Method for producing β-bromoethylbenzene

Abstract

To provide a method for efficiently producing β-bromoethylbenzene while enabling miniaturization of an electromagnetic wave irradiation device and reducing formation of by-products such as photopolymers and dimers.SOLUTION: A method for producing β-bromoethylbenzene comprises: irradiating hydrogen bromide gas with electromagnetic waves; and contacting the hydrogen bromide gas irradiated with electromagnetic waves with styrene.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for producing β-bromoethylbenzene.

Background Art

[0002] β-Bromoethylbenzene is useful as a synthetic intermediate for medical and agricultural chemicals and functional materials. β-Bromoethylbenzene can be obtained by a reaction in which hydrogen bromide is added to styrene according to the anti-Markovnikov rule. As a general method for producing β-bromoethylbenzene, a method is known in which hydrogen bromide is made into radicals and added to styrene in the coexistence of radical species such as oxygen, peroxide, and azo compounds, or while irradiating the reaction system with electromagnetic waves.

[0003] Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2021-130650) and Patent Document 2 (Japanese Unexamined Patent Application Publication No. 9-040591) describe a method of irradiating the entire reaction system with electromagnetic waves such as ultraviolet rays using an LED (Patent Document 1) or a high-pressure mercury lamp (Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] When the entire reaction system is irradiated with electromagnetic waves, a large amount of by-products derived from raw materials or reaction products, such as photopolymers of styrene, dimers by [2+2] photocyclization reaction or ion addition reaction, such as bromodiphenylbutane, are generated, and in some cases, the β-bromoethylbenzene product is colored by a part of the by-products. These by-products may have an adverse effect on the quality of the β-bromoethylbenzene product.

[0006] When by-products such as photopolymers of styrene adhere to the side surface of the glass reactor, the irradiation of electromagnetic waves to the reaction system is blocked, and there is a risk that the production efficiency of β-bromoethylbenzene may decrease. When the irradiation of electromagnetic waves is insufficient, the production amount of α-bromoethylbenzene, which is a structural isomer, may increase.

[0007] When irradiating the entire reaction system with electromagnetic waves, increasing the production scale requires enlarging the electromagnetic wave irradiation device. Therefore, the cost related to the electromagnetic wave irradiation device may increase, or there may be restrictions on the installation location.

[0008] An object of the present invention is to provide a method for producing β-bromoethylbenzene with high efficiency while being able to miniaturize the electromagnetic wave irradiation device and suppressing the generation of by-products such as photopolymers and dimers.

Means for Solving the Problems

[0009] The inventors of the present invention have found that by irradiating hydrogen bromide gas with electromagnetic waves and then bringing it into contact with styrene, β-bromoethylbenzene can be efficiently produced while suppressing the generation of by-products such as photopolymers and dimers, and thus have completed the present invention.

[0010] This application includes the following aspects.

[0011] [Aspect 1] A method for producing β-bromoethylbenzene, comprising irradiating hydrogen bromide gas with electromagnetic waves and bringing the hydrogen bromide gas irradiated with electromagnetic waves into contact with styrene. [Aspect 2] The method for producing β-bromoethylbenzene according to Aspect 1, wherein the peak wavelength of the electromagnetic waves is in the range of 250 nm or more and 600 nm or less. [Aspect 3] The method according to Aspect 1 or 2, wherein the hydrogen bromide gas irradiated with electromagnetic waves is brought into contact with styrene within 1×10 -3 seconds from the irradiation of the electromagnetic waves. [Aspect 4] The production method of β-bromoethylbenzene according to any one of Aspects 1 to 3, wherein the light source of the electromagnetic wave is at least one selected from the group consisting of ultraviolet LEDs, visible light LEDs, organic ELs, inorganic ELs, mercury lamps, and mercury-free lamps.

Advantages of the Invention

[0012] According to the present invention, it is possible to miniaturize the electromagnetic wave irradiation device, and it is possible to produce β-bromoethylbenzene with high efficiency while suppressing the generation of by-products such as photopolymers and dimers.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0014] The radical addition reaction of styrene and hydrogen bromide under electromagnetic wave irradiation is a complex reaction in which, in addition to β-bromoethylbenzene, α-bromoethylbenzene, dibromoethylbenzene, bromodiphenylbutane dimerized, etc. are by-produced. In addition to the compounds shown in the following formula, a photopolymer of styrene is also by-produced.

Chemical formula

[0015] [Production Method of β-Bromoethylbenzene] The present invention provides a method for producing β-bromoethylbenzene. The method for producing β-bromoethylbenzene according to one embodiment includes irradiating hydrogen bromide gas with electromagnetic waves and bringing the hydrogen bromide gas irradiated with electromagnetic waves into contact with styrene.

[0016] According to this embodiment, after irradiating hydrogen bromide gas with electromagnetic waves, by bringing the hydrogen bromide gas irradiated with electromagnetic waves into contact with styrene, the production of β-bromoethylbenzene can be promoted while avoiding irradiation of styrene or the reaction product with electromagnetic waves. Thereby, side reactions derived from styrene or the reaction product, such as photopolymerization of styrene and dimerization reaction of styrene or the reaction product, can be suppressed, and impurities in the β-bromoethylbenzene product can be reduced. In addition, since the adhesion of by-products such as photopolymers of styrene to the inner wall of the reactor can be suppressed, it is possible to reduce the cost related to the maintenance management of the reactor and the working hours of the operator, thereby improving the production efficiency of β-bromoethylbenzene.

[0017] In this embodiment, since the electromagnetic wave irradiation device only needs to irradiate electromagnetic waves on hydrogen bromide gas rather than the entire reaction system, the electromagnetic wave irradiation device can be miniaturized, and the degree of freedom of its arrangement can also be increased.

[0018] In this embodiment, since the photopolymerization of styrene can be suppressed, the concentration of styrene in the reaction system may be increased in some cases. Thereby, the capacity of the production facility for β-bromoethylbenzene can be enhanced, and the man-hours and manufacturing costs can be reduced.

[0019] Electromagnetic waves may be irradiated only on hydrogen bromide gas, or may be irradiated on a mixed gas of hydrogen bromide gas and an inert gas. By irradiating electromagnetic waves only on hydrogen bromide gas, the deactivation of the activated hydrogen bromide gas can be minimized, the production efficiency of β-bromoethylbenzene can be increased, and the generation of by-products can be suppressed. The inert gas can be used as a carrier gas for adjusting the flow rate or velocity of hydrogen bromide gas. Thereby, the production efficiency of β-bromoethylbenzene can be optimized according to the reaction apparatus to be used. Examples of the inert gas include nitrogen gas, carbon dioxide, neon, argon, and a mixed gas thereof. The content of hydrogen bromide gas in the mixed gas is not particularly limited, but can be 50% by volume or more, preferably 75% by volume or more, more preferably 90% by volume or more.

[0020] The supply amount of hydrogen bromide gas is preferably 1 mol or more, more preferably 1.02 mol to 1.5 mol, and still more preferably 1.05 mol to 1.3 mol per 1 mol of styrene. By setting the supply amount of hydrogen bromide gas to 1 mol or more per 1 mol of styrene, the yield of β-bromoethylbenzene can be increased. By setting the supply amount of hydrogen bromide gas to 1.5 mol or less per 1 mol of styrene, the selectivity of β-bromoethylbenzene can be increased. By setting the supply amount of hydrogen bromide gas to 1.5 mol or less per 1 mol of styrene, the amount of hydrogen bromide gas that does not dissolve in the reaction system can be reduced, and hydrogen bromide gas can be effectively utilized.

[0021] The flow rate of hydrogen bromide gas can be appropriately set according to the size of the pipe for supplying hydrogen bromide gas, the distance between the electromagnetic wave irradiation position and the blowing point, etc. The flow rate of hydrogen bromide gas can be, for example, 0.01 NL / min to 3 NL / min per 1 mol of styrene, preferably 0.1 NL / min to 2 NL / min, and more preferably 0.5 NL / min to 1 NL / min.

[0022] Hydrogen bromide gas can be introduced into the reaction system through a supply pipe. It is preferable to provide a blowing port at the tip of the supply pipe and blow the hydrogen bromide gas irradiated with electromagnetic waves into styrene or a styrene solution through the blowing port. Thereby, the contact efficiency between the hydrogen bromide gas irradiated with electromagnetic waves and styrene can be increased.

[0023] Irradiation with electromagnetic waves can be performed at a desired position of the supply pipe of hydrogen bromide gas. The material of the supply pipe is not particularly limited as long as it can transmit electromagnetic waves at the electromagnetic wave irradiation position. Examples include borosilicate glass, quartz, acrylic resin, and fluororesin, and it is preferably selected from the group consisting of borosilicate glass and quartz.

[0024] The electromagnetic wave is not particularly limited as long as it activates hydrogen bromide gas to promote the radical addition reaction with styrene. From the viewpoints of the production efficiency and selectivity of β-bromoethylbenzene, the peak wavelength of the electromagnetic wave is preferably in the range of 250 nm or more and 600 nm or less, more preferably in the range of 250 nm or more and 500 nm or less, and still more preferably in the range of 300 nm or more and 400 nm or less. From the viewpoint of the availability of the light source, the peak wavelength is preferably about 254 nm, about 365 nm, about 385 nm, about 405 nm, or about 435 nm.

[0025] Although not bound by any theory, it is considered important to generate H radicals and Br radicals from hydrogen bromide in order to efficiently produce β-bromoethylbenzene in the radical addition reaction between hydrogen bromide and styrene. Generally, in order to homolytically cleave hydrogen bromide, external energy equal to or higher than the bond energy of H-Br (363 kJ / mol) is required, and when this external energy is converted to the wavelength of light, it corresponds to 340 nm or less. However, the inventors have unexpectedly found that β-bromoethylbenzene is efficiently produced by irradiating hydrogen bromide gas with electromagnetic waves using an ultraviolet LED having a peak wavelength of 365 nm as a light source and then bringing it into contact with styrene. From this finding, although the reactive species in the hydrogen bromide gas irradiated with the electromagnetic wave may be different from H radicals or Br radicals, further verification is required in the future to elucidate the reaction mechanism.

[0026] The light source of the electromagnetic wave is not particularly limited, but it is preferably at least one selected from the group consisting of ultraviolet LEDs, visible light LEDs, organic ELs, inorganic ELs, mercury lamps, and mercury-free lamps. The mercury-free lamp is a type of metal halide lamp and is a light source that uses metals such as zinc, iron, cobalt, and nickel as luminescent metals instead of mercury. Since ultraviolet LEDs and visible light LEDs generally have a narrow wavelength distribution, by appropriately selecting the light source, a desired peak wavelength can be obtained without using a band-pass filter. When using an organic EL, inorganic EL, mercury lamp, or mercury-free lamp, light of unnecessary wavelengths may be cut using a band-pass filter, and electromagnetic waves having a desired peak wavelength may be irradiated.

[0027] The illuminance of the light source of the electromagnetic wave is not particularly limited, but at the position where the electromagnetic wave irradiates the hydrogen bromide gas, for example, 0.1 mW / cm 2 ~500 mW / cm 2 can be set, preferably 1 mW / cm 2 ~300 mW / cm 2 , more preferably 10 mW / cm 2 ~250 mW / cm 2 is.

[0028] It is preferable to bring the hydrogen bromide gas irradiated with the electromagnetic wave into contact with styrene within 1×10 -3 seconds from the irradiation of the electromagnetic wave, more preferably bring it into contact with styrene within 5×10 -4 seconds, and even more preferably bring it into contact with styrene within 1×10 -5 seconds. By setting the transfer time of the hydrogen bromide gas from the electromagnetic wave irradiation to the contact with styrene within 1×10 -3 seconds, the deactivation of the activated hydrogen bromide gas can be minimized, the production efficiency of β-bromoethylbenzene can be increased, and the production of by-products can be suppressed. The transfer time is defined as the average time calculated based on the position where the hydrogen bromide gas first contacts styrene, for example, the distance between the blowing port and the electromagnetic wave irradiation position, the flow rate of the hydrogen bromide gas, and the internal cross-sectional area of the supply pipe.

[0029] Styrene can be used in the reaction in the form of a solution using a reaction solvent. Styrene can also be used directly in the reaction without using a reaction solvent.

[0030] Examples of the reaction solvent include aliphatic hydrocarbons such as n - hexane, n - heptane, n - octane, isooctane, and methylcyclohexane; aromatic hydrocarbons such as benzene, toluene, o - xylene, m - xylene, p - xylene, mesitylene, ethylbenzene, propylbenzene, and isopropylbenzene; halogenated aliphatic hydrocarbons such as tetrachloroethylene, carbon tetrachloride, and 1,1,1 - trichloroethane; and mixtures of two or more of these. The reaction solvent preferably can dissolve styrene, hydrogen bromide, and β - bromoethylbenzene, does not react with styrene, hydrogen bromide, and β - bromoethylbenzene, and does not absorb electromagnetic waves irradiated from a light source. From the viewpoint of electromagnetic wave absorption, aliphatic hydrocarbons and halogenated aliphatic hydrocarbons are preferred. From the viewpoint of post - treatment of the reaction, aliphatic hydrocarbons are preferred. For the purpose of promoting the dissolution of hydrogen bromide into the reaction system, within a range that does not inhibit the reaction, fatty acids such as acetic acid and propionic acid; aliphatic nitrile compounds such as acetonitrile and propionitrile; aliphatic nitro compounds such as nitromethane; or mixtures of two or more of these may be used in combination as the reaction solvent.

[0031] When using a reaction solvent, the amount of the reaction solvent used is not particularly limited, but based on 100 parts by mass of styrene, it can be 50 parts by mass to 5,000 parts by mass, preferably 100 parts by mass to 1,000 parts by mass, more preferably 150 parts by mass to 500 parts by mass.

[0032] During the reaction, it is preferable to stir styrene or a styrene solution using a stirring device. Stirring can increase the contact efficiency between hydrogen bromide gas irradiated with electromagnetic waves and styrene.

[0033] The reaction temperature is preferably 0°C to 90°C, more preferably 20°C to 80°C, and even more preferably 25°C to 70°C. By setting the reaction temperature to 0°C or higher, the conversion rate of β-bromoethylbenzene can be increased. By setting the reaction temperature to 90°C or lower, the selectivity of β-bromoethylbenzene can be increased.

[0034] The reaction pressure is preferably 0.1 MPaA (absolute pressure) to 1.5 MPaA, more preferably 0.1 MPaA to 1.0 MPaA, and even more preferably 0.1 MPaA to 0.5 MPaA. By setting the reaction pressure to 0.1 MPaA or higher, the solubility of hydrogen bromide gas can be increased to increase the conversion rate. By setting the reaction pressure to 1.5 MPaA or lower, the cost related to the equipment can be reduced.

[0035] The reaction time is generally 0.1 hour to 100 hours, and preferably 0.5 hour to 10 hours.

[0036] The reaction may be carried out in an inert gas atmosphere such as nitrogen gas, carbon dioxide, neon, or argon.

[0037] The reaction may be a batch reaction in which styrene or a styrene solution is placed in a reactor and hydrogen bromide gas irradiated with electromagnetic waves is blown into the reaction system while the reaction is carried out, or a continuous reaction in which styrene or a styrene solution and hydrogen bromide gas irradiated with electromagnetic waves are continuously supplied to the reactor to carry out the reaction.

[0038] During the reaction, radical species such as oxygen, peroxide, and azo compounds may be used in combination as auxiliary agents. Examples of peroxides include di-t-butyl peroxide, dicumyl peroxide, t-butyl cumyl peroxide, benzoyl peroxide, dilauryl peroxide, cumene hydroperoxide, and t-butyl hydroperoxide. Examples of azo compounds include 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylpropionitrile), 2,2'-azobis(2-methylbutyronitrile), and 1,1'-azobis(cyclohexane-1-carbonitrile). The amount of oxygen used can be, for example, 0.2 to 10 parts by volume based on 100 parts by volume of hydrogen bromide gas. The amount of peroxide and azo compound used can be, for example, 0.01 to 10 parts by mass based on 100 parts by mass of styrene.

[0039] All documents mentioned in this specification are incorporated herein by reference in their entirety.

[0040] The examples of the present invention described below are for illustrative purposes only and do not limit the technical scope of the present invention. The technical scope of the present invention is limited only by the description in the claims. Changes to the present invention, such as addition, deletion, and substitution of the constituent elements of the present invention, can be made on the condition that the gist of the present invention is not deviated from.

Examples

[0041] The present invention will be described in more detail below based on examples, but these do not limit the present invention in any way.

[0042] [Reaction apparatus] In this example, the reaction apparatus schematically shown in FIG. 1 was used. The reaction apparatus included a glass reactor 1 with an inner diameter of 2 cm, a height of 30 cm, and a volume of 92.4 mL, a glass raw material gas supply pipe 2, and an LED device 3.

[0043] A rotor was placed at the bottom of Reactor 1. Reactor 1 was connected to a water bath and a pump circulator for maintaining the temperature of the reaction system constant. A cap 11 was attached to the upper part of the inclined and narrowed Reactor 1, and the cap 11 was equipped with an exhaust gas outlet 12 and a nitrogen gas supply port 13. During the reaction, nitrogen gas was supplied from the nitrogen gas supply port 13, and waste gas WG containing unreacted hydrogen bromide gas and other volatile components was discharged from the exhaust gas outlet 12, thereby maintaining the inside of Reactor 1 at 0.1 MPaA (atmospheric pressure) and in a nitrogen atmosphere. Reactor 1 had a glass injection port 15 with an inner diameter of 1 cm at the lower part. The raw material gas supply pipe 2 was branched into three, and hydrogen bromide gas was supplied from above and nitrogen gas was supplied from the side as required. The LED device 3 was a spot-type UV-LED irradiator (model number: MP-HLDL-200U65CLKPSC, CCS Inc., peak wavelength: 365 nm, illuminance: 0~250 mW / cm 2 , irradiation window: diameter 10 mm, full width at half maximum (FWHM) of peak wavelength: 10 nm).

[0044] [Gas Chromatography (GC) Measurement] Gas Chromatography (GC) measurement of the reaction product was carried out under the following conditions. Device: GC-2014 (Shimadzu Corporation) Column: NB-5 (GL Sciences Inc., 30 m × 0.32 mm, df = 0.40 μm) Column temperature: rising from 100 °C to 250 °C Temperature rising rate: 5 °C / min Injection temperature: 220 °C Detector temperature: 250 °C Injection volume: 0.2 μL

[0045] Each peak of the chromatograph obtained by GC measurement of the reaction product was assigned to each of the target substance, β-bromoethylbenzene, and α-bromoethylbenzene, styrene, phenylethanol, dibromoethylbenzene, and bromodiphenylbutane, and their peak areas were determined. The sum of the obtained peak areas was taken as 100 (area %), and the peak area ratios of β-bromoethylbenzene (β form), α-bromoethylbenzene (α form), and bromodiphenylbutane (dimer, total of 2-bromo-1,4-diphenylbutane and 1-bromo-1,4-diphenylbutane) were determined and taken as the GC purity (area %). The peak derived from heptane as the reaction solvent was excluded from the calculation of the peak area ratio. The β form selectivity was calculated from the following formula. β form selectivity (%) = α form (area %) / [α form (area %) + β form (area %)]

[0046] [Examples 1 to 3] The entire reactor 1 was covered with aluminum foil to shield light. 30 mL of a mixed solution of styrene (8.14 g, 78.3 mmol) and n-heptane (14.4 g, 143.4 mmol) (176 parts by mass of n-heptane per 100 parts by mass of styrene) was placed in the reactor 1 as a reaction solution. The reaction system was purged with nitrogen gas for 10 minutes. While stirring the reaction solution at 600 rpm, ultraviolet light with a peak wavelength of 365 nm and an illuminance of 230 mW / cm 2 was irradiated at the electromagnetic wave irradiation position 14, which was 2 cm (Example 1), 10 cm (Example 2), or 40 cm (Example 3) away from the blowing port 15, and hydrogen bromide gas was supplied at a flow rate of 0.035 NL / min to start the reaction. The temperature of the reaction system was maintained at 40°C. After the start of the reaction, the reaction was terminated when hydrogen bromide gas was flowed for 60 minutes. GC measurement of the obtained reaction product was carried out to analyze the composition of the reaction product. The gas transfer time from the electromagnetic wave irradiation position to the blowing port, calculated from the distance between the electromagnetic wave irradiation position 14 and the blowing port 15, the flow rate of hydrogen bromide gas, and the internal cross-sectional area of the raw material gas supply pipe 2, was 9.34×10 -6 seconds in Example 1, 186×10 -6 seconds in Example 2, and 750×10 -6 seconds in Example 3.

[0047] [Comparative Example 1] The reaction was carried out under the same conditions as in Example 1 except that no ultraviolet light was irradiated. GC measurement of the obtained reaction product was carried out to analyze the composition of the reaction product.

[0048] The results of Examples 1 to 3 and Comparative Example 1 are shown in Table 1 below. In Fig. 2, the relationship between the distance (horizontal axis, cm) from the irradiation position of the electromagnetic wave to the blowing port, the GC purity (first vertical axis, area %), and the β-form selectivity (second vertical axis, %) is shown as a graph.

[0049] [Table 1]

[0050] In Examples 1 to 3, the formation of dimers was suppressed, and the β-form selectivity improved as the distance from the irradiation position to the blowing port decreased. In Comparative Example 1 where no ultraviolet light was irradiated, a large amount of the α-form was generated.

[0051] As described above, the embodiments of the present invention have been described, but the present invention is not limited thereto, and the devices, materials, various conditions, etc. used can be appropriately changed without departing from the spirit of the invention. [Explanation of Signs]

[0052] 1 Reactor 11 Cap 12 Waste gas outlet 13 Nitrogen gas supply port 14 Electromagnetic wave irradiation position 15 Blowing port 2 Raw material gas supply pipe 3 LED device WG Waste gas

Claims

1. A method for producing β-bromoethylbenzene, comprising irradiating hydrogen bromide gas with electromagnetic waves and bringing the hydrogen bromide gas irradiated with the electromagnetic waves into contact with styrene.

2. The method for producing β-bromoethylbenzene according to claim 1, wherein the peak wavelength of the electromagnetic waves is in the range of 250 nm or more and 600 nm or less.

3. The hydrogen bromide gas irradiated with the electromagnetic wave is brought into contact with styrene within 1×10 －３ seconds from the irradiation of the electromagnetic wave, according to the method of claim 1 or 2.

4. The method for producing β-bromoethylbenzene according to claim 1 or 2, wherein the light source of the electromagnetic waves is at least one selected from the group consisting of ultraviolet LEDs, visible light LEDs, organic ELs, inorganic ELs, mercury lamps, and mercury-free lamps.

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