Method for synthesizing benzoic acid by oxidizing benzaldehyde

Abstract

The invention relates to a method for synthesizing benzoic acid by oxidizing benzaldehyde, which belongs to the technical field of fine organic synthesis, and can solve the defects of harsh reaction conditions, difficult catalyst separation and the like in the existing benzoic acid synthesis, an oxidation system in the invention is constructed by O3 / TEMPO / HCl, and the product benzoic acid is obtained at an excellent yield under the conditions of normal pressure and room temperature. The method has the advantages of being simple in process, mild in reaction condition, efficient, environmentally friendly and the like, and the method shows huge potential and application value in the field of benzoic acid preparation.

Description

Technical Field

[0001] The invention belongs to the technical field of fine organic synthesis, and particularly relates to a method for synthesizing benzoic acid by oxidizing benzaldehyde. Background Art

[0002] Benzoic acid, as one of the most common organic acids, is widely used in medicine, food, chemical industry, etc. Benzoic acid and its sodium salt can be used as antibacterial agents for latex, toothpaste, jam or other foods, and can also be used as mordants for dyeing and printing. Traditional methods for producing benzoic acid include phthalic anhydride hydrolysis and decarboxylation, toluene chlorination and hydrolysis, toluene liquid phase oxidation, etc. However, these methods have problems such as low production efficiency, high raw material cost, and environmental pollution. For example, heavy metal cobalt salts are mainly used as catalysts in the industry to catalytically oxidize toluene to prepare benzoic acid. Although the process is mature, it is seriously polluting, and it is urgent to develop a green and clean preparation process.

[0003] In recent years, the development of a new process for synthesizing benzoic acid using benzaldehyde as raw material has attracted widespread attention. The literature (Green synthesis of benzoic acid by oxidation of benzaldehyde with phosphotungstomolybdic acid with Dawson structure, Petrochemicals, 2020, 49(9): 836-840) reported that Dawson structure phosphotungstomolybdic acid was prepared by hydrothermal method using sodium molybdate, sodium tungstate and concentrated phosphoric acid as raw materials. The optimized conditions were: phosphotungstomolybdic acid dosage was 2.9% (w), (based on the mass of benzaldehyde), n (benzaldehyde: n (30% (w): H2O2) = 1:5, reaction temperature was 80 °C, and reaction time was 3.0 h. Although this method has a high yield, the catalyst preparation process is cumbersome and the catalyst performance is significantly reduced after being recycled for 5 times.

[0004] Patent CN201711016188.9 discloses a method for synthesizing benzoic acid using organic molecules as catalysis. This method requires thiophenone compounds as photocatalysts, which can avoid the use of a large amount of acidic solvents and cobalt acetate or manganese acetate in the traditional synthesis of benzoic acid. However, this method also has major defects, such as low light energy utilization and transmittance problems, resulting in a particularly long reaction time; in addition, the synthesis, separation, and purification process of the organic small molecule thiophenone compounds used in this method are complicated. Summary of the invention

[0005] The invention aims at the disadvantages of the existing synthesis of benzoic acid, such as harsh reaction conditions and complicated catalyst preparation, and provides a method for synthesizing benzoic acid by oxidizing benzaldehyde. The preparation method has the advantages of mild process conditions, high atom economy, high product yield, etc.

[0006] The present invention adopts the following technical solution: A method for synthesizing benzoic acid by oxidation of benzaldehyde comprises the following steps: In the first step, benzaldehyde, TEMPO (2,2,6,6-tetramethylpiperidinyl oxide), dilute hydrochloric acid and a reaction solvent are sequentially added into a reaction kettle; The second step is to adjust the pressure reducing valve of the oxygen cylinder and set the partial pressure to 0.1 MPa. After the oxygen enters the ozone generator, the gas phase concentration of ozone is controlled to be 50-100 mg / L to generate an ozone mixed gas. The gas flow rate is set to 50 L / h. The ozone mixed gas enters the micro-nano bubble generator and then enters the reactor to react with benzaldehyde in the liquid phase. The reaction liquid circulates in the micro-nano bubble generator and the reactor. The third step is to add a saturated sodium thiosulfate solution to the reaction solution after the reaction is completed, extract and separate the organic phase, or pass nitrogen into the reaction solution to blow out the residual ozone, remove the reaction solvent with a rotary evaporator, and then use column chromatography to obtain high-purity benzoic acid.

[0007] Furthermore, in the first step, the molar ratio of benzaldehyde to TEMPO is 1:(0.05-0.1).

[0008] Furthermore, the reaction solvent in the first step is ethylene dichloride, and the amount used is 500 mL.

[0009] Furthermore, the concentration of the dilute hydrochloric acid in the first step is 0.1 mol / L, and the amount used is 1-3 mL.

[0010] Furthermore, in the second step, the reaction temperature is 25° C. and the reaction time is 30 min.

[0011] Furthermore, the eluent for the column chromatography in the third step is a mixture of petroleum ether and dichloromethane in a volume ratio of 5:1.

[0012] The beneficial effects of the present invention are as follows: The invention uses benzaldehyde as a raw material, ozone as an oxidant, and adds TEMPO and dilute hydrochloric acid as additives. Under normal pressure and room temperature conditions, TEMPO first captures hydrogen atoms of benzaldehyde to generate benzoyl radicals, which then react with ozone under acidic conditions to finally oxidize benzaldehyde to synthesize benzoic acid. The method has the advantages of simple process, mild reaction conditions, high product yield, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is the equation for synthesizing benzoic acid by oxidation of benzaldehyde of the present invention; Figure 2 The present invention is a flow chart of the synthesis of benzoic acid by oxidation of benzaldehyde; Figure 3 This is a schematic diagram of a reaction device for oxidizing benzaldehyde to synthesize benzoic acid according to the present invention; Figure 4 The hydrogen spectrum of the synthesized benzoic acid of the present invention (1 H NMR); Among them: 1- oxygen cylinder; 2- gas flow meter; 3- ozone generator; 4- gas phase ozone concentration detector; 5- micro-nano bubble generator; 6- reaction bottle; 7- tail gas absorption device. DETAILED DESCRIPTION

[0014] In order to make the purpose, technical scheme and advantages of the present invention more clear, the specific embodiments of the present invention are described in detail, but are not limited thereto. The raw materials used in the embodiments are all common commercial products unless otherwise specified; the methods used are all commonly used methods in the art unless otherwise specified.

[0015] Example 1 Weigh 10 mmol and 0.5 mmol of benzaldehyde and TEMPO, respectively, dissolve in 500 mL of dichloroethane and place in a reaction flask, then add 1 mL of 0.1 mol / L dilute hydrochloric acid to the reaction flask. Adjust the ozone concentration of the ozone phase to 50 mg / L. React at room temperature and pressure for 30 minutes. After the reaction is completed, add saturated sodium thiosulfate solution to the reaction solution, extract and separate the organic phase, remove the organic solvent with a rotary evaporator, and chromatograph on a silica gel column (eluent: V 石油醚 / V 二氯甲烷 =5:1) to obtain 0.009 mol of benzoic acid with a yield of 90%.

[0016] 1 H NMR (600 MHz, CDCl3) δ 8.14 (d, J = 6 Hz, 2H), 7.62 (t, J = 6 Hz, 1H),7.49 (t, J = 6 Hz, 2H).

[0017] Example 2 Weigh 10 mmol and 0.6 mmol of benzaldehyde and TEMPO, respectively, dissolve in 500 mL of dichloroethane and place in a reaction flask, then add 1.5 mL of 0.1 mol / L dilute hydrochloric acid to the reaction flask. Adjust the ozone concentration of the ozone phase to 50 mg / L. React for 30 minutes at room temperature and normal pressure. After the reaction is completed, add saturated sodium thiosulfate solution to the reaction solution, extract and separate the organic phase, remove the organic solvent with a rotary evaporator, and chromatograph on a silica gel column (eluent: V 石油醚 / V 二氯甲烷 =5:1) to give 9.2 mmol of benzoic acid with a yield of 92%.

[0018] 1H NMR (600 MHz, CDCl3) δ 8.14 (d, J = 6 Hz, 2H), 7.62 (t, J = 6 Hz, 1H),7.49 (t, J = 6 Hz, 2H).

[0019] Example 3 Weigh 10 mmol and 1 mmol of benzaldehyde and TEMPO, respectively, dissolve in 500 mL of dichloroethane and place in a reaction flask, then add 3 mL of 0.1 mol / L dilute hydrochloric acid to the reaction flask. Adjust the ozone concentration of the ozone phase to 100 mg / L. React at room temperature and pressure for 30 minutes. After the reaction is completed, add saturated sodium thiosulfate solution to the reaction solution, extract and separate the organic phase, remove the organic solvent with a rotary evaporator, and purify it by silica gel column chromatography (eluent: V 石油醚 / V 二氯甲烷 =5:1) to give 9.6 mmol of benzoic acid with a yield of 96%.

[0020] 1 H NMR (600 MHz, CDCl3) δ 8.14 (d, J = 6 Hz, 2H), 7.62 (t, J = 6 Hz, 1H),7.49 (t, J = 6 Hz, 2H).

[0021] Example 4 Weigh 10 mmol and 0.8 mmol of benzaldehyde and TEMPO, respectively, dissolve in 500 mL of dichloroethane and place in a reaction flask, then add 2 mL of 0.1 mol / L dilute hydrochloric acid to the reaction flask. Adjust the ozone concentration of the ozone phase to 75 mg / L. React at room temperature and normal pressure for 30 minutes. After the reaction is completed, add saturated sodium thiosulfate solution to the reaction solution, extract and separate the organic phase, remove the organic solvent with a rotary evaporator, and chromatograph on a silica gel column (eluent: V 石油醚 / V 二氯甲烷 =5:1) to give 9.4 mmol of benzoic acid with a yield of 94%.

[0022] 1 H NMR (600 MHz, CDCl3) δ 8.14 (d, J = 6 Hz, 2H), 7.62 (t, J = 6 Hz, 1H),7.49 (t, J = 6 Hz, 2H).

[0023] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although detailed description is given with reference to the embodiments of the present invention, those skilled in the art should understand that modifications or equivalent substitutions of the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and should be covered by the protection scope of the claims of the present invention.

Claims

1. A method for synthesizing benzoic acid by oxidation of benzaldehyde, characterized in that: The steps include: In the first step, benzaldehyde, 2,2,6,6-tetramethylpiperidinyl oxide, dilute hydrochloric acid and a reaction solvent are sequentially added into a reaction kettle; The second step is to adjust the pressure reducing valve of the oxygen cylinder and set the partial pressure to 0.1 MPa. After the oxygen enters the ozone generator, the gas phase concentration of ozone is controlled to be 50-100 mg / L to generate an ozone mixed gas. The gas flow rate is set to 50 L / h. The ozone mixed gas enters the micro-nano bubble generator and then enters the reactor to react with benzaldehyde in the liquid phase. The reaction liquid circulates in the micro-nano bubble generator and the reactor. The third step is to add a saturated sodium thiosulfate solution to the reaction solution after the reaction is completed, extract and separate the organic phase, or pass nitrogen into the reaction solution to blow out the residual ozone, remove the reaction solvent with a rotary evaporator, and then use column chromatography to obtain high-purity benzoic acid.

2. The method for synthesizing benzoic acid by oxidation of benzaldehyde according to claim 1, characterized in that: The molar ratio of benzaldehyde to 2,2,6,6-tetramethylpiperidinyl oxide in the first step is 1:(0.05-0.1).

3. The method for synthesizing benzoic acid by oxidation of benzaldehyde according to claim 1, characterized in that: The reaction solvent in the first step is ethylene dichloride, and the amount used is 500 mL.

4. The method for synthesizing benzoic acid by oxidation of benzaldehyde according to claim 1, characterized in that: The concentration of the dilute hydrochloric acid in the first step is 0.1 mol / L, and the amount used is 1-3 mL.

5. The method for synthesizing benzoic acid by oxidation of benzaldehyde according to claim 1, characterized in that: In the second step, the reaction temperature is 25° C. and the reaction time is 30 min.

6. The method for synthesizing benzoic acid by oxidation of benzaldehyde according to claim 1, characterized in that: The eluent for the column chromatography in the third step is a mixture of petroleum ether and dichloromethane in a volume ratio of 5:1.

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