Method for preparating synthetic precursors for polybrominated biphenyls

Abstract

Disclosed in the present invention is a method for preparing synthetic precursors for polybrominated biphenyls, which method comprises the following steps: step 1, using 3,5-dibromoaniline as a raw material, reacting same with N-bromosuccinimide in an organic solvent, and purifying the reaction product, so as to obtain 2,3,4,5-tetrabromoaniline and 2,3,4,5,6-pentabromoaniline; and step 2, separately subjecting the 2,3,4,5-tetrabromoaniline and the 2,3,4,5,6-pentabromoaniline prepared in step 1 to a diazotization reaction by means of an aqueous sulfuric acid solution and an aqueous sodium nitrite solution to obtain diazonium salts, and reducing the diazonium salts by means of an aqueous hypophosphorous acid solution, so as to obtain corresponding tetrabromobenzene or pentabromobenzene. In the present invention, commercially available N-bromosuccinimide (NBS) is used as a bromine source, and the raw material can be completely converted, by means of a one-step reaction, into 2,3,4,5-tetrabromoaniline and 2,3,4,5,6-pentabromoaniline, which can be used as synthetic precursors for polybrominated biphenyls; therefore, the cost of synthesis is lower, and good economical efficiency and application value are obtained. Moreover, the present invention is simple in terms of synthesis steps, the products are easy to separate and purify, and the chemical purity of the obtained products reaches 99% or higher.

Description

Preparation method of a synthesis precursor of polybrominated biphenyl compounds TECHNICAL FIELD

[0001] The present application relates to the technical field of polybrominated biphenyl compound synthesis, and particularly relates to a preparation method of a synthesis precursor of polybrominated biphenyl compounds. BACKGROUND

[0002] Polybrominated biphenyls (PBBs) belong to brominated flame retardants (BFRs), which are widely used industrial chemicals and are widely used in printed circuit boards, plastics, coatings, wire and cable, and resin electronic components. As important synthesis precursors of polybrominated biphenyls, polybrominated benzene and polybrominated aniline compounds are synthesized by using bromine as a halogenating reagent in the existing synthesis method (J. Agric. Food Chem. 1989, 37, 1160-1164.). Since it is difficult to accurately control the stoichiometry of bromine in chemical reactions, side reactions are easily induced, resulting in a decrease in yield. In the synthesis of this series of compounds, there are problems such as difficulty in controlling the reaction site and low utilization rate of raw materials. Moreover, bromine is a dangerous chemical for making drugs, and its sale has been stopped on the market.

[0003] Therefore, it is of great value to develop an efficient and green preparation method of polybrominated benzene and polybrominated aniline compounds for the synthesis and research of polybrominated biphenyl compounds.

[0004] SUMMARY

[0005] The present application aims at the deficiencies in the prior art and provides a preparation method of a synthesis precursor of polybrominated biphenyl compounds.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] The present application provides a preparation method of a synthesis precursor of polybrominated biphenyl compounds, which comprises the following steps:

[0008] Step one: 3,5-dibromoaniline is used as a raw material and reacts with N-bromosuccinimide in an organic solvent to obtain 2,3,4,5-tetrabromoaniline and 2,3,4,5,6-pentabromoaniline after purification;

[0009] Step two: 2,3,4,5-tetrabromoaniline and 2,3,4,5,6-pentabromoaniline prepared in step one are respectively subjected to diazotization reaction by sulfuric acid aqueous solution and sodium nitrite aqueous solution to obtain diazonium salt, and then the diazonium salt is reduced by hydrosulfurous acid aqueous solution to obtain the corresponding tetrabromobenzene or pentabromobenzene.

[0010] Further, in the step one, the molar ratio of 3,5-dibromoaniline to N-bromosuccinimide is 1:(1.5-3), the reaction temperature is 0℃-60℃, and the reaction time is 2-5 hours.

[0011] Further, in the step one, the solvent is selected from benzene, carbon tetrachloride or acetonitrile; preferably acetonitrile.

[0012] Further, in the step two,

[0013] The molecular structure of tetrabromobenzene is:

[0014] The molecular structure of pentabromobenzene is:

[0015] Further, in the step two, the temperature of diazotization reaction is 0℃-25℃, and the reaction time is 2-5 hours.

[0016] Further, in the step two, the concentration of aqueous sulfuric acid used for diazotization is 50-60wt%; the concentration of aqueous sodium nitrite used for diazotization is 10-20wt%.

[0017] Further, in the step two, the temperature of reduction reaction of diazonium salt is 15℃-25℃, and the reaction time is 12-24 hours.

[0018] Further, in the step two, the concentration of aqueous hypophosphorous acid used for reduction reaction of diazonium salt is 50-60wt%.

[0019] Further, in the step one, purification is carried out by column chromatography separation or recrystallization.

[0020] The present application adopts the above technical scheme, and has the following technical effects compared with the prior art:

[0021] In the prior art, the synthesis method of 2,3,4,5-tetrabromoaniline and 2,3,4,5,6-pentabromoaniline compounds uses bromine as a halogenating reagent, however, this method has problems of difficult control of reaction site and low utilization rate of raw materials when synthesizing the series of compounds, which easily causes side reactions to reduce the yield, and bromine is a dangerous chemical for making drugs, which has been stopped selling on the market.

[0022] The present application uses commercially available N-bromosuccinimide (NBS) as a bromine source, which can convert the raw material into 2,3,4,5-tetrabromoaniline and 2,3,4,5,6-pentabromoaniline through one-step reaction, which can be used as a synthesis precursor of polybrominated biphenyl series compounds, so that the cost of synthesis is lower, which has good economic efficiency and application value; and the synthesis steps of the present application are simple, the product is easy to separate and purify, and the chemical purity of the obtained product reaches more than 99%. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a nuclear magnetic resonance hydrogen spectrum of the 2,2',3,3',4,4',5,5',6- nonabromodiphenyl (PBB206) compound obtained in Example 1 of the present application.

[0024] Figure 2 is a gas chromatography purity spectrum of the 2,2',3,3',4,4',5,5',6- nonabromodiphenyl (PBB206) compound obtained in Example 1 of the present application.

[0025] Figure 3 is a nuclear magnetic resonance hydrogen spectrum of the 2,3,3',4,4',5,5',6- octabromodiphenyl (PBB201) compound obtained in Example 2 of the present application.

[0026] Figure 4 is a gas chromatography purity spectrum of the 2,3,3',4,4',5,5',6- octabromodiphenyl (PBB201) compound obtained in Example 2 of the present application.

[0027] Figure 5 is a synthetic route of 2,2',3,3',4,4',5,5',6-nonabromodiphenyl (PBB206) in Example 1. DETAILED DESCRIPTION

[0028] The present application will be further described with reference to the drawings and specific examples, but not as a limitation. It should be noted that the examples in the present application and the features in the examples can be combined with each other without conflict.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. If there is a conflict between the description, definitions and terms, the description shall prevail.

[0030] The term "polybromodiphenyl" represents a compound having the following general structure:

[0031] In the formula, each m is independently an integer between 0 and 5, and each n is independently an integer between 4 and 5.

[0032] The reaction principle for preparing polybromobenzene used in the present application is known (for example, see: J. Agric. Food Chem. 1989, 37, 1160-1164.).

[0033] The reaction principle for coupling aniline and polybromobenzene used in the present application is known (for example, see: J. Agric. Food Chem. 1984, 32, 1107-1111.).

[0034] The synthesis method of 2,3,4,5-tetrabromoaniline and 2,3,4,5,6-pentabromoaniline compounds in the prior art uses bromine as a halogenating reagent, however, the method has problems of difficult control of reaction sites and low utilization rate of raw materials when synthesizing the series of compounds, which can easily cause side reactions to reduce the yield, and bromine is a dangerous chemical for drug making, and the market has stopped selling it.

[0035] The application provides a preparation method of a synthesis precursor of a polybromophenyl compound, comprising the following steps:

[0036] Step one, using 3,5-dibromoaniline as a raw material, reacting with N-bromosuccinimide (NBS) in acetonitrile to obtain compounds 2,3,4,5-tetrabromoaniline and 2,3,4,5,6-pentabromoaniline;

[0037] The molecular structure of 2,3,4,5-tetrabromoaniline is as follows:

[0038] The molecular structure of 2,3,4,5,6-pentabromoaniline is as follows:

[0039] Step two, the aniline compound prepared in step one is first subjected to a diazotization reaction by using a sulfuric acid aqueous solution and a sodium nitrite aqueous solution to obtain a diazonium salt, and then the diazonium salt is reduced by using a hypophosphorous acid aqueous solution to obtain the corresponding tetrabromobenzene or pentabromobenzene compound;

[0040] The molecular structure of tetrabromobenzene is as follows:

[0041] The molecular structure of pentabromobenzene is as follows:

[0042] The synthesis method of polybromophenyl compounds (prior art) comprises the following steps: coupling the polybromophenylamine compound and the polybromobenzene compound by using nitrous acid n-pentyl ester to obtain the corresponding polybromophenyl compound.

[0043] The polybromophenyl compound has the following general structure:

[0044] In the formula, each of m is independently an integer between 0 and 5, and each of n is independently an integer between 4 and 5.

[0045] Each raw material used in the following examples of the application is commercially available or can be self-made according to known technology, and the purity of each raw material is industrial grade.

[0046] Example 1 Synthesis of 2,2',3,3',4,4',5,5',6-nona bromophenyl (PBB206)

[0047] The molecular structure of 2,2',3,3',4,4',5,5',6-nona- bromobiphenyl (PBB206) is as follows:

[0048] The synthetic route of 2,2',3,3',4,4',5,5',6-nona- bromobiphenyl (PBB206) is as follows:

[0049] The specific synthesis steps are as follows:

[0050] Step one, 3,5-dibromoaniline (2.0 g, 8.0 mmol) was dissolved in 20 mL acetonitrile and heated to 60 °C, and N-bromosuccinimide (3.5 g, 20.0 mmol) in acetonitrile (20 mL) was added dropwise to the acetonitrile solution of 3,5-dibromoaniline, after the dropwise addition was completed, heating and stirring was continued for 4 h, and the reaction progress was monitored by TLC (V n-hexane:V ethyl acetate = 10:1). The reaction equation is as follows:

[0051] After the reaction was completed, the reaction device was cooled to room temperature, and the solvent was rotary evaporated. The mixture was purified by column chromatography (V n-hexane:V ethyl acetate = 20:1) to obtain the product 2,3,4,5-tetrabromoaniline 2.24 g (light yellow solid, 5.6 mmol, yield: 70%) and the product 2,3,4,5,6-pentabromoaniline 1.1 g (white solid, 2.2 mmol, yield: 27%).

[0052] Step two, 2.1 g (5.0 mol) of compound 2,3,4,5-tetrabromoaniline was suspended in 20 mL of cooled 50 wt% aqueous sulfuric acid solution, stirred rapidly and 5.0 mL of aqueous sodium nitrite solution (10 wt%) was added dropwise, and the resulting solution was stirred for 2 hours, then 5.0 mL of 50 wt% aqueous hypophosphorous acid solution was slowly added, and the reaction was stirred overnight. The reaction equation is as follows:

[0053] After the reaction was completed, the reaction liquid was filtered to obtain a yellow mixture. The mixture was purified by column chromatography (n-hexane) to obtain white solid compound 1,2,3,4-tetrabromobenzene 1.8 g (4.5 mmol, yield: 90%).

[0054] Step three, 2,3,4,5,6-pentabromoaniline (1.0 g, 2.1 mmol) prepared in step one was mixed with 1,2,3,4-tetrabromobenzene (1.8 g, 4.5 mmol) prepared in step two, heated to 150 °C, and after the reaction was completely melted, n-pentyl nitrite (0.6 g, 5.0 mmol) was added dropwise within 0.5 h, and stirring was continued for 1.5 h. The reaction progress was monitored by TLC (n-hexane). The reaction equation is as follows:

[0055] After the reaction was completed, the product 2,2',3,3',4,4',5,5',6-nona bromodiphenyl 0.9 g was obtained by column chromatography purification (eluent: n-hexane), yield: 48%.

[0056] The product obtained in this example was detected by Bruke-400M nuclear magnetic resonance instrument to obtain the nuclear magnetic resonance hydrogen spectrum shown in Figure 1, which can be seen that the nuclear magnetic hydrogen spectrum data of the compound 2,2',3,3',4,4',5,5',6-nona bromodiphenyl is 1 H NMR (CDCl3, 400MHz, ppm) δ 7.92 (s, 1H), which is consistent with the reported literature.

[0057] At the same time, the product sample obtained in this example was detected by gas chromatography-mass spectrometry (GC-MS), and the mass spectrum data showed GC-MS m / z 864.2 [M + ] which is consistent with the molecular weight (M=785.4) of the PBB 206 compound.

[0058] The product sample obtained in this example was measured by gas chromatography (GC) with dichloromethane as the solvent according to the following conditions:

[0059] Chromatographic column: CD-1HT, 30m*0.25mm*0.1um

[0060] Column temperature: programmed temperature, initial temperature 50℃, temperature rising to 370℃ at 20℃ / min and keeping for 20min

[0061] Detector: FID detector.

[0062] The measured GC spectrum is shown in Figure 2, which can be seen that the purity of the sample reaches more than 99%, which can be used as a high-purity RM level standard product.

[0063] Example 2 Synthesis of 2,3,3',4,4',5,5',6-octabromodiphenyl (PBB201)

[0064] The molecular structure of 2,3,3',4,4',5,5',6-octabromodiphenyl (PBB201) is as follows:

[0065] The specific synthesis steps are as follows:

[0066] Step one, dissolve 3,5-dibromoaniline (2.0 g, 8.0 mmol) in 20 mL acetonitrile and heat to 60℃, add N-bromosuccinimide (2.8 g, 16.0 mmol) in acetonitrile (20 mL) dropwise to the acetonitrile solution of 3,5-dibromoaniline, continue to heat and stir for 4 h after the dropwise addition is completed, monitor the reaction progress by TLC (V n-hexane:V ethyl acetate = 10:1). The reaction formula is as follows:

[0067] After the reaction is completed, the reaction device is cooled to room temperature, and the solvent is rotary evaporated. The mixture is purified by column chromatography (V n-hexane:V ethyl acetate = 20:1) to obtain the product 2,3,4,5-tetrabromoaniline 2.8 g (light yellow solid, 5.6 mmol, yield: 90%).

[0068] Step two, mix 2,3,4,5-tetrabromoaniline (2.0 g, 5.0 mmol) obtained in step one with commercially available 1,2,4,5-tetrabromobenzene (10.0 g, 25.0 mmol) and heat to 200℃, after the reaction is completely melted, add n-pentyl nitrite (1.2 g, 10.0 mmol) dropwise within 0.5 h, continue to stir for 1.5 h. Monitor the reaction progress by TLC (n-hexane). The reaction formula is as follows:

[0069] After the reaction is completed, the product 2,3,3',4,4',5,5',6-octabromobiphenyl 2.2 g is obtained by purification by column chromatography (eluent: n-hexane), with a yield of 45%.

[0070] The product obtained in this example is detected by Bruke-400M nuclear magnetic resonance instrument with CDCl3 as the solvent, and the nuclear magnetic resonance hydrogen spectrum diagram shown in FIG. 3 is obtained. It can be seen that the nuclear magnetic hydrogen spectrum data of the compound 2,3,3',4,4',5,5',6-octabromobiphenyl is 1 H NMR (CDCl3, 400MHz, ppm) δ 8.00 (s, 1H), 7.38 (s, 1H), which is consistent with the reported literature.

[0071] At the same time, the product sample obtained in this example is detected by gas chromatography-mass spectrometry (GC-MS), and the mass spectrum data shows that the GC-MS m / z 785.5 [M + ] is consistent with the molecular weight (M = 785.4) of the PBB 201 compound.

[0072] The product sample obtained in this example is measured by gas chromatography (GC) with dichloromethane as the solvent in the same way as in Example 1, and the GC spectrum diagram obtained is shown in FIG. 4. It can be seen that the purity of the sample reaches more than 99%, which can be used as a high-purity RM level standard product.

[0073] Synthesis of 2,2',3,3',4,4',5,5',6-nonaBromobiphenyl (PBB206)

[0074] The specific synthesis steps are as follows:

[0075] Step one, 3,5-dibromoaniline (2.0 g, 8.0 mmol) was dissolved in 20 mL acetonitrile and heated to 40 °C, N-bromosuccinimide (3.5 g, 20.0 mmol) in acetonitrile (20 mL) was added dropwise to the acetonitrile solution of 3,5-dibromoaniline, after the dropwise addition was completed, heating and stirring was continued for 5 h, TLC was used to monitor the progress of the reaction (V n-hexane:V ethyl acetate = 10:1). The reaction equation is as follows:

[0076] After the reaction was completed, the reaction device was lowered to room temperature, and the solvent was rotary evaporated. The mixture was purified using column chromatography (V n-hexane:V ethyl acetate = 20:1) to obtain the product 2,3,4,5-tetrabromoaniline 2.1 g (yellow solid, 5.1 mmol, yield: 64%) and the product 2,3,4,5,6-pentabromoaniline 0.9 g (white solid, 1.9 mmol, yield: 24%).

[0077] Step two, 2.1 g (5.0 mol) of compound 2,3,4,5-tetrabromoaniline was suspended in 20 mL of cooled 60 wt% aqueous sulfuric acid solution, stirred rapidly and 5.0 mL of aqueous sodium nitrite solution (20 wt%) was added dropwise, the resulting solution was stirred for 2 hours, then 5.0 mL of 60 wt% aqueous hypophosphorous acid solution was slowly added, and the solution was stirred overnight. The reaction equation is as follows:

[0078] After the reaction was completed, the reaction solution was filtered to obtain a yellow mixture. The mixture was purified using column chromatography (n-hexane) to obtain white solid compound 1,2,3,4-tetrabromobenzene 1.6 g (4.1 mmol, yield: 82%).

[0079] Step three, 2,3,4,5,6-pentabromoaniline (0.9 g, 1.9 mmol) prepared in step one was mixed with 1,2,3,4-tetrabromobenzene (1.6 g, 4.5 mmol) prepared in step two, heated to 150 °C, and after the reaction was completely melted, n-pentyl nitrite (0.6 g, 4.5 mmol) was added dropwise within 0.5 h, and stirring was continued for 1.5 h. TLC was used to monitor the progress of the reaction (n-hexane). The reaction equation is as follows:

[0080] After the reaction was completed, the product 2,2',3,3',4,4',5,5',6-nonaBromobiphenyl was obtained by column chromatography purification (eluent: n-hexane), yield: 43%.

[0081] The above description is merely that of the preferred embodiments of the application, and is not intended to limit its application and protection scope. It should be noted by those skilled in the art that any equivalent replacements and obvious changes made according to the content of the description and drawings of the application should be included in the protection scope of the application.

Claims

1. A method for producing a synthetic precursor of a polybrominated diphenyl compound, characterized by, The method comprises the following steps: Step one, 3, 5-dibromoaniline is used as raw material to react with N-bromosuccinimide in an organic solvent, and 2, 3, 4, 5-tetrabromoaniline and 2, 3, 4, 5, 6-pentabromoaniline are obtained after purification; Step two, 2, 3, 4, 5-tetrabromoaniline and 2, 3, 4, 5, 6-pentabromoaniline prepared in step one are respectively subjected to diazotization reaction by using sulfuric acid aqueous solution and sodium nitrite aqueous solution to obtain diazonium salt, and then the diazonium salt is reduced by using hypophosphorous acid aqueous solution to obtain corresponding tetrabromobenzene or pentabromobenzene.

2. The production method according to claim 1, characterized by, In the step one, the molar ratio of 3, 5-dibromoaniline to N-bromosuccinimide is 1: (1.5-3), the reaction temperature is 0-60℃, and the reaction time is 2-5 hours.

3. The preparation method according to claim 1, characterized in that, In the step one, the solvent is selected from benzene, carbon tetrachloride or acetonitrile.

4. The production method according to claim 1, characterized by, In the step two, The molecular structure of tetrabromobenzene is: The molecular structure of pentabromobenzene is:

5. The preparation method according to claim 1, characterized in that, In the step two, the diazotization reaction temperature is 0-25℃, and the reaction time is 2-5 hours.

6. The method of claim 1, wherein, In the step two, the concentration of the sulfuric acid aqueous solution used for diazotization is 50-60wt%; the concentration of the sodium nitrite aqueous solution used for diazotization is 10-20wt%.

7. The preparation method according to claim 1, characterized in that, In the step two, the reduction reaction temperature of the diazonium salt is 15-25℃, and the reaction time is 12-24 hours.

8. The method of claim 1, wherein, In the step two, the concentration of the hypophosphorous acid aqueous solution used for the reduction reaction of the diazonium salt is 50-60wt%.

9. The method of claim 1, wherein, In the step one, the purification is performed by column chromatography separation or recrystallization.

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