A microwave-assisted method for the efficient reduction of nitroaromatic hydrocarbons by tetra(dimethylamino)diboron
By using microwave-assisted mixing of tetra(dimethylamino)diboron with alkaline substances under an inert atmosphere, the dehalogenation problem of tetra(dimethylamino)diboron in the reduction process of nitroaromatics was solved, realizing the preparation of aromatic amine compounds in a highly efficient and environmentally friendly manner, and reducing costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- FUZHOU UNIV
- Filing Date
- 2026-02-22
- Publication Date
- 2026-05-26
AI Technical Summary
In the existing technology, tetra(dimethylamino)diboron is limited in its application due to its sensitivity to water and oxygen, complex operation and high cost, and the fact that it is prone to dehalogenation reaction during the reduction of nitroaromatics under metal catalyst-free conditions.
Microwave-assisted tetra(dimethylamino)diboron is mixed with an alkaline substance under an inert atmosphere, and the reaction is carried out by microwave heating to achieve efficient reduction of nitroaromatics, avoiding the occurrence of dehalogenation reaction.
It achieves highly selective and rapid reduction of nitroaromatics, retains halogens, reduces costs, simplifies the operation process, increases yield, and uses environmentally friendly solvents, thus reducing environmental pollution.
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Figure CN122079786A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of chemical technology, specifically a microwave-assisted method for the efficient reduction of nitroaromatic hydrocarbons by tetra(dimethylamino)diboron. Background Technology
[0002] Aromatic amines are important intermediates in the synthesis of dyes, pharmaceuticals, agrochemicals, and synthetic polymers. The highly selective reduction of nitro groups to amino groups is an effective conversion method for preparing valuable amines. Therefore, developing new conversion methods for the reduction of nitro groups to amino groups is of great value.
[0003] In the past decade, diboron reagents, commonly used as boronizing agents, have been applied to clean processes for efficient nitro reduction. These diboron reagents offer new options for amine derivatives containing various reducible functional groups, thus avoiding the use of high-pressure hydrogen or metal reagents. Notably, several methods using diboron reagents have performed well under metal-free conditions in the presence of Lewis bases or in aqueous solutions. For example, the group led by Yangjie Wu at Zhengzhou University discovered a method for efficient reduction of isopropanol using bis(pinalol)diboron (B2pin2) and potassium tert-butoxide. The group led by Caiqin Qin at Hubei University of Technology developed a method for rapid reduction of bis(pinalol)diboron and sodium hydroxide in methanol / aqueous solution at 50°C, but in this method, debromination of halogenated nitroaromatics may occur during nitro reduction. The group led by Uozumi extended an efficient reduction method in which nitro reacts with diboronic acid in water at 80°C. Du et al. extended a DNA-compatible nitro reduction method using diboronic acid in NaOH aqueous solution, but dehalogenation inevitably occurred under the reaction conditions. Hosoya et al. reported a similar reduction reaction using bis(neopentylethylene glycol)diboron (B2nep2) under bipyridine organic catalysis. However, the reducing agent used in the above method is bis(pinacol)diboron, or diboronic acid, or bis(neopentylethylene glycol)diboron, which are all expensive per gram from an economic perspective, and the reaction time is long with the yield needing improvement. In addition, the synthesis techniques in related technologies are basically solution methods, which require the use of large amounts of non-environmentally friendly solvents, potentially causing environmental pollution, and require solvent recovery and treatment, resulting in high production costs.
[0004] Although reagents such as tetra(dimethylamino)diboron and bis(pinacol)diboron belong to the same diboron compound family, their chemical properties differ significantly. The former is sensitive to water and air and is typically operated under inert atmospheres and strictly anhydrous conditions; while the latter (B2pin2) is relatively stable in air and moisture, making it more convenient to use. This difference in stability leads to fundamentally different application scenarios and technical challenges for the two.
[0005] Tetra(dimethylamino)diboron B2(NMe2)4 is extremely sensitive to water and oxygen, has a high operational threshold, and is highly unstable in water and air, easily hydrolyzed and oxidized, requiring operation under strictly anhydrous and oxygen-free inert atmospheres (such as glove boxes or Schlenk techniques). In contrast, mainstream reagents such as B2pin2 are stable in air, can be weighed in open containers, and react in water / alcohol solvents. This convenience creates strong technological inertia and path dependence. In the chemical reagent market, B2(NMe2)4 is often perceived as an expensive precursor for the synthesis of stable reagents like B2pin2. Its price and sensitivity give it a preconceived notion of being "more delicate and less practical."
[0006] In existing literature, B2(NMe2)4 is mainly used as a "boration reagent" or "synthetic intermediate," and is explicitly excluded from the list of candidate reagents for nitro reduction because of its insufficient stability and unsuitability for conventional reduction processes. The above-mentioned technical bias, together with the dehalogenation problem, constitutes a long-term obstacle to achieving efficient and highly selective nitro reduction under metal-free conditions. Summary of the Invention
[0007] (a) Technical problems to be solved
[0008] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a microwave-assisted method for the efficient reduction of nitroaromatic hydrocarbons by tetra(dimethylamino)diboron, which can effectively avoid the dehalogenation reaction of halogen-containing substituents and solve the technical problem of high cost of diboron reducing reagent in the absence of metal catalyst.
[0009] (II) Technical Solution To achieve the above objectives, the main technical solutions adopted by this invention include:
[0010] In a first aspect, the present invention provides a microwave-assisted method for the efficient reduction of nitroaromatic hydrocarbons by tetra(dimethylamino)diboron, comprising the following steps: under an inert gas atmosphere, mixing nitroaromatic hydrocarbons, tetra(dimethylamino)diboron and an alkaline substance, and then heating the mixture with microwave until the reduction produces aromatic amine compounds.
[0011] This invention uses readily available nitroaromatic hydrocarbons as raw materials to achieve efficient one-pot reduction of aromatic amine compounds under microwave assistance. It solves the problems of high cost of diborone reducing reagent in the absence of metal catalysts in existing aromatic amine reduction methods. It can also effectively avoid dehalogenation reactions of halogen-containing substituents. It has the advantages of short reaction time, simple reaction process, high yield, high economic benefits, and safety (metal-free, hydrogen-free, one-pot method).
[0012] It is noteworthy that tetra(dimethylamino)diboron is extremely sensitive to water and oxygen, and its operational complexity and cost are generally considered obstacles to its application. Furthermore, its strongly electron-donating amine ligand may result in excessive nucleophilicity of the boron center. Based on this, those skilled in the art have reasonable grounds to expect that it may lead to more severe dehalogenation side reactions than B2pin2 when reducing halonitroaromatics. Existing technologies not only fail to provide insights into using this reagent to solve dehalogenation problems, but also offer a reverse lesson. This invention unexpectedly discovers that, in a specific synergistic system assisted by microwave and protected by an inert atmosphere, tetra(dimethylamino)diboron can selectively reduce only the nitro group while perfectly preserving the halogen, overcoming long-standing technical biases and cognitive barriers.
[0013] Therefore, this invention, through a combination of specific technical means (microwave + inert gas protection + alcohol / water solvent + short-time reaction), has for the first time realized the practical application of this reagent in the field of nitro reduction, and unexpectedly achieved technical effects that the technology for halogen retention could not achieve.
[0014] Optionally, the alkaline substance is an alkali metal hydroxide.
[0015] Furthermore, the alkaline substance is, but is not limited to, sodium hydroxide.
[0016] Optionally, the molar ratio of nitroaromatic hydrocarbon, tetra(dimethylamino)diboron and alkaline substance is 1:2~10:2~10.
[0017] Optionally, the microwave heating temperature is 90~110℃.
[0018] Optionally, the reaction time for microwave heating is 0.5 to 3.0 hours.
[0019] Optionally, the reaction is carried out in the presence of a solvent.
[0020] Optionally, the solvent is one of methanol, ethanol, and water, or a mixture of at least two of them.
[0021] Optionally, the amount of solvent added is 5 to 20 ml per millimole of nitroaromatic hydrocarbon.
[0022] Optionally, the inert gas is at least one of argon and nitrogen.
[0023] Optionally, the nitroaromatic hydrocarbon is a halonitroaromatic hydrocarbon, and the reaction yields the corresponding haloaromatic amine compound.
[0024] Optionally, the nitroaromatic hydrocarbon contains at least one of electron-withdrawing substituents and electron-donating substituents.
[0025] The electron-withdrawing substituents include, but are not limited to: halogens (such as fluorine, chlorine, bromine, iodine), trifluoromethyl (-CF3), cyano (-CN), ester (-COOR), aldehyde (-CHO), ketone (-COR), and nitro (-NO2). These substituents reduce the electron cloud density of the aromatic ring, but the method of this invention can still efficiently reduce the nitro group and exhibits excellent retention ability for sensitive groups such as halogens (as shown in Examples 2, 3, and 4 of this invention).
[0026] The electron-donating substituents include, but are not limited to: C1-C4 straight-chain or branched alkyl groups (such as methyl, ethyl, isopropyl, tert-butyl, as shown in Example 1), alkoxy groups (such as methoxy-OCH3, ethoxy-OC2H5), hydroxyl groups (-OH), and amino groups (-NH2). These substituents increase the electron cloud density of the aromatic ring, and the method of this invention can still achieve efficient reduction, demonstrating the good adaptability of this invention to electron-rich aromatic rings.
[0027] (III) Beneficial Effects
[0028] Compared with existing technologies, this invention provides a microwave-assisted method for the efficient reduction of nitroaromatics using tetra(dimethylamino)diboron. The use of tetra(dimethylamino)diboron effectively avoids dehalogenation reactions involving halogen-containing substituents because it is a mild and highly selective boron-based reducing agent. The strong electron-withdrawing property of the nitro group makes it a preferred reduction site, while simultaneously reducing the reactivity of the carbon containing the halogen atom. Rapid heating and directional energy transfer shorten the reaction time (suppressing slow-kinetic dehalogenation pathways), thus offering advantages such as short reaction time, simple reaction process, and high yield. Furthermore, the nitroaromatics used in this invention are common, readily available, and inexpensive, resulting in high economic benefits. Additionally, the solvents used in this invention are methanol, ethanol, and water, making it environmentally friendly and avoiding environmental pollution problems. Attached Figure Description
[0029] Figure 1 This is a synthetic route diagram for the reduction preparation of aromatic amine compounds according to the present invention;
[0030] Figure 2 The 1H NMR spectrum of 4-ethylaniline prepared by reduction in Example 1 of this invention;
[0031] Figure 3 The 1H NMR spectrum of 4-trifluoromethylaniline prepared by reduction in Example 2 of this invention;
[0032] Figure 4 The 1H NMR spectrum of 4-chloroaniline prepared by reduction in Example 3 of this invention;
[0033] Figure 5The 1H NMR spectrum of 2,4,6-tribromoaniline prepared by reduction in Example 4 of this invention is shown. Detailed Implementation
[0034] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below through specific embodiments.
[0035] To illustrate the possible application scenarios, technical principles, implementable specific solutions, and achievable objectives and effects of this application in detail, the following description is provided in conjunction with the specific embodiments listed. The embodiments described herein are merely illustrative of the technical solutions of this application and are therefore intended only as examples, not as limiting the scope of protection of this application.
[0036] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.
[0037] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.
[0038] In the description of this application, the term "and / or" is used to describe the logical relationship between objects, indicating that three relationships can exist. For example, A and / or B means: A exists, B exists, and A and B exist simultaneously. Additionally, the character " / " in this document generally indicates that the preceding and following objects have an "or" logical relationship.
[0039] In this application, terms such as “first” and “second” are used only to distinguish one entity or operation from another, and do not necessarily require or imply any actual quantity, hierarchy or order relationship between these entities or operations.
[0040] Unless otherwise specified, the use of terms such as “comprising,” “including,” “having,” or other similar expressions in this application is intended to cover non-exclusive inclusion, which does not exclude the presence of additional elements in a process, method, or product that includes the stated elements, such that a process, method, or product that includes a list of elements may include not only those defined elements but also other elements not expressly listed, or elements inherent to such a process, method, or product.
[0041] As understood in the Examination Guidelines, in this application, expressions such as "greater than," "less than," and "exceeding" are understood to exclude the stated number; expressions such as "above," "below," and "within" are understood to include the stated number. Furthermore, in the description of the embodiments in this application, "multiple" means two or more (including two), and similar expressions related to "multiple" are also understood in this way, such as "multiple groups" and "multiple times," unless otherwise explicitly specified.
[0042] In the description of the embodiments of this application, the space-related expressions used, such as "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "vertical," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," indicate the orientation or positional relationship based on the orientation or positional relationship shown in the specific embodiments or drawings. They are only for the purpose of describing the specific embodiments of this application or for the reader's understanding, and do not indicate or imply that the device or component referred to must have a specific position, a specific orientation, or be constructed or operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.
[0043] Unless otherwise expressly specified or limited, the terms "installation," "connection," "linking," "fixing," and "setting," as used in the description of the embodiments of this application, should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral setting; it can be a mechanical connection, an electrical connection, or a communication connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two components or the interaction between two components. For those skilled in the art to which this application pertains, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.
[0044] Example 1
[0045] like Figure 1 ( Figure 1The compound 1 shown is 4-ethylaniline obtained in this embodiment. This embodiment provides a method for preparing 4-ethylaniline (compound 1) by reduction, the steps of which are as follows:
[0046] In a 50 mL Schlenk reaction tube equipped with a magnetic stirrer, 2.0 mmol of 4-ethylnitrobenzene, 5.0 mmol of tetra(dimethylamino)diboron, and 4.0 mmol of solid sodium hydroxide were added, and the inert gas was purged three times. Then, 10 mL of ethanol and 10 mL of deionized water were added sequentially to the reaction system. The reaction was heated to 100 °C for 1 hour under microwave assistance.
[0047] After natural cooling, some ethanol was removed by rotary evaporation. The reaction mixture was then extracted with ethyl acetate (2 × 20 mL). The ethyl acetate liquid mixture was dried over anhydrous sodium sulfate and then filtered through a Buchner funnel to remove the solids. The filtrate was collected, and the solvent was removed under reduced pressure to obtain the corresponding crude reduced amine product. The crude product was then purified by rapid silica gel column chromatography using an ethyl acetate / petroleum ether eluent mixture (v / v = 1:20) to finally obtain the corresponding high-purity product (218 mg, 90% yield).
[0048] The high-purity product obtained in this embodiment was subjected to nuclear magnetic resonance (NMR) testing, and the results are as follows: Figure 2 As shown.
[0049] The 1H NMR spectrum is 1 H NMR (400 MHz, CDCl3) δ6.83-6.69 (m, 2H), 6.68-6.53 (m, 2H), 3.95 (q, J = 7.0 Hz, 2H), 3.48 (s, 2H), 1.38 (t, J = 7.0 Hz, 3H). 13 C NMR (100MHz, CDCl3) δ 151.40, 140.02, 115.96, 115.23, 63.58, 14.60.
[0050] Mass spectrometry (EI-MS) for C8H 11 N; m / z: 121.1 (M + , 100.0%).
[0051] This example demonstrates that 4-ethylaniline was obtained.
[0052] Example 2
[0053] like Figure 1 ( Figure 1Compound 2 shown is 4-trifluoromethylaniline obtained in this embodiment. This embodiment provides a method for the reduction preparation of 4-trifluoromethylaniline (compound 2) as follows:
[0054] In a 50 mL Schlenk reaction tube equipped with a magnetic stirrer, 2.0 mmol of 4-nitrotrifluorotoluene, 5.0 mmol of tetrakis(dimethylamino)diboron, and 4.0 mmol of solid sodium hydroxide were added, and the inert gas was purged three times. 10 mL of ethanol and 10 mL of deionized water were then added sequentially to the reaction system. The reaction was heated to 100 °C for 1 hour under microwave assistance. After natural cooling, some ethanol was removed by rotary evaporation. The reaction system was then extracted with ethyl acetate (2 × 20 mL). The ethyl acetate liquid mixture was dried over anhydrous sodium sulfate and then filtered through a Buchner funnel to remove the solids. The filtrate was collected, and the solvent was removed under reduced pressure to obtain the corresponding crude reduced amine product. The crude product was then purified by rapid silica gel column chromatography using an ethyl acetate / petroleum ether eluent mixture (v / v = 1:20) to obtain the corresponding high-purity product (300 mg, yield 93%).
[0055] The high-purity product obtained in this embodiment was subjected to nuclear magnetic resonance (NMR) testing, and the results are as follows: Figure 3 As shown.
[0056] 1H NMR spectrum 1 H NMR (400 MHz, CDCl3) δ7.47 (d, J = 8.3 Hz, 2H), 6.68 (d, J =8.4 Hz, 2H), 3.98 (s, 2H). 13 C NMR (100 MHz, CDCl3)δ149.91, 149.90, 129.33,126.72, 126.69, 126.65, 126.61, 123.96, 121.27, 120.11, 119.79, 119.47,119.15, 114.51, 114.23, 113.90. 19 F NMR (376 MHz, CDCl3) delta-61.3.
[0057] Mass spectrometry (EI-MS) was performed on C7H6F3N; m / z: 161.0 (M+, 100.0%).
[0058] This embodiment demonstrates that 4-trifluoromethylaniline was obtained.
[0059] Example 3
[0060] like Figure 1 ( Figure 1Compound 3 shown is 4-chloroaniline obtained in this embodiment. This embodiment also provides a method for the reduction preparation of 4-chloroaniline (compound 3):
[0061] In a 50 mL Schlenk reaction tube equipped with a magnetic stirrer, 2.0 mmol of 4-chloronitrobenzene, 5.0 mmol of tetrakis(dimethylamino)diboron, and 4.0 mmol of solid sodium hydroxide were added, and the inert gas was purged three times. 10 mL of ethanol and 10 mL of deionized water were then added sequentially to the reaction system. The reaction was heated to 100 °C for 1 hour under microwave assistance. After natural cooling, some ethanol was removed by rotary evaporation. The reaction system was then extracted with ethyl acetate (2 × 20 mL). The ethyl acetate liquid mixture was dried over anhydrous sodium sulfate and then filtered through a Buchner funnel to remove the solids. The filtrate was collected, and the solvent was removed under reduced pressure to obtain the corresponding crude reduced amine product. The crude product was then purified by rapid silica gel column chromatography using an ethyl acetate / petroleum ether eluent mixture (v / v = 1:20) to obtain the corresponding high-purity product (235 mg, yield 92%).
[0062] The high-purity product obtained in this embodiment was subjected to nuclear magnetic resonance (NMR) testing, and the results are as follows: Figure 4 As shown.
[0063] 1H NMR spectrum 1 H NMR (400 MHz, CDCl3) δ7.15-7.07 (m, 2H), 6.63-6.54 (m, 2H), 3.65 (s, 2H). 13 C NMR (100 MHz, CDCl3) δ145.11, 128.99, 122.71, 116.20.
[0064] Mass spectrometry (EI-MS) results were obtained for C6H6ClN; m / z: 127.0 (M+, 100.0%).
[0065] This example demonstrates that 4-chloroaniline was obtained.
[0066] Example 4
[0067] like Figure 1 ( Figure 1 Compound 3 shown is 2,4,6-tribromoaniline obtained in this embodiment. This embodiment provides a method for the reduction preparation of 2,4,6-tribromoaniline (compound 4) as follows:
[0068] In a 50 mL Schlenk reaction tube equipped with a magnetic stirrer, 2,4,6-tribromonitrobenzene (2.0 mmol), tetrakis(dimethylamino)diboron (5.0 mmol), and solid sodium hydroxide (4.0 mmol) were added, and the inert gas was purged three times. 10 mL of ethanol and 10 mL of deionized water were then added sequentially to the reaction system. The reaction was heated to 100 °C for 1 hour under microwave assistance. After natural cooling, some ethanol was removed by rotary evaporation. The reaction system was then extracted with ethyl acetate (2 × 20 mL). The ethyl acetate liquid mixture was dried over anhydrous sodium sulfate and then filtered through a Buchner funnel to remove the solids. The filtrate was collected, and the solvent was removed under reduced pressure to obtain the corresponding crude reduced amine product. The crude product was then purified by rapid silica gel column chromatography using an ethyl acetate / petroleum ether eluent mixture (v / v = 1:20) to obtain the corresponding high-purity product (587 mg, yield 89%).
[0069] The high-purity product obtained in this embodiment was subjected to nuclear magnetic resonance (NMR) testing, and the results are as follows: Figure 5 As shown.
[0070] 1H NMR spectrum 1 H NMR (400 MHz, CDCl3) δ7.50 (s, 1H), 4.56 (s, 1H). 13 C NMR (100MHz, CDCl3) δ141.50, 133.97, 108.99.
[0071] Mass spectrometry (EI-MS) results were obtained for C6H4Br3N; m / z: 328.8 (M+, 100.0%).
[0072] This example demonstrates that 2,4,6-tribromoaniline was obtained.
[0073] The yield calculation formulas in Examples 1-4 of this invention are as follows:
[0074] Yield (%) = [(Actual mass of high-purity product obtained (mg) / Theoretical yield (mg)] × 100%;
[0075] Wherein, theoretical yield (mg) = amount of substance of nitroaromatic feedstock (mmol) × molar mass of target aromatic amine product (g / mol).
[0076] Comparative Example 1
[0077] The method provided in Comparative Example 1 is the same as that in Example 3, except that the tetrakis(dimethylamino)diboron in Example 3 is replaced with the same molar amount of B2pin2.
[0078] The results showed that the yield of 4-chloroaniline was significantly lower than that of Example 3, and a large amount of the dechlorination byproduct aniline was detected.
[0079] In Examples 1, 2, and 4, the yields of the products decreased significantly when tetrakis(dimethylamino)diboron was replaced with the same molar amount of B2pin2, and a large amount of the dehalogenation byproduct aniline was detected in Examples 2 and 4.
[0080] Example 5
[0081] This embodiment provides a method for preparing 4-aminobenzonitrile by reducing cyanonitroaromatic hydrocarbons, the steps of which are the same as in Example 4.
[0082] The difference is that 2,4,6-tribromonitrobenzene is replaced with the same molar amount of 4-cyanonitrobenzene to obtain 4-aminobenzonitrile.
[0083] The high-purity product obtained in this embodiment was subjected to nuclear magnetic resonance testing to obtain 4-aminobenzonitrile, confirming that the cyano group was not reduced.
[0084] Examples 6-8
[0085] The methods for preparing aromatic amine compounds provided in Examples 6-8 are the same as those in Example 1, except that the amounts of 4-ethylnitrobenzene (2.0 mmol), tetrakis(dimethylamino)diboron (5.0 mmol), and solid sodium hydroxide (4.0 mmol) added, as well as the microwave heating temperature and time, are different, as shown in Table 1.
[0086] Table 1
[0087] Example Amount of 4-ethylnitrobenzene added (mmol) Amount of tetra(dimethylamino)diboron added (mmol) Amount of solid sodium hydroxide added (mmol) Microwave heating temperature ℃ Microwave heating reaction time (hours) Example 6 2 4 4 90℃ 2.0 Example 7 2 20 10 100℃ 0.5 Example 8 2 9 20 95℃ 3.0
[0088] The 4-ethylaniline prepared in Examples 6-8 had a lower yield than that in Example 1, but a significantly higher yield than the products prepared in each corresponding comparative example.
[0089] The corresponding comparative example refers to the fact that tetra(dimethylamino)diboron was replaced with the same molar amount of B2pin2 in the corresponding embodiment.
[0090] In summary, this invention unexpectedly reveals that, under the specific synergistic effect of microwave and inert gas protection, B2(NMe2)4 not only achieves successful reduction but also perfectly preserves the halogen. Under the same operating conditions, B2pin2 still undergoes severe dehalogenation, resulting in a significantly reduced yield. This demonstrates that the effect of this invention is not simply a conventional optimization of "microwave + diboron + alkali," but rather the result of the synergistic effect of the specific reducing agent B2(NMe2)4 and the reaction conditions, and this result overturns reasonable expectations in the field.
[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A microwave-assisted method for the efficient reduction of nitroaromatic hydrocarbons by tetrakis(dimethylamino)diboron, characterized in that, It includes the following steps: Under an inert gas atmosphere, nitroaromatic hydrocarbons, tetra(dimethylamino)diboron and alkaline substances are mixed and microwave-heated until they are reduced to aromatic amine compounds.
2. The microwave-assisted method for the efficient reduction of nitroaromatic hydrocarbons by tetrakis(dimethylamino)diboron as described in claim 1, characterized in that: The molar ratio of nitroaromatic hydrocarbons, tetra(dimethylamino)diboron and alkaline substances is 1:2~10:2~10.
3. The microwave-assisted method for the efficient reduction of nitroaromatic hydrocarbons by tetrakis(dimethylamino)diboron as described in claim 1, characterized in that: The microwave heating temperature is 90~110℃.
4. The microwave-assisted method for the efficient reduction of nitroaromatic hydrocarbons by tetrakis(dimethylamino)diboron as described in claim 1, characterized in that: The reaction time for microwave heating is 0.5 to 3.0 hours.
5. The microwave-assisted method for the efficient reduction of nitroaromatic hydrocarbons by tetrakis(dimethylamino)diboron as described in claim 1, characterized in that: The reaction is carried out in the presence of a solvent.
6. The microwave-assisted method for the efficient reduction of nitroaromatic hydrocarbons by tetrakis(dimethylamino)diboron as described in claim 5, characterized in that: The solvent is one of methanol, ethanol, and water, or a mixture of at least two of them.
7. The microwave-assisted method for the efficient reduction of nitroaromatic hydrocarbons by tetrakis(dimethylamino)diboron as described in claim 6, characterized in that: The solvent is added in an amount of 5 to 20 ml per millimole of nitroaromatic hydrocarbon.
8. The microwave-assisted method for the efficient reduction of nitroaromatic hydrocarbons by tetrakis(dimethylamino)diboron as described in claim 1, characterized in that: The inert gas is at least one of argon and nitrogen.
9. The microwave-assisted method for the efficient reduction of nitroaromatic hydrocarbons by tetrakis(dimethylamino)diboron as described in claim 1, characterized in that: The nitroaromatic hydrocarbon is a halonitroaromatic hydrocarbon, and the reaction yields the corresponding haloaromatic amine compound.
10. The microwave-assisted method for the efficient reduction of nitroaromatic hydrocarbons by tetrakis(dimethylamino)diboron as described in claim 1, characterized in that, The nitroaromatic hydrocarbon contains at least one of electron-withdrawing substituents and electron-donating substituents.