CN120366800A - Synthetic preparation method of p-methylbenzaldehyde - Google Patents

Abstract

The present invention belongs to the field of electrochemical technology, and is specifically a method for synthesizing and preparing p-methylbenzaldehyde, comprising: weighing anhydrous manganese sulfate, dissolving it in a sulfuric acid solution, configuring it into an acid solution, adding glycerol to the configured acid solution, and obtaining an electrolyte; injecting the electrolyte into an electrolytic cell, and performing constant current electrolysis; when the concentration of Mn3 ⁺ in the electrolytic cell reaches a preset value, sending it to a reactor, adding p-xylene and a surfactant, performing an oxidation reaction, and obtaining a reaction solution; reacting for 30 minutes, pumping the reaction solution to a corresponding centrifugal extractor, extracting the reaction solution through a centrifugal extractor, obtaining an organic phase and an aqueous phase, and performing reduced pressure distillation on the organic phase to obtain the target product p-methylbenzaldehyde. Active oxidation species are generated by electrolysis, and selective oxidation of methyl is achieved, and combined with the design of a continuous reactor, the product yield and process sustainability are significantly improved.

Description

Synthetic preparation method of p-methylbenzaldehyde

Technical Field

The invention belongs to the technical field of electrochemistry, and particularly relates to a synthetic preparation method of p-methylbenzaldehyde.

Background

Para-methylbenzaldehyde has an irreplaceable position as an important organic synthesis intermediate in the fields of medicines, pesticides, fragrances and polymeric materials. The aldehyde group in the molecular structure and the methyl benzene ring together endow the compound with unique reactivity and chemical stability, so that the compound becomes a key precursor for synthesizing high-added-value chemicals such as terephthalic acid, p-methyl benzoic acid and the like.

The existing industrialized route mainly depends on a chemical oxidation method, such as using cobalt/manganese salt as a catalyst, and oxidizing paraxylene by air or oxygen to prepare the paramethylbenzaldehyde. However, the method has insufficient selectivity, and is easy to excessively oxidize to generate the p-methylbenzoic acid, so that the yield of the target product is low. Because a large amount of organic solvent (such as acetic acid) and heavy metal catalyst are needed to be used, waste catalyst and waste liquid containing heavy metal are formed, and if the waste catalyst and the waste liquid are improperly treated, environmental pollution can be caused.

Disclosure of Invention

Aiming at the problems existing in the prior art, the invention provides a method for synthesizing and preparing p-methylbenzaldehyde, which realizes the selective oxidation of methyl by generating active oxidation species through electrolysis, and remarkably improves the product yield and the process sustainability by combining with the design of a continuous reactor. The method is realized by the following technical scheme:

a synthetic preparation method of p-methylbenzaldehyde comprises the following steps:

1) Weighing anhydrous manganese sulfate, dissolving the anhydrous manganese sulfate in a sulfuric acid solution with the concentration of 6.5-8.5 mol/L to prepare an acid solution with the Mn ²⁺ concentration of 0.8-2 mol/L, adding 5-10% of glycerol in the prepared acid solution, and uniformly stirring to obtain an electrolyte;

2) Injecting electrolyte into the electrolytic tank, setting the current density to be 15-20 mA/cm ², and carrying out constant current electrolysis at the tank voltage of 2.5-3V;

3) Preparing at least two closed reactors, wherein each reactor is connected with a centrifugal extractor, when the concentration of Mn ³⁺ in an electrolytic tank reaches a preset value, maintaining the liquid level of the electrolytic tank, continuously pumping electrolyte to one of the reactors to obtain an oxidizing liquid, simultaneously supplementing fresh electrolyte, and when the oxidizing liquid in a target reactor reaches a set capacity, switching to the other reactor and continuously pumping;

4) Adding paraxylene and a surfactant accounting for 0.5% -1% of the mass of the paraxylene into a target reactor, wherein the molar ratio of the paraxylene to Mn ³⁺ in the target reactor is 1.2-2:1, starting a stirrer of the target reactor, maintaining the temperature at 55-65 ℃, and carrying out oxidation reaction to obtain a reaction solution;

5) And (3) reacting for 45min, pumping 90% of the reaction liquid to a corresponding centrifugal extractor, supplementing new oxidizing liquid, adding paraxylene and surfactant again, performing the reaction of the next period, extracting the reaction liquid by the centrifugal extractor to obtain an organic phase and a water phase, returning the water phase to an electrolytic tank, recycling Mn ²⁺, performing reduced pressure distillation on the organic phase, and returning unreacted paraxylene to a storage tank for recycling to obtain the target product paramethylbenzaldehyde.

Preferably, the surfactant is polyethylene glycol.

Preferably, the anode of the electrolytic tank is a boron-doped diamond electrode, and the cathode is graphite.

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

Preferably, the cathode is a rotary electrode with a rotation speed of 200rpm.

Preferably, in the 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 tank.

Preferably, a stirrer is arranged in the electrolytic tank and driven by a magnetic stirrer arranged at the bottom of the electrolytic tank externally.

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

After the technical scheme is adopted, the invention has the beneficial effects that:

The medium of the route is circulated in a closed loop, no waste catalyst is discharged, and heavy metal pollution is avoided. The active oxidation species are generated through electrolysis, so that the selective oxidation of methyl is realized, and the product yield and the process sustainability are obviously improved by combining with the design of a continuous reactor.

Detailed Description

The present invention will be described in further detail with reference to specific embodiments in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are merely configured to illustrate the invention and are not configured to limit the invention. It will be apparent to one skilled in the art that the present invention may be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the invention by showing examples of the invention.

Example 1

The embodiment provides a synthetic preparation method of p-methylbenzaldehyde, and the specific preparation steps and technical details of the preparation method are as follows.

Electrolyte preparation

Anhydrous manganese sulfate is weighed and dissolved in sulfuric acid solution with the concentration of 6.5mol/L to prepare acid liquor with the concentration of Mn ²⁺ of 0.8 mol/L. Adding 5% glycerol by volume of the prepared acid solution to inhibit disproportionation of Mn ³⁺. Stirring uniformly to obtain electrolyte. And nitrogen is introduced into the prepared electrolyte, so that the oxygen content of the electrolyte is reduced.

Electrolysis

Electrolyte is injected into the electrolytic tank, the anode material of the electrolytic tank is a boron-doped diamond electrode, the cathode material is graphite, and the surface area ratio of the cathode to the anode is 1:2. The anode is a core region where Mn ³⁺ is generated, and enough surface area can improve the generation efficiency. The cathode is a rotary electrode with the rotating speed of 200rpm, which enhances mass transfer and prevents Mn ³⁺ from depositing on the surface of the electrode. Constant current electrolysis was carried out by setting the current density to 15mA/cm ² and the cell voltage to 2V.

The stirrer is placed in the electrolytic tank and driven by a magnetic stirrer arranged at the bottom of the electrolytic tank to inhibit concentration polarization.

Oxidation reaction

At least two closed reactors are prepared, and each reactor is connected with a centrifugal extractor. When the concentration of Mn ³⁺ in the cell reaches a preset value (e.g., 0.5 mol/L), the cell level is maintained, and electrolyte is continuously pumped to one of the reactors to obtain an oxidizing solution, while fresh electrolyte is replenished, and the pumping flow rate (L/min) =0.15×cell volume (L). When the oxidizing liquid in the target reactor reaches the set capacity, the oxidizing liquid is switched to the other reactor, and pumping is continued.

Paraxylene and polyethylene glycol accounting for 0.5 percent of the mass of the paraxylene are added into the target reactor, and the mol ratio of the paraxylene to Mn ³⁺ in the target reactor is 1.2:1. Starting a stirrer of the target reactor, maintaining the temperature at 55 ℃ and carrying out oxidation reaction to obtain a reaction liquid.

Polyethylene glycol is used as a surfactant, and by reducing interfacial tension between an aqueous phase (electrolyte) and an organic phase (paraxylene), mn ³⁺ is accelerated to diffuse from the aqueous phase to the organic phase, and the reaction efficiency of an oxidant (Mn ³⁺) and a substrate (paraxylene) is improved.

Mn ³⁺ generated by electrolysis is used as a strong oxidant, and methyl groups of paraxylene can be selectively oxidized into aldehyde groups, so that paramethylbenzaldehyde is generated.

Separation and purification

The reaction is carried out for 45min, 90% of the volume of the reaction solution is pumped to a corresponding centrifugal extractor, then new oxidizing solution is supplemented, and paraxylene and polyethylene glycol are added again to carry out the reaction of the next period. The rotational speed of the centrifugal extractor was set at 4000rpm to obtain an organic phase (containing p-methylbenzaldehyde and unreacted p-xylene) and an aqueous phase (containing Mn ²⁺, water and a small amount of acid). The water phase is returned to the electrolytic tank to recycle Mn ²⁺. The organic phase is distilled under reduced pressure, unreacted paraxylene is returned to a storage tank for recycling, and the target product paramethylbenzaldehyde is obtained, wherein the yield is 65.2%.

Example 2

This example provides a synthetic preparation method of p-methylbenzaldehyde, which is different from example 1 in that:

1) Weighing anhydrous manganese sulfate, dissolving the anhydrous manganese sulfate in a sulfuric acid solution with the concentration of 8mol/L to prepare an acid solution with the concentration of Mn ²⁺ of 1.2mol/L, adding glycerol with the volume of 5.5% of the acid solution into the prepared acid solution, and uniformly stirring to obtain an electrolyte;

2) Injecting electrolyte into the electrolytic tank, wherein the surface area ratio of the cathode to the anode is 1:5, the current density is set to 15mA/cm ², the tank voltage is 3V, and constant current electrolysis is carried out;

3) When the concentration of Mn ³⁺ in the electrolytic tank reaches a preset value, maintaining the liquid level of the electrolytic tank, continuously pumping the electrolyte to one of the reactors, adding paraxylene and polyethylene glycol accounting for 0.55% of the mass of the paraxylene after the oxidizing liquid in the target reactor reaches a set capacity, maintaining the temperature at 60 ℃ when the molar ratio of the paraxylene to Mn ³⁺ in the target reactor is 1.5:1, and carrying out oxidation reaction to obtain a reaction solution;

4) And (3) reacting for 45min, pumping 90% of the volume of reaction liquid into a corresponding centrifugal extractor, extracting the reaction liquid by the centrifugal extractor to obtain an organic phase and a water phase, returning the water phase to an electrolytic tank, recycling Mn ²⁺, performing reduced pressure distillation on the organic phase, and returning unreacted paraxylene to a storage tank for recycling to obtain the target product paramethylbenzaldehyde, wherein the yield is 68.7%.

Example 3

This example provides a synthetic preparation method of p-methylbenzaldehyde, which is different from example 1 in that:

1) Weighing anhydrous manganese sulfate, dissolving the anhydrous manganese sulfate in a sulfuric acid solution with the concentration of 8.5mol/L to prepare an acid solution with the Mn ²⁺ concentration of 2mol/L, adding 10% glycerol with the volume of the acid solution into the prepared acid solution, and uniformly stirring to obtain an electrolyte;

2) Injecting electrolyte into the electrolytic tank, wherein the surface area ratio of the cathode to the anode is 1:7, the current density is set to be 20mA/cm ², the tank voltage is 2.5V, and constant current electrolysis is carried out;

3) When the concentration of Mn ³⁺ in the electrolytic tank reaches a preset value, maintaining the liquid level of the electrolytic tank, continuously pumping the electrolyte to one of the reactors, adding paraxylene and polyethylene glycol accounting for 0.1% of the mass of the paraxylene after the oxidizing liquid in the target reactor reaches a set capacity, maintaining the temperature at 65 ℃ when the molar ratio of the paraxylene to Mn ³⁺ in the target reactor is 2:1, and carrying out oxidation reaction to obtain a reaction solution;

4) And (3) reacting for 45min, pumping 90% of the volume of reaction liquid into a corresponding centrifugal extractor, extracting the reaction liquid by the centrifugal extractor to obtain an organic phase and a water phase, returning the water phase to an electrolytic tank, recycling Mn ²⁺, performing reduced pressure distillation on the organic phase, and returning unreacted paraxylene to a storage tank for recycling to obtain the target product paramethylbenzaldehyde, wherein the yield is 63.5%.

Example 4

This example provides a synthetic preparation method of p-methylbenzaldehyde, which is different from example 1 in that:

1) Weighing anhydrous manganese sulfate, dissolving the anhydrous manganese sulfate in a sulfuric acid solution with the concentration of 8mol/L to prepare an acid solution with the concentration of Mn ²⁺ of 1.5mol/L, adding glycerol with the volume of 5% of the acid solution into the prepared acid solution, and uniformly stirring to obtain an electrolyte;

2) Injecting electrolyte into the electrolytic tank, wherein the surface area ratio of the cathode to the anode is 1:7, the current density is set to be 20mA/cm ², the tank voltage is 3V, and constant current electrolysis is carried out;

3) When the concentration of Mn ³⁺ in the electrolytic tank reaches a preset value, maintaining the liquid level of the electrolytic tank, continuously pumping the electrolyte to one of the reactors, adding paraxylene and polyethylene glycol accounting for 0.1% of the mass of the paraxylene after the oxidizing liquid in the target reactor reaches a set capacity, maintaining the temperature at 60 ℃ when the molar ratio of the paraxylene to Mn ³⁺ in the target reactor is 2:1, and carrying out oxidation reaction to obtain a reaction solution;

4) And (3) reacting for 45min, pumping 90% of the volume of reaction liquid into a corresponding centrifugal extractor, extracting the reaction liquid by the centrifugal extractor to obtain an organic phase and a water phase, returning the water phase to an electrolytic tank, recycling Mn ²⁺, performing reduced pressure distillation on the organic phase, and returning unreacted paraxylene to a storage tank for recycling to obtain the target product paramethylbenzaldehyde, wherein the yield is 65.4%.

Example 5

This example provides a synthetic preparation method of p-methylbenzaldehyde, which is different from example 1 in that:

1) Weighing anhydrous manganese sulfate, dissolving the anhydrous manganese sulfate in a sulfuric acid solution with the concentration of 8mol/L to prepare an acid solution with the concentration of Mn ²⁺ of 1.5mol/L, adding glycerol with the volume of 5% of the acid solution into the prepared acid solution, and uniformly stirring to obtain an electrolyte;

2) Injecting electrolyte into the electrolytic tank, wherein the surface area ratio of the cathode to the anode is 1:7, the current density is set to be 20mA/cm ², the tank voltage is 3V, and constant current electrolysis is carried out;

3) When the concentration of Mn ³⁺ in the electrolytic tank reaches a preset value, maintaining the liquid level of the electrolytic tank, continuously pumping the electrolyte to one of the reactors, adding paraxylene and polyethylene glycol accounting for 0.1% of the mass of the paraxylene after the oxidizing liquid in the target reactor reaches a set capacity, maintaining the temperature at 65 ℃ when the molar ratio of the paraxylene to Mn ³⁺ in the target reactor is 2:1, and carrying out oxidation reaction to obtain a reaction solution;

4) And (3) reacting for 45min, pumping 90% of the volume of reaction liquid into a corresponding centrifugal extractor, extracting the reaction liquid by the centrifugal extractor to obtain an organic phase and a water phase, returning the water phase to an electrolytic tank, recycling Mn ²⁺, performing reduced pressure distillation on the organic phase, and returning unreacted paraxylene to a storage tank for recycling to obtain the target product paramethylbenzaldehyde, wherein the yield is 60.8%.

Example 6

This example provides a synthetic preparation method of p-methylbenzaldehyde, which is different from example 1 in that:

1) Weighing anhydrous manganese sulfate, dissolving the anhydrous manganese sulfate in a sulfuric acid solution with the concentration of 8mol/L to prepare an acid solution with the concentration of Mn ²⁺ of 1.2mol/L, adding glycerol with the volume of 5.5% of the acid solution into the prepared acid solution, and uniformly stirring to obtain an electrolyte;

2) Injecting electrolyte into the electrolytic tank, wherein the surface area ratio of the cathode to the anode is 1:5, the current density is set to 15mA/cm ², the tank voltage is 3V, and constant current electrolysis is carried out;

3) When the concentration of Mn ³⁺ in the electrolytic tank reaches a preset value, maintaining the liquid level of the electrolytic tank, continuously pumping the electrolyte to one of the reactors, adding paraxylene and polyethylene glycol accounting for 0.55% of the mass of the paraxylene after the oxidizing liquid in the target reactor reaches a set capacity, maintaining the temperature at 55 ℃ when the molar ratio of the paraxylene to Mn ³⁺ in the target reactor is 1.5:1, and carrying out oxidation reaction to obtain a reaction solution;

4) And (3) reacting for 45min, pumping 90% of the volume of reaction liquid into a corresponding centrifugal extractor, extracting the reaction liquid by the centrifugal extractor to obtain an organic phase and a water phase, returning the water phase to an electrolytic tank, recycling Mn ²⁺, carrying out reduced pressure distillation on the organic phase, and returning unreacted paraxylene to a storage tank for recycling to obtain the target product paramethylbenzaldehyde, wherein the yield is 66.1%.

If the Mn ³⁺ concentration in the electrolytic tank is taken as a preset value, the yield of each embodiment after the reaction of the reactor is calculated for 45min, and the calculation steps of the yield are as follows:

1. calculation of theoretical yield (N ₁)

N (Mn ³⁺) =v (electrolyte volume), assuming 10L) ×c (0.5 mol/L) =5 mol in the electrolyte. The theoretical amount of Mn ³⁺ in the reactor was 4mol, assuming a reactor electrolyte feed of 8L. The molar ratio of paraxylene to Mn ³⁺ in the reactor was assumed to be 1.5:1, so the theoretical amount of paraxylene in the reactor was 6mol. Every 1mol of p-tolualdehyde is produced, 2molMn ³⁺ parts of the reaction liquid with 90% volume is consumed, and the reaction liquid is pumped to a corresponding centrifugal extractor, so that the final theoretical yield is 1.8mol.

2. Actual yield (N) calculation

The molar mass of p-tolualdehyde is 120.15g/mol, and if the mass of p-tolualdehyde actually produced is 80g, the actual yield is:

N=80g/120.15g/mol≈0.67mol。

3. Yield calculation

Yield = N/N ₁ x 100% = 0.67/1.8 x 100% ≡37.2%.

An increase in sulfuric acid concentration may increase the Mn ³⁺ production efficiency, but an excessively high concentration may cause an increase in the disproportionation of Mn ³⁺ and increase in byproducts. When the Mn ²⁺ concentration is increased from 0.8mol/L to 2mol/L, the viscosity of the electrolyte is increased, the mass transfer resistance is increased, and the reaction selectivity may be reduced. The increase in the anode surface area ratio (1:2→1:7) increases the amount of Mn ³⁺ produced, and the increase in cell voltage generally increases the electrolysis efficiency, but exceeding the critical value leads to an increase in side reactions such as oxygen evolution. As the molar ratio of para-xylene to Mn ³⁺ increases from 1.2:1 to 2:1, mn ³⁺ is reduced in excess and substrate conversion decreases. Example 2, efficient oxidation was achieved by synergistic optimization of sulfuric acid concentration, temperature, molar ratio.

In accordance with the above embodiments of the invention, these embodiments are not exhaustive of all details, nor are they intended to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various modifications as are suited to the particular use contemplated. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (8)

1. The synthetic preparation method of the p-methylbenzaldehyde is characterized by comprising the following steps of:

1) Weighing anhydrous manganese sulfate, dissolving the anhydrous manganese sulfate in a sulfuric acid solution with the concentration of 6.5-8.5 mol/L to prepare an acid solution with the Mn ²⁺ concentration of 0.8-2 mol/L, adding 5-10% of glycerol in the prepared acid solution, and uniformly stirring to obtain an electrolyte;

2) Injecting electrolyte into the electrolytic tank, setting the current density to be 15-20 mA/cm ², and carrying out constant current electrolysis at the tank voltage of 2.5-3V;

3) Preparing at least two closed reactors, wherein each reactor is connected with a centrifugal extractor, when the concentration of Mn ³⁺ in an electrolytic tank reaches a preset value, maintaining the liquid level of the electrolytic tank, continuously pumping electrolyte to one of the reactors to obtain an oxidizing liquid, simultaneously supplementing fresh electrolyte, and when the oxidizing liquid in a target reactor reaches a set capacity, switching to the other reactor and continuously pumping;

4) Adding paraxylene and a surfactant accounting for 0.5% -1% of the mass of the paraxylene into a target reactor, wherein the molar ratio of the paraxylene to Mn ³⁺ in the target reactor is 1.2-2:1, starting a stirrer of the target reactor, maintaining the temperature at 55-65 ℃, and carrying out oxidation reaction to obtain a reaction solution;

5) And (3) reacting for 45min, pumping 90% of the reaction liquid to a corresponding centrifugal extractor, supplementing new oxidizing liquid, adding paraxylene and surfactant again, performing the reaction of the next period, extracting the reaction liquid by the centrifugal extractor to obtain an organic phase and a water phase, returning the water phase to an electrolytic tank, recycling Mn ²⁺, performing reduced pressure distillation on the organic phase, and returning unreacted paraxylene to a storage tank for recycling to obtain the target product paramethylbenzaldehyde.

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 tank is a boron-doped diamond electrode, and the cathode is graphite.

4. The method for synthesizing and preparing p-methylbenzaldehyde according to claim 3, wherein the surface area ratio of the cathode to the anode is 1:2-7.

5. The method for synthesizing and preparing p-methylbenzaldehyde as claimed in claim 4, wherein the cathode is a rotary electrode and the rotating speed is 200rpm.

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

7. The method for synthesizing and preparing p-tolualdehyde according to claim 1, wherein a stirrer is arranged in the electrolytic tank and driven by a magnetic stirrer arranged at the bottom of the electrolytic tank.

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