A process for the preparation of 2-alkanoyloxypropionic acids

Abstract

The application discloses a preparation method of 2-alkanoyloxypropionic acid. The application uses waste polylactic acid as raw material to prepare 2-alkanoyloxypropionic acid with high yield, and the operation is simple, suitable for industrial production, and recycling of the polylactic acid is realized at the same time.

Description

Technical Field

[0001] This invention belongs to the field of organic compound preparation, specifically relating to a method for preparing 2-alkanoyloxypropionic acid from polylactic acid. Background Technology

[0002] 2-Acetoxypropionic acid is a class of organic compounds whose molecular structure contains ester and carboxyl functional groups. These functional groups endow it with diverse chemical properties and important applications. For example, 2-acetoxypropionic acid is an important synthetic intermediate with significant roles in the chemical and pharmaceutical fields. In the pharmaceutical field, it is a key intermediate in the synthesis of many drugs, such as ibuprofen and naproxen; in the food industry, it can be used to prepare food preservatives and other additives; furthermore, its derivatives have shown potential as pesticides and plant growth regulators in the agricultural field.

[0003] Currently, the main methods for synthesizing 2-alkanoyloxypropionic acid are esterification and acylation. Esterification uses lactic acid and alkyl anhydrides as raw materials, undergoing an esterification reaction under the catalysis of concentrated sulfuric acid to obtain 2-alkanoyloxypropionic acid. However, this method generates a large amount of waste acid in subsequent processing due to the use of concentrated sulfuric acid, causing environmental pollution, and also requires equipment with high corrosion resistance. Acylation uses lactic acid and alkyl acyl chlorides as reactants, undergoing an acylation reaction under the catalysis of an alkali to prepare 2-alkanoyloxypropionic acid. However, this method also requires high-quality materials for the reaction equipment due to the high reactivity and strong corrosiveness of alkyl acyl chlorides.

[0004] Polylactic acid (PLA) is a bio-based, biodegradable material primarily polymerized from lactic acid obtained through the fermentation of plants such as corn and cassava. With the implementation of plastic bans and restrictions both domestically and internationally, PLA, as a substitute for traditional petroleum-based plastics, has seen its production capacity and market size continuously increase.

[0005] Although polylactic acid (PLA) is a biodegradable plastic, its degradation environment is subject to certain requirements. PLA degrades relatively quickly only in high-humidity, closed industrial composting environments; under natural conditions, the decomposition rate remains slow, and complete degradation is difficult. Especially in seawater, PLA shows almost no change in surface morphology, weight, molecular weight, or mechanical properties after 52 weeks, so indiscriminate disposal in the natural environment will still cause pollution. Furthermore, in 2020, Zimmermann et al. detected biotoxicity in PLA plastic leachates using a comprehensive microtoxicity detection technique. Therefore, strengthening the recycling and utilization of PLA is of significant research importance. Summary of the Invention

[0006] To address the shortcomings of the prior art, this invention provides a method for preparing 2-alkanoyloxypropionic acid in high yield using polylactic acid as a raw material.

[0007] The present invention provides a method for preparing 2-alkanoyloxypropionic acid from polylactic acid, which involves mixing organic acid and waste polylactic acid and reacting them at high temperature to obtain 2-alkanoyloxypropionic acid.

[0008] The reaction route is shown below:

[0009] ;

[0010] Where R is a C1-C6 straight-chain, branched, or cyclic alkyl group.

[0011] The mass ratio of the organic acid to polylactic acid is 100:1 to 1:1. Preferably, the mass ratio is 10:1.

[0012] Organic acids serve as both solvents and reactants in the reaction.

[0013] The reaction temperature is 150~280℃, and the reaction time is 1~24 hours.

[0014] Furthermore, the reaction temperature is 220~250℃, and the reaction time is 10~14 hours.

[0015] The reaction system also includes a catalyst, which is selected from one or a combination of several of HCl, H2SO4, HOTf, CF3COOH, MeSO3H, TsOH, and ZnCl2.

[0016] The mass ratio of polylactic acid to catalyst is 200:1-10:1.

[0017] Furthermore, the amount of catalyst added is 1-10% of the mass of polylactic acid.

[0018] When a catalyst is present, the reaction temperature is 150~180℃ and the reaction time is 1~5 hours.

[0019] The present invention has the following advantages: high product yield and simple operation. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the preparation process using PLA straws as raw materials.

[0021] Figure 2 It is the 2-acetoxypropionic acid prepared in this invention. 1 H NMR spectrum.

[0022] Figure 3 It is the 2-acetoxypropionic acid prepared in this invention. 13 C10 NMR spectrum. Detailed Implementation

[0023] The technical solution of the present invention will be further analyzed and explained through specific embodiments below.

[0024] Example 1:

[0025]

[0026] 4 g of polylactic acid granules, 20 g of glacial acetic acid, and 0.4 g of HOTf catalyst were added sequentially to a 25 mL hydrothermal reactor. After sealing the reactor, it was placed in a homogeneous synthesizer. The synthesizer was set to a rotation speed of 15 Hz and heated to 170 °C, then reacted at 170 °C for 4 hours. After the reaction was complete, gas chromatography analysis showed that the yield of 2-acetoxypropionic acid was 67%.

[0027] Examples 2-8:

[0028] The operation process is similar to that in Example 1, except that the HOTf catalyst is replaced with a different acid catalyst. The reaction results are shown in Table 1.

[0029]

[0030] Examples 8-11:

[0031] The operation process is similar to that in Example 1, except that the amount of HOTf catalyst used is different. The reaction results are shown in Table 2.

[0032]

[0033] Example 12:

[0034]

[0035] 4 g of polylactic acid granules and 20 g of glacial acetic acid were added sequentially to a 25 mL hydrothermal reactor. After sealing the reactor, it was placed in a homogeneous synthesizer. The homogeneous synthesizer was set to a rotation speed of 15 Hz and heated to 220 °C, then reacted at 220 °C for 8 hours. After the reaction was completed, gas chromatography analysis showed that the yield of 2-acetoxypropionic acid was 61%.

[0036] Examples 13-15:

[0037] The operation process is similar to that in Example 12, except that the reaction temperature is different, and the reaction results are shown in Table 3.

[0038]

[0039] Examples 16-20:

[0040] The operation process is similar to that in Example 12, except that the reaction time is different, and the reaction effect is shown in Table 4.

[0041]

[0042] Examples 21-23:

[0043] The operation process is similar to that in Example 12, except that the reaction time is 12 hours and the mass ratio of polylactic acid and glacial acetic acid is different. The reaction results are shown in Table 5.

[0044]

[0045] Example 24:

[0046] 45 g of polylactic acid granules and 450 g of glacial acetic acid were added sequentially to a 500 mL hydrothermal reactor. The reactor was then sealed and placed in a homogeneous synthesizer. The reactor was set to a rotation speed of 15 Hz and heated to 220 °C, where it was reacted for 12 hours. After the reaction was complete, gas chromatography analysis showed that the yield of 2-acetoxypropionic acid was 90%. Glacial acetic acid was removed by rotary evaporation, followed by vacuum distillation. The fraction collected at 132–134 °C (2200 Pa) yielded 66.5 g of 2-acetoxypropionic acid (81% separation yield).

[0047] Example 25:

[0048] Commercial PLA pipettes (containing 60% PLA) were cut into segments less than 1 cm long. 2 g of the segments were weighed and added to a hydrothermal reactor, followed by 12 g of glacial acetic acid. The hydrothermal reactor was sealed and placed in a homogeneous synthesizer. The synthesizer was set to a speed of 15 Hz and heated to 220°C, then reacted at 220°C for 12 hours. After the reaction was complete, the mixture was filtered, and the filtrate was analyzed by gas chromatography. The yield of 2-acetoxypropionic acid was 86% (e.g., ...). Figure 1 (As shown).

[0049] Examples 26-30:

[0050]

[0051] The operation process is similar to that in Example 12, except that the reaction time is 12 hours, the amount of polylactic acid used is 2g, the amount of acid used is 20g, and the acid is replaced with different organic acids. The reaction results are shown in Table 6.

[0052]

[0053] A comparison of the preparation parameters and effect data from the above embodiments shows that:

[0054] When Brönsted acids, such as HOTf and HCl, are added as catalysts, 2-levulinic acid is unstable in the presence of these strongly acidic catalysts due to the high reaction temperature. The yield initially increases with time, but after reaching a peak, it decreases. Increasing the temperature also leads to a decrease in yield due to carbonization. For example, when using 1 wt% HOTf as a catalyst, the yield decreases to 25% after 8 hours of reaction at 170°C; and after 4 hours of reaction at 180°C, complete carbonization occurs, resulting in undetectable product.

[0055] When Lewis acids, such as ZnCl, are used as catalysts, increasing the reaction temperature within a certain range can effectively accelerate the depolymerization rate; however, excessively high temperatures can lead to carbonization. Extending the reaction time can increase the yield, but the reaction rate will be slower. For example, at 170℃ for 8 hours, the yield of 2-acetoxy groups is 38%; at 200℃ for 4 hours, the yield reaches 41%.

[0056] Without a catalyst, when the temperature reaches 240°C and the reaction time is too long, 2-acetoxypropionic acid becomes unstable in the reaction system and undergoes carbonization. For example, at 240°C, the yield of 2-acetoxypropionic acid is 71% after 8 hours of reaction, but when the reaction time is extended to 12 hours, the yield decreases to 59%.

Claims

1. A method for preparing 2-alkanoyloxypropionic acid, characterized in that: 2-Alkyloxypropionic acid was prepared by mixing organic acid and waste polylactic acid and reacting them at high temperature without adding a catalyst. The reaction route is shown below: ； RCOOH is one of glacial acetic acid, propionic acid, butyric acid, isobutyric acid, and valeric acid. The reaction temperature is 220~250℃, and the reaction time is 10~14 hours.

2. The preparation method according to claim 1, characterized in that: The mass ratio of the organic acid to polylactic acid is 100:1 to 1:

1.

3. The preparation method according to claim 2, characterized in that: The mass ratio of the organic acid to polylactic acid is 10:1.

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