A method for preparing 3,6-di-tert-butylcarbazole

Abstract

The present application relates to a kind of preparation methods of 3,6-di-tert-butyl carbazole, belong to the technical field of synthesis of carbazole compounds.The preparation method includes: with carbazole and tert-butyl alcohol as raw material, with ionic liquid as catalyst, 3,6-di-tert-butyl carbazole is prepared by reaction, wherein ionic liquid is not only catalyst, but also reaction solvent.The present application uses cheap, easily available carbazole and tert-butyl alcohol as raw material, uses ionic liquid as catalyst and solvent, without using a large amount of organic solvent, at lower temperature, can prepare 3,6-di-tert-butyl carbazole in one step, method is simple, reaction condition is mild, target product is easy to purify and separate, after reaction ionic liquid state can be recycled, almost no waste liquid is generated, and environmental protection is good.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of synthesis of carbazole compounds, and particularly relates to a preparation method of 3,6-di-tert-butyl carbazole. BACKGROUND

[0002] Carbazole and its derivatives are a kind of rich electron fused heterocyclic aromatic compounds with a large π electron conjugated system and strong intramolecular electron transfer characteristics: the electrophilic N atom of carbazole absorbs the electrons on the double bond through the inductive effect; at the same time, the unshared electrons of the N atom are supplied to the double bond due to the p-π conjugation effect, so that the double bond is electron-rich. Carbazole and its derivatives have a high triplet state energy level and high hole mobility, and as the hole transport layer of organic electroluminescent devices, can reduce the crystallization of small molecule materials, improve the device life, increase the opportunity of electron-hole recombination, and improve the luminous efficiency of the device, and play an irreplaceable role in phosphorescent light host materials. The position of the substituent group on the carbazole group affects its electronic effect, and further affects its hole transport capacity. The carbazole group has high hole mobility, but its electron mobility is low. In order to further balance the injection and transport of electrons and holes, an electron-type group needs to be introduced into the carbazole skeleton to improve the efficiency of the phosphorescent device; at the same time, due to the rigid structure of carbazole, its solubility in common organic solvents is poor, and the introduction of groups such as tert-butyl and 9-substituted fluorenyl groups at the 3,6 position can effectively improve the solubility and thermal stability of the carbazole compound, which can save the cost of spin coating devices. 3,6-di-tert-butyl carbazole is an intermediate of an organic light-emitting material with excellent solubility, thermal stability and photoelectric performance, which can be further derived to prepare carbazole compounds modified at 1,8 positions. Therefore, the synthesis of 3,6-di-tert-butyl carbazole is of great significance to the development of OLED industry.

[0003] According to the literature reports, there are several synthesis routes of 3,6-di-tert-butyl carbazole.

[0004] Route one: carbazole, halogenated tert-butane (such as chlorinated tert-butane, brominated tert-butane) as raw material, under the catalysis of Lewis acid (such as zinc chloride, aluminum chloride, iron chloride, etc.), the Friedel-Crafts alkylation reaction occurs at the 3,6 position of carbazole to generate 3,6-di-tert-butyl carbazole, which is the most commonly used method for industrial production of 3,6-di-tert-butyl carbazole. For example, patent CN201410085106.6 reports a preparation method of 3,6-di-tert-butyl carbazole, which uses carbazole and chlorinated tert-butane as raw materials, nitromethane as solvent, and 3 equivalent zinc chloride as catalyst to synthesize 3,6-di-tert-butyl carbazole through Friedel-Crafts alkylation reaction, with a yield of 91%, and the reaction formula is as follows:

[0005]

[0006] Route two: patent CN201610255780.3 reports a preparation method of 3,6-di-tert-butyl carbazole, which takes 3,6-dibromo carbazole and tert-butyl boronic acid as raw materials, N,N-dimethylformamide / water mixture as reaction solvent, 0.4 equivalent of palladium trisphenylphosphine as catalyst, reacts at 80℃ for 4 hours, and then is treated by water washing, extraction, drying, column chromatography and other post-processing methods to obtain 3,6-di-tert-butyl carbazole, with a yield of 90%, and the reaction formula is as follows:

[0007]

[0008] Route three: in 2016, Maheswaran Hariharasarma et al. (Asian Journal Of Organic Chemistry, 2017, 6, 59-62) reported a preparation method of 3,6-di-tert-butyl carbazole, which takes 4-tert-butyl phenylhydrazine and 4-tert-butyl cyclohexanone as raw materials, and first undergoes Fischer indole synthesis reaction under the catalysis of acetic acid to obtain 3,6-di-tert-butyl-1,2,3,4-tetrahydro-9H-carbazole, and then 3,6-di-tert-butyl-1,2,3,4-tetrahydro-9H-carbazole is subjected to aromatization reaction under the catalysis of iodine to synthesize 3,6-di-tert-butyl carbazole, with a yield of about 90%, and the reaction formula is as follows:

[0009]

[0010] Route four: in 2020, Hakjune Rhee et al. (Synthesis, 2020, 52, 917-927) reported a preparation method of 3,6-di-tert-butyl carbazole, which takes 2-bromo-4-tert-butyl aniline as raw material, first generates N-(2-bromo-4-(tert-butyl) phenyl) acetamide under the catalysis of 4-(dimethylamino) pyridine (DMAP) and acetic anhydride, then undergoes Ullmann coupling reaction under the catalysis of 3 equivalent copper powder, and finally undergoes ring closure under the catalysis of phosphoric acid and diethylene glycol as solvent at 200℃ to synthesize 3,6-di-tert-butyl carbazole, with a total yield of about 26%, and the reaction formula is as follows:

[0011]

[0012] In the above synthesis routes, the following problems exist:

[0013] ​The route one has short synthesis steps and low raw material cost, but a large amount of zinc chloride (3 times of the equivalent) is used as a catalyst in the reaction process, and nitromethane, which is easy to explode, is used as a solvent. Since the reaction is carried out in a homogeneous condition, a large amount of zinc chloride is dissolved in nitromethane, and the reaction is too violent to require dropwise addition of chlorinated tertiary butane. Moreover, the zinc chloride catalyst cannot be recycled, and a large amount of acidic waste gas and waste liquid is generated in the reaction process and the post-treatment process, so there are problems of poor atom economy, serious environmental pollution, high post-treatment cost, and difficult purification of the product. The route two has short synthesis steps, but the raw materials used are expensive, and the mixture of N,N-dimethylformamide / water is used as a reaction solvent, which cannot be recycled. At the same time, 0.4 equivalent of tetrakis triphenylphosphine palladium is used as a catalyst, and the post-treatment process needs to go through a column chromatography purification process, which is not suitable for industrial production. Therefore, there are defects of high raw material cost, high production cost, high purification process requirement, and serious environmental problems. The route three has mild reaction conditions and high yield, but the reaction steps are long, acetic acid is used as a reaction solvent in the first step, and dimethyl sulfoxide is used as a solvent in the second step, which cannot be recycled. The production cost is high, the environmental pollution is serious, and the purification is difficult. The route four has high raw material cost, long reaction steps, and low reaction yield. A large amount of phosphoric acid is used as a catalyst in the third step reaction, and diethylene glycol is used as a solvent. The reaction is carried out at a high temperature of 200 DEG C. The final product has a deep color, and the purification is difficult. The production cost is high, and the environmental problems are serious.

[0014] In summary, the existing synthesis methods of 3,6-di-tert-butylcarbazole generally have technical problems of high production cost, harsh reaction conditions, serious environmental problems, and difficult purification. Therefore, it is necessary to continuously research the synthesis method of 3,6-di-tert-butylcarbazole, so as to obtain a more economical, green and efficient industrial production method of 3,6-di-tert-butylcarbazole.

[0015] The information disclosed in this BACKGROUND section is only for the purpose of increasing the understanding of the overall background of the invention and shall not be taken as an acknowledgement or any form of suggestion that this information forms prior art with regard to any patentable matter disclosed in or related to the invention. SUMMARY

[0016] In order to solve the technical problems of high production cost, harsh reaction conditions, serious environmental problems, and difficult purification in the existing synthesis method of 3,6-di-tert-butylcarbazole, a preparation method of 3,6-di-tert-butylcarbazole is provided.

[0017] The reaction mechanism of the present application is as follows:

[0018] The reaction mechanism of the present application is similar to the mechanism of Lewis acid catalyzed alkylation of aromatic ring. First, tert-butyl alcohol is generated under the action of sulfonic acid type ionic liquid catalyst to form tert-butyl carbonium ion. Then, the tert-butyl carbonium ion attacks the 3,6 position of carbazole which is more rich in electricity to form a σ complex with electron deficiency. Finally, dehydrogenation proton is generated to form 3,6-di-tert-butylcarbazole.

[0019] The application provides a preparation method of 3,6-di-tert-butyl carbazole, characterized in that the preparation method comprises the following steps: taking carbazole and tert-butyl alcohol as raw materials, taking a sulfonic acid type ionic liquid as a catalyst, and reacting to obtain 3,6-di-tert-butyl carbazole, and a reaction formula is as follows:

[0020]

[0021] The sulfonic acid type ionic liquid mainly has a condensed benzimidazole or quinoline structure, is miscible with tert-butyl alcohol, has good solubility to carbazole, and is beneficial to the catalytic reaction.

[0022] In some embodiments, the molar ratio of the carbazole to the tert-butyl alcohol is 1:(2-6);

[0023] And / or, the molar ratio of the carbazole to the sulfonic acid type ionic liquid is 1:(0.2-2).

[0024] In some embodiments, the ionic liquid is a sulfonic acid type ionic liquid, and the structural formula of the sulfonic acid type ionic liquid is selected from one or more of the following:

[0025]

[0026] In some embodiments, the preferred structural formula of the sulfonic acid type ionic liquid is IL1, IL3 or IL4.

[0027] In some embodiments, the sulfonic acid type ionic liquid is a reaction solvent.

[0028] In some embodiments, the sulfonic acid type ionic liquid can be recycled and reused after the reaction. The structure and properties of the ionic liquid catalyst do not change obviously before and after the reaction, and the recycled ionic liquid catalyst can also catalyze the reaction, so that recycling and reuse have little effect on the conversion rate and selectivity of the reaction.

[0029] In some embodiments, the reaction is carried out under the protection of a protective gas; preferably, the reaction is carried out under the protection of nitrogen. Nitrogen and the like are mainly used for protection because tert-butyl carbocation is generated in the reaction process, and the tert-butyl carbocation cannot be stably stored under the condition of air, and needs to be carried out under the protection of inert gas. At the same time, carbazole as an aromatic amine compound will undergo oxidation reaction under the reaction temperature condition, so that the color of the reaction system becomes dark, and it is not easy to purify after treatment.

[0030] And / or, the temperature of the reaction is 60-80 DEG C;

[0031] And / or, the reaction time is 6-12 hours.

[0032] Under the above reaction conditions, the catalytic effect is the best, the reaction conversion rate is low when the temperature is lower than the above range, and the raw material conversion rate is also low by increasing the reaction time, which is not conducive to the post-treatment and purification, and is not economical; when the reaction temperature is higher than the temperature range, the tertiary butyl carbonium ion will undergo obvious isomerization and dealkylation reaction, causing the increase of side reactions, and the reaction system involving tertiary butyl alcohol (boiling point 83℃) and ionic liquid will have a phenomenon of violent reflux, which affects the catalytic reaction effect, so the catalytic reaction effect is reduced when the reaction temperature is higher than the temperature range, which is not conducive to the reaction.

[0033] In some embodiments, after the reaction, 3,6-di-tert-butylcarbazole is obtained by extraction, concentration and crystallization.

[0034] In some embodiments, after the extraction, the upper organic phase is 3,6-di-tert-butylcarbazole phase, and the lower aqueous phase is ionic liquid phase.

[0035] In some embodiments, the extractant used in the extraction is selected from one or more of n-hexane, dichloromethane and ethyl acetate;

[0036] And / or, the crystallization solvent used in the crystallization is selected from one or more of methanol, ethanol, petroleum ether, n-hexane and o-xylene.

[0037] In some embodiments, a method for preparing 3,6-di-tert-butylcarbazole mainly comprises the following steps:

[0038] The target amount of carbazole, tert-butyl alcohol and ionic liquid are mixed, stirred uniformly, heated to 60-80℃, and continuously stirred at a suitable stirring speed (such as 550 rpm) for 6-12 hours of incubation;

[0039] After the reaction, an extractant is added to the reaction liquid, the organic phase and the aqueous phase are separated after the extraction, the obtained organic phase is concentrated, and the concentrated organic phase is crystallized with a crystallization solvent to obtain 3,6-di-tert-butylcarbazole; wherein the aqueous phase is the recovered ionic liquid, which is saved for later use.

[0040] Compared with the prior art, the technical effects achieved by the present application are as follows:

[0041] (1) The present application uses cheap and readily available carbazole and tert-butyl alcohol as raw materials, and uses ionic liquid as catalyst and solvent, without using a large amount of organic solvent, and 3,6-di-tert-butylcarbazole can be prepared in one step at a lower temperature, the method is simple, the reaction conditions are mild, the target product is easy to purify and separate, the ionic liquid after the reaction can be recycled, almost no waste liquid is generated, and the environmental protection is good.

[0042] (2) The method for preparing 3,6-di-tert-butylcarbazole has the advantages of almost no waste liquid after reaction, no generation of a large amount of acidic gas and acidic waste liquid in the reaction process, recycling use of the acidic ionic liquid catalyst, high atom economy, energy saving, green environmental protection and the like.

[0043] (3) The method has the advantages of simplicity, mild reaction conditions, low cost, green environmental protection and the like, and is suitable for large-scale production. DETAILED DESCRIPTION

[0044] The technical scheme of the present application is described below through specific examples. It should be understood that the one or more steps mentioned in the present application do not exclude other methods and steps before and after the combined steps, or other methods and steps can be inserted between the explicitly mentioned steps. It should also be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application. Unless otherwise specified, the numbering of each method step is only for the purpose of identifying each method step, and is not limited to the arrangement order of each method or the scope of the implementation of the present application. Changes or adjustments of the relative relationship, without substantial technical content changes, can also be considered as the implementation scope of the present application.

[0045] The raw materials and instruments used in the examples are not specifically limited in source, and can be purchased on the market or prepared according to the conventional methods well known to those skilled in the art.

[0046] Example 1: A preparation method of 3,6-di-tert-butylcarbazole

[0047] Under the protection of nitrogen, 33.5 g of carbazole (99%, 0.2 mol), 44.5 g of tert-butyl alcohol (99%, 0.6 mol) and 83.7 g of ionic liquid catalyst IL1 (0.2 mol) were added into a 500 mL reaction bottle, and after mixing, the temperature was raised to 60°C, the stirring speed was 550 rpm, and the reaction was kept for 6 h. After the reaction was completed, n-hexane was added to the reaction liquid for extraction, the organic phases were combined and concentrated, and 3,6-di-tert-butylcarbazole was obtained by crystallization with n-hexane / methanol mixed solvent, and the yield was 41.0 g, 73.4%.

[0048] Example 2: A preparation method of 3,6-di-tert-butylcarbazole

[0049] Into a 500 mL reaction flask, 33.5 g of carbazole (99%, 0.2 mol), 44.5 g of tert-butyl alcohol (99%, 0.6 mol), 83.1 g of ionic liquid catalyst IL3 (0.2 mol) were added under nitrogen protection, and after mixing, the temperature was raised to 80°C, the stirring speed was 550 rpm, and the reaction was kept for 8 h. After the reaction was completed, ethyl acetate was added to the reaction solution for extraction, the organic phases were combined and concentrated, and 3,6-di-tert-butylcarbazole was obtained by crystallization with n-hexane / methanol mixed solvent, with a yield of 42.6 g, 76.2%.

[0050] Example 3: A preparation method of 3,6-di-tert-butylcarbazole

[0051] Into a 500 mL reaction flask, 33.5 g of carbazole (99%, 0.2 mol), 44.5 g of tert-butyl alcohol (99%, 0.6 mol), 83.1 g of ionic liquid catalyst IL3 (0.2 mol) were added under nitrogen protection, and after mixing, the temperature was raised to 80°C, the stirring speed was 550 rpm, and the reaction was kept for 8 h. After the reaction was completed, ethyl acetate was added to the reaction solution for extraction, the organic phases were combined and concentrated, and 3,6-di-tert-butylcarbazole was obtained by crystallization with n-hexane / methanol mixed solvent, with a yield of 42.6 g, 76.2%.

[0052] Example 4: A preparation method of 3,6-di-tert-butylcarbazole

[0053] Into a 500 mL reaction flask, 33.5 g of carbazole (99%, 0.2 mol), 44.5 g of tert-butyl alcohol (99%, 0.6 mol), 83.1 g of ionic liquid catalyst IL3 (0.2 mol) were added under nitrogen protection, and after mixing, the temperature was raised to 80°C, the stirring speed was 550 rpm, and the reaction was kept for 8 h. After the reaction was completed, ethyl acetate was added to the reaction solution for extraction, the organic phases were combined and concentrated, and 3,6-di-tert-butylcarbazole was obtained by crystallization with n-hexane / methanol mixed solvent, with a yield of 42.6 g, 76.2%.

[0054] Example 5: A preparation method of 3,6-di-tert-butylcarbazole

[0055] Into a 500 mL reaction flask, 33.5 g of carbazole (99%, 0.2 mol), 44.5 g of tert-butyl alcohol (99%, 0.6 mol), 83.1 g of ionic liquid catalyst IL3 (0.2 mol) were added under nitrogen protection, and after mixing, the temperature was raised to 80°C, the stirring speed was 550 rpm, and the reaction was kept for 8 h. After the reaction was completed, ethyl acetate was added to the reaction solution for extraction, the organic phases were combined and concentrated, and 3,6-di-tert-butylcarbazole was obtained by crystallization with n-hexane / methanol mixed solvent, with a yield of 42.6 g, 76.2%.

[0056] Comparative Example 3 vs. Examples 1-2 and 4-5It can be found that the yield of 3,6-di-tert-butylcarbazole in Example 2 is relatively low, and the amount of catalyst IL2 used in Example 3 is only 20% of the amount of catalyst used in Example 1 and 2, and 10% of the amount of catalyst IL4 used in Example 4. The main reason is that the reaction is carried out under solvent-free reaction conditions, and the sulfonic acid type ionic liquid acts as both a catalyst and a reaction solvent in the reaction. If the amount of catalyst is too small, the carbazole cannot be completely dissolved, and the contact between the catalyst and the carbazole is limited, resulting in poor catalytic effect.

[0057] Examples 6-9: A recycled ionic liquid for the preparation of 3,6-di-tert-butylcarbazole

[0058] Example 6 uses the recycled and dried ionic liquid IL1 in Example 1 as catalyst (vacuum dried for 2 hours), Example 7 uses the recycled and dried ionic liquid IL1 catalyst in Example 6, Example 8 uses the recycled and dried ionic liquid IL1 catalyst in Example 7, and Example 9 uses the recycled and dried ionic liquid IL1 catalyst in Example 8. That is, the catalysts in Examples 6-9 are recycled 1-4 times of the catalyst in Example 1. The catalyst is recycled and used for synthesis reaction (the specific reaction conditions are the same as those in Example 1), and the performance of the recycled catalyst is verified. The results are shown in Table 1. As shown in Table 1, the ionic liquid catalyst can be reused at least 4 times and the reaction yield does not decrease significantly.

[0059] Table 1 Reaction conditions and results of Examples 6-9

[0060]

[0061]

[0062] The foregoing description of specific exemplary embodiments of the application is intended to be illustrative only and is not intended to limit the application to the precise forms described. Many modifications and variations are possible in light of the above teachings without departing from the spirit or essential characteristics of the application. The exemplary embodiments were chosen and described in order to explain the principles of the application and its practical application and to allow others skilled in the art to understand the application for various exemplary embodiments with various modifications being suited to the particular use contemplated. The scope of the application is intended to be defined by the claims and their equivalents.

Claims

1. A method for producing 3,6-di-tert-butylcarbazole, characterized by, The preparation method comprises: taking carbazole and tert-butyl alcohol as raw materials, taking a sulfonic acid type ionic liquid as a catalyst, and reacting to obtain 3,6-di-tert-butyl carbazole, wherein the structure and properties of the sulfonic acid type ionic liquid do not change obviously before and after the reaction, and the reaction formula is as follows: The structural formula of the sulfonic acid type ionic liquid is selected from one or more of the following:

2. The production method according to claim 1, characterized by, The molar ratio of the carbazole to the tert-butyl alcohol is 1:(2-6); And / or, the molar ratio of the carbazole to the sulfonic acid type ionic liquid is 1:(0.2-2).

3. The preparation method according to claim 1, characterized in that, The structural formula of the sulfonic acid type ionic liquid is IL1, IL3 or IL4.

4. The method of claim 1, wherein, The sulfonic acid type ionic liquid is a reaction solvent.

5. The preparation method according to claim 1, characterized in that, The sulfonic acid type ionic liquid can be recycled and reused after the reaction.

6. The method of claim 1, wherein, The reaction is carried out under the protection of a protective gas; And / or, the temperature of the reaction is 60-80 DEG C; And / or, the time of the reaction is 6-12 hours.

7. The preparation method according to claim 1, characterized in that, After the reaction is completed, 3,6-di-tert-butyl carbazole is obtained through extraction, concentration and crystallization.

8. The preparation method according to claim 7, characterized in that, After the extraction is completed, the upper organic phase is 3,6-di-tert-butyl carbazole phase, and the lower aqueous phase is ionic liquid phase.

9. The preparation method according to claim 7, characterized in that, The extractant used in the extraction is selected from one or more of the following: n-hexane, dichloromethane and ethyl acetate; And / or, the crystallization solvent used in the crystallization is selected from one or more of the following: methanol, ethanol, petroleum ether, n-hexane and o-xylene.

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