A process for the preparation of alpha, beta-unsaturated alkenals
By using an alkaline ionic liquid catalyst to catalyze the Aldol condensation reaction of aldehydes, the problems of low yield and equipment corrosion of α,β-unsaturated alkenals were solved, achieving efficient and environmentally friendly synthesis of α,β-unsaturated alkenals.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- INSTITUTE OF APPLIED CHEMISTRY JIANGXI ACADEMY OF SCIENCES
- Filing Date
- 2023-12-07
- Publication Date
- 2026-07-24
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Figure QLYQS_1 
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Abstract
Description
Technical Field
[0001] This invention relates to the field of α,β-unsaturated enal preparation technology, and more specifically to a method for preparing α,β-unsaturated enal. Background Technology
[0002] α,β-Unsaturated enal is an important intermediate in organic synthesis. For example, 2-methyl-2-pentenal is an important intermediate in the synthesis of strawberry acid; 2-ethyl-2-hexenal is an intermediate in the synthesis of isooctanoic acid, which is used in the synthesis of paint and ink driers and pharmaceutical intermediates; 2-propyl-2-heptenal is an important raw material for the synthesis of 2-propylheptanol, which can be used to produce DPHP plasticizer.
[0003] Currently, the preparation of α,β-unsaturated alkenes typically involves the condensation of Aldol with NaOH solution as a catalyst. However, aldehydes are only slightly soluble in water, making this Aldol condensation reaction difficult to complete and resulting in low yields of α,β-unsaturated alkenes. Furthermore, the NaOH aqueous solution can corrode equipment and cause significant difficulties in post-reaction processing, potentially leading to environmental pollution if not handled properly. Therefore, developing a high-performance, efficient, and environmentally friendly Aldol condensation catalyst is crucial for the synthesis and production of α,β-unsaturated alkenes. Summary of the Invention
[0004] Therefore, the purpose of this invention is to provide a method for preparing α,β-unsaturated enal. The catalyst prepared by the method provided by this invention has superior catalytic performance, and the yield of α,β-unsaturated enal is high.
[0005] To achieve the above objectives, the present invention provides the following technical solution:
[0006] This invention provides a method for preparing α,β-unsaturated enal, comprising the following steps:
[0007] Aldehyde compounds and basic ionic liquid catalysts are mixed and subjected to Aldol condensation reaction to obtain the corresponding α,β-unsaturated enaldehydes.
[0008] The aldehyde compound is n-propanal, n-butyral, n-pentanal, or n-hexanal; the α,β-unsaturated enal is 2-methyl-2-pentenal, 2-ethyl-2-hexenal, 2-propyl-2-heptenal, or 2-butyl-2-octenal; the alkaline ionic liquid catalyst has the structure shown in Formula I-1, Formula I-2, or Formula I-3.
[0009]
[0010] In formula I-1, formula I-2 or formula I-3, R1 and R2 are independently C1 to C5 alkyl groups;
[0011] M is OH or Ac; Y is CO3. 2- Z is PO4 3- .
[0012] Preferably, the preparation method of the alkaline ionic liquid catalyst includes the following steps:
[0013] An imidazole having the structure of formula II-1 is mixed with a haloalkane having the structure of II-2 and subjected to a first substitution reaction to obtain intermediate II-3 with the structure shown in formula II-3.
[0014]
[0015] R2X formula II-2; in formula II-2, X is Cl - or Br - ;
[0016]
[0017] After dissolving the intermediate II-3 and the sodium salt, a second substitution reaction is carried out to obtain the basic ionic liquid catalyst; the sodium salt is NaM, NaY, or NaZ.
[0018] The NaM is NaOH or NaAc; the NaY is Na2CO3; and the NaZ is Na3PO4.
[0019] Preferably, the temperature of the first substitution reaction is 70–90°C and the time is 45–48 h.
[0020] Preferably, the molar ratio of intermediate II-3 to sodium salt is 1:1 to 1:1.2.
[0021] Preferably, the temperature of the second substitution reaction is 70–80°C and the time is 6–8 hours.
[0022] Preferably, the molar ratio of the alkaline ionic liquid catalyst to the aldehyde compound is 1:30 to 60.
[0023] Preferably, the temperature of the Aldol condensation reaction is 0–25°C and the time is 0.5–1.5 h.
[0024] Preferably, after the Aldol condensation reaction, the Aldol condensation reaction system is further divided into layers, and the water layer is discarded.
[0025] This invention provides a method for preparing α,β-unsaturated enal, comprising the following steps: mixing an aldehyde compound with a basic ionic liquid catalyst, and obtaining the corresponding α,β-unsaturated enal through an Aldol condensation reaction; wherein the aldehyde compound is n-propanal, n-butyral, n-pentanal, or n-hexanal; wherein the α,β-unsaturated enal is 2-methyl-2-pentenal, 2-ethyl-2-hexenal, 2-propyl-2-heptenal, or 2-butyl-2-octenal; and in formula I-1, I-2, or I-3, R and R1 are independently C1-C5 alkyl groups; M is OH or Ac; and Y is CO3. 2- Z is PO4 3- Compared to traditional catalysts, this invention uses alkaline ionic liquid catalysis, resulting in superior catalytic performance and better compatibility with aldehyde compounds. Therefore, the reaction is more complete, and the yield of α,β-unsaturated enal is high. Consequently, there is almost no byproduct sodium organic acid. The sodium salt byproduct produced has good water solubility and can be directly removed by layering without causing corrosion to the reaction equipment. Attached Figure Description
[0026] Figure 1 The 1H NMR spectrum of 2-ethyl-2-hexenal prepared in Example 2;
[0027] Figure 2 The carbon spectrum of 2-ethyl-2-hexenal prepared in Example 2. Detailed Implementation
[0028] This invention provides a method for preparing α,β-unsaturated enal, comprising the following steps:
[0029] Aldehyde compounds and basic ionic liquid catalysts are mixed and subjected to Aldol condensation reaction to obtain the corresponding α,β-unsaturated enaldehydes.
[0030] The aldehyde compound is n-propanal, n-butyral, n-pentanal, or n-hexanal; the α,β-unsaturated enal is 2-methyl-2-pentenal, 2-ethyl-2-hexenal, 2-propyl-2-heptenal, or 2-butyl-2-octenal; the alkaline ionic liquid catalyst has the structures shown in Formula I-1, Formula I-2, and Formula I-3.
[0031]
[0032] In formula I-1, formula I-2 or formula I-3, R1 and R2 are independently C1 to C5 alkyl groups;
[0033] M is OH or Ac; Y is CO3. 2- Z is PO4 3- .
[0034] Unless otherwise specified, all reagents used in this invention are commercially available products well known to those skilled in the art.
[0035] This invention involves mixing aldehyde compounds with a basic ionic liquid catalyst and then performing an Aldol condensation reaction to obtain the corresponding α,β-unsaturated enaldehydes.
[0036] In this invention, the alkaline ionic liquid catalyst has the structures shown in Formula I-1, Formula I-2, and Formula I-3:
[0037]
[0038] In this invention, in formula I-1, formula I-2, or formula I-3, R1 and R2 are independently C1 to C5 alkyl groups, preferably methyl, ethyl, n-propyl, n-butyl, or n-pentyl; M is OH or Ac; and Y is CO3. 2- Z is PO4 3- .
[0039] In this invention, the preparation method of the alkaline ionic liquid catalyst includes the following steps:
[0040] An imidazole having the structure of formula II-1 is mixed with a haloalkane having the structure of II-2 and subjected to a first substitution reaction to obtain intermediate II-3 with the structure shown in formula II-3.
[0041]
[0042] R2X formula II-2; in formula II-2, X is Cl - or Br - ;
[0043]
[0044] After dissolving the intermediate II-3 and the sodium salt, a second substitution reaction is carried out to obtain the basic ionic liquid catalyst; the sodium salt is NaM, NaY, or NaZ.
[0045] The NaM is NaOH or NaAc; the NaY is Na2CO3; and the NaZ is Na3PO4.
[0046] In this invention, an imidazole having the structure of formula II-1 is mixed with a haloalkane having the structure of II-2 and subjected to a first substitution reaction to obtain intermediate II-3 having the structure shown in formula II-3.
[0047] In this invention, the molar ratio of the imidazole having the structure of formula II-1 to the haloalkane is preferably 1:1.2 to 1.5. In this invention, the temperature of the first substitution reaction is preferably 70 to 90°C, more preferably 80°C, and the time is preferably 45 to 48 hours, more preferably 46 to 47 hours.
[0048] In this invention, after the first substitution reaction, the product obtained from the first substitution reaction is further subjected to washing, concentration, and drying sequentially. In this invention, the washing reagent is preferably ethyl acetate, the number of washings is preferably ≥3, the concentration method is preferably rotary evaporation, and this invention does not specifically limit the drying process, as long as it removes ethyl acetate from the surface of the intermediate.
[0049] After obtaining intermediate II-3, the present invention dissolves intermediate II-3 and sodium salt and carries out a second substitution reaction to obtain the alkaline ionic liquid catalyst.
[0050] In this invention, the sodium salt is preferably NaM, NaY, or NaZ; NaM is preferably NaOH or NaAc; NaY is preferably Na2CO3; and NaZ is preferably Na3PO4.
[0051] In this invention, the molar ratio of intermediate II-3 to sodium salt is preferably 1:1 to 1:1.2, more preferably 1:1.1.
[0052] In this invention, the temperature of the second substitution reaction is preferably 70–80°C, more preferably 75°C, and the time is preferably 6–8 hours, more preferably 7 hours. In this invention, after the second substitution reaction, the system obtained from the second substitution reaction is preferably subjected to standing, filtration, and concentration sequentially.
[0053] In this invention, the molar ratio of the alkaline ionic liquid catalyst to the aldehyde compound is preferably 1:30 to 60, more preferably 1:50.
[0054] In this invention, the temperature of the Aldol condensation reaction is preferably 0–25°C, more preferably 10–20°C. In this invention, the time of the Aldol condensation reaction is preferably 0.5–1.5 h, more preferably 1 h.
[0055] In this invention, after the Aldol condensation reaction, it is preferable to further separate the system obtained by the Aldol condensation reaction into layers and discard the water layer.
[0056] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.
[0057] Example 1
[0058] First substitution reaction: N-ethylimidazole and CH3CH2CH2Br were added to a reaction flask equipped with a reflux condenser at a molar ratio of 1:1.3. The mixture was refluxed at 70°C for 45 h. The product was washed three times with ethyl acetate, evaporated to near dryness, and then dried in a drying oven at 60°C for 20 h to obtain the corresponding N,N-disubstituted imidazole intermediate.
[0059] Second substitution reaction: 1 mol of the above intermediate and 1.1 mol of NaOH were dissolved in 50 mL of methanol / water mixed solution (V:V = 1:1). The temperature was slowly increased (the heating rate was controlled at 2℃ / min) to 70℃ and the reaction was continued for 8 h. The system obtained from the second substitution reaction was then allowed to stand for 2 h, filtered to remove the NaBr precipitate, and the resulting liquid phase was rotary evaporated to near dryness. It was then dried to constant weight in a vacuum drying oven at 60℃ to obtain an alkaline ionic liquid catalyst with R1 being ethyl, R2 being propyl, and M being OH, which is alkaline ionic liquid catalyst-1.
[0060] Alkaline ionic liquid catalyst-1 and propionaldehyde were mixed at a molar ratio of 1:50 and subjected to an Aldol condensation reaction at 20°C for 1 hour. The resulting reaction solution was allowed to stand and separate into layers. The lower layer, representing the ionic liquid catalyst, was released for recycling, while the upper layer, representing the condensation product, was separated. The yield was 98.6%. GC-MS analysis of the product layer showed a purity of 99.2% for 2-methyl-2-pentenal.
[0061] Example 2
[0062] The alkaline ionic liquid catalyst-1 from Example 1 and butyraldehyde were mixed at a molar ratio of 1:50 and subjected to an Aldol condensation reaction at a reaction temperature of 20°C for 1 hour. After the reaction solution was allowed to stand and separate into layers, the purity of 2-ethyl-2-hexenal in the product was tested by GC-MS. The purity of the product was found to be 96.1%, and the yield was 99.4%.
[0063] Figure 1 The 1H NMR spectrum of 2-ethyl-2-hexenal prepared in Example 2 is shown below. 1H-NMR (300MHz, CDCl3): δ0.94(t,J=7.4Hz,3H),0.95(t,J=7.4Hz,3H),1.51(m,2H),2.28(m,4H),6.39(t,J=7.2,1H),9.33(s,1H);
[0064] Figure 2 The carbon spectrum of 2-ethyl-2-hexenal prepared in Example 2 is shown below.
[0065] 13 C-NMR (75MHz, CDCl3): δ13.4,13.9,17.4,22.1,30.8,145.5,154.6,195.2.
[0066] Example 3
[0067] Alkaline ionic liquid catalyst-1 and pentanal were mixed at a molar ratio of 1:50 and then subjected to an Aldol condensation reaction at a temperature of 20°C for 1 hour. After the reaction solution was allowed to stand and separate into layers, the purity of 2-propyl-2-heptenal in the product was determined by liquid chromatography. The purity of the product was found to be 95.2%, and the yield was 98.9%.
[0068] Example 4
[0069] Alkaline ionic liquid catalyst-1 and hexanal were mixed at a molar ratio of 1:50 and then subjected to an Aldol condensation reaction. The Aldol condensation reaction was carried out at a temperature of 20℃ for 1 h. After the reaction solution was allowed to stand and separate into layers, the purity of 2-butyl-2-octenal in the product was tested by GC-MS. The purity of the product was found to be 93.2%, and the yield was 99.2%.
[0070] Example 5
[0071] N-ethylimidazole and CH3CH2CH2Br were added to a reaction flask equipped with a reflux condenser at a molar ratio of 1:1.3. The mixture was refluxed and subjected to the first substitution reaction at 90°C for 45 h. The resulting product was washed three times with ethyl acetate, evaporated to near dryness, and then dried in a drying oven at 60°C for 20 h to obtain the intermediate.
[0072] 1 mol of the intermediate and 1.1 mol of NaAc were dissolved in 50 mL of 50% methanol aqueous solution. The temperature was slowly increased (the heating rate was controlled at 2 °C / min) to 90 °C for a second substitution reaction for 8 h. After the system obtained from the second substitution reaction was allowed to stand for 2 h, it was filtered to remove the NaBr precipitate. The resulting liquid phase was rotary evaporated to near dryness and then dried to constant weight in a vacuum drying oven at 60 °C to obtain an alkaline ionic liquid catalyst with R1 being ethyl, R2 being propyl, and M being Ac, which is alkaline ionic liquid catalyst-2.
[0073] Alkaline ionic liquid catalyst-2 and propionaldehyde were mixed at a molar ratio of 1:50 and then subjected to an Aldol condensation reaction under a nitrogen protective atmosphere. The Aldol condensation reaction was carried out at a temperature of 20°C for 1 hour. After the resulting reaction solution was allowed to stand and separate into layers, the purity of 2-methyl-2-pentenal was determined by GC-MS to be 98.2%, and the yield was 99.2%.
[0074] Comparative Example 1
[0075] A 1 mol / L sodium hydroxide solution was added to a reaction vessel, and propionaldehyde was added dropwise. The molar ratio of sodium hydroxide to propionaldehyde was 1:50. Then, the Aldol condensation reaction was carried out at 20 °C with stirring for 1 h. After the product was allowed to stand and separate into layers, it was distilled to obtain 2-methyl-2-pentenal. The purity of 2-methyl-2-pentenal was tested by GC-MS and found to be 42.3%, with a yield of 51.2%.
[0076] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.
Claims
1. A method for preparing α,β-unsaturated enal, characterized in that, Includes the following steps: Aldehyde compounds and basic ionic liquid catalysts are mixed and subjected to Aldol condensation reaction to obtain the corresponding α,β-unsaturated enal. The aldehyde compound is n-propanal, n-butyral, n-pentanal, or n-hexanal; the α,β-unsaturated enal is 2-methyl-2-pentenal, 2-ethyl-2-hexenal, 2-propyl-2-heptenal, or 2-butyl-2-octenal; the alkaline ionic liquid catalyst has the structure shown in Formula I-1. Formula I-1 In Formula I-1, R1 is ethyl; R2 is propyl; and M is OH or Ac. The preparation method of the alkaline ionic liquid catalyst includes the following steps: N-ethylimidazole and CH3CH2CH2Br were mixed at a molar ratio of 1:1.3 to carry out the first substitution reaction, yielding an N,N-disubstituted imidazole intermediate; After dissolving the N,N-disubstituted imidazole intermediate and its sodium salt, a second substitution reaction was carried out to obtain the alkaline ionic liquid catalyst. The sodium salt is NaOH or NaAc; The Aldol condensation reaction is carried out at a temperature of 0~25℃ for a time of 0.5~1.5h. The temperature of the first substitution reaction is 70~90℃, and the time is 45~48h; The second substitution reaction is carried out at a temperature of 70-80°C for 6-8 hours.
2. The preparation method according to claim 1, characterized in that, The molar ratio of the N,N-disubstituted imidazole intermediate to the sodium salt is 1:1 to 1:1.
2.
3. The preparation method according to claim 1, characterized in that, The molar ratio of the alkaline ionic liquid catalyst to the aldehyde compound is 1:30~60.
4. The preparation method according to claim 1, characterized in that, Following the Aldol condensation reaction, the Aldol condensation reaction system is further divided into layers, and the water layer is discarded.