Method for synthesizing and preparing p-tolualdehyde

Abstract

The invention belongs to the technical field of electrochemistry, and particularly relates to a p-tolualdehyde synthesis preparation method which comprises the following steps: weighing anhydrous manganese sulfate, dissolving the anhydrous manganese sulfate in a sulfuric acid solution to prepare an acid solution, and adding glycerol into the prepared acid solution to obtain an electrolyte; injecting an electrolyte into the electrolytic bath, and carrying out constant-current electrolysis; when the concentration of Mn < 3 + > in the electrolytic bath reaches a preset value, feeding to a reactor, adding p-xylene and a surfactant, and carrying out oxidation reaction to obtain a reaction solution; the method comprises the following steps: adding p-tolualdehyde into a reaction kettle, reacting for 30 minutes, pumping reaction liquid into a corresponding centrifugal extractor, extracting the reaction liquid by the centrifugal extractor to obtain an organic phase and a water phase, and carrying out reduced pressure distillation on the organic phase to obtain the target product p-tolualdehyde. Active oxide species are generated through electrolysis, selective oxidation of methyl is achieved, and the product yield and process sustainability are remarkably improved in combination with continuous reactor design.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemistry technology, and specifically relates to a preparation method for synthesizing p-methylbenzaldehyde. Background Art

[0002] As an important organic synthesis intermediate, p-methylbenzaldehyde has an irreplaceable position in the fields of medicine, pesticides, spices, and polymer materials. The aldehyde group and methyl benzene ring in its molecular structure endow the compound with unique reactivity and chemical stability, making it a key precursor for synthesizing high-value-added chemicals such as terephthalic acid and p-methylbenzoic acid.

[0003] Existing industrial routes mainly rely on chemical oxidation methods, such as using cobalt / manganese salts as catalysts to oxidize p-xylene with air or oxygen to prepare p-methylbenzaldehyde. However, this method has insufficient selectivity and is prone to over-oxidation to produce p-methylbenzoic acid, resulting in a low yield of the target product. Due to the need to use a large amount of organic solvents (such as acetic acid) and heavy metal catalysts, waste catalysts and waste liquids containing heavy metals are formed. If not properly treated, it will cause environmental pollution. Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention proposes a preparation method for synthesizing p-methylbenzaldehyde, which realizes the selective oxidation of methyl by electrolyzing to generate active oxidation species, and combines the design of a continuous reactor to significantly improve the product yield and process sustainability. Specifically, it is realized through the following technical solutions: A preparation method for synthesizing p-methylbenzaldehyde, comprising the following steps: 1) Weigh anhydrous manganese sulfate and dissolve it in a sulfuric acid solution with a concentration of 6.5 - 8.5 mol / L to prepare an acid solution with a Mn 2+ concentration of 0.8 - 2 mol / L. Add glycerol with a volume of 5% - 10% of the acid solution volume to the prepared acid solution, and stir evenly to obtain an electrolyte solution; 2) Inject the electrolyte solution into the electrolytic cell, set the current density to 15 - 20 mA / cm 2 , and the cell voltage to 2.5 - 3 V, and perform constant current electrolysis; 3) Prepare at least two closed reactors, and each reactor is connected to a centrifugal extractor. When the concentration of Mn in the electrolytic cell 3+ reaches the preset value, maintain the liquid level of the electrolytic cell, continuously pump the electrolyte solution to one of the reactors to obtain an oxidation solution, and at the same time supplement fresh electrolyte solution. When the oxidation solution in the target reactor reaches the set capacity, switch to another reactor and continue pumping; 4) Add p-xylene and a surfactant accounting for 0.5% - 1% of the mass of p-xylene to the target reactor. The p-xylene and Mn in the target reactor 3+The molar ratio is 1.2 - 2:1. Start the stirrer of the target reactor, maintain the temperature at 55 - 65°C, and conduct the oxidation reaction to obtain a reaction solution. 5) React for 45 min, pump 90% by volume of the reaction solution to the corresponding centrifugal extractor, then supplement fresh oxidation solution, re - charge p - xylene and surfactant, and conduct the reaction in the next cycle. The reaction solution is extracted by the centrifugal extractor to obtain an organic phase and an aqueous phase. The aqueous phase is returned to the electrolytic cell for recycling of Mn 2+ , and the organic phase is subjected to vacuum distillation. The unreacted p - xylene is returned to the storage tank for recycling to obtain the target product p - methylbenzaldehyde.

[0005] Preferably, the surfactant is polyethylene glycol.

[0006] Preferably, the anode of the electrolytic cell is a boron - doped diamond electrode, and the cathode is graphite.

[0007] Preferably, the surface area ratio of the cathode to the anode is 1:2 - 7.

[0008] Preferably, the cathode is a rotating electrode with a rotation speed of 200 rpm.

[0009] Preferably, in step 3, the electrolyte is continuously pumped to one of the reactors, and the pumping flow rate per minute is 0.15 times the volume of the electrolytic cell.

[0010] Preferably, a magnetic stirrer is placed outside the bottom of the electrolytic cell to drive a magnetic stir bar placed inside the electrolytic cell.

[0011] Preferably, in step 1, nitrogen is introduced into the obtained electrolyte to reduce the oxygen content of the electrolyte.

[0012] After adopting the above - mentioned technical solution, the beneficial effects of the present invention are: In this process, the medium is in a closed - loop cycle, there is no waste catalyst discharge, and zero heavy - metal pollution. Active oxidation species are generated through electrolysis to achieve the selective oxidation of methyl. Combined with the design of a continuous reactor, the product yield and process sustainability are significantly improved. Detailed Embodiments

[0013] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only configured to explain the present invention and are not configured to limit the present invention. For those skilled in the art, the present invention can be implemented without some of these specific details. The following description of the embodiments is only intended to provide a better understanding of the present invention by showing examples of the present invention.

[0014] Example 1 This embodiment provides a method for synthesizing p-methylbenzaldehyde. The following are the specific preparation steps and technical details of this preparation method.

[0015] Electrolyte preparation Weigh anhydrous manganese sulfate and dissolve it in a sulfuric acid solution with a concentration of 6.5 mol / L to prepare an acid solution with a Mn 2+ concentration of 0.8 mol / L. Add glycerol with a volume of 5% of the acid solution volume to the prepared acid solution to inhibit the disproportionation of Mn 3+ . Stir evenly to obtain the electrolyte. After the preparation, nitrogen is introduced into the electrolyte to reduce the oxygen content of the electrolyte.

[0016] Electrolysis Inject the electrolyte into the electrolytic cell. The anode material of the electrolytic cell is a boron-doped diamond electrode, and the cathode material is graphite. The surface area ratio of the cathode to the anode is 1:2. The anode is the core area where Mn 3+ is generated. A sufficient surface area can improve the generation efficiency. The cathode is a rotating electrode with a rotation speed of 200 rpm to enhance mass transfer and prevent Mn 3+ from depositing on the electrode surface. Set the current density to 15 mA / cm 2 , and the cell voltage to 2 V for constant current electrolysis.

[0017] Place a magnetic stirrer in the electrolytic cell and drive it with an external magnetic stirrer at the bottom of the electrolytic cell to inhibit concentration polarization.

[0018] Oxidation reaction Prepare at least two closed reactors, and connect each reactor to a centrifugal extractor. When the concentration of Mn 3+ in the electrolytic cell reaches the preset value (such as 0.5 mol / L), keep the liquid level of the electrolytic cell, and continuously pump the electrolyte into one of the reactors to obtain the oxidation solution. At the same time, replenish fresh electrolyte, and the pumping flow rate (L / min) = 0.15 × the volume of the electrolytic cell (L). When the oxidation solution in the target reactor reaches the set capacity, switch to another reactor and continue pumping.

[0019] Add p-xylene and polyethylene glycol accounting for 0.5% of the mass of p-xylene to the target reactor. The molar ratio of p-xylene to Mn 3+ in the target reactor is 1.2:1. Start the stirrer of the target reactor, maintain the temperature at 55 °C, and carry out the oxidation reaction to obtain the reaction solution.

[0020] As a surfactant, polyethylene glycol accelerates the diffusion of Mn 3+ from the aqueous phase (electrolyte) to the organic phase (p-xylene) by reducing the interfacial tension between the aqueous phase and the organic phase, and improves the reaction efficiency between the oxidant (Mn 3+ ) and the substrate (p-xylene).

[0021] Electrolytically generated Mn 3+ As a strong oxidant, it can selectively oxidize the methyl group of p - xylene to an aldehyde group, and then generate p - tolualdehyde.

[0022] Separation and purification After reacting for 45 min, 90% of the reaction solution is pumped to the corresponding centrifugal extractor, and then fresh oxidation solution is added. p - Xylene and polyethylene glycol are re - introduced to carry out the reaction in the next cycle. The rotation speed of the centrifugal extractor is set at 4000 rpm to obtain an organic phase (containing p - tolualdehyde and unreacted p - xylene) and an aqueous phase (containing Mn 2+ , water and a small amount of acid). The aqueous phase is returned to the electrolytic cell for recycling of Mn 2+ . The organic phase is subjected to vacuum distillation. The unreacted p - xylene is returned to the storage tank for reuse, and the target product p - tolualdehyde is obtained with a yield of 65.2%.

[0023] Example 2 This example provides a method for synthesizing p - tolualdehyde. Different from Example 1: 1) Weigh anhydrous manganese sulfate and dissolve it in a sulfuric acid solution with a concentration of 8 mol / L to prepare an acid solution with a Mn 2+ concentration of 1.2 mol / L. Glycerol with a volume of 5.5% of the acid solution volume is added to the prepared acid solution and stirred evenly to obtain the electrolyte solution; 2) Inject the electrolyte solution into the electrolytic cell. The surface area ratio of the cathode to the anode is 1:5, and the current density is set at 15 mA / cm 2 , and the cell voltage is 3 V for constant - current electrolysis; 3) When the concentration of Mn in the electrolytic cell 3+ reaches the preset value, keep the liquid level of the electrolytic cell, and continuously pump the electrolyte solution into one of the reactors. When the oxidation solution in the target reactor reaches the set capacity, add p - xylene and polyethylene glycol accounting for 0.55% of the mass of p - xylene. The molar ratio of p - xylene to Mn in the target reactor 3+ is 1.5:1, maintain the temperature at 60 °C, and carry out the oxidation reaction to obtain the reaction solution; 4) After reacting for 45 min, 90% of the reaction solution is pumped to the corresponding centrifugal extractor. The reaction solution is extracted by the centrifugal extractor to obtain an organic phase and an aqueous phase. The aqueous phase is returned to the electrolytic cell for recycling of Mn 2+ , and the organic phase is subjected to vacuum distillation. The unreacted p - xylene is returned to the storage tank for reuse, and the target product p - tolualdehyde is obtained with a yield of 68.7%.

[0024] Example 3 This example provides a method for synthesizing p - tolualdehyde. Different from Example 1: 1) Weigh anhydrous manganese sulfate and dissolve it in a sulfuric acid solution with a concentration of 8.5 mol / L to prepare an acid solution with a Mn 2+ concentration of 2 mol / L. Add glycerol with a volume of 10% of the acid solution to the prepared acid solution and stir evenly to obtain an electrolyte solution; 2) Inject the electrolyte solution into the electrolytic cell. The surface area ratio of the cathode to the anode is 1:7. Set the current density to 20 mA / cm 2 , and the cell voltage is 2.5 V. Perform constant current electrolysis; 3) When the concentration of Mn in the electrolytic cell 3+ reaches the preset value, maintain the liquid level of the electrolytic cell. Continuously pump the electrolyte solution into one of the reactors. When the oxidation liquid in the target reactor reaches the set capacity, add p-xylene and polyethylene glycol accounting for 0.1% of the mass of p-xylene. The molar ratio of p-xylene to Mn in the target reactor 3+ is 2:1. Maintain the temperature at 65 °C and carry out an oxidation reaction to obtain a reaction solution; 4) React for 45 min. Pump 90% of the volume of the reaction solution to the corresponding centrifugal extractor. The reaction solution is extracted by the centrifugal extractor to obtain an organic phase and an aqueous phase. The aqueous phase is returned to the electrolytic cell for recycling of Mn 2+ , and the organic phase is subjected to vacuum distillation. The unreacted p-xylene is returned to the storage tank for recycling to obtain the target product p-methylbenzaldehyde with a yield of 63.5%.

[0025] Example 4 This example provides a method for synthesizing and preparing p-methylbenzaldehyde. Different from Example 1: 1) Weigh anhydrous manganese sulfate and dissolve it in a sulfuric acid solution with a concentration of 8 mol / L to prepare an acid solution with a Mn 2+ concentration of 1.5 mol / L. Add glycerol with a volume of 5% of the acid solution to the prepared acid solution and stir evenly to obtain an electrolyte solution; 2) Inject the electrolyte solution into the electrolytic cell. The surface area ratio of the cathode to the anode is 1:7. Set the current density to 20 mA / cm 2 , and the cell voltage is 3 V. Perform constant current electrolysis; 3) When the concentration of Mn in the electrolytic cell 3+ reaches the preset value, maintain the liquid level of the electrolytic cell. Continuously pump the electrolyte solution into one of the reactors. When the oxidation liquid in the target reactor reaches the set capacity, add p-xylene and polyethylene glycol accounting for 0.1% of the mass of p-xylene. The molar ratio of p-xylene to Mn in the target reactor 3+ is 2:1. Maintain the temperature at 60 °C and carry out an oxidation reaction to obtain a reaction solution; 4) React for 45 min. Pump 90% of the volume of the reaction solution to the corresponding centrifugal extractor. The reaction solution is extracted by the centrifugal extractor to obtain an organic phase and an aqueous phase. The aqueous phase is returned to the electrolytic cell for recycling of Mn2+ , the organic phase is subjected to vacuum distillation, and the unreacted p-xylene is returned to the storage tank for reuse, obtaining the target product p-methylbenzaldehyde with a yield of 65.4%.

[0026] Example 5 This example provides a method for synthesizing and preparing p-methylbenzaldehyde. Different from Example 1: 1) Weigh anhydrous manganese sulfate and dissolve it in a sulfuric acid solution with a concentration of 8 mol / L to prepare an acid solution with a Mn 2+ concentration of 1.5 mol / L. Add glycerol with a volume of 5% of the acid solution to the prepared acid solution and stir evenly to obtain the electrolyte solution; 2) Inject the electrolyte solution into the electrolytic cell. The surface area ratio of the cathode to the anode is 1:7, and the set current density is 20 mA / cm 2 , with a cell voltage of 3 V, and perform constant current electrolysis; 3) When the concentration of Mn in the electrolytic cell 3+ reaches the preset value, maintain the liquid level of the electrolytic cell, and continuously pump the electrolyte solution into one of the reactors. When the oxidation liquid in the target reactor reaches the set capacity, add p-xylene and polyethylene glycol accounting for 0.1% of the mass of p-xylene. The molar ratio of p-xylene to Mn in the target reactor 3+ is 2:1, maintain the temperature at 65 °C, and perform the oxidation reaction to obtain the reaction solution; 4) React for 45 min, pump 90% of the volume of the reaction solution to the corresponding centrifugal extractor. The reaction solution is extracted by the centrifugal extractor to obtain an organic phase and an aqueous phase. The aqueous phase is returned to the electrolytic cell for reuse of Mn 2+ , the organic phase is subjected to vacuum distillation, and the unreacted p-xylene is returned to the storage tank for reuse, obtaining the target product p-methylbenzaldehyde with a yield of 60.8%.

[0027] Example 6 This example provides a method for synthesizing and preparing p-methylbenzaldehyde. Different from Example 1: 1) Weigh anhydrous manganese sulfate and dissolve it in a sulfuric acid solution with a concentration of 8 mol / L to prepare an acid solution with a Mn 2+ concentration of 1.2 mol / L. Add glycerol with a volume of 5.5% of the acid solution to the prepared acid solution and stir evenly to obtain the electrolyte solution; 2) Inject the electrolyte solution into the electrolytic cell. The surface area ratio of the cathode to the anode is 1:5, and the set current density is 15 mA / cm 2 , with a cell voltage of 3 V, and perform constant current electrolysis; 3) When the concentration of Mn in the electrolytic cell 3+When the concentration reaches the preset value, maintain the electrolyte level in the electrolytic cell, and continuously pump the electrolyte into one of the reactors. When the oxidation liquid in the target reactor reaches the set capacity, add p-xylene and polyethylene glycol accounting for 0.55% of the mass of p-xylene. The molar ratio of p-xylene to Mn 3+ in the target reactor is 1.5:1. Maintain the temperature at 55°C and carry out the oxidation reaction to obtain the reaction liquid; 4) React for 45 minutes, pump 90% of the volume of the reaction liquid to the corresponding centrifugal extractor. The reaction liquid is extracted by the centrifugal extractor to obtain an organic phase and an aqueous phase. The aqueous phase is returned to the electrolytic cell for recycling of Mn 2+ , and the organic phase is subjected to vacuum distillation. The unreacted p-xylene is returned to the storage tank for recycling to obtain the target product p-tolualdehyde with a yield of 66.1%.

[0028] If the preset value of the Mn 3+ concentration in the electrolytic cell is 0.5 mol / L, calculate the yield of each example after the reactor reacts for 45 minutes. The calculation steps of the yield are as follows: 1. Calculation of theoretical yield (N1) n(Mn 3+ ) in the electrolyte = V (volume of the electrolyte, assumed to be 10 L) × C (0.5 mol / L) = 5 mol. Assume that the amount of electrolyte fed into the reactor is 8 L. Therefore, the theoretical amount of Mn 3+ in the reactor is 4 mol. Assume that the molar ratio of p-xylene to Mn 3+ in the reactor is 1.5:1. Therefore, the theoretical amount of p-xylene in the reactor is 6 mol. 2 mol of Mn 3+ is consumed for each mole of p-tolualdehyde produced. 90% of the volume of the reaction liquid is pumped to the corresponding centrifugal extractor. Therefore, the final theoretical yield is 1.8 mol.

[0029] 2. Calculation of actual yield (N) The molar mass of p-tolualdehyde is 120.15 g / mol. If the actual mass of p-tolualdehyde produced is 80 g, then the actual yield is: N = 80 g / 120.15 g / mol ≈ 0.67 mol.

[0030] 3. Calculation of yield Yield = N / N1 × 100% = 0.67 / 1.8 × 100% ≈ 37.2%.

[0031] Increasing the sulfuric acid concentration can improve the production efficiency of Mn 3+ , but too high a concentration may lead to an increase in the disproportionation of Mn 3+ and an increase in by-products. Mn 2+When the concentration increases from 0.8 mol / L to 2 mol / L, the viscosity of the electrolyte increases, the mass transfer resistance increases, which may reduce the reaction selectivity. The expansion of the anode surface area ratio (1:2 → 1:7) can increase the Mn 3+ production amount. The increase in the cell voltage usually improves the electrolysis efficiency, but exceeding the critical value will lead to an increase in side reactions (such as oxygen evolution reaction). The molar ratio of p-xylene to Mn 3+ increases from 1.2:1 to 2:1, the Mn 3+ excess decreases, and the substrate conversion rate decreases. In Example 2, through the synergistic optimization of sulfuric acid concentration, temperature, and molar ratio, high-efficiency oxidation is achieved.

[0032] According to the embodiments of the present invention as described above, these embodiments do not describe all the details in detail, nor limit the invention to only the specific embodiments. Obviously, according to the above description, many modifications and variations can be made. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the art can make good use of the present invention and its modified use based on the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method for synthesizing p-methylbenzaldehyde, characterized in that, It includes the following steps: 1) Weigh anhydrous manganese sulfate and dissolve it in a sulfuric acid solution with a concentration of 6.5 - 8.5 mol / L to prepare an acid solution with a Mn 2+ concentration of 0.8 - 2 mol / L. Add glycerol with a volume of 5% - 10% of the acid solution volume to the prepared acid solution and stir evenly to obtain an electrolyte solution; 2) Inject the electrolyte into the electrolytic cell, and set the current density to 15 - 20 mA / cm 2 , with the cell voltage of 2.5 - 3 V, and perform constant current electrolysis; 3) Prepare at least two sealed reactors, and each reactor is connected to a centrifugal extractor. When the concentration of Mn in the electrolytic cell reaches the preset value, maintain the liquid level of the electrolytic cell, continuously pump the electrolyte into one of the reactors to obtain the oxidized liquid, and at the same time supplement fresh electrolyte. When the oxidized liquid in the target reactor reaches the set capacity, switch to the other reactor and continue pumping; 3+ When the concentration of Mn in the electrolytic cell reaches the preset value, maintain the liquid level of the electrolytic cell, continuously pump the electrolyte into one of the reactors to obtain the oxidized liquid, and at the same time supplement fresh electrolyte. When the oxidized liquid in the target reactor reaches the set capacity, switch to the other reactor and continue pumping; 4) Add p-xylene and a surfactant accounting for 0.5% - 1% of the mass of p-xylene into the target reactor. The molar ratio of p-xylene to Mn in the target reactor is 1.2 - 2:

1. Start the stirrer of the target reactor, maintain the temperature at 55 - 65 °C, and carry out the oxidation reaction to obtain a reaction solution; 3+ ​ 5) React for 45 min, pump 90% of the reaction solution volume to the corresponding centrifugal extractor, then supplement new oxidation solution, reintroduce p-xylene and surfactant, and carry out the reaction for the next cycle. The reaction solution is extracted by the centrifugal extractor to obtain an organic phase and an aqueous phase. The aqueous phase is returned to the electrolytic cell for reuse of Mn 2+ , and the organic phase is subjected to vacuum distillation. The unreacted p-xylene is returned to the storage tank for reuse, and the target product p-tolualdehyde is obtained.

2. The method for synthesizing and preparing p-tolualdehyde according to claim 1, wherein: The surfactant is polyethylene glycol.

3. The method for synthesizing and preparing p-tolualdehyde according to claim 1, wherein: The anode of the electrolytic cell is a boron-doped diamond electrode, and the cathode is graphite.

4. The preparation method of p-tolualdehyde according to claim 3, wherein: The surface area ratio of the cathode to the anode is 1:2 to 7.

5. The method for synthesizing and preparing p-tolualdehyde according to claim 4, characterized in that: The cathode is a rotating electrode with a rotation speed of 200 rpm.

6. The method for synthesizing and preparing p-tolualdehyde according to claim 1, wherein: In step 3, the electrolyte is continuously pumped into one of the reactors, and the pumping flow rate per minute is 0.15 times the volume of the electrolytic cell.

7. The method for synthesizing and preparing p-tolualdehyde according to claim 1, characterized in that: A magnetic stir bar is placed in the electrolytic cell and driven by an external magnetic stirrer at the bottom of the electrolytic cell.

8. The method for synthesizing and preparing p-tolualdehyde according to claim 1, wherein: In step 1, nitrogen is introduced into the obtained electrolyte to reduce the oxygen content of the electrolyte.