A method for synthesizing 2,4-hexadienal

Abstract

The present invention relates to the technical field of catalytic synthesis of 2,4-hexadienal, specifically a kind of 2,4-hexadienal synthesis method, including: synthesizing two catalytic reagents: ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt, ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt; utilizing molecular imprinting technology to prepare a region-selective aldol condensation catalyst, which can be magnetically recovered and reused; the region-selective aldol condensation catalyst can selectively remove the α-H of acetaldehyde to promote the generation of enolate anion, and the enolate anion and the carbonyl carbon of crotonaldehyde undergo nucleophilic addition to generate β-hydroxy aldehyde, which is dehydrated to generate 2,4-hexadienal. The region-selective aldol condensation catalyst of the present invention has recognition and selection ability for the target product 2,4-hexadienal, can improve catalytic selectivity, and reduce reaction by-products.

Description

Technical Field

[0001] The invention relates to the technical field of catalytic synthesis of 2,4-hexadienal, in particular to a method for synthesizing 2,4-hexadienal. Background Art

[0002] 2,4-Hexadienal (sorbitol) is a food additive and mildew inhibitor. It is prepared by the aldol condensation reaction of crotonaldehyde and acetaldehyde. During the preparation of 2,4-hexadienal, many side reactions occur, such as the formation of the by-product 2-vinyl-2-butenal. In addition, crotonaldehyde also undergoes self-condensation reaction, and acetaldehyde also undergoes self-condensation reaction to produce trimeraldehyde, tetraacetaldehyde or polyacetaldehyde. The occurrence of side reactions results in the final yield of the target product 2,4-hexadienal generally being less than 45%.

[0003] According to literature reports, acids, bases, and mixed acids and bases can all catalyze the aldol condensation reaction. Among them, triphenylphosphine is a Lewis base with one lone pair of electrons and three unpaired electrons on the phosphorus atom, as well as five empty 3d orbitals. Triphenylphosphine can also catalyze the aldol condensation reaction. Summary of the Invention

[0004] The invention synthesizes a regioselective aldol condensation catalyst, which can catalyze the condensation of acetaldehyde and crotonaldehyde to generate 2,4-hexadienal, and has the ability to identify and select the target product 2,4-hexadienal, thereby improving the product purity of 2,4-hexadienal.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A method for synthesizing 2,4-hexadienal comprises the following steps:

[0007] Step 1: Preparation of a regioselective aldol condensation catalyst, the specific process is as follows:

[0008] Using molecular imprinting technology, 3-aminopropyltriethoxysilane is used as a functional monomer and adipic acid is used as a regioselective template molecule for the aldol condensation reaction. 3-aminopropyltriethoxysilane and adipic acid are combined through hydrogen bonding to form a templated functional monomer. A sol-gel polymerization reaction is initiated using carboxylated magnetic nanospheres as a polymer matrix, tetraethyl orthosilicate as a crosslinker, and hydrochloric acid as an initiator to immobilize the templated functional monomer on the surface of the magnetic nanospheres. The adipic acid template is then removed using an eluent to prepare a regioselective aldol condensation catalyst.

[0009] The regioselective aldol condensation catalyst comprises: one or a combination of a catalytic agent ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt and a catalytic agent ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3; the ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt acts as a functional monomer, and the ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3 acts as a cross-linking agent;

[0010] Step 2: Using a regioselective aldol condensation catalyst to remove the α-H of acetaldehyde to generate an enolate anion, the enolate anion undergoes a nucleophilic addition reaction with the carbonyl carbon of crotonaldehyde to generate β-hydroxyaldehyde, and the β-hydroxyaldehyde undergoes a dehydration reaction under acidic conditions to generate 2,4-hexadienal.

[0011] Preferably, the preparation method of the catalytic reagent ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt is:

[0012] Step S1, using a direct oxidation iodination method under acidic conditions, using potassium iodide as an iodination agent and hydrogen peroxide as an iodination reaction activator, the activator converts the iodine anion of the iodination agent into a highly electrophilic iodine cation, and the iodine cation undergoes an electrophilic substitution reaction on the benzene ring of ethoxytriphenylsilane to prepare ethoxyiodophenylsilane;

[0013] In step S2, under the action of a composite catalyst of cuprous iodide and N,N-dimethylethylenediamine and an alkaline reagent of cesium carbonate, the phosphine hydrogen functional group of diphenylphosphine and the iodobenzene functional group of ethoxyiodophenylsilane directly undergo a dehydroiodination coupling reaction to prepare ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt.

[0014] Preferably, the preparation method of the catalytic reagent ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3 is:

[0015] Step S1, 4-bromophenyltriethoxysilane undergoes a Grignard reaction with iodine-activated magnesium powder in anhydrous tetrahydrofuran to prepare an ethoxysilylphenyl Grignard reagent;

[0016] In step S2, three equivalents of ethoxysilylphenyl Grignard reagent are used as strong nucleophiles to provide three equivalents of phenyl synthons, which react with one equivalent of phosphorus trichloride to undergo nucleophilic substitution reaction to prepare ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3.

[0017] Preferably, the preparation method of the carboxylated magnetic nanospheres is: preparing nano-ferroferric oxide magnetic fluid by chemical coprecipitation, coating the surface of the nano-ferroferric oxide magnetic fluid with oleic acid, and synthesizing azelaic acid by oxidizing oleic acid with potassium permanganate to form carboxyl functional groups on the surface of the magnetic nanospheres to prepare carboxylated magnetic nanospheres.

[0018] Preferably, the eluent is acetic acid-methanol solution.

[0019] Preferably, the regioselective aldol condensation catalyst comprises: ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt and ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3.

[0020] Preferably, the regioselective aldol condensation catalyst includes ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt, and does not include ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3.

[0021] Preferably, the regioselective aldol condensation catalyst includes ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3, and does not include ethoxytriphenylphosphine silane Si-(PPh3)3-OEt.

[0022] The yield of 2,4-hexadienal synthesized by the method is 60-85% and the purity is 80-95%.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects:

[0024] Firstly, two catalytic reagents were synthesized: ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt and ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt;

[0025] Then, molecular imprinting technology is used, with 3-aminopropyltriethoxysilane and a catalytic reagent ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt as functional monomers, adipic acid as a regioselective template molecule for the aldol condensation reaction, and 3-aminopropyltriethoxysilane and adipic acid are combined through hydrogen bonding to form a templated functional monomer; carboxylated magnetic nanoparticles are used as a polymer matrix, tetraethyl orthosilicate and a catalytic reagent ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3 are used as cross-linking agents, and hydrochloric acid is used as an initiator. By initiating a sol-gel polymerization reaction, the templated functional monomer is fixed on the surface of the magnetic nanoparticles, and the adipic acid template is removed to prepare a regioselective aldol condensation catalyst, which can be magnetically recovered and reused;

[0026] The catalytic mechanism of regioselective aldol condensation catalyst is:

[0027] On the one hand, the phosphorus atom of triphenylphosphine has a lone pair of electrons, which can act as an electron-rich active center to remove the α-H of acetaldehyde and / or crotonaldehyde;

[0028] On the other hand, it has an imprinted cavity capable of accommodating the target product 2,4-hexadienal;

[0029] And there is a fixed catalytic active center triphenylphosphine in the imprinted cavity;

[0030] Based on this, the regioselective aldol condensation catalyst can selectively remove the α-H of acetaldehyde to promote the formation of an enolate anion, which then undergoes nucleophilic addition to the carbonyl carbon of crotonaldehyde to form β-hydroxyaldehyde, which then dehydrates to form 2,4-hexadienal.

[0031] Experiments have found that the regioselective aldol condensation catalyst can effectively catalyze the condensation of acetaldehyde and crotonaldehyde to produce 2,4-hexadienal, reduce reaction by-products, improve the product purity of 2,4-hexadienal, and improve the catalytic selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1-1 is the chemical structural formula of ethoxysilylphenyl Grignard reagent;

[0033] Figure 1-2 The chemical structural formula of ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3;

[0034] Figure 2-1 is the chemical structural formula of ethoxyiodophenylsilane;

[0035] Figure 2-2 is the chemical structural formula of ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt;

[0036] Figure 3 The chemical structure of the template functional monomer formed by 3-aminopropyltriethoxysilane and adipic acid combined through hydrogen bonding;

[0037] Figure 4 is the chemical reaction formula of 2,4-hexadienal;

[0038] Figure 5 This is the chemical reaction formula of the by-product 2-vinyl-2-butenal. DETAILED DESCRIPTION

[0039] Example 1:

[0040] Preparation of ethoxysilyl triphenylphosphine PPh3-[Si-(OEt)3]3, its preparation method is as follows:

[0041] Step S1, preparing an ethoxysilylphenyl Grignard reagent, the preparation mechanism of which is: p-bromophenyltriethoxysilane reacts with iodine-activated magnesium powder in anhydrous tetrahydrofuran to produce an ethoxysilylphenyl Grignard reagent, the chemical structure of which is as follows: Figure 1-1 As shown;

[0042] Step S2, prepare ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3, the preparation mechanism of which is: three equivalents of ethoxysilylphenyl Grignard reagent as a strong nucleophile, which provides three equivalents of phenyl synthon, and undergoes nucleophilic substitution reaction with one equivalent of phosphorus trichloride to prepare ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3, whose chemical structure is as follows Figure 1-2 As shown;

[0043] The specific preparation steps of ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3 are as follows: under the protection of nitrogen, 481 mg of magnesium powder, 1 particle of iodine, and 20 mL of anhydrous tetrahydrofuran are added to the flask in sequence, and nitrogen is purged for 5 minutes. At room temperature and under rapid stirring, 30 mL of anhydrous tetrahydrofuran containing 6.36 g of p-bromophenyltriethoxysilane is added dropwise to the flask using a dropping funnel. After the addition is complete, the mixture is heated to 60°C in a water bath and stirred for 2 hours, then cooled to 0°C to obtain ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3. Silylphenyl Grignard reagent, then, in an ice-water bath at 0°C, slowly stirring, 920 mg of phosphorus trichloride dissolved in 10 mL of anhydrous tetrahydrofuran was added dropwise to the flask using a dropping funnel. After the addition was complete, the mixture was heated to 60°C in a water bath and stirred for 2 h. The mixture was quenched with ice water, extracted with ethyl acetate, dried over anhydrous magnesium sulfate, filtered to remove the solvent, and purified by silica gel column chromatography (mobile phase: 4 parts by volume of petroleum ether and 1 part by volume of ethyl acetate) to obtain ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3;

[0044] The nuclear magnetic resonance hydrogen spectrum characterization results of ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3 are as follows:

[0045] 1 H NMR (400MHz, CDCl3, δ): 1.41 (t, 27H, -CH3), 3.81 (q, 18H, Si-O-CH2-), 7.09-7.21 (m, 12H, Ar-H);

[0046] Ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3(C 36 H 57 The elemental analysis results of O9PSi3 are as follows:

[0047] Detection values: 57.75% C, 7.62% H, 19.25% O, 4.14% P, 11.23% Si;

[0048] Theoretical values: 57.72% C, 7.67% H, 19.22% O, 4.13% P, 11.25% Si.

[0049] Example 2:

[0050] Preparation of ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt, the preparation method is as follows:

[0051] Step S1, preparing ethoxyiodophenylsilane, the preparation mechanism of which is: using direct oxidation iodination method, under acidic conditions, using potassium iodide as the iodination agent and hydrogen peroxide as the iodination reaction activator, the activator converts the iodine anion of the iodination agent into a highly electrophilic iodine cation, and the iodine cation undergoes an electrophilic substitution reaction on the benzene ring of ethoxytriphenylsilane to prepare ethoxyiodophenylsilane, whose chemical structure is as follows: Figure 2-1 As shown;

[0052] The specific preparation steps of ethoxyiodophenylsilane are as follows: 3.32g of potassium iodide, 6.09g of ethoxytriphenylsilane, 2g of concentrated sulfuric acid, 60mL of deionized water, and 20mL of methanol are added to a four-necked flask; 3mL of 35wt% hydrogen peroxide is added dropwise to the flask in an ice-water bath at 4°C under slow stirring using a constant pressure dropping funnel; after the addition is complete, the temperature is raised to 60°C in a water bath and stirred for 4h; 0.1mol / L sodium thiosulfate solution is added to remove iodine, the mixture is filtered, and recrystallized from acetone to obtain ethoxyiodophenylsilane;

[0053] Step S2, preparing ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt, the preparation mechanism of which is: under the joint action of the composite catalyst cuprous iodide and N,N-dimethylethylenediamine, and the alkaline reagent cesium carbonate, the phosphine hydrogen functional group of diphenylphosphine and the iodobenzene functional group of ethoxyiodophenylsilane directly undergo dehydroiodination coupling reaction to prepare ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt, whose chemical structure is as follows Figure 2-2 As shown;

[0054] The specific preparation steps of ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt are as follows: under nitrogen protection, 2.8 g of diphenylphosphine, 150 mg of cuprous iodide, 0.5 mL of N,N'-dimethylethylenediamine, and 100 mL of anhydrous toluene are added to a flask in sequence, nitrogen purged for 5 minutes, stirred at room temperature for 5 minutes, 3.4 g of ethoxyiodophenylsilane and 10 g of cesium carbonate are added to the flask, the temperature is raised to 110°C and stirred for 12 hours, cooled to room temperature, filtered, and purified by silica gel column chromatography (mobile phase: 4 parts by volume of petroleum ether and 1 part by volume of ethyl acetate) to obtain ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt;

[0055] The nuclear magnetic resonance hydrogen spectrum characterization results of ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt are as follows:

[0056] 1 H NMR (400MHz, CDCl3, δ): 1.39 (t, 3H, -CH3), 3.82 (q, 2H, Si-O-CH2-), 7.11-7.49 (m, 42H, Ar-H);

[0057] Ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt(C 56 H 47 The elemental analysis results of OP3Si are as follows:

[0058] Detection values: 78.50% C, 5.49% H, 1.87% O, 10.86% P, 3.27% Si;

[0059] Theoretical values: 78.49% C, 5.53% H, 1.87% O, 10.84% ​​P, 3.28% Si.

[0060] Example 3:

[0061] Carboxylated magnetic nanospheres were prepared. The specific preparation steps were as follows: under nitrogen protection and mechanical stirring, 5.96 g of ferrous chloride tetrahydrate, 13.52 g of ferric chloride hexahydrate, and 120 mL of deionized water were added to a three-necked flask, ammonia water was added dropwise to the flask using a dropping funnel until a brown precipitate was generated, the pH value of the system was adjusted to 10, 25 mL of oleic acid was added, the reaction was carried out at a water bath temperature of 70° C. for 2 h, the temperature was lowered to 50° C., 6.32 g of potassium permanganate was added, the temperature was raised to a water bath temperature of 50° C., the reaction was carried out for 8 h, the generated precipitate was separated using an external magnetic field, and the product was washed with anhydrous ethanol and deionized water in sequence. The product was vacuum dried at 40° C. to constant weight to obtain carboxylated magnetic nanospheres.

[0062] Example 4:

[0063] A regioselective aldol condensation catalyst I was prepared. The preparation mechanism is as follows: using molecular imprinting technology, 3-aminopropyltriethoxysilane and a catalytic reagent ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt are functional monomers, adipic acid is used as a regioselective template molecule for the aldol condensation reaction, and 3-aminopropyltriethoxysilane and adipic acid are combined through hydrogen bonding to form a templated functional monomer. Its chemical structure is as follows Figure 3 As shown;

[0064] Using carboxylated magnetic nanospheres as the polymer matrix, tetraethyl orthosilicate and the catalyst reagent ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3 as crosslinkers, and hydrochloric acid as the initiator, a sol-gel polymerization reaction was initiated to immobilize the templated functional monomer on the surface of the magnetic nanospheres. The adipic acid template was then eluted with an acetic acid-methanol solution as the eluent to prepare a regioselective aldol condensation catalyst I.

[0065] The specific preparation steps of the regioselective aldol condensation catalyst I are as follows: 20 mg of adipic acid is dissolved in 5 mL of anhydrous ethanol, 1 mL of 3-aminopropyltriethoxysilane is added, 3-aminopropyltriethoxysilane and adipic acid are hydrogen-bonded to form a templated functional monomer, the volume is adjusted to 20 mL with 0.2 M citrate-phosphate buffer at pH 6.5, the mixture is transferred to a three-necked flask, and the reaction is stirred at room temperature for 1 hour;

[0066] Add 50 mg of ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt, 150 mg of ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3, 3 mL of ethyl orthosilicate, and 100 mg of carboxylated magnetic nanospheres into a three-necked flask and stir the reaction at room temperature for 2 h.

[0067] 1 mL of 0.2 M hydrochloric acid was added to a three-necked flask, and a sol-gel polymerization reaction was initiated at room temperature for 12 h. The product was separated and collected by applying an external magnetic field, washed with deionized water until the pH value was neutral, and the adipic acid template was eluted with an eluent (eluent: 2 parts by volume of acetic acid and 8 parts by volume of methanol) to prepare a regioselective aldol condensation catalyst I, which can be magnetically recovered and reused.

[0068] Preparation of 2,4-hexadienal, the preparation mechanism is as follows: using regioselective aldol condensation catalyst I to remove the α-H of acetaldehyde to generate an enolate anion, the enolate anion undergoes a nucleophilic addition reaction with the carbonyl carbon of crotonaldehyde to generate β-hydroxyaldehyde, and the β-hydroxyaldehyde undergoes a dehydration reaction under acidic conditions to generate 2,4-hexadienal. The chemical reaction formula is as follows: Figure 4 As shown;

[0069] And when preparing 2,4-hexadienal, if the α-H of crotonaldehyde is removed, 2-vinyl-2-butenal will be generated, and its chemical reaction formula is as follows: Figure 5 As shown;

[0070] Among them, 2-vinyl-2-butenal is an isomer of 2,4-hexadienal;

[0071] The specific preparation steps of 2,4-hexadienal are as follows: 25 mL of a 0.01 mol / mL acetaldehyde aqueous solution is added to a three-necked flask equipped with an electric stirrer, a thermometer, and a dropping funnel in an ice-water bath at 4°C, stirring is started, 1 g of a regioselective aldol condensation catalyst I is added, the pH value is adjusted to 11.5, 20.5 mL of crotonaldehyde (0.25 mol) is added dropwise to the flask using a constant pressure dropping funnel, the reaction is sealed for 0.5 h, acetic acid is added to adjust the pH value to 6, the mixture is allowed to stand for 10 min, and the product P-I is extracted with anhydrous ether, and the regioselective aldol condensation catalyst I is recovered by applying an external magnetic field;

[0072] The product P-Ⅰ was analyzed using a GC7890Ⅱ gas chromatograph (injection port temperature 200°C, detector temperature 250°C, column temperature 90°C, injection volume 0.2 μL, split ratio 60:1). The results showed that the yield of 2,4-hexadienal was 82.4% and the purity was 89.7%.

[0073] Example 5:

[0074] A regioselective aldol condensation catalyst II was prepared. The preparation method thereof was similar to the preparation method of the regioselective aldol condensation catalyst I in Example 4, except that the regioselective aldol condensation catalyst II did not use the catalytic reagent ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt, which served as a functional monomer in the regioselective aldol condensation catalyst I.

[0075] According to the preparation method of 2,4-hexadienal in Example 4, and using the regioselective aldol condensation catalyst II instead of the regioselective aldol condensation catalyst I, the product P-II was prepared;

[0076] The results of product P-II analysis using GC7890Ⅱ gas chromatograph showed that the yield of 2,4-hexadienal was 57.9% and the purity was 80.7%.

[0077] Example 6:

[0078] A regioselective aldol condensation catalyst III was prepared. The preparation method thereof was similar to the preparation method of the regioselective aldol condensation catalyst I in Example 4, except that the regioselective aldol condensation catalyst III did not use the catalytic reagent ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3, which served as a crosslinking agent in the regioselective aldol condensation catalyst I.

[0079] According to the preparation method of 2,4-hexadienal in Example 4, and using the regioselective aldol condensation catalyst III instead of the regioselective aldol condensation catalyst I, the product P-III was prepared;

[0080] The results of product P-III analysis using GC7890Ⅱ gas chromatograph showed that the yield of 2,4-hexadienal was 61.6% and the purity was 94.3%.

[0081] Example 7:

[0082] A regioselective aldol condensation reagent was prepared. The preparation method thereof was similar to the preparation method of the regioselective aldol condensation catalyst I in Example 4, except that the regioselective aldol condensation reagent did not use the catalytic reagent ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt, nor did it use the catalytic reagent ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3;

[0083] According to the preparation method of 2,4-hexadienal in Example 4, and using a regioselective aldol condensation reagent instead of the regioselective aldol condensation catalyst I, the product P-IV was prepared;

[0084] The results of product P-IV analysis using GC7890Ⅱ gas chromatograph showed that the yield of 2,4-hexadienal was 48.3% and the purity was 70.6%.

[0085] Example 8:

[0086] Prepare an aldol condensation catalyst. The preparation method thereof refers to the preparation method of the regioselective aldol condensation catalyst I in Example 4, except that:

[0087] Adipic acid is not used as the aldol condensation catalyst, and its role in the regioselective aldol condensation catalyst I is as a regioselective template molecule for the aldol condensation reaction;

[0088] According to the preparation method of 2,4-hexadienal in Example 4, and using an aldol condensation catalyst instead of the regioselective aldol condensation catalyst I, a product P-V is prepared;

[0089] The results of product P-V analysis using GC7890Ⅱ gas chromatograph showed that the yield of 2,4-hexadienal was 81.5% and the purity was 32.0%.

[0090] Example 9:

[0091] According to the preparation method of 2,4-hexadienal in Example 4, but without using the regioselective aldol condensation catalyst I, the product P-VI was prepared;

[0092] The results of product P-VI analysis using GC7890Ⅱ gas chromatograph showed that the yield of 2,4-hexadienal was 76.1% and the purity was 27.4%.

Claims

1. A method for synthesizing 2,4-hexadienal, characterized in that: The following steps are involved: Step 1: Preparation of a regioselective aldol condensation catalyst, the specific process is as follows: Using molecular imprinting technology, 3-aminopropyltriethoxysilane and the catalytic reagent ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt were used as functional monomers, and adipic acid was used as the regioselective template molecule for the aldol condensation reaction. 3-aminopropyltriethoxysilane and adipic acid were combined through hydrogen bonding to form a templated functional monomer. The chemical structure of the templated functional monomer is as follows: ； The chemical structure of ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt is: ； Using carboxylated magnetic nanospheres as the polymer matrix, tetraethyl orthosilicate and the catalyst ethoxysilyltriphenylphosphine (PPh3-[Si-(OEt)3]3) as crosslinkers, and hydrochloric acid as the initiator, a sol-gel polymerization reaction was initiated to immobilize the templated functional monomer on the surface of the magnetic nanospheres. The adipic acid template was then removed using an eluent to prepare a regioselective aldol condensation catalyst. The chemical structure of ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3 is: ； Step 2: Using a regioselective aldol condensation catalyst to remove the α-H of acetaldehyde to generate an enolate anion, the enolate anion undergoes a nucleophilic addition reaction with the carbonyl carbon of crotonaldehyde to generate β-hydroxyaldehyde, and the β-hydroxyaldehyde undergoes a dehydration reaction under acidic conditions to generate 2,4-hexadienal.

2. The method for synthesizing 2,4-hexadienal according to claim 1, wherein The preparation method of the catalytic reagent ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt is: Step S1, using a direct oxidation iodination method under acidic conditions, using potassium iodide as an iodination agent and hydrogen peroxide as an iodination reaction activator, the activator converts the iodine anion of the iodination agent into a highly electrophilic iodine cation, and the iodine cation undergoes an electrophilic substitution reaction on the benzene ring of ethoxytriphenylsilane to prepare ethoxyiodophenylsilane; In step S2, under the action of a composite catalyst of cuprous iodide and N,N-dimethylethylenediamine and an alkaline reagent of cesium carbonate, the phosphine hydrogen functional group of diphenylphosphine and the iodobenzene functional group of ethoxyiodophenylsilane directly undergo a dehydroiodination coupling reaction to prepare ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt.

3. The method for synthesizing 2,4-hexadienal according to claim 1, wherein The preparation method of the catalytic reagent ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3 is: Step S1, 4-bromophenyltriethoxysilane undergoes a Grignard reaction with iodine-activated magnesium powder in anhydrous tetrahydrofuran to prepare an ethoxysilylphenyl Grignard reagent; In step S2, three equivalents of ethoxysilylphenyl Grignard reagent are used as strong nucleophiles to provide three equivalents of phenyl synthons, which react with one equivalent of phosphorus trichloride to undergo nucleophilic substitution reaction to prepare ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3.

4. The method for synthesizing 2,4-hexadienal according to claim 1, wherein The preparation method of the carboxylated magnetic nanospheres comprises the following steps: preparing nano-ferroferric oxide magnetic fluid by a chemical coprecipitation method, coating the surface of the nano-ferroferric oxide magnetic fluid with oleic acid, and synthesizing azelaic acid by oxidizing oleic acid with potassium permanganate to form carboxyl functional groups on the surface of the magnetic nanospheres, thereby preparing the carboxylated magnetic nanospheres.

5. The method for synthesizing 2,4-hexadienal according to claim 1, wherein The eluent is acetic acid-methanol solution.

6. The method for synthesizing 2,4-hexadienal according to claim 1, wherein The regioselective aldol condensation catalyst includes ethoxytriphenylphosphinosilane Si-(PPh3)3-OEt, and does not include ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3.

7. The method for synthesizing 2,4-hexadienal according to claim 1, wherein The regioselective aldol condensation catalyst includes ethoxysilyltriphenylphosphine PPh3-[Si-(OEt)3]3, and does not include ethoxytriphenylphosphine silane Si-(PPh3)3-OEt.

8. The method for synthesizing 2,4-hexadienal according to any one of claims 1 to 7, characterized in that: The yield of 2,4-hexadienal synthesized by the method is 60-85% and the purity is 80-95%.

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