Method for preparing anisole by using dimethyl carbonate as methylation reagent

Abstract

The invention discloses a method for preparing anisole by taking dimethyl carbonate as a methylation reagent, a ternary concerted catalytic system is created for the first time to break through temperature limitation, phenol is efficiently activated by [BMIM] OH to generate high-activity phenoxy anions through a composite catalytic design of an alkaline ionic liquid / quaternary ammonium salt / nano metal oxide, the quaternary ammonium salt executes phase transfer and reaction path switching, and the anisole is prepared by taking dimethyl carbonate as a methylation reagent. The nano metal oxide has the effects of balance regulation and structural protection, and the conversion rate of phenol is gt according to the mass ratio of phenol to dimethyl carbonate to basic ionic liquid to quaternary ammonium salt compound to nano metal oxide being 94: (99-117): (2.82-7.52): (0.94-4.7): (0.47-3.76); the selectivity of anisole is gt; the method has the advantages that the concentration is 99%, decomposition of DMC and generation of by-products such as o-cresol are inhibited from the source, a self-settling separation-circulation method subverts a catalyst recovery mode, the by-products are directionally inhibited, the separation process is simplified, and the product can reach gt through single washing and reduced pressure distillation; and high-energy-consumption multi-tower rectification for substances with approximate boiling points in the traditional method is omitted, so that the economic benefit is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic synthesis, and particularly relates to a method for preparing anisole using dimethyl carbonate as a methylation reagent. Background Art

[0002] Anisole, also known as methoxybenzene, is an important chemical intermediate and is widely used in fields such as spices, dyes, pharmaceuticals, solvents, and gasoline additives.

[0003] The synthesis methods of anisole are as follows: ① Anisole is prepared by reacting sodium phenoxide with dimethyl sulfate. However, dimethyl sulfate is highly toxic and corrosive, and a large amount of sodium hydroxide is required in the method, generating salty wastewater and causing serious environmental pollution; it has gradually been phased out. ② Methanol as a methylation reagent has the advantages of low raw material cost and a green method, but requires a catalyst with high activity, high selectivity, and long life. The catalyst is prone to coking or deactivation and requires regeneration, and high temperature and high pressure are needed. ③ Using dimethyl carbonate (DMC) as a methylation reagent is a green chemical alternative route and is currently a research hotspot.

[0004] Currently, although the industrial production of the reaction of phenol with DMC to produce anisole has been achieved, it still faces the following technical bottlenecks and method defects:

[0005] 1. Phenol has weak acidity and insufficient nucleophilicity. The carbonyl group of DMC is protected by a methoxy group, and the electrophilicity is poor. Without a catalyst, high temperature (>150 °C) and a long time are required to promote the reaction.

[0006] 2. Traditional homogeneous basic catalysts (NaOH, KOH, organic bases) are difficult to separate and recycle from the products and may cause reactions such as DMC hydrolysis; heterogeneous solid base catalysts (such as supported alkali metal / alkaline earth metal oxides, etc.) have problems such as insufficient activity, poor stability, easy deactivation, and difficult regeneration.

[0007] 3. Dimethyl carbonate will undergo hydrolysis or thermal decomposition to produce methanol and carbon dioxide under high-temperature basic conditions. Moreover, by-products such as o-cresol and dimethylphenol, which have boiling points close to that of anisole, are easily generated, making the separation difficult and the equipment investment large. Summary of the Invention

[0008] The present invention makes improvements in view of the deficiencies of the prior art and provides a method for preparing anisole using dimethyl carbonate as a methylation reagent, an efficient method for preparing anisole.

[0009] To achieve the above object, the present invention is realized by such a technical solution:

[0010] The present invention discloses a method for preparing anisole, comprising the following steps:

[0011] 1) Put phenol, dimethyl carbonate (DMC), basic ionic liquid, quaternary ammonium salt compound, and nano metal oxide into a reaction kettle equipped with a carbon dioxide outlet tube;

[0012] 2) Replace the air with nitrogen, start stirring, raise the temperature to 105 ± 5 °C and react for 0.5 - 1.5 h, then raise the temperature to 120 - 130 °C and continue to react for 2 - 4 h;

[0013] 3) After the reaction is completed, transfer the reaction solution to a conical settling tank preheated to 50 - 70 °C and let it stand for layering for 10 - 15 min;

[0014] 4) Remove the upper layer, wash and dry it, and obtain anisole by vacuum distillation. Add phenol and dimethyl carbonate to the lower layer and directly carry out the next round of reaction.

[0015] As a further improvement, the basic ionic liquid in step 1) of the present invention is 1-butyl-3-methylimidazolium hydroxide [BMIM]OH.

[0016] As a further improvement, the quaternary ammonium salt compound in step 1) of the present invention is tetrabutylammonium bromide (TBAB) or tetraethylammonium bromide (TEAB).

[0017] As a further improvement, the nano metal oxide in step 1) of the present invention is any one of magnesium oxide (MgO), calcium oxide (CaO), and zinc oxide (ZnO).

[0018] As a further improvement, the mass ratio of phenol:dimethyl carbonate:basic ionic liquid:quaternary ammonium salt compound:nano metal oxide in step 1) of the present invention is: 94:99 - 117:2.82 - 7.52:0.94 - 4.7:0.47 - 3.76.

[0019] As a further improvement, the cone angle of the conical settling tank in step 3) of the present invention is 60°.

[0020] As a further improvement, the conversion rate of phenol in the method of the present invention is greater than 99.5%, and the selectivity of anisole is greater than 99%.

[0021] The beneficial effects of the present invention are as follows:

[0022] 1. The first ternary synergistic catalytic system breaks through the temperature limit.

[0023] Through the composite catalytic design of alkaline ionic liquid ([BMIM]OH) / quaternary ammonium salt (TBAB / TEAB) / nanometallic oxide (MgO, etc.), [BMIM]OH efficiently activates phenol to generate highly active phenoxide anions, the quaternary ammonium salt performs phase transfer and reaction path switching, and the nanometallic oxide plays the role of balance regulation and structural protection. According to the mass ratio of phenol: dimethyl carbonate: alkaline ionic liquid: quaternary ammonium salt compound: nanometallic oxide: 94:99-117:2.82-7.52:0.94-4.7:0.47-3.76, the catalytic effect is optimal, resulting in a phenol conversion rate of >99.5% and anisole selectivity of >99%, completely avoiding the high temperature (>150°C) environment required by traditional methods, inhibiting the decomposition of DMC and the formation of by-products such as o-cresol from the source, and resolving the technical contradiction that catalyst activity and selectivity cannot be achieved at the same time.

[0024] 2. The self-sedimentation separation-circulation method subverts the catalyst recovery model.

[0025] It was discovered by chance that [BMIM]OH(1.12g / cm 3 ) and the product anisole (0.99 g / cm 3) Spontaneous phase separation (density difference) is utilized. An innovative conical settling tank is used with a cone angle of 60° to increase the contact area between the two phases. The tank is preheated (50-70°C) to achieve rapid stratification (10-15 minutes). The lower catalytic phase (containing ionic liquid, quaternary ammonium salt and nano-oxide) can be directly supplemented with phenol and diphenyl carbonate for recycling, achieving zero regeneration loss of the catalyst and extending its life by more than 5 times. This overcomes the industry problems of rapid deactivation of heterogeneous catalysts and difficult recovery of homogeneous catalysts.

[0026] 3. Targeted suppression of by-products simplifies the separation process

[0027] Through segmented temperature control of the pre-activation (105±5°C) and main reaction (120–130°C) stages, precise regulation of the alkaline microenvironment of the composite catalyst, and installation of a carbon dioxide outlet pipe in the reactor, this interlocking design achieves efficient reaction while completely blocking the DMC hydrolysis and C-alkylation pathways (byproducts such as o-cresol ≈ 0). The product reaches a purity of >99.5% after a single wash and vacuum distillation, eliminating the traditional method of high-energy multi-tower distillation for products with similar boiling points, greatly improving economic benefits. DETAILED DESCRIPTION

[0028] The present invention discloses a method for preparing anisole by using dimethyl carbonate as a methylating agent. The technical solution of the present invention is further described in detail below in conjunction with specific examples, but the scope of the present invention is not limited to the examples.

[0029] Example 1

[0030] 1) Put 94 g of phenol, 99 g of dimethyl carbonate (DMC), 2.82 g of 1-butyl-3-methylimidazolium hydroxide, 0.94 g of tetrabutylammonium bromide, and 0.47 g of nano-MgO into a reaction kettle equipped with a gas outlet tube.

[0031] 2) Replace the air with nitrogen three times, start stirring, raise the temperature to 100 °C and pre-react for 0.5 h. Then raise the temperature to 120 °C and react for 2 h.

[0032] 3) After the reaction is completed, transfer the reaction solution to a conical sedimentation tank preheated to 50 °C and let it stand for layering for 10 min.

[0033] 4) Remove the upper layer, wash and dry it, and obtain anisole by vacuum distillation. Add phenol and diphenyl carbonate to the lower layer and directly carry out the next round of reaction.

[0034] Through the above operations, the conversion rate of phenol reaches 99.6%, and the selectivity of anisole reaches 99%.

[0035] Example 2

[0036] 1) Put 94 g of phenol, 108 g of dimethyl carbonate (DMC), 5.17 g of [BMIM]OH, 2.82 g of tetrabutylammonium bromide, and 2.12 g of nano-MgO into a reaction kettle equipped with a gas outlet tube.

[0037] 2) Replace the air with nitrogen three times, start stirring, raise the temperature to 105 °C and react for 1 h. Then raise the temperature to 125 °C and react for 3 h.

[0038] 3) After the reaction is completed, transfer the reaction solution to a conical sedimentation tank preheated to 60 °C and let it stand for layering for 10 min.

[0039] 4) Remove the upper layer, wash and dry it, and obtain anisole by vacuum distillation. Add phenol and diphenyl carbonate to the lower layer and directly carry out the next round of reaction.

[0040] Through the above operations, the conversion rate of phenol reaches 99.8%, and the selectivity of anisole reaches 99.5%.

[0041] Example 3

[0042] 1) Put 94 g of phenol, 117 dimethyl carbonate (DMC), 7.52 g of [BMIM]OH, 4.7 g of TBAB, and 3.76 g of nano-MgO into a reaction kettle equipped with a gas outlet tube.

[0043] 2) Replace the air with nitrogen three times, start stirring, raise the temperature to 110 °C and react for 1.5 h. Then raise the temperature to 130 °C and react for 4 h.

[0044] 3) After the reaction is completed, the reaction solution is transferred to a 1 L conical settler preheated at 70°C and allowed to stand for 15 minutes to separate layers.

[0045] 4) The upper layer was removed, washed and dried, and distilled under reduced pressure to obtain anisole. Phenol and diphenyl carbonate were added to the lower layer and the next round of reaction was directly carried out.

[0046] Through the above operation, the phenol conversion rate reached 99.6%, and the anisole selectivity reached 99.3%.

[0047] Example 4

[0048] 1) 94g of phenol, 108g of dimethyl carbonate (DMC), 5.17g of [BMIM]OH, 2.82g of tetraethylammonium bromide, and 2.12 nanometers of CaO were placed in a reactor equipped with a gas outlet tube.

[0049] 2) Replace the air with nitrogen three times, start stirring, and raise the temperature to 105°C for 1 hour. Then raise the temperature to 125°C and react for 3 hours.

[0050] 3) After the reaction is completed, the reaction solution is transferred to a conical settler preheated at 70°C and allowed to stand for 10 minutes to separate the layers.

[0051] 4) The upper layer was removed, washed and dried, and distilled under reduced pressure to obtain anisole. Phenol and diphenyl carbonate were added to the lower layer and the next round of reaction was directly carried out.

[0052] Through the above operation, the phenol conversion rate reached 99.6%, and the anisole selectivity reached 99.3%.

[0053] Example 5

[0054] 1) 94g of phenol, 108g of dimethyl carbonate (DMC), 5.17g of [BMIM]OH, 2.82g of tetrabutylammonium bromide, and 2.12 nanometers of ZnO were placed in a reactor equipped with a gas outlet tube.

[0055] 2) Replace the air with nitrogen three times, start stirring, and raise the temperature to 105°C for a preliminary reaction of 1 hour. Then raise the temperature to 125°C and react for 3 hours.

[0056] 3) After the reaction is completed, the reaction solution is transferred to a conical settler preheated at 70°C and allowed to stand for 10 minutes to separate the layers.

[0057] 4) The upper layer was removed, washed and dried, and distilled under reduced pressure to obtain anisole. Phenol and diphenyl carbonate were added to the lower layer and the next round of reaction was directly carried out.

[0058] Through the above operation, the phenol conversion rate reached 99.7% and the anisole selectivity reached 99.4%.

[0059] Example 6

[0060] 1) 94 g of phenol, 108 g of dimethyl carbonate (DMC), 5.17 g of [BMIM]OH, 2.82 g of tetrabutylammonium bromide, and 2.12 g of nano-MgO were put into a reactor equipped with a gas outlet tube.

[0061] 2) The air was replaced with nitrogen three times, the stirring was started, and the temperature was raised to 105 °C for a pre-reaction of 1 h. Then the temperature was raised to 130 °C and the reaction was carried out for 4 h.

[0062] 3) After the reaction was completed, the reaction solution was transferred to a 1 L conical settler preheated to 70 °C and allowed to stand for layering for 15 min.

[0063] 4) The upper layer was removed, washed, dried, and subjected to vacuum distillation to obtain anisole. The lower layer was added with phenol and diphenyl carbonate and directly subjected to the next round of reaction.

[0064] Through the above operations, the conversion rate of phenol reached 99.9%, and the selectivity of anisole reached 99.7%.

[0065] Example 7

[0066] Referring to the formulation and process of Example 6, without adding a new catalyst, the cycle operation was carried out 10 times, and the results are shown in the following table:

[0067] Table 1 Catalyst cycle performance data

[0068]

[0069]

[0070] From the data in the above table, it can be seen that after the catalytic phase was cycled 10 times, the conversion rate of phenol remained > 99%, the selectivity was greater than 99.5%, and the activity decay rate was < 0.8%. The present invention achieved "zero regeneration loss", and the ternary catalytic system had high stability, overcoming the industry problems of fast deactivation of heterogeneous catalysts and difficult recovery of homogeneous catalysts.

[0071] Comparative Example 1 (Single ionic liquid catalyst)

[0072] [[ID= 37]] Only [BMIM]OH was used as the catalyst, and the experiment was carried out according to Example 6. The conversion rate of phenol reached 82.4%, and the selectivity of anisole reached 90.2%.

[0073] Comparative Example 2 (Without adding quaternary ammonium salt)

[0074] The quaternary ammonium salt was not added to the catalyst, and the experiment was carried out according to Example 6. The conversion rate of phenol reached 84.2%, and the conversion rate of anisole was 92.8%.

[0075] Comparative Example 3 (Without adding nano-metal oxide)

[0076] Without adding nano metal oxide to the catalyst, the experiment was carried out according to Example 6. The phenol conversion rate reached 86.4%, and the anisole selectivity reached 94.6%.

[0077] It can be seen that by comparing Control Examples 1-3 with Example 6, the synergistic effect of the three has obvious advantages over the two-by-two linkage. The three form a self-circulating catalytic network of "base activation-path optimization-equilibrium breakthrough", which greatly improves the phenol conversion rate and anisole selectivity.

[0078] Comparative Example 4

[0079] Under the same other conditions as in Example 6, the temperature was directly raised to 120-130° C. and the reaction was carried out for 5 hours.

[0080] The phenol conversion rate reached 84.2%, and the anisole selectivity reached 79.4%.

[0081] It can be seen that by comparing Control Example 4 with Example 6, the staged heating process has significant advantages in phenol conversion rate and anisole selectivity compared with the traditional single-end 130°C process. This may be because the raw material DMC is hydrolyzed in large quantities at high temperature, and high temperature may lead to ortho-substitution.

[0082] Finally, it should be noted that the examples listed above are merely specific implementation examples of the present invention. Obviously, the present invention is not limited to the examples listed above and is subject to numerous variations. Any variations that can be directly derived or conceived by a person skilled in the art from the disclosure of this invention should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing anisole using dimethyl carbonate as a methylation reagent, characterized in that, It includes the following steps: 1) Put phenol, dimethyl carbonate (DMC), basic ionic liquid, quaternary ammonium salt compound, and nano-metal oxide into a reaction kettle equipped with a carbon dioxide outlet tube; 2) Replace the air with nitrogen, start stirring, raise the temperature to 105 ± 5 °C and react for 0.5 - 1.5 h, then raise the temperature to 120 - 130 °C and continue to react for 2 - 4 h; 3) After the reaction is completed, transfer the reaction solution to a conical settling tank preheated to 50 - 70 °C and let it stand for layering for 10 - 15 min; 4) Remove the upper layer, wash and dry it, and obtain anisole by vacuum distillation. Add phenol and dimethyl carbonate to the lower layer and directly carry out the next round of reaction.

2. The method for preparing anisole using dimethyl carbonate as a methylation reagent according to claim 1, wherein The basic ionic liquid in step 1) is 1-butyl-3-methylimidazolium hydroxide [BMIM]OH.

3. The method for preparing anisole using dimethyl carbonate as a methylation reagent according to claim 1, wherein The quaternary ammonium salt compound in step 1) is tetrabutylammonium bromide (TBAB) or tetraethylammonium bromide (TEAB).

4. The method for preparing anisole using dimethyl carbonate as a methylation reagent according to claim 1 or 2 or 3, characterized in that, The nano-metal oxide in step 1) is any one of magnesium oxide (MgO), calcium oxide (CaO), and zinc oxide (ZnO).

5. The method for preparing anisole using dimethyl carbonate as a methylation reagent according to claim 4, characterized in that, The mass ratio of phenol:dimethyl carbonate:basic ionic liquid:quaternary ammonium salt compound:nano-metal oxide in step 1) is: 94:99 - 117:2.82 - 7.52:0.94 - 4.7:0.47 - 3.

76.

6. The method for preparing anisole using dimethyl carbonate as a methylation reagent according to claim 5, characterized in that, The cone angle of the conical settling tank in step 3) is 60°.

7. The method for preparing anisole using dimethyl carbonate as a methylation reagent according to claim 1 or 2 or 3 or 5 or 6, characterized in that, In the said method, the conversion rate of phenol is greater than 99.5%, and the selectivity of anisole is greater than 99%.

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