Method for selective oxidation of aniline

Abstract

The invention provides an aniline selective oxidation method which comprises the following steps: mixing aniline and an organic solvent to obtain a mixed organic solution, then mixing peroxymonosulfate and a rare earth oxide catalyst, and stirring for reaction to obtain an azo compound. The aniline selective oxidation method provided by the invention is simple and convenient in steps and excellent in yield, avoids the use of precious metals, has the advantages of mild reaction conditions, high yield, simple process, convenience in operation, low cost and the like, and is expected to realize large-scale industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical synthesis, and particularly relates to a method for selective oxidation of aniline. Background Art

[0002] Aniline is a fundamental and versatile aromatic amine used in a wide range of applications, including pharmaceuticals, dyes, polymers, and pesticides. Its unique chemical structure, with an amino group directly attached to a benzene ring, enables it to undergo a range of reactions, including oxidation, to synthesize high-value products. Among these reactions, the selective oxidation of aniline has attracted significant attention due to its ability to produce key intermediates such as nitrobenzene, azobenzene, and azoxybenzene, all of which play crucial roles in the manufacture of pharmaceuticals, pigments, and advanced materials.

[0003] A key aspect of the selective oxidation of aniline is controlling the reaction pathway to selectively form specific products. For example, by adjusting the catalyst composition, reaction conditions, or both, researchers can steer the oxidation reaction toward the synthesis of nitrobenzene, an intermediate in dye and pesticide production, or toward the synthesis of azobenzene and azoxybenzene, which are used in pharmaceuticals and liquid crystals.

[0004] The selective oxidation of aniline faces several challenges, primarily controlling the reaction pathway and maximizing the yield and selectivity of the desired product. Traditional methods typically employ harsh conditions, such as high temperature and pressure, and use toxic and environmentally unfriendly oxidants, resulting in low product selectivity and the generation of large amounts of waste. To improve aniline conversion and selectivity of azobenzene products, precious metal materials are often used as catalysts, which in turn leads to high production costs. Catalytic oxidation systems for aniline using H2O2 and O2 as oxidants typically require the addition of expensive metal catalysts under high temperature and pressure. These harsh reaction conditions and expensive catalysts limit the large-scale industrial application of this reaction.

[0005] Furthermore, CN 119285477A discloses a cobalt-based catalyst for the oxidative coupling of aniline to prepare azobenzene and its application. Specifically, it discloses the selective oxidation of aniline to prepare azobenzene using hydrogen peroxide and a cobalt-based catalyst. Although the reaction conditions during the selective oxidation process are relatively mild, the preparation of the cobalt-based catalyst requires high temperature and is relatively expensive, which still limits the large-scale implementation of this solution in industry.

[0006] In summary, there is an urgent need to develop environmentally friendly, economical, simple and highly selective strategies for the catalytic oxidation of aniline to prepare azobenzene. Summary of the Invention

[0007] In response to the shortcomings of the prior art, the present invention provides a method for the selective oxidation of aniline. The method provides advantages such as mild reaction conditions, high yield, simple process, convenient operation, and low cost. Azobenzene can be obtained after selective oxidation, potentially enabling large-scale industrial production of azobenzene.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] The present invention provides a method for selective oxidation of aniline, comprising:

[0010] Aniline and an organic solvent are mixed to obtain a mixed organic solution, and then peroxymonosulfate and a rare earth oxide catalyst are mixed, and the mixture is stirred for reaction to obtain an azo compound.

[0011] The method provided by the present invention can achieve efficient and selective oxidation of aniline by a simple stirring reaction at room temperature and pressure to obtain an intermediate (azo compound) with wide applicability. In addition, the method provided by the present invention has the advantages of mild reaction conditions, high yield, simple process, convenient operation, low cost, etc.; and is expected to achieve industrial large-scale production.

[0012] As a preferred technical solution of the present invention, the conversion rate of aniline is ≥60%, for example, it can be 60%, 65%, 70%, 75%, 80%, 85% or 90%, etc., but is not limited to the listed values. Other values not listed within the numerical range are also applicable.

[0013] As a preferred technical solution of the present invention, the organic solvent includes any one of methanol, ethanol or propanol or a combination of at least two of them. Typical but non-limiting combinations include: a combination of methanol and ethanol, a combination of methanol and propanol, a combination of ethanol and propanol, or a combination of methanol, ethanol and propanol.

[0014] Preferably, the volume ratio of aniline to the organic solvent is 1:45 to 55, for example, 1:45, 1:47, 1:49, 1:51, 1:53 or 1:55, etc., but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0015] The organic solvent used in the present invention has strong polarity and can stabilize nitrosobenzene in the reaction product through hydrogen bonding, thereby inhibiting its further oxidation to nitrobenzene, and is beneficial to enhancing the selectivity of azobenzene.

[0016] As a preferred technical solution of the present invention, the peroxymonosulfate includes potassium hydrogen persulfate.

[0017] Preferably, the molar ratio of aniline to peroxymonosulfate is 10:1 to 6, for example, 10:1, 10:2, 10:3, 10:4, 10:5 or 10:6, etc., but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0018] In the present invention, the peroxymonosulfate (PMS) as an oxidant can be better combined with a synthetic heterogeneous catalyst (rare earth oxide catalyst), which is beneficial for the oxidation of aniline. Compared with traditional oxidants (hydrogen peroxide or oxygen), the reaction conditions of PMS are milder. More specifically, hydrogen peroxide itself is very easy to decompose and has high requirements for the pH of the reaction system, while oxygen needs to react at high temperature and high pressure, which makes the selection of reaction conditions more stringent.

[0019] If the amount of the peroxymonosulfate used is too high, PMS will not only react with aniline, but also have side reactions with other intermediates or products in the reaction system, thereby reducing the conversion rate of aniline; if the amount of the peroxymonosulfate used is too low, it will be difficult to produce a sufficient amount of singlet oxygen, thereby reducing the yield of the azo compound.

[0020] As a preferred technical solution of the present invention, the rare earth oxide catalyst includes any one or a combination of at least two of lanthanum oxide, cerium oxide, praseodymium oxide or neodymium oxide. Typical but non-limiting combinations include: a combination of lanthanum oxide and cerium oxide, a combination of lanthanum oxide and praseodymium oxide, a combination of lanthanum oxide and praseodymium oxide, a combination of lanthanum oxide and neodymium oxide, a combination of cerium oxide and praseodymium oxide, a combination of cerium oxide and neodymium oxide, a combination of praseodymium oxide and neodymium oxide, or a combination of lanthanum oxide, cerium oxide, praseodymium oxide and neodymium oxide.

[0021] Preferably, the mass ratio of the rare earth oxide catalyst to aniline is 8 to 12:1, for example, 8:1, 8.5:1, 9:1, 9.5:1, 10:1, 10.5:1, 11:1, 11.5:1 or 12:1, etc., but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0022] Preferably, the specific surface area of the rare earth oxide catalyst is 320 to 380 m 2 / g, for example, it can be 320m 2 / g、330m 2 / g、340m 2 / g、350m 2 / g、360m 2 / g or 380m 2 / g, etc., but are not limited to the listed values. Other values not listed within the numerical range are also applicable.

[0023] As a preferred technical solution of the present invention, the temperature of the stirring reaction is 20-30°C, for example, it can be 20°C, 22°C, 24°C, 26°C, 28°C or 30°C, but is not limited to the listed values. Other values not listed within the numerical range are also applicable.

[0024] In the present invention, the selective oxidation reaction of aniline is carried out at room temperature and pressure, the reaction conditions are relatively mild, and industrial-scale production is expected to be achieved.

[0025] Preferably, the stirring reaction time is 3 to 9 hours, for example, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours or 9 hours, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0026] In the present invention, the stirring reaction time affects the reaction process. If the reaction time is too short, the reaction will be incomplete, thereby affecting the selective oxidation of aniline. If the reaction time is too long, the complete conversion rate of aniline will not change, but the content of by-products (nitrobenzene or nitrosobenzene) will increase, and the proportion of selectively generated azo compounds will decrease.

[0027] Preferably, the stirring rate of the stirring reaction is 450 to 550 r / min, for example, it can be 450 r / min, 470 r / min, 490 r / min, 510 r / min, 530 r / min or 550 r / min, but is not limited to the listed values. Other values not listed within the numerical range are also applicable.

[0028] As a preferred technical solution of the present invention, the azo compound includes azobenzene and azoxybenzene.

[0029] As a preferred technical solution of the present invention, the method for selective oxidation of aniline provided by the present invention comprises:

[0030] Aniline and an organic solvent are mixed to obtain a mixed organic solution, and then peroxymonosulfate and a rare earth oxide catalyst are sequentially mixed, and the mixture is stirred to react to obtain an azo compound;

[0031] The volume ratio of aniline to organic solvent is 1:45-55; the molar ratio of aniline to peroxymonosulfate is 10:1-6; the mass ratio of rare earth oxide catalyst to aniline is 8-12:1;

[0032] The stirring reaction temperature is 20-30°C, the time is 3-9 hours, and the stirring rate is 450-550 r / min;

[0033] The azo compounds include azobenzene and azoxybenzene.

[0034] It is worth noting that the organic monomers in the azo compound obtained after the selective oxidation reaction of aniline all play a vital role in the manufacture of pharmaceuticals, pigments and advanced materials; and the mixture can be simply separated and treated later to obtain organic monomers with higher purity.

[0035] The numerical range described in the present invention includes not only the point values listed above, but also any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values included in the range.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) The method for selective oxidation of aniline provided by the present invention can achieve efficient selective oxidation of aniline by a simple stirring reaction at room temperature and pressure, thereby obtaining an intermediate (azo compound) with wide applicability;

[0038] (2) The method for selective oxidation of aniline provided by the present invention has the advantages of mild reaction conditions, high yield, simple process, convenient operation, and low cost; it is expected to achieve industrial large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a scanning electron microscope image of the catalyst (cerium oxide) used in Example 1 of the present invention;

[0040] Figure 2 This is a high-resolution transmission electron microscopy image of the catalyst (cerium oxide) used in Example 1 of the present invention at a scale of 1 mm;

[0041] Figure 3 This is the EPR spectrum of singlet oxygen in the selective oxidation reaction system described in Example 1 of the present invention. DETAILED DESCRIPTION

[0042] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0043] Example 1

[0044] This embodiment provides a method for selective oxidation of aniline, comprising:

[0045] 10 mmol of aniline and 50 mL of an organic solvent (methanol) were mixed to obtain a mixed organic solution, followed by sequentially adding 3 mmol of peroxymonosulfate (potassium hydrogen persulfate) and 700 mg of a rare earth oxide catalyst (cerium oxide), and the mixture was stirred to react to obtain an azo compound;

[0046] The stirring reaction was carried out at a temperature of 25°C, a time of 6 hours, and a stirring rate of 500 r / min.

[0047] The scanning electron microscope image of the catalyst (cerium oxide) is as follows Figure 1 As shown, the high-resolution transmission electron microscopy image at 1mm scale is as follows Figure 2 As shown;

[0048] The EPR spectrum of singlet oxygen in the selective oxidation reaction system provided in this embodiment is as follows: Figure 3 shown.

[0049] The chemical reaction equation of the selective oxidation reaction of aniline described in this embodiment is as follows:

[0050]

[0051] Example 2

[0052] This embodiment provides a method for selective oxidation of aniline, comprising:

[0053] Aniline and an organic solvent (methanol and ethanol in a volume ratio of 1:1) are mixed to obtain a mixed organic solution, followed by sequentially adding a peroxymonosulfate (potassium hydrogen persulfate) and a rare earth oxide catalyst (praseodymium oxide), and the mixture is stirred to react to obtain an azo compound;

[0054] The volume ratio of aniline to organic solvent is 1:48; the molar ratio of aniline to peroxymonosulfate is 10:4; and the mass ratio of rare earth oxide catalyst to aniline is 9:1.

[0055] The stirring reaction was carried out at a temperature of 20° C., a time of 8 h, and a stirring rate of 450 r / min.

[0056] Example 3

[0057] This embodiment provides a method for selective oxidation of aniline, comprising:

[0058] Aniline and an organic solvent (methanol, ethanol, and propanol in a volume ratio of 1:1:1) are mixed to obtain a mixed organic solution, followed by sequentially adding a peroxymonosulfate (potassium hydrogen persulfate) and a rare earth oxide catalyst (neodymium oxide), and the mixture is stirred to react to obtain an azo compound;

[0059] The volume ratio of aniline to organic solvent is 1:52; the molar ratio of aniline to peroxymonosulfate is 10:5; and the mass ratio of the rare earth oxide catalyst to aniline is 11:1.

[0060] The stirring reaction was carried out at a temperature of 30° C., a time of 4.5 h, and a stirring rate of 550 r / min.

[0061] Example 4

[0062] This embodiment provides a method for selective oxidation of aniline, which differs from that of Example 1 only in that:

[0063] In this embodiment, the organic solvent is adjusted to ethanol.

[0064] Example 5

[0065] This embodiment provides a method for selective oxidation of aniline, which differs from that of Example 1 only in that:

[0066] In this embodiment, the organic solvent is adjusted to acetonitrile.

[0067] Example 6

[0068] This embodiment provides a method for selective oxidation of aniline, which differs from that of Example 1 only in that:

[0069] In this embodiment, the organic solvent is adjusted to mesitylene.

[0070] Example 7

[0071] This embodiment provides a method for selective oxidation of aniline, which differs from that of Example 1 only in that:

[0072] In this example, the amount of the peroxymonosulfate was adjusted to 0.3 mmol.

[0073] Example 8

[0074] This embodiment provides a method for selective oxidation of aniline, which differs from that of Example 1 only in that:

[0075] In this example, the dosage of the peroxymonosulfate was adjusted to 1 mmol.

[0076] Example 9

[0077] This embodiment provides a method for selective oxidation of aniline, which differs from that of Example 1 only in that:

[0078] In this example, the amount of the peroxymonosulfate was adjusted to 6 mmol.

[0079] Example 10

[0080] This embodiment provides a method for selective oxidation of aniline, which differs from that of Example 1 only in that:

[0081] In this example, the amount of the peroxymonosulfate was adjusted to 18 mmol.

[0082] Example 11

[0083] This embodiment provides a method for selective oxidation of aniline, which differs from that of Example 1 only in that:

[0084] In this embodiment, the rare earth oxide catalyst is adjusted to an equal amount of lanthanum oxide.

[0085] Example 12

[0086] This embodiment provides a method for selective oxidation of aniline, which differs from that of Example 1 only in that:

[0087] In this embodiment, the rare earth oxide catalyst is adjusted to an equal amount of praseodymium oxide.

[0088] Example 13

[0089] This embodiment provides a method for selective oxidation of aniline, which differs from that of Example 1 only in that:

[0090] In this embodiment, the rare earth oxide catalyst is adjusted to an equal amount of neodymium oxide.

[0091] Example 14

[0092] This embodiment provides a method for selective oxidation of aniline, which differs from that of Example 1 only in that:

[0093] In this embodiment, the rare earth oxide catalyst is adjusted to an equal amount of samarium oxide.

[0094] Example 15

[0095] This embodiment provides a method for selective oxidation of aniline, which differs from that of Example 1 only in that:

[0096] In this embodiment, the rare earth oxide catalyst is adjusted to an equal amount of dysprosium oxide.

[0097] Example 16

[0098] This embodiment provides a method for selective oxidation of aniline, which differs from that of Example 1 only in that:

[0099] In this embodiment, the rare earth oxide catalyst is adjusted to an equal amount of holmium oxide.

[0100] Example 17

[0101] This embodiment provides a method for selective oxidation of aniline, which differs from that of Example 1 only in that:

[0102] In this embodiment, the stirring reaction time is adjusted to 1 h.

[0103] Example 18

[0104] This embodiment provides a method for selective oxidation of aniline, which differs from that of Example 1 only in that:

[0105] In this embodiment, the stirring reaction time is adjusted to 3 hours.

[0106] Example 19

[0107] This embodiment provides a method for selective oxidation of aniline, which differs from that of Example 1 only in that:

[0108] In this embodiment, the stirring reaction time is adjusted to 9 hours.

[0109] Example 20

[0110] This embodiment provides a method for selective oxidation of aniline, which differs from that of Example 1 only in that:

[0111] In this embodiment, the stirring reaction time is adjusted to 12 hours.

[0112] Comparative Example 1

[0113] This comparative example provides a method for selective oxidation of aniline, which differs from Example 1 only in that:

[0114] In this comparative example, the peroxymonosulfate was adjusted to an equal amount of hydrogen peroxide.

[0115] Comparative Example 2

[0116] This comparative example provides a method for selective oxidation of aniline, which differs from Example 1 only in that:

[0117] In this comparative example, the peroxymonosulfate was adjusted to an equal amount of sodium thiosulfate.

[0118] Performance testing:

[0119] The azo compounds obtained by the methods provided in the above examples and comparative examples were analyzed and tested to obtain the conversion rate of aniline and the generation rate of azo compounds. The results are shown in Table 1.

[0120] The analysis and detection were performed using a gas chromatography-mass spectrometer (GC-MS) using a DB-FFAP capillary column, controlling the He flow rate to 30-50 cm / s, setting the split ratio to 30:1, setting the inlet temperature to 320°C, and setting the heating program to an initial temperature of 60°C and hold for 5 minutes, then increase the temperature to 130°C at a rate of 10°C / min, then hold for 5 minutes, and then continue to increase the temperature to 320°C at a rate of 10°C / min. The concentrations of the raw materials aniline and the azo compound in the reaction system were detected by GC-MS, so that the aniline conversion rate and the formation rate of the azo compound could be calculated.

[0121] In addition, according to Figure 3 It can be seen that a typical 1:1:1 peak signal was detected in the reaction system, confirming the presence of singlet oxygen in the system.

[0122] Table 1

[0123]

[0124]

[0125] According to Table 1, the following points can be made:

[0126] (1) Comprehensive analysis of Example 1 and Examples 4-6 shows that the catalyst has higher reactivity in methanol and ethanol solvents, and a positively charged intermediate is formed in the nucleophilic substitution reaction of aniline; and methanol and ethanol solvents have strong polarity, which can further stabilize the azo compound through the organic solvent, reduce the activation energy of the reaction, and make the reaction easier to proceed;

[0127] On the contrary, organic solvents such as acetonitrile and mesitylene will cause environmental pollution, and even if they work synergistically with catalysts, they still cannot effectively achieve the selective oxidation of aniline.

[0128] (2) Comprehensive analysis of Example 1 and Examples 7-10 shows that with the increase in the amount of PMS added, the aniline conversion rate, azobenzene formation rate, azoxybenzene formation rate, nitrosobenzene formation rate and nitrobenzene formation rate show different change trends;

[0129] When the amount of PMS added is too low, the aniline conversion rate and the azobenzene formation rate decrease, while the azobenzene oxide formation rate increases. When the amount of PMS added is too high, PMS not only reacts with aniline, but also reacts with other intermediates or products in the reaction system. For example, excess PMS may oxidize the generated intermediates such as azobenzene and azobenzene oxide, converting them into other substances, thereby reducing the chance of aniline being converted into the target product and resulting in a lower aniline conversion rate.

[0130] (3) Comprehensive analysis of Example 1 and Examples 11-16 shows that the catalytic effects of different rare earth oxides on aniline are also different; from Example 1, it can be seen that the catalytic effect of cerium oxide catalyst on aniline is the best. At room temperature and pressure, the conversion rate of aniline can reach 83.52% after 6 hours of reaction, of which the selective generation of azobenzene accounts for 85.4% and the selective generation of azobenzene oxide accounts for 14.6%. This is because Ce in CeO2 4+ / Ce 3+ The existence of redox cycles provides an active electronic environment for the occurrence of catalytic reactions;

[0131] However, other metal oxides cannot activate peroxymonosulfate to produce a sufficient concentration of singlet oxygen, resulting in a decrease in aniline conversion rate;

[0132] (4) Comprehensive analysis of Example 1 and Examples 17-20 shows that as the reaction time increases, the aniline conversion rate gradually increases and tends to be stable, which is related to factors such as the reactant concentration in the reaction system, reaction kinetics, and reaction equilibrium;

[0133] When the reaction time is too long, azobenzene is reacted to generate other substances such as azoxybenzene; when the reaction time is too short, the conversion rate of aniline gradually decreases, while the formation rate of nitrosobenzene increases.

[0134] (5) Comprehensive analysis of Example 1 and Comparative Examples 1-2 shows that the selection of a suitable oxidant is one of the important factors affecting the selective oxidation reaction of aniline;

[0135] When the PMS is replaced with hydrogen peroxide or sodium thiosulfate, the conversion rate of aniline is greatly reduced, thereby proving that under the reaction conditions provided by the present invention, neither hydrogen peroxide nor sodium thiosulfate can achieve selective oxidation of aniline.

[0136] In summary, the method for selective oxidation of aniline provided by the present invention has simple steps, excellent yield, and avoids the use of precious metals. It has the advantages of mild reaction conditions, high yield, simple process, convenient operation, and low cost, and is expected to achieve industrial-scale production.

[0137] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for selective oxidation of aniline, characterized in that: The method comprises: Aniline and an organic solvent are mixed to obtain a mixed organic solution, and then peroxymonosulfate and a rare earth oxide catalyst are mixed, and the mixture is stirred for reaction to obtain an azo compound.

2. The method according to claim 1, characterized in that The conversion rate of the aniline is ≥60%.

3. The method according to claim 1 or 2, characterized in that The organic solvent includes any one of methanol, ethanol or propanol or a combination of at least two; Preferably, the volume ratio of the aniline to the organic solvent is 1:45-55.

4. The method according to any one of claims 1 to 3, characterized in that The peroxymonosulfate salt includes potassium hydrogen persulfate.

5. The method according to claim 4, characterized in that The molar ratio of the aniline to the peroxymonosulfate is 10:1-6.

6. The method according to any one of claims 1 to 5, characterized in that The rare earth oxide catalyst includes any one or a combination of at least two of lanthanum oxide, cerium oxide, praseodymium oxide or neodymium oxide; Preferably, the mass ratio of the rare earth oxide catalyst to aniline is 8 to 12:1; Preferably, the specific surface area of the rare earth oxide catalyst is 320 to 380 m 2 / g.

7. The method according to any one of claims 1 to 6, characterized in that The temperature of the stirring reaction is 20-30°C.

8. The method according to any one of claims 1 to 7, characterized in that The stirring reaction time is 3 to 9 hours; Preferably, the stirring rate of the stirring reaction is 450 to 550 r / min.

9. The method according to any one of claims 1 to 8, characterized in that The azo compounds include azobenzene and azoxybenzene.

10. The method according to any one of claims 1 to 9, characterized in that The method comprises: Aniline and an organic solvent are mixed to obtain a mixed organic solution, and then peroxymonosulfate and a rare earth oxide catalyst are sequentially mixed, and the mixture is stirred to react to obtain an azo compound; The volume ratio of aniline to organic solvent is 1:45-55; the molar ratio of aniline to peroxymonosulfate is 10:1-6; the mass ratio of rare earth oxide catalyst to aniline is 8-12:1; The stirring reaction temperature is 20-30°C, the time is 3-9 hours, and the stirring rate is 450-550 r / min; The azo compounds include azobenzene and azoxybenzene.

Images