Method for preparing 2-isopropyl-4, 5-dimethylphenol

Abstract

The invention discloses a method for preparing 2-isopropyl-4, 5-dimethylphenol, which mainly comprises the following steps: S1, weighing a mixture of 3, 4-and 3, 5-dimethylphenol, a catalyst and an alkylated compound in parts by mass, adding the dimethylphenol mixture and the catalyst into a reactor, starting stirring, heating to a first temperature in an oil bath, introducing the alkylated compound for reaction, and cooling to a second temperature in the oil bath; ventilating for a period of time; s2, after introducing the alkylated compound, heating to a second temperature, carrying out heat preservation reaction, sampling and analyzing, and if the 2, 6-isopropyl-4, 5-xylenol is less than or equal to 1.0%, continuing to add the alkylated compound until the 2, 6-isopropyl-4, 5-xylenol is qualified, if the 2, 6-isopropyl-4, 5-xylenol is not qualified; and S3, separating the catalyst from the reaction product generated in the previous step, adding the reaction product into a rectifying still, rectifying to obtain an alkylated compound at normal pressure, then rectifying under reduced pressure to distill out the front component for mechanical application, continuously rectifying under reduced pressure to obtain 3, 5-xylenol and 2-isopropyl-4, 5-dimethylphenol fractions in sequence, and obtaining the residues of diisopropyl by-products, namely 2, 6-diisopropyl-4, 5-xylenol and 3, 5-dimethylphenol in the still, namely the diisopropyl by-products, namely 2, 6-diisopropyl-4, 5-xylenol and 2, 6-diisopropyl-4, 5-dimethylphenol. The method comprises the following steps: adding 2, 6-diisopropyl 4, 5-xylenol mixed fractions into a solvent;

Description

Technical Field

[0001] The invention relates to the field of chemical industry, and more specifically to a method for preparing 2-isopropyl-4,5-dimethylphenol. Background Art

[0002] 2-isopropyl-4,5-dimethylphenol, structure Figure 1 , is a component used to prepare certain monodentate or bidentate organophosphorus compounds. Organophosphorus compounds derived from aromatic alcohols have many important commercial applications, including their use as antioxidants, stabilizers, antiwear additives, and as ligands in various catalytic processes such as the hydrocyanation or hydroformylation of olefins.

[0003] 2-isopropyl-4,5-dimethylphenol (boiling point 238°C, melting point about 69°C) is generally obtained in industry by alkylation reaction with 3,4-dimethylphenol as raw material under the action of alkylation catalyst. The alkylation catalyst used can be one of benzenesulfonic acid, cationic sulfonic acid exchange resin or phenol aluminum; reaction such as Figure 2 shown.

[0004] 3,4-Dimethylphenol is an organic synthetic raw material, colorless needle-shaped crystal, melting point 66℃, boiling point 225℃, slightly soluble in water, soluble in organic solvents such as ethanol and sodium hydroxide solution. 3,4-Dimethylphenol is mainly used to make fusible polyimide, and is also used to make resins, medicines, fragrances, dyes, disinfectants and stabilizers for various organic compounds.

[0005] The sources and production methods of 3,4-dimethylphenol are as follows: the crude phenol obtained from the washing oil fraction of coal tar, after sodium hydroxide saponification and sulfuric acid acidification, contains phenol, cresol and xylenol; mixed xylenol can be separated from the crude phenol, 3,5-xylenol (boiling point is 219 ℃) is removed by distillation, the residue is distilled, the 225℃~229℃ fraction is collected, cooled and crystallized, and 3,4-xylenol is obtained by centrifugation. The source of 3,4-dimethylphenol in this method is limited and difficult to separate. In addition, the product can also be obtained by sulfonation, alkali fusion, acid precipitation and distillation with o-xylene as raw material. However, this process is seriously polluting and dangerous and has been eliminated.

[0006] The content of 3,4-dimethylphenol in the mixed dimethylphenol refined from coking cresol is 8-10%, and the content of 3,5-dimethylphenol is 35-45%. The mixed dimethylphenol is distilled to obtain 3,4-dimethylphenol with a mass fraction of 85% to 92% and a yield of 50%. This fraction also contains pyridine, methylpyridine, 2,4-dimethylphenol, 2,5-dimethylphenol, p-ethylphenol, m-ethylphenol, 2,3-dimethylphenol, 3,5-dimethylphenol, trimethylphenol, methylethylphenol, neutral oil and other impurities, among which 3,5-dimethylphenol and trimethylphenol are mainly 3,5-dimethylphenol and trimethylphenol, and their boiling points are 219 ℃, 220 ℃ (2,4,6-trimethylphenol), and 226 ℃ (2,3,6-trimethylphenol), respectively. In particular, the difference between 2,3,6-trimethylphenol and 3,4-dimethylphenol is very small. However, most processes have poor purification effects on 3,5-dimethylphenol and 3,4-dimethylphenol in mixed dimethylphenol, and some processes have poor quality of 3,5-dimethylphenol and 3,4-dimethylphenol, which affects their use. Therefore, a processing technology for extracting 2-isopropyl-4,5-dimethylphenol and 3,5-dimethylphenol is proposed to solve the above problems.

[0007] 3,5-Dimethylphenol (boiling point 219 ℃, melting point 63 ℃) is an intermediate for the preparation of carbamate insecticides and is widely used in the production of vitamins, disinfectants, dyes, drugs, fragrances, rubber accelerators, anti-aging agents, phenolic resins, etc. In addition, 3,5-dimethylphenol is used as a cold rolling oil additive for steel rolling and a high-quality flame-resistant and non-toxic turbine oil additive, which can extend the life of cold rolling oil and turbine oil for steel rolling mills. The most important domestic use is to chlorinate 3,5-dimethylphenol to produce 4-chloro-3,5-dimethylphenol, which is a highly effective disinfectant and preservative used in detergents such as soaps and hand sanitizers.

[0008] Traditional 3,5-dimethylphenol is mainly derived from coal tar, but its quantity is extremely limited and cannot meet the needs of industrial production. At the same time, it is quite difficult to separate 3,5-dimethylphenol from the complex coal tar components. At present, the production methods of 3,5-dimethylphenol include: meta-xylene sulfonation alkali fusion method, 3,5-dimethyl-2-cyclohexenone dehydrogenation method, halogenated benzene hydrolysis method, and isophorone aromatization method. The main problems of the first two methods are: low product selectivity, strong acid and / or strong base are used in the process, equipment corrosion is serious, the process is complicated, and it is difficult to obtain a product with high purity. The method of preparing 3,5-dimethylphenol by aromatization of isophorone has the advantages of high atomic utilization and green environmental protection, and is considered to be a method with industrial potential, but the catalyst is a homogeneous catalyst with high separation energy consumption, or a solid catalyst but poor activity, the reaction conditions are relatively harsh, and the yield is low, which needs further optimization.

[0009] However, the present inventors have discovered a method for preparing 2-isopropyl-4,5-dimethylphenol by alkylation of 3,4-dimethylphenol with available positions from 3,5- and 3,4-dimethylphenol having approximately the same boiling point, and co-producing 3,5-dimethylphenol with no available positions for alkylation, and separating the reaction products by distillation and crystallization. Summary of the invention

[0010] The technical problem to be solved by the present invention is to provide a method for preparing 2-isopropyl-4,5-dimethylphenol and co-producing 3,5-dimethylphenol, which can overcome the problem that most processes in the prior art have poor purification effects on 3,5-dimethylphenol and 3,4-dimethylphenol in mixed dimethylphenols, and that some processes have poor quality of 3,4-dimethylphenol, which affects its use.

[0011] In order to solve the above problems, the present invention provides a method for preparing 2-isopropyl-4,5-dimethylphenol, comprising the following steps: S1: weigh a mixture of 3,4- and 3,5-dimethylphenol, a catalyst, and an alkylating compound according to a mass ratio, put the dimethylphenol mixture and the catalyst into a reactor, start stirring, heat the oil bath to a first temperature, introduce the alkylating compound to react, and ventilate for a period of time; S2: After the alkylated compound is passed, the temperature is raised to the second temperature for heat preservation and reaction, and sampling is performed for analysis. The content of 2,6-isopropyl-4,5-dimethylphenol is required to be ≤1.0% for passing. If it is not passed, the alkylated compound is continuously added until it is passed; S3: Separating the catalyst from the reaction product produced in the above steps and adding it to a distillation kettle, first distilling out the alkylated compound under normal pressure, then distilling out the former under reduced pressure, and continuing the distillation under reduced pressure to obtain 3,5-dimethylphenol and 2-isopropyl-4,5-dimethylphenol fractions in turn, and the residue in the distillation kettle is a mixed fraction of the diisopropyl by-product 2,6-diisopropyl-4,5-dimethylphenol and 3,6-diisopropyl-4,5-dimethylphenol.

[0012] Preferably, in step S1, the first temperature is 70°C-130°C, and the ventilation time is 4-10 hours.

[0013] Preferably, in step S2, the second temperature is 85°C-145°C, and the insulation reaction time is 2 hours.

[0014] Preferably, in step S1, the molar ratio of 3,4-dimethylphenol to the alkylated compound in the mixture is 1.00 to 1.15.

[0015] Preferably, the alkylated compound is propylene.

[0016] Preferably, the catalyst is one of sulfuric acid, phosphoric acid, aromatic sulfonic acid, cationic sulfonic acid exchange resin, aluminum oxide type solid acid and aluminum phenolate.

[0017] Preferably, in step S1, the catalyst is a liquid acid catalyst; in step S3, the catalyst is separated from the reaction product by washing and neutralizing with a 10% dilute alkali aqueous solution.

[0018] Preferably, in step S1, the catalyst is a solid acid catalyst; in step S3, the catalyst is separated from the reaction product by filtration.

[0019] Preferably, at least a portion of the diisopropyl by-product in the reaction product is converted through transalkylation and isomerization reaction to achieve the target product yield. This process step can be carried out simultaneously with the alkylation reaction, or at a later time point, in the same container or in a different container; the transalkylation and isomerization reactions can be carried out at a reaction temperature (second temperature) that is 15-20° C. higher than the initial temperature (first temperature) of the olefin alkylation reaction.

[0020] Preferably, in step S3, the reaction product is subjected to vacuum distillation to produce crude 2-isopropyl-4,5-dimethylphenol substantially free of 3,5-dimethylphenol, which can be purified by distillation and crystallization to obtain purified 2-isopropyl-4,5-dimethylphenol.

[0021] Compared with the prior art, the present invention has the following technical advantages: 1. The process of the present invention is simple and the reaction conditions are mild. The characteristic of 3,5-xylenol that it does not react with propylene is utilized. The isopropylation reaction is performed and then distillation is used to separate the propylene. The corresponding pure 2-isopropyl-4,5-xylenol and 3,5-xylenol are obtained by distillation or crystallization. The process is relatively simple, the pollution is small and the overall efficiency is high.

[0022] 2. The yield of the product of this process technology is very high. Using a mixture of 3,4- and 3,5-dimethylphenol as raw materials, the total yield of 99% grade 3,5-dimethylphenol extracted is above 90%; the total yield of 98% grade 2-isopropyl-4,5-dimethylphenol is above 85-95%.

[0023] 3. The alkylation reaction of propylene directly with a mixture of 3,4- and 3,5-dimethylphenol under acidic conditions to produce 2-isopropyl-4,5-dimethylphenol has very low requirements on the purity of raw materials and does not require high-purity 3,4-dimethylphenol raw materials; the method utilizes the characteristics that 3,5-dimethylphenol does not react with propylene, and 3,4-dimethylphenol reacts with propylene to form first- or second-generation isopropyl, and is separated. Compared with various traditional methods of separating 3,5-dimethylphenol and 3,4-dimethylphenol and then obtaining 2-isopropyl-4,5-dimethylphenol, this method is simpler and easier to operate, has a wide source of raw materials, and has a low production cost. The process has better operability and strong practicality, and has good economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is the structural formula of 2-isopropyl-4,5-dimethylphenol.

[0025] Figure 2 The invention discloses a reaction process for preparing 2-isopropyl-4,5-dimethylphenol. DETAILED DESCRIPTION

[0026] The technical scheme of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention. The purity of the product obtained in the embodiment is HPLC purity unless otherwise specified. Example

[0027] A 1500 mL stirred autoclave was charged with 705 g of a mixture of 3,4- and 3,5-dimethylphenol (71% by mass of 3,4-dimethylphenol and 26% by mass of 3,5-dimethylphenol), 3,4-dimethylphenol (4 moles) and a catalyst (10 g) cation exchange resin.

[0028] Before adding propylene, the autoclave was evacuated to 30 kPa and heated to 135°C. The impeller speed was kept constant at 1000 rpm. Propylene was added continuously to maintain a pressure of 400 kPa until 176 g of propylene (4 mol) was consumed.

[0029] Subsequently, the propylene supply was disconnected and the reaction mixture was heated to 140° C. and maintained at that temperature for 180 minutes to complete the subsequent transalkylation and isomerization reactions.

[0030] The yield refers to the number of moles of 2-isopropyl-4,5-dimethylphenol in the product mixture relative to the number of moles of 3,4-dimethylphenol added, and the conversion rate (CONV) refers to the molar fraction of the converted initial material 3,4-dimethylphenol. The residue of the product mixture contains other phenol by-products. After the reaction is completed, the catalyst is removed and the mixed solution is distilled under reduced pressure to obtain 466.38g of 2-isopropyl-4,5-dimethylphenol with a purity of 99.5% and a yield of 71%. 162.92g of 3,5-dimethylphenol with a purity of 99.54% is co-produced. Example

[0031] 705kg of a mixture of 3,4- and 3,5-dimethylphenol (3,4-dimethylphenol with a mass content of 71% and 3,5-dimethylphenol with a mass content of 26%), including 3,4-dimethylphenol (4 kmol) and 10kg of benzenesulfonic acid, was added into a reactor, stirred and heated to 70°C; 176kg of propylene (4 kmol) was continuously added dropwise into the reactor within 3 hours, maintaining the reaction temperature at 70±2°C. After the addition was completed, the reaction temperature was raised to 65°C and the reaction was maintained for 180 minutes; after the reaction was completed, the catalyst was removed, and the mixed solution was subjected to vacuum distillation to obtain 468kg of 2-isopropyl-4,5-dimethylphenol with a purity of 99.5%, with a yield of 73%. 165kg of 3,5-dimethylphenol with a purity of 99.5% was co-produced. Example

[0032] 705kg of a mixture of 3,4- and 3,5-dimethylphenol (3,4-dimethylphenol with a mass content of 71% and 3,5-dimethylphenol with a mass content of 26%), including 3,4-dimethylphenol (4 kmol) and 10kg of phenol aluminum catalyst, were added into a reactor, stirred and heated to 125°C; 176kg of propylene (4 kmol) was continuously added dropwise into the reactor within 3 hours, maintaining the reaction temperature at 130±2°C. After the addition was completed, the reaction temperature was raised to 140°C and the reaction was maintained for 180 minutes; after the reaction was completed, the catalyst was filtered off, and the mixed solution was subjected to vacuum distillation to obtain 476.1 kg of 2-isopropyl-4,5-dimethylphenol with a purity of 99.5% and a yield of 78%. 166kg of 3,5-dimethylphenol with a purity of 99.5% was co-produced.

[0033] The above examples further prove that the yield of the product of the process technology is very high. Using a mixture of 3,4- and 3,5-dimethylphenol as raw materials, the total yield of 99% grade 3,5-dimethylphenol extracted is above 90%; the total yield of 98% grade 2-isopropyl-4,5-dimethylphenol is above 85-95%.

[0034] The above description shows and describes several preferred embodiments of the invention, but as mentioned above, it should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the invention concept described herein through the above description or the technology or knowledge of the relevant field. And the changes and modifications made by those skilled in the art do not depart from the spirit and scope of the present invention, and should be within the scope of protection of the claims attached to the present invention.

[0035] Although the disclosure is disclosed as above, the protection scope of the disclosure is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the disclosure, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A method for preparing 2-isopropyl-4,5-dimethylphenol, characterized in that: The following steps are involved: S1: weigh a mixture of 3,4- and 3,5-dimethylphenol, a catalyst, and an alkylating compound according to a mass ratio, put the dimethylphenol mixture and the catalyst into a reactor, start stirring, heat the oil bath to a first temperature, introduce the alkylating compound to react, and ventilate for a period of time; S2: After the alkylated compound is passed, the temperature is raised to the second temperature for heat preservation and reaction, and sampling is performed for analysis. The content of 2,6-isopropyl-4,5-dimethylphenol is required to be ≤1.0% for passing. If it is not passed, the alkylated compound is continuously added until it is passed; S3: Separating the catalyst from the reaction product produced in the above steps and adding it to a distillation kettle, first distilling out the alkylated compound under normal pressure, then distilling out the former under reduced pressure, and continuing the distillation under reduced pressure to obtain 3,5-dimethylphenol and 2-isopropyl-4,5-dimethylphenol fractions in turn, and the residue in the distillation kettle is a mixed fraction of the diisopropyl by-product 2,6-diisopropyl-4,5-dimethylphenol and 3,6-diisopropyl-4,5-dimethylphenol.

2. The method for preparing 2-isopropyl-4,5-dimethylphenol according to claim 1, characterized in that: In step S1, the first temperature is 70°C-130°C, and the ventilation time is 4-10 hours.

3. The method for preparing 2-isopropyl-4,5-dimethylphenol according to claim 1, characterized in that: In step S2, the second temperature is 85°C-145°C, and the insulation reaction time is 2 hours.

4. The method for preparing 2-isopropyl-4,5-dimethylphenol according to claim 1, characterized in that: In step S1, the molar ratio of 3,4-dimethylphenol to the alkylated compound in the mixture is 1.00 to 1.

15.

5. The method for preparing 2-isopropyl-4,5-dimethylphenol according to claim 1 or 4, characterized in that: The alkylated compound is propylene.

6. The method for preparing 2-isopropyl-4,5-dimethylphenol according to claim 1, characterized in that: The catalyst is one of sulfuric acid, phosphoric acid, aromatic sulfonic acid, cationic sulfonic acid exchange resin, aluminum oxide type solid acid and aluminum phenolate.

7. The method for preparing 2-isopropyl-4,5-dimethylphenol according to claim 1, characterized in that: In step S1, the catalyst is a liquid acid catalyst; in step S3, the catalyst is separated from the reaction product by washing and neutralizing with a 10% dilute alkali aqueous solution.

8. The method for preparing 2-isopropyl-4,5-dimethylphenol according to claim 1, characterized in that: In step S1, the catalyst is a solid acid catalyst; in step S3, the catalyst is separated from the reaction product by filtering.

9. The method for preparing 2-isopropyl-4,5-dimethylphenol according to claim 1, characterized in that: At least a portion of the diisopropyl by-product in the reaction product is converted through transalkylation and isomerization reactions to achieve the target product yield. This process step can be carried out simultaneously with the alkylation reaction, or at a later time point, in the same container or in a different container; the transalkylation and isomerization reactions can be carried out at a reaction temperature that is 15-20° C. higher than the initial temperature of the olefin alkylation reaction.

10. The method for preparing 2-isopropyl-4,5-dimethylphenol according to claim 1, characterized in that: In step S3, the reaction product is subjected to vacuum distillation to produce crude 2-isopropyl-4,5-dimethylphenol substantially free of 3,5-dimethylphenol, which can be purified by distillation and crystallization to obtain purified 2-isopropyl-4,5-dimethylphenol.

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