A method for the oxidation of benzaldehyde to benzoic acid

Abstract

The application discloses a method for synthesizing benzoic acid by oxidizing benzaldehyde, belongs to the technical field of fine organic synthesis, and can solve the defects of harsh reaction conditions and difficult separation of a catalyst existing in the synthesis of benzoic acid at present. An oxidation system in the application is constructed by O3 / TEMPO / HCl, and the product benzoic acid is obtained under normal pressure and at room temperature with an excellent yield. The method has the advantages of simple process, mild reaction condition, high efficiency and environmental protection, and has great potential and application value in the preparation of benzoic acid.

Description

Technical Field

[0001] This invention belongs to the field of fine organic synthesis technology, specifically relating to a method for synthesizing benzoic acid by oxidizing benzaldehyde. Background Technology

[0002] Benzoic acid, as one of the most common organic acids, has a wide range of applications in medicine, food, and chemical industries. Benzoic acid and its sodium salt can be used as antibacterial agents in latex, toothpaste, jam, and other foods, and also as mordants for dyeing and printing. Traditional methods for producing benzoic acid include phthalic anhydride hydrolysis and decarboxylation, toluene chlorination and hydrolysis, and toluene liquid-phase oxidation. However, these methods suffer from low production efficiency, high raw material costs, and environmental pollution. For example, in industry, heavy metal cobalt salts are mainly used as catalysts for the catalytic oxidation of toluene to produce benzoic acid. Although the process is mature, it causes severe pollution, necessitating the development of green and clean production processes.

[0003] In recent years, the development of a new process for synthesizing benzoic acid from benzaldehyde has attracted widespread attention. The literature (Dawson-structured phosphotungsticolaminated acid catalyzes the green synthesis of benzoic acid from benzaldehyde, Petrochemical Technology, 2020, 49(9): 836-840) reports the preparation of Dawson-structured phosphotungsticolaminated acid using a hydrothermal method with sodium molybdate, sodium tungstate, and concentrated phosphoric acid as raw materials. The optimized conditions were: phosphotungsticolaminated acid dosage of 2.9% (w) (based on benzaldehyde mass), n(benzaldehyde: n(30% (w): H2O2) = 1:5), reaction temperature of 80℃, and reaction time of 3.0 h. Although this method yields a high yield, the catalyst preparation process is cumbersome, and the catalyst performance significantly decreases after five cycles of recycling.

[0004] Patent CN201711016188.9 discloses a method for synthesizing benzoic acid using organic molecules as a photocatalyst. This method requires thiophene ketone compounds as photocatalysts, which avoids the use of large amounts of acidic solvents and cobalt acetate or manganese acetate in traditional benzoic acid synthesis. However, this method also has significant drawbacks, such as low light energy utilization and transmittance issues, resulting in a particularly long reaction time. In addition, the synthesis, separation, and purification processes of the small organic molecule thiophene ketone compounds used in this method are complex. Summary of the Invention

[0005] This invention addresses the shortcomings of existing methods for synthesizing benzoic acid, such as harsh reaction conditions and cumbersome catalyst preparation, by providing a method for synthesizing benzoic acid by the oxidation of benzaldehyde. This method has the advantages of mild process conditions, high atom economy, and high product yield.

[0006] The present invention adopts the following technical solution:

[0007] A method for synthesizing benzoic acid by oxidizing benzaldehyde includes the following steps:

[0008] The first step involves adding benzaldehyde, TEMPO (2,2,6,6-tetramethylpiperidine oxide), dilute hydrochloric acid, and the reaction solvent sequentially into the reaction vessel.

[0009] 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 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 reaction vessel to react with benzaldehyde in the liquid phase. The reaction liquid circulates in the micro-nano bubble generator and the reaction vessel.

[0010] The third step is to add a saturated sodium thiosulfate solution to the reaction solution after the reaction is complete, extract and separate the organic phase, or pass nitrogen gas 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.

[0011] Furthermore, the molar ratio of benzaldehyde to TEMPO in the first step is 1:(0.05~0.1).

[0012] Furthermore, the reaction solvent in the first step is dichloroethane, and the amount used is 500 mL.

[0013] Furthermore, the concentration of the dilute hydrochloric acid mentioned in the first step is 0.1 mol / L, and the amount used is 1~3 mL.

[0014] Furthermore, the reaction temperature in the second step is 25°C, and the reaction time is 30 min.

[0015] Furthermore, the eluent for column chromatography in the third step is a mixture of petroleum ether and dichloromethane in a volume ratio of 5:1.

[0016] The beneficial effects of this invention are as follows:

[0017] This invention uses benzaldehyde as a raw material, ozone as an oxidant, and adds TEMPO and dilute hydrochloric acid. Under normal pressure and room temperature conditions, TEMPO first abstracts a hydrogen atom from benzaldehyde to generate a benzoyl radical, which then reacts with ozone under acidic conditions to finally oxidize benzaldehyde into benzoic acid. This method has the advantages of simple process, mild reaction conditions, and high product yield. Attached Figure Description

[0018] Figure 1 This is the equation for the synthesis of benzoic acid from benzaldehyde by oxidation according to the present invention;

[0019] Figure 2 This is a flowchart of the synthesis of benzoic acid from benzaldehyde by oxidation according to the present invention;

[0020] Figure 3 This is a schematic diagram of the reaction apparatus for the oxidation of benzaldehyde to synthesize benzoic acid according to the present invention;

[0021] Figure 4 The 1H NMR spectrum of benzoic acid synthesized in this invention (…) 1 H NMR);

[0022] 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 flask; 7-Tail gas absorption device. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, specific embodiments of the invention are described in detail, but are not limited thereto. Unless otherwise specified, the raw materials used in the embodiments are all commercially available products; and unless otherwise specified, the methods used are methods commonly used in the art.

[0024] Example 1

[0025] Weigh out 10 mmol of benzaldehyde and 0.5 mmol of TEMPO, dissolve them in 500 mL of dichloroethane, and place them in a reaction flask. Then add 1 mL of 0.1 mol / L dilute hydrochloric acid to the reaction flask. Adjust the ozone concentration in the ozone gas phase to 50 mg / L. React at room temperature and atmospheric pressure for 30 min. After the reaction is complete, add saturated sodium thiosulfate solution to the reaction solution, extract and separate the organic phase, remove the organic solvent using a rotary evaporator, and then perform silica gel column chromatography (eluent: V). 石油醚 / V 二氯甲烷 The ratio of 5:1 yielded 0.009 mol of benzoic acid, with a yield of 90%.

[0026] 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).

[0027] Example 2

[0028] Weigh out 10 mmol of benzaldehyde and 0.6 mmol of TEMPO, dissolve them in 500 mL of dichloroethane, and place them 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 in the ozone gas phase to 50 mg / L. React at room temperature and atmospheric pressure for 30 min. After the reaction is complete, add saturated sodium thiosulfate solution to the reaction solution, extract and separate the organic phase, remove the organic solvent using a rotary evaporator, and then perform silica gel column chromatography (eluent: V). 石油醚 / V 二氯甲烷 The ratio of 5:1 yielded 9.2 mmol of benzoic acid, with a yield of 92%.

[0029] 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).

[0030] Example 3

[0031] Weigh out 10 mmol of benzaldehyde and 1 mmol of TEMPO, dissolve them in 500 mL of dichloroethane, and place them in a reaction flask. Then add 3 mL of 0.1 mol / L dilute hydrochloric acid to the reaction flask. Adjust the ozone concentration in the ozone gas phase to 100 mg / L. React at room temperature and atmospheric pressure for 30 min. After the reaction is complete, add saturated sodium thiosulfate solution to the reaction solution, extract and separate the organic phase, remove the organic solvent using a rotary evaporator, and then perform silica gel column chromatography (eluent: V). 石油醚 / V 二氯甲烷 The ratio of 5:1 yielded 9.6 mmol of benzoic acid, with a yield of 96%.

[0032] 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).

[0033] Example 4

[0034] Weigh out 10 mmol of benzaldehyde and 0.8 mmol of TEMPO, dissolve them in 500 mL of dichloroethane, and place them in a reaction flask. Then add 2 mL of 0.1 mol / L dilute hydrochloric acid to the reaction flask. Adjust the ozone concentration in the ozone gas phase to 75 mg / L. React at room temperature and atmospheric pressure for 30 min. After the reaction is complete, add saturated sodium thiosulfate solution to the reaction solution, extract and separate the organic phase, remove the organic solvent using a rotary evaporator, and then perform silica gel column chromatography (eluent: V). 石油醚 / V 二氯甲烷 The ratio of 5:1 yielded 9.4 mmol of benzoic acid, with a yield of 94%.

[0035] 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).

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the embodiments of the present invention have been described in detail, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of protection of the claims of the present invention.

Claims

1. A process for the oxidation of benzaldehyde to benzoic acid, characterized in that: The method comprises the following steps: In the first step, benzaldehyde, 2,2,6,6-tetramethylpiperidine oxide, dilute hydrochloric acid and a reaction solvent are sequentially added into a reaction kettle; the concentration of the dilute hydrochloric acid is 0.1 mol / L, and the amount of the dilute hydrochloric acid is 1-3 mL; In the second step, a pressure-reducing valve of an oxygen cylinder is adjusted, and the partial pressure is set to 0.1 MPa; after oxygen enters an ozone generator, the gas-phase concentration of ozone is controlled to be 50-100 mg / L, ozone mixed gas is generated, the gas flow is set to 50 L / h, the ozone mixed gas enters a micro-nano bubble generator, and then enters the reaction kettle to react with benzaldehyde in a liquid phase; the reaction liquid is circulated in the micro-nano bubble generator and the reaction kettle; the reaction temperature is 25°C, and the reaction time is 30 min; In the third step, after the reaction is completed, saturated sodium thiosulfate solution is added into the reaction liquid, organic phase is extracted and separated, or nitrogen is introduced into the reaction liquid to blow off residual ozone; after the reaction solvent is removed by a rotary evaporator, high-purity benzoic acid is obtained by column chromatography.

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

3. The process for the oxidation of benzaldehyde to benzoic acid according to claim 1, characterized in that: In the first step, the reaction solvent is dichloroethane, and the amount of the dichloroethane is 500 mL.

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

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