A method for continuously producing 2-anthracene carboxylic acid

Abstract

The present application relates to a kind of continuous preparation 2-anthracene formic acid method, comprising: (1) 2-vinylanthracene is dissolved in organic solvent, and is prepared into homogeneous solution;(2) the homogeneous solution obtained in step (1) is mixed with oxygen, and forms gas-liquid mixture;(3) the gas-liquid mixture obtained in step (2) is continuously passed into tubular reactor, and reaction is carried out;Reaction temperature 150~190 ℃, reaction pressure 0.5~2.0 MPa, reaction time 1~15 min;(4) the reaction mixture flowing from tubular reactor is collected, and is obtained after cooling, separation and purification, 2-anthracene formic acid.The present application can shorten the reaction time to several minutes, the yield and purity of target product are high, suitable for large-scale industrial production;Realize automation, continuous operation, process is stable, operation window is wide, easy to enlarge and control;Without any external catalyst and additive, use oxygen as oxidant, atomic economy is high, environment-friendly.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, and specifically relates to a method for the continuous preparation of 2-anthracarboxylic acid. Background Technology

[0002] Carboxylic acids are an important class of chemical raw materials and organic synthesis intermediates, widely used in pharmaceuticals, pesticides, materials, and other fields. The selective oxidative cracking of alkenes to prepare carboxylic acids is one of the important synthetic routes. Among them, 2-anthracarboxylic acid is an important anthraquinone aromatic carboxylic acid and an indispensable key raw material in organic synthesis, pharmaceuticals, and optoelectronic materials; developing an efficient, low-cost, and environmentally friendly method for preparing 2-anthracarboxylic acid is of great significance. In functional group transformation, the direct conversion of alkenes into carboxylic acids is one of the methods for preparing acid compounds.

[0003] Currently, there are many methods for achieving oxidative cracking of olefins, with commonly used oxidants including hydrogen peroxide, ozone, tert-butyl hydroperoxide (TBHP), ruthenium tetroxide (RuO4), osmium tetroxide (OsO4), and m-chloroperoxybenzoic acid (m-CPBA). However, these methods often have some drawbacks, such as: using stoichiometric oxidants generates a large amount of waste; oxidants such as ozone and hydrogen peroxide pose safety hazards under certain conditions; and metal-based oxidants (such as Ru and Os) are expensive, toxic, and environmentally unfriendly. Molecular oxygen, due to its abundant reserves, low price, environmental friendliness, and the fact that its reaction byproduct is water, is considered an ideal green oxidant to replace traditional oxidants.

[0004] In recent years, Jinhua Ou et al. reported a general method for the oxidative cracking of a series of olefins into carboxylic acids using oxygen as the oxidant under conditions without external initiators, catalysts, and additives (J. Org. Chem. 2021, 86, 14974-14982). This method provides a new approach for green oxidation. However, when applied to the oxidation of 2-vinylanthracene, significant drawbacks remain: First, in large-scale industrial production, the reaction time is as long as 8–16 hours, resulting in low production efficiency; second, the anthracene ring structure has a large conjugated system and high reactivity, and under prolonged heating conditions, 2-vinylanthracene is prone to side reactions such as self-polymerization or over-oxidation, leading to a decrease in the yield of the target product and limiting its application in industrial production.

[0005] To address the problems of long reaction time, easy substrate polymerization, low production efficiency, and difficulty in continuous production in the existing technologies, this invention provides an innovative solution. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a method for the continuous preparation of 2-anthracarboxylic acid suitable for industrial production. This method employs a continuous tubular reactor, using oxygen as an oxidant in a specific high-boiling-point ether solvent under high-temperature, short-time conditions, without the addition of any catalyst, to rapidly and selectively oxidize 2-vinylanthracene to 2-anthracarboxylic acid.

[0007] The technical solution adopted in this invention is as follows: A method for the continuous preparation of 2-anthracarboxylic acid includes the following steps: (1) Dissolve 2-vinylanthracene in an organic solvent to prepare a homogeneous solution; (2) Mix the homogeneous solution obtained in step (1) with oxygen to form a gas-liquid mixture; (3) The gas-liquid mixture obtained in step (2) is continuously fed into a tubular reactor for reaction; the reaction temperature is 150-190℃, the reaction pressure is 0.5-2.0 MPa, and the reaction time is 1-15 min. (4) Collect the reaction mixture flowing out of the tubular reactor, cool it, separate and purify it to obtain 2-anthracarboxylic acid.

[0008] This invention employs a tubular reactor, enabling continuous production. Compared to existing technologies (reaction time > 8 hours), this invention shortens the reaction time to 1–15 minutes. The extremely short reaction time effectively suppresses side reactions such as the self-polymerization of 2-vinylanthracene at high temperatures, significantly improving reaction selectivity and production efficiency.

[0009] This invention raises the reaction temperature to 150–190°C, precisely controlling the residence time of the gas-liquid mixture in the tubular reactor to 1–15 minutes (preferably 2–10 minutes). The high temperature significantly accelerates the reaction rate, while the short reaction time avoids further decomposition of the product or the occurrence of side reactions. The oxygen pressure is controlled at 0.5–2.0 MPa to ensure effective gas-liquid mixing and a sufficient oxygen source. Without the addition of any catalyst, 2-vinylanthracene can be rapidly and selectively oxidized to 2-anthracarboxylic acid.

[0010] The reaction process is as follows: Preferably, in step (1), the organic solvent is one of 1,2-di(2-chloroethoxy)ethane, 1,2-di-tert-butoxyethane, or ethylene glycol dibutyl ether. High-boiling-point ethers such as 1,2-di(2-chloroethoxy)ethane, 1,2-di-tert-butoxyethane, or ethylene glycol dibutyl ether are chosen as solvents because they not only have good solubility for oxygen, promoting the oxidation reaction, but more importantly, their high boiling point makes them suitable for high-temperature reaction systems of 150–190°C, ensuring the stable conduct of the reaction in the liquid phase.

[0011] Preferably, in step (1), the amount of organic solvent used is 2 to 10 times the molar amount of 2-vinylanthracene, expressed in mL / mmol.

[0012] Preferably, the amount of organic solvent used is 3 to 5 times the molar amount of 2-vinylanthracene.

[0013] Preferably, in step (2), the homogeneous solution is mixed with oxygen at a flow rate of 2 to 10 mL / min.

[0014] Preferably, the molar equivalent ratio of oxygen to 2-vinylanthracene is 10 to 200:1.

[0015] Preferably, in step (3), the reaction time is 2 to 10 minutes.

[0016] Preferably, the tubular reactor is heated and its temperature is controlled by a heating furnace.

[0017] Preferably, the tubular reactor is made of stainless steel or Hastelloy.

[0018] Preferably, in step (4), the separation and purification are carried out by: concentrating the cooled reaction mixture under reduced pressure, recovering the solvent, and purifying the residue by recrystallization or column chromatography.

[0019] The beneficial effects of this invention are as follows: (1) High efficiency and speed: The reaction time is shortened from more than ten hours in traditional processes to a few minutes, with extremely high time and space yield, making it suitable for large-scale industrial production.

[0020] (2) Suppressing side reactions: By using high temperature and short time reaction, the self-polymerization and excessive oxidation of 2-vinyl anthracene are effectively avoided, and the yield and purity of the target product are improved.

[0021] (3) Continuous production: The use of tubular reactors enables automated and continuous operation, with stable process, wide operating window, and easy scale-up and control.

[0022] (4) Green and environmentally friendly: It does not require any external catalysts or additives, uses oxygen as an oxidant, has high atom economy, and is environmentally friendly. Attached Figure Description

[0023] Figure 1 This is the 1H NMR spectrum of 2-anthracarboxylic acid prepared in Example 1 of this invention; Figure 2 This is the carbon NMR spectrum of 2-anthracarboxylic acid prepared in Example 1 of this invention. Detailed Implementation

[0024] The technical solution of the present invention will be further described in detail below through embodiments. These embodiments are illustrative of the present invention and not intended to limit the present invention. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] Unless otherwise specified, the experimental methods described in the embodiments are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0026] Example 1 2-Vinylanthracene (20.4 g, 0.1 mol) was dissolved in 300 mL of 1,2-bis(2-chloroethoxy)ethane to prepare a homogeneous solution. This solution was mixed in a mixer with oxygen from an oxygen cylinder (pressure set at 1.0 MPa, oxygen flow rate controlled by a gas mass flow meter, molar equivalent ratio of oxygen to 2-vinylanthracene approximately 100:1) at a flow rate of 5 mL / min using a high-pressure constant flow pump. The resulting gas-liquid mixture was fed into a 50 mL stainless steel tubular reactor with an inner diameter of 3 mm, placed in a furnace at a temperature of 175 °C. The residence time of the material in the reactor was approximately 10 minutes. The reaction mixture exiting the reactor was cooled by water and then collected in a collection tank. The collected reaction liquid was concentrated under reduced pressure to recover the solvent. The residue was recrystallized from cyclohexane to obtain 21.1 g of yellow crystalline 2-anthracarboxylic acid, with a yield of 95% and a purity of 99.3%. Melting point: 283-285 °C. 1 H NMR (400 MHz, DMSO- d6 ): 8.82 (2H, s), 8.66 (1H, s), 8.16-8.13 (3H, m), 7.96-7.94 (1H, dd), 7.63-7.56(2H, m), 3.37(1H, s). 13 C NMR (100MHz, DMSO- d6): 166.7, 131.6, 131.2, 130.8, 130.7, 129.1, 127.7, 127.6, 127.4,127.2, 126.8, 125.8, 125.2, 123.3. HREI: calcd for (C 15 H 10 O2), 222.0681; found, 222.0685.

[0027] Example 2 2-Vinylanthracene (20.4 g, 0.1 mol) was dissolved in ethylene glycol dibutyl ether (400 mL) to prepare a homogeneous solution. This solution was mixed with oxygen (pressure set at 1.5 MPa, molar ratio of oxygen to 2-vinylanthracene approximately 150:1) in a mixer using a high-pressure constant flow pump at a flow rate of 10 mL / min. The resulting gas-liquid mixture was fed into a Hastelloy tubular reactor with an inner diameter of 4 mm and a volume of 40 mL, placed in a furnace with a temperature control of 185 °C. The residence time of the material in the reactor was approximately 4 minutes. The reaction mixture exiting the reactor outlet was collected after cooling. The reaction solution was concentrated under reduced pressure, and the residue was recrystallized from n-hexane to give 20.9 g of yellow crystalline 2-anthracarboxylic acid, with a yield of 94.1% and a purity of 99.4%.

[0028] Example 3 2-Vinylanthracene (20.4 g, 0.1 mol) was dissolved in 500 mL of 1,2-di-tert-butoxyethane to prepare a homogeneous solution. This solution was mixed with oxygen (pressure set at 1.2 MPa, molar ratio of oxygen to 2-vinylanthracene approximately 120:1) in a mixer using a high-pressure constant-flow pump at a flow rate of 8 mL / min. The resulting gas-liquid mixture was fed into a 40 mL stainless steel tubular reactor with an inner diameter of 3 mm, placed in a furnace at a controlled temperature of 165 °C. The residence time of the material in the reactor was approximately 5 minutes. The reaction mixture exiting the reactor was collected after cooling. The reaction solution was concentrated under reduced pressure, and the residue was recrystallized from toluene to give 20.7 g of yellow crystalline 2-anthracarboxylic acid, with a yield of 93.2% and a purity of 99.3%.

[0029] Comparative Example 1 Using a batch process, 100℃ In a 250 mL reaction flask, 10.2 g (0.05 mol) of 2-vinylanthracene and 150 mL of 1,2-dibutoxyethane were added. An oxygen bulb was attached to replace the gas with oxygen. The reaction flask was placed in an oil bath at 100 °C and stirred for 12 hours. After the reaction was completed, the mixture was cooled, concentrated, and the residue was recrystallized from cyclohexane to give 7.7 g of yellow crystalline 2-anthracarboxylic acid, with a yield of 69.4% and a purity of 98.5%.

[0030] Comparative Example 2 Using a batch reactor process, 110℃ In a 250 mL reaction flask, 10.2 g (0.05 mol) of 2-vinylanthracene and 150 mL of 1,2-dibutoxyethane were added. An oxygen bulb was attached to replace the gas with oxygen. The reaction flask was placed in an oil bath at 110 °C and stirred for 12 hours. After the reaction was completed, the mixture was cooled, concentrated, and the residue was recrystallized from n-hexane to give 7.9 g of yellow crystalline 2-anthracarboxylic acid, with a yield of 71.2% and a purity of 98.7%.

[0031] Comparative Example 3 Using a batch reactor process, 120℃ In a 250 mL reaction flask, 10.2 g (0.05 mol) of 2-vinylanthracene and 150 mL of 1,2-dibutoxyethane were added. An oxygen bulb was attached to replace the gas with oxygen. The reaction flask was placed in an oil bath at 120 °C and stirred for 12 hours. After the reaction was completed, the mixture was cooled, concentrated, and the residue was recrystallized from toluene to give 8.1 g of yellow crystalline 2-anthracarboxylic acid, with a yield of 73.0% and a purity of 98.3%.

[0032] Comparative Example 4 Using a batch reactor process, 170℃ In a 250 mL reaction flask, 10.2 g (0.05 mol) of 2-vinylanthracene and 150 mL of 1,2-dibutoxyethane were added. An oxygen bulb was attached to replace the gas with oxygen. The reaction flask was placed in an oil bath at 170 °C and stirred for 12 hours. After the reaction was completed, the mixture was cooled, concentrated, and the residue was recrystallized from toluene to give 6.9 g of yellow crystalline 2-anthracarboxylic acid, with a yield of 62.2% and a purity of 98.1%.

[0033] As can be seen from the above comparative examples, when using a batch reactor process, the reaction yield slightly increases (69%–73%) as the reaction temperature increases from 100℃ to 120℃. However, when the temperature is further increased to 170℃, the yield decreases to 62% due to the significant aggravation of side reactions such as substrate self-polymerization caused by prolonged heating. This indicates that the batch reactor process is limited by the excessively long reaction time and cannot effectively improve the yield by simply increasing the temperature.

[0034] In contrast, Examples 1-3 of the present invention employ a continuous process, shortening the reaction time to 4-10 minutes and conducting the reaction at a high temperature of 150-190°C, which not only avoids the self-polymerization side reaction of the substrate but also achieves a significantly higher yield of 93%-95%.

[0035] Finally, it should be noted that the above examples are merely some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for the continuous preparation of 2-anthracarboxylic acid, characterized in that, Includes the following steps: (1) Dissolve 2-vinylanthracene in a high-boiling-point ether organic solvent to prepare a homogeneous solution; the high-boiling-point ether organic solvent is one of 1,2-bis(2-chloroethoxy)ethane, 1,2-di-tert-butoxyethane or ethylene glycol dibutyl ether; the amount of organic solvent used is 2 to 10 times the molar amount of 2-vinylanthracene; (2) The homogeneous solution obtained in step (1) is delivered to the mixer at a flow rate of 2 to 10 mL / min by a high-pressure constant flow pump. Oxygen is continuously introduced into the mixer after the flow rate is controlled by a gas mass flow meter. The homogeneous solution and oxygen are mixed in the mixer to form a gas-liquid mixture. The molar equivalent ratio of oxygen to 2-vinyl anthracene is 10 to 200:

1. (3) The gas-liquid mixture obtained in step (2) is continuously fed into a tubular reactor for reaction; the reaction temperature is 165-185℃, the reaction pressure is 0.5-2.0 MPa, and the reaction time is 4-10 min. (4) Collect the reaction mixture flowing out of the tubular reactor, cool it, concentrate it under reduced pressure to recover the solvent, recrystallize it or separate and purify it by column chromatography to obtain 2-anthracarboxylic acid.

2. The method for continuous preparation of 2-anthracarboxylic acid according to claim 1, characterized in that, The amount of organic solvent used is 3 to 5 times the molar amount of 2-vinylanthracene.

3. The method for continuous preparation of 2-anthracarboxylic acid according to claim 1, characterized in that, The tubular reactor is heated and its temperature is controlled by a heating furnace.

4. The method for continuous preparation of 2-anthracarboxylic acid according to claim 1, characterized in that, The tubular reactor is made of stainless steel or Hastelloy.

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