A method for the direct oxidation of nitrotoluene to prepare nitrobenzaldehyde

Abstract

This invention provides a method for the direct oxidation of nitrobenzaldehyde to nitrobenzaldehyde, belonging to the field of organic synthesis technology. The method includes the following steps: mixing nitrobenzaldehyde, an organic solvent, a catalyst, an oxidant, and a strongly oxidizing acid, and carrying out an oxidation reaction to obtain nitrobenzaldehyde; the catalyst is a heteropolyacid salt; the oxidant is Mn₂O₃, sodium hypochlorite, or hydrogen peroxide. This invention develops a highly efficient metal heteropolyacid salt catalyst, which, in conjunction with the oxidant, achieves highly selective direct catalytic oxidation of nitrobenzaldehyde to nitrobenzaldehyde, avoiding the numerous steps, severe over-oxidation, and large amounts of bromine / acid-containing wastewater generated by traditional methods. The direct oxidation method is simple, has high chemical selectivity, produces no wastewater, and the reaction medium can be recovered, showing broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and in particular to a method for the direct oxidation of nitrotoluene to prepare nitrobenzaldehyde. Background Technology

[0002] Nitrobenzaldehyde includes o-nitrobenzaldehyde, m-nitrobenzaldehyde, and p-nitrobenzaldehyde, all of which are important chemical intermediates widely used in pharmaceutical synthesis and dye intermediates. For example, o-nitrobenzaldehyde is used to synthesize the antianginal drug nitropyridine (Adalat), o-nitrostyrene derivatives, and o-nitrosinic acid derivatives. After reducing its nitro group to an amino group, the resulting o-aminobenzaldehyde can be used in the synthesis of quinoline compounds. m-nitrobenzaldehyde is mainly used as a dye, surfactant, and pharmaceutical organic synthesis intermediate. In the pharmaceutical industry, it is used in the production of calcium iodosporate, iodopic acid, calcium cholestyramine, and nitrobenzidine. The domestic and international market demand for nitrobenzaldehyde is substantial, making the research and improvement of its processing routes of great significance.

[0003] The main synthetic methods for o-nitrobenzaldehyde include condensation, bromination, oxidative nitration, displacement, reduction, and electrochemical oxidation. Industrially, o-nitrobenzaldehyde is prepared using o-nitrotoluene as a raw material via a bromination-hydrolysis-nitric acid oxidation process, with yields mostly around 40%. This method suffers from drawbacks such as demanding reaction conditions, high toxicity, high equipment requirements, and environmental pollution. Currently, the industrial synthesis of m-nitrobenzaldehyde primarily relies on the benzaldehyde nitration method, which generates large amounts of industrial waste acid, severely polluting the environment. Furthermore, using benzaldehyde as a raw material results in relatively high costs. Therefore, developing a simple and efficient direct oxidation method for nitrobenzaldehyde is of great significance.

[0004] The direct oxidation of nitrotoluene is a simple process with few steps, but it is currently only in the theoretical research stage and faces many problems, such as low oxidation efficiency, many by-products, and unsatisfactory economics. Summary of the Invention

[0005] The purpose of this invention is to provide a method for the direct oxidation of nitrotoluene to prepare nitrobenzaldehyde, which has the advantages of high conversion rate, good selectivity and low cost.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for the direct oxidation of nitrobenzaldehyde to obtain nitrobenzaldehyde, comprising the following steps: mixing nitrobenzaldehyde, an organic solvent, a catalyst, an oxidant and an acid with strong oxidizing properties, and carrying out an oxidation reaction to obtain nitrobenzaldehyde;

[0008] The catalyst is a heteropolyacid salt;

[0009] The oxidant is Mn2O3, sodium hypochlorite, or hydrogen peroxide.

[0010] Preferably, the heteropolyacid salt includes one or more of phosphomolybdate, phosphotungstate, and silicotungstate; the phosphomolybdate may or may not contain water of crystallization, and has the molecular formula M3PMo. 12 O 40 ·nH2O; the phosphotungstic acid may or may not contain water of crystallization, and its molecular formula is M6P2W. 18 O 62 ·nH2O; the silicotungstic acid may or may not contain water of crystallization, and its molecular formula is M4SiW 12 O 40 ·nH2O; the metal cations in the heteropolyacid salt include one or more of Na, K, Rb, Cs, Mg, Ca and Ba.

[0011] Preferably, the nitrotoluene is o-nitrotoluene, m-nitrotoluene, or p-nitrotoluene.

[0012] Preferably, the molar ratio of the oxidant to nitrotoluene is (0.9-2.0):1.

[0013] Preferably, the amount of catalyst used is 1 to 18 wt% of nitrotoluene.

[0014] Preferably, the acid with strong oxidizing properties includes concentrated sulfuric acid.

[0015] Preferably, the molar ratio of the oxidant to the acid with strong oxidizing power is 1:(1.5 to 10).

[0016] Preferably, the oxidation reaction is carried out at a temperature of 60–130°C.

[0017] Preferably, the organic solvent includes one or more of liquid alkanes, liquid cycloalkanes, liquid aromatics and their derivatives.

[0018] Preferably, the volume ratio of the nitrotoluene to the organic solvent is 1:(1-5).

[0019] This invention provides a method for the direct oxidation of nitrobenzaldehyde to obtain nitrobenzaldehyde, comprising the following steps: mixing nitrobenzaldehyde, an organic solvent, a catalyst, an oxidant and an acid with strong oxidizing properties, and carrying out an oxidation reaction to obtain nitrobenzaldehyde; wherein the catalyst is a heteropoly acid salt; and the oxidant is Mn2O3, sodium hypochlorite or hydrogen peroxide.

[0020] This invention develops a highly efficient metal heteropolyacid acid salt catalyst, which, in synergistic with an oxidant, enables the direct catalytic oxidation of nitrobenzaldehyde with high selectivity, avoiding the numerous steps, severe over-oxidation, and large-scale generation of bromine / acid-containing wastewater associated with traditional methods. The direct oxidation method is simple, exhibits high chemical selectivity, produces no wastewater, and the reaction medium can be recovered, demonstrating broad application prospects.

[0021] This invention uses inexpensive catalytic species to regulate the main reaction rate while suppressing side reactions, resulting in a significant improvement in the selectivity of the target product. This improved selectivity can shorten the separation process steps and reduce energy consumption.

[0022] Most of the media after the reaction of this invention can be recycled and reused, which is in line with the concept of green synthesis; the clean process is of great significance to environmental protection; when Mn2O3 is used as an oxidant in this invention, manganese sulfate is generated in the process, which can be easily recycled and reused; sodium hypochlorite is converted into sodium chloride after the reaction, which is non-toxic; hydrogen peroxide is used as an oxidant, and the reduction product is water, making the process clean.

[0023] The results of the examples show that the catalyst of the present invention has high reactivity and target product selectivity, with a conversion rate of 50-95% for nitrotoluene and a selectivity of >97% for nitrobenzaldehyde. The catalyst can be recycled and reused at least 10 times without significant reduction in activity. Detailed Implementation

[0024] This invention provides a method for the direct oxidation of nitrobenzaldehyde to obtain nitrobenzaldehyde, comprising the following steps: mixing nitrobenzaldehyde, an organic solvent, a catalyst, an oxidant and an acid with strong oxidizing properties, and carrying out an oxidation reaction to obtain nitrobenzaldehyde;

[0025] The catalyst is a heteropolyacid salt;

[0026] The oxidant is Mn2O3, sodium hypochlorite, or hydrogen peroxide.

[0027] Unless otherwise specified, all raw materials used in this invention are commercially available products well known in the art.

[0028] In this invention, the nitrotoluene is preferably o-nitrotoluene, m-nitrotoluene, or p-nitrotoluene; the organic solvent is preferably one or more of liquid alkanes, liquid cycloalkanes, liquid aromatics, and their derivatives. This invention does not specifically limit the type of organic solvent, as long as it is relatively stable, does not react with any substance in the reaction system, and can effectively dissolve the product, facilitating separation from the acid phase after the reaction, and also facilitating product separation. Specifically, the liquid alkane can be n-hexane, the liquid cycloalkanes can be cyclohexane; the liquid aromatics can be benzene and / or xylene; the derivatives of the liquid aromatics can be one or more of anisole, chlorobenzene, and nitrobenzene. In this invention, the volume ratio of the nitrotoluene to the organic solvent is preferably 1:(1-5), more preferably 1:(2-4).

[0029] In this invention, the catalyst is a heteropoly acid salt; the heteropoly acid salt preferably includes one or more of phosphomolybdate, phosphotungstate, and silicotungstate; the phosphomolybdate may or may not contain water of crystallization, and the molecular formula is preferably M3PMo. 12 O 40 ·nH2O; the phosphotungstic acid may or may not contain water of crystallization, and the preferred molecular formula is M6P2W. 18 O 62 ·nH2O; the silicotungstic acid may or may not contain water of crystallization, and the preferred molecular formula is M4SiW 12 O 40 • nH2O; the metal cation in the heteropolyacid salt includes one or more of Na, K, Rb, Cs, Mg, Ca, and Ba. In this invention, the amount of the catalyst is preferably 1-18 wt% of nitrotoluene, more preferably 3-15 wt%, and even more preferably 5-10 wt%. In this invention, the heteropolyacid salt can be prepared using commercially available products or methods well known in the art.

[0030] In this invention, the oxidant is Mn2O3, sodium hypochlorite, or hydrogen peroxide; the concentration of the hydrogen peroxide is preferably 20-30 wt%, more preferably 25-30 wt%. In this invention, the molar ratio of the oxidant to nitrotoluene is preferably (0.9-2.0):1, more preferably (1.1-1.8):1, and even more preferably (1.3-1.6):1.

[0031] In this invention, the acid with strong oxidizing properties preferably includes concentrated sulfuric acid, and the concentration of the concentrated sulfuric acid is preferably 5 to 9 mol / L. In this invention, the molar ratio of the oxidant to the acid with strong oxidizing properties is preferably 1:(1.5 to 10), more preferably 1:(3 to 8), and even more preferably 1:(5 to 6).

[0032] In this invention, the temperature of the oxidation reaction is preferably 60–130°C, more preferably 70–120°C, and even more preferably 80–100°C. This invention does not have special requirements regarding the time of the oxidation reaction; it is preferable to monitor the reaction to completion using TLC.

[0033] After the oxidation reaction is completed, the reaction system automatically separates into two phases. Preferably, the organic phase is separated and then distilled to obtain the target product. In an embodiment of the invention, to detect the product composition, the system is divided into layers after the reaction, the organic phase is separated, washed with sodium bicarbonate solution, dried, and its composition is analyzed using gas chromatography.

[0034] This invention develops a highly efficient metal heteropolyacid acid salt catalyst, which, in synergistic with an oxidant, enables the direct catalytic oxidation of nitrobenzaldehyde with high selectivity, avoiding the numerous steps, severe over-oxidation, and large-scale generation of bromine / acid-containing wastewater associated with traditional methods. The direct oxidation method is simple, exhibits high chemical selectivity, produces no wastewater, and the reaction medium can be recovered, demonstrating broad application prospects.

[0035] The following detailed description of the method for preparing nitrobenzaldehyde by direct oxidation of nitrobenzyl toluene provided by the present invention, with reference to the embodiments, should not be construed as limiting the scope of protection of the present invention.

[0036] Example 1

[0037] 10g of phosphomolybdate catalyst containing 0.3g Na ions and 0.1g K ions was added to a batch reactor. 50.5g of Mn₂O₃ oxidant was also added, along with 30mL of o-nitrotoluene and 250mL of n-hexane. Then, 137mL of 7mol / L sulfuric acid solution was added dropwise. The molar ratio of oxidant to sulfuric acid was 1:3. The liquid content of the reactor was 43.7% of the total volume. The reaction temperature was 60℃, and the reaction progress was monitored by TLC for 8 hours. After the reaction, the system separated into layers. The organic phase was washed with sodium bicarbonate solution, dried, and its composition was analyzed by gas chromatography. The conversion rate of o-nitrotoluene was 88%, and the selectivity of nitrobenzaldehyde was 99.5%. The catalyst was recycled 15 times without significant decrease in activity (86% conversion rate of o-nitrotoluene and 97.5% selectivity of o-nitrobenzaldehyde). Both TLC monitoring and gas chromatography analysis, qualitative and quantitative, used purchased standards.

[0038] Example 2

[0039] 15g of phosphotungstenate catalyst containing 0.45g of Rb ions was added to a batch reactor. 23.8g of sodium hypochlorite oxidant was also added, followed by 30mL of m-nitrotoluene and 200mL of n-hexane. Then, 200mL of 8mol / L sulfuric acid solution was added dropwise. The molar ratio of oxidant to sulfuric acid was 1:5. The liquid material comprised 45% of the reactor volume. The reaction temperature was 80℃, and the reaction progress was monitored by TLC for 10 hours. The conversion rate of m-nitrotoluene was 86%, and the selectivity of nitrobenzaldehyde was 100%. The catalyst could be recycled 21 times without significant decrease in activity (conversion rate of m-nitrotoluene was 83.5%, and selectivity of m-nitrobenzaldehyde was 97.2%).

[0040] Example 3

[0041] 10g of silicotungstic acid catalyst containing 0.5g of Cs ions was added to a batch reactor. 60.8g of 30wt% hydrogen peroxide oxidant was added to the batch reactor, followed by 50mL of p-nitrotoluene and 150mL of n-hexane. Then, 213mL of 9mol / L sulfuric acid solution was added dropwise. The molar ratio of oxidant to sulfuric acid was 1:3.6. The liquid material accounted for 41.3% of the reactor volume. The reaction temperature was 90℃, and the reaction progress was monitored by TLC for 12 hours. The conversion rate of p-nitrotoluene was 91%, and the selectivity of nitrobenzaldehyde was 99.2%. The catalyst could be recycled 13 times without significant decrease in activity (p-nitrotoluene conversion rate 87%, p-nitrobenzaldehyde selectivity 96.7%).

[0042] Example 4

[0043] 15g of phosphomolybdate catalyst containing 0.6g of Mg ions and 0.6g of Ca ions was added to a batch reactor. 53.6g of Mn₂O₃ oxidant was also added, along with 30mL of o-nitrotoluene and 100mL of cyclohexane. Then, 114mL of 5mol / L sulfuric acid solution was added dropwise. The molar ratio of oxidant to sulfuric acid was 1:1.7, and the liquid material comprised 26.4% of the reactor volume. The reaction temperature was 110℃, and the reaction progress was monitored by TLC for 9 hours. The conversion rate of o-nitrotoluene was 90%, and the selectivity of nitrobenzaldehyde was 99.6%. The catalyst could be recycled 16 times without significant decrease in activity (o-nitrotoluene conversion rate 89%, o-nitrobenzaldehyde selectivity 98.5%).

[0044] Example 5

[0045] 10g of phosphotungstenate catalyst containing 1g of potassium ions was added to a batch reactor. 50.6g of sodium hypochlorite oxidant was also added, along with 50mL of m-nitrotoluene and 100mL of cyclohexane. Then, 220mL of 6mol / L sulfuric acid solution was added dropwise. The molar ratio of oxidant to sulfuric acid was 1:2.1. The liquid material comprised 32% of the reactor volume. The reaction temperature was 100℃, and the reaction progress was monitored by TLC for 15 hours. The conversion rate of m-nitrotoluene was 93%, and the selectivity of nitrobenzaldehyde was 98.9%. The catalyst could be recycled 18 times without significant decrease in activity (m-nitrotoluene conversion rate 89%, nitrobenzaldehyde selectivity 97.5%).

[0046] Example 6

[0047] 10g of silicotungstic acid catalyst containing 1.2g of Ca ions was added to a batch reactor. 110.56g of 30wt% hydrogen peroxide oxidant was also added, followed by 100mL of p-nitrotoluene and 150mL of cyclohexane. Then, 370mL of 5mol / L sulfuric acid solution was added dropwise. The molar ratio of oxidant to sulfuric acid was 1:1.9. The liquid material comprised 38% of the reactor volume. The reaction temperature was 130℃, and the reaction progress was monitored by TLC for 11 hours. The conversion rate of p-nitrotoluene was 89%, and the selectivity of nitrobenzaldehyde was 100%. The catalyst could be recycled 14 times without significant decrease in activity (p-nitrotoluene conversion rate 87%, p-nitrobenzaldehyde selectivity 98.7%).

[0048] Example 7

[0049] 10g of phosphomolybdate catalyst and 8g of phosphotungsten catalyst were added to a batch reactor. The phosphomolybdate catalyst contained 2g of Mg ions, and the phosphotungsten catalyst contained 0.52g of Ca ions. 56.8g of Mn₂O₃ oxidant was added to the batch reactor, followed by 30mL of m-nitrotoluene and 200mL of benzene. Then, 103mL of 6mol / L sulfuric acid solution was added dropwise. The molar ratio of oxidant to sulfuric acid was 1:1.7, and the liquid material accounted for 40.3% of the reactor volume. The reaction temperature was 120℃, and the reaction progress was monitored by TLC. The reaction time was 16h. The conversion rate of m-nitrotoluene was 92%, and the selectivity of nitrobenzaldehyde was 98.5%. The catalyst could be recycled 17 times without significant decrease in activity (conversion rate of m-nitrotoluene was 91%, and selectivity of m-nitrobenzaldehyde was 96.5%).

[0050] Example 8

[0051] 10g of phosphomolybdate catalyst and 8g of silicotungstenate catalyst were added to a batch reactor. The phosphomolybdate catalyst contained 0.3g of Na ions, and the silicotungstenate catalyst contained 0.06g of Cs ions. 53.6g of 0.36% sodium hypochlorite oxidant was added to the batch reactor, followed by 50mL of p-nitrotoluene and 400mL of nitrobenzene. Then, 216mL of 5mol / L sulfuric acid solution was added dropwise. The molar ratio of oxidant to sulfuric acid was 1:1.5, and the liquid material accounted for 60.8% of the reactor volume. The reaction temperature was 95℃, and the reaction progress was monitored by TLC for 13 hours. The conversion rate of p-nitrotoluene was 87%, and the selectivity of nitrobenzenealdehyde was 99.4%. The catalyst could be recycled 15 times without significant decrease in activity (p-nitrotoluene conversion rate 86%, p-nitrobenzenealdehyde selectivity 97.9%).

[0052] Comparative Example 1: No oxidant added

[0053] 10g of phosphomolybdate catalyst containing 0.3g of Na ions and 0.1g of K ions was added to a batch reactor. No oxidant was added to this system. 50mL of o-nitrotoluene and 250mL of n-hexane were added to the batch reactor, followed by the dropwise addition of 137mL of 7mol / L sulfuric acid solution. The liquid content comprised 43.7% of the reactor volume. The reaction temperature was 60℃, and the reaction time was 8 hours. The conversion rate of o-nitrotoluene was 26%, and the selectivity of nitrobenzaldehyde was 15.3%.

[0054] As can be seen from the results of Example 1 and Comparative Example 1, concentrated sulfuric acid itself has limited oxidizing power. Without the addition of an oxidant, the conversion rate of o-nitrotoluene and the selectivity of the target product are both low.

[0055] Comparative Example 2: Without using concentrated sulfuric acid

[0056] 15g of phosphotungstenate catalyst containing 0.45g of Rb ions was added to a batch reactor. 47.6g of sodium hypochlorite oxidant was also added to the batch reactor. 50mL of m-nitrotoluene and 200mL of n-hexane were added, respectively. The reaction temperature was 80℃, and the reaction time was 10h. The conversion rate of m-nitrotoluene was 17%, and the selectivity of nitrobenzaldehyde was 5.6%.

[0057] The results of Example 2 and Comparative Example 2 show that when concentrated sulfuric acid is not used, the conversion rate of nitrotoluene and the selectivity of the target product are both low, indicating that concentrated sulfuric acid provides a good oxidizing environment for the oxidation reaction.

[0058] Comparative Example 3: No catalyst used

[0059] No catalyst was added to this system. 60.8 g of 30 wt% hydrogen peroxide oxidant was added to a batch reactor, followed by 50 mL of p-nitrotoluene and 150 mL of n-hexane. Then, 213 mL of 9 mol / L sulfuric acid solution was added dropwise. The molar ratio of oxidant to sulfuric acid was 1:3.6, the liquid material accounted for 41.3% of the reactor volume, the reaction temperature was 90℃, and the reaction time was 12 h. The conversion rate of p-nitrotoluene was 44%, and the selectivity of nitrobenzaldehyde was 51.2%.

[0060] The results of Example 3 and Comparative Example 3 show that without a catalyst, the reaction is complex and cannot be directionally controlled to specifically prepare nitrobenzaldehyde.

[0061] As can be seen from the above examples and comparative examples, the method for preparing nitrobenzaldehyde by direct oxidation of nitrobenzyl toluene provided by the present invention has the advantages of high conversion rate and good selectivity.

[0062] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing nitrobenzaldehyde by direct oxidation of nitrobenzyl toluene, characterized in that, The process includes the following steps: mixing nitrotoluene, an organic solvent, a catalyst, an oxidant, and a strongly oxidizing acid to carry out an oxidation reaction, thereby obtaining nitrobenzaldehyde; The catalyst is a heteropolyacid salt; The oxidant is Mn2O3, sodium hypochlorite, or hydrogen peroxide; The nitrotoluene is ortho-nitrotoluene or meta-nitrotoluene; The heteropoly acid salt is one or more of phosphomolybdate, phosphotungstate, and silicotungstate; the phosphomolybdate may or may not contain water of crystallization, and its molecular formula is M3PMo. 12 O 40 ·nH2O; the phosphotungstic acid may or may not contain water of crystallization, and its molecular formula is M6P2W. 18 O 62 ·nH2O; the silicotungstic acid may or may not contain water of crystallization, and its molecular formula is M4SiW 12 O 40 ·nH2O; the metal cation in the heteropolyacid salt is one or more of Na, K, Rb, Cs, Mg, Ca and Ba; The acid with strong oxidizing properties is concentrated sulfuric acid; the concentration of the concentrated sulfuric acid is 5~9 mol / L; The molar ratio of the oxidant to nitrotoluene is (0.9~2.0):1; The amount of catalyst used is 1-18 wt% of nitrotoluene; The molar ratio of the oxidant to the acid with strong oxidizing power is 1:(1.5~10). The oxidation reaction is carried out at a temperature of 60~130℃.

2. The method according to claim 1, characterized in that, The organic solvent includes one or more of liquid alkanes, liquid cycloalkanes, liquid aromatic hydrocarbons, and derivatives of liquid aromatic hydrocarbons; the derivatives of liquid aromatic hydrocarbons are one or more of anisole, chlorobenzene, and nitrobenzene.

3. The method according to claim 1 or 2, characterized in that, The volume ratio of the nitrotoluene to the organic solvent is 1:(1~5).