acid catalyzed by p-toluenesulfonic acid to obtain propylene glycol methyl ether acetate I. In the first step, due to the regioselectivity of the ring-opening reaction of propylene oxide with sodium methoxide, byproduct A is generated simultaneously with intermediate II, triggering a series of side reactions. This leads to a decrease in the yield of the target product; furthermore, the production of multiple byproducts increases the difficulty of purifying the target product I. Therefore, developing a highly regioselective ring-opening reaction of propylene oxide to achieve the efficient and highly selective synthesis of intermediate II is of great significance for the efficient preparation of propylene glycol methyl ether acetate I, and this is a research problem that urgently needs to be solved.

[0003] Eutectic solvents are low-melting-point mixtures formed by the interactions of two or more components through hydrogen bonding and other means, with melting points significantly lower than those of individual components. Due to their unique physicochemical properties and environmentally friendly characteristics, these solvents have attracted widespread attention in fields such as green chemistry, materials science, and biomass processing. Based on this, we developed a highly selective ring-opening reaction of propylene oxide using eutectic solvents, efficiently generating 1-methoxy-2-propanol (intermediate II), which was then applied to the synthesis of propylene glycol methyl ether acetate I. Summary of the Invention

[0004] To address the challenges of the prior art, the present invention aims to provide an efficient synthetic method for propylene glycol methyl ether acetate I.

[0005] The objective of this invention is achieved through the following technical solution: An efficient method for synthesizing propylene glycol methyl ether acetate I includes the following steps: Step 1 (Highly Selective Ring-Opening Reaction of Propylene Oxide Based on Eutectic Solvent for Efficient Synthesis of 1-Methoxy-2-Propanol): In a reactor, hydrogen bond donors and acceptors are added, and the reaction is carried out at 40–60 °C. A eutectic solvent system is formed by heating at ℃ for 0.5–3 hours, followed by the sequential addition of methanol and propylene oxide, and then heating at 40–60 °C. At ℃, the reaction was stirred for 0.1–12 hours. After the reaction was completed, water was added, and the reaction solution was extracted with an organic solvent. The aqueous phase was removed by separation, and the organic solvent was removed by rotary evaporation under reduced pressure to obtain the crude product. The crude product was purified by column chromatography to obtain 1-methoxy-2-propanol (intermediate II). Alternatively, after the reaction was completed, 1-methoxy-2-propanol (intermediate II) was obtained by distillation under reduced pressure.

[0006] The preferred hydrogen bond donors are: acetamide, urea, 1-methylurea, benzamide, imidazole, 2-imidazolium ketone, lauric acid, adipic acid, oxalic acid, benzoic acid, malonic acid, lactic acid, and citric acid.

[0007] The preferred hydrogen bond acceptors are: choline nitrate, choline tetrafluoroborate, choline chloride, chlorocholine chloride, betaine, nicotinic acid, tetramethylammonium chloride, glycine, proline, tetrabutylammonium chloride, tetraethylammonium bromide, and benzyltriphenylphosphine chloride.

[0008] The preferred molar ratio of hydrogen bond donor to hydrogen bond acceptor is 1:(1-2).

[0009] The preferred reaction temperature is 40–60°C. ℃.

[0010] The preferred reaction time is 0.1 to 12 hours.

[0011] The organic extraction solvent is preferably one or more of ethyl acetate, dichloromethane, and diethyl ether.

[0012] The column chromatography purification mentioned above refers to column chromatography purification using a mixed solvent of petroleum ether and ethyl acetate with a volume ratio of (2-100):1 as the eluent.

[0013] Step 2: In the reactor, add 1-methoxy-2-propanol, acetic acid, solid acid catalyst and solvent, and stir the reaction at 50-100 °C for 1-24 hours. After the reaction is completed, cool to room temperature, filter, remove the solvent by rotary evaporation under reduced pressure to obtain crude product, and purify by column chromatography to obtain propylene glycol methyl ether acetate.

[0014] The catalyst is preferably phosphotungstic acid or zeolite imidazole ester framework material-5.

[0015] The solvent is preferably one or a mixture of two or more of toluene, benzene, and xylene.

[0016] The column chromatography purification mentioned above refers to column chromatography purification using a mixed solvent of petroleum ether and ethyl acetate with a volume ratio of (2-100):1 as the eluent.

[0017] A propylene glycol methyl ether acetate I was prepared by the above method (Figure 2).

[0018] The preparation method of the present invention has the following advantages: (1) The synthesis method of the present invention is the first to achieve selective synthesis of 1-methoxy-2-propanol (intermediate II) using a eutectic solvent.

[0019] (2) The synthesis method of the present invention utilizes a solid acid catalyst to realize the esterification reaction of 1-methoxy-2-propanol (intermediate II) with acetic acid to synthesize propylene glycol methyl ether acetate I, which has good prospects for industrial application. Attached Figure Description

[0020] Figure 1. Synthetic route of propylene glycol methyl ether acetate I and the challenges it faces; Figure 2. Reaction equations involved in the method of the present invention; Detailed Implementation

[0021] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0022] first step: Example 1

[0023] Acetamide (20 mmol) and choline tetrafluoroborate (10 mmol) were added to a 50 mL reactor equipped with a reflux condenser, and the mixture was heated to 60 °C. A eutectic solvent system was formed by heating at ℃ for 3 hours, followed by the sequential addition of methanol (10 mmol) and propylene oxide (10.1 mmol). The reaction mixture was stirred at ℃ for 12 hours. Water was added, and the reaction solution was extracted with ethyl acetate. The aqueous phase was removed by separation, and the organic solvent was removed by rotary evaporation under reduced pressure to obtain the crude product. The regioselectivity of the reaction was >99:1. The product was purified by column chromatography to obtain 1-methoxy-2-propanol. The column chromatography eluent was a mixture of petroleum ether and ethyl acetate at a volume ratio of 10:1, with a yield of 97%. Example 2

[0024] Urea (20 mmol) and choline tetrafluoroborate (10 mmol) were added to a 50 mL reactor equipped with a reflux condenser, and the mixture was heated to 60 °C. A eutectic solvent system was formed by heating at ℃ for 3 hours, followed by the sequential addition of methanol (10 mmol) and propylene oxide (10.1 mmol). The reaction mixture was stirred at ℃ for 12 hours. Water was added, and the reaction solution was extracted with ethyl acetate. The aqueous phase was removed by separation, and the organic solvent was removed by rotary evaporation under reduced pressure to obtain the crude product. The regioselectivity of the reaction was >99:1. The product was purified by column chromatography to obtain 1-methoxy-2-propanol. The column chromatography eluent was a mixture of petroleum ether and ethyl acetate at a volume ratio of 10:1, with a yield of 65%. Example 3

[0025] 2-Imidazolidinone (20 mmol) and choline tetrafluoroborate (10 mmol) were added to a 50 mL reactor equipped with a reflux condenser, and the mixture was heated to 60 °C. A eutectic solvent system was formed by heating at ℃ for 3 hours, followed by the sequential addition of methanol (10 mmol) and propylene oxide (10.1 mmol). The reaction mixture was stirred at ℃ for 12 hours. Water was added, and the reaction solution was extracted with ethyl acetate. The aqueous phase was removed by separation, and the organic solvent was removed by rotary evaporation under reduced pressure to obtain the crude product. The regioselectivity of the reaction was >99:1. The product was purified by column chromatography to obtain 1-methoxy-2-propanol. The column chromatography eluent was a mixture of petroleum ether and ethyl acetate at a volume ratio of 10:1, with a yield of 43%. Example 4

[0026] Lactic acid (20 mmol) and choline tetrafluoroborate (10 mmol) were added to a 50 mL reactor equipped with a reflux condenser, and the mixture was heated to 60 °C. A eutectic solvent system was formed by heating at ℃ for 3 hours, followed by the sequential addition of methanol (10 mmol) and propylene oxide (10.1 mmol). The reaction mixture was stirred at ℃ for 12 hours. Water was added, and the reaction solution was extracted with ethyl acetate. The aqueous phase was removed by separation, and the organic solvent was removed by rotary evaporation under reduced pressure to obtain the crude product. The regioselectivity of the reaction was >99:1. The product was purified by column chromatography to obtain 1-methoxy-2-propanol. The column chromatography eluent was a mixture of petroleum ether and ethyl acetate at a volume ratio of 10:1, with a yield of 56%. Example 5

[0027] Benzoic acid (20 mmol) and choline tetrafluoroborate (10 mmol) were added to a 50 mL reactor equipped with a reflux condenser, and the mixture was heated to 60 °C. A eutectic solvent system was formed by heating at ℃ for 3 hours, followed by the sequential addition of methanol (10 mmol) and propylene oxide (10.1 mmol). The reaction mixture was stirred at ℃ for 12 hours. Water was added, and the reaction solution was extracted with ethyl acetate. The aqueous phase was removed by separation, and the organic solvent was removed by rotary evaporation under reduced pressure to obtain the crude product. The regioselectivity of the reaction was >99:1. The product was purified by column chromatography to obtain 1-methoxy-2-propanol. The column chromatography eluent was a mixture of petroleum ether and ethyl acetate at a volume ratio of 10:1, with a yield of 48%. Example 6

[0028] Add adipic acid (10 mmol) and choline tetrafluoroborate (10 mmol) to a 50 mL reactor equipped with a reflux condenser, and heat at 40 °C. A eutectic solvent system was formed by heating at ℃ for 0.5 hours, followed by the sequential addition of methanol (10 mmol) and propylene oxide (20 mmol). The reaction mixture was stirred at ℃ for 0.1 hours, water was added, and the reaction solution was extracted with dichloromethane. The aqueous phase was removed by separation, and the organic solvent was removed by rotary evaporation under reduced pressure to obtain the crude product. The regioselectivity of the reaction was >99:1. 1-Methoxy-2-propanol was purified by column chromatography using a petroleum ether:ethyl acetate mixture (v / v) of 100:1, with a yield of 4%. Example 7

[0029] Add imidazole (20 mmol) and choline tetrafluoroborate (10 mmol) to a 50 mL reactor equipped with a reflux condenser, and heat at 60 °C. A eutectic solvent system was formed by heating at ℃ for 3 hours, followed by the sequential addition of methanol (10 mmol) and propylene oxide (10.1 mmol). The reaction mixture was stirred at ℃ for 12 hours. Water was added, and the reaction solution was extracted with ethyl acetate. The aqueous phase was removed by separation, and the organic solvent was removed by rotary evaporation under reduced pressure to obtain the crude product. The regioselectivity of the reaction was >99:1. The product was purified by column chromatography to obtain 1-methoxy-2-propanol. The column chromatography eluent was a mixture of petroleum ether and ethyl acetate in a volume ratio of 2:1, with a yield of 81%. Example 8

[0030] Add imidazole (20 mmol) and betaine (10 mmol) to a 50 mL reactor equipped with a reflux condenser, and heat at 60 °C. A eutectic solvent system was formed by heating at ℃ for 2 hours, followed by the sequential addition of methanol (10 mmol) and propylene oxide (10.1 mmol). The reaction mixture was stirred at ℃ for 12 hours. Water was added, and the reaction solution was extracted with ethyl acetate. The aqueous phase was removed by separation, and the organic solvent was removed by rotary evaporation under reduced pressure to obtain the crude product. The regioselectivity of the reaction was >99:1. The product was purified by column chromatography to obtain 1-methoxy-2-propanol. The column chromatography eluent was a mixture of petroleum ether and ethyl acetate at a volume ratio of 10:1, with a yield of 53%. Example 9

[0031] Add imidazole (20 mmol) and tetrabutylammonium chloride (10 mmol) to a 50 mL reactor, and heat at 60 °C. A eutectic solvent system was formed by heating at ℃ for 2 hours, followed by the sequential addition of methanol (10 mmol) and propylene oxide (10.1 mmol). The reaction was carried out at ℃ for 12 hours with stirring, followed by vacuum distillation to give 1-methoxy-2-propanol in 72% yield. Example 10

[0032] Add imidazole (20 mmol) and benzyltriphenylphosphine chloride (10 mmol) to a 50 mL reactor equipped with a reflux condenser, and heat at 60 °C. A eutectic solvent system was formed by heating at ℃ for 3 hours, followed by the sequential addition of methanol (10 mmol) and propylene oxide (10.1 mmol). The reaction mixture was stirred at ℃ for 12 hours. Water was added, and the reaction solution was extracted with ethyl acetate. The aqueous phase was removed by separation, and the organic solvent was removed by rotary evaporation under reduced pressure to obtain the crude product. The regioselectivity of the reaction was >99:1. The product was purified by column chromatography to obtain 1-methoxy-2-propanol. The column chromatography eluent was a mixture of petroleum ether and ethyl acetate at a volume ratio of 10:1, with a yield of 25%.

[0033] Step Two: Example 11

[0034] In a 25 mL reaction flask equipped with a reflux condenser, 5 mmol of 1-methoxy-2-propanol, 10 mmol of acetic acid, 0.5 g of phosphotungstic acid, and 10 mL of toluene were added. The mixture was stirred at 100 °C for 2 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the solvent was removed by rotary evaporation under reduced pressure to obtain the crude product. The crude product was purified by column chromatography to obtain propylene glycol methyl ether acetate. The column chromatography eluent was a mixed solvent of petroleum ether and ethyl acetate with a volume ratio of 10:1, and the product was obtained in 98% yield. Example 12

[0035] In a 25 mL reaction flask equipped with a reflux condenser, 5 mmol of 1-methoxy-2-propanol, 10 mmol of acetic acid, 0.5 g of phosphotungstic acid, and 10 mL of xylene were added. The mixture was stirred at 100 °C for 1 hour. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the solvent was removed by rotary evaporation under reduced pressure to obtain the crude product. The crude product was purified by column chromatography to obtain propylene glycol methyl ether acetate. The column chromatography eluent was a mixed solvent of petroleum ether and ethyl acetate with a volume ratio of 10:1, yielding the product with a yield of 91%. Example 13

[0036] In a 25 mL reaction flask equipped with a reflux condenser, 5 mmol of 1-methoxy-2-propanol, 10 mmol of acetic acid, 0.05 g of phosphotungstic acid, and 10 mL of toluene were added. The mixture was stirred at 100 °C for 2 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the solvent was removed by rotary evaporation under reduced pressure to obtain the crude product. The crude product was purified by column chromatography to obtain propylene glycol methyl ether acetate. The column chromatography eluent was a mixed solvent of petroleum ether and ethyl acetate with a volume ratio of 10:1, and the product was obtained in a yield of 78%. Example 14

[0037] In a 25 mL reaction flask equipped with a reflux condenser, 5 mmol of 1-methoxy-2-propanol, 10 mmol of acetic acid, 0.5 g of zeolite imidazole ester framework material-5, and 10 mL of toluene were added. The mixture was stirred at 100 °C for 24 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the solvent was removed by rotary evaporation under reduced pressure to obtain the crude product. The crude product was purified by column chromatography to obtain propylene glycol methyl ether acetate. The column chromatography eluent was a mixed solvent of petroleum ether and ethyl acetate with a volume ratio of 100:1, yielding the product in 81% yield. Example 15

[0038] In a 25 mL reaction flask equipped with a reflux condenser, 5 mmol of 1-methoxy-2-propanol, 5 mmol of acetic acid, 0.5 g of phosphotungstic acid, and 10 mL of benzene were added. The mixture was stirred at 50 °C for 1 hour. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the solvent was removed by rotary evaporation under reduced pressure to obtain the crude product. The crude product was purified by column chromatography to obtain propylene glycol methyl ether acetate using a 2:1 (v / v) petroleum ether:ethyl acetate mixture. The yield was 33%. The structural characterization data of the products obtained in Examples 11-15 are shown below: 1 H NMR (500 MHz, CDCl3): δ = 5.03-4.97 (m, 1H), 3.39-3.36 (m, 1H), 3.34-3.31 (m, 1H), 3.30 (s, 3H), 1.99 (s, 3H), 1.17 (d, J = 10 Hz, 3H). 13 C NMR (125 MHz, CDCl3): δ =170.5, 75.0, 69.2, 59.1, 21.2, 16.5. Based on the above data, the structures of the products obtained in Examples 11-15 are inferred as follows: .

[0039] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

[0040] Figure 1. Synthetic route of propylene glycol methyl ether acetate I and the challenges encountered. Figure 2. Reaction equations involved in the method of the present invention.

Claims

1. A novel process for the efficient synthesis of propylene glycol methyl ether acetate I, characterized by: The following steps are included: Step 1: In a reactor, add hydrogen bond donors and hydrogen bond acceptors, and heat at 40–60°C for 0.5–3 hours to form a eutectic solvent system. Add methanol and propylene oxide sequentially, and stir the reaction at 40–60°C for 0.1–12 hours. Add water, extract the reaction mixture with an organic solvent, separate the aqueous phase, remove the organic solvent by rotary evaporation under reduced pressure to obtain the crude product, and purify by column chromatography to obtain 1-methoxy-2-propanol (intermediate II). Alternatively, after the reaction is complete, distill under reduced pressure to obtain 1-methoxy-2-propanol (intermediate II). Step 2: In the reactor, add 1-methoxy-2-propanol, acetic acid, solid acid catalyst and solvent. Stir the reaction at 50-100 °C for 1-24 hours. After the reaction is completed, cool to room temperature, filter, remove the solvent by rotary evaporation under reduced pressure to obtain crude product, and purify by column chromatography to obtain propylene glycol methyl ether acetate. A propylene glycol methyl ether acetate I was prepared by the above method.

2. A novel process for the efficient synthesis of propylene glycol methyl ether acetate I as claimed in claim 1, wherein: The hydrogen bond donor is preferably one or more of acetamide, urea, 1-methylurea, benzamide, imidazole, 2-imidazolium ketone, lauric acid, adipic acid, oxalic acid, benzoic acid, malonic acid, lactic acid, and citric acid.

3. A novel process for the efficient synthesis of propylene glycol methyl ether acetate I as claimed in claim 1, wherein: The hydrogen bond acceptor is preferably one or more of the following: choline nitrate, choline tetrafluoroborate, choline chloride, chlorocholine chloride, betaine, nicotinic acid, tetramethylammonium chloride, glycine, proline, tetrabutylammonium chloride, tetraethylammonium bromide, and benzyltriphenylphosphine chloride.

4. The novel method for the efficient synthesis of propylene glycol methyl ether acetate I according to claim 1, characterized in that: The preferred molar ratio of hydrogen bond donor to hydrogen bond acceptor is 1:(1-2).

5. The novel method for the efficient synthesis of propylene glycol methyl ether acetate I according to claim 1, characterized in that: The preferred reaction temperature is 40–60°C.

6. The novel method for the efficient synthesis of propylene glycol methyl ether acetate I according to claim 1, characterized in that: The preferred reaction time is 0.1 to 12 hours.

7. The novel method for the efficient synthesis of propylene glycol methyl ether acetate I according to claim 1, characterized in that: The organic extraction solvent is preferably one or more of ethyl acetate, dichloromethane, and diethyl ether.

8. A novel method for the efficient synthesis of propylene glycol methyl ether acetate I according to claim 1, characterized in that: The column chromatography purification mentioned above refers to column chromatography purification using a mixed solvent of petroleum ether and ethyl acetate with a volume ratio of (2-100):1 as the eluent.

9. A novel method for the efficient synthesis of propylene glycol methyl ether acetate I according to claim 1, characterized in that: The catalyst is preferably phosphotungstic acid or zeolite imidazole ester framework material-5.

10. A novel method for the efficient synthesis of propylene glycol methyl ether acetate I according to claim 1, characterized in that: The solvent is preferably one or a mixture of two or more of toluene, benzene, and xylene.

11. A novel and efficient method for the synthesis of propylene glycol methyl ether acetate I, characterized in that: It is prepared by the method described in any one of claims 1 to 9.

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