Method for preparing ester compound by oxidizing benzyl bromide compound

Abstract

The invention provides a method for preparing ester compounds by oxidizing and breaking carbon-bromine bonds (C-Br) of benzyl bromide compounds. The method comprises the following steps: adding a benzyl bromide compound, an additive and a cobalt-doped manganese oxide catalyst into an acetonitrile solvent, sealing in a pressure container, introducing 1.0 MPa oxygen source gas, and reacting at 120-170 DEG C for 4-12 hours, so as to oxidize and break a carbon-bromine bond into a corresponding ester compound. The system has the advantages that the catalyst activity is high, the method is wide in application range, reaction conditions are easy to control, the catalyst can be recycled, post-treatment is simple and the like, and the system has a good application prospect.

Description

Technical Field

[0001] The invention relates to the field of chemistry and chemical engineering, and is a method for preparing ester compounds by oxidizing benzyl bromide compounds. Background Art

[0002] Organic carboxylic acid esters are a very important class of chemical products and organic synthesis intermediates, which are widely used in the fields of food, organic synthesis, coatings, fragrances, cosmetics, medicine and polymer materials. Therefore, esterification reaction is an important organic chemical reaction as a general way to prepare ester substances. Benzyl bromide compounds are an important class of organic compounds that can be transformed and synthesized into a variety of organic chemicals. The esterification of benzyl bromide compounds through oxidative cleavage of the carbon-bromine bond to obtain organic carboxylic acid esters is an effective way to transform and utilize benzyl bromide compounds.

[0003] The traditional synthesis method of organic carboxylic acid esters is generally to use acid and alcohol as raw materials, concentrated sulfuric acid as catalyst, long-term heating, and direct esterification synthesis. Although concentrated sulfuric acid as a catalyst has high activity, it also has many disadvantages: poor selectivity, many side reactions, poor product purity, and strong acid causes serious environmental pollution and equipment corrosion. The subsequent mild ester synthesis method generally first makes carboxylic acid into highly active acyl chloride or anhydride, and then reacts with alcohol to form the corresponding ester. If these methods use aldehyde as the starting material to prepare esters first, they need to go through three steps of oxidation, activation and esterification. These methods usually reduce the yield of esters and require a long reaction time. Subsequently, further efforts have been devoted to the direct oxidation and esterification of aldehydes to synthesize esters in one step, but such methods often use stoichiometric or excessive oxidants, such as manganese dioxide, potassium persulfate, and peroxide. Although these methods are useful, a large number of toxic and useless byproducts are generated, and the aldehydes used as substrates are usually oxidized from alcohols. Another method for preparing carboxylic acid esters is the direct oxidative esterification of primary alcohols to synthesize esters in one step. However, the catalysts used in this method are mainly precious metals Au and Pd, and some catalytic systems use cobalt-based catalysts supported by carbon materials.

[0004] At present, there is no report on the route of preparing ester compounds from a benzyl bromide compound by oxidation in multiple systems. This method not only provides a way to prepare organic carboxylic acid esters, but also provides a way to convert and utilize benzyl bromide compounds. Summary of the invention

[0005] The invention provides a novel method for preparing an organic carboxylic acid ester. In the method, benzyl bromide is used as a substrate and oxygen is used as an oxygen source. Under the action of a catalyst and an additive, benzyl bromide undergoes self-coupling or cross-coupling with an aliphatic bromide to generate an organic carboxylic acid ester.

[0006] According to the present invention, the other substituents on the benzene ring are one or more of -CH3, -OCH3, -C(CH3)3, -F, -Cl, -Br, -CF3, -NO2;

[0007] In alkynes with other substituents on the benzene ring, the positions of the other substituents are ortho, meta or para; according to the present invention, environmentally friendly oxygen is used as the oxygen source. The three forms of oxygen molecules are not active enough, and a catalyst is needed to activate oxygen to form active oxygen. The present invention uses one or more of the oxides or metal salts of transition metals such as Fe, Co, Mn, Cu, etc. as catalysts to activate oxygen molecules, achieve oxidative cleavage of benzyl bromide, and prepare organic carboxylic acid esters.

[0008] According to the present invention, the catalytic performance is related to the amount of the catalyst used. Too low an amount will affect the activity of the catalytic reaction, and too high an amount will increase the cost of the catalyst; therefore, an appropriate amount needs to be selected. In order to ensure the activity of the catalyst while reducing the cost of the catalyst, the molar ratio of the catalyst used to the benzyl bromide compound is preferably 20-40 mg.

[0009] According to the present invention, the benzyl bromide oxidation effect is related to the oxygen pressure, reaction temperature and time, wherein the oxygen partial pressure is 0.2-1MPa, the reaction temperature is 140-170°C, and the reaction time is 1-30h; preferably, the oxygen partial pressure is 0.5-1MPa, the reaction temperature is 150-160°C, and the reaction time is 4-12h.

[0010] According to the present 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 be evenly dispersed, which is conducive to contact with the catalyst. The solvent used for benzyl bromide oxidation is one or more of toluene, N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetonitrile, n-heptane, methanol, and ethanol.

[0011] The system of the present invention has many advantages such as high catalyst activity, wide application range of the method, easy control of reaction conditions, recyclable catalyst, simple post-treatment, etc., and has good application prospects. DETAILED DESCRIPTION

[0012] The following examples will help to understand the present invention, but the present invention is not limited thereto.

[0013] The preparation method of the cobalt-doped manganese oxide catalyst is as follows:

[0014] Example 1

[0015] Catalyst preparation: Weigh 15.1001 g of manganese sulfate, add it to 50 ml of water, stir at room temperature to obtain solution A; weigh 15.8030 g of potassium permanganate, add it to 500 ml of water, stir at room temperature to obtain solution B: then weigh 0.1679 g of cobalt sulfate, add it to 10 ml of water, stir at room temperature to obtain solution C, add solution A dropwise to solution B at a rate of, the mixture is stirred at room temperature for 0.5-3 hours, then solution C is added dropwise to solution B at a rate of, then condensed and refluxed at 120°C for 24 hours, cooled to room temperature, filtered, washed with deionized water until neutral, and finally dried at 100°C for 18 hours to obtain the target catalyst Co-OMS-2; the mass fraction of Co element is 3%.

[0016] Co-OMS-2 (5 mol% relative to the raw material, in terms of moles of Co), benzyl bromide (0.5 mmol), Na2CO3 (1 mmol), and 2 mL of acetonitrile were added to a 10 mL reaction bottle in sequence, and then transferred to a stainless steel autoclave, filled with oxygen pressure to 0.5 MPa, and placed in a 150°C oil bath, stirred at 500 rpm for 4 hours. After the reaction, the autoclave was cooled to room temperature, opened, and internal standard naphthalene (64 mg) was added. The qualitative product was detected by gas chromatography-mass spectrometry, and the conversion rate of substrate benzyl bromide and the yield of product benzyl benzoate were quantified by gas chromatography internal standard method.

[0017] Comparative Examples 1-10

[0018] The operating steps and conditions are the same as those in Example 1, but the reaction conditions are changed. The specific differences are: in Example 1, the temperature is reduced to 130°C; in Example 2, the amount of the catalyst is reduced to 10 mg; in Examples 3-5, the types of catalysts are changed to KMnO4, Mn2O3, and MnO2, respectively; in Example 6, cobalt sulfate is not added when preparing the catalyst, and the catalyst is recorded as OMS-2 and thrown into the reaction; in Examples 7-8, equal amounts of chromium sulfate and ferrous sulfate are added when preparing the catalyst instead of cobalt sulfate, and the catalysts are recorded as Cr-OMS-2 and Fe-OMS-2, respectively, and thrown into the reaction; in Examples 9-10, the reaction solvents are changed to tert-amyl alcohol and dioxane, respectively, and the reaction time is extended to 24 h.

[0019] Embodiment 2-5

[0020] The operation steps are the same as those in Example 1, but the reaction conditions are changed. In Example 2, the oxygen pressure is adjusted to 0.4 MPa, the additive is changed to NaHCO3, and the reaction time is extended to 12 h; in Example 3, the amount of the additive is reduced to 20 mg, the additive is changed to Cs2CO3, and the reaction time is extended to 12 h; in Example 4, the amount of the additive is reduced to 20 mg, and the reaction time is extended to 12 h; in Example 5, the amount of the additive is reduced to 20 mg, the additive is changed to K2CO3, and the reaction time is extended to 12 h.

[0021] The results of Comparative Examples 1-8 and Examples 1-5 are shown in Table 1.

[0022] Table 1 Preparation of benzyl benzoate by oxidation of benzyl bromide

[0023]

[0024] The amount of catalyst refers to the mol% of the raw material based on the metal; OMS-2 means that it has the same mass as metal-OMS-2;

[0025] Example 6-28

[0026] Except for the different substrates, the operation steps are the same as those in Example 1. The reaction conditions and catalytic reaction results are shown in Tables 2 and 3. All brominated benzyl substrates can undergo oxidative cleavage to generate corresponding organic carboxylic acid ester compounds.

[0027] Table 2 Self-coupling of bromobenzyl substrate

[0028]

[0029]

[0030] Table 3 Cross-coupling of brominated benzyl substrates

[0031]

[0032]

[0033] The invention has high oxidation efficiency, good selectivity and high product yield; it uses oxygen as an oxygen source, is economical and environmentally friendly, and has good application prospects.

[0034] The above embodiments are partial implementation processes of the present invention, but the implementation methods of the present invention are not limited to the above embodiments. Any other changes, substitutions, combinations, and simplifications that violate the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. The method for preparing ester compounds by oxidizing and breaking carbon of benzyl bromide compounds is characterized in that: A benzyl bromide compound, or a benzyl bromide compound and an aliphatic bromide, an additive and a cobalt-doped manganese oxide catalyst are added to acetonitrile; the mixture is placed in a sealed pressure vessel, an oxygen source gas (air and / or oxygen) of 0.1-1.0 MPa is introduced, and the mixture is reacted at 80-150° C. for 6-30 hours, so that a carbon-bromine bond (C-Br) can be oxidatively broken into a corresponding ester compound.

2. The method for preparing ester compounds by oxidative cleavage of carbon-bromine bonds of benzyl bromide compounds according to claim 1, characterized in that: The preparation method of the cobalt-doped manganese oxide catalyst is as follows: weigh manganese sulfate, add it to 50 ml of water, stir at room temperature, and obtain a manganese sulfate solution with a mass fraction of 5.00%-37.50% (preferably 10.00%-25.00%), which is recorded as solution A; weigh potassium permanganate, add it to 500 ml of water, stir at room temperature, and obtain a potassium permanganate solution with a mass fraction of 0.10%-5.00% (preferably 1.00%-3.00%), which is recorded as solution B; weigh cobalt sulfate, add it to 10 ml of water, stir at room temperature, and obtain a mass fraction of It is a 0.09%-23.67% cobalt sulfate solution (preferably 0.63%-17.13%), recorded as solution C, solution A is added dropwise to solution B, the mixture is stirred at room temperature for 0.5-3 hours, and then solution C is added dropwise to solution B at a rate, and then condensed and refluxed at 90-120°C for 12-48h, cooled to room temperature, filtered and washed with deionized water to neutrality, and finally dried at 60-100°C for 18-36h to obtain the target catalyst Co-OMS-2; wherein the mass fraction of Co element is 0.5%-6%.

3. The method for preparing ester compounds by oxidative cleavage of carbon-bromine bonds of benzyl bromide compounds according to claim 1, characterized in that: Based on the molar number of Co, the amount of the catalyst used is 0.1 mol%-10 mol%, preferably 1 mol%-8 mol%, of the benzyl bromide compound.

4. The method for preparing ester compounds by oxidative cleavage of carbon-bromine bonds of bromine compounds according to claim 1, characterized in that: The additive is 20mol%-500mol%, preferably 50mol%-300mol% of the benzyl bromide compound.

5. The method for preparing ester compounds by oxidative cleavage of carbon-bromine bonds of bromine compounds according to claim 1 or 4, characterized in that: The additive is an alkaline inorganic compound, including one or more of potassium hydroxide, potassium carbonate, sodium carbonate, cesium carbonate and potassium phosphate.

6. The method for preparing ester compounds by oxidative cleavage of carbon-bromine bonds of bromine compounds according to claim 1, characterized in that: The reaction temperature is 80-150° C., preferably 120-150° C.; the gas pressure is 0.1-1 MPa, preferably 0.5 MPa; and the reaction time is 2-30 h, preferably 4-12 h.

7. The method for preparing ester compounds by oxidative cleavage of carbon-bromine bonds of benzyl bromide compounds according to claim 1 or 2, characterized in that: The general structural formula of the benzyl bromide compound is as follows The substituent -R can be one or more of -CH3, -OCH3, -C(CH3)3, -F, -Cl, -Br, -CF3, -NO2, and the number can be 1-5. The position of the substituent is ortho, meta or para; or the benzene ring in the structural formula can be replaced by a naphthalene ring, a pyridine ring, a furan ring or a thiophene ring.

8. The method for preparing ester compounds by oxidative cleavage of carbon-bromine bonds of benzyl bromide compounds according to claim 1 or 2, characterized in that: Aliphatic bromides are C1-C20 alkyl groups containing 1 or 2 bromines.

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