Method for preparing hexanoic acid through catalytic oxidation of sec-octanol

Abstract

The invention discloses a method for preparing hexanoic acid by catalytic oxidation of sec-octanol, and relates to the technical field of chemical synthesis, and the method comprises the following steps: firstly, adding dichloromethane into a reaction kettle, sequentially adding sec-octanol, an oxidation catalyst, a cocatalyst and a phase transfer catalyst, and introducing oxygen for reaction to obtain a reaction product; filtering the reaction product, standing for layering, separating an organic layer into a washing kettle, adding purified water into the washing kettle, standing for 1 hour, discharging wastewater into a sewage pipe network, and washing the organic layer again to obtain a washed organic layer; placing the washed organic layer in a concentration kettle, wherein the concentrated solution is crude caproic acid; adding the crude caproic acid into a rectifying tower for reaction to obtain refined caproic acid; according to the method for preparing hexanoic acid through catalytic oxidation of sec-octanol, efficient, environment-friendly, safe and economical conversion from sec-octanol to hexanoic acid is achieved by accurately controlling reaction conditions, optimizing a catalyst system, selecting an environment-friendly oxidizing agent, simple and convenient operation steps and efficient post-treatment processes.

Description

Technical Field

[0001] The invention relates to chemical synthesis technology, and in particular to a method for preparing caproic acid by catalytic oxidation of secondary octanol. Background Art

[0002] Hexanoic acid, also known as n-hexanoic acid, is a colorless or light yellow transparent liquid with the smell of coconut oil. It is a saturated fatty acid with the chemical formula C6H 12 O2, molecular weight is 116.16. Hexanoic acid is an oily liquid at room temperature and is corrosive. The melting point of hexanoic acid is about -4°C, the boiling point is between 202-203°C, the density is 0.927g / mL at 25°C, it is slightly soluble in water, and easily soluble in organic solvents such as ethanol and ether.

[0003] Hexanoic acid is mainly used in organic synthesis, manufacturing esters for artificial flavors, manufacturing rubber and paint drying agent, and is also the main intermediate in the production of long-acting contraceptives - norethindrone caproate and tinea drugs.

[0004] Most existing methods for synthesizing caproic acid involve dropping nitric acid into 2-octanol, dehydrating under normal pressure, distilling under reduced pressure, and then distilling to obtain caproic acid after further removing water. This synthesis method requires the use of nitric acid as a reaction raw material. Due to the strong corrosiveness of nitric acid, it requires high corrosion resistance of the equipment, increases equipment maintenance costs, and has high costs for the treatment of three wastes. There are uncertain safety hazards, and the synthesis time is relatively long and the process is relatively complicated. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing caproic acid by catalytic oxidation of secondary octanol, so as to solve the above-mentioned shortcomings in the prior art.

[0006] In order to achieve the above object, the present invention provides the following technical solution: a method for preparing caproic acid by catalytic oxidation of secondary octanol, comprising:

[0007] S1, first add dichloromethane into the reactor, start stirring and add sec-octanol, oxidation catalyst, co-catalyst and phase transfer catalyst in sequence, then introduce oxygen into the reactor to react, and the reaction is considered to be complete when there is no sec-octanol point by thin layer chromatography monitoring to obtain a reaction product;

[0008] S2, stopping stirring and filtering the reaction product to obtain an intermediate product;

[0009] S3, the intermediate product was allowed to stand for stratification, the organic layer was separated into a water washing kettle, the water layer entered the acetic acid recovery kettle, pure water was added to the water washing kettle, stirred for 45 minutes and then allowed to stand for 1 hour, the wastewater was discharged into the sewage pipe network, and the organic layer was washed again to obtain a washed organic layer;

[0010] S4, placing the washed organic layer in a concentration kettle, slowly heating it to 70°C under normal pressure, and the concentrated liquid is the crude caproic acid;

[0011] S5. Add crude caproic acid into the distillation tower kettle for steam heating, collect the fraction when the pressure is -0.098MPa and the kettle temperature is 125℃~135℃, so as to obtain fine caproic acid.

[0012] Furthermore, the oxidation catalyst in S1 is tetramethylpiperidinium oxide, the co-catalyst in S1 is ferric nitrate, cupric chloride and potassium chloride, and the phase transfer catalyst in S1 is tetrabutylammonium chloride.

[0013] Furthermore, the mass ratio of the added amount of dichloromethane to octanol in S1 is 1.5:1, and the mass ratio of the added amount of octanol to oxygen in S1 is 1:0.55.

[0014] Furthermore, the mass ratio of the added amount of 2-octanol to tetramethylpiperidinyl oxide is 1:0.02-0.06.

[0015] Furthermore, the mass ratio of the added amount of 2-octanol to ferric nitrate is 1:0.02-0.07.

[0016] Furthermore, the mass ratio of the added amount of sec-octanol to cupric chloride is 1:0.02-0.07, and the mass ratio of the added amount of sec-octanol to potassium chloride is 1:0.02-0.07.

[0017] Furthermore, the temperature inside the reactor of S1 is 25-45°C.

[0018] Furthermore, the reaction conditions for introducing oxygen into the reactor for reaction in S1 are oxygen pressure of 0.25 MPa, average oxygen flow rate of 13.8 kg / h, and oxygen feeding time of 8 hours.

[0019] Furthermore, the developing solvent of the thin layer chromatography in S1 is a mixture of ethyl acetate and petroleum ether, and the mixing ratio of ethyl acetate and petroleum ether is 10:1.

[0020] Furthermore, the standing time for standing the intermediate product for stratification in S3 is 1 hour.

[0021] Compared with the prior art, the method for preparing caproic acid by catalytic oxidation of sec-octanol provided by the present invention uses tetramethylpiperidinyl oxide (TEMPO) as an oxidation catalyst, combines ferric nitrate, cupric chloride and potassium chloride as co-catalysts, and tetrabutylammonium chloride as a phase transfer catalyst, thereby constructing an efficient catalytic system, and accurately controlling the conditions in the reactor, which helps to improve the selectivity and conversion rate of the reaction, thereby ensuring the uniformity and efficiency of the reaction, reducing the generation of harmful byproducts, thereby reducing the impact on the environment, and embodying the concept of sustainable development; the reaction progress is monitored by thin layer chromatography (TLC), and the reaction is considered to be completed when no sec-octanol point appears. The method is simple and fast, convenient for experimental operation and industrial amplification, and a high-purity caproic acid product is obtained;

[0022] Precise mass ratio control helps optimize the use of raw materials, reduce waste, and improve the conversion rate of raw materials, thereby reducing production costs. In addition, this method is carried out at relatively low temperature and pressure, reducing the safety risks brought about by high temperature and high pressure operations.

[0023] In summary, this method achieves the efficient, environmentally friendly, safe and economical conversion of 2-octanol to hexanoic acid by precisely controlling the reaction conditions, optimizing the catalyst system, selecting an environmentally friendly oxidation catalyst, simple operation steps and efficient post-treatment process, and has a good prospect for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0025] Figure 1 A schematic diagram of the overall reaction principle provided by an embodiment of the present invention;

[0026] Figure 2 The present invention provides an overall schematic diagram of the method for preparing caproic acid according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0028] Embodiment 1:

[0029] See also Figure 1-Figure 2 , a method for preparing caproic acid by catalytic oxidation of secondary octanol, comprising:

[0030] S1. First, add dichloromethane into the reactor, start stirring, add 2-octanol, oxidation catalyst, co-catalyst and phase transfer catalyst in sequence, then introduce oxygen into the reactor for reaction. The reaction is considered to be complete when there is no 2-octanol point in thin layer chromatography monitoring, and a reaction product is obtained; the oxidation catalyst is tetramethyl piperidine oxide, the co-catalyst is ferric nitrate, copper chloride and potassium chloride, and the phase transfer catalyst is tetrabutylammonium chloride; the mass ratio of dichloromethane to 2-octanol is 1.5:1, the mass ratio of 2-octanol to oxygen is 1:0.55; the mass ratio of 2-octanol to tetramethyl piperidine oxide is 1:0. 02-0.06; the mass ratio of sec-octanol to ferric nitrate is 1:0.02-0.07; the mass ratio of sec-octanol to cupric chloride is 1:0.02-0.07, and the mass ratio of sec-octanol to potassium chloride is 1:0.02-0.07; the temperature in the reactor is 25-45°C; the reaction conditions for introducing oxygen into the reactor for reaction are oxygen pressure of 0.25MPa, average oxygen flow rate of 13.8kg / h, and oxygen time of 8 hours; the developing solvent for thin layer chromatography is a mixture of ethyl acetate and petroleum ether, and the mixing ratio of ethyl acetate and petroleum ether is 10:1;

[0031] The specific implementation method is to add 300kg of dichloromethane (DCM) into the reactor, start the stirring device to ensure that the materials are evenly mixed. Then add 200kg of sec-octanol, 4kg of TEMPO, and 4kg of ferric nitrate, cupric chloride, and potassium chloride in sequence, and finally add 0.4kg of tetrabutylammonium chloride. Unscrew the valve of the oxygen bottle, and adjust the oxygen pressure in the reactor to 0.25MPa through the pressure reducing valve. During the whole process, the temperature in the reactor is controlled within the range of 25-45°C, and the average oxygen flow rate is maintained at 13.8kg / h. Oxygen is continuously introduced, and the total introduction amount is 110kg, and the oxygen time is maintained for 8 hours. Thin layer chromatography is used to monitor the oxidation reaction process, and the developing agent adopts ethyl acetate / petroleum ether (ratio is 10 / 1). When no raw material sec-octanol point appears, it is considered that the reaction ends.

[0032] Oxygen is used as an oxidant, which is a clean oxidant that does not produce harmful byproducts and is beneficial to environmental protection; TEMPO is used as an oxidation catalyst, which can highly selectively oxidize 2-octanol to hexanoic acid, reduce the occurrence of side reactions, and increase the yield of the target product; iron nitrate, copper chloride and potassium chloride are used as co-catalysts to enhance the activity of the oxidation catalyst and improve the reaction efficiency; tetrabutylammonium chloride is used as a phase transfer catalyst to improve the transfer efficiency of reactants between different phases and accelerate the reaction process; during the entire reaction process, the temperature in the autoclave is controlled to fluctuate within the range of 25 to 45°C. This mild reaction condition is conducive to improving the safety of the reaction. and convenience of operation; by controlling the oxygen flow and pressure, as well as the temperature, the reaction process can be easily controlled, the operation is simple, and it is easy to industrialize; using dichloromethane as a solvent, 2-octanol and oxygen as reactants, these raw materials are relatively cheap and easy to obtain, which helps to reduce production costs; catalytic oxidation technology has the characteristics of low ignition temperature and low energy consumption. In some cases, no external heating is required after the ignition temperature is reached, and there is no open flame in the reaction process, which is safe; this method can handle almost all types of alcohol oxidation, and has a good treatment effect on low-concentration, multi-component, and non-recyclable waste gases in industries such as organic chemicals, coatings, and insulating materials.

[0033] Use thin layer chromatography to monitor the progress of oxidation reactions. Thin layer chromatography (TLC) is a commonly used chemical analysis technique used to monitor the progress of chemical reactions. The general operating procedures are as follows: take a small amount of reaction solution in the reactor and dissolve it with the least amount of developing agent, dip the sample solution with a capillary, and spot the sample on the thin layer plate to form a thin line parallel to the bottom edge of the glass plate; after blowing the sample point dry, put the plate vertically into a covered developing bottle containing the developing agent, the developing agent contacts the lower edge of the adsorbent but does not contact the sample point, cover the lid and develop until the developing agent rises to a certain height; after the developing agent is evaporated, select a suitable color development method to develop the color, measure the moving distance of the developing agent and each component, and calculate the relative movement value (Rf value) of each component;

[0034] Thin layer chromatography uses the difference in adsorption or solubility of each component in a mixture in a certain substance, or the difference in affinity with other substances, to make the solution of the mixture flow through the substance, and perform repeated adsorption or distribution, so as to separate the components.

[0035] Monitoring the content of 2-octanol by thin layer chromatography can effectively monitor the progress of chemical reactions and help workers determine whether the reaction is complete. This is a prior art and will not be described in detail here.

[0036] S2, stopping stirring and filtering the reaction product to obtain an intermediate product;

[0037] The specific implementation method is that after the oxidation reaction is completed, stirring is stopped and unreacted catalyst and co-catalyst are removed by filtration to obtain an intermediate product.

[0038] S3, the intermediate product is allowed to stand for stratification, the organic layer is separated into a water washing kettle, the water layer enters an acetic acid recovery kettle, pure water is added to the water washing kettle, stirred for 45 minutes and then allowed to stand for 1 hour, the wastewater is discharged into the sewage pipe network, and the organic layer is washed again to obtain a washed organic layer; the intermediate product is allowed to stand for 1 hour;

[0039] The specific implementation method is to let the intermediate product stand for 1 hour to separate the intermediate products. The organic layer is divided into a water washing kettle, and the water layer enters the acetic acid recovery kettle for treatment. 100 kg of pure water is added to the water washing kettle, and the mixture is stirred for 45 minutes and then allowed to stand for another hour. The wastewater is then discharged into the sewage pipe network for treatment, and the organic layer is washed twice to ensure its purity.

[0040] The standing time (1 hour) is to ensure that the two phases in the intermediate product have enough time to separate completely to avoid incomplete separation caused by incomplete mixing. The water layer enters the acetic acid recovery kettle for treatment. This step is for resource recovery and waste reduction.

[0041] The organic layer contains the target product, and it is transferred to the water washing kettle to further remove residual impurities (unreacted raw materials or by-products); 100 kg of pure water is added to the water washing kettle to further remove polar impurities dissolved in the organic layer through water washing, and stirring helps to fully contact between the water and organic layers and improve the water washing efficiency; standing is to allow the water and organic layers to separate again; the wastewater is discharged into the sewage network for treatment to meet environmental protection requirements and avoid pollution to the environment.

[0042] S4, placing the washed organic layer in a concentration kettle, slowly heating it to 70°C under normal pressure, and the concentrated liquid is the crude caproic acid;

[0043] The specific implementation method is that the organic layer after washing is transferred to a concentration kettle and slowly heated to a maximum of 70° C. under normal pressure to recover DCM therein. The liquid obtained after concentration treatment is crude caproic acid, weighing about 198.5 kg.

[0044] S5. Add crude caproic acid into the distillation tower kettle for steam heating, collect the fraction when the pressure is -0.098MPa and the kettle temperature is 125℃~135℃, so as to obtain fine caproic acid.

[0045] The specific implementation method is to add crude caproic acid into the distillation tower kettle and further purify it by steam heating. The pressure in the distillation tower kettle is set to -0.098MPa, and the kettle temperature is controlled between 125℃ and 135℃ to collect the distillate. Under this condition, 162.2kg of fine caproic acid can be finally obtained, the mass yield reaches 89.5%, and the product purity is as high as 98%.

[0046] Embodiment 2:

[0047] See also Figure 1-Figure 2 This embodiment provides a technical solution based on the first embodiment: a method for preparing caproic acid by catalytic oxidation of secondary octanol, comprising:

[0048] S1. First, add 300 kg of DCM into the reactor and start the stirring device to ensure uniform mixing. Then add 200 kg of octanol, 8 kg of TEMPO, and 9 kg each of ferric nitrate, cupric chloride and potassium chloride. Next, add 0.4 kg of tetrabutylammonium chloride; then unscrew the valve of the oxygen cylinder and adjust the oxygen pressure in the reactor to 0.25 MPa through the pressure reducing valve. During the whole process, the temperature in the reactor was controlled to fluctuate within the range of 25 to 45 ° C, and the average oxygen flow rate was maintained at 13.8 kg / h. The entire oxygen flow process lasted for 8 hours, and the total amount of oxygen introduced was 110 kg. During this period, thin layer chromatography technology was used to monitor the progress of the oxidation reaction, and ethyl acetate / petroleum ether (ratio of 10 / 1) was used as the developing agent. When no raw material octanol point was detected, the reaction was deemed to be over and the reaction product was obtained;

[0049] S2. After the oxidation reaction is completed, stirring is stopped and unreacted catalyst and co-catalyst in the reaction product are removed by filtration to obtain an intermediate product;

[0050] S3, let the intermediate product stand for 1 hour to allow the solution to fully separate. The organic layer is separated into a water washing kettle, and the water layer enters the acetic acid recovery kettle for treatment. Add 100 kg of pure water into the water washing kettle, continue stirring for 45 minutes and then stand for another hour. After that, the wastewater is discharged into the sewage pipe network for treatment. Wash the organic layer a second time to ensure thorough cleaning;

[0051] S4. After the washing, the organic layer is transferred to a concentration kettle and slowly heated to a maximum of 70° C. under normal pressure to recover DCM. The final concentrated liquid is crude caproic acid, weighing about 198.5 kg.

[0052] S5. Next, the crude product is added to the still of the distillation tower and further purified by steam heating. The pressure in the still of the distillation tower is set to -0.098MPa, and the fraction is collected when the still temperature reaches the range of 125℃ to 135℃. After this step, about 174.7kg of fine caproic acid can be obtained, with a mass yield of 96.4% and a purity of up to 98%.

[0053] Embodiment three:

[0054] See also Figure 1-Figure 2 This embodiment provides a technical solution based on the first embodiment: a method for preparing caproic acid by catalytic oxidation of secondary octanol, comprising:

[0055] S1. First, add 300kg of DCM to the reactor and start the stirring device to ensure uniform mixing. Then add 200kg of sec-octanol, 12kg of TEMPO, and 14kg each of ferric nitrate, cupric chloride and potassium chloride. Then, add 0.4kg of tetrabutylammonium chloride; then unscrew the valve of the oxygen cylinder and adjust the oxygen pressure in the reactor to 0.25MPa through the pressure reducing valve. During the whole process, the temperature in the reactor was controlled to fluctuate within the range of 25-45°C, and the average oxygen flow rate was maintained at 13.8kg / h. The whole oxygenation process lasted for 8 hours, and the total amount of oxygen introduced was 110kg. During this period, thin layer chromatography was used to monitor the progress of the oxidation reaction, and ethyl acetate / petroleum ether (ratio of 10 / 1) was used as the developing agent. When no sec-octanol point of the raw material was detected, the reaction was deemed to be over and the reaction product was obtained.

[0056] S2. After the oxidation reaction is completed, stirring is stopped and the unreacted catalyst and co-catalyst in the reaction product are removed by filtration to obtain an intermediate product.

[0057] S3, the intermediate product is allowed to stand for 1 hour to allow the solution to be fully separated. The organic layer is separated into a water washing kettle, and the water layer enters the acetic acid recovery kettle for treatment. 100 kg of pure water is added to the water washing kettle, and the stirring is continued for 45 minutes and then allowed to stand for another hour. After that, the wastewater is discharged into the sewage pipe network for treatment. The organic layer is washed with water for a second time to ensure thorough cleaning.

[0058] S4. After washing, the organic layer is transferred to a concentration kettle and slowly heated to a maximum of 70° C. under normal pressure to recover DCM. The final concentrated solution is crude caproic acid, weighing about 198.5 kg.

[0059] S5. Next, the crude product is added to the still of the distillation tower and further purified by steam heating. The pressure in the still of the distillation tower is set to -0.098MPa, and the fraction is collected when the still temperature reaches the range of 125℃ to 135℃. After this step, about 174.7kg of fine caproic acid can be obtained, with a mass yield of 96.4% and a purity of up to 98%.

[0060] The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for preparing caproic acid by catalytic oxidation of secondary octanol, characterized in that: include: S1, first add dichloromethane into the reactor, start stirring and add sec-octanol, oxidation catalyst, co-catalyst and phase transfer catalyst in sequence, then introduce oxygen into the reactor to react, and the reaction is considered to be complete when there is no sec-octanol point by thin layer chromatography monitoring to obtain a reaction product; S2, stopping stirring and filtering the reaction product to obtain an intermediate product; S3, the intermediate product was allowed to stand for stratification, the organic layer was separated into a water washing kettle, the water layer entered the acetic acid recovery kettle, pure water was added to the water washing kettle, stirred for 45 minutes and then allowed to stand for 1 hour, the wastewater was discharged into the sewage pipe network, and the organic layer was washed again to obtain a washed organic layer; S4, placing the washed organic layer in a concentration kettle, slowly heating it to 70°C under normal pressure, and the concentrated liquid is the crude caproic acid; S5. Add crude caproic acid into the distillation tower kettle for steam heating, collect the fraction when the pressure is -0.098MPa and the kettle temperature is 125℃~135℃, so as to obtain fine caproic acid.

2. The method for preparing caproic acid by catalytic oxidation of secondary octanol according to claim 1, characterized in that: The oxidation catalyst described in S1 is tetramethyl piperidine oxide, the co-catalyst described in S1 is ferric nitrate, cupric chloride and potassium chloride, and the phase transfer catalyst described in S1 is tetrabutylammonium chloride.

3. The method for preparing caproic acid by catalytic oxidation of secondary octanol according to claim 1, characterized in that: The mass ratio of the added amount of dichloromethane to octanol in S1 is 1.5:1, and the mass ratio of the added amount of octanol to oxygen in S1 is 1:0.

55.

4. The method for preparing caproic acid by catalytic oxidation of secondary octanol according to claim 2, characterized in that: The mass ratio of the added amount of 2-octanol to tetramethylpiperidinyl oxide is 1:0.02-0.

06.

5. The method for preparing caproic acid by catalytic oxidation of secondary octanol according to claim 2, characterized in that: The mass ratio of the added amount of 2-octanol to ferric nitrate is 1:0.02-0.

07.

6. The method for preparing caproic acid by catalytic oxidation of secondary octanol according to claim 2, characterized in that: The mass ratio of the added amount of sec-octanol to copper chloride is 1:0.02-0.07, and the mass ratio of the added amount of sec-octanol to potassium chloride is 1:0.02-0.

07.

7. The method for preparing caproic acid by catalytic oxidation of secondary octanol according to claim 1, characterized in that: The temperature inside the reactor of S1 is 25-45°C.

8. The method for preparing caproic acid by catalytic oxidation of secondary octanol according to claim 1, characterized in that: The reaction conditions for introducing oxygen into the reactor for reaction in S1 are as follows: an oxygen pressure of 0.25 MPa, an average oxygen flow rate of 13.8 kg / h, and an oxygen passing time of 8 hours.

9. The method for preparing caproic acid by catalytic oxidation of secondary octanol according to claim 1, characterized in that: S1 The developing solvent of the thin layer chromatography is a mixture of ethyl acetate and petroleum ether, and the mixing ratio of ethyl acetate and petroleum ether is 10:

1.

10. The method for preparing caproic acid by catalytic oxidation of secondary octanol according to claim 1, characterized in that: The intermediate product is allowed to stand for 1 hour for separation.

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