Method for preparing cumene hydroperoxide through selective oxidation of cumene

Abstract

The invention provides a method for preparing cumene hydroperoxide through selective oxidation of cumene, and the method comprises the following steps: cumene, ionic liquid BmimBr and NHPI are placed in a three-neck flask to be mixed, at the temperature of 90-120 DEG C, air with the flow of 50-150 mLmin is introduced for cumene oxidation reaction, and the molar ratio of cumene to BmimBr to NHPI is 10000: (1-3): (1.5-3). According to the method, the catalyst is combined with NHPI + BmimBr, cumene can be selectively oxidized to prepare cumene hydroperoxide under the conditions of no solvent, no transition metal salt and no initiator, the two catalytic substances have a synergistic effect and have good catalytic performance, the reaction time can be shortened, the reaction yield can be increased to 90% or above, and the method is suitable for industrial production. And the conversion rate of the isopropyl benzene reaches 16-30%.

Description

Technical Field

[0001] The present invention relates to the field of chemical catalysis, and particularly relates to a method for the selective oxidation of cumene to cumene hydroperoxide. Background Art

[0002] The selective oxidation of cumene to cumene hydroperoxide (CHP) is a key reaction in the petrochemical industry. CHP is a key raw material for the production of fine chemicals, and in particular, it can be used as an important intermediate for the production of phenol. Nearly 90% of the phenol produced globally is obtained through the cumene oxidation process. All along, the dominant CHP preparation process in the industry is the cumene oxidation process. Cumene is oxidized in an alkaline atmosphere at about 0.6 - 0.7 MPa with oxygen or air in the temperature range of 100 - 140 °C. The conversion of cumene and the selectivity of cumene hydroperoxide reach 20% and 90 - 95% respectively. However, this process route has problems such as long reaction time, high reaction temperature, high pressure requirements, low yield, and poor safety. Therefore, new preparation methods are needed to improve the technical and economic indicators.

[0003] In recent years, various catalytic systems have been tried for the cumene oxidation reaction to shorten the reaction time and improve the yield. For example, some transition metal species, metal - organic frameworks, metal porphyrins, carbon nanotubes, silver nanoparticles, etc. have all been applied to the cumene oxidation reaction. Using these catalysts, cumene can be oxidized to cumene hydroperoxide at relatively low temperatures. However, from an industrial perspective, the relatively complex preparation methods, high cost, and toxicity of these catalysts limit their wide application.

[0004] Recently, researchers have found that NHPI (N - hydroxyphthalimide) or ionic liquids show good catalytic performance in the cumene oxidation. Under mild conditions, not only the reaction time is shortened, but also a high yield of cumene hydroperoxide is obtained. For example, CN101977896A discloses a method for preparing hydroperoxides of alkylbenzenes. An alkylbenzene is reacted with oxygen in the presence of a catalytic system and a polar solvent. The catalytic system includes N - hydroxyimide or N - hydroxysulfonamide. This reaction is carried out at a temperature of 50 - 100 °C, and the polar solvent includes ketones, nitriles, esters, tertiary alcohols, and dialkyl carbonates. Since NHPI has poor solubility in cumene, a polar solvent needs to be added and a lipophilic group needs to be introduced. However, the polar solvent and the lipophilic group are not environmentally friendly, and the preparation process of this reaction is also relatively complex, which all limit the wide application of NHPI in the cumene oxidation reaction.

[0005] In addition, the use of NHPI as a catalyst usually requires the addition of transition metal salts. However, the use of transition metal salts promotes the decomposition of cumene hydroperoxide. Since there is currently no better method to replace the role of transition metal salts as initiators, it is an urgent problem to develop a new technical route for the selective oxidation of cumene to prepare cumene hydroperoxide, so as to overcome the defects of easy decomposition of products, environmental unfriendliness, complex process, etc. caused by the use of initiators and polar solvents when using NHPI as a catalyst. Summary of the Invention

[0006] In view of the problems of the prior art, the present invention provides a method for the selective oxidation of cumene to prepare cumene hydroperoxide. The present invention uses NHPI + BmimBr as a combined catalyst to selectively oxidize cumene to prepare cumene hydroperoxide under the conditions of no solvent, no transition metal salt, and no initiator. Through the synergistic catalytic effect of NHPI + BmimBr, the selectivity of CHP reaches more than 90%, solving the problems of cumbersome process and low product selectivity in the prior art synthesis route of cumene hydroperoxide.

[0007] The technical solution of the present invention is as follows:

[0008] The present invention provides a method for the selective oxidation of cumene to prepare cumene hydroperoxide, and the method includes the following steps:

[0009] Mix cumene, ionic liquid BmimBr and NHPI in a three-necked flask, and at a temperature of 90 - 120 °C, introduce air with a flow rate of 50 - 150 mL / min for the cumene oxidation reaction. Among them, the molar ratio of cumene, BmimBr and NHPI is 10000:(1 - 3):(1.5 - 3).

[0010] Further, the cumene is unsubstituted or substituted cumene, and the substituent is selected from C 1 -C 6 alkyl groups, such as methyl, ethyl, etc.

[0011] Further, the three-necked flask is placed in an oil bath equipped with a stirring device and a condensing device.

[0012] Further, the cumene oxidation reaction is carried out at a stirring rate of 400 - 600 r / min.

[0013] Further, the reaction pressure of the cumene oxidation reaction is controlled at 0.1 MPa.

[0014] Further, the reaction time of the cumene oxidation reaction is controlled at 2 - 6 h.

[0015] Further, the preparation method of the ionic liquid BmimBr is as follows:

[0016] Add 0.1 mol of 1-methylimidazole into a 100 mL three-necked flask, and place the three-necked flask with a condensation device in a 70 °C oil bath with a stirring device. Slowly add a slightly excessive amount of 0.11 mol of n-butyl bromide dropwise into the reaction system using a dropping funnel. After the addition is completed, react for 24 h;

[0017] After the reaction is completed, cool the reaction solution to room temperature, and then wash it twice with toluene and ethyl acetate respectively to obtain a pale yellow viscous liquid. Place the pale yellow viscous liquid in a rotary evaporator and evaporate it until no liquid drips out. Dry it in a vacuum drying oven at 70 °C for 24 h to obtain 1-butyl-3-methylimidazolium bromide ionic liquid BmimBr, and seal it and place it in a drying oven for standby.

[0018] The reaction mechanism of the method of the present invention (as Figure 1 shown):

[0019] (1) NHPI (N-hydroxyphthalimide) forms PINO (N-oxylphthalimide radical) and BmimHBr under the action of BmimBr (1-butyl-3-methylimidazolium bromide ionic liquid). Subsequently, PINO is converted to cumene to form isopropyl radicals, and at the same time NHPI is reduced. The isopropyl radicals finally form CHP (cumene hydroperoxide) through a chain transfer process;

[0020] (2) BmimHBr is reduced to BmimBr through O 2 interaction. The CHP formed in step (1) decomposes under the action of BmimBr to form isopropyl hydroxy radicals (RO·) and carbene-Br and H 2 O. Subsequently, both RO· and carbene-Br can be converted to cumene to form isopropyl radicals, and at the same time BmimBr is reduced. The isopropyl radicals finally form the main product CHP through a chain transfer process;

[0021] RO· reacts with cumene to generate dimethylbenzyl alcohol and isopropyl radicals, and the isopropyl radicals also form the main product CHP through a chain transfer process later.

[0022] The beneficial effects of the present invention are as follows:

[0023] 1. The present invention utilizes the catalyst combination NHPI + BmimBr to achieve the selective oxidation of cumene to cumene hydroperoxide under the conditions of solvent-free, transition metal salt-free, and initiator-free. The two catalytic substances have a synergistic effect and good catalytic performance, which can shorten the reaction time, increase the reaction yield to over 90%, preferably 91 - 96%, and the conversion rate of cumene reaches 16 - 30%. Compared with the catalytic reaction of cumene when the two are used alone as catalysts without an initiator, the reaction route of the present invention can shorten the reaction time to within 6 h, while the separate catalysis of BmimBr requires 9 h and the separate catalysis of NHPI requires 24 h.

[0024] 2. Generally speaking, due to the poor solubility of cumene, polar solvents such as acetonitrile usually need to be added to dissolve it better before the PINO radical can be generated. Ionic liquids usually need to add CHP as an initiator to form carbon-centered radicals in order to exhibit better catalytic performance. The catalytic activity of NHPI stems from the formation of PINO with the ability to extract H, and the catalytic activity of the ionic liquid BmimBr stems from the formation of carbon-centered radicals with the ability to extract H. In the method of the present invention, the essence of the synergistic effect is that NHPI forms PINO radicals with the ability to absorb hydrogen through interaction with Br in BmimBr, and the interaction between BmimBr and the intermediate CHP can form carbon-centered radicals. The mutual synergistic effect between NHPI and BmimBr in the present invention realizes the effect of eliminating the need to add polar solvents and initiators and significantly improving the catalytic efficiency and reaction yield. - 5. The present invention uses density functional (DFT) calculations to propose the reaction mechanism of the synergistic catalysis of NHPI + BmimBr, and uses electron paramagnetic resonance (EPR) analysis to demonstrate the radicals, in order to rationalize the catalytic results and effects of the adopted catalyst combination.

[0025] 8. It is the mechanism diagram of the synergistic catalysis of cumene selective oxidation by NHPI and BmimBr of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is the mechanism diagram of the synergistic catalysis of cumene selective oxidation by NHPI and BmimBr of the present invention.

[0027] Figure 2 It is to measure PINO at different reaction times using an electron paramagnetic resonance spectrometer (Electron paramagnetic resonance, abbreviated as EPR). DETAILED DESCRIPTION OF THE INVENTION

[0028] The following further illustrates the present invention with reference to embodiments, but the present invention is not limited to the following embodiments.

[0029] Example 1

[0030] A method for the selective oxidation of cumene to prepare CHP, comprising the following steps:

[0031] Place 12 g (0.1 mol) of cumene, 0.01 mmol of BmimBr and 0.015 mmol of NHPI in a 50 mL three-necked flask. Under atmospheric pressure, heat to 90 °C and introduce air at a rate of 80 mL / min for the cumene oxidation reaction. The reaction time is 6 h.

[0032] Analysis method:

[0033] 1) After the reaction is completed, cool the reaction solution to room temperature. Take 50 μL of the reaction solution and dilute it to a 25 mL volumetric flask. Measure the contents of cumene and the oxidation product CHP by high performance liquid chromatography, and calculate the conversion rate of cumene and the selectivity of CHP.

[0034] 2) By calculation, the conversion rate of cumene is 16.2%, and the selectivity of CHP is 94.8%.

[0035] Example 2

[0036] A method for the selective oxidation of cumene to prepare CHP, comprising the following steps:

[0037] Place 12 g (0.1 mol) of cumene, 0.02 mmol of BmimBr and 0.015 mmol of NHPI in a 50 mL three-necked flask. Under atmospheric pressure, heat to 90 °C and introduce air at a rate of 80 mL / min for the cumene oxidation reaction. The reaction time is 6 h.

[0038] Analysis method:

[0039] 1) After the reaction is completed, cool the reaction solution to room temperature. Take 50 μL of the reaction solution and dilute it to a 25 mL volumetric flask. Measure the contents of cumene and the oxidation product CHP by high performance liquid chromatography, and calculate the conversion rate of cumene and the selectivity of CHP.

[0040] 2) By calculation, the conversion rate of cumene is 20.9%, and the selectivity of CHP is 91.3%.

[0041] Example 3

[0042] A method for the selective oxidation of cumene to prepare CHP, comprising the following steps:

[0043] Place 12 g of cumene, 0.03 mmol of BmimBr and 0.015 mmol of NHPI in a 50 mL three-necked flask. Under atmospheric pressure, heat to 90 °C and introduce air at a rate of 80 mL / min for the cumene oxidation reaction. The reaction time is 6 h.

[0044] Analysis method:

[0045] 1) After the reaction was completed, the reaction solution was cooled to room temperature. 50 μL of the reaction solution was taken and diluted to a 25 mL volumetric flask. The contents of cumene and the oxidation product CHP were measured by high performance liquid chromatography, and the conversion rate of cumene and the selectivity of CHP were calculated.

[0046] 2) By calculation, the conversion rate of cumene was 23.5%, and the selectivity of CHP was 93.2%.

[0047] Comparative Example 1

[0048] Cumene (12 g) and 0.015 mmol of NHPI were placed in a 50 mL three-necked flask. Under atmospheric pressure, the temperature was raised to 90 °C, and air was introduced at 80 mL / min for the oxidation reaction of cumene. The reaction time was 6 h.

[0049] Comparative Example 2

[0050] Cumene (12 g) and 0.01 mmol of BmimBr were placed in a 50 mL three-necked flask. Under atmospheric pressure, the temperature was raised to 90 °C, and air was introduced at 80 mL / min for the oxidation reaction of cumene. The reaction time was 6 h.

[0051] Comparative Example 3

[0052] Cumene (12 g) and 0.02 mmol of BmimBr were placed in a 50 mL three-necked flask. Under atmospheric pressure, the temperature was raised to 90 °C, and air was introduced at 80 mL / min for the oxidation reaction of cumene. The reaction time was 6 h.

[0053] Comparative Example 4

[0054] Cumene (12 g) and 0.03 mmol of BmimBr were placed in a 50 mL three-necked flask. Under atmospheric pressure, the temperature was raised to 90 °C, and air was introduced at 80 mL / min for the oxidation reaction of cumene for 6 h.

[0055] Analysis method for the products of Comparative Examples 1-4 above: After the reaction was completed, the reaction solution was cooled to room temperature. 50 μL of the reaction solution was taken and diluted to a 25 mL volumetric flask. The contents of cumene and the oxidation product CHP were measured by high performance liquid chromatography, and the conversion rate of cumene and the selectivity of CHP were calculated. All results are summarized in Table 1.

[0056] Table 1 Synergistic catalytic effect of NHPI and BmimBr.

[0057]

[0058] It can be seen from Examples 1-3 and Comparative Examples 1-4 that the conversion rates of cumene (16.2%, 20.9%, 23.5%) are higher when NHPI and BmimBr are used as catalysts than those when NHPI and BmimBr are used alone as catalysts (3.4%, 7.6%, 11.3%, 12.7%), indicating that NHPI and BmimBr have a synergistic catalytic effect.

[0059] Figure 2 In this case, within 6 h of the reaction time of the present invention, the radical signal from PINO (g = 1.9309) was detected, which is clear evidence of the existence of PINO radicals.

[0060] As described above, it is only the preferred embodiment of the present invention, and it does not impose any other form of limitation on the present invention. Any modification or equivalent change made according to the technical essence of the present invention still falls within the scope claimed by the present invention.

Claims

1. A method for preparing cumene hydroperoxide by selective oxidation of cumene, characterized in that: The method comprises the following steps: Isopropylbenzene, ionic liquid BmimBr and NHPI are placed in a three-necked flask and mixed, and air with a flow rate of 50-150 mL min is introduced at a temperature of 90-120° C. to carry out an oxidation reaction of propylbenzene, wherein the molar ratio of propylbenzene, BmimBr and NHPI is 10000:(1-3):(1.5-3).

2. The method according to claim 1, characterized in that The cumene is unsubstituted or substituted cumene, and the substituent is selected from C1-C6 alkyl.

3. The method according to claim 1 or 2, characterized in that: The three-necked flask was placed in an oil bath equipped with a stirring device and a condensing device.

4. The method according to claim 1 or 2, characterized in that: The cumene oxidation reaction is carried out at a stirring rate of 400-600 r / min.

5. The method according to claim 1 or 2, characterized in that: The pressure of the cumene oxidation reaction was controlled to be 0.1 MPa.

6. The method according to claim 1 or 2, characterized in that: The time of the cumene oxidation reaction is controlled to be 2-6h.

7. The method according to claim 1 or 2, characterized in that: The preparation method of the ionic liquid BmimBr is as follows: Add 0.1 mol of 1-methylimidazole into a 100 mL three-necked flask, and place the three-necked flask with a condenser in a 70°C oil bath with a stirrer. Use a dropping funnel to slowly drop a slightly excess of 0.11 mol of n-butyl bromide into the reaction system, and react for 24 hours after the addition is completed. After the reaction is completed, the reaction solution is cooled to room temperature, and then washed twice with toluene and ethyl acetate to obtain a light yellow viscous liquid. The light yellow viscous liquid is placed in a rotary evaporator and rotary evaporated until no liquid drips out. It is dried in a vacuum drying oven at 70°C for 24 hours to obtain 1-butyl-3-methylimidazolium bromide ionic liquid BmimBr, which is sealed and placed in a drying oven for standby use.

8. The method according to claim 1 or 2, characterized in that: The reaction yield of the method reaches 91-96%, and the conversion rate of isopropylbenzene reaches 16-30%.

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