Method for preparing benzenediol through hydroxylation of phenol

Abstract

The invention discloses a method for preparing benzenediol through hydroxylation of phenol, which comprises the following steps: by taking hydrogen peroxide as a hydroxylating agent, carrying out hydroxylation on a phenol aqueous solution in a reactor under the action of a TS-1 catalyst pretreated by a silane coupling agent alcoholic solution to synthesize benzenediol. Due to the unique pore structure of the pretreated TS-1 catalyst and steric hindrance generated by the action of a silane coupling agent and an alcohol substance in the catalyst, the phenol conversion rate and the benzenediol selectivity are improved, the hydroquinone content in the product is increased, and the economic value is improved; and the method is simple in operation process, convenient in subsequent product treatment and suitable for large-scale industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of hydroquinone synthesis and relates to a method for preparing hydroquinone by hydroxylating phenol. Background Art

[0002] Phenol is a colorless needle-shaped crystal with corrosiveness and a special odor. The melting point is 42°C and the boiling point is 182°C. It is slightly soluble in water at room temperature and easily soluble in organic solvents such as ethanol, chloroform and ether. When the temperature reaches 65°C, it can be miscible with water. The oxygen atom of the phenolic hydroxyl group of phenol is sp2 hybridized and can provide a pair of lone electrons to form a delocalized π bond with the carbon atom of the benzene ring. The electron-donating effect of the hydroxyl group strengthens the polarity of the OH bond, so the hydrogen of the hydroxyl group in phenol can be ionized and has weak acidity. Catechol is the oxidation product of phenol, and there are three isomers, namely: catechol, resorcinol, and hydroquinone. In the reaction process of preparing catechol by selective oxidation using phenol as a raw material, catechol and hydroquinone are the main products.

[0003] Catechol, which was first obtained by dry distillation from catechin, is also called catechol. It is a colorless crystal with a melting point of 105°C and a boiling point of 245°C. It is soluble in organic solvents such as water, ethanol and ether. It has reducing properties and exists in nature in the form of derivatives. As an organic intermediate, catechol is not only widely used in pesticides, spices and pharmaceutical industries, but also can be used to synthesize antioxidants, hair dyes and developers. It is an important fine chemical intermediate. Half of the global consumption of catechol is used to produce low-toxic and high-efficiency pesticides. In the spice industry, catechol is one of the main raw materials for synthesizing spices such as vanillin. Hydroquinone, also known as hydroquinone, is a white needle-shaped crystal with a special odor, a melting point of 172°C and a boiling point of 287°C. It is soluble in organic solvents such as water, ethanol and ether, slightly soluble in benzene, and easily oxidized to form p-benzoquinone. Hydroquinone is also an important fine chemical intermediate that can be used in photosensitive materials, rubber, dyes and daily chemical industries. Nearly 40% of the world's hydroquinone is used in the photosensitive materials industry. Hydroquinone and its derivatives can be used as photographic developers or added to photosensitive resins as thermal inhibitors.

[0004] Traditional production processes for hydroquinone include: o-chlorophenol hydrolysis, disulfonic acid phenol alkali melting, aniline oxidation, and benzoquinone reduction, but the traditional production methods are complex and polluting. In the 1970s, the production process of hydroquinone using phenol as a substrate through hydroxylation was the most valuable production method due to its mild reaction conditions, less pollution, and simple production conditions. Although there are various catalysts for phenol hydroxylation and the process conditions are constantly being optimized, there are still technical problems in the current production process, such as low phenol conversion rate, low ratio of para-position to ortho-position in the product hydroquinone, and poor economic efficiency. Summary of the invention

[0005] The present invention provides a method for preparing hydroquinone by hydroxylation of phenol, which effectively solves the technical problems of low conversion rate of hydroquinone prepared by hydroxylation of phenol and low ratio of para-position to ortho-position in hydroquinone product, improves economic value and is suitable for large-scale industrial production. The method of pre-treating the catalyst before the reaction can not only effectively improve the conversion rate of phenol and the content of para-position in the product, but also solves the problems of difficulty in separating the product from alcohol substances after the reaction and complicated separation process.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing hydroquinone by hydroxylation of phenol comprises the following steps: using hydrogen peroxide as a hydroxylation agent, and hydroxylating a phenol aqueous solution to synthesize hydroquinone in a reactor under the action of a TS-1 catalyst pretreated with a silane coupling agent alcohol solution.

[0008] The specific steps include: putting a phenol aqueous solution and a pretreated TS-1 catalyst into a reactor, and when the reaction temperature reaches 30-100° C., adding hydrogen peroxide dropwise, and continuing to keep the temperature for reaction after the addition is completed to obtain a hydroquinone product.

[0009] The pretreatment process comprises placing the TS-1 catalyst into a silane coupling agent alcohol solution, heating and refluxing at 40-160° C. for 4-6 hours, and drying to obtain the pretreated TS-1 catalyst.

[0010] The solvent of the silane coupling agent alcohol solution is one or both of monohydric alcohol and dihydric alcohol, and preferably the solvent is one or more of methanol, 1,2-cyclohexanediol and 1,4-cyclohexanediol.

[0011] The silane coupling agent is one or more of KH570, APTES and DETAS, preferably APTES.

[0012] The mass fraction of the silane coupling agent in the silane coupling agent alcohol solution is 2% to 10%, preferably 4% to 8%.

[0013] The phenol content of the phenol aqueous solution is 5%-60%, preferably 15%-50%.

[0014] The molar ratio of phenol to hydrogen peroxide is 0.5-5:1, preferably 2-4:1.

[0015] The hydrogen peroxide drops are added in 60-90 minutes.

[0016] The reaction temperature is 50-80°C.

[0017] The TS-1 catalyst has a short b-axis flake and mesoporous structure, which is beneficial to the diffusion of reactants and products in the pores.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] The present invention uses phenol aqueous solution as a reaction raw material, uses hydrogen peroxide as a hydroxylating agent, and prepares hydroquinone under the catalysis of TS-1 pretreated with a silane coupling agent alcohol solution. The para-proportion in the obtained product is significantly improved, which increases the economic value of the reaction. In addition, it effectively avoids adding alcohol substances to the reaction system, and solves the problem of complex separation process of reaction products. The unique pore structure of the catalyst and the steric hindrance generated by the silane coupling agent and the alcohol substance acting inside the catalyst improve the phenol conversion rate and hydroquinone selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the SEM image of TS-1 catalyst. DETAILED DESCRIPTION

[0021] Example 1

[0022] Preparation of TS-1 catalyst: 320g of tetrabutyl silicate was added to an aqueous solution containing 0.35g of hydroxypropyltrimethylammonium fluoride chitosan and 40.6g of tetrapropylammonium hydroxide, and stirred vigorously at room temperature for 2h; 26.75g of tetrabutyl titanate was dissolved in isopropanol and added dropwise to the above solution, stirred at room temperature for 4h, heated under reflux at 70°C for 30min, and then the isopropanol was evaporated; the sample was placed in a polytetrafluoroethylene-lined crystallization reactor and crystallized at 180°C for 24h, the crystallized sample was poured into a centrifuge tube, centrifuged for 5min, the sample was collected and washed 3 times, dried at 100°C for 2h, and calcined at 550°C for 4h to obtain TS-1 catalyst, such as Figure 1 As shown, it has a short b-axis flake and mesoporous structure.

[0023] Example 2

[0024] First, the silane coupling agent APTES was dissolved in methanol, 1,2-cyclohexanediol, 1,4-cyclohexanediol and their mixed alcohols to obtain 5 kinds of alcohol solutions, as shown in Table 1, wherein the various alcohol solutions were added at a molar ratio of 1:1, and the mass fraction of APTES was 5%. The catalyst was pretreated by heating and reflux. 10g TS-1 catalyst and an equal volume of reaction solution were loaded into the reactor, and heated to reflux for 2h after the temperature rose to 110°C. The reacted catalyst was filtered out and vacuum dried at 80-100°C to obtain a pretreated catalyst, which was named according to the composition of the reaction solution as shown in Table 1.

[0025] Table 1 Catalyst nomenclature

[0026]

[0027]

[0028] Example 3

[0029] 3g M-TS-1 and 40% phenol aqueous solution were added to a three-necked flask. When the reaction temperature reached 65°C, hydrogen peroxide was slowly added dropwise. The molar ratio of phenol to hydrogen peroxide was 2:1. The hydrogen peroxide was added dropwise within 70-85 minutes. After the addition of hydrogen peroxide was completed, the reaction was continued for 1 hour. The obtained product was analyzed by gas chromatography, and the conversion rate of phenol was 37.87%, the selectivity of hydroquinone was 82.71%, and the ratio of ortho-hydroquinone was 1.6.

[0030] Example 4

[0031] 3g 1,2-TS-1 and 40% phenol aqueous solution were added to a three-necked flask. When the reaction temperature reached 65°C, hydrogen peroxide was slowly added dropwise. The molar ratio of phenol to hydrogen peroxide was 2:1. The hydrogen peroxide was added dropwise within 70-85 minutes. After the addition of hydrogen peroxide was completed, the reaction was continued for 1 hour. The obtained product was analyzed by gas chromatography, and the conversion rate of phenol was 37.56%, the selectivity of dihydroxybenzene was 87.16%, and the ratio of orthobenzene was 1.9.

[0032] Example 5

[0033] 3g 1,4-TS-1 and 40% phenol aqueous solution were added to a three-necked flask. When the reaction temperature reached 65°C, hydrogen peroxide was slowly added dropwise. The molar ratio of phenol to hydrogen peroxide was 2:1. The hydrogen peroxide was added dropwise within 70-85 minutes. After the addition of hydrogen peroxide was completed, the reaction was continued for 1 hour. The obtained product was analyzed by gas chromatography, and the conversion rate of phenol was 38.86%, the selectivity of dihydroxybenzene was 88.42%, and the ratio of ortho-benzene was 1.8.

[0034] Example 6

[0035] 3g 1,2-M-TS-1 and 40% phenol aqueous solution were added to a three-necked flask. When the reaction temperature reached 65°C, hydrogen peroxide was slowly added dropwise. The molar ratio of phenol to hydrogen peroxide was 2:1. The hydrogen peroxide was added dropwise within 70-85 minutes. After the addition of hydrogen peroxide was completed, the reaction was continued for 1 hour. The obtained product was analyzed by gas chromatography, and the conversion rate of phenol was 39.78%, the selectivity of dihydroxybenzene was 92.08%, and the ratio of ortho-benzene was 2.6.

[0036] Example 7

[0037] 3g 1,4-M-TS-1 and 40% phenol aqueous solution were added to a three-necked flask. When the reaction temperature reached 65°C, hydrogen peroxide was slowly added dropwise. The molar ratio of phenol to hydrogen peroxide was 2:1. The hydrogen peroxide was added dropwise within 70-85 minutes. After the addition of hydrogen peroxide was completed, the reaction was continued for 1 hour. The obtained product was analyzed by gas chromatography, and the conversion rate of phenol was 37.96%, the selectivity of hydroquinone was 90.42%, and the ratio of ortho-hydroquinone was 2.2.

Claims

1. A method for preparing hydroquinone by hydroxylation of phenol, characterized in that: The method comprises using hydrogen peroxide as a hydroxylating agent, and under the action of a TS-1 catalyst pretreated with a silane coupling agent alcohol solution, hydroxylating a phenol aqueous solution in a reactor to synthesize hydroquinone.

2. A method for preparing hydroquinone by hydroxylation of phenol as claimed in claim 1, characterized in that: The specific steps include: putting phenol aqueous solution and pretreated TS-1 catalyst into a reactor, adding hydrogen peroxide dropwise when the reaction temperature reaches 30-100°C, and continuing to keep warm for reaction after the addition is completed to obtain hydroquinone.

3. A method for preparing hydroquinone by hydroxylation of phenol as claimed in claim 1, characterized in that: The pretreatment process comprises placing the TS-1 catalyst into a silane coupling agent alcohol solution, heating and refluxing at 40-160° C. for 4-6 hours, and drying to obtain the pretreated TS-1 catalyst.

4. A method for preparing hydroquinone by hydroxylation of phenol as claimed in any one of claims 1 to 3, characterized in that: The solvent of the silane coupling agent alcohol solution is one or two of monohydric alcohol and dihydric alcohol.

5. A method for preparing hydroquinone by hydroxylation of phenol as claimed in any one of claims 1 to 3, characterized in that: The silane coupling agent is one or more of KH570, APTES and DETAS.

6. A method for preparing hydroquinone by hydroxylation of phenol as claimed in any one of claims 1 to 3, characterized in that: The mass fraction of the silane coupling agent in the silane coupling agent alcohol solution is 2% to 10%.

7. A method for preparing hydroquinone by hydroxylation of phenol as claimed in any one of claims 1 to 3, characterized in that: The phenol aqueous solution has a phenol content of 5% to 60% by mass; and / or, The molar ratio of the phenol to the hydrogen peroxide is 0.5-5:

1.

8. A method for preparing hydroquinone by hydroxylation of phenol as claimed in any one of claims 1 to 3, characterized in that: The reaction temperature is 50-80°C.

9. A method for preparing hydroquinone by hydroxylation of phenol as claimed in claim 2, characterized in that: The hydrogen peroxide drops are added in 60-90 minutes.

10. A method for preparing hydroquinone by hydroxylation of phenol according to any one of claims 1 to 3, characterized in that: The TS-1 catalyst has a short b-axis flake and mesoporous structure.

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