A process for the preparation of o-phthaldehyde from o-xylene

Abstract

The application discloses a method for preparing o-phthalaldehyde from o-xylene. V2O5-TiO2 doped with metal elements is used as a catalyst, o-xylene and an oxygen-containing gas are reacted to obtain a mixed oxidation product containing o-phthalic anhydride, o-phthalic acid and phthalide; the mixed oxidation product is reacted with a reducing agent in a solvent, and o-phthalalcohol is obtained after separation; and the o-phthalalcohol is reacted with an oxidizing agent, and o-phthalaldehyde is obtained after separation. The application avoids the use of corrosive substances such as bromine or chlorine and nitric acid, has low requirements on equipment, is small in environmental pollution, and is high in overall yield of o-phthalaldehyde.

Description

Technical Field

[0001] This invention belongs to the field of organic chemistry technology, specifically relating to a method for preparing o-phthalaldehyde from o-xylene. Background Technology

[0002] Phthalate is a pale yellow crystalline solid, soluble in water, ethanol, ether, and organic solvents, slightly soluble in petroleum ether, and has an irritating effect. Phthalate is a safe and highly effective antibacterial disinfectant. Compared with traditional glutaraldehyde disinfectants, it has the advantages of shorter treatment time, superior bactericidal performance, and low corrosiveness, and can be used for sterilizing endoscopic surgical instruments in hospitals. In addition, phthalate can be used as a pharmaceutical intermediate in the determination of amine alkaloids, fluorescent histamine, and in pharmaceutical testing.

[0003] Currently, there are several methods for synthesizing o-phthalaldehyde:

[0004] (1) o-xylene bromide hydrolysis method

[0005]

[0006] This method is simple, using o-xylene as a raw material, and the intermediate product tetrabromo-o-xylene has a yield of 90%. However, it requires bromine as a raw material, which increases the cost. The hydrolysis yield is about 60%, and the reaction yield is about 50%, resulting in a high reaction cost.

[0007] (2) Chlorination hydrolysis of o-xylene

[0008]

[0009] This method involves a simple reaction using chlorine gas, but the yield of the intermediate product o-tetrachloromethylbenzene is no higher than 40%, and it is difficult to separate. The hydrolysis yield is no higher than 75%, and the final product has high cost and low yield.

[0010] (3) Naphthalene ozone oxidation hydrogenation method

[0011]

[0012] Using naphthalene as a raw material, the naphthalene is ozonated and decomposed in a solvent, and the resulting peroxide is catalytically reduced, followed by extraction or crystallization to obtain phthalaldehyde. This method requires KI or dimethyl sulfoxide as a reducing agent and noble metals as catalysts. Controlling the process conditions is difficult, and it is challenging to separate the byproduct ester from phthalaldehyde, resulting in low product purity. This leads to high cost, significant pollution, high equipment investment, and is not suitable for industrial-scale production of phthalaldehyde.

[0013] (4) Oxidation of o-phthalimide

[0014]

[0015] High-purity phthalaldehyde is obtained from phthalimide via an acetic acid-nitric acid oxidation system. However, this method generates a large amount of nitrogen oxides during the reaction due to the use of nitric acid as the oxidant; furthermore, phthalimide is expensive and difficult to obtain, resulting in high costs.

[0016] The aforementioned methods for synthesizing phthalaldehyde all suffer from drawbacks such as high cost and significant environmental pollution. Therefore, there is an urgent need to develop a clean and environmentally friendly method for synthesizing phthalaldehyde. Summary of the Invention

[0017] Objective of this invention: The objective of this invention is to address the shortcomings of existing technologies by providing a method for preparing phthalaldehyde from o-xylene. This invention uses o-xylene as a raw material and prepares phthalaldehyde through an oxidation-reduction-oxidation reaction. This method avoids the use of corrosive substances such as bromine, chlorine, and nitric acid, reduces equipment requirements, mitigates environmental pollution, and produces a product free of bromine and chlorine, thus having a wide range of applications.

[0018] Technical solution: The objective of this invention is achieved through the following technical solution:

[0019] This invention provides a method for preparing o-phthalaldehyde from o-xylene, comprising the following steps:

[0020] (1) Using V2O5-TiO2 doped with metal elements as a catalyst, o-xylene and oxygen-containing gas are reacted to obtain a mixed oxidation product containing phthalic anhydride, phthalic acid and phthalphthalene.

[0021] (2) The mixed oxidation product obtained in step (1) is reacted with a reducing agent in a solvent, and after separation, o-phthalic acid is obtained;

[0022] (3) The phthalic acid obtained in step (2) is reacted with an oxidant and separated to obtain phthalaldehyde.

[0023] This invention uses o-xylene as a raw material to produce o-phthalaldehyde through an "oxidation-reduction-oxidation" process.

[0024] The synthetic route of the preparation method of this invention is as follows:

[0025]

[0026] The V2O5-TiO2 catalyst doped with metal elements described in this invention was prepared according to the method in CN110872265A.

[0027] Preferably, in step (1), the content of V2O5 in the catalyst is 10-20 wt%; the doped metal element is Sb, Zr, K, Nb or Cs; and the content of the doped metal element in the catalyst is 0.3-1.0 wt%.

[0028] The addition of metal additives in this invention can alter the activity, stability, and selectivity of V₂O₅-TiO₂ catalysts for phthalic anhydride. K and Sb can inhibit the deep oxidation of o-xylene and improve the selectivity of phthalic anhydride; Nb and Cs elements can adjust the acidic sites and concentrations on the catalyst surface; Zr element can improve the thermal stability of the catalyst and extend its service life.

[0029] Exceeding the limit for the content of the doped metal element in the catalyst will cause blockage of the surface pore structure of the catalyst, reducing its activity. Within the content range of this invention, a small amount of additive is used, resulting in high catalyst activity.

[0030] Preferably, in step (1), the oxygen-containing gas is oxygen or air; the reaction temperature is 350–450°C; and the liquid hourly space velocity (LISH) is 0.3–1.0 h⁻¹. -1 The gas hourly space velocity (HSV) of the reaction is 2500–3500 h⁻¹. -1 .

[0031] Preferably, in step (2), the reducing agent is one or both of lithium aluminum hydride or sodium borohydride.

[0032] Preferably, in step (2), the solvent is one or more of tetrahydrofuran, 2-methyltetrahydrofuran, methanol, or ethanol.

[0033] Preferably, in step (2), the molar amount of the reducing agent is 1 to 2 times the molar amount of the mixed oxidation product.

[0034] Furthermore, the molar amount of the reducing agent is 1.2 to 1.8 times the molar amount of the mixed oxidation products.

[0035] Preferably, in step (2), the reaction temperature is 25–120°C; the reaction time is 1–12 h, more preferably 4–10 h.

[0036] Preferably, in step (3), the oxidant is one or more of ferric nitrate, copper nitrate, cerium nitrate, cobalt nitrate, chromium nitrate, lanthanum nitrate, or manganese nitrate. The present invention selects the above-mentioned oxidants to achieve efficient and rapid reactions while minimizing corrosion to equipment.

[0037] Furthermore, the oxidant is one or more of ferric nitrate, copper nitrate, or manganese nitrate.

[0038] Preferably, in step (3), the molar amount of the oxidant is 1 to 2 times the molar amount of phthalic acid.

[0039] Preferably, in step (3), the reaction temperature is 40–150°C and the reaction time is 10–100 min.

[0040] Beneficial effects:

[0041] This invention achieves highly efficient preparation of phthalaldehyde from o-xylene, with a conversion rate of up to 100% for o-xylene and a total yield of up to 70% for phthalaldehyde. The preparation process does not use corrosive substances such as chlorine, bromine, or nitric acid, is simple, and produces minimal pollution. Furthermore, the produced product is bromine- and chlorine-free, making it suitable for a wide range of applications. Detailed Implementation

[0042] The technical solution of the present invention will be described in detail below through specific embodiments, but the scope of protection of the present invention is not limited to the embodiments described.

[0043] In this embodiment of the invention, the V2O5-TiO2 catalyst doped with metal elements was prepared according to the method of CN110872265A. The required metal salts were mixed to prepare a mixed metal salt solution, TiO2 was added to the solution for impregnation, and finally dried and calcined.

[0044] In the examples, "0.5% Cs-15% V2O5-84.5% TiO2" means that the content of metal element Cs in the catalyst is 0.5wt%, the content of V2O5 in the catalyst is 15wt%, and the content of TiO2 in the catalyst is 84.5wt%.

[0045] Example 1: Preparation of o-phthalaldehyde

[0046] 10 mL of 0.5% Cs-15% V2O5-84.5% TiO2 catalyst was packed into a fixed-bed reactor. Air was introduced and the temperature was raised to 400°C. After stabilization, o-xylene was introduced, with a liquid hourly space velocity (LHSV) of 0.4 h⁻¹. -1 The air space velocity is 3200 h⁻¹. -1 The reaction temperature was 400℃, and the effluent was condensed and separated into gas and liquid phases before entering a collection tank. The product was collected after the reaction stabilized. Gas chromatography analysis showed that the conversion rate of o-xylene was 100%, and the total selectivity for phthalic anhydride, phthalic acid, and phthalamide was 93.8%.

[0047] In a reactor equipped with a mechanical stirrer and reflux device, 0.018 mol of lithium aluminum hydride and 5 mL of tetrahydrofuran solution were added. Then, under vigorous stirring at approximately 0°C, 25 mL of tetrahydrofuran solution containing 0.01 mol of the above mixed oxidation product was slowly added dropwise. After stirring for 15 min, the reaction was carried out at 120°C for 4 h. After cooling to room temperature, the reaction solution was first added dropwise to 10 mL of water, followed by 1 mL of 30% hydrochloric acid solution. The mixture was then extracted with ethyl acetate, and the organic phase was washed with saturated sodium chloride solution. Phthalate was obtained by vacuum distillation. Gas chromatography analysis showed that the conversion rate of the mixed oxidation product was 100%, and the selectivity for phthalic acid was 99.6%.

[0048] 1 mmol of the above-mentioned phthalic acid and 1.3 mmol of Fe(NO3)3·9H2O were added to a reactor, and the reaction was carried out at 60 °C for 20 min. After cooling to room temperature, the reaction solution was extracted with ethyl acetate, and the product was obtained by vacuum distillation. Gas chromatography analysis showed that the conversion of phthalic acid was 100%, and the selectivity for phthalaldehyde was 74.6%. The yield of phthalaldehyde was 69.7%.

[0049] Example 2

[0050] 10 mL of 0.5% Cs-20% V2O5-79.5% TiO2 catalyst was packed into a fixed-bed reactor. Air was introduced and the temperature was raised to 400°C. After stabilization, o-xylene was introduced, with a liquid hourly space velocity (LHSV) of 0.3 h⁻¹. -1 The air space velocity is 3500 h⁻¹. -1 The reaction temperature was 400℃, and the effluent was condensed and separated into gas and liquid before entering a collection tank. After the reaction stabilized, the product was collected, and the product was analyzed by gas chromatography. The conversion rate of o-xylene was 95.4%, and the total selectivity of phthalic anhydride, phthalic acid, and phthalamide was 86.5%.

[0051] In a reactor equipped with a mechanical stirrer and reflux device, 0.012 mol of lithium aluminum hydride and 5 mL of tetrahydrofuran solution were added. Then, under vigorous stirring at approximately 0°C, 25 mL of tetrahydrofuran solution containing 0.01 mol of the mixed oxidation products was slowly added dropwise. After stirring for 15 min, the reaction was carried out at 60°C for 10 h. After cooling to room temperature, the reaction solution was first added dropwise to 10 mL of water, followed by 1 mL of 30% hydrochloric acid solution. The mixture was then extracted with ethyl acetate, and the organic phase was washed with saturated sodium chloride solution. Gas chromatography analysis showed that the conversion rate of the mixed oxidation products was 91.6%, and the selectivity for phthalic acid was 89.4%.

[0052] 1 mmol of the above-mentioned phthalic acid and 1 mmol of Fe(NO3)3·9H2O were added to the reactor, and the reaction was carried out at 150 °C for 10 min. After cooling to room temperature, the product was extracted with ethyl acetate. The product was analyzed by gas chromatography, and the conversion rate of phthalic acid was 90.2%, the selectivity of phthalaldehyde was 64.8%, and the yield of phthalaldehyde was 39.5%.

[0053] Example 3

[0054] A fixed-bed reactor was loaded with 10 mL of 0.5% Cs-15% V2O5-84.5% TiO2 catalyst. Air was introduced and the temperature was raised to 450°C. After stabilization, o-xylene was introduced, with a liquid hourly space velocity (LHSV) of 1.0 h⁻¹. -1 The air space velocity is 3000 h⁻¹. -1 The reaction temperature was 450℃, and the effluent was condensed and separated into gas and liquid before entering a collection tank. After the reaction stabilized, the product was collected, and the product was analyzed by gas chromatography. The conversion rate of o-xylene was 95.7%, and the total selectivity of phthalic anhydride, phthalic acid, and phthalamide was 81.5%.

[0055] In a reactor equipped with a mechanical stirrer and reflux device, 0.015 mol of lithium aluminum hydride and 5 mL of tetrahydrofuran solution were added. Then, under vigorous stirring at approximately 0°C, 25 mL of tetrahydrofuran solution containing 0.01 mol of the mixed oxidation products was slowly added dropwise. After stirring for 15 min, the reaction was carried out at 80°C for 6 h. After cooling to room temperature, the reaction solution was first added dropwise to 10 mL of water, followed by 1 mL of 30% hydrochloric acid solution. The mixture was then extracted with ethyl acetate, and the organic phase was washed with saturated sodium chloride solution. Gas chromatography analysis showed that the conversion rate of the mixed oxidation products was 100%, and the selectivity for phthalic acid was 99.6%.

[0056] 1 mmol of the above-mentioned phthalic acid and 2 mmol of Fe(NO3)3·9H2O were added to the reactor, and the reaction was carried out at 40 °C for 100 min. After cooling to room temperature, the product was extracted with ethyl acetate. The product was analyzed by gas chromatography, and the conversion rate of phthalic acid was 80.5%, the selectivity of phthalaldehyde was 51.6%, and the yield of phthalaldehyde was 32.3%.

[0057] Example 4

[0058] A fixed-bed reactor was loaded with 10 mL of 1% Sb-20% V2O5-79% TiO2 catalyst. Air was introduced and the temperature was raised to 400°C. After stabilization, o-xylene was introduced, with a liquid hourly space velocity (LHSV) of 0.4 h⁻¹. -1 The air space velocity is 2500 h⁻¹. -1The reaction temperature was 400℃, and the effluent was condensed and separated into gas and liquid before entering a collection tank. After the reaction stabilized, the product was collected, and the product was analyzed by gas chromatography. The conversion rate of o-xylene was 97.6%, and the total selectivity of phthalic anhydride, phthalic acid, and phthalamide was 80.6%.

[0059] In a reactor equipped with a mechanical stirrer and reflux device, 0.015 mol of sodium borohydride and 5 mL of methanol solution were added. Then, under vigorous stirring at approximately 0°C, 5 mL of methanol solution containing 0.01 mol of the mixed oxidation products was slowly added dropwise. The reaction was carried out at 25°C for 10 h. The reaction solution was added dropwise to 10 mL of water, extracted with ethyl acetate, and the organic phase was washed with saturated sodium chloride solution. Gas chromatography analysis showed that the conversion rate of the mixed oxidation products was 80.5%, and the selectivity for phthalic acid was 85.2%.

[0060] 1 mmol of the above-mentioned phthalic acid and 1.5 mmol of Cu(NO3)2·3H2O were added to the reactor, and the reaction was carried out at 80 °C for 20 min. After cooling to room temperature, the product was extracted with ethyl acetate. Gas chromatography analysis showed that the conversion rate of phthalic acid was 93.6%, the selectivity of phthalaldehyde was 46.8%, and the yield of phthalaldehyde was 23.6%.

[0061] Example 5

[0062] A fixed-bed reactor was loaded with 10 mL of 1% Zr-15% V2O5-84% TiO2 catalyst. Air was introduced and the temperature was raised to 400℃. After stabilization, o-xylene was introduced, with a liquid hourly space velocity (LHSV) of 0.4 h⁻¹. -1 The air space velocity is 3000 h⁻¹. -1 The reaction temperature was 400℃, and the effluent was condensed and separated into gas and liquid before entering a collection tank. After the reaction stabilized, the product was collected, and the product was analyzed by gas chromatography. The conversion rate of o-xylene was 98.6%, and the total selectivity of phthalic anhydride, phthalic acid, and phthalamide was 85.6%.

[0063] In a reactor equipped with a mechanical stirrer and reflux device, 0.013 mol of lithium aluminum hydride and 5 mL of 2-methyltetrahydrofuran solution were added. Then, under vigorous stirring at approximately 0°C, 25 mL of 2-methyltetrahydrofuran solution containing 0.01 mol of the mixed oxidation products was slowly added dropwise. After stirring for 15 min, the reaction was carried out at 90°C for 10 h. After cooling to room temperature, the reaction solution was first added dropwise to 10 mL of water, followed by 1 mL of 30% hydrochloric acid solution. The mixture was then extracted with ethyl acetate, and the organic phase was washed with saturated sodium chloride solution. Gas chromatography analysis showed that the conversion rate of the mixed oxidation products was 99.4%, and the selectivity for phthalic acid was 97.5%.

[0064] 1 mmol of the above-mentioned phthalic acid and 1.4 mmol of Mn(NO3)2·4H2O were added to the reactor, and the reaction was carried out at 60 °C for 20 min. After cooling to room temperature, the product was extracted with ethyl acetate. Gas chromatography analysis showed that the conversion rate of phthalic acid was 92.8%, the selectivity of phthalaldehyde was 47.5%, and the yield of phthalaldehyde was 36.1%.

[0065] Example 6

[0066] A fixed-bed reactor was loaded with 10 mL of 0.7% Nb-20% V2O5-79.3% TiO2 catalyst. Oxygen was introduced and the temperature was raised to 400°C. After stabilization, o-xylene was introduced, with a liquid hourly space velocity (LHSV) of 0.4 h⁻¹. -1 The air space velocity is 3200 h⁻¹. -1 The reaction temperature was 400℃, and the effluent was condensed and separated into gas and liquid before entering a collection tank. After the reaction stabilized, the product was collected, and the product was analyzed by gas chromatography. The conversion rate of o-xylene was 100%, and the total selectivity of phthalic anhydride, phthalic acid, and phthalamide was 87.3%.

[0067] In a reactor equipped with a mechanical stirrer and reflux device, 0.015 mol of sodium borohydride and 5 mL of ethanol solution were added. Then, under vigorous stirring at approximately 0°C, 5 mL of ethanol solution containing 0.01 mol of the mixed oxidation products was slowly added dropwise. The reaction was carried out at 25°C for 10 h. The reaction solution was added dropwise to 10 mL of water, extracted with ethyl acetate, and the organic phase was washed with saturated sodium chloride solution. Gas chromatography analysis showed that the conversion rate of the mixed oxidation products was 75.6%, and the selectivity for o-phthalaldehyde was 83.1%.

[0068] 1 mmol of the above-mentioned phthalic acid and 1.3 mmol of Ce(NO3)3·6H2O were added to the reactor, and the reaction was carried out at 70 °C for 25 min. After cooling to room temperature, the product was extracted with ethyl acetate. Gas chromatography analysis showed that the conversion rate of phthalic acid was 84.6%, the selectivity of phthalaldehyde was 50.3%, and the yield of phthalaldehyde was 23.3%.

[0069] Example 7

[0070] A fixed-bed reactor was loaded with 10 mL of 0.3% K-15% V2O5-84.7% TiO2 catalyst. Air was introduced and the temperature was raised to 400°C. After stabilization, o-xylene was introduced, with a liquid hourly space velocity (LHSV) of 0.4 h⁻¹. -1 The air space velocity is 3200 h⁻¹. -1The reaction temperature was 400℃, and the effluent was condensed and separated into gas and liquid before entering a collection tank. After the reaction stabilized, the product was collected and analyzed by gas chromatography. The conversion rate of o-xylene was 100%, and the total selectivity of phthalic anhydride, phthalic acid, and phthalamide was 88.6%.

[0071] In a reactor equipped with a mechanical stirrer and reflux device, 0.018 mol of lithium aluminum hydride and 5 mL of 2-methyltetrahydrofuran solution were added. Then, under vigorous stirring at approximately 0°C, 25 mL of 2-methyltetrahydrofuran solution containing 0.01 mol of the mixed oxidation products was slowly added dropwise. After stirring for 15 min, the reaction was carried out at 120°C for 4 h. After cooling to room temperature, the reaction solution was first added dropwise to 10 mL of water, followed by 1 mL of 30% hydrochloric acid solution. The mixture was then extracted with ethyl acetate, and the organic phase was washed with saturated sodium chloride solution. Gas chromatography analysis showed that the conversion rate of the mixed oxidation products was 100%, and the selectivity for phthalic acid was 99.7%.

[0072] 1 mmol of the above-mentioned phthalic acid and 1.2 mmol of Cr(NO3)3·9H2O were added to the reactor, and the reaction was carried out at 60 °C for 20 min. After cooling to room temperature, the product was extracted with ethyl acetate. Gas chromatography analysis showed that the conversion rate of phthalic acid was 65.2%, the selectivity of phthalaldehyde was 54.3%, and the yield of phthalaldehyde was 31.3%.

[0073] Example 8

[0074] A fixed-bed reactor was loaded with 10 mL of 0.7% Cs-15% V2O5-84.3% TiO2 catalyst. Air was introduced and the temperature was raised to 420°C. After stabilization, o-xylene was introduced, with a liquid hourly space velocity (LHSV) of 0.5 h⁻¹. -1 The air space velocity is 3200 h⁻¹. -1 The reaction temperature was 420℃. The effluent was condensed and separated into gas and liquid phases before entering a collection tank. After the reaction stabilized, the product was collected and analyzed by gas chromatography. The conversion rate of o-xylene was 100%, and the total selectivity of phthalic anhydride, phthalic acid, and phthalamide was 89.6%.

[0075] In a reactor equipped with a mechanical stirrer and reflux device, 0.017 mol of lithium aluminum hydride and 5 mL of tetrahydrofuran solution were added. Then, under vigorous stirring at approximately 0°C, 25 mL of tetrahydrofuran solution containing 0.01 mol of the mixed oxidation products was slowly added dropwise. After stirring for 15 min, the reaction was carried out at 100°C for 5 h. After cooling to room temperature, the reaction solution was first added dropwise to 10 mL of water, followed by the addition of 1 mL of 30% hydrochloric acid solution. Extraction was performed with ethyl acetate, and the organic phase was washed with saturated sodium chloride solution. Gas chromatography analysis showed that the conversion rate of the mixed oxidation products was 100%, and the selectivity for phthalic acid was 99.6%.

[0076] 1 mmol of the above-mentioned phthalic acid and 1.3 mmol of Co(NO3)2·6H2O were added to the reactor, and the reaction was carried out at 80 °C for 30 min. After cooling to room temperature, the product was extracted with ethyl acetate. Gas chromatography analysis showed that the conversion rate of phthalic acid was 87.9%, the selectivity of phthalaldehyde was 52.8%, and the yield of phthalaldehyde was 41.5%.

[0077] Example 9

[0078] 10 mL of 0.5% Cs-10% V2O5-79.5% TiO2 catalyst was packed into a fixed-bed reactor. Air was introduced and the temperature was raised to 400 °C. After stabilization, o-xylene was introduced, with a liquid hourly space velocity (LHSV) of 0.4 h⁻¹. -1 The air space velocity is 3200 h⁻¹. -1 The reaction temperature was 400℃, and the effluent was condensed and separated into gas and liquid before entering a collection tank. After the reaction stabilized, the product was collected, and the product was analyzed by gas chromatography. The conversion rate of o-xylene was 91.3%, and the total selectivity of phthalic anhydride, phthalic acid, and phthalamide was 84.2%.

[0079] In a reactor equipped with a mechanical stirrer and reflux device, 0.015 mol of lithium aluminum hydride and 5 mL of tetrahydrofuran solution were added. Then, under vigorous stirring at approximately 0°C, 25 mL of tetrahydrofuran solution containing 0.01 mol of the mixed oxidation products was slowly added dropwise. After stirring for 15 min, the reaction was carried out at 90°C for 5 h. After cooling to room temperature, the reaction solution was first added dropwise to 10 mL of water, followed by the addition of 1 mL of 30% hydrochloric acid solution. The mixture was extracted with ethyl acetate, and the organic phase was washed with saturated sodium chloride solution. Gas chromatography analysis showed that the conversion rate of the mixed oxidation products was 100%, and the selectivity for phthalic acid was 99.7%.

[0080] 1 mmol of the above-mentioned phthalic acid and 1.5 mmol of Fe(NO3)3·9H2O were added to the reactor, and the reaction was carried out at 60 °C for 15 min. After cooling to room temperature, the product was extracted with ethyl acetate. The product was analyzed by gas chromatography, and the conversion rate of phthalic acid was 97.6%, the selectivity of phthalaldehyde was 69.8%, and the yield of phthalaldehyde was 52.2%.

[0081] Comparative Example 1

[0082] 10 mL of 15% V₂O₅-85% TiO₂ catalyst was packed into a fixed-bed reactor. Air was introduced and the temperature was raised to 400 °C. After stabilization, o-xylene was introduced, with a liquid hourly space velocity (LHSV) of 0.4 h⁻¹. -1 The air space velocity is 3200 h⁻¹. -1The reaction temperature was 400℃, and the effluent was condensed and separated into gas and liquid before entering a collection tank. After the reaction stabilized, the product was collected, and the product was analyzed by gas chromatography. The conversion rate of o-xylene was 85.4%, and the total selectivity of phthalic anhydride, phthalic acid, and phthalamide was 78.5%.

[0083] Comparative Example 2

[0084] 10 mL of 10% V₂O₅-90% TiO₂ catalyst was packed into a fixed-bed reactor. Air was introduced and the temperature was raised to 400 °C. After stabilization, o-xylene was introduced, with a liquid hourly space velocity (LHSV) of 0.5 h⁻¹. -1 The air space velocity is 3000 h⁻¹. -1 The reaction temperature was 400℃, and the effluent was condensed and separated into gas and liquid before entering a collection tank. After the reaction stabilized, the product was collected, and the product was analyzed by gas chromatography. The conversion rate of o-xylene was 79.6%, and the total selectivity of phthalic anhydride, phthalic acid, and phthalamide was 74.3%.

[0085] As can be seen from Comparative Examples 1 and 2, when preparing a mixed oxidation product containing phthalic anhydride, phthalic acid, and phthalide by oxidizing o-xylene in the first step reaction, the conversion rate of o-xylene and the total selectivity of the oxidation product are significantly reduced when using unmodified V2O5-TiO2 (i.e., V2O5-TiO2 without metal doping) as a catalyst.

[0086] In this case, carrying out the subsequent two reaction steps will increase the difficulty of separating and purifying the final product, o-phthalaldehyde, thus affecting the preparation effect of the final product.

[0087] As described above, although the invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the invention itself. Various changes in form and detail may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A method for preparing o-phthalaldehyde from o-xylene, characterized in that, Includes the following steps: (1) Using V2O5-TiO2 doped with metal elements as a catalyst, o-xylene and oxygen-containing gas are reacted to obtain a mixed oxidation product containing phthalic anhydride, phthalic acid and phthalphthalene. (2) The mixed oxidation product obtained in step (1) is reacted with a reducing agent in a solvent, and after separation, o-phthalic acid is obtained; (3) The phthalic acid obtained in step (2) is reacted with an oxidant and separated to obtain phthalaldehyde.

2. The method according to claim 1, characterized in that, In step (1), the content of V2O5 in the catalyst is 10-20 wt%; the doped metal element is Sb, Zr, K, Nb or Cs; and the content of the doped metal element in the catalyst is 0.3-1.0 wt%.

3. The method according to claim 1, characterized in that, In step (1), the oxygen-containing gas is oxygen or air; the reaction temperature is 350–450°C; and the liquid hourly space velocity (LISH) is 0.3–1.0 h⁻¹. -1 The gas hourly space velocity (HSV) of the reaction is 2500–3500 h⁻¹. -1 .

4. The method according to claim 1, characterized in that, In step (2), the reducing agent is one or both of lithium aluminum hydride or sodium borohydride.

5. The method according to claim 1, characterized in that, In step (2), the solvent is one or more of tetrahydrofuran, 2-methyltetrahydrofuran, methanol or ethanol.

6. The method according to claim 1, characterized in that, In step (2), the molar amount of the reducing agent is 1 to 2 times the molar amount of the mixed oxidation product; preferably 1.2 to 1.8 times.

7. The method according to claim 1, characterized in that, In step (2), the reaction temperature is 25-120°C; the reaction time is 1-12 hours, preferably 4-10 hours.

8. The method according to claim 1, characterized in that, In step (3), the oxidant is one or more of ferric nitrate, copper nitrate, cerium nitrate, cobalt nitrate, chromium nitrate, lanthanum nitrate, or manganese nitrate.

9. The method according to claim 1, characterized in that, In step (3), the molar amount of the oxidant is 1 to 2 times the molar amount of phthalic acid.

10. The method according to claim 1, characterized in that, In step (3), the reaction temperature is 40–150°C; the reaction time is 10–100 min.

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