Synthesis method of hydroxyl-substituted benzaldehyde

Abstract

The invention belongs to the technical field of synthesis of organic compounds, and particularly relates to a synthesis method of hydroxyl-substituted benzaldehyde, which comprises the following steps: in an organic solvent, carrying out catalytic oxidation reaction on a reaction system containing methyl-substituted phenol, an alumina-supported cobalt-copper-rare earth metal oxide catalyst and oxygen-containing gas, the hydroxyl-substituted benzaldehyde is obtained; the catalyst is cheap, easy to obtain and recyclable, and a large amount of alkali and acid are not used in the reaction process, so that the production cost can be more effectively reduced. And secondly, the catalytic oxidation reaction based on the oxidant and the catalyst is mild in reaction condition, good in reaction selectivity and free of additional pollution waste, a target product with relatively high purity and yield can be obtained through simple post-treatment after the reaction, and the green and environment-friendly properties are good. In a word, based on the synthesis method, the hydroxyl-substituted benzaldehyde is synthesized more economically, more environmentally friendly and more efficiently.

Description

Technical Field

[0001] This invention belongs to the field of organic compound synthesis technology, and specifically relates to a method for synthesizing hydroxyl-substituted benzaldehyde. Background Technology

[0002] Hydroxyl-substituted benzaldehyde is an important organic intermediate, and the continuous development of efficient, low-cost, and green synthesis processes is of great significance. For example, p-hydroxybenzaldehyde is widely used in industries such as fragrances, daily chemicals, food additives, pharmaceuticals, photoresists, liquid crystal materials, pesticides, dyes, printing and dyeing, and electroplating. Its unique chemical properties allow for the further synthesis of numerous high-value-added fine chemical products from it. There are multiple process routes for the production of p-hydroxybenzaldehyde. Currently, industrial production mainly uses phenol, p-cresol, and p-nitrotoluene as raw materials. The phenol method is further divided into several synthetic routes, including the Reimer-Tiemann reaction, the Gattermann reaction, the phenol-trichloroacetaldehyde route, the phenol-glyoxylic acid route, and the phenol-formaldehyde route.

[0003] The phenol process is characterized by readily available raw materials and a relatively simple manufacturing process, but the yield is low and the cost is high. The p-nitrotoluene process for producing p-hydroxybenzaldehyde involves three steps: oxidation-reduction, diazotization, and hydrolysis. This process has the advantage of inexpensive raw materials, but its disadvantages include a long process route, large equipment requirements, the toxicity of the intermediate product p-aminobenzaldehyde, low reaction temperature, and high refrigeration requirements.

[0004] The catalytic oxidation of p-cresol involves the direct oxidation of p-cresol to p-hydroxybenzaldehyde using air or oxygen under the action of a catalyst. This process typically requires heating p-cresol, sodium hydroxide, and methanol in a stainless steel pressure vessel with a homogeneous catalyst, and then introducing oxygen to a pressure of 1.5 MPa to achieve a good conversion. Post-treatment requires the addition of a large amount of acid for neutralization to obtain p-hydroxybenzaldehyde. This process generates significant wastewater, requires a large excess of sodium hydroxide, and results in high demand for neutralization acid, leading to high production costs. The catalytic oxidation of p-cresol has considerable room for improvement, particularly in the development of novel heterogeneous catalysts to improve reaction selectivity and product yield, and to refine the process for environmental friendliness. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for synthesizing hydroxylated benzaldehyde, which effectively improves the yield and purity of the reaction, and reduces pollution and production costs.

[0006] This invention provides a method for synthesizing hydroxylated benzaldehyde, comprising the following steps: In an organic solvent, a reaction system containing methyl-substituted phenol, an alumina-supported cobalt-copper-rare earth metal oxide catalyst, and an oxygen-containing gas is subjected to a catalytic oxidation reaction to obtain hydroxy-substituted benzaldehyde.

[0007] Preferably, in the alumina-supported cobalt-copper-rare earth metal oxide catalyst, the rare earth metal is one or more of Sc, Y, La, Ce, Pr, and Nd.

[0008] Preferably, the rare earth metal is Ce.

[0009] Preferably, in the alumina-supported cobalt-copper-rare earth metal oxide catalyst, the mass of cobalt is 1-10% (preferably 5%) of the support mass, the mass of copper is 1-10% (preferably 5%) of the support mass, and the mass of rare earth metal is 1-10% (preferably 5%) of the support mass.

[0010] Preferably, the preparation method of the alumina-supported cobalt-copper-rare earth metal oxide catalyst is as follows: the activated alumina, cobalt source, copper source, rare earth metal source and water are mixed evenly, dried, calcined in an oxygen-containing gas atmosphere (preferably at 400°C), and cooled to obtain the alumina-supported cobalt-copper-rare earth metal oxide catalyst.

[0011] The cobalt source is preferably cobalt nitrate, the copper source is preferably copper nitrate, and the rare earth metal source is preferably a rare earth metal nitrate.

[0012] The activated alumina is obtained by calcining alumina at high temperature (300-500℃), preferably spherical Al2O3, which has the characteristics of large specific surface area, high activity, good formability, and easy recycling. Therefore, it can load a large amount of active components, increase catalytic sites, and improve catalytic performance. Furthermore, Al2O3 has moderate acidity and basicity, which increases the yield and selectivity of the product, and the prepared catalyst is not prone to agglomeration and has a long service life, making it suitable for industrial applications.

[0013] In the above schemes, when the loading of the active component is within the aforementioned range, the reaction yield can also increase with the increase of the loading. However, when the loading of all metals reaches 10%, further increasing the loading of the active component does not significantly improve the reaction yield and increases the preparation cost; if the loading is too low, the reaction yield will decrease due to insufficient catalytic sites. Therefore, under the premise of ensuring high product yield and low production cost, the loading of the metal active component is determined to be 1~10%, preferably 5%.

[0014] Preferably, the methyl-substituted phenol is 2-methylphenol, 3-methylphenol, or 4-methylphenol, and the corresponding hydroxy-substituted benzaldehyde is 2-hydroxybenzaldehyde, 3-hydroxybenzaldehyde, or 4-hydroxybenzaldehyde.

[0015] Preferably, the organic solvent is one or more selected from hexafluoroisopropanol, trifluoroethanol, acetonitrile, methanol, ethanol, isopropanol, or tetrahydrofuran.

[0016] Preferably, the organic solvent is hexafluoroisopropanol; the mass-to-volume ratio of the methyl-substituted phenol to the organic solvent is 0.02~0.3 g / mL. Hexafluoroisopropanol is most effective, possibly because a relatively strong hydrogen bond can be formed between hexafluoroisopropanol and the hydroxy-substituted benzaldehyde, preventing further deep oxidation to hydroxy-substituted benzoic acid.

[0017] Preferably, the oxygen volume concentration in the oxygen-containing gas is 10~100%, and the pressure is 0.1~1.0 MPa.

[0018] Preferably, the mass ratio of the alumina-supported cobalt-copper-rare earth metal oxide catalyst to the methyl-substituted phenol is 1:10~100, more preferably 1:20~40.

[0019] When the mass of the catalyst and the mass of the methyl-substituted phenol are within the aforementioned limits, the catalyst can efficiently promote the formation of the corresponding hydroxyl-substituted benzaldehyde product. When the catalyst dosage is low, the production cycle is prolonged and production efficiency is reduced; however, when the catalyst dosage is excessive, too much raw material is adsorbed, which is detrimental to product separation, and the reaction rate is not significantly improved, but rather increases production costs. This type of catalyst is a basic substance, and its main active component is a metal oxide, with synergistic catalytic effects between different metals.

[0020] Preferably, the reaction temperature of the catalytic oxidation reaction is 20~70℃ (preferably 35~60℃, more preferably 55-60℃), and the time is 6~48h (preferably 12~24h).

[0021] The beneficial effects of this invention are as follows: Using methyl-substituted phenol as a raw material, this invention achieves hydroxylated benzaldehyde by catalytic oxidation in an organic solvent using a reaction system comprising methyl-substituted phenol, an alumina-supported cobalt-copper-rare earth metal oxide catalyst, and an oxygen-containing gas. The catalyst is inexpensive, readily available, and recyclable. The reaction process avoids the use of large amounts of alkali and acid, thus effectively reducing production costs. Furthermore, the catalytic oxidation reaction based on the aforementioned oxidant and catalyst operates under mild conditions, exhibits good selectivity, and generates no additional polluting waste. Simple post-treatment after the reaction yields the target product with high purity and yield, demonstrating excellent environmental friendliness. In summary, based on the above synthesis method, this invention provides a more economical, greener, more environmentally friendly, and more efficient synthesis of hydroxylated benzaldehyde. Detailed Implementation

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The following embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. The present invention will be described in detail below with reference to the embodiments.

[0023] Example 1 Weigh 100 g of spherical Al2O3 support and calcine it in a muffle furnace at 400 °C for 1 h to activate the support. Weigh 24.691 g of Co(NO3)2·6H2O, 18.875 g of Cu(NO3)2·3H2O and 15.486 g of Ce(NO3)3·6H2O, dissolve them in 100 mL of deionized water, add the above support with vigorous stirring, and sonicate for 60 min to ensure uniform distribution of the impregnation solution.

[0024] The resulting mixture was dried in an oven at 110°C for 2 hours, and then placed in a muffle furnace. In an air atmosphere, the temperature was increased to 400°C at a rate of 10°C / min, and calcined for 4 hours. After cooling to room temperature, the spherical catalyst of 5% Co-Cu-Ce@Al2O3 was obtained.

[0025] The 5% refers to the fact that the mass of Co, Cu, and Ce in the catalyst is 5% of the mass of the support (Al2O3). By changing the amount of nitrate, catalysts with different loadings can be prepared. By replacing the nitrate with other rare earth metals, various alumina-supported cobalt-copper-rare earth metal oxide catalysts can be prepared.

[0026] This type of catalyst can also be regenerated. Specific regeneration methods are as follows: If the catalyst becomes deactivated after repeated use, rinse the catalyst bed with a 5% NaOH solution until the pH of the washing solution no longer decreases. Then wash with deionized water until the washing solution is neutral. Regenerate the catalyst by vacuum drying at 110℃ for 2 hours. If necessary, it can be placed back into a muffle furnace and calcined at 400℃ for 1 hour in an air atmosphere.

[0027] Example 2 A method for synthesizing a hydroxyl-substituted benzaldehyde, comprising the following steps: 100 mL of hexafluoroisopropanol solvent, 1 g of 5% Co-Cu-Ce@Al2O3 spherical catalyst (the catalyst in Example 1), and 15 g of p-methylphenol were added to a pressure vessel and mixed thoroughly. The mixture was purged with oxygen three times, and then oxygen was continuously introduced under a sealed environment. The pressure was controlled at 0.1-0.11 MPa, and the reaction temperature was controlled at 55-56 °C. The reaction was stirred for 16 hours, and then the reaction was terminated. The mixture was filtered, and the filter residue was washed with hexafluoroisopropanol to recover the catalyst. The filtrate was an aqueous solution of p-hydroxybenzaldehyde in hexafluoroisopropanol. After drying with 3 g of anhydrous sodium sulfate, the hexafluoroisopropanol was removed by distillation, and the product was recrystallized from toluene and dried under vacuum to obtain 15.2 g of p-hydroxybenzaldehyde. The product structure was confirmed by infrared spectroscopy and gas chromatography-mass spectrometry. The molar yield was 90%, the purity was 99.5%, and the melting point was 115-116 °C.

[0028] Example 3 50 mL of hexafluoroisopropanol, 50 mL of methanol solvent, 1 g of 5% Co-Cu-Ce@Al2O3 spherical catalyst (the catalyst in Example 1), and 15 g of p-methylphenol were added to a pressure vessel and mixed thoroughly. The mixture was purged with oxygen three times, and then oxygen was continuously introduced under a sealed environment. The pressure was controlled at 0.1-0.11 MPa, and the reaction temperature was controlled at 55-56 °C. The reaction was stirred for 16 hours, and then the reaction was terminated. The mixture was filtered, and the filter residue was washed with methanol to recover the catalyst. The filtrate was an aqueous solution of p-hydroxybenzaldehyde in hexafluoroisopropanol and methanol. After drying with 3 g of anhydrous sodium sulfate, hexafluoroisopropanol and methanol were removed by distillation. The solution was then recrystallized from toluene and dried under vacuum to obtain 13.5 g of p-hydroxybenzaldehyde, with a molar yield of 79%, a purity of 99.2%, and a melting point of 115-116 °C.

[0029] Example 4 100 mL of hexafluoroisopropanol solvent, 1 g of 5% Co-Cu-Ce@Al2O3 spherical catalyst (the catalyst in Example 1), and 15 g of p-methylphenol were added to a pressure vessel and mixed thoroughly. The mixture was purged with oxygen three times, and then oxygen was continuously introduced under a sealed environment. The pressure was controlled at 0.1-0.11 MPa, and the reaction temperature was controlled at 50-51 °C. The reaction was stirred for 24 hours, and then the reaction was terminated. The mixture was filtered, and the filter residue was washed with hexafluoroisopropanol to recover the catalyst. The filtrate was an aqueous solution of p-hydroxybenzaldehyde in hexafluoroisopropanol. After drying with 3 g of anhydrous sodium sulfate, the hexafluoroisopropanol was removed by distillation, and the solution was recrystallized from toluene and dried under vacuum to obtain 13.6 g of p-hydroxybenzaldehyde, with a molar yield of 80%, a purity of 99.1%, and a melting point of 115-116 °C.

[0030] Example 5 100 mL of methanol solvent, 1 g of 5% Co-Cu-Ce@Al2O3 spherical catalyst (the catalyst in Example 1), and 15 g of p-methylphenol were added to a pressure vessel and mixed thoroughly. The mixture was purged with oxygen three times, and then oxygen was continuously introduced under a sealed environment. The pressure was controlled at 0.15-0.16 MPa, the reaction temperature was controlled at 65 °C, and the reaction was stirred for 16 hours to terminate the reaction. The mixture was filtered, and the filter residue was washed with methanol to recover the catalyst. The filtrate was a methanol solution containing water-soluble p-hydroxybenzaldehyde. After drying with 3 g of anhydrous sodium sulfate, methanol was removed by distillation, and the solution was recrystallized from toluene and dried under vacuum to obtain 11.3 g of p-hydroxybenzaldehyde, with a molar yield of 67%, a purity of 99.0%, and a melting point of 115-116 °C.

[0031] Example 6 100 mL of hexafluoroisopropanol solvent, 1 g of 5% Co-Cu-Ce@Al2O3 spherical catalyst (the catalyst in Example 1), and 15 g of p-methylphenol were added to a pressure vessel and mixed thoroughly. The mixture was purged with oxygen three times, and then continuously purged with air under a sealed environment. The pressure was controlled at 0.3-0.31 MPa, and the reaction temperature was controlled at 58-59 °C. The reaction was stirred for 12 hours, and then the reaction was terminated. The mixture was filtered, and the filter residue was washed with hexafluoroisopropanol to recover the catalyst. The filtrate was an aqueous solution of p-hydroxybenzaldehyde in hexafluoroisopropanol. After drying with 3 g of anhydrous sodium sulfate, the hexafluoroisopropanol was removed by distillation, and the solution was recrystallized from toluene and dried under vacuum to obtain 13.6 g of p-hydroxybenzaldehyde, with a molar yield of 80%, a purity of 99.2%, and a melting point of 115-116 °C.

[0032] Example 7 100 mL of hexafluoroisopropanol solvent, 1 g of 5% Co-Cu-Ce@Al2O3 spherical catalyst (the catalyst in Example 1), and 15 g of m-methylphenol were added to a pressure vessel and mixed thoroughly. The mixture was purged with oxygen three times, and then oxygen was continuously introduced under a sealed environment. The pressure was controlled at 0.1-0.11 MPa, and the reaction temperature was controlled at 55-56 °C. The reaction was stirred for 16 hours, and then the reaction was terminated. The mixture was filtered, and the filter residue was washed with hexafluoroisopropanol to recover the catalyst. The filtrate was a hexafluoroisopropanol solution containing aqueous m-hydroxybenzaldehyde. After drying with 3 g of anhydrous sodium sulfate, the hexafluoroisopropanol was removed by distillation, and the product was dried under vacuum to obtain 14.3 g of m-hydroxybenzaldehyde. The product structure was confirmed by infrared spectroscopy and gas chromatography-mass spectrometry, with a yield of 85% and a melting point of 102-103 °C.

[0033] Example 8 A method for synthesizing a hydroxyl-substituted benzaldehyde, comprising the following steps: 100 mL of hexafluoroisopropanol solvent, 1 g of 5% Co-Cu-La@Al2O3 spherical catalyst (the catalyst preparation method is the same as in Example 1, except that 15.486 g of Ce(NO3)3·6H2O is replaced with 15.446 g of La(NO3)3·6H2O, otherwise it is the same as in Example 1) and 15 g of p-methylphenol were added to a pressure vessel and mixed evenly. The mixture was replaced with oxygen three times, and then oxygen was continuously introduced under a sealed environment. The pressure was controlled at 0.1-0.11 MPa, the reaction temperature was controlled at 55-56 °C, and the reaction was stirred for 16 hours to end the reaction. The catalyst was recovered by washing the filter residue with hexafluoroisopropanol. The filtrate was an aqueous solution of p-hydroxybenzaldehyde in hexafluoroisopropanol. After drying with 3 g of anhydrous sodium sulfate, the hexafluoroisopropanol was removed by distillation, and the product was recrystallized from toluene and dried under vacuum to obtain 11.4 g of p-hydroxybenzaldehyde. The structure of the product was confirmed by infrared spectroscopy and gas chromatography-mass spectrometry. The molar yield was 68%, the purity was 99%, and the melting point was 115-116 °C.

[0034] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of protection of this application is limited to these examples; within the framework of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of one or more embodiments of this application as described above, which are not provided in detail for the sake of brevity.

[0035] One or more embodiments in this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments in this application should be included within the protection scope of this application.

Claims

1. A process for the synthesis of a hydroxy-substituted benzaldehyde, characterized in that, The method comprises the following steps: The catalytic oxidation reaction is carried out in an organic solvent by using a reaction system containing a methyl-substituted phenol, an alumina-supported cobalt-copper-rare earth metal oxide catalyst and an oxygen-containing gas, so as to obtain a hydroxyl-substituted benzaldehyde.

2. The method of synthesis of claim 1, wherein, In the alumina-supported cobalt-copper-rare earth metal oxide catalyst, the rare earth metal is one or more of Sc, Y, La, Ce, Pr and Nd.

3. The method of synthesis of claim 2, wherein, The rare earth metal is Ce.

4. The synthesis method of any one of claims 1-3, wherein, In the alumina-supported cobalt-copper-rare earth metal oxide catalyst, the mass of the cobalt is 1-10% of the mass of the carrier, the mass of the copper is 1-10% of the mass of the carrier, and the mass of the rare earth metal is 1-10% of the mass of the carrier.

5. The method of synthesis according to any one of claims 1 to 3, wherein The preparation method of the alumina-supported cobalt-copper-rare earth metal oxide catalyst comprises uniformly mixing activated alumina, a cobalt source, a copper source, a rare earth metal source and water, drying, calcining in an oxygen-containing gas atmosphere, and cooling to obtain the alumina-supported cobalt-copper-rare earth metal oxide catalyst.

6. The method of synthesis of claim 1 wherein, The methyl-substituted phenol is 2-methylphenol, 3-methylphenol or 4-methylphenol, and the corresponding hydroxyl-substituted benzaldehyde is 2-hydroxybenzaldehyde, 3-hydroxybenzaldehyde or 4-hydroxybenzaldehyde.

7. The method of synthesis of claim 1 wherein, The organic solvent is one or more of hexafluoroisopropanol, trifluoroethanol, acetonitrile, methanol, ethanol, isopropanol or tetrahydrofuran.

8. The method of synthesis of claim 7 wherein, The organic solvent is hexafluoroisopropanol, and the mass-volume ratio of the methyl-substituted phenol to the organic solvent is 0.02-0.3 g / mL.

9. The method of synthesis of claim 1 wherein, In the oxygen-containing gas, the volume concentration of oxygen is 10-100%, the pressure is 0.1-1.0 MPa, and the mass ratio of the alumina-supported cobalt-copper-rare earth metal oxide catalyst to the methyl-substituted phenol is 1:100-110.

10. The method of synthesis of claim 1 wherein, The reaction temperature of the catalytic oxidation reaction is 20-70°C, and the reaction time is 6-48 h.