A method for separating o-bromotoluene and m-bromotoluene

Abstract

The present invention discloses a method for separating o-bromotoluene and m-bromotoluene. The dibromoethoxycalix[5]arene crystal material is contacted with a mixture containing o-bromotoluene and m-bromotoluene. The dibromoethoxycalix[5]arene crystal material selectively adsorbs and complexes m-bromotoluene, realizing the adsorption separation of o-bromotoluene and m-bromotoluene. The chemical structural formula of the dibromoethoxycalix[5]arene crystal material is as follows: The separation process of the present invention is simple in operation and has low equipment requirements; the separation process does not require rectification operation, has low energy consumption, saves energy, and reduces the production cost of m-bromotoluene; the crystal material used has high stability and can be recycled without reducing the separation effect.

Description

Technical Field

[0001] The present invention relates to the technical field of adsorption separation, and particularly relates to a method for separating o-bromotoluene and m-bromotoluene. Background Art

[0002] m-Bromotoluene is an important chemical raw material and is widely used in the synthesis fields of fine chemicals such as pharmaceuticals and pesticides. m-Bromotoluene is an important intermediate for preparing the pesticide residue detector 5,5'-dithiobis(2-nitrobenzoic acid). In the field of clinical drugs, m-bromotoluene is an important intermediate for synthesizing cinnamate derivatives, and cinnamate derivatives can be used to produce drugs for treating joint pain. The demand for high-purity m-bromotoluene in the chemical industry is increasing.

[0003] There are mainly two production methods for m-bromotoluene. The first one is to prepare it through the electrophilic substitution reaction of toluene and hydrobromic acid. Due to the electron-donating effect of the methyl group, during the production of m-bromotoluene, o-bromotoluene and p-bromotoluene will also be produced simultaneously. Among them, the melting point of p-bromotoluene is relatively high, at 28.5°C, and it can be separated by the method of cooling crystallization. For example, the patent specification with the publication number CN105669361A discloses a method for separating o-bromotoluene and p-bromotoluene. Utilizing the difference in their melting points (p-bromotoluene: melting point 28.5°C; o-bromotoluene: melting point -27.8°C), a process of distillation connected with melt crystallization is developed to obtain high-purity p-bromotoluene.

[0004] Therefore, the separation of o-bromotoluene and m-bromotoluene is the key step to obtain high-purity m-bromotoluene. The separation method of o-bromotoluene and m-bromotoluene is mainly rectification, which separates the two by utilizing the physical property differences between o-bromotoluene and m-bromotoluene.

[0005] Rectification is a separation method widely used in industry, with simple operation and mature technology. However, since the boiling points of o-bromotoluene (181.7°C) and m-bromotoluene (183.7°C) are very close, only differing by 2°C, separating o-bromotoluene and m-bromotoluene by rectification is accompanied by huge energy consumption and high costs.

[0006] Another production method is to first synthesize the corresponding precursor methylaniline, add hydrobromic acid to a reaction kettle and stir, and then continuously add sodium nitrite for diazotization reaction. Use starch potassium iodide test paper to test the reactants in the kettle. After the test paper turns blue, add a certain amount of copper powder into the kettle, and then obtain the crude product through steam distillation. For example, the patent specification with the publication number CN104045512A discloses a synthesis process of m-bromotoluene. Select 95% ethanol and add it to an enamel reaction kettle, start the stirrer to stir, add concentrated sulfuric acid and 3-bromo-aminomethylbenzene and stir evenly, and then add sodium nitrite and aqueous solution. After washing with ether, pour in copper powder and heat the reaction until no bubbles overflow. After the liquid material changes from reddish-brown to yellow, the reaction ends, and then distillation, washing, separating the aqueous phase, drying, filtering, and rectifying are carried out to obtain a colorless product, which is the finished product of m-bromotoluene. However, the reaction process is too cumbersome and accompanied by the generation of waste liquid. Compared with the rectification method, this method has lower energy consumption, but the steps are too cumbersome and a large amount of waste water and waste gas are generated. Summary of the Invention

[0007] In view of the above technical problems and the deficiencies in the art, the present invention provides a method for separating o-bromotoluene and m-bromotoluene, which uses bis(dibromoethoxy)pillar[5]arene crystal material to adsorb and separate the mixture containing o-bromotoluene and m-bromotoluene, with low energy consumption and a simple process, overcoming the defects of high energy consumption, cumbersome process, and the generation of waste liquid and waste gas in the existing separation technology of o-bromotoluene and m-bromotoluene.

[0008] The specific technical solution is as follows:

[0009] A method for separating o-bromotoluene and m-bromotoluene, which contacts bis(dibromoethoxy)pillar[5]arene crystal material with a mixture containing o-bromotoluene and m-bromotoluene, and the bis(dibromoethoxy)pillar[5]arene crystal material selectively adsorbs and complexes m-bromotoluene to achieve the adsorption separation of o-bromotoluene and m-bromotoluene;

[0010] The chemical structural formula of the bis(dibromoethoxy)pillar[5]arene crystal material is as follows:

[0011]

[0012] Due to the difference in the molecular structures of o-bromotoluene and m-bromotoluene, the bis(dibromoethoxy)pillar[5]arene crystal material can form a host-guest complex with a stoichiometric ratio of 1:1 with m-bromotoluene. This host-guest complex is unstable and will gradually desorb when heated, releasing the adsorbed m-bromotoluene. The bis(dibromoethoxy)pillar[5]arene crystal material is stable at the desorption temperature and can be reused after the desorption process is completed, and the selectivity will not decrease.

[0013] The bis(dibromoethoxy)calix[5]arene crystal material can be obtained by recrystallization in a poor solvent. Generally, the poor solvents used are tetrahydrofuran or acetone, but are not limited thereto. The bis(dibromoethoxy)calix[5]arene crystal material obtained by recrystallization can be activated by heating to remove solvent molecules. The activated bis(dibromoethoxy)calix[5]arene crystal material can be directly used for the adsorption separation of the mixture of o-bromotoluene and m-bromotoluene. Preferably, the activation temperature is not lower than 150 °C and the time is not less than 2 hours.

[0014] In one embodiment, the method of contacting the bis(dibromoethoxy)calix[5]arene crystal material with the mixture containing o-bromotoluene and m-bromotoluene is specifically as follows: The bis(dibromoethoxy)calix[5]arene crystal material is placed in a mixed vapor atmosphere containing o-bromotoluene and m-bromotoluene, and the temperature is controlled below 80 °C. The adsorption time can be changed with factors such as the sample amount, adsorption temperature, and the proportion of m-bromotoluene in the mixture. During the adsorption process, the crystal form of the bis(dibromoethoxy)calix[5]arene crystal material will change. Due to the CH-π, π-π stacking, and multiple hydrogen bond interactions between CH-Br, m-bromotoluene in the mixed vapor will form a host-guest complex with bis(dibromoethoxy)calix[5]arene, and the stoichiometric ratio of this host-guest complex is 1:1.

[0015] After the adsorption separation of o-bromotoluene and m-bromotoluene is completed, vacuum heating or reduced-pressure heating can be used to remove the mixture containing o-bromotoluene and m-bromotoluene adsorbed on the surface of the bis(dibromoethoxy)calix[5]arene crystal material, and then heating is used to desorb the m-bromotoluene adsorbed and complexed by the bis(dibromoethoxy)calix[5]arene crystal material, obtaining high-purity m-bromotoluene while realizing the regeneration of the bis(dibromoethoxy)calix[5]arene crystal material.

[0016] The temperature of the vacuum heating or reduced-pressure heating is preferably lower than 80 °C, and the time can be adjusted according to the sample amount. Under the condition of lower than 80 °C, the host-guest compound still exists stably, while the mixture containing o-bromotoluene and m-bromotoluene adsorbed on the surface can be gradually removed. By removing the mixture adsorbed on the surface, the purity of the adsorbed m-bromotoluene is improved.

[0017] The temperature of the heating desorption is preferably 80-100 °C, and the desorption time can be adjusted according to the sample amount. At this temperature, the host-guest complex is unstable, and the adsorbed m-bromotoluene molecules will be gradually released, while the bis(dibromoethoxy)calix[5]arene crystal material is stable and only undergoes a crystal form change during the desorption process. After the desorption is completed, the regenerated bis(dibromoethoxy)calix[5]arene crystal material is obtained, which can be used for the adsorption separation of o-bromotoluene and m-bromotoluene again for the next cycle.

[0018] As a general inventive concept, the present invention also provides an application of the bis(dibromoethoxy)calix[5]arene crystal material in selectively adsorbing and complexing m-bromotoluene in a mixture containing o-bromotoluene and m-bromotoluene to achieve the separation of o-bromotoluene and m-bromotoluene.

[0019] In the process of forming the technical solution of the present invention, the inventors once tried to use the bis(dibromoethoxy)calix[6]arene crystal material for contact adsorption separation with a mixture containing o-bromotoluene and m-bromotoluene, and it was found that this material was difficult to achieve the object of the present invention.

[0020] Compared with the prior art, the present invention has the following beneficial effects: the separation process is simple to operate and has low equipment requirements; the separation process does not require rectification operation, has low energy consumption, and no waste liquid or waste gas is generated during the production process, reducing the production cost of m-bromotoluene; the crystal material used has high stability and can be recycled without reducing the separation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the powder X-ray diffraction (PXRD) pattern of the bis(dibromoethoxy)calix[5]arene crystal material for Examples 1 to 5.

[0022] Figure 2 It is the gas chromatographic characterization result diagram of the bis(dibromoethoxy)calix[5]arene crystal material for Example 4 in adsorbing and separating o-bromotoluene and m-bromotoluene, where: the abscissa represents the retention time, with the unit of min; the ordinate represents the detector signal current intensity, with the unit of pA.

[0023] Figure 3 It is the adsorption and separation effect diagram of the bis(dibromoethoxy)calix[5]arene crystal material for Example 5 when recycled for o-bromotoluene and m-bromotoluene.

[0024] Figure 4 It is the gas chromatographic characterization result diagram of the bis(dibromoethoxy)calix[6]arene crystal material for Comparative Example 2 in adsorbing and separating o-bromotoluene and m-bromotoluene, where: the abscissa represents the retention time, with the unit of min; the ordinate represents the detector signal current intensity, with the unit of pA. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0026] For the operating methods without specific conditions indicated in the following embodiments, they are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer.

[0027] Example 1

[0028] Preparation of bis(dibromoethoxy)calix[5]arene crystal material: Weigh 2 g of bis(dibromoethoxy)calix[5]arene and place it in 20 mL of tetrahydrofuran. Heat it to boiling, and add the tetrahydrofuran solution dropwise until it is completely dissolved. Keep the solution at 0 °C overnight, filter to collect the precipitated crystals, and dry the obtained crystals under vacuum at 50 °C and activate them at 150 °C for 2 hours to obtain a white powder, denoted as BrP5.

[0029] The characterization data of the product prepared in this example are as follows:

[0030] BrP5, 1 H NMR (400 MHz, CDCl 3 , 298 K, ppm) δ 6.91 (s, 10H), 4.22 (t, 20H), 3.84 (s, 10H), 3.63 (t, 20H).

[0031] The PXRD detection results are as shown by line a in Figure 1 . The obtained bis(dibromoethoxy)calix[5]arene crystal material has good crystallinity.

[0032] Example 2

[0033] Adsorption of bis(dibromoethoxy)calix[5]arene crystal material on o-bromotoluene or m-bromotoluene alone: Take two 20 mL culture flasks, add 1 mL of o-bromotoluene and 1 mL of m-bromotoluene respectively, and name them BrP5-OBT and BrP5-MBT. Take 200 mg of the bis(dibromoethoxy)calix[5]arene crystal material obtained in Example 1 and place it in two 5 mL culture flasks respectively. Place the two open 5 mL culture flasks in two 20 mL culture flasks, seal the 20 mL culture flasks, and place them in a 25 °C water bath for 30 hours.

[0034] The characterization data of the product prepared in this example are as follows:

[0035] BrP5-OBT, 1 H NMR (400 MHz, CDCl 3 , 298 K, ppm) δ 6.91 (s, 10H), 4.22 (t, 20H), 3.84 (s, 10H), 3.63 (t, 20H).

[0036] BrP5-MBT, 1 H NMR (400 MHz, CDCl 3 , 298 K, ppm) δ 7.32 (q, 2H), 7.10 (q, 2H), 6.91 (s, 10H), 4.22 (t, 20H), 3.84 (s, 10H), 3.63 (t, 20H), 2.29 (s, 3H).

[0037] 1 The \(^1H\) NMR results indicated that dibromoethoxyl calix[5]arene crystal material adsorbed m-bromotoluene in a stoichiometric ratio of 1:1, and did not adsorb o-bromotoluene.

[0038] The PXRD detection results of BrP5-OBT are as Figure 1 shown by line b in the figure. The spectral changes of dibromoethoxyl calix[5]arene crystal material after being placed in o-bromotoluene vapor for a period of time were very small, indicating that its unit cell parameters did not change, meaning that dibromoethoxyl calix[5]arene crystal material had no adsorption capacity for o-bromotoluene. The PXRD detection results of BrP5-MBT are as Figure 1 shown by line c in the figure. Compared with the PXRD pattern of the initially activated dibromoethoxyl calix[5]arene crystal material, the PXRD pattern of dibromoethoxyl calix[5]arene crystal material after being placed in m-bromotoluene vapor for a period of time changed, indicating that its unit cell parameters had changed, meaning that m-bromotoluene had been adsorbed into dibromoethoxyl calix[5]arene crystal material.

[0039] Example 3

[0040] Adsorption of dibromoethoxyl calix[5]arene crystal material on a 1:1 mixture of o-bromotoluene and m-bromotoluene: Take a 20 mL culture bottle, add 0.5 mL of o-bromotoluene and 0.5 mL of m-bromotoluene, named BrP5-OMBT. Take 200 mg of the dibromoethoxyl calix[5]arene crystal material obtained in Example 1 and place it in a 5 mL culture bottle. Place the open 5 mL culture bottle in the above 20 mL culture bottle, seal the 20 mL culture bottle, place it in a 25 °C water bath for 30 hours, and place the obtained powder in a 50 °C vacuum oven for 30 minutes.

[0041] The characterization data of the product prepared in this example are as follows:

[0042] BrP5-OMBT, 1 \(^1H\) NMR (400 MHz, CDCl 3 , 298 K, ppm) δ 7.32 (q, 2H), 7.10 (q, 2H), 6.91 (s, 10H), 4.22 (t, 20H), 3.84 (s, 10H), 3.63 (t, 20H), 2.29 (s, 3H).

[0043] In the 1 \(^1H\) NMR spectrum, only the signals of the hydrogen atoms corresponding to m-bromotoluene were found, indicating that dibromoethoxyl calix[5]arene crystal material could selectively adsorb m-bromotoluene.

[0044] The PXRD detection results are as Figure 1As shown by the middle d line, compared with the PXRD pattern of the initially activated bis(dibromoethoxy)pillar[5]arene crystal material, the PXRD pattern of the bis(dibromoethoxy)pillar[5]arene crystal material after being placed in the mixed vapor of o-bromotoluene and m-bromotoluene for a period of time changed, and the pattern change was the same as that of BrP5-MBT, indicating that the bis(dibromoethoxy)pillar[5]arene crystal material can selectively adsorb m-bromotoluene.

[0045] The results of headspace gas chromatography are as Figure 2 shown, and the results show that the bis(dibromoethoxy)pillar[5]arene crystal material can selectively adsorb m-bromotoluene with a selectivity of 97.094%.

[0046] Example 4

[0047] Regeneration of bis(dibromoethoxy)pillar[5]arene crystal material: 200 mg of the bis(dibromoethoxy)pillar[5]arene crystal material saturated with m-bromotoluene in Example 3 was heated in a vacuum oven at 100 °C for 2 hours, and the sample was denoted as BrP5-D.

[0048] The characterization data of the product prepared in this example are as follows:

[0049] BrP5-D, 1 H NMR (400 MHz, CDCl 3 , 298 K, ppm) δ 6.91 (s, 10H), 4.22 (t, 20H), 3.84 (s, 10H), 3.63 (t, 20H).

[0050] In the 1 H NMR spectrum, the signal of the hydrogen atoms corresponding to m-bromotoluene was found to have disappeared, indicating that the bis(dibromoethoxy)pillar[5]arene crystal material has completed desorption regeneration and all m-bromotoluene molecules have been released.

[0051] The PXRD test results are as Figure 1 shown by the middle e line. Compared with the PXRD pattern of the initially activated bis(dibromoethoxy)pillar[5]arene crystal material, the PXRD pattern of the desorbed bis(dibromoethoxy)pillar[5]arene crystal material changed very little, indicating that the bis(dibromoethoxy)pillar[5]arene crystal material has completed the desorption process.

[0052] Example 5

[0053] Reuse of bis(dibromoethoxy)pillar[5]arene crystal material: 200 mg of the bis(dibromoethoxy)pillar[5]arene crystal material regenerated in Example 4 was used to repeat Examples 3 and 4.

[0054] The results of headspace gas chromatography show that, as Figure 3As shown, the bis(dibromoethoxy)calix[5]arene crystal material can selectively adsorb m-bromotoluene with a selectivity as high as 97.094%, and its selectivity does not decrease significantly after being reused 5 times.

[0055] Comparative Example 1

[0056] Preparation of bis(dibromoethoxy)calix[6]arene crystal material: Weigh 2 g of bis(dibromoethoxy)calix[6]arene and place it in 20 mL of tetrahydrofuran. Heat it to boiling, and add the tetrahydrofuran solution dropwise until it is completely dissolved. Keep the solution at 0 °C overnight, filter to collect the precipitated crystals, and vacuum dry the obtained crystals at 50 °C. Activate them at 150 °C for 2 hours to obtain a white powder, denoted as BrP6.

[0057] The chemical structural formula of the bis(dibromoethoxy)calix[6]arene crystal material is as follows:

[0058]

[0059] The characterization data of the product prepared in this comparative example are as follows:

[0060] BrP6, 1 H NMR (400 MHz, CDCl 3 , 298 K, ppm) δ 6.78 (s, 12H), 4.16 (t, 24H), 3.87 (s, 12H), 3.55 (t, 24H).

[0061] Comparative Example 2

[0062] Adsorption of bis(dibromoethoxy)calix[6]arene crystal material on a 1:1 mixture of o-bromotoluene and m-bromotoluene: Take a 20 mL culture bottle, add 0.5 mL of o-bromotoluene and 0.5 mL of m-bromotoluene, and name it BrP6-OMBT. Take 200 mg of the bis(dibromoethoxy)calix[6]arene crystal material obtained in Comparative Example 1 and place it in a 5 mL culture bottle. Place the open 5 mL culture bottle in the above 20 mL culture bottle, seal the 20 mL culture bottle, and place it in a 25 °C water bath for 30 hours. Place the obtained powder in a 50 °C vacuum oven for 30 minutes.

[0063] The characterization data of the product prepared in this example are as follows:

[0064] BrP6-OMBT, 1 H NMR (400 MHz, CDCl 3 , 298 K, ppm) δ 7.32 (q, 2H), 7.10 (q, 2H), 6.78 (s, 12H), 4.16 (t, 24H), 3.87 (s, 12H), 3.55 (t, 24H), 2.40 (s, 1H), 2.29 (s, 3H).

[0065] The results of headspace gas chromatography are as Figure 4 shown. The results indicate that although the bis(dibromoethoxy)pillar[6]arene crystal material can selectively adsorb o-bromotoluene to a certain extent, the selectivity is not high, only 68.345%.

[0066] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. A method for separating o-bromotoluene and m-bromotoluene, characterized in that, the dibromoethoxycalix[5]arene crystal material is contacted with a mixture containing o-bromotoluene and m-bromotoluene, and the dibromoethoxycalix[5]arene crystal material selectively adsorbs and complexes m-bromotoluene to achieve the adsorption separation of o-bromotoluene and m-bromotoluene; the chemical structural formula of the dibromoethoxycalix[5]arene crystal material is as follows: the dibromoethoxycalix[5]arene crystal material is obtained by recrystallization in a poor solvent and then activated; the temperature of the activation is not lower than 150 °C and the time is not less than 2 hours; the specific way of contacting the dibromoethoxycalix[5]arene crystal material with the mixture containing o-bromotoluene and m-bromotoluene is: placing the dibromoethoxycalix[5]arene crystal material in a mixed vapor atmosphere containing o-bromotoluene and m-bromotoluene, and controlling the temperature below 80 °C.

2. The separation method according to claim 1, characterized in that, the poor solvent is tetrahydrofuran or acetone.

3. The separation method according to claim 1, characterized in that, after the adsorption separation of o-bromotoluene and m-bromotoluene is completed, the mixture containing o-bromotoluene and m-bromotoluene adsorbed on the surface of the dibromoethoxycalix[5]arene crystal material is removed by vacuum heating or reduced-pressure heating, and then the m-bromotoluene adsorbed and complexed by the dibromoethoxycalix[5]arene crystal material is desorbed by heating, obtaining high-purity m-bromotoluene while realizing the regeneration of the dibromoethoxycalix[5]arene crystal material.

4. The separation method according to claim 3, characterized in that, the temperature of the vacuum heating or reduced-pressure heating is lower than 80 °C.

5. The separation method according to claim 3, characterized in that, the temperature of the heating desorption is 80 - 100 °C.

6. The application of the dibromoethoxycalix[5]arene crystal material in selectively adsorbing and complexing m-bromotoluene in a mixture containing o-bromotoluene and m-bromotoluene to achieve the separation of o-bromotoluene and m-bromotoluene, characterized in that, the chemical structural formula of the dibromoethoxycalix[5]arene crystal material is as follows:

Images