A method for preparing ester compounds from benzyl bromide under photocatalytic conditions

Abstract

This invention provides a method for preparing ester compounds from benzyl bromide under photocatalytic conditions. The method involves adding benzyl bromide, additives, and a manganese oxide catalyst to an acetonitrile solvent, placing the solution in a photoreactor, and reacting under blue light irradiation in an oxygen atmosphere for 12–24 hours to oxidize and break the carbon-bromine bond into the corresponding ester compounds. The system described in this invention has many advantages, including high catalyst activity, wide applicability, easy control of reaction conditions, recyclable catalyst, and simple post-processing, making it a promising candidate for application.

Description

Technical Field

[0001] This invention relates to the field of chemical engineering, and provides a method for preparing ester compounds from benzyl bromide under photocatalytic conditions. Background Technology

[0002] Organic carboxylic acid esters play a vital role in food, organic synthesis, fragrances, cosmetics, pharmaceuticals, and polymer materials. Traditional synthesis methods typically use acids and alcohols as raw materials, with the acid acting as a catalyst, to synthesize the corresponding ester products through esterification reactions under prolonged heating. The acid used as the catalyst is usually concentrated sulfuric acid, which, while highly reactive, suffers from poor selectivity, numerous side reactions, significant environmental pollution, and severe corrosion. Some literature and patents have indicated the use of other acids, such as benzenesulfonic acid and chlorosulfonic acid, as catalysts, but these also still present the aforementioned problems. With ongoing research, some literature and patents have reported the use of solid organic sulfonic acid polymers as catalysts to prepare corresponding esters, but these only target the esterification of small-molecule organic alcohols and carboxylic acids.

[0003] Other methods for ester synthesis, such as first converting carboxylic acids into highly reactive intermediates like acyl chlorides or anhydrides, and then reacting them with alcohols to generate the corresponding esters, are less economical and present storage and equipment corrosion problems. If aldehydes are used as starting materials, the preparation of esters requires three steps: oxidation, activation, and esterification. These methods typically reduce ester yields and require long reaction times. Subsequently, some literature has explored one-step synthesis of esters via the direct oxidative esterification of aldehydes. However, these methods often use excessive amounts of strong oxidants, such as activated manganese dioxide, potassium persulfate, and peroxides. While achieving some yield, these methods cause significant environmental damage and increase post-processing costs. Alternatively, esters can be synthesized in one step via the direct oxidative esterification of primary alcohols. However, this method requires catalysts with precious metals such as Au and Pd as active centers, resulting in high costs. Some catalytic systems use cobalt-based catalysts supported on carbon materials, but their application is limited. Benzyl bromides are aromatic compounds whose aromatic rings are replaced by bromomethyl groups. They can effectively benzylate various heteroatom functional groups under different conditions, thus having wide applications in organic synthesis and being used to synthesize a variety of organic chemicals. Research has revealed that under photoreaction and oxygen-rich conditions, benzyl bromides can be esterified to obtain new organic carboxylic acid esters through oxidative cleavage of the carbon-bromine bond. This route represents a new and effective way to convert and utilize benzyl bromides. Currently, there are no reported methods for the oxidation of benzyl bromides to esters under photoreaction conditions, thus this method provides a new route for the preparation of organic carboxylic acid esters. Compared to other routes, this method offers advantages such as milder reaction conditions, easier control, less environmental pollution, wider applicability, recyclable catalysts, and simple post-processing, making it highly promising for application. Summary of the Invention

[0004] This invention provides a novel method for preparing organic carboxylic acid esters. In this method, benzyl bromide is used as a substrate and oxygen is used as an oxygen source. Under the action of a catalyst and irradiation by a light source, benzyl bromide undergoes self-coupling to generate organic carboxylic acid esters.

[0005] According to the present invention, the other substituents on the benzene ring are one or more of the following: -CH3, -OCH3, -C(CH3)3, -F, -Cl, -Br, -CF3, and -NO2;

[0006] In alkynes with other substituents on the benzene ring, the positions of the substituents are ortho, meta, or para. According to this invention, environmentally friendly oxygen is used as the oxygen source. Oxygen molecules in their three states are not sufficiently reactive and require a catalyst to activate them into reactive oxygen species. This invention uses transition metal Mn oxide as a catalyst to activate oxygen molecules, achieving the oxidative cracking of benzyl bromide to prepare organic carboxylic acid esters.

[0007] According to the present invention, the catalytic performance is related to the amount of catalyst used. Too little catalyst will affect the activity of the catalytic reaction, while too much catalyst will increase the cost of the catalyst; therefore, it is necessary to select an appropriate amount. In order to ensure the activity of the catalyst while reducing the cost of the catalyst, the amount of catalyst used is 30%-150% of the mass of the benzyl bromide compound, preferably 45%-120%.

[0008] According to the present invention, the oxidation effect of benzyl bromide is related to the reaction atmosphere, the reaction light source, and the time. The reaction atmosphere is oxygen-enriched air and / or an oxygen atmosphere, preferably an oxygen atmosphere. The light source is one of visible light violet (390nm-435nm), visible light blue (435nm–490nm), or visible light green (490nm–560nm), preferably a visible light blue light source (435nm–490nm). The reaction time is 12-48 hours, preferably 16-24 hours.

[0009] According to this invention, the reaction needs to be carried out in a solvent, especially for some solid benzyl bromide substrate molecules, which need to be dissolved in a solvent to achieve uniform dispersion and facilitate contact with the catalyst. The solvent used for the oxidation of benzyl bromide is one or more of toluene, tert-amyl alcohol, 1,4-dioxane, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetonitrile, n-heptane, methanol, and ethanol.

[0010] The method for preparing the γ-MnO2 catalyst is as follows: A certain amount of manganese sulfate is weighed and then prepared into 50 ml of a manganese sulfate solution with a mass fraction of 1.00%-30.00% (preferably 10.00%-20.00%), denoted as solution A; a certain amount of potassium permanganate is weighed and then prepared into 500 ml of a potassium permanganate solution with a mass fraction of 0.50%-4.50% (preferably 2.00%-4.00%), denoted as solution B. Solution A is added dropwise to solution B under a water bath at 50-60℃. After the addition is complete, the mixture is stirred at room temperature for 1-3 hours, then allowed to stand for precipitation for 12-24 hours. The mixture is filtered, washed with deionized water until the filtrate is neutral, and dried to obtain the target catalyst γ-MnO2.

[0011] The system described in this invention has many advantages, such as high catalyst activity, wide applicability of the method, easy control of reaction conditions, recyclable catalyst, and simple post-processing, and has a promising application prospect. Detailed Implementation

[0012] The following examples illustrate the specific implementation steps of the present invention in detail. These examples should not be construed as limiting the scope of the present invention.

[0013] The method for preparing the γ-MnO2 catalyst is as follows: A certain amount of manganese sulfate is weighed and then prepared into a 50 ml solution with a mass fraction of 15.00%, denoted as solution A; a certain amount of potassium permanganate is weighed and then prepared into a 500 ml solution with a mass fraction of 3.50%, denoted as solution B. Solution A is added dropwise to solution B under a 60°C water bath. After the addition is complete, the mixture is stirred at room temperature for 2 hours, then allowed to stand for 18 hours to precipitate. The mixture is then filtered, washed with deionized water until the filtrate is neutral, and dried to obtain the target catalyst γ-MnO2.

[0014] Example 1

[0015] Preparation of benzyl benzoate by benzyl bromide under visible blue light conditions

[0016]

[0017] γ-MnO2 (40 mg), benzyl bromide (0.5 mmol), Na2CO3 (1 mmol), and 4 mL of acetonitrile were sequentially added to a 10 mL photoreaction tube. The tube was purged with oxygen three times, and then purged with oxygen at 0.6 MPa. The photoreaction tube was placed in a photoreactor, and the reaction was stirred at 500 rpm under blue light (435 nm–490 nm) for 24 h. After the reaction was completed, the reaction vessel was cooled to room temperature, the reaction vessel was opened, and naphthalene (64 mg) was added as an internal standard. The product was identified by gas chromatography-mass spectrometry, and the product yield was 20.4%.

[0018] Example 2

[0019] Preparation of benzyl benzoate by benzyl bromide under visible-violet light

[0020]

[0021] γ-MnO2 (40 mg), benzyl bromide (0.5 mmol), Na2CO3 (1 mmol), and 4 mL of acetonitrile were sequentially added to a 10 mL photoreaction tube. The tube was purged with oxygen three times, and then purged with oxygen at 0.5 MPa. The photoreaction tube was placed in a photoreactor, and the reaction was stirred at 500 rpm under ultraviolet light (390 nm-435 nm) for 24 h. After the reaction was completed, the reaction vessel was cooled to room temperature, the reaction vessel was opened, and naphthalene (64 mg) was added as an internal standard. The product was identified by gas chromatography-mass spectrometry, and the product yield was 18.1%.

[0022] Example 3

[0023] Preparation of benzyl benzoate by benzyl bromide under visible green light conditions

[0024]

[0025] γ-MnO2 (40 mg), benzyl bromide (0.5 mmol), Na2CO3 (1 mmol), and 4 mL of acetonitrile were sequentially added to a 10 mL photoreaction tube. The tube was purged with oxygen three times, and then purged with oxygen at 0.4 MPa. The photoreaction tube was placed in a photoreactor, and the reaction was stirred at 500 rpm under green light (490 nm–560 nm) for 24 h. After the reaction was completed, the reaction vessel was cooled to room temperature, the reaction vessel was opened, and naphthalene (64 mg) was added as an internal standard. The product was identified by gas chromatography-mass spectrometry, and the product yield was 10.6%.

[0026] Example 4

[0027] Preparation of benzyl benzoate by benzyl bromide under visible blue light conditions

[0028]

[0029] γ-MnO2 (40 mg), benzyl bromide (0.5 mmol), Na2CO3 (0.5 mmol), and 4 mL of acetonitrile were sequentially added to a 10 mL photoreaction tube. The tube was purged with oxygen three times, and then purged with oxygen at 0.8 MPa. The photoreaction tube was placed in a photoreactor, and the reaction was stirred at 500 rpm under blue light (435 nm–490 nm) for 24 h. After the reaction was completed, the reaction vessel was cooled to room temperature, the reaction vessel was opened, and naphthalene (64 mg) was added as an internal standard. The product was identified by gas chromatography-mass spectrometry, and the product yield was 10.2%.

[0030] Example 5

[0031] Preparation of benzyl benzoate by benzyl bromide under visible blue light conditions

[0032]

[0033] γ-MnO2 (40 mg), benzyl bromide (0.5 mmol), Na2CO3 (0.25 mmol), and 4 mL of acetonitrile were sequentially added to a 10 mL photoreaction tube. The tube was purged with oxygen three times, and then purged with oxygen at 0.6 MPa. The photoreaction tube was placed in a photoreactor, and the reaction was stirred at 500 rpm under blue light (435 nm–490 nm) for 24 h. After the reaction was completed, the reaction vessel was cooled to room temperature, the reaction vessel was opened, and naphthalene (64 mg) was added as an internal standard. The product was identified by gas chromatography-mass spectrometry, and the product yield was 5.4%.

[0034] Example 6

[0035] Preparation of benzyl benzoate by benzyl bromide under visible blue light conditions

[0036]

[0037] γ-MnO2 (20 mg), benzyl bromide (0.5 mmol), Na2CO3 (0.25 mmol), and 4 mL of acetonitrile were sequentially added to a 10 mL photoreaction tube. The tube was purged with oxygen three times, and then purged with oxygen at 0.6 MPa. The photoreaction tube was placed in a photoreactor, and the reaction was stirred at 500 rpm under blue light (435 nm–490 nm) for 24 h. After the reaction was completed, the reaction vessel was cooled to room temperature, the reaction vessel was opened, and naphthalene (64 mg) was added as an internal standard. The product was identified by gas chromatography-mass spectrometry, and the product yield was 10.8%.

[0038] Example 7

[0039] Preparation of benzyl benzoate by benzyl bromide under visible blue light conditions

[0040]

[0041] γ-MnO2 (60 mg), benzyl bromide (0.5 mmol), Na2CO3 (0.25 mmol), and 4 mL of acetonitrile were sequentially added to a 10 mL photoreaction tube. The tube was purged with oxygen three times, and then purged with oxygen at 0.6 MPa. The photoreaction tube was placed in a photoreactor, and the reaction was stirred at 500 rpm under blue light (435 nm–490 nm) for 24 h. After the reaction was completed, the reaction vessel was cooled to room temperature, the reaction vessel was opened, and naphthalene (64 mg) was added as an internal standard. The product was identified by gas chromatography-mass spectrometry, and the product yield was 14.4%.

[0042] Example 8

[0043] Preparation of benzyl benzoate by benzyl bromide under visible blue light conditions

[0044]

[0045] γ-MnO2 (80 mg), benzyl bromide (0.5 mmol), Na2CO3 (0.25 mmol), and 4 mL of acetonitrile were sequentially added to a 10 mL photoreaction tube. The tube was purged with oxygen three times, and then purged with oxygen at 0.9 MPa. The photoreaction tube was placed in the photoreactor, and the reaction was stirred at 500 rpm under blue light (435 nm–490 nm) for 24 h. After the reaction was complete, the reactor was cooled to room temperature. The reactor was then opened, and naphthalene (64 mg) was added as an internal standard. The product was identified by gas chromatography-mass spectrometry, yielding a product yield of 12.5%.

[0046] Example 9

[0047] Preparation of benzyl benzoate by benzyl bromide under visible blue light conditions

[0048]

[0049] γ-MnO2 (100 mg), benzyl bromide (0.5 mmol), Na2CO3 (0.25 mmol), and 4 mL of acetonitrile were sequentially added to a 10 mL photoreaction tube. The tube was purged with oxygen three times, and then purged with oxygen at 1.0 MPa. The photoreaction tube was placed in the photoreactor, and the reaction was stirred at 500 rpm under blue light (435 nm–490 nm) for 24 h. After the reaction was complete, the reactor was cooled to room temperature. The reactor was then opened, and naphthalene (64 mg) was added as an internal standard. The product was identified by gas chromatography-mass spectrometry, yielding a product yield of 11.2%.

[0050] Example 10

[0051] Preparation of benzyl benzoate by benzyl bromide under visible blue light conditions

[0052]

[0053] γ-MnO2 (40 mg), benzyl bromide (0.5 mmol), Na2CO3 (0.25 mmol), and 4 mL of acetonitrile were sequentially added to a 10 mL photoreaction tube. The tube was purged with oxygen three times, and then purged with oxygen at 0.6 MPa. The photoreaction tube was placed in a photoreactor, and the reaction was stirred at 500 rpm under blue light (435 nm–490 nm) for 12 h. After the reaction was complete, the reactor was cooled to room temperature, and the internal standard naphthalene (64 mg) was added. The product was identified by gas chromatography-mass spectrometry, yielding a product yield of 10.3%.

[0054] Example 11

[0055] Preparation of benzyl benzoate by benzyl bromide under visible blue light conditions

[0056]

[0057] γ-MnO2 (40 mg), benzyl bromide (0.5 mmol), Na2CO3 (0.25 mmol), and 4 mL of acetonitrile were sequentially added to a 10 mL photoreaction tube. The tube was purged with oxygen three times, and then purged with oxygen at 0.6 MPa. The photoreaction tube was placed in the photoreactor, and the reaction was stirred at 500 rpm under blue light (435 nm–490 nm) for 16 h. After the reaction was complete, the reactor was cooled to room temperature. The reactor was then opened, and naphthalene (64 mg) was added as an internal standard. The product was identified by gas chromatography-mass spectrometry, yielding a product yield of 13.3%.

[0058] Example 12

[0059] Preparation of benzyl benzoate by benzyl bromide under visible blue light conditions

[0060]

[0061] γ-MnO2 (40 mg), benzyl bromide (0.5 mmol), Na2CO3 (0.25 mmol), and 4 mL of acetonitrile were sequentially added to a 10 mL photoreaction tube. The tube was purged with oxygen three times, and then purged with oxygen at 0.6 MPa. The photoreaction tube was placed in a photoreactor, and the reaction was stirred at 500 rpm under blue light (435 nm–490 nm) for 36 h. After the reaction was complete, the reactor was cooled to room temperature. The reactor was then opened, and naphthalene (64 mg) was added as an internal standard. The product was identified by gas chromatography-mass spectrometry, yielding a product yield of 20.8%.

[0062] Example 13

[0063] Preparation of benzyl benzoate by benzyl bromide under visible blue light conditions

[0064]

[0065] γ-MnO2 (40 mg), benzyl bromide (0.5 mmol), Na2CO3 (0.25 mmol), and 4 mL of acetonitrile were sequentially added to a 10 mL photoreaction tube. The tube was purged with oxygen three times, and then purged with oxygen at 0.6 MPa. The photoreaction tube was placed in a photoreactor, and the reaction was stirred at 500 rpm under blue light (435 nm–490 nm) for 48 h. After the reaction was completed, the reaction vessel was cooled to room temperature, the reaction vessel was opened, and naphthalene (64 mg) was added as an internal standard. The product was identified by gas chromatography-mass spectrometry, and the product yield was 21.4%.

[0066] This invention features high oxidation efficiency, good selectivity, and high product yield; using oxygen as the oxygen source is economical and environmentally friendly, and has excellent application prospects.

[0067] The above embodiments are part of the implementation process of the present invention, but the implementation of the present invention is not limited to the above embodiments. Any changes, substitutions, combinations, or simplifications made in violation of the spirit and principle of the present invention shall be equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing ester compounds from benzyl bromide under photocatalytic conditions, characterized in that: Benzyl bromide compounds, additives, and γ-MnO2 catalysts are added to acetonitrile solvent and placed in a sealed photoreactor. Under an oxygen-enriched atmosphere and light irradiation, the reaction proceeds for 12–48 hours, during which benzyl bromide undergoes self-coupling to generate corresponding ester compounds. The additives are basic inorganic compounds, including one or more of potassium hydroxide, potassium carbonate, sodium carbonate, cesium carbonate, and potassium phosphate. The general structural formula of the benzyl bromide compounds is shown below: ； The substituent -R is one of H, -CH3, -OCH3, -C(CH3)3, -F, -Cl, -Br, -CF3, -NO2, and the position of the substituent -R is ortho, meta, or para.

2. The method for preparing ester compounds from benzyl bromide under photocatalytic conditions according to claim 1, characterized in that: The amount of catalyst used is 30%-150% of the mass of the benzyl bromide compound.

3. The method for preparing ester compounds from benzyl bromide under photocatalytic conditions according to claim 2, characterized in that, The amount of catalyst used is 45%-120% of the mass of the benzyl bromide compound.

4. The method for preparing ester compounds from benzyl bromide under photocatalytic conditions according to claim 1, characterized in that, The amount of the additive used is 100 mol%-500 mol% of benzyl bromide compounds.

5. The method for preparing ester compounds from benzyl bromide under photocatalytic conditions according to claim 4, characterized in that, The amount of the additive used is 150 mol%-300 mol% of benzyl bromide compounds.

6. The method for preparing ester compounds from benzyl bromide under photocatalytic conditions according to claim 1, characterized in that, The acetonitrile solvent is an anhydrous solvent.

7. The method for preparing ester compounds from benzyl bromide under photocatalytic conditions according to claim 1, characterized in that, The light source is one or more of the following: visible light violet, visible light blue, and visible light green.

8. The method for preparing ester compounds from benzyl bromide under photocatalytic conditions according to claim 1, characterized in that, The gas atmosphere is an oxygen-rich atmosphere with an oxygen volume concentration of 80%-100% and a pressure of 0.2-2 MPa.

9. The method for preparing ester compounds from benzyl bromide under photocatalytic conditions according to claim 1, characterized in that: The reaction time is 12-24 hours.

10. The method for preparing ester compounds from benzyl bromide under photocatalytic conditions according to claim 9, characterized in that: The reaction time is 16-18 hours.

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