Method for preparing anisic aldehyde

Abstract

The invention relates to a method for preparing anisic aldehyde, which comprises the following steps: adding 4-methoxybenzyl methyl ether, a Pd / g-C3N4 catalyst, lithium chloride, water and a solvent into a reaction container in an inert gas atmosphere, sealing the reaction container, and reacting for 5-30 hours under the conditions of illumination and room temperature to obtain anisic aldehyde. According to the method, 4-methoxybenzyl methyl ether is taken as a raw material, no oxidant is added, and the problems of more wastes, high comprehensive cost and the like caused by the use of the oxidant in the existing reaction method are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of organic chemical synthesis, and particularly relates to a method for preparing anisaldehyde. Background Art

[0002] Anisaldehyde, also known as 4-methoxybenzaldehyde, has the aroma of hawthorn and is widely used not only in flavors and fragrances, but also in technical fields such as drug synthesis (Organic Letters, 2022, Vol. 24, pp. 1152–1157). There are many methods for synthesizing anisaldehyde, some examples are listed below.

[0003] (1) Using ethyl 4-methoxybenzoate or 4-methoxybenzoyl chloride as raw material, reduction hydrogenation is carried out under the action of a hydrogenation agent to obtain anisaldehyde (ChemistrySelect, 2022, Vol. 7, Document No.: e202202351).

[0004] (2) Using 4-methoxybenzyl alcohol as the raw material, the hydroxyl group undergoes oxidative dehydrogenation under the action of an oxidant to obtain anisaldehyde (Scientific Reports, 2024, Vol. 14, Document No.: 536).

[0005] (3) Using 4-methoxytoluene as the raw material, the methyl group undergoes oxidation reaction under the action of an oxidant to obtain anisaldehyde (Angewandte Chemie International Edition, 2024, Vol. 63, Document No.: e202400101).

[0006] (4) Using 4-methoxybenzyl methyl ether as the raw material, anisaldehyde was obtained through oxidation reaction (Organic & Biomolecular Chemistry, 2023, Vol. 21, 5382-5386).

[0007] The reaction usually uses metal nitrates, H2O2 / Br2, t -BuOOH, nitrogen dioxide, oxygen and other oxidants. Obviously, not using oxidants can effectively reduce the overall cost and reduce the generation of pollutants. However, as far as we know, there is no report on the oxidation method of 4-methoxybenzyl methyl ether without adding an oxidant.

[0008] Based on this, this application was developed. Summary of the invention

[0009] The present invention aims to overcome the defects of the prior art and provide a method for preparing anisaldehyde. The method uses 4-methoxybenzyl methyl ether as a raw material and does not add any oxidant, thereby overcoming the problems of large amount of waste and high comprehensive cost caused by using oxidants in the existing reaction method.

[0010] To achieve the above object, the present invention adopts the following technical solution: A method for preparing anisaldehyde comprises adding 4-methoxybenzyl methyl ether, a Pd / g-C3N4 catalyst, lithium chloride, water and a solvent into a reaction container under an inert gas atmosphere (such as argon, helium, nitrogen, etc.), sealing the reaction container, and reacting for 5-30 hours under light and room temperature conditions to obtain anisaldehyde.

[0011] Specifically, the Pd / g-C3N4 is a palladium catalyst supported by graphite-like carbon nitride.

[0012] The structural formula of the 4-methoxybenzyl methyl ether is: .

[0013] The structural formula of the anisaldehyde is: .

[0014] Specifically, the amount of the Pd / g-C3N4 catalyst used can be 25-150 mg Pd / g-C3N4 catalyst per millimole of 4-methoxybenzyl methyl ether, preferably 75 mg.

[0015] Specifically, the loading amount of metal palladium in the Pd / g-C3N4 catalyst can be 1-5wt%, preferably 3wt%.

[0016] Specifically, the amount of lithium chloride used can be 0.5-2.5 mmol of lithium chloride per mmol of 4-methoxybenzyl methyl ether, preferably 1.5 mmol.

[0017] Specifically, the amount of water used can be 5-35 mL of water per mmol of 4-methoxybenzyl methyl ether, preferably 25 mL.

[0018] Specifically, the organic solvent includes but is not limited to any one of acetonitrile, tetrahydrofuran, dichloroethane, dimethyl sulfoxide, 1,4-dioxane, etc., preferably 1,4-dioxane.

[0019] Specifically, the amount of the organic solvent is 5 to 35 mL, preferably 15 mL, per mmol of 4-methoxybenzyl methyl ether.

[0020] Specifically, the wavelength of the light is 340-460 nm, preferably 365 nm.

[0021] Specifically, the power of the light is 30-100W, preferably 75W.

[0022] Preferably, the reaction temperature is room temperature, generally 25±5°C, and the reaction time is 5-30h, preferably 15-25h. Optimally, the reaction time is 20h.

[0023] Compared with the prior art, the present invention has the following beneficial effects: The basic principle of the invention is that under the irradiation of light and the catalytic action of Pd / g-C3N4, the methylene group in 4-methoxybenzyl methyl ether removes a hydrogen to generate a free radical; the free radical then reacts with water to generate a hemiacetal intermediate; and the hemiacetal generates anisaldehyde product under the action of lithium chloride.

[0024] 4-methoxybenzyl methyl ether, Pd / g-C3N4 catalyst, lithium chloride, water and organic solvent were added to a reaction vessel, and the reaction vessel was sealed. Anisaldehyde product was obtained by reaction at room temperature, under inert gas protection and light conditions. The reaction formula is as follows: The obtained anisaldehyde product was quantified by gas chromatography internal standard method, and the yield was up to 96%. It was purified by column chromatography (mobile phase: a mixed solvent of petroleum ether and ethyl acetate with a volume ratio of 15:1). 13 C-NMR and 1 H-NMR confirmed the product structure as follows: .

[0025] The present invention uses 4-methoxybenzyl methyl ether as a raw material without adding any external oxidant, thereby overcoming the problems of large amount of waste and high comprehensive cost caused by using oxidants in the existing reaction method. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The anisaldehyde obtained in Example 1 1 H-NMR spectrum: δ (ppm) = 9.88 (s, 1H), 7.83 (d, J = 8.7 Hz, 2H), 7.00 (d, J = 8.8 Hz, 2H), 3.88 (s, 3H). This spectrum is consistent with the spectrum of the compound in the literature (ACSSustainable Chemistry&Engineering, 2016, Vol. 4, pp. 2333–2336); Figure 2 The anisaldehyde obtained in Example 1 13 C-NMR spectrum: δ(ppm) = 190.9, 164.7, 132.0,130.0, 114.3, 55.6. This spectrum is consistent with the spectrum of this compound in the literature (ACS Sustainable Chemistry & Engineering, 2016, Vol. 4, pp. 2333–2336). DETAILED DESCRIPTION

[0027] In order to make the technical purpose, technical scheme and beneficial effects of the present invention clearer, the technical scheme of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments. However, the embodiments are intended to explain the present invention and cannot be understood as limiting the present invention. If no specific technology or conditions are specified in the embodiments, the technology or conditions described in the literature in the field or the product instructions shall be followed. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0028] In the following examples, the raw materials used are all common commercial products that can be directly purchased or can be prepared using conventional techniques in the art.

[0029] The Pd / g-C3N4 is a palladium catalyst supported on graphite-like carbon nitride (the preparation process of Pd / g-C3N4 can be found in the literature: Nature Communications, 2022, Vol. 13, Literature Number: 6186).

[0030] Example 1 0.2mmol 4-methoxybenzyl methyl ether, 15mg Pd / g-C3N4 catalyst (palladium loading 3 wt%), 1.5mmol lithium chloride, 5mL distilled water and 3mL solvent 1,4-dioxane were added to the reaction tube. Then the air in the reaction tube was replaced with argon three times. After the reaction tube was sealed, the reaction was allowed to react for 20 hours under argon protection and illumination conditions (light power: 75W, light wavelength: 365nm). After the reaction was completed, quantitative analysis was performed using the gas chromatography internal standard method, and the yield was 96%; the anisaldehyde product was separated and purified by column chromatography (mobile phase: a mixed solvent of petroleum ether and ethyl acetate with a volume ratio of 15:1). According to the following Figure 1 shown 1 H-NMR and Figure 2 shown 13 C-NMR confirmed the structure of the product as follows: , thus identified as anisaldehyde.

[0031] Embodiment 2-7 The amount of Pd / g-C3N4 catalyst in Example 1 was changed to 5 mg, 10 mg, 15 mg, 20 mg, 25 mg, and 30 mg, respectively, and the other conditions were the same as in Example 1. The yields of anisaldehyde products were 35%, 73%, 96%, 95%, 88%, and 93%, respectively.

[0032] Examples 8-12 The catalyst palladium loading in Example 1 was changed to 1 wt%, 2 wt%, 3 wt%, 4 wt%, and 5 wt%, respectively, and the other conditions were the same as Example 1. The yields of anisaldehyde products were 65%, 76%, 96%, 81%, and 87%, respectively.

[0033] Examples 13-17 The amount of lithium chloride in Example 1 was changed to 0.5 mmol, 1 mmol, 1.5 mmol, 2 mmol, and 2.5 mmol, respectively, and the other conditions were the same as in Example 1. The yields of anisaldehyde products were 65%, 72%, 96%, 95%, and 93%, respectively.

[0034] Examples 18-24 The amount of distilled water in Example 1 was changed to 1 mL, 2 mL, 3 mL, 4 mL, 5 mL, 6 mL, and 7 mL, respectively, and the other conditions were the same as in Example 1. The yields of anisaldehyde products were 80%, 82%, 85%, 89%, 96%, 87%, and 81%, respectively.

[0035] Examples 25-28 The 1,4-dioxane in Example 1 was replaced by equal amounts of acetonitrile, tetrahydrofuran, dichloroethane, and dimethyl sulfoxide, respectively, and the other conditions were the same as in Example 1. The yields of anisaldehyde products were 39%, 90%, 24%, and 53%, respectively.

[0036] Examples 29-35 The amount of 1,4-dioxane in Example 1 was changed to 1 mL, 2 mL, 3 mL, 4 mL, 5 mL, 6 mL, and 7 mL, respectively, and the other conditions were the same as in Example 1. The yields of anisaldehyde products were 56%, 91%, 96%, 93%, 82%, 73%, and 70%, respectively.

[0037] Examples 36-39 The wavelength of the light in Example 1 was changed to 340 nm, 365 nm, 420 nm, and 460 nm, respectively, and the other conditions were the same as in Example 1. The yields of anisaldehyde products were 85%, 96%, 50%, and 34%, respectively.

[0038] Examples 40-44 The power of the light in Example 1 was changed to 30 W, 50 W, 60 W, 75 W, and 100 W, respectively, and the other conditions were the same as in Example 1. The yields of anisaldehyde products were 27%, 44%, 70%, 96%, and 95%, respectively.

[0039] Examples 45-50 The reaction time in Example 1 was changed to 5 h, 10 h, 15 h, 20 h, 25 h, and 30 h, respectively, and the other conditions were the same as in Example 1. The yields of anisaldehyde products were 45%, 65%, 78%, 96%, 93%, and 90%, respectively.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate but not limit the technical solutions of the present invention, and any equivalent substitutions of the present invention and any modifications or partial substitutions that do not depart from the spirit and scope of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for preparing anisaldehyde, characterized in that: Under an inert gas atmosphere, 4-methoxybenzyl methyl ether, Pd / g-C3N4 catalyst, lithium chloride, water and solvent are added to a reaction container. After the reaction container is sealed, the reaction is carried out under light and room temperature for 5-30 hours to obtain anisaldehyde.

2. The method for preparing anisaldehyde according to claim 1, wherein: The Pd / g-C3N4 is a palladium catalyst supported by graphite-like carbon nitride.

3. The method for preparing anisaldehyde according to claim 1, wherein: The amount of the Pd / g-C3N4 catalyst used is 25-150 mg Pd / g-C3N4 catalyst per millimole of 4-methoxybenzyl methyl ether.

4. The method for preparing anisaldehyde according to claim 1, wherein: The loading amount of metal palladium in the Pd / g-C3N4 catalyst is 1-5wt%.

5. The method for preparing anisaldehyde according to claim 1, wherein: The amount of lithium chloride used is 0.5-2.5 mmol lithium chloride per mmol of 4-methoxybenzyl methyl ether.

6. The method for preparing anisaldehyde according to claim 1, wherein: The amount of water used is 5-35 mL of water per mmol of 4-methoxybenzyl methyl ether.

7. The method for preparing anisaldehyde according to claim 1, wherein: The organic solvent is any one of acetonitrile, tetrahydrofuran, dichloroethane, dimethyl sulfoxide, and 1,4-dioxane.

8. The method for preparing anisaldehyde according to claim 1, wherein: The amount of the organic solvent used is 5-35 mL of the organic solvent per millimole of 4-methoxybenzyl methyl ether.

9. The method for preparing anisaldehyde according to claim 1, wherein: The lighting conditions are: the wavelength of light is 340~460nm, and the power of light is 30~100W.

10. The method for preparing anisaldehyde according to claim 1, characterized in that: The reaction time is 15-25h.

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