The invention relates to 3, 3apos; 4, 4 apos, 4, 4 apos; preparation method of-tetramethyldiphenylalkane

Abstract

The invention belongs to the field of organic chemical industry, and relates to a preparation method of 3, 3 ', 4, 4'-tetramethyl diphenyl alkane. Adding aldehyde into a reactor filled with o-xylene and organic sulfonic acid, reacting for 20-90 minutes under normal pressure to obtain a crude product, cooling after the reaction is completed, washing the crude product with water for three times, separating water and oil phases, and distilling and purifying under reduced pressure or normal pressure to obtain a 3, 3 ', 4, 4'-tetramethyl diphenyl alkane product. Compared with the prior art, the method has the advantages that the use of a large amount of concentrated sulfuric acid is avoided, the reaction time is greatly shortened through the catalytic action of organic sulfonic acid, the selectivity of 3, 3 ', 4, 4'-tetramethyl diphenylalkane is improved, and the synthesis efficiency of 3, 3 ', 4, 4'-tetramethyl diphenylalkane is improved.

Description

Technical Field

[0001] The present invention belongs to the field of organic chemical industry and relates to a method for efficiently producing 3,3',4,4'-tetramethyldiphenylalkane. Background Art

[0002] 3,3',4,4'-Benzophenone tetracarboxylic dianhydride is a raw material for preparing advanced composite polyimide, and can also be used as a curing agent for epoxy resin and a raw material for high-temperature resistant polyester. 3,3',4,4'-Tetramethyldiphenylalkane is an important raw material for synthesizing 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and is generally obtained by reacting o-xylene with aldehyde. In the reaction, the selectivity of the target product 3,3',4,4'-tetramethyldiphenylalkane is often low, and the isomer contents of 2,3',3,4'-tetramethyldiphenylalkane and 2,3',2,3'-tetramethyldiphenylalkane are high, making it difficult to separate them.

[0003] Patent US5254768 discloses a technique using sulfuric acid as a catalyst: a stirred solution of 425 g (4 mol) of o-xylene and 306 g (2 mol) of 64% sulfuric acid, to which 81 g (1 mol) of 37% aqueous formaldehyde solution is added dropwise, and refluxed at 121 °C for 3 hours. The product after the reaction is cooled for 30 min, and the separated oil phase is washed three times with water and dehydrated with anhydrous sodium sulfate to provide 427 g of an oil phase reaction solution. The composition analysis result is 52.5% o-xylene, 38.1% tetramethyldiphenylmethane, and 9.4% miscellaneous substances. The produced tetramethyldiphenylmethane has the following isomeric composition: 59.4% 3,3',4,4'-tetramethyldiphenylmethane, 37.4% 2,3',3,4'-tetramethyldiphenylmethane, and 3.2% 2,3',2,3'-tetramethyldiphenylmethane. The yield of tetramethyldiphenylmethane calculated based on formaldehyde is 72.6%, and the yield of 3,3',4,4'-tetramethyldiphenylmethane is 43.1%. This method uses sulfuric acid as a catalyst and the reaction temperature is as high as 121 °C, and the yield of the product 3,3',4,4'-tetramethyldiphenylmethane is low. Patent JPH02134332A discloses a technique for catalytic synthesis of diarylmethane using sulfuric acid and a surfactant at low temperature. CN101302137B discloses a technique for catalytic alkylation reaction to prepare 3,3',4,4'-tetramethyldiphenylalkane at low temperature using a mixed catalyst. The mixed acid catalyst is a mixture of sulfuric acid with a concentration of 82% - 92% and any one of fatty acids such as formic acid, acetic acid, or propionic acid. This technique significantly reduces the reaction temperature, but requires 76 mol% of sulfuric acid based on the raw material amount and is supplemented with a large amount of fatty acid as a catalyst, and there are problems such as low conversion rate of o-xylene and selectivity of 3,3',4,4'-tetramethyldiphenylalkane, and too long reaction time.

[0004] The above-mentioned patents all have problems such as a large amount of catalyst used, long reaction time, and low selectivity of 3,3',4,4'-tetramethyldiphenylalkane. Developing a new catalytic synthesis process to reduce the amount of catalyst used and improve the selectivity of 3,3',4,4'-tetramethyldiphenylalkane has important practical significance. The purpose of the present invention is to provide a method for obtaining highly selective 3,3',4,4'-tetramethyldiphenylalkane with a small amount of catalyst and a short reaction time. Through a large number of previous literature research and experimental exploration, we found that by using organic sulfonic acid as a catalyst and combining with the regulation of the carbon atom number of the raw material aldehyde, the selectivity of 3,3',4,4'-tetramethyldiphenylalkane can be improved. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for synthesizing 3,3',4,4'-tetramethyldiphenylalkane with high selectivity. Using organic sulfonic acid as a catalyst and aldehydes with different carbon atom numbers as reaction raw materials can reduce the generation of by-products in the reaction and improve the selectivity of 3,3',4,4'-tetramethyldiphenylalkane.

[0006] The above technical object of the present invention is achieved by the following technical solutions:

[0007] A method for preparing 3,3',4,4'-tetramethyldiphenylalkane. Add aldehyde to a reactor containing o-xylene and organic sulfonic acid, and react for 20 - 90 min under atmospheric pressure to obtain a crude product, which is purified to obtain 3,3',4,4'-tetramethyldiphenylalkane product; specifically, add o-xylene and organic sulfonic acid catalyst to a reactor equipped with a stirring and condensation reflux device in sequence, and the aldehyde is slowly added to the reaction system through an injection pump. The reaction is carried out by heating under stirring conditions, and the stirring rate is 300 - 700 rpm. After the reaction is completed, it is cooled to room temperature, and the crude product is washed with water three times. The water and oil phases are separated and purified by vacuum distillation to obtain 3,3',4,4'-tetramethyldiphenylalkane product.

[0008] Among them, in the 3,3',4,4'-tetramethyldiphenylalkane product, the isomer content < 1%, and the purity of the product ≥ 99%.

[0009] Furthermore, the organic sulfonic acid is one of trifluoromethanesulfonic acid, methanesulfonic acid, and p-toluenesulfonic acid. Preferably, it is trifluoromethanesulfonic acid. Compared with the conventional sulfuric acid catalyst that requires high temperature and long reaction time, there are problems such as too strong acidity (resulting in over-alkylation of o-xylene and formation of multi-substituted by-products), poor steric selectivity (sulfuric acid is difficult to control the orientation of the substitution site, and the isomer ratio is significantly high), and complex post-treatment (requiring multiple water washes and dehydration, with low product purity). In the present invention, the organic sulfonic acid (such as trifluoromethanesulfonic acid) as a strong protonic acid promotes the Friedel-Crafts alkylation reaction of aldehyde and o-xylene to generate the target product directionally. Its high catalytic activity and selectivity can inhibit the occurrence of side reactions and ensure that the isomer content is <1%.

[0010] In terms of the steric effect of the catalyst, the CF 3 group of trifluoromethanesulfonic acid enables the aldehyde to preferentially attack the 3-position and 4-position of o-xylene through the steric hindrance effect (the energy difference ΔE = 2.1 eV, compared with ΔE = 0.3 eV of sulfuric acid). Under the catalysis of the organic sulfonic acid, the rate constant (k 1 = 0.15 s -1 ) of the formation of the target product is significantly higher than that of the side reaction (k 2 = 0.002 s -1 ), and the selectivity ratio (k 1 / k 2 = 75) is much higher than that of sulfuric acid catalysis (k 1 / k 2 = 3). Through the synergistic effect of the organic sulfonic acid catalytic system and the optimization of process parameters, the present invention realizes the highly selective synthesis of 3,3',4,4'-tetramethyldiphenylalkane.

[0011] Furthermore, the molar ratio of o-xylene to the organic sulfonic acid is 1:0.03 - 0.2. Compared with the conventional sulfuric acid catalyst, the catalyst dosage is reduced by more than 80 mol%. Excessive catalyst dosage is likely to lead to the formation of by-products 1,2-dimethyl-4-alkylbenzene and isomers; too little catalyst dosage results in low reaction efficiency.

[0012] Furthermore, the raw material aldehyde is one of formaldehyde, methylal, trioxane, paraformaldehyde, acetaldehyde, paraldehyde, acetal, dimethyl acetal, propionaldehyde, isobutyraldehyde. Preferably, it is propionaldehyde, and the molar ratio of aldehyde to o-xylene is 1:3 - 7. Excessive aldehyde will reduce the selectivity of the target product; too little aldehyde dosage results in low production efficiency of 3,3',4,4'-tetramethyldiphenylalkane.

[0013] Furthermore, the aldehyde is continuously added dropwise into the reactor, and the dropping rate of the aldehyde is controlled by an injection pump, which is beneficial to maintaining the concentration gradient of the aldehyde in the reaction system and reducing the risk of local overreaction. In every 1 mL of o-xylene, the dropping rate of the aldehyde is 0.05 - 0.45 mL / h. If the dropping rate is too slow, it is easy to cause the decomposition of 3,3',4,4'-tetramethyldiphenylalkane into the by-product 1,2-dimethyl-4-alkylbenzene; if the dropping rate is too fast, the reaction selectivity is poor. By controlling the dropping rate, the present invention improves the reaction uniformity, avoids polyalkylation by-products, and increases the yield of the target product.

[0014] Furthermore, the temperature of the condenser for condensation reflux is -5°C to 10°C. The control of the condensation temperature can reduce the loss of aldehyde volatilization, and the linear correlation between the dropping rate and the stirring rate ensures the uniform dispersion of the reactants, reducing the by-product formation rate.

[0015] Furthermore, the purification includes washing the crude product with water 3 - 5 times to remove the organic sulfonic acid catalyst, separating the water and oil phases, separating the excessive raw materials (o-xylene, aldehyde) by vacuum distillation, and monitoring the distillation end point by on-line gas chromatography. When the residual amount of o-xylene is <0.1%, the distillation is stopped, and the 3,3',4,4'-tetramethyldiphenylalkane product is obtained after purification. In the present invention, the purification step is simplified, the product purity is high, the process cost is low, and it is suitable for large-scale production.

[0016] Furthermore, the reaction temperature is 50°C to 90°C. The reaction temperature is controlled in two stages: from 0 to 30 min, it is controlled at 50°C to 70°C; after 30 min, it is controlled at 80°C to 90°C. Under atmospheric pressure, the reaction kinetics is controlled by the temperature and the dropping rate to avoid the formation of isomers and the by-product 1,2-dimethyl-4-alkylbenzene caused by high temperature and high pressure; if the temperature is too low, the reaction efficiency is affected.

[0017] Furthermore, the reaction time is 20 - 90 min. If the reaction time is too long, it is easy to cause the formation of isomers and the by-product 1,2-dimethyl-4-alkylbenzene; if the reaction time is short, the conversion rate decreases, affecting the reaction rate.

[0018] The present invention has the following advantages and effects compared with the prior art:

[0019] The present invention uses an organic sulfonic acid as a catalyst to catalytically react o-xylene and aldehyde to synthesize 3,3',4,4'-tetramethyldiphenylalkane with high selectivity. Compared with the prior art, the present invention greatly shortens the reaction time, reduces the formation of by-products, increases the conversion rate of aldehyde and the selectivity of 3,3',4,4'-tetramethyldiphenylalkane, reduces the difficulty of purifying 3,3',4,4'-tetramethyldiphenylalkane, has high product purity, and high production efficiency. Specific Embodiments

[0020] The present invention will be further described in detail below in conjunction with embodiments, but the embodiments of the present invention are not limited thereto.

[0021] Example 1

[0022] 180 mmol (19.11 g) of o-xylene and 18 mmol (2.70 g) of trifluoromethanesulfonic acid were successively added to a reactor equipped with a stirring and condensing reflux device. 45 mmol (2.61 g) of propionaldehyde was slowly dropped into the reactor at a dropping rate of 0.28 mL / h·mL (o-xylene). The temperature was raised to 65 °C, and after reacting for 50 min, it was cooled to room temperature. The masses of the raw material o-xylene and the product 3,3',4,4'-tetramethyldiphenylpropane in the reaction solution were analyzed by gas chromatography internal standard method, with biphenyl as the internal standard. After calculation, the conversion rate of propionaldehyde was 93.66%, and the selectivity was 99.51%. The crude product was washed three times with 100 mL of water, the water and oil phases were separated, and after purification by vacuum distillation, 10.59 g of 3,3',4,4'-tetramethyldiphenylpropane was obtained. The yield based on propionaldehyde was 93.20%, and the purity was 99.82%.

[0023] Example 2

[0024] 180 mmol (19.11 g) of o-xylene and 18 mmol (2.70 g) of trifluoromethanesulfonic acid were successively added to a reactor equipped with a stirring and condensing reflux device. 30 mmol (2.43 g) of formaldehyde aqueous solution (37 wt%) was slowly dropped into the reactor at a dropping rate of 0.18 mL / h·mL (o-xylene). The temperature was raised to 50 °C, and after reacting for 80 min, it was cooled to room temperature. The masses of the raw material o-xylene and the product 3,3',4,4'-tetramethyldiphenylmethane in the reaction solution were analyzed by gas chromatography internal standard method, with biphenyl as the internal standard. After calculation, the conversion rate of o-xylene was 81.44%, and the selectivity was 95.43%. The crude product was washed three times with 100 mL of water, the water and oil phases were separated, and after purification by vacuum distillation, 5.23 g of 3,3',4,4'-tetramethyldiphenylmethane was obtained. The yield based on formaldehyde was 77.72%, and the purity was 99.03%.

[0025] Example 3

[0026] 180 mmol (19.11 g) of o - xylene and 10 mmol (1.50 g) of trifluoromethanesulfonic acid were successively added to a reactor equipped with a stirring and condensation reflux device. 15 mmol (1.98 g) of paraldehyde was slowly dropped into the reactor at a dropping rate of 0.18 mL / h·mL (o - xylene). The temperature was raised to 55 °C, and after reacting for 80 min, it was cooled to room temperature. The masses of the raw material o - xylene and the product 3,3’,4,4’ - tetramethyldiphenylethane in the reaction solution were analyzed by gas chromatography internal standard method, with biphenyl as the internal standard. After calculation, the conversion rate of o - xylene was 76.49% and the selectivity was 94.43%. The crude product was washed three times with 100 mL of water, the water and oil phases were separated, and after purification by vacuum distillation, 7.75 g of 3,3’,4,4’ - tetramethyldiphenylethane was obtained, and the yield based on acetaldehyde was 72.23% and the purity was 99.22%.

[0027] Example 4

[0028] 180 mmol (19.11 g) of o - xylene and 18 mmol (2.70 g) of trifluoromethanesulfonic acid were successively added to a reactor equipped with a stirring and condensation reflux device. 45 mmol (2.61 g) of propionaldehyde was slowly dropped into the reactor at a dropping rate of 0.18 mL / h·mL (o - xylene). The temperature was raised to 55 °C, and after reacting for 50 min, it was cooled to room temperature. The masses of the raw material o - xylene and the product 3,3’,4,4’ - tetramethyldiphenylpropane in the reaction solution were analyzed by gas chromatography internal standard method, with biphenyl as the internal standard. After calculation, the conversion rate of propionaldehyde was 74.77% and the selectivity was 95.12%. The crude product was washed three times with 100 mL of water, the water and oil phases were separated, and after purification by vacuum distillation, 8.08 g of 3,3’,4,4’ - tetramethyldiphenylpropane was obtained, and the yield based on propionaldehyde was 71.12% and the purity was 99.55%.

[0029] Example 5

[0030] 180 mmol (19.11 g) of o - xylene and 18 mmol (2.70 g) of trifluoromethanesulfonic acid were successively added to a reactor equipped with a stirring and condensing reflux device. 45 mmol (3.24 g) of isobutyraldehyde was slowly dropped into the reactor at a dropping rate of 0.18 mL / h·mL (o - xylene). The temperature was raised to 55 °C, and after reacting for 50 min, it was cooled to room temperature. The gas chromatography internal standard method was used to analyze the masses of the raw material o - xylene and the product 3,3’,4,4’ - tetramethyldiphenylisobutane in the reaction solution. Biphenyl was used as the internal standard. After calculation, the conversion rate of isobutyraldehyde was 64.68% and the selectivity was 96.25%. The crude product was washed three times with 100 mL of water, the water and oil phases were separated, and after purification by vacuum distillation, 7.46 g of 3,3’,4,4’ - tetramethyldiphenylisobutane was obtained. The yield based on isobutyraldehyde was 62.25% and the purity was 99.92%.

[0031] Example 6

[0032] 180 mmol (19.11 g) of o - xylene and 10 mmol (0.96 g) of methanesulfonic acid were successively added to a reactor equipped with a stirring and condensing reflux device. 30 mmol (1.74 g) of propionaldehyde was slowly dropped into the reactor at a dropping rate of 0.18 mL / h·mL (o - xylene). The temperature was raised to 65 °C, and after reacting for 90 min, it was cooled to room temperature. The gas chromatography internal standard method was used to analyze the masses of the raw material o - xylene and the product 3,3’,4,4’ - tetramethyldiphenylpropane in the reaction solution. Biphenyl was used as the internal standard. After calculation, the conversion rate of propionaldehyde was 60.59% and the selectivity was 86.32%. The crude product was washed three times with 100 mL of water, the water and oil phases were separated, and after purification by vacuum distillation, 3.96 g of 3,3’,4,4’ - tetramethyldiphenylpropane was obtained. The yield based on propionaldehyde was 52.30% and the purity was 99.13%.

[0033] Example 7

[0034] 180 mmol (19.11 g) of o - xylene and 12 mmol (3.10 g) of p - toluenesulfonic acid were successively added to a reactor equipped with a stirring and condensing reflux device. 30 mmol (1.74 g) of propionaldehyde was slowly dropped into the reactor at a dropping rate of 0.18 mL / h·mL (o - xylene). The temperature was raised to 55 °C, and after reacting for 80 min, it was cooled to room temperature. The masses of the raw material o - xylene and the product 3,3’,4,4’ - tetramethyldiphenylpropane in the reaction solution were analyzed by gas chromatography internal standard method, with biphenyl as the internal standard. After calculation, the conversion rate of propionaldehyde was 69.73%, and the selectivity was 88.29%. The crude product was washed three times with 100 mL of water, the water and oil phases were separated, and after purification by vacuum distillation, 4.66 g of 3,3’,4,4’ - tetramethyldiphenylpropane was obtained. The yield based on propionaldehyde was 61.56%, and the purity was 99.19%.

[0035] Example 8

[0036] 180 mmol (19.11 g) of o - xylene and 18 mmol (2.70 g) of trifluoromethanesulfonic acid were successively added to a reactor equipped with a stirring and condensing reflux device. 25.71 mmol (1.49 g) of propionaldehyde was slowly dropped into the reactor at a dropping rate of 0.18 mL / h·mL (o - xylene). The temperature was raised to 55 °C, and after reacting for 50 min, it was cooled to room temperature. The masses of the raw material o - xylene and the product 3,3’,4,4’ - tetramethyldiphenylpropane in the reaction solution were analyzed by gas chromatography internal standard method, with biphenyl as the internal standard. After calculation, the conversion rate of propionaldehyde was 78.63%, and the selectivity was 93.89%. The crude product was washed three times with 100 mL of water, the water and oil phases were separated, and after purification by vacuum distillation, 4.78 g of 3,3’,4,4’ - tetramethyldiphenylpropane was obtained. The yield based on propionaldehyde was 73.83%, and the purity was 99.23%.

[0037] Example 9

[0038] 180 mmol (19.11 g) of o - xylene and 18 mmol (2.70 g) of trifluoromethanesulfonic acid were successively added to a reactor equipped with stirring and condensing reflux device. 60 mmol (3.48 g) of propionaldehyde was slowly dropped into the reactor at a dropping rate of 0.18 mL / h·mL (o - xylene). The temperature was raised to 55 °C, and after reacting for 50 min, it was cooled to room temperature. The masses of the raw material o - xylene and the product 3,3’,4,4’ - tetramethyldiphenylpropane in the reaction solution were analyzed by gas chromatography internal standard method, with biphenyl as the internal standard. After calculation, the conversion rate of propionaldehyde was 79.66%, and the selectivity was 93.17%. The crude product was washed three times with 100 mL of water, the water and oil phases were separated, and after purification by vacuum distillation, 11.23 g of 3,3’,4,4’ - tetramethyldiphenylpropane was obtained. The yield based on propionaldehyde was 74.22%, and the purity was 99.09%.

[0039] Example 10

[0040] 180 mmol (19.11 g) of o - xylene and 18 mmol (2.70 g) of trifluoromethanesulfonic acid were successively added to a reactor equipped with a stirring and condensation reflux device. 45 mmol (2.61 g) of propionaldehyde was slowly dropped into the reactor at a dropping rate of 0.18 mL / h·mL (o - xylene). The temperature was raised to 55 °C, and after reacting for 20 min, it was cooled to room temperature. The masses of the raw material o - xylene and the product 3,3’,4,4’ - tetramethyldiphenylpropane in the reaction solution were analyzed by gas chromatography internal standard method, with biphenyl as the internal standard. After calculation, the conversion rate of propionaldehyde was 69.56%, and the selectivity was 96.29%. The crude product was washed three times with 100 mL of water, the water and oil phases were separated, and after purification by vacuum distillation, 7.61 g of 3,3’,4,4’ - tetramethyldiphenylpropane was obtained. The yield based on propionaldehyde was 66.98%, and the purity was 99.59%.

[0041] Example 11

[0042] 180 mmol (19.11 g) of o - xylene and 18 mmol (2.70 g) of trifluoromethanesulfonic acid were successively added to a reactor equipped with a stirring and condensation reflux device. 45 mmol (2.61 g) of propionaldehyde was slowly dropped into the reactor at a dropping rate of 0.18 mL / h·mL (o - xylene). The temperature was raised to 55 °C, and after reacting for 90 min, it was cooled to room temperature. The masses of the raw material o - xylene and the product 3,3’,4,4’ - tetramethyldiphenylpropane in the reaction solution were analyzed by gas chromatography internal standard method, with biphenyl as the internal standard. After calculation, the conversion rate of propionaldehyde was 81.55%, and the selectivity was 89.45%. The crude product was washed three times with 100 mL of water, the water and oil phases were separated, and after purification by vacuum distillation, 8.28 g of 3,3’,4,4’ - tetramethyldiphenylpropane was obtained. The yield based on propionaldehyde was 72.95%, and the purity was 99.01%.

[0043] Example 12

[0044] 180 mmol (19.11 g) of o-xylene and 5.4 mmol (0.68 g) of trifluoromethanesulfonic acid were successively added to a reactor equipped with a stirring and condensing reflux device. 45 mmol (2.61 g) of propionaldehyde was slowly dropped into the reactor at a dropping rate of 0.18 mL / h·mL (o-xylene). The temperature was raised to 55 °C, and after reacting for 50 min, it was cooled to room temperature. The gas chromatography internal standard method was used to analyze the masses of the raw material o-xylene and the product 3,3’,4,4’-tetramethyldiphenylpropane in the reaction solution. Biphenyl was used as the internal standard. After calculation, the conversion rate of propionaldehyde was 61.28%, and the selectivity was 96.83%. The crude product was washed three times with 100 mL of water, the water and oil phases were separated, and after purification by vacuum distillation, 6.74 g of 3,3’,4,4’-tetramethyldiphenylpropane was obtained. The yield based on propionaldehyde was 59.34%, and the purity was 99.57%.

[0045] Example 13

[0046] 180 mmol (19.11 g) of o-xylene and 36 mmol (4.86 g) of trifluoromethanesulfonic acid were successively added to a reactor equipped with a stirring and condensing reflux device. 45 mmol (2.61 g) of propionaldehyde was slowly dropped into the reactor at a dropping rate of 0.18 mL / h·mL (o-xylene). The temperature was raised to 55 °C, and after reacting for 50 min, it was cooled to room temperature. The gas chromatography internal standard method was used to analyze the masses of the raw material o-xylene and the product 3,3’,4,4’-tetramethyldiphenylpropane in the reaction solution. Biphenyl was used as the internal standard. After calculation, the conversion rate of propionaldehyde was 91.18%, and the selectivity was 80.09%. The crude product was washed three times with 100 mL of water, the water and oil phases were separated, and after purification by vacuum distillation, 8.29 g of 3,3’,4,4’-tetramethyldiphenylpropane was obtained. The yield based on propionaldehyde was 73.03%, and the purity was 99.13%.

[0047] Example 14

[0048] 180 mmol (19.11 g) of o-xylene and 18 mmol (2.70 g) of trifluoromethanesulfonic acid were successively added to a reactor equipped with a stirring and condensing reflux device. 45 mmol (2.61 g) of propionaldehyde was slowly dropped into the reactor at a dropping rate of 0.18 mL / h·mL (o-xylene). The temperature was raised to 50 °C, and after reacting for 50 min, it was cooled to room temperature. The gas chromatography internal standard method was used to analyze the masses of the raw material o-xylene and the product 3,3’,4,4’-tetramethyldiphenylpropane in the reaction solution. Biphenyl was used as the internal standard. After calculation, the conversion rate of propionaldehyde was 68.81%, and the selectivity was 96.12%. The crude product was washed three times with 100 mL of water, the water and oil phases were separated, and after purification by vacuum distillation, 7.51 g of 3,3’,4,4’-tetramethyldiphenylpropane was obtained. The yield based on propionaldehyde was 66.14%, and the purity was 99.24%.

[0049] Example 15

[0050] 180 mmol (19.11 g) of o - xylene and 18 mmol (2.70 g) of trifluoromethanesulfonic acid were successively added to a reactor equipped with a stirring and condensation reflux device. 45 mmol (2.61 g) of propionaldehyde was slowly dropped into the reactor at a dropping rate of 0.18 mL / h·mL (o - xylene). The temperature was raised to 90 °C, and after reacting for 50 min, it was cooled to room temperature. The quality of the raw material o - xylene and the product 3,3’,4,4’ - tetramethyldiphenylpropane in the reaction solution was analyzed by gas chromatography internal standard method, with biphenyl as the internal standard. After calculation, the conversion rate of propionaldehyde was 84.91%, and the selectivity was 86.97%. The crude product was washed three times with 100 mL of water, the water and oil phases were separated, and after purification by vacuum distillation, 8.38 g of 3,3’,4,4’ - tetramethyldiphenylpropane was obtained. The yield based on propionaldehyde was 73.85%, and the purity was 99.33%.

[0051] Example 16

[0052] 180 mmol (19.11 g) of o - xylene and 18 mmol (2.70 g) of trifluoromethanesulfonic acid were successively added to a reactor equipped with a stirring and condensation reflux device. 45 mmol (2.61 g) of propionaldehyde was slowly dropped into the reactor at a dropping rate of 0.05 mL / h·mL (o - xylene). The temperature was raised to 65 °C, and after reacting for 50 min, it was cooled to room temperature. The quality of the raw material o - xylene and the product 3,3’,4,4’ - tetramethyldiphenylpropane in the reaction solution was analyzed by gas chromatography internal standard method, with biphenyl as the internal standard. After calculation, the conversion rate of propionaldehyde was 82.36%, and the selectivity was 94.93%. The crude product was washed three times with 100 mL of water, the water and oil phases were separated, and after purification by vacuum distillation, 8.87 g of 3,3’,4,4’ - tetramethyldiphenylpropane was obtained. The yield based on propionaldehyde was 78.18%, and the purity was 99.13%.

[0053] Example 17

[0054] 180 mmol (19.11 g) of o-xylene and 18 mmol (2.70 g) of trifluoromethanesulfonic acid were successively added to a reactor equipped with a stirring and condensation reflux device. 45 mmol (2.61 g) of propionaldehyde was slowly dropped into the reactor at a dropping rate of 0.45 mL / h·mL (o-xylene). The temperature was raised to 65 °C, and after reacting for 50 min, it was cooled to room temperature. The masses of the raw material o-xylene and the product 3,3’,4,4’-tetramethyldiphenylpropane in the reaction solution were analyzed by gas chromatography internal standard method, with biphenyl as the internal standard. After calculation, the conversion rate of propionaldehyde was 67.68% and the selectivity was 95.93%. The crude product was washed three times with 100 mL of water, the water and oil phases were separated, and after purification by vacuum distillation, 7.37 g of 3,3’,4,4’-tetramethyldiphenylpropane was obtained, with a yield based on propionaldehyde of 64.93% and a purity of 99.21%.

[0055] Comparative Example 1

[0056] 180 mmol (19.11 g) of o-xylene and 18 mmol (2.70 g) of trifluoromethanesulfonic acid were successively added to a reactor equipped with a stirring and condensation reflux device. 45 mmol (1.35 g) of aqueous formaldehyde solution (37 wt%) was slowly dropped into the reactor at a dropping rate of 0.18 mL / h·mL (o-xylene). The temperature was raised to 55 °C, and after reacting for 50 min, it was cooled to room temperature. The masses of the raw material o-xylene and the product 3,3’,4,4’-tetramethyldiphenylmethane in the reaction solution were analyzed by gas chromatography internal standard method, with biphenyl as the internal standard. After calculation, the conversion rate of o-xylene was 85.38% and the selectivity was 92.31%. The crude product was washed three times with 100 mL of water, the water and oil phases were separated, and after purification by vacuum distillation, 7.94 g of 3,3’,4,4’-tetramethyldiphenylmethane was obtained, with a yield based on formaldehyde of 78.81% and a purity of 97.18%.

[0057] Comparative Example 2

[0058] 180 mmol (19.11 g) of o - xylene and 18 mmol (2.70 g) of trifluoromethanesulfonic acid were successively added to a reactor equipped with a stirring and condensation reflux device. 15 mmol (1.98 g) of paraldehyde was slowly dropped into the reactor at a dropping rate of 0.18 mL / h·mL (o - xylene). The temperature was raised to 55 °C, and after reacting for 50 min, it was cooled to room temperature. The quality of the raw material o - xylene and the product 3,3’,4,4’ - tetramethyldiphenylethane in the reaction solution was analyzed by gas chromatography internal standard method, with biphenyl as the internal standard. After calculation, the conversion rate of o - xylene was 75.60% and the selectivity was 94.42%. The crude product was washed three times with 100 mL of water, the water - oil phase was separated, and after purification by vacuum distillation, 7.61 g of 3,3’,4,4’ - tetramethyldiphenylethane was obtained, and the yield based on acetaldehyde was 71.38% and the purity was 98.35%.

[0059] Comparative Example 3

[0060] 180 mmol (19.11 g) of o - xylene and 18 mmol (2.70 g) of trifluoromethanesulfonic acid were successively added to a reactor equipped with a stirring and condensation reflux device. 45 mmol (2.61 g) of propionaldehyde was slowly dropped into the reactor at a dropping rate of 0.02 mL / h·mL (o - xylene). The temperature was raised to 65 °C, and after reacting for 50 min, it was cooled to room temperature. The quality of the raw material o - xylene and the product 3,3’,4,4’ - tetramethyldiphenylpropane in the reaction solution was analyzed by gas chromatography internal standard method, with biphenyl as the internal standard. After calculation, the conversion rate of propionaldehyde was 85.36% and the selectivity was 89.72%. The crude product was washed three times with 100 mL of water, the water - oil phase was separated, and after purification by vacuum distillation, 8.70 g of 3,3’,4,4’ - tetramethyldiphenylpropane was obtained, and the yield based on propionaldehyde was 76.58% and the purity was 97.33%.

[0061] Explanation of performance results

[0062] Specifically, it can be seen from the above examples that the carbon chain length of the aldehyde has a significant regulatory effect on the product selectivity. When the alkyl substituent of the aldehyde is extended, its steric effect significantly changes the regioselectivity of 3,3’,4,4’ - tetramethyldiphenylalkane. In terms of the catalyst, compared with methanesulfonic acid and p - toluenesulfonic acid, trifluoromethanesulfonic acid, due to its significantly enhanced acidity (pKa ≈ - 12), can more efficiently catalyze the synthesis of 3,3’,4,4’ - tetramethyldiphenylpropane. Therefore, in the reaction of synthesizing 3,3’,4,4’ - tetramethyldiphenylpropane with o - xylene and propionaldehyde as raw materials and trifluoromethanesulfonic acid as the catalyst under the conditions of a reaction temperature of 65 °C and normal pressure, it has a relatively high selectivity and yield.

[0063] The above are only the preferred embodiments of the present invention, and there is no limitation to the present invention in any form. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments with equivalent changes within the scope of the technical solution of the present invention by using the technical content disclosed above. However, as long as it does not depart from the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing 3,3',4,4'-tetramethyldiphenylalkane, characterized in that: The aldehyde is added into a reactor containing o-xylene and an organic sulfonic acid, and reacted for 20 to 90 minutes under normal pressure to obtain a crude product, which is purified to obtain a 3,3',4,4'-tetramethyldiphenylalkane product; Among them, the isomer content of the 3,3',4,4'-tetramethyldiphenylalkane product is less than 1%, and the purity of the product is ≥99%.

2. The method for preparing 3,3',4,4'-tetramethyldiphenylalkane according to claim 1, characterized in that: The organic sulfonic acid is any one of trifluoromethanesulfonic acid, methanesulfonic acid and p-toluenesulfonic acid.

3. The method for preparing 3,3',4,4'-tetramethyldiphenylalkane according to claim 1, characterized in that: The molar ratio of the o-xylene to the organic sulfonic acid is 1:0.03-0.

2.

4. The method for preparing 3,3',4,4'-tetramethyldiphenylalkane according to claim 1, characterized in that: The aldehyde is any one of formaldehyde, acetaldehyde, propionaldehyde and isobutyraldehyde, and the molar ratio of the aldehyde to the o-xylene is 1:3-7.

5. The method for preparing 3,3',4,4'-tetramethyldiphenylalkane according to claim 1, characterized in that: The reactor is equipped with a condensation reflux and magnetic stirring device, the stirring rate is 300-700 rpm, and the aldehyde is continuously dripped into the reactor.

6. The method for preparing 3,3',4,4'-tetramethyldiphenylalkane according to claim 5, characterized in that: The dropping rate of the aldehyde is controlled by a syringe pump, and the dropping rate of the aldehyde in 1 mL of o-xylene is 0.05-0.45 mL / h.

7. A method for preparing 3,3',4,4'-tetramethyldiphenylalkane according to claim 5 or 6, characterized in that: The temperature of the condenser tube for condensation reflux is -5°C to 10°C.

8. The method for preparing 3,3',4,4'-tetramethyldiphenylalkane according to claim 1, characterized in that: The reaction temperature is 50~90℃.

9. The method for preparing 3,3',4,4'-tetramethyldiphenylalkane according to claim 1, characterized in that: The purification comprises washing the crude product with water for 3 to 5 times, separating the water-oil phase, and distilling under reduced pressure or atmospheric pressure at 85 to 145° C. to remove excess raw materials and obtain 3,3',4,4'-tetramethyldiphenylalkane product.

10. The method for preparing 3,3',4,4'-tetramethyldiphenylalkane according to claim 9, characterized in that: The distillation endpoint was monitored by online gas chromatography, and the distillation was stopped when the residual o-xylene content was less than 0.1%.