Method for preparing medium-chain carboxylic acid from cyclohexanone compound

Abstract

The invention relates to a method for preparing medium-chain carboxylic acid from a cyclohexanone compound, which is characterized in that an alpha-C-C bond of the cyclohexanone compound is driven by an iron-anthraquinone photocatalytic system to crack at 0 DEG C to directly generate the medium-chain carboxylic acid. According to the method, the cyclohexanone compound is efficiently catalyzed by visible light to generate the medium-chain carboxylic acid under a mild condition. An anthraquinone (AQ) compound is used as a photocatalyst, an acidic auxiliary agent is used, and the yield of hexanoic acid prepared from cyclohexanone is 80% through visible light excitation in a low-carbon alcohol / 1-phenylethanol mixed solvent. Dependence of a traditional process on high temperature or a strong oxidant is avoided, and the method has the advantages of being environmentally friendly, easy to operate, low in energy consumption and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of organic synthesis, and particularly relates to a method for preparing medium-chain carboxylic acid from cyclohexanone compounds. BACKGROUND

[0002] Medium-chain carboxylic acid (MCCA, C6-C12) has wide application value in the fields of food, medicine, chemical industry and energy. Its derivatives are the core raw materials of the perfume industry, which are used for liquor flavoring, food flavoring and preparation of cosmetic fragrances. In addition, medium-chain carboxylic acid can be used as a precursor of liquid biofuel due to its low solubility and high energy density, and can be further upgraded to high-value hexyl hexanoate and applied to the field of sustainable energy. In recent years, with the increasing demand for environmental protection, the technology for synthesizing medium-chain carboxylic acid from renewable resources such as kitchen waste and agricultural waste has attracted much attention. Not only does it realize the high-value utilization of waste, but also reduces the dependence on fossil raw materials for traditional chemical synthesis, which is in line with the development trend of green chemical industry.

[0003] There are three major methods for the industrial synthesis of medium-chain carboxylic acid: direct extraction method, chemical synthesis method and biological synthesis method. The direct extraction method extracts medium-chain carboxylic acid by hydrolysis of animal and vegetable fats or separation of natural products, but is limited by the limited source of raw materials, high extraction cost and difficult to guarantee the purity, and is less used in industrial scale. The chemical synthesis method usually includes the oxidation of secondary alcohol and the oxidation of primary alcohol. The oxidation of secondary alcohol uses secondary alcohol as raw material and nitric acid as oxidant to generate medium-chain carboxylic acid through oxidation reaction, which is the mainstream chemical synthesis process in China. However, the traditional batch reaction has safety hazards (such as overflow and explosion), high energy consumption and poor selectivity. In recent years, the continuous oxidation process has significantly improved the production efficiency by optimizing material circulation and heat recovery through layered reaction design, and has reduced the risk of overflow. The oxidation of primary alcohol is a method in which primary alcohol is oxidized to generate corresponding medium-chain carboxylic acid under the action of catalysts such as platinum and palladium. This method has high conversion rate, but requires high temperature (200-300℃) and noble metal catalyst, which is high in cost and difficult to control side reactions, and is limited in industrial application. The biological synthesis method uses renewable resources as substrate, and has mild reaction conditions, which has become a research hotspot in recent years. Through the diversion fermentation strategy, kitchen waste is divided into ethanol fermentation section and hydrolysis acidification section, and endogenous ethanol and volatile fatty acids (VFAs) are used as electron donor and acceptor to synthesize various medium-chain carboxylic acids through carbon chain extension reaction, with a yield of 122.07 mg COD / g VS and a carbon conversion efficiency of 87.3%. Although the biological synthesis method has obvious advantages in terms of raw material sustainability and process greenness, it still faces problems such as poor stability of bacterial flora, low mass transfer efficiency and high cost of large-scale production.

[0004] In summary, the existing technology for synthesizing medium-chain carboxylic acid has the following problems:

[0005] (1) The synthesis efficiency is low, the extraction cost is high, and the product purity is difficult to meet industrial needs (direct extraction)

[0006] (2) There are potential safety hazards such as overflow and explosion during the reaction process, high costs, and difficult to control side reactions. (Chemical synthesis method)

[0007] (3) Bacterial strain degeneration and the metabolic pathways of functional strains (such as Clostridium kluyveri) are easily affected by the environment, requiring frequent optimization of culture conditions, and the cost of large-scale production is high (biosynthesis method). Summary of the Invention

[0008] To address the technical problems in the background art, the present invention provides a method for directly generating high-value-added medium-chain carboxylic acids by driving the α-C-C bond cleavage of cyclohexanone compounds at 0°C using an iron-anthraquinone (Fe / AQ) photocatalytic system. This strategy relies on inexpensive and readily available catalysts and raw materials as the reaction system, using environmentally friendly light to catalyze the reaction, achieving efficient reaction conversion and precise control of the reaction pathway, significantly improving functional group compatibility and regioselectivity. The resulting product can meet the needs of practical applications.

[0009] Specifically, the present invention provides a method for preparing medium-chain carboxylic acids from cyclohexanone compounds. This method utilizes an iron-anthraquinone (Fe / AQ) photocatalytic system to drive the α-C-C bond cleavage of cyclohexanone compounds at 0°C, directly generating medium-chain carboxylic acids. This method, based on inexpensive catalysts and green oxidants, utilizes light energy to precisely control the reaction pathway, significantly improving conversion efficiency and selectivity. The resulting product purity meets the requirements for industrial application.

[0010] The method comprises the following steps: reacting a cyclohexanone compound, an iron salt catalyst, an anthraquinone photocatalyst, an acidic auxiliary agent and an oxidant in a mixed solvent under visible light irradiation, the reaction temperature being -10 to 20°C (preferably 0°C) and the irradiation time being 1 to 10 hours.

[0011] For the technical solution described above, preferably, the structural formula of the cyclohexanone compound is as shown in general formula (II):

[0012]

[0013] in:

[0014] R1 and R2 are each independently selected from one of hydrogen, halogen, alkyl of 1-3 carbon atoms, amide, aryl, and ester groups; more preferably, the halogen is selected from one of F, Cl, Br, and I; the aryl is phenyl; the alkyl is selected from one of methyl, ethyl, and propyl; the amide is acetamido; the aryl is phenyl; and the ester is ethoxycarbonyl.

[0015] More preferably, ①.R1=H, R2=H, ②.R1=H, R2=methyl, ③.R1=H, R2=ethyl, ④.R1=H, R2=propyl, ⑤.R1=H, R2=acetylamino, ⑥.R1=H, R2=phenyl, ⑦.R1=H, R2=ethoxycarbonyl, ⑧.R1=F, R2=F, ⑨.R1=Cl, R2=Cl, ⑩.R1=methyl, R2=methyl; more specifically, the preferred structures are shown in general formula (I) (II) (III) and structural formula (IV), (V):

[0016]

[0017] In general formula (I), R is one of hydrogen atom, methyl, ethyl, propyl, acetylamino, phenyl, ethoxycarbonyl;

[0018] R is one of hydrogen atom, methyl, ethyl, propyl, acetylamino, phenyl, ethoxycarbonyl;

[0019] In general formula (II), R1 is one of methyl, fluorine atom, chlorine atom;

[0020] R1 is one of methyl, fluorine atom, chlorine atom;

[0021] In general formula (III), R2 is one of oxygen atom, methylamino, sulfur atom;

[0022] R2 is one of oxygen atom, methylamino, sulfur atom;

[0023] Structural formula (IV) and structural formula (V) are 2-adamantanone and cyclohexanone ethylene ketal, respectively.

[0024] For the technical solution described above, preferably, the iron salt catalyst is Fe3+ or Fe2+ salt (preferably Fe2(SO4)3, the amount is 0.01-0.05 mol% of the molar amount of cyclohexanone compound, more preferably 0.025 mol%);

[0025] For the technical solution described above, preferably, the anthraquinone photocatalyst is 2-ethylanthraquinone (EAQ), anthraquinone-2-carboxylic acid or 2-tert-butylanthraquinone; the amount is 5-15 mol% of the molar amount of cyclohexanone compound, more preferably 10 mol%);

[0026] For the technical solution described above, preferably, the acidic auxiliary is p-toluenesulfonic acid (TsOH), hydrochloric acid or trifluoromethanesulfonic acid; the amount is 10-15 mol% of the molar amount of cyclohexanone compound, more preferably 12 mol%);

[0027] For the technical solution described above, preferably, the mixed solvent is composed of isopropyl alcohol and 1-phenylethanol in a volume ratio of 2-5:1 (preferably 4:1);

[0028] For the technical solutions described above, preferably, the oxidizing agent is 30wt% hydrogen peroxide, and the molar ratio of the hydrogen peroxide to the cyclohexanone compound is 1.5-2:1;

[0029] For the technical solutions described above, preferably, the light source is an LED lamp with a wavelength of 350-450nm (preferably 427nm, power 100W);

[0030] For the technical solutions described above, preferably, the product is separated by column chromatography after the reaction is completed (preferably, the eluent is petroleum ether: ethyl acetate = 20:1, containing 1% formic acid).

[0031] The beneficial effects of the present application are:

[0032] (1) high efficiency and selectivity:

[0033] The yield of cyclohexanone as the substrate is ≥80%, and the reaction time is shortened to 3 hours;

[0034] The α-C-C bond of the electron-withdrawing substituted cyclohexanone derivative (such as 4-phenylcyclohexanone, 4-ethoxycarbonylcyclohexanone) is cleaved, and the yield is 60-82%.

[0035] (2) safety and cost optimization:

[0036] Normal temperature and pressure operation, avoiding the explosion risk of high temperature and nitric acid oxidation method;

[0037] The cost of iron salt catalyst is reduced by 90% compared with noble metals (platinum, palladium), and the production cost of ton hexanoic acid is reduced by 40%.

[0038] (3) Process greenization:

[0039] Hydrogen peroxide is used as a green oxidizing agent, and the COD value of wastewater is reduced by 85% compared with the nitric acid process;

[0040] The recycling rate of the mixed solvent is >98%, and the waste solvent discharge is reduced by 70%.

[0041] (4) Product quality advantage:

[0042] The one-step separation yield of column chromatography is ≥90%, and the purity reaches the pharmaceutical grade standard (Example 1, GC >99%);

[0043] The nuclear magnetic resonance spectrum verifies that the product structure has no impurity residue, which directly meets the requirements of industrial application. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 : It is the nuclear magnetic hydrogen spectrum of n-hexanoic acid. The figure shows that the purity of n-hexanoic acid product is high. It proves the accuracy of the number of hydrogen atoms in the nuclear magnetic hydrogen spectrum of n-hexanoic acid and the accuracy of its structure.

[0045] Figure 2 Figure 9 is the 13C NMR spectrum of n-hexanoic acid; the results shown in the figure prove the high purity of the n-hexanoic acid product; and the accuracy of the number of carbon atoms and the accuracy of the structure of n-hexanoic acid in the 13C NMR spectrum are proved. DETAILED DESCRIPTION

[0046] In order for those skilled in the art to better understand the present application, the present application is further described below by way of examples, but these examples cannot limit the scope of the present application, and the technical means used in the examples are conventional means known to those skilled in the art.

[0047] In the present application, unless otherwise specified, the experimental methods used are conventional methods, and the materials, reagents, etc. used can be purchased through commercial channels.

[0048] The reaction equation for generating medium-chain carboxylic acid from cyclohexanone is as follows:

[0049]

[0050] The high-yield (≥60%) examples (such as Examples 1, 7-12) prove the promotion of the reaction efficiency by specific substituents, and demonstrate the superiority of the technical solution.

[0051] The medium-yield (40%-60%) examples (Examples 2-6) demonstrate the applicable boundaries.

[0052] Example 1

[0053] Cyclohexanone (0.1864 g, 1.9 mmol), 2-ethylanthraquinone (EAQ, 0.0449 g, 0.19 mmol), p-toluenesulfonic acid monohydrate (TsOH·H2O, 0.0437 g, 0.23 mmol), isopropanol (1.569 g, 26.1 mmol), and 1-phenylethanol (0.798 g, 6.53 mmol) were added to a jacketed quartz reactor. A ferric sulfate (III) stock solution was prepared by dissolving 0.09497 g of ferric sulfate (III) in deionized water and transferring to a 10 mL volumetric flask to make up to volume. Using a micropipette, 20 microliters of this solution was added to the reaction mixture. The system was allowed to reach thermal equilibrium by circulating coolant through the jacket and placing a stir bar in it. A 30 wt% aqueous hydrogen peroxide solution (0.377 g, 3.325 mmol) was added over 1 minute using a syringe pump. The reaction was carried out under irradiation from a 427 nm LED light source mounted on top and an air atmosphere with vigorous stirring (800 rpm) for 3 h. After the reaction was completed, the solvent was evaporated, and column chromatography was performed using petroleum ether: ethyl acetate = 20:1 and 1% formic acid to obtain n-hexanoic acid, with an isolated yield of 80% (0.177 g).

[0054] Example 2

[0055] Into a jacketed quartz reactor was added 4-methylcyclohexanone (0.2130 g, 1.9 mmol), 2-ethylanthraquinone (EAQ, 0.0449 g, 0.19 mmol), p-toluenesulfonic acid monohydrate (TsOH-H20, 0.0437 g, 0.23 mmol), isopropyl alcohol (1.569 g, 26.1 mmol), and 1-phenylethanol (0.798 g, 6.53 mmol). A ferric sulfate (III) stock solution was prepared by dissolving 0.09497 g of ferric sulfate (III) in deionized water and transferring to a 10 mL volumetric flask and making up to volume. Using a micropipette, 20 microliters of this solution was added to the reaction mixture. After the jacket was circulated with coolant and a stir bar was placed in, the system was allowed to come to thermal equilibrium. A 30 wt% aqueous hydrogen peroxide solution (0.377 g, 3.325 mmol) was added over 1 minute using a syringe pump. The reaction was run under irradiation from a 427 nm LED light source mounted on top and an air atmosphere with vigorous stirring (800 rpm) for 6 h. After the reaction was complete, the solvent was spun down and column chromatography using petroleum ether: ethyl acetate = 20: 1 and 1% formic acid gave 4-methylhexanoic acid in 55% isolated yield. (0.1352 g)

[0056] Example 3

[0057] Into a jacketed quartz reactor was added 4-methylcyclohexanone (0.2130 g, 1.9 mmol), 2-ethylanthraquinone (EAQ, 0.0449 g, 0.19 mmol), p-toluenesulfonic acid monohydrate (TsOH-H20, 0.0437 g, 0.23 mmol), isopropyl alcohol (1.569 g, 26.1 mmol), and 1-phenylethanol (0.798 g, 6.53 mmol). A ferric sulfate (III) stock solution was prepared by dissolving 0.09497 g of ferric sulfate (III) in deionized water and transferring to a 10 mL volumetric flask and making up to volume. Using a micropipette, 20 microliters of this solution was added to the reaction mixture. After the jacket was circulated with coolant and a stir bar was placed in, the system was allowed to come to thermal equilibrium. A 30 wt% aqueous hydrogen peroxide solution (0.377 g, 3.325 mmol) was added over 1 minute using a syringe pump. The reaction was run under irradiation from a 427 nm LED light source mounted on top and an air atmosphere with vigorous stirring (800 rpm) for 6 h. After the reaction was complete, the solvent was spun down and column chromatography using petroleum ether: ethyl acetate = 20: 1 and 1% formic acid gave 4-methylhexanoic acid in 55% isolated yield. (0.1352 g)

[0058] Example 4

[0059] Into a jacketed quartz reactor was added 4-propylcyclohexanone (0.2662 g, 1.9 mmol), 2-ethylanthraquinone (EAQ, 0.0449 g, 0.19 mmol), p-toluenesulfonic acid monohydrate (TsOH-H20, 0.0437 g, 0.23 mmol), isopropyl alcohol (1.569 g, 26.1 mmol), and 1-phenylethanol (0.798 g, 6.53 mmol). A ferric sulfate (III) stock solution was prepared by dissolving 0.09497 g of ferric sulfate (III) in deionized water and transferring to a 10 mL volumetric flask and making up to volume. Using a micropipette, 20 microliters of this solution was added to the reaction mixture. After the jacket was circulated with coolant and a stir bar was placed in the reactor, the system was allowed to come to thermal equilibrium. A 30 wt% aqueous hydrogen peroxide solution (0.377 g, 3.325 mmol) was added over 1 minute using a syringe pump. The reaction was irradiated with a 427 nm LED light source mounted on top and under an air atmosphere with vigorous stirring (800 rpm) for 6 h. After the reaction was complete, the solvent was evaporated and column chromatography using petroleum ether: ethyl acetate = 20: 1 and 1% formic acid gave 4-ethylheptanoic acid in 45% isolated yield. (0.1352 g)

[0060] Example 5

[0061] Into a jacketed quartz reactor was added 4,4-dimethylcyclohexanone (0.2396 g, 1.9 mmol), 2-ethylanthraquinone (EAQ, 0.0449 g, 0.19 mmol), p-toluenesulfonic acid monohydrate (TsOH-H20, 0.0437 g, 0.23 mmol), isopropyl alcohol (1.569 g, 26.1 mmol), and 1-phenylethanol (0.798 g, 6.53 mmol). A ferric sulfate (III) stock solution was prepared by dissolving 0.09497 g of ferric sulfate (III) in deionized water and transferring to a 10 mL volumetric flask and making up to volume. Using a micropipette, 20 microliters of this solution was added to the reaction mixture. After the jacket was circulated with coolant and a stir bar was placed in the reactor, the system was allowed to come to thermal equilibrium. A 30 wt% aqueous hydrogen peroxide solution (0.377 g, 3.325 mmol) was added over 1 minute using a syringe pump. The reaction was irradiated with a 427 nm LED light source mounted on top and under an air atmosphere with vigorous stirring (800 rpm) for 6 h. After the reaction was complete, the solvent was evaporated and column chromatography using petroleum ether: ethyl acetate = 20: 1 and 1% formic acid gave 4,4-dimethylhexanoic acid in 47% isolated yield. (0.1295 g)

[0062] Example 6

[0063] Into a jacketed quartz reactor was added 2-adamantanone (0.2854 g, 1.9 mmol), 2- ethylanthraquinone (EAQ, 0.0449 g, 0.19 mmol), p-toluenesulfonic acid monohydrate (TsOH-H20, 0.0437 g, 0.23 mmol), isopropyl alcohol (1.569 g, 26.1 mmol), and 1-phenylethanol (0.798 g, 6.53 mmol). A ferric sulfate (III) stock solution was prepared by dissolving 0.09497 g of ferric sulfate (III) in deionized water and transferring to a 10 mL volumetric flask and making up to volume. Using a micropipette, 20 microliters of this solution was added to the reaction mixture. After the jacket was circulated with coolant and a stir bar was placed in, the system was allowed to come to thermal equilibrium. A 30 wt% aqueous hydrogen peroxide solution (0.377 g, 3.325 mmol) was added over 1 minute via syringe pump. The reaction was run under irradiation from a 427 nm LED light source mounted on top and an air atmosphere with vigorous stirring (800 rpm) for 6 h. After the reaction was complete, the solvent was spun down and column chromatography was performed using petroleum ether: ethyl acetate = 20: 1 and 1% formic acid to give bicyclo[3.3.1]nonane-3-carboxylic acid 4-ethyl ester with an isolated yield of 41% (0.1316 g).

[0064] Example 7

[0065] Into a jacketed quartz reactor was added 2-adamantanone (0.2854 g, 1.9 mmol), 2- ethylanthraquinone (EAQ, 0.0449 g, 0.19 mmol), p-toluenesulfonic acid monohydrate (TsOH-H20, 0.0437 g, 0.23 mmol), isopropyl alcohol (1.569 g, 26.1 mmol), and 1-phenylethanol (0.798 g, 6.53 mmol). A ferric sulfate (III) stock solution was prepared by dissolving 0.09497 g of ferric sulfate (III) in deionized water and transferring to a 10 mL volumetric flask and making up to volume. Using a micropipette, 20 microliters of this solution was added to the reaction mixture. After the jacket was circulated with coolant and a stir bar was placed in, the system was allowed to come to thermal equilibrium. A 30 wt% aqueous hydrogen peroxide solution (0.377 g, 3.325 mmol) was added over 1 minute via syringe pump. The reaction was run under irradiation from a 427 nm LED light source mounted on top and an air atmosphere with vigorous stirring (800 rpm) for 6 h. After the reaction was complete, the solvent was spun down and column chromatography was performed using petroleum ether: ethyl acetate = 20: 1 and 1% formic acid to give bicyclo[3.3.1]nonane-3-carboxylic acid 4-ethyl ester with an isolated yield of 41% (0.1316 g).

[0066] Example 8

[0067] To a jacketed quartz reactor was added 4-phenylcyclohexanone (0.3308 g, 1.9 mmol), 2-ethylanthraquinone (EAQ, 0.0449 g, 0.19 mmol), p-toluenesulfonic acid monohydrate (TsOH-H2O, 0.0437 g, 0.23 mmol), isopropyl alcohol (1.569 g, 26.1 mmol), and 1-phenylethanol (0.798 g, 6.53 mmol). A stock solution of iron (III) sulfate was prepared by dissolving 0.09497 g of iron (III) sulfate in deionized water and transferring to a 10 mL volumetric flask and making up to volume. Using a micropipette, 20 microliters of this solution was added to the reaction mixture. After the jacket was circulated with coolant and a stir bar was placed in the reactor, the system was allowed to come to thermal equilibrium. A 30 wt% solution of hydrogen peroxide in water (0.377 g, 3.325 mmol) was added over 1 minute using a syringe pump. The reaction was irradiated with a 427 nm LED light source mounted on top and an air atmosphere with vigorous stirring (800 rpm) for 6 h. After the reaction was complete, the solvent was evaporated and column chromatography using petroleum ether: ethyl acetate = 20: 1 and 1% formic acid gave 4-phenylhexanoic acid in 72% isolated yield. (0.2635 g)

[0068] Example 9

[0069] To a jacketed quartz reactor was added 4-phenylcyclohexanone (0.3308 g, 1.9 mmol), 2-ethylanthraquinone (EAQ, 0.0449 g, 0.19 mmol), p-toluenesulfonic acid monohydrate (TsOH-H2O, 0.0437 g, 0.23 mmol), isopropyl alcohol (1.569 g, 26.1 mmol), and 1-phenylethanol (0.798 g, 6.53 mmol). A stock solution of iron (III) sulfate was prepared by dissolving 0.09497 g of iron (III) sulfate in deionized water and transferring to a 10 mL volumetric flask and making up to volume. Using a micropipette, 20 microliters of this solution was added to the reaction mixture. After the jacket was circulated with coolant and a stir bar was placed in the reactor, the system was allowed to come to thermal equilibrium. A 30 wt% solution of hydrogen peroxide in water (0.377 g, 3.325 mmol) was added over 1 minute using a syringe pump. The reaction was irradiated with a 427 nm LED light source mounted on top and an air atmosphere with vigorous stirring (800 rpm) for 6 h. After the reaction was complete, the solvent was evaporated and column chromatography using petroleum ether: ethyl acetate = 20: 1 and 1% formic acid gave 4-phenylhexanoic acid in 72% isolated yield. (0.2635 g)

[0070] Example 10

[0071] Into a jacketed quartz reactor was added 4-cyclohexanone ethyl carbonate (0.3232 g, 1.9 mmol), 2-ethylanthraquinone (EAQ, 0.0449 g, 0.19 mmol), p-toluenesulfonic acid monohydrate (TsOH-H20, 0.0437 g, 0.23 mmol), isopropyl alcohol (1.569 g, 26.1 mmol), and 1-phenylethanol (0.798 g, 6.53 mmol). A ferric sulfate (III) stock solution was prepared by dissolving 0.09497 g of ferric sulfate (III) in deionized water and transferring to a 10 mL volumetric flask and making up to volume. Using a micropipette, 20 microliters of this solution was added to the reaction mixture. After the jacket was circulated with coolant and a stir bar was placed in the reactor, the system was allowed to come to thermal equilibrium. A 30 wt% aqueous hydrogen peroxide solution (0.377 g, 3.325 mmol) was added over 1 minute using a syringe pump. The reaction was irradiated with a 427 nm LED light source mounted on top and under an air atmosphere with vigorous stirring (800 rpm) for 6 h. After the reaction was complete, the solvent was evaporated and column chromatography using petroleum ether: ethyl acetate = 20: 1 and 1% formic acid gave 4- ethoxycarbonylhexanoic acid in 62% isolated yield (0.2223 g).

[0072] Example 11

[0073] Into a jacketed quartz reactor was added 2,2-pentamethylene-l,3-dioxolane (0.2700 g, 1.9 mmol), 2-ethylanthraquinone (EAQ, 0.0449 g, 0.19 mmol), p-toluenesulfonic acid monohydrate (TsOH-H20, 0.0437 g, 0.23 mmol), isopropyl alcohol (1.569 g, 26.1 mmol), and 1-phenylethanol (0.798 g, 6.53 mmol). A ferric sulfate (III) stock solution was prepared by dissolving 0.09497 g of ferric sulfate (III) in deionized water and transferring to a 10 mL volumetric flask and making up to volume. Using a micropipette, 20 microliters of this solution was added to the reaction mixture. After the jacket was circulated with coolant and a stir bar was placed in the reactor, the system was allowed to come to thermal equilibrium. A 30 wt% aqueous hydrogen peroxide solution (0.377 g, 3.325 mmol) was added over 1 minute using a syringe pump. The reaction was irradiated with a 427 nm LED light source mounted on top and under an air atmosphere with vigorous stirring (800 rpm) for 6 h. After the reaction was complete, the solvent was evaporated and column chromatography using petroleum ether: ethyl acetate = 20: 1 and 1% formic acid gave n-hexanoic acid in 74% isolated yield (0.1632 g).

[0074] Example 12

[0075] Tetrahydro-4H-pyran-4-one (0.1901 g, 1.9 mmol), 2-ethylanthraquinone (EAQ, 0.0449 g, 0.19 mmol), p-toluenesulfonic acid monohydrate (TsOH-H20, 0.0437 g, 0.23 mmol), isopropanol (1.569 g, 26.1 mmol), and 1-phenylethanol (0.798 g, 6.53 mmol) were added to a jacketed quartz reactor. A stock solution of iron (III) sulfate was prepared by dissolving 0.09497 g of iron (III) sulfate in deionized water and transferring to a 10 mL volumetric flask and making up to volume. Using a micropipette, 20 microliters of this solution was added to the reaction mixture. The system was allowed to come to thermal equilibrium by circulating coolant through the jacket and placing a stir bar in the reactor. A 30 wt% aqueous hydrogen peroxide solution (0.377 g, 3.325 mmol) was added over 1 minute using a syringe pump. The reaction was irradiated with a 427 nm LED light source mounted on top and an air atmosphere with vigorous stirring (800 rpm) for 6 h. After the reaction was complete, the solvent was spun down and column chromatography using petroleum ether: ethyl acetate = 20: 1 and 1% formic acid gave 3-ethoxypropanoic acid in 68% isolated yield (0.1521 g).

[0076] The above description is only the preferred specific embodiments of the application, but the protection scope of the application is not limited to this. The changes or replacements within the disclosed technical scope of the application can be easily thought by the person skilled in the art, which should be covered in the protection scope of the application. Therefore, the protection scope of the application should be subject to the protection scope of the claims.

Claims

1. A method for preparing medium-chain carboxylic acids from cyclohexanone compounds, characterized in that: The following steps are involved: The iron-anthraquinone photocatalytic system, an oxidant and an acidic auxiliary are used to drive the α-CC bond cracking of cyclohexanone compounds at -10 to 20° C. to directly generate medium-chain carboxylic acids.

2. The method according to claim 1, wherein: The following steps are involved: Under visible light irradiation, cyclohexanone compounds, iron salt catalysts, anthraquinone photocatalysts, acidic auxiliary agents and oxidants are mixed in a solvent for reaction at a reaction temperature of -10 to 20° C. and an irradiation time of 1 to 10 hours.

3. The method according to claim 1 or 2, characterized in that: The structural formula of the cyclohexanone compound is shown in general formula (II): Wherein: R1 and R2 are each independently selected from one of hydrogen, halogen, alkyl group of 1-3 carbon atoms, amide group, aryl group, and ester group.

4. The method according to claim 2 or 3, characterized in that: The halogen is selected from one of F, Cl, Br, and I; the aryl group is a phenyl group; the alkyl group of 1 to 3 carbon atoms is selected from one of methyl, ethyl, and propyl groups; the amide group is an acetylamino group; the aryl group is a phenyl group; and the ester group is an ethoxycarbonyl group.

5. The method according to claim 2 or 3, characterized in that: The iron salt catalyst is Fe 3+ or Fe 2+ Salt; its amount is 0.01-0.05mol% of the molar amount of the cyclohexanone compound.

6. The method according to claim 2 or 3, characterized in that: The anthraquinone photocatalyst is 2-ethylanthraquinone, anthraquinone-2-carboxylic acid, 2-pentylanthraquinone or 2-tert-butylanthraquinone; and its usage is 2-15 mol% of the molar amount of the cyclohexanone compound.

7. The method according to claim 2 or 3, characterized in that: The acid auxiliary agent is p-toluenesulfonic acid, hydrochloric acid or trifluoromethanesulfonic acid, and its usage is 10-15 mol% of the molar amount of the cyclohexanone compound.

8. The method according to claim 2 or 3, characterized in that: The mixed solvent consists of isopropyl alcohol and 1-phenylethanol in a volume ratio of 2 to 5:

1.

9. The method according to claim 2 or 3, characterized in that: The oxidant is 10-30 wt% hydrogen peroxide, and the molar ratio of hydrogen peroxide to the cyclohexanone compound is 1.5-2:

1.

10. The method according to claim 2 or 3, characterized in that: The light source of the illumination is an LED lamp with a wavelength of 350-450nm.

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