A method for preparing and using 3,4-dihydroxyphenylacetic acid alkyl esters
By synthesizing 3,4-dihydroxyphenylacetic acid esters with different alkyl chain lengths through an improved esterification reaction, the problem of insufficient antioxidant enrichment at the interface in O/W emulsions was solved, achieving a high-efficiency and low-cost antioxidant effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SOUTH CHINA UNIV OF TECH
- Filing Date
- 2026-03-26
- Publication Date
- 2026-05-29
AI Technical Summary
In O/W emulsions, the high hydrophilicity of 3,4-dihydroxyphenylacetic acid limits its accumulation at the oil-water interface, resulting in low antioxidant efficiency. Existing esterification reactions are slow and costly, and traditional catalysts pose corrosive and environmental safety issues.
Using 1-ethyl-3-(3-dimethylpropylamine)carbodiimide (EDCI) and 4-dimethylaminopyridine (DMAP) as catalysts, 3,4-dihydroxyphenylacetic acid esters with different alkyl chain lengths were synthesized at low temperature via Steglich esterification, which improved the reaction rate and yield. The high-purity products were obtained by silica gel column chromatography.
The synthesized alkyl 3,4-dihydroxyphenylacetic acid can be efficiently enriched at the O/W emulsion interface, significantly improving antioxidant performance. It is low in cost and suitable for large-scale production, exhibiting excellent antioxidant effects.
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Figure CN122102901A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the technical field of antioxidants for O / W type emulsions, and in particular relates to a method for preparing and applying alkyl 3,4-dihydroxyphenylacetic acid ester. Background Technology
[0002] Edible oils often exist in the form of open-liquid (O / W) emulsions in foods such as mayonnaise, sauces, and salad dressings. Compared to pure oils, O / W emulsion systems have a large oil-water interface area. This structural feature leads to a high concentration of lipid oxidation reactions in the oil-water interface region, which is enriched with surfactants, prooxidants, and amphiphilic molecules. This creates a localized chemical environment that is more prone to oxidation than a homogeneous oil phase, ultimately resulting in significantly lower lipid oxidation stability in O / W emulsions compared to pure oil systems.
[0003] 3,4-Dihydroxyphenylacetic acid (DHPA) is a natural phenolic compound widely found in plant-based foods such as olives and grapes, and is known to have antioxidant, antibacterial, anti-inflammatory, and insulin-regulating effects. However, in emulsion systems, the high hydrophilicity of DHPA limits its accumulation at the oil-water interface, reducing its antioxidant efficacy in O / W emulsions.
[0004] Esterification reactions can be carried out using chemical or biocatalytic methods. Lipases can catalyze the formation of ester or amide bonds in phenolic acid molecules, but lipase-catalyzed esterification using DHPA suffers from slow reaction rates and low yields, and heating easily destroys the phenolic structure. Traditional acid-catalyzed esterification, on the other hand, is highly corrosive and has environmental safety concerns. Summary of the Invention
[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing and applying alkyl esters of 3,4-dihydroxyphenylacetic acid. On one hand, the present invention involves esterifying 3,4-dihydroxyphenylacetic acid with an alkyl alcohol, improving the reaction rate and yield through process optimization. On the other hand, the present invention aims to design and synthesize a series of 3,4-dihydroxyphenylacetic acid esters with different alkyl chain lengths, in order to obtain derivatives that can be efficiently enriched at the O / W emulsion interface and exhibit excellent antioxidant properties.
[0006] To achieve the above objectives, the present invention adopts the following technical solution:
[0007] A method for preparing alkyl 3,4-dihydroxyphenylacetic acid involves reacting 3,4-dihydroxyphenylacetic acid and an alkyl alcohol in an organic solvent under the action of a condensing agent and a catalyst to undergo a Steglich esterification reaction, thereby obtaining alkyl 3,4-dihydroxyphenylacetic acid.
[0008] The condensing agent is 1-ethyl-3-(3-dimethylpropylamine)carbodiimide (EDCI), the catalyst is 4-dimethylaminopyridine (DMAP), and the organic solvent is N,N-dimethylformamide (DMF).
[0009] The reaction process is as follows:
[0010] R is an alkyl group.
[0011] Preferably, the molar ratio of the 3,4-dihydroxyphenylacetic acid, alkyl alcohol, condensing agent and catalyst is 1:(0.5-2):(1-3):(0.1-0.5).
[0012] Preferably, the molar ratio of the 3,4-dihydroxyphenylacetic acid, alkyl alcohol, condensing agent, and catalyst is 1:1.2:2:0.2.
[0013] Preferably, the esterification reaction conditions are: temperature of 0-4℃, reaction time of 8-12h, and oscillation speed of 600-800 rpm.
[0014] Preferably, the purification of the alkyl 3,4-dihydroxyphenylacetic acid ester is as follows: the product is washed with ice water, extracted with ethyl acetate, and washed successively with dilute hydrochloric acid, saturated NaHCO3 solution and saturated NaCl solution, then dried with anhydrous MgSO4, filtered and concentrated, the crude product is purified by silica gel column chromatography, followed by rotary evaporation and vacuum drying.
[0015] Preferably, the eluent ratio used in the silica gel column chromatography is petroleum ether: ethyl acetate = 10:1 to 5:1.
[0016] Preferably, the alkyl alcohol is a C2-C12 n-alkyl alcohol. More preferably, the alkyl alcohol is a C3-C8 n-alkyl alcohol.
[0017] The n-alkyl alcohol is at least one of ethanol, n-butanol, n-octanol, and lauryl alcohol. The esterification product includes any one of ethyl 3,4-dihydroxyphenylacetate (DHPA-ET), n-butanol 3,4-dihydroxyphenylacetate (DHPA-BU), n-octanol 3,4-dihydroxyphenylacetate (DHPA-OC), and lauryl 3,4-dihydroxyphenylacetate (DHPA-DO).
[0018] Application of the alkyl 3,4-dihydroxyphenylacetic acid ester prepared by the method as an antioxidant in oil-in-water (O / W) emulsions.
[0019] Preferably, the oil is rapeseed oil; and the surfactant in the emulsion is Tween 80.
[0020] The alkyl 3,4-dihydroxyphenylacetic acid synthesized in this invention has outstanding antioxidant effects on O / W emulsions prepared from (refined) rapeseed oil.
[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:
[0022] (1) Low cost and mild reaction conditions: This invention uses 3,4-dihydroxyphenylacetic acid and a series of n-alkyl alcohols with different alkyl chain lengths as raw materials and uses EDCI / DMAP to catalyze the esterification reaction. Compared with traditional acid catalysis or enzyme catalysis, this invention has a higher reaction rate, higher yield of the target product, and is easier to purify; the reagents used are cheaper, the preparation method is simpler and milder, and it is suitable for large-scale production.
[0023] (2) Significant antioxidant effect: The alkyl 3,4-dihydroxyphenylacetic acid synthesized in this invention is more effective than the traditional antioxidant BHT in inhibiting lipid oxidation in O / W emulsions. In particular, when it has an alkyl chain of appropriate length (such as C4), it can specifically locate at the main site of lipid oxidation - the oil-water interface, thus exhibiting the best antioxidant performance in O / W emulsions. Attached Figure Description
[0024] Figure 1 This is a reaction flow diagram of the present invention.
[0025] Figure 2 This is a reaction mechanism diagram of the present invention.
[0026] Figure 3 This is a high-resolution mass spectrum (HRMS) of ethyl 3,4-dihydroxyphenylacetate from Example 1.
[0027] Figure 4 This is a high-resolution mass spectrum (HRMS) of n-butanol ester of 3,4-dihydroxyphenylacetic acid from Example 2.
[0028] Figure 5 The high-resolution mass spectrometry (HRMS) spectrometry of 3,4-dihydroxyphenylacetic acid n-octanol ester in Example 3 is shown.
[0029] Figure 6 The high-resolution mass spectrum (HRMS) of lauryl ester of 3,4-dihydroxyphenylacetic acid from Example 4 is shown.
[0030] Figure 7 The following are the Fourier Transform Infrared (FTIR) spectra of alkyl 3,4-dihydroxyphenylacetic acid esters from Examples 1-4.
[0031] Figure 8 Peroxide value (POV) analysis charts for O / W emulsions containing alkyl 3,4-dihydroxyphenylacetic acid esters from Examples 1-4.
[0032] Figure 9 The chart shows the thiobarbituric acid (TBA) values of the O / W emulsions containing alkyl 3,4-dihydroxyphenylacetic acid esters from Examples 1-4.
[0033] Figure 10 P-AV (P-AV) analysis charts for O / W emulsions containing alkyl 3,4-dihydroxyphenylacetic acid esters from Examples 1-4.
[0034] Figure 11 Total oxidation value (TOTOX) analysis of O / W emulsions containing alkyl 3,4-dihydroxyphenylacetic acid esters from Examples 1-4. Detailed Implementation
[0035] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. All raw materials involved in the present invention can be purchased directly from the market. For process parameters not specifically specified, conventional techniques can be referred to.
[0036] Example 1:
[0037] In a 50 mL round-bottom flask, ethanol (6 mmol, 1.2 eq), EDCI (10 mmol, 2 eq), and DMAP (1 mmol, 0.2 eq) were added, followed by the addition of 35 mL DMF to dissolve the ethanol and stirring until clear. Then, DHPA (5 mmol, 1 eq) was added. The mixture was reacted at 0–4 °C with shaking at 600 rpm for 8 h to obtain the reaction solution. The reaction solution was washed with ice water, extracted three times with ethyl acetate, and washed three times successively with 1 mol / L HCl solution, saturated NaHCO3 solution, and saturated NaCl solution. After washing, the organic phase was dried over anhydrous MgSO4 and concentrated by rotary evaporation. The solution was then purified by silica gel column chromatography to remove the solvent, yielding DHPA-ET.
[0038] The obtained compound DHPA-ET was a brownish-red oily substance with a yield of 69.1%. 1 ¹H NMR (400 MHz, DMSO) δ: 9.35 (s, 2H; phenolic hydroxyl hydrogen atom), 6.67–6.61 (m, 2H; aromatic hydrogen atom), 6.48 (m, 1H; aromatic hydrogen atom), 4.04 (t, J = 6.6 Hz, 2H; proton adjacent to the hydroxyl oxygen in alcohol), 3.42 (s, 2H; hydrogen atom adjacent to the benzene ring), 1.16 (t, J = 7.1 Hz, 3H; terminal hydrogen atom of alkyl chain, -CH₃); 13C NMR (101 MHz, DMSO) δ: 171.98, 145.54, 144.64, 125.51, 120.42, 117.02, 115.89, 60.51, 39.98, 14.56. 171.98ppm 13 The C chemical shift corresponds to the signal on the acyl ester carbon; 145.54–115.89 ppm corresponds to the signal on the aromatic carbon of 3,4-dihydroxyphenylacetic acid; and 60.51–14.56 ppm corresponds to the signal on the alkyl carbon. HRMS m / z: C 10 H 12 O4 {[MH] - The calculated value is 195.20, and the actual value is 195.07.
[0039] Example 2:
[0040] In a 50 mL round-bottom flask, n-butanol (6 mmol, 1.2 eq), EDCI (10 mmol, 2 eq), and DMAP (1 mmol, 0.2 eq) were added, followed by the addition of 35 mL DMF to dissolve the mixture and stirring until clear. Then, DHPA (5 mmol, 1 eq) was added. The reaction mixture was reacted at 0–4 °C with shaking at 800 rpm for 8 h to obtain the reaction solution. The reaction solution was rinsed with ice water, extracted three times with ethyl acetate, and washed three times successively with 1 mol / L HCl solution, saturated NaHCO3 solution, and saturated NaCl solution. After washing, the organic phase was dried over anhydrous MgSO4 and concentrated by rotary evaporation. The solution was then purified by silica gel column chromatography to remove the solvent, yielding DHPA-BU.
[0041] The obtained compound DHPA-BU was a brownish-red oily substance with a yield of 70.3%. 1 ¹H NMR (400 MHz, DMSO) δ: 8.84 (s, 2H; phenolic hydroxyl hydrogen atom), 6.67–6.61 (m, 2H; aromatic hydrogen atom), 6.51–6.44 (m, 1H; aromatic hydrogen atom), 4.00 (t, J = 6.6 Hz, 2H; adjacent proton of alcoholic hydroxyl oxygen), 3.42 (s, 2H; adjacent hydrogen atom of benzene ring, -CH²⁻), 1.58–1.47 (m, 2H; alkyl chain hydrogen atom, -CH²⁻), 1.29 (h, J = 7.5 Hz, 2H; alkyl chain hydrogen atom, -CH²⁻), 0.86 (t, J = 7.4 Hz, 3H; terminal hydrogen atom of alkyl chain, -CH³⁻); 13C NMR (101 MHz, DMSO): δ 172.02, 145.54, 144.64, 125.55, 120.40, 117.03, 115.89, 64.19, 40.02, 30.66, 19.02, 13.98; 172.02 ppm 13 The C chemical shift corresponds to the signal on the acyl ester carbon, 145.54–115.89 ppm corresponds to the signal on the aromatic carbon of 3,4-dihydroxyphenylacetic acid, and 64.19–13.98 ppm corresponds to the signal on the alkyl carbon; HRMS m / z: C 12 H 16 O4 {[MH] - Calculated value: 223.25, Actual value: 223.08, {[2M-H]} - The calculated value is 447.5, and the actual value is 447.17.
[0042] Example 3:
[0043] In a 50 mL round-bottom flask, add n-octanol (6 mmol, 1.2 eq), EDCI (10 mmol, 2 eq), and DMAP (1 mmol, 0.2 eq), then add 35 mL of DMF to dissolve and stir until clear. Next, add DHPA (5 mmol, 1 eq). React at 0–4 °C with shaking at 800 rpm for 12 h to obtain the reaction solution. Wash the reaction solution with ice water, extract three times with ethyl acetate, and wash three times successively with 1 mol / L HCl solution, saturated NaHCO3 solution, and saturated NaCl solution. After washing, the organic phase is dried over anhydrous MgSO4 and concentrated by rotary evaporation. Purify by silica gel column chromatography to remove the solvent, yielding DHPA-OC.
[0044] The obtained compound DHPA-OC was a yellow oily substance with a yield of 67.6%. 1¹H NMR (400 MHz, DMSO) δ: 8.80 (s, 2H; phenolic hydroxyl hydrogen atom), 6.67–6.60 (m, 2H; aromatic hydrogen atom), 6.47 (dd, J = 8.1, 2.1 Hz, 1H; aromatic hydrogen atom), 3.99 (t, J = 6.6 Hz, 2H; adjacent proton of alcoholic hydroxyl oxygen), 3.42 (s, 2H; adjacent hydrogen atom of benzene ring), 1.52 (q, J = 6.7 Hz, 2H; alkyl chain hydrogen atom, -CH²⁻), 1.27 (s, 2H; alkyl chain hydrogen atom, -CH²⁻), 1.23 (s, 8H; alkyl chain hydrogen atom, -CH²⁻), 0.86 (t, J = 6.7 Hz, 3H; terminal hydrogen atom of alkyl chain, -CH³⁻); 13 C NMR (101 MHz, DMSO) δ: 172.00, 145.56, 144.66, 125.53,120.36, 117.04, 115.86, 64.46, 40.40, 40.03, 31.64, 29.03, 28.58, 25.76,22.52, 14.40; 172.00 ppm 13 The C chemical shift corresponds to the signal on the acyl ester carbon, 145.56–115.86 ppm corresponds to the signal on the aromatic carbon of 3,4-dihydroxyphenylacetic acid, and 64.46–14.40 ppm corresponds to the signal on the alkyl carbon; HRMS m / z: C 16 H 24 O4 {[MH] - Calculated value: 279.36, Actual value: 279.16, {[2M-H]} - The calculated value is 559.72, and the actual value is 559.32.
[0045] Example 4:
[0046] In a 50 mL round-bottom flask, lauryl alcohol (6 mmol, 1.2 eq), EDCI (10 mmol, 2 eq), and DMAP (1 mmol, 0.2 eq) were added, followed by 35 mL of DMF to dissolve and stir until clear. Then, DHPA (5 mmol, 1 eq) was added. The mixture was reacted at 0–4 °C with shaking at 800 rpm for 12 h to obtain the reaction solution. The reaction solution was rinsed with ice water, extracted three times with ethyl acetate, and washed three times successively with 1 mol / L HCl solution, saturated NaHCO3 solution, and saturated NaCl solution. After washing, the organic phase was dried over anhydrous MgSO4 and concentrated by rotary evaporation. The solution was then purified by silica gel column chromatography to remove the solvent, yielding DHPA-DO.
[0047] The obtained compound DHPA-DO was a white solid with a yield of 61.8%. 1 ¹H NMR (400 MHz, DMSO): δ 8.78 (s, 2H; phenolic hydroxyl hydrogen atom), 6.67–6.61 (m, 2H; aromatic hydrogen atom), 6.51–6.44 (m, 1H; aromatic hydrogen atom), 3.99 (t, J = 6.7 Hz, 2H; adjacent proton of alcohol hydroxyl oxygen), 3.41 (s, 2H; adjacent hydrogen atom of benzene ring), 1.52 (q, J = 6.9 Hz, 2H; alkyl chain hydrogen atom, -CH₂-), 1.24 (s, 18H; alkyl chain hydrogen atom, -CH₂-), 0.85 (d, J = 7.1 Hz, 3H; terminal hydrogen atom of alkyl chain, -CH₃); 13 C NMR (101 MHz, DMSO): δ171.98, 145.54, 144.64, 125.53, 120.36, 117.04, 115.86, 64.47, 40.39, 40.03,31.77, 29.48, 29.42, 29.38, 29.18, 29.08, 28.58, 25.76, 22.56, 14.39.171.98ppm 13 The C chemical shift corresponds to the signal on the acyl ester carbon, 145.54–115.86 ppm corresponds to the signal on the aromatic carbon of 3,4-dihydroxyphenylacetic acid, and 64.47–14.39 ppm corresponds to the signal on the alkyl carbon. HRMS m / z: C 20 H 32 O4 {[MH] - Calculated value: 335.47, Actual value: 335.19, {[M+Cl] - Calculated value: 371.57, Actual value: 371.16, {[2M-H]} - The calculated value is 971.94, and the actual value is 971.38.
[0048] Based on the experimental results, the inventors speculated on the possible reaction mechanism (see...). Figure 2 First, the carboxyl group of 3,4-dihydroxyphenylacetic acid is activated by EDCI coupling agent to generate a highly reactive O-acyl isourea intermediate. This intermediate is further converted into an acyl-DMAP complex under the action of 4-dimethylaminopyridine (DMAP), which has a stronger acylation ability. Finally, an alkyl alcohol (R-OH) acts as a nucleophile to attack the acyl carbon, complete the formation of the ester bond and release the byproduct.
[0049] Example 5:
[0050] An emulsifier solution was prepared by dissolving 2 g of Tween 80 in 48 g of deionized water. Then, 12 g of oil sample was mixed with 8 g of the emulsifier solution and homogenized for 5 min using a high-speed homogenizer to obtain an emulsion. The prepared emulsions were then mixed with 4 mmol / L DHPA and alkyl esters, and BHT was selected for comparison. An emulsion without any added antioxidants was used as a blank control. The emulsion samples were stored in a 60°C oven protected from light, and samples were taken within a specified time for relevant index testing.
[0051] Determination of peroxide value (POV): Dissolve the emulsion sample (0.1~0.15 g) in 1.5 mL of a mixed solution of isooctane and isopropanol (volume ratio 3:1). Dissolve the upper organic phase of the emulsion in 1.45 mL of a mixed solution of methanol and n-butanol (volume ratio 2:1), and react with 10 μL of ferrous ion solution (prepared by dissolving 0.806 g of barium chloride, 1 g of ferrous sulfate, and 1 mL of 10 mol / L hydrochloric acid in 25 mL of deionized water) and 10 μL of 3.94 mol / L ammonium thiocyanate solution under light-protected conditions for 20 min. Measure the absorbance at 510 nm. Based on the cumene hydrogen peroxide standard curve (y = 0.7076x - 0.2242, R...), the POV is determined. 2 = 0.9982) Calculate the POV level of the sample;
[0052] Determination of thiobarbituric acid (TBA) value: Dissolve the emulsion sample (0.1~0.15 g) in 1 mL of a chloroform and ethanol mixture (volume ratio 1:1), then add 2.5 mL of thiobarbituric acid (TBA) reagent. After boiling in a water bath for 10 min and cooling to room temperature, centrifuge at 2500 r / min for 10 min. Measure the absorbance of the reaction mixture at 532 nm using the supernatant. The absorbance is determined according to the malondialdehyde standard curve (y=0.0748x+0.0417, R0). 2 = 0.997) Calculate the TBA level of the sample;
[0053] Determination of p-AV value: The emulsion sample (0.1–0.15 g) was diluted to 5 mL with a mixture of isooctane and isopropanol (volume ratio 3:1), and the absorbance was measured at 350 nm. The mixture (1.25 mL) was then reacted with 0.25 mL of 0.25% p-anisidine reagent (prepared by dissolving 0.25 g of p-anisidine in 100 mL of glacial acetic acid) for 10 min, and the absorbance was measured again at 350 nm. The p-AV level of the sample was calculated using the following formula:
[0054]
[0055] In the formula: Q is the mass concentration of the sample in the determination solution, 1 g / dL; V is the volume of the sample dissolved, 5 mL; A2 is the absorbance of the sample solution after reaction with p-anisidine reagent; A1 is the absorbance of the sample solution; m is the mass of the sample, g;
[0056] Calculation of Total Oxidation Value (TOTOX):
[0057]
[0058] In the formula: POV is the peroxide value of the O / W emulsion; p-AV is the anisidine value of the O / W emulsion.
[0059] Figure 8-11 This study demonstrates the antioxidant properties of DHPA and alkyl esters with different chain lengths in O / W emulsions. Peroxide value (POV) is a key indicator of the initial degree of lipid oxidation. However, as lipid oxidation progresses, primary oxidation products continue to decompose into secondary oxidation products such as aldehydes and ketones, leading to flavor degradation. Thiobarbituric acid value (TBA) and anisidine value (p-AV) are key indicators of the degree of secondary oxidation. The total peroxide value (TOTOX value) integrates the POV and p-AV values reflecting the initial oxidation stage of O / W emulsions, thus providing a more comprehensive evaluation of the overall oxidative stability of O / W emulsions.
[0060] Depend on Figure 8-11 It is evident that DHPA-BU exhibits the strongest inhibitory effect on lipid oxidation in O / W emulsions. This is because lipid oxidation reactions in O / W emulsions mainly occur at the oil-water interface, and the efficacy of antioxidants depends on their local concentration at the interface. DHPA and DHPA-ET, being highly polar, primarily partition in the aqueous phase of O / W emulsions, making it difficult to accumulate at the oil-water interface, thus resulting in the lowest inhibitory activity against lipid oxidation. Introducing a butyl chain (C4) provides DHPA-BU with a suitable hydrophilic-lipophilic balance, allowing it to effectively detach from the aqueous phase without excessively dissolving in the oil phase, thus accumulating at the interface and exhibiting the highest inhibitory activity against lipid oxidation. As the alkyl chain extends to octyl (C8) and lauryl (C12), the hydrophobicity of the molecule further increases, causing DHPA-OC and DHPA-DO to tend to partition into the oil droplets, resulting in a relatively lower interfacial concentration and thus lower inhibitory activity against lipid oxidation compared to DHPA-BU. Therefore, the lipid oxidation inhibitory activity of DHPA n-alkyl ester derivatives in O / W emulsions is optimal when the alkyl chain length is near the butyl chain (C4).
[0061] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.
Claims
1. A method for preparing an alkyl ester of 3,4-dihydroxyphenylacetic acid, characterized in that, 3,4-Dihydroxyphenylacetic acid and alkyl alcohol undergo Steglich esterification in an organic solvent under the action of a condensing agent and a catalyst to obtain alkyl esters of 3,4-dihydroxyphenylacetic acid. The condensing agent is 1-ethyl-3-(3-dimethylpropylamine)carbodiimide, the catalyst is 4-dimethylaminopyridine, and the organic solvent is N,N-dimethylformamide.
2. The preparation method according to claim 1, characterized in that, The molar ratio of the 3,4-dihydroxyphenylacetic acid, alkyl alcohol, condensing agent and catalyst is 1:(0.5-2):(1-3):(0.1-0.5).
3. The preparation method according to claim 2, characterized in that, The molar ratio of 3,4-dihydroxyphenylacetic acid, alkyl alcohol, condensing agent and catalyst is 1:1.2:2:0.
2.
4. The preparation method according to any one of claims 1 to 3, characterized in that, The conditions for the esterification reaction are: temperature of 0-4℃, reaction time of 8-12h, and oscillation speed of 600-800 rpm.
5. The preparation method according to any one of claims 1 to 3, characterized in that, Purification of the alkyl 3,4-dihydroxyphenylacetic acid ester: The product was washed with ice water, extracted with ethyl acetate, and washed successively with dilute hydrochloric acid, saturated NaHCO3 solution and saturated NaCl solution. After drying with anhydrous MgSO4, filtration and concentration, the crude product was purified by silica gel column chromatography, followed by rotary evaporation and vacuum drying.
6. The preparation method according to claim 5, characterized in that, The eluent ratio used in the silica gel column chromatography is petroleum ether: ethyl acetate = 10:1 to 5:
1.
7. The preparation method according to claim 6, characterized in that, The alkyl alcohol is a C2-C12 n-alkyl alcohol.
8. The preparation method according to claim 7, characterized in that, The alkyl alcohol is a C3-C8 n-alkyl alcohol.
9. The use of alkyl 3,4-dihydroxyphenylacetic acid ester prepared by the method according to any one of claims 1 to 8 as an antioxidant in oil-in-water (O / W) emulsions.
10. The application according to claim 9, characterized in that, The oil is rapeseed oil; the surfactant in the emulsion is Tween 80.