Method for preparing methylacrolein by mildly catalyzing aldol condensation

Abstract

The invention belongs to the technical field of organic synthesis, and particularly discloses a method for preparing methylacrolein by mildly catalyzing aldol condensation. The method comprises the following steps: mixing a metal chelating ionic liquid catalyst, a formaldehyde solution, a propionaldehyde solution and water, and reacting to obtain methylacrolein; the reaction temperature is greater than or equal to 60 DEG C. The method provided by the invention can realize high conversion rate and high selectivity preparation of methylacrolein under mild conditions.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and in particular to a mild catalytic aldol condensation method for preparing methacrolein. Background Technology

[0002] Methacrolein is an important chemical intermediate with wide applications. It is a basic chemical product that, through oxidation and esterification, yields methacrylic acid (MAA) and methyl methacrylate (MMA). MMA is commonly used as a monomer in the polymerization of polymethyl methacrylate (PMMA), which is known as "acrylic glass." Furthermore, methacrolein can be used as a modifying additive in polymer materials, significantly improving various performance characteristics of the products.

[0003] Currently, there are three main methods for preparing methacrolein: isobutylene oxidation, isobutane oxidation, and direct condensation of formaldehyde / propionaldehyde. Chinese patent applications CN117399024A, CN115260015B, CN114591156B, and CN112871182B disclose a method for preparing methacrolein by isobutylene / isobutane oxidation, but this method suffers from problems such as complex operation, harsh reaction conditions, high energy consumption, and an inability to simultaneously achieve high conversion rate and high selectivity. Existing methods for preparing methacrolein through direct condensation of formaldehyde / propionaldehyde still have other technical problems. For example, Chinese patent applications CN112638856A, CN113248359A, CN104311403A, and CN101074192A, which use direct condensation of formaldehyde / propionaldehyde to prepare methacrolein, suffer from problems such as easy catalyst deactivation and poor selectivity.

[0004] Therefore, it is crucial to develop a mild catalytic aldol condensation method for the preparation of methacrolein. Summary of the Invention

[0005] In view of this, the present invention provides a mild catalytic aldol condensation method for preparing methacrolein, in order to solve the problems of existing methacrolein preparation methods, such as complex operation, harsh reaction conditions, high energy consumption, and inability to achieve both high conversion rate and high selectivity.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A mild catalytic aldol condensation method for preparing methacrolein includes the following steps: An ionic liquid catalyst, formaldehyde solution, propionaldehyde solution, and water are mixed to carry out an aldol condensation reaction to obtain methacrolein. The ionic liquid catalyst is a metal chelated ionic liquid; The reaction temperature is ≥60℃.

[0007] Preferably, the molar ratio of the metal chelate ionic liquid, formaldehyde, and propionaldehyde in the mixed system is 1~1.5:0.6~1.4:1.

[0008] Preferably, in the mixed system, the mass fraction of water is 28-55% of the total reaction system.

[0009] Preferably, the reaction temperature is 60~70℃ and the reaction time is ≥30min.

[0010] Preferably, the method for preparing the metal chelate ionic liquid includes: The reaction of ionic liquid with metal chloride yields a metal chelate ionic liquid, which is then used as an ionic liquid catalyst for the preparation of methacrolein by aldol condensation. The ionic liquid is protonated morpholine hydrochloride or 1-butyl-3-methylimidazolium chloride.

[0011] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: 1. Ionic liquid catalysts are simple to synthesize, have mild reaction conditions, do not require high-temperature calcination, high-pressure reaction or complex post-treatment, have simple process flow, readily available raw materials, and have good industrial scale-up potential. 2. This method effectively suppresses common side reactions during aldol condensation, thereby achieving highly selective synthesis of methacrolein, with a maximum selectivity of 98.30%. 3. This invention reveals the synergistic mechanism among various parameters by systematically studying the influence of reaction conditions on catalytic performance. Detailed Implementation

[0012] This invention provides a mild catalytic aldol condensation method for preparing methacrolein, comprising the following steps: An ionic liquid catalyst, formaldehyde solution, propionaldehyde solution, and water are mixed to induce an aldol condensation reaction, yielding methacrolein. In the classic aldol condensation reaction, two aldehyde molecules (or one aldehyde and one ketone) first react under catalysis to form an intermediate product containing both a hydroxyl and an aldehyde group; this product is called a β-hydroxyaldehyde. The reaction is named after its first stable product.

[0013] In this invention, the ionic liquid catalyst is a metal chelate ionic liquid.

[0014] In this invention, the reaction temperature is ≥60℃, specifically 65℃, 70℃, 75℃, or 80℃.

[0015] In this invention, the molar ratio of the metal chelate ionic liquid, formaldehyde and propionaldehyde in the mixed system is 1~1.5:0.6~1.4:1, preferably 1.1~1.4:0.8~1.2:1, further preferably 1.2~1.4:0.9~1.1:1, and even more preferably 1.4:1:1.

[0016] In this invention, the mass fraction of water in the mixed system is 28-55% of the total reaction system, specifically 30%, 32%, 35%, 38%, 39%, 40%, 42%, 45%, 48%, 50%, 52%, and 54%.

[0017] In this invention, the reaction temperature is 60~70℃, specifically 62℃, 64℃, 65℃, 66℃, or 68℃; the reaction time is ≥30min, specifically 30min, 40min, or 50min.

[0018] In this invention, the preparation method of the metal chelate ionic liquid includes: The reaction of ionic liquid with metal chloride yields a metal chelate ionic liquid, which is then used as an ionic liquid catalyst for the preparation of methacrolein by aldol condensation.

[0019] In this invention, the ionic liquid is protonated morpholine hydrochloride or 1-butyl-3-methylimidazolium chloride.

[0020] In this invention, the molar ratio of the ionic liquid to the metal chloride is 1:0.5~2, preferably 1:0.8~1.5, and more preferably 1:1.

[0021] In this invention, the reaction temperature is 0~10℃, specifically 1℃, 2℃, 3℃, 4℃, 5℃, 6℃, 7℃, 8℃, or 9℃; the reaction time is 5~20min, specifically 6min, 8min, 10min, 12min, 14min, 15min, 16min, or 18min.

[0022] In this invention, the metal chloride includes one or more of CuCl2, CuCl, ZnCl2, CoCl3, MnCl2, FeCl3, NiCl2, and AlCl3; the metal chloride also includes the hydrate corresponding to the metal chloride.

[0023] In this invention, the protonated morpholine hydrochloride is prepared by reacting a morpholine solution with a hydrochloric acid solution to obtain the protonated morpholine hydrochloride.

[0024] In this invention, the molar ratio of morpholine in the morpholine solution to hydrogen chloride in the hydrochloric acid solution is 1:0.8~1.2, preferably 1:0.9~1.1, and more preferably 1:1.

[0025] In this invention, the mass fraction of the hydrochloric acid solution is 35-40%, specifically 36%, 36.5%, 37%, 38%, or 39%.

[0026] In this invention, the reaction temperature is 0~10℃, specifically 1℃, 2℃, 3℃, 4℃, 5℃, 6℃, 7℃, 8℃, or 9℃; the reaction time is 5~20min, specifically 6min, 8min, 10min, 12min, 14min, 15min, 16min, or 18min.

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1

[0029] 4.356 g of morpholine was diluted with 4.356 g of deionized water to prepare an aqueous solution of morpholine, which was then added dropwise to a 36.5% hydrochloric acid solution. The molar ratio of morpholine to hydrogen chloride in the hydrochloric acid was 1:1. The solution was stirred at 5 °C for 10 min, and the water was removed by rotary evaporation to obtain morpholine hydrochloride Cat-1. A certain amount of 3.0895g Cat-1 was dissolved in 3.0895g deionized water, and a certain amount of 6.0358g AlCl3·6H2O was dissolved in 6.0358g deionized water. The Cat-1 aqueous solution was added dropwise to the aluminum chloride aqueous solution, with a molar ratio of Cat-1 to aluminum chloride of 1:1. The mixture was stirred at 5℃ for 10 min, and the water was removed by rotary evaporation to obtain the metal chelate ionic liquid Cat-2, which is the ionic liquid catalyst for the preparation of methacrolein by aldol condensation.

[0030] 3.6501g Cat-2, 0.8928g formaldehyde solution, 0.5988g propionaldehyde solution, and 3.336g deionized water were mixed (Cat-2:formaldehyde:propionaldehyde (molar ratio) = 1:1.1:1, and the mass fraction of the deionized water was 39%). After stirring in a water bath at 30℃ for 30 min, the contents of propionaldehyde and methacrolein were determined by gas chromatography. The calculated conversion rate of propionaldehyde was 25.09%, and the selectivity of methacrolein was 50.85%.

[0031] Under the same preparation conditions as described above, only the reaction temperature of methacrolein was adjusted from 30℃ to 40℃, 50℃, 60℃, and 70℃. The test results are shown in Table 1.

[0032] Table 1 Test Results

[0033] Table 1 shows that temperature has a significant effect on the selectivity of methacrolein. The conversion rate and selectivity increase with increasing reaction temperature. When the reaction temperature is 60℃, the selectivity no longer increases, with a maximum of 83.75%.

[0034] Example 2

[0035] 3.6501g Cat-2, 0.8928g formaldehyde solution, 0.5988g propionaldehyde solution and 3.336g deionized water were mixed (Cat-2:formaldehyde:propionaldehyde (molar ratio) = 1:1.1:1, and the mass fraction of the deionized water was 39%). After stirring in a water bath at 60℃ for 10 min, the contents of propionaldehyde and methacrolein were determined by gas chromatography.

[0036] Then, keeping the above conditions in place, the reaction time was adjusted to 20 min, 30 min, 40 min, and 50 min. The test results are shown in Table 2.

[0037] Table 2 Test Results

[0038] Table 2 shows that the reaction time has a significant effect on the selectivity of methacrolein, increasing with the increase of reaction time, but the selectivity no longer increases when the reaction time is 40 min.

[0039] Example 3

[0040] 3.6501 g Cat-2, 0.8928 g formaldehyde solution, 0.5988 g propionaldehyde solution and 3.336 g deionized water were mixed (Cat-2:formaldehyde:propionaldehyde (molar ratio) = 1:1.1:1, and the mass fraction of the deionized water was 39%). After stirring in a water bath at 60 °C for 40 min, the contents of propionaldehyde and methacrolein were determined by gas chromatography.

[0041] Then, keeping the above conditions in place, only the molar ratio of Cat-2 to propionaldehyde was adjusted to 0.2:1, 0.5:1, 1.2:1, and 1.5:1. The test results are shown in Table 3.

[0042] Table 3 Test Results

[0043] Table 3 shows that the content of ionic liquid catalyst in the reaction system has a significant impact on the conversion rate and selectivity. Within a certain range, increasing the content of ionic liquid catalyst can increase the number of active sites and thus significantly improve the selectivity. However, when the content of ionic liquid catalyst is greater than 1:1, excessive ionic liquid catalyst will hinder the reaction at the active sites.

[0044] Example 4

[0045] 3.6501 g Cat-2, 0.8928 g formaldehyde solution, 0.5988 g propionaldehyde solution and 3.336 g deionized water were mixed (Cat-2:formaldehyde:propionaldehyde (molar ratio) = 1:1.1:1, and the mass fraction of the deionized water was 39%). After stirring in a water bath at 60 °C for 40 min, the contents of propionaldehyde and methacrolein were determined by gas chromatography.

[0046] Then, keeping the above conditions in place, the mass fraction of deionized water was adjusted to 6%, 17%, 28%, and 50%. The test results are shown in Table 4.

[0047] Table 4 Test Results

[0048] As shown in Table 4, the selectivity of methacrolein is the highest at 89.58% when the mass fraction of deionized water is 39%.

[0049] Example 5

[0050] 3.6501 g Cat-2, 0.8928 g formaldehyde solution, 0.5988 g propionaldehyde solution and 3.336 g deionized water were mixed (Cat-2:formaldehyde:propionaldehyde (molar ratio) = 1:1.1:1, and the mass fraction of the deionized water was 39%). After stirring in a water bath at 60 °C for 40 min, the contents of propionaldehyde and methacrolein were determined by gas chromatography.

[0051] Then, keeping the above conditions in place, only the molar ratio of formaldehyde to propionaldehyde was adjusted to 1.4:1, 1.2:1, 1.1:1, 1:1, 0.9:1, 0.8:1, and 0.6:1. The test results are shown in Table 5.

[0052] Table 5 Test Results

[0053] As shown in Table 5, when the formaldehyde:propionaldehyde ratio is 1.4:1, the selectivity of methacrolein is the highest at 98.30%.

[0054] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0055] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing methacrolein by mild catalytic aldol condensation, characterized in that, Includes the following steps: An ionic liquid catalyst, formaldehyde solution, propionaldehyde solution, and water are mixed to carry out an aldol condensation reaction to obtain methacrolein. The ionic liquid catalyst is a metal chelated ionic liquid; The reaction temperature is ≥60℃.

2. The method for preparing methacrolein by mild catalytic aldol condensation according to claim 1, characterized in that, The molar ratio of the metal chelate ionic liquid, formaldehyde, and propionaldehyde in the mixed system is 1~1.5:0.6~1.4:

1.

3. The method for preparing methacrolein by mild catalytic aldol condensation according to claim 2, characterized in that, In the mixed system, the mass fraction of water is 28-55% of the total reaction system.

4. A method for preparing methacrolein by mild catalytic aldol condensation according to any one of claims 1 to 3, characterized in that, The reaction temperature is 60~70℃, and the reaction time is ≥30min.

5. The method for preparing methacrolein by mild catalytic aldol condensation according to claim 4, characterized in that, The preparation method of the metal chelate ionic liquid includes: The reaction of ionic liquid with metal chloride yields a metal chelate ionic liquid, which is then used as an ionic liquid catalyst for the preparation of methacrolein by aldol condensation. The ionic liquid is protonated morpholine hydrochloride or 1-butyl-3-methylimidazolium chloride.

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