Preparation method of 2-alkanoyloxy propionic acid

Abstract

The invention discloses a preparation method of 2-alkanoyloxy propionic acid. According to the method, the waste polylactic acid is used as the raw material, the 2-alkanoyloxy propionic acid is prepared at high yield, the operation is simple, the method is suitable for industrial production, and meanwhile, the recycling of the polylactic acid is realized.

Description

Technical Field

[0001] The invention belongs to the field of organic compound preparation, and specifically relates to a method for preparing 2-alkanoyloxypropionic acid by taking polylactic acid as a raw material. Background Art

[0002] 2-Alkanoyloxypropionic acid is a class of organic compounds that contain ester and carboxyl functional groups in their molecular structure. These functional groups give it diverse chemical properties and important application value. For example, 2-acetoxypropionic acid is an important synthetic intermediate and plays an important role in the chemical and pharmaceutical fields. In the pharmaceutical field, it is a key intermediate for the synthesis of a variety of drugs, such as ibuprofen and naproxen; in the food industry, it can be used to prepare additives such as food preservatives and preservatives; in addition, its derivatives have also shown potential as pesticides and plant growth regulators in the agricultural field.

[0003] At present, the synthesis methods of 2-alkanoyloxypropionic acid mainly include esterification method and acylation method. The esterification method uses lactic acid and alkyl anhydride as raw materials, and an esterification reaction occurs under the catalytic action of concentrated sulfuric acid to obtain 2-alkanoyloxypropionic acid. However, due to the use of concentrated sulfuric acid, a large amount of waste acid will be generated in the subsequent treatment, which will cause pollution to the environment and require high corrosion resistance of the equipment. The acylation method uses lactic acid and alkyl acyl chloride as reactants, and an acylation reaction is carried out under the catalysis of a base to prepare 2-alkanoyloxypropionic acid. However, due to the high activity and strong corrosiveness of alkyl acyl chloride, this method also has high requirements on the material of the reaction equipment.

[0004] Polylactic acid is a bio-based biodegradable material, which is mainly polymerized from lactic acid obtained from fermentation of plants such as corn and cassava. With the implementation of plastic bans and restrictions at home and abroad, as a substitute for traditional petroleum-based plastics, the production capacity and market size of polylactic acid continue to increase. my country's polylactic acid industry is also developing rapidly. In 2020, my country's polylactic acid production capacity was about 185,000 tons. It is expected that by 2025, my country's polylactic acid production capacity will reach more than 1 million tons, accounting for about two-thirds of the global production capacity.

[0005] Although polylactic acid is a biodegradable plastic, it also has certain requirements for the degradation environment. Polylactic acid can only be degraded quickly in a closed industrial composting environment with high humidity. The decomposition rate is still slow under natural conditions, and it also faces the problem of difficulty in complete degradation. Especially in seawater, after 52 weeks, the surface morphology, weight, molecular weight and mechanical properties of polylactic acid have hardly changed, so arbitrarily discarding it in the natural environment will also cause environmental pollution. In addition, in 2020, Zimmermann et al. used micro-toxicity comprehensive detection technology to detect biological toxicity from polylactic acid plastic extracts. Therefore, it is of great research significance to strengthen the recycling and utilization of polylactic acid. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for preparing 2-alkanoyloxypropionic acid with high yield by using polylactic acid as a raw material.

[0007] The method for preparing 2-alkanoyloxy propionic acid by using polylactic acid as a raw material comprises mixing an organic acid and waste polylactic acid, reacting them at a high temperature, and preparing 2-alkanoyloxy propionic acid.

[0008] The reaction route is as follows:

[0009] ;

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

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

[0012] The organic acid serves as a reaction solvent and a reactant in the reaction.

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

[0014] Furthermore, the reaction temperature is 220-250° C., 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 HCl, H2SO4, HOTf, CF3COOH, MeSO3H, TsOH, and ZnCl2.

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

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

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

[0019] The invention has the following advantages: high product yield and simple operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the preparation process using PLA straws as raw materials.

[0021] Figure 2 The 2-acetoxypropionic acid prepared by the present invention 1 H NMR spectrum.

[0022] Figure 3The 2-acetoxypropionic acid prepared by the present invention 13 C NMR spectrum. DETAILED DESCRIPTION

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

[0024] Embodiment 1:

[0025]

[0026] 4 g of polylactic acid particles, 20 g of glacial acetic acid and 0.4 g of HOTf catalyst were added to a 25 mL hydrothermal reactor in sequence, the hydrothermal reactor was sealed and placed in a homogeneous synthesizer, the speed of the homogeneous synthesizer was set to 15 Hz, heated to 170°C, and then reacted at 170°C for 4 hours. After the reaction was completed, the yield of 2-acetoxypropionic acid was 67% according to gas chromatography analysis.

[0027] Embodiment 2-8:

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

[0029]

[0030] Embodiment 8-11:

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

[0032]

[0033] Embodiment 12:

[0034]

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

[0036] Embodiment 13-15:

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

[0038]

[0039] Embodiment 16-20:

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

[0041]

[0042] Embodiment 21-23:

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

[0044]

[0045] Embodiment 24:

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

[0047] Embodiment 25:

[0048] Commercial PLA straws (containing 60% PLA) were cut into small pieces less than 1 cm, and then 2 g was 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 speed of the homogeneous synthesizer was set to 15 Hz, heated to 220°C, and then reacted at 220°C for 12 hours. After the reaction was completed, the filtrate was filtered and then analyzed by gas chromatography. The yield of 2-acetoxypropionic acid was 86% (e.g. Figure 1 shown).

[0049] Embodiment 26-30:

[0050]

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

[0052]

[0053] By comparing the preparation parameters and effect data of the above examples, it can be seen that:

[0054] When adding Brönsted acid, such as HOTf, HCl, etc., as a catalyst, due to the high reaction temperature, 2-levulinic acid is not very stable in the presence of these strong acid catalysts. Within a certain period of time, the yield will increase with time, but after reaching the maximum value, the yield will decrease. If the temperature is increased, the yield will also decrease due to carbonization. For example, when using 1wt% HOTf as a catalyst, the yield drops to 25% after reacting at 170℃ for 8h; reacting at 180℃ for 4h results in complete carbonization and no product can be detected.

[0055] When Lewis acid, such as ZnCl, is used as a catalyst, increasing the reaction temperature within a certain temperature range will effectively accelerate the depolymerization rate, but too high a temperature will also lead to carbonization; while extending the reaction time can increase the reaction yield, but the reaction rate will be slower. For example, at 170°C for 8h, the yield of 2-acetoxy is 38%; at 200°C for 4h, the yield of 2-acetoxy can reach 41%.

[0056] Without adding a catalyst, when the temperature reaches 240°C, the reaction time is too long, and 2-acetoxypropionic acid will also be unstable in the reaction system and carbonize. 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 reaction yield drops to 59%.

Claims

1. A method for preparing 2-alkanoyloxypropionic acid, characterized in that: The organic acid and the waste polylactic acid are mixed and reacted at a high temperature to prepare 2-alkanoyloxypropionic acid; The reaction route is as follows: ； Wherein R is a C1-C6 straight chain, branched chain or cyclic alkyl group.

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

1.

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

1.

4. The preparation method according to claim 1, characterized in that: The reaction temperature is 150~280°C, and the reaction time is 1~24 hours.

5. The preparation method according to claim 4, characterized in that: The reaction temperature is 220~250°C and the reaction time is 10~14 hours.

6. The preparation method according to claim 1, characterized in that: The reaction system also includes a catalyst, which is selected from one or a combination of HCl, H2SO4, HOTf, CF3COOH, MeSO3H, TsOH, and ZnCl2.

7. The preparation method according to claim 6, characterized in that: The mass ratio of the polylactic acid to the catalyst is 200:1-10:

1.

8. The preparation method according to claim 7, characterized in that: The amount of catalyst added is 1-10% of the mass of polylactic acid.

9. The preparation method according to claim 6, characterized in that: The reaction temperature is 150~180°C and the reaction time is 1~5 hours.

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