CN115433076B - Method for preparing aromatic acid by metal-free photocatalytic oxidation - Google Patents

Method for preparing aromatic acid by metal-free photocatalytic oxidation Download PDF

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CN115433076B
CN115433076B CN202211004576.6A CN202211004576A CN115433076B CN 115433076 B CN115433076 B CN 115433076B CN 202211004576 A CN202211004576 A CN 202211004576A CN 115433076 B CN115433076 B CN 115433076B
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李坚军
彭晓庆
许宁
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Zhejiang University of Technology ZJUT
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
    • C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
    • C07C51/21—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen
    • C07C51/255—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of compounds containing six-membered aromatic rings without ring-splitting
    • C07C51/265—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of compounds containing six-membered aromatic rings without ring-splitting having alkyl side chains which are oxidised to carboxyl groups
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07B—GENERAL METHODS OF ORGANIC CHEMISTRY; APPARATUS THEREFOR
    • C07B41/00—Formation or introduction of functional groups containing oxygen
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C67/00—Preparation of carboxylic acid esters
    • C07C67/28—Preparation of carboxylic acid esters by modifying the hydroxylic moiety of the ester, such modification not being an introduction of an ester group
    • C07C67/29—Preparation of carboxylic acid esters by modifying the hydroxylic moiety of the ester, such modification not being an introduction of an ester group by introduction of oxygen-containing functional groups
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    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D307/00—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom
    • C07D307/02—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom not condensed with other rings
    • C07D307/34—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom not condensed with other rings having two or three double bonds between ring members or between ring members and non-ring members
    • C07D307/56—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom not condensed with other rings having two or three double bonds between ring members or between ring members and non-ring members with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
    • C07D307/68—Carbon atoms having three bonds to hetero atoms with at the most one bond to halogen
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    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D333/00—Heterocyclic compounds containing five-membered rings having one sulfur atom as the only ring hetero atom
    • C07D333/02—Heterocyclic compounds containing five-membered rings having one sulfur atom as the only ring hetero atom not condensed with other rings
    • C07D333/04—Heterocyclic compounds containing five-membered rings having one sulfur atom as the only ring hetero atom not condensed with other rings not substituted on the ring sulphur atom
    • C07D333/26—Heterocyclic compounds containing five-membered rings having one sulfur atom as the only ring hetero atom not condensed with other rings not substituted on the ring sulphur atom with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
    • C07D333/38—Carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals
    • C07D333/40—Thiophene-2-carboxylic acid

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Abstract

The invention discloses a method for preparing aromatic acid by metal-free photocatalytic oxidation, which comprises the following steps: adding a compound shown in a formula (I), a photocatalyst and an additive into a solvent, exposing the mixture to air, stirring the mixture at 25-60 ℃ under the irradiation of a light source for reaction, and after the reaction is finished, carrying out post-treatment on the reaction solution to obtain an aromatic acid compound shown in a formula (II), wherein the reaction equation is as follows:wherein Ar is benzene ring, furyl, thienyl, naphthyl or benzophenone, and H on Ar group is R 1 Monosubstituted, substituent R 1 Is alkyl, substituted hydroxy, aldehyde or substituted alkyl, H on Ar group is replaced by R 2 Substituted or unsubstituted, R being the substituent 2 Is monosubstituted or polysubstituted, n=1-2, n is an integer, and the substituent R 2 Is alkyl, alkoxy, halogen, trifluoromethyl, aryl, substituted aryl or substituted phenolic hydroxyl. The invention uses nitrogen heterocycle as photocatalysis under illumination conditionThe preparation reduces the production cost, and has simple operation and mild reaction condition.

Description

Method for preparing aromatic acid by metal-free photocatalytic oxidation
Technical Field
The invention belongs to the technical field of organic synthesis, and particularly relates to a method for preparing aromatic acid by metal-free photocatalytic oxidation.
Background
Aromatic acid is a basic chemical raw material and is widely applied to the fields of organic synthesis of medicines, foods, pigments, plasticizers, preservatives and the like. Benzoic acid is one of the simplest aromatic acid compounds, and the annual output of China can reach 49 ten thousand tons at present, and the market demand is large. Therefore, the method utilizes a cheap and easily available raw material which can be obtained in large quantity, seeks a green and economic catalytic system for preparing the aromatic acid, and has great economic and environmental protection value in industrial production.
At present, various synthetic approaches are available for the preparation of aromatic acids, such as oxidation of aromatic hydrocarbons, benzyl alcohol, aromatic aldehydes, aromatic alkenes or aromatic alkynes, hydrolysis of acid chlorides, cyano groups, and the like. Generally, the aromatic acid is prepared by direct oxidation from cheap and easily available methyl aromatic hydrocarbon, so that the method best meets the requirement of industrial production. The most common industrial production methods of benzoic acid at present are a liquid-phase air oxidation method of toluene, a phthalic anhydride decarboxylation method, toluene chlorination hydrolysis and the like, but the process generally has the problems of high energy consumption, difficult separation of a catalyst, serious equipment corrosion pollution and the like. For example: the traditional hydrocarbon oxidation method mainly adopts strong oxidants such as potassium permanganate, nitric acid and the like, and the result is that a large amount of wastewater and solid waste containing inorganic salts are generated, so that the industrial production cost and the damage to the environment are increased. The toluene liquid phase oxidation is usually accompanied with high-temperature and high-pressure operation conditions, the energy consumption is high, most of the catalytic systems use acetic acid as a reaction solvent, and the equipment corrosion is strong. Chemists have continually optimized the benzylic oxidation system, for example, in 2016, robert Wolf et al, using a mixture of riboflavin tetraacetate and a non-heme complex, to effectively catalyze the oxidation of alkylbenzenes to ketones and carboxylic acid derivatives (Angew. Chem. Int. Ed.2016,55, 427-430). In addition, liu Wenjun et al use potassium persulfate as an oxidant to effectively oxidize methyl aromatic hydrocarbon to benzoic acid and its derivatives under the catalysis of pyridine, but the system requires the use of an excessive amount of chemical oxidant and the reaction temperature is high (Synthesis 2017,49, 4007-4016). GovindasamySekar et al developed a binaphthyl-stabilized Pt nano-ion catalyst, which achieved selective oxidation of methyl aromatic hydrocarbon without significant reduction in the reusable activity, but the catalyst had a complex structure and was costly to produce (appl. Catalyst. B. Environ.2019,250, 325-336). Although a series of progress has been made, it is still difficult to solve a series of problems such as heavy metal participation, expensive catalyst, and the need for a stoichiometric amount of oxidizing agent, and as the global environment is continuously worsened, the need for green catalytic oxidation is increasing.
The photocatalytic oxidation reaction is an emerging green oxidation process, the reaction condition of the method is mild, the method can be carried out at normal temperature and normal pressure, and the reaction operation is safe and environment-friendly. The initiation of the photoinduced reaction is not independent of the photocatalyst. The existing common photocatalyst mainly comprises transition metals such as ruthenium, palladium, rubidium, iridium and the like, and TiO 2 、ZnO、V 2 O 5 Inorganic metal oxides, metal modified supported catalysts, organic dyes, and the like. However, the existing traditional photocatalyst is generally expensive, has higher cost, is easy to cause heavy metal residue and is not beneficial to industrial production.
Therefore, it is important to find an oxidation system which is free of metal participation and in which the photocatalyst is inexpensive and readily available.
Disclosure of Invention
Aiming at the problems, the invention aims to provide a method for preparing aromatic acid by metal-free photocatalytic oxidation, which has the advantages of simple operation, low price and easy acquisition of catalyst and green method.
In order to achieve the above purpose, the following technical scheme is provided:
the method for preparing the aromatic acid by metal-free photocatalytic oxidation is characterized by comprising the following steps of: adding a compound shown in a formula (I), a photocatalyst and an additive into a solvent, exposing the mixture to air or oxygen, stirring the mixture at 25-60 ℃ under the irradiation of a light source for reaction, and after the reaction is finished, carrying out post-treatment on the reaction solution to obtain an aromatic acid compound shown in a formula (II), wherein the reaction equation is as follows:
wherein Ar is benzene ring, furyl, thienyl, naphthyl or benzophenone, and H on Ar group is R 1 Monosubstituted, substituent R 1 Is alkyl, substituted hydroxy, aldehyde or substituted alkyl, H on Ar group is replaced by R 2 Substituted or unsubstituted, R being the substituent 2 Is monosubstituted or polysubstituted, n=1-2, n is an integer, and the substituent R 2 Is alkyl, alkoxy, halogen, trifluoromethyl, aryl, substituted aryl or substituted phenolic hydroxyl;
the structure of the photocatalyst is shown as a formula (III), wherein H on the benzene ring is substituted or not substituted by a substituent R, R is halogen, methyl, alkoxy, trifluoromethoxy, nitro or acetyl when substituted,
preferably, the substituent R 1 is-CH 3 、-CH 2 OH、-CHO、-CH 2 Cl or-CH 2 OCH 3 Substituent R 2 Is methyl, methoxy, chlorine, fluorine, trifluoromethyl, benzene ring, trifluoromethyl phenyl or acetyl substituted phenolic hydroxyl.
Preferably, the solvent is acetonitrile, dichloromethane, 1, 2-dichloroethane, ethyl acetate or acetone.
Preferably, the additive is one or more of hydrochloric acid, sulfuric acid, sodium bromide, potassium chloride, tetrabutylammonium chloride and trifluoroacetic acid.
Preferably, the light source is blue light, white light or purple light, preferably purple light.
Preferably, the reaction temperature is 50-60 ℃.
Preferably, the mass ratio of the compounds of formula (I), the catalyst and the additives is 1:0.1-0.5:0.2-1, preferably 1:0.1-0.2:0.4-0.5.
Preferably, the reaction time is from 6 to 48 hours.
Preferably, the post-treatment process is as follows: the reaction mixture was quenched with saturated brine, extracted with ethyl acetate, the organic layer was separated, dried over anhydrous sodium sulfate and concentrated under reduced pressure, and finally purified on a silica gel column with petroleum ether/ethyl acetate or dichloromethane/methanol.
According to the invention, under the illumination condition, the nitrogen heterocycle is used as the photocatalyst, so that the problem of using expensive catalysts such as rare metals is solved, and the production cost is reduced. The method has the advantages of simple reaction operation, mild reaction conditions, and further cost saving by using oxygen in air as an oxidant at normal temperature and normal pressure, and is suitable for industrial popularization. In addition, the invention also utilizes the photocatalyst system to realize the synthesis of aspirin and bifidus, and further proves that the system has wide application potential in the fields of synthesizing natural products, medicine molecules and the like.
Detailed Description
The present invention will be further described with reference to examples, but the scope of the present invention is not limited thereto.
EXAMPLE 1 benzoic acid
In a 20mL reaction flask, toluene (46 mg,0.5 mmol), 6-bromobenzothiazole (21 mg,0.1 mmol), concentrated hydrochloric acid (36 wt%,25mg,0.25 mmol) and acetonitrile (2 mL) were added to the mixture, the mixture was exposed to air and was reacted under 25W of violet light with stirring at 30℃for 24 hours, the reaction solution was further washed with saturated brine, the mixture was extracted with ethyl acetate (3X 10 mL) and the combined organic phases were extracted with anhydrous Na 2 SO 4 Drying, concentrating under reduced pressure, and separating and purifying by petroleum ether/ethyl acetate column chromatography to obtain the target product benzoic acid shown as formula (II-a), wherein the yield is 76%, and the HPLC purity is 98.6%. 1 H NMR(400MHz,DMSO-d 6 )δ12.98(brs,1H),7.99–7.92(m,2H),7.62(tt,1H),7.50(t,J＝7.6Hz,2H).； 13 C NMR(100MHz,DMSO-d 6 )δ167.78,133.33,131.19,129.72,129.02.
Examples 2 to 7
Examples 2-7 in the same manner as in example 1, wherein the reaction substrates were 0.5mmol, the additives were concentrated hydrochloric acid (36 wt%) and the feed ratios of the substrates, the photocatalyst and the additives were 1:0.1:0.5, the mixture was exposed to air and reacted under irradiation of 25W of violet light, and the reaction products were benzoic acid, and the reaction conditions are shown in Table 1.
TABLE 1 specific reaction conditions for examples 2-7
Example 8 4-methylbenzoic acid
In a 20mL reaction flask, 4-methyl toluene (53 mg,0.5 mmol), 6-chlorobenzothiazole (17 mg,0.1 mmol), concentrated hydrochloric acid (36 wt%,25mg,0.25 mmol) and acetone (2 mL) were added to the mixture, the mixture was exposed to air and was reacted under 25W of violet light with stirring at 30℃for 24 hours, the reaction solution was further washed with saturated brine, the mixture was extracted with ethyl acetate (3X 10 mL), and the combined organic phases were extracted with anhydrous Na 2 SO 4 Drying, concentrating under reduced pressure, and separating and purifying by petroleum ether/ethyl acetate column chromatography to obtain the target product 4-methylbenzoic acid shown as formula (II-b), wherein the yield is 86%, and the HPLC purity is 97.8%. 1 H NMR (400MHz,DMSO-d 6 )δ12.77(brs,1H),7.84(d,J＝8.2Hz,2H),7.29(d,J＝8.0Hz,2H),2.36(s,3H)； 13 C NMR(100MHz,DMSO-d 6 )δ167.76,143.45,129.78,129.55,128.49,21.56.
Example 9 4-chlorobenzoic acid
In a 20mL reaction flask, 4-chlorotoluene (63 mg,0.5 mmol), 4-methoxybenzothiazole (16 mg,0.1 mmol), concentrated hydrochloric acid (36 wt%,20mg,0.2 mmol) and acetonitrile (2 mL) were added to the mixture, the mixture was exposed to air and irradiated with 25W of ultraviolet light, the reaction was stirred at 30℃for 20 hours, the reaction solution was further washed with saturated brine, and the mixture was washed with ethyl acetate(3×10 ml) extraction, combined organic phases with anhydrous Na 2 SO 4 Drying, concentrating under reduced pressure, and separating and purifying by petroleum ether/ethyl acetate column chromatography to obtain the target product 4-chlorobenzoic acid shown in formula (II-c), wherein the yield is 71%, and the HPLC purity is 98.6%. 1 H NMR(400MHz,DMSO-d 6 )δ13.20(brs,1H),7.94(d,J＝8.5Hz,2H),7.55(d,J＝8.6Hz,2H)； 13 C NMR(100MHz,DMSO-d 6 )δ166.92,138.26,131.58,130.06,129.17.
Example 10 4-fluorobenzoic acid
In a 20mL reaction flask, 4-fluorotoluene (55 mg,0.5 mmol), 5-bromobenzothiazole (21 mg,0.1 mmol), concentrated hydrochloric acid (36 wt%,25mg,0.25 mmol) and acetonitrile (2 mL) were added to the mixture, the mixture was connected to a tee joint with an oxygen balloon, and vacuum was applied, oxygen (1 atm) was applied, the mixture was irradiated with 25W white light, the reaction was stirred at 55℃for 24 hours, the reaction mixture was washed with saturated brine, the mixture was extracted with ethyl acetate (3X 10 mL), and the combined organic phase was dried over anhydrous Na 2 SO 4 Drying, concentrating under reduced pressure, and separating and purifying by petroleum ether/ethyl acetate column chromatography to obtain the target product 4-fluorobenzoic acid shown as formula (II-d), wherein the yield is 70%, and the HPLC purity is 98.1%.
1 H NMR (400MHz,DMSO-d 6 )δ13.08(brs,1H),8.00(dd,J＝8.8,5.6Hz,2H),7.31(t,J＝8.9Hz,2H)； 13 C NMR(100MHz,DMSO-d 6 )δ165.36(d,J＝250.4Hz),132.55(d,J＝9.5Hz),127.78(d,J＝2.7Hz),116.05(d,J＝21.9Hz).
EXAMPLE 11 4-Methoxybenzoic acid
In a 20mL reaction flask, 4-methoxytoluene (62 mg,0.5 mmol), 5-fluorobenzothiazole (15 mg,0.1 mmol), concentrated hydrochloric acid (36 wt%,25mg,0.25 mm) was addedol), methylene chloride (2 mL) was added to the mixture, the mixture was exposed to air and was reacted under ultraviolet light of 25W with stirring at 30 ℃ for 18 hours, the reaction solution was further washed with saturated brine, the mixture was extracted with ethyl acetate (3×10 mL), and the combined organic phases were extracted with anhydrous Na 2 SO 4 Drying, concentrating under reduced pressure, and separating and purifying by petroleum ether/ethyl acetate column chromatography to obtain the target product 4-methoxybenzoic acid shown as formula (II-e), wherein the yield is 91%, and the HPLC purity is 99.1%.
1 H NMR(400MHz,DMSO-d 6 )δ12.66(brs,1H),7.94–7.87(m,2H),7.04–6.99(m,2H),3.82(s,3H)； 13 C NMR(100MHz,DMSO-d 6 )δ167.48,163.28,131.80,123.39,114.25,55.86.
Example 12 4-phenylbenzoic acid
In a 20mL reaction flask, 4-phenyltoluene (84 mg,0.5 mmol), benzothiazole (26 mg,0.2 mmol), concentrated hydrochloric acid (36 wt%,30mg,0.3 mmol), 1, 2-dichloroethane (2 mL) were added to the mixture, the mixture was exposed to air and was reacted under ultraviolet light of 25W with stirring at 40℃for 20 hours, the reaction solution was further washed with saturated brine, the mixture was extracted with ethyl acetate (3X 10 mL), and the combined organic phases were extracted with anhydrous Na 2 SO 4 Drying, concentrating under reduced pressure, and separating and purifying by petroleum ether/ethyl acetate column chromatography to obtain the target product 4-phenylbenzoic acid shown in formula (II-f), wherein the yield is 98%, and the HPLC purity is 98.7%.
1 H NMR(400MHz,DMSO-d 6 )δ13.00(s,1H)8.07–8.01(m,2H),7.82–7.78(m,2H),7.75–7.71(m,2H),7.53–7.47(m,2H),7.45–7.39(m,1H)； 13 C NMR(100MHz,DMSO-d 6 )δ167.6,144.8,139.5,130.4,130.1,129.5,128.7,127.4,127.3.
EXAMPLE 13 4-Trifluoromethylbenzoic acid
In a 20mL reaction flask, 4-trifluoromethyltoluene (80 mg,0.5 mmol), 4-methylbenzothiazole (15 mg,0.1 mmol), concentrated hydrochloric acid (36 wt%,25mg,0.25 mmol) were added, acetonitrile (2 mL) was added to the mixture, the mixture was exposed to air and irradiated with blue light of 25W, the reaction was stirred at 60℃for 30 hours, the reaction solution was further washed with saturated brine, the mixture was extracted with ethyl acetate (3X 10 mL), and the combined organic phase was extracted with anhydrous Na 2 SO 4 Drying, concentrating under reduced pressure, and separating and purifying by petroleum ether/ethyl acetate column chromatography to obtain the target product 4-trifluoromethyl benzoic acid shown in formula (II-g), wherein the yield is 53%, and the HPLC purity is 97.4%.
1 H NMR(400MHz,DMSO-d 6 )δ13.50(s,1H),8.13(d,J＝8.0Hz,2H),7.85(d,J＝8.2Hz,2H)； 13 C NMR(100MHz,DMSO-d 6 )δ166.65,135.01(d,J＝1.5Hz),132.93(q,J＝31.9Hz),130.53,124.24(q,J＝273.2Hz).
EXAMPLE 14 Fumonic acid
In a 20mL reaction flask, 2-methylfuran (41 mg,0.5 mmol), 6-nitrobenzothiazole (18 mg,0.1 mmol), concentrated hydrochloric acid (36 wt%,25mg,0.25 mmol) and acetonitrile (2 mL) were added to the mixture, the mixture was exposed to air and was reacted under 25W of violet light with stirring at 25℃for 6 hours, the reaction solution was further washed with saturated brine, the mixture was extracted with ethyl acetate (3X 10 mL), and the combined organic phases were extracted with anhydrous Na 2 SO 4 Drying, concentrating under reduced pressure, and separating and purifying by petroleum ether/ethyl acetate column chromatography to obtain the target product furoic acid shown in formula (II-h), wherein the yield is 56%, and the HPLC purity is 99.1%.
1 H NMR (400MHz,DMSO-d 6 )δ13.06(s,1H),7.91(dd,J＝1.8,0.8Hz,1H),7.21(dd,J＝3.6,0.8Hz,1H),6.65(dd,J＝3.6,1.6Hz,1H)； 13 C NMR(100MHz,DMSO-d 6 )δ159.7,147.5,145.4,118.1,112.5.
Example 15 thiophene-2-carboxylic acid
In a 20mL reaction flask, 2-methylthiophene (49 mg,0.5 mmol), ethyl 5-carboxylate benzothiazole (10 mg,0.05 mmol), concentrated hydrochloric acid (36 wt%,15mg,0.15 mmol), acetonitrile (2 mL) was added to the mixture, the mixture was exposed to air and irradiated with blue light at 25W, the reaction was stirred at 25℃for 20 hours, the reaction solution was further washed with saturated brine, the mixture was extracted with ethyl acetate (3X 10 mL), and the combined organic phases were extracted with anhydrous Na 2 SO 4 Drying, concentrating under reduced pressure, and separating and purifying by petroleum ether/ethyl acetate column chromatography to obtain the target product thiophene-2-formic acid shown as formula (II-i), wherein the yield is 67%, and the HPLC purity is 98.4%.
1 H NMR(400MHz,DMSO-d 6 )δ13.05(brs,1H),7.88(d,J＝5.0Hz,1H),7.74(dd,J＝3.7,1.3Hz,1H),7.18(dd,J＝4.9,3.8Hz,1H)； 13 C NMR(100MHz,DMSO)δ163.4,135.1,133.7,133.6,128.7.
EXAMPLE 16 2, 4-dichlorobenzoic acid
In a 20mL reaction flask, 2, 4-dichlorotoluene (80 mg,0.5 mmol), 6-bromobenzothiazole (11 mg,0.05 mmol), concentrated sulfuric acid (98.3 wt%,10mg,0.1 mmol) and sodium chloride (12 mg,0.2 mmol) were added, acetonitrile (2 mL) and water (0.5 mL) were added to the mixture, the mixture was exposed to air and irradiated with 25W of violet light, the reaction was stirred at 60℃for 30 hours, the reaction solution was further washed with saturated brine, the mixture was extracted with ethyl acetate (3X 10 mL), and the combined organic phase was washed with anhydrous Na 2 SO 4 Drying, concentrating under reduced pressure, and separating and purifying by petroleum ether/ethyl acetate column chromatography to obtain the target product 2, 4-dichlorobenzoic acid shown as formula (II-j), wherein the yield is 64%, and the HPLC purity is 98.1%.
1 H NMR(400MHz,DMSO-d 6 )δ13.60(brs,1H),7.83(d,J＝8.4Hz,1H),7.73(d,J＝1.9Hz,1H),7.53(dd,J＝8.4,2.1Hz,1H)； 13 C NMR(101MHz,DMSO-d 6 )δ166.30,137.01,133.51,132.85,130.68,130.52,127.97.
EXAMPLE 17 1-naphthoic acid
In a 20mL reaction flask, 1-methylnaphthalene (71 mg,0.5 mmol), 6-bromobenzothiazole (21 mg,0.1 mmol), hydrogen bromide (68.85 wt%,59mg,0.5 mmol), acetonitrile (2 mL) was added to the mixture, the mixture was exposed to air and was reacted under ultraviolet light of 25W with stirring at 40℃for 20 hours, the reaction solution was further washed with saturated brine, the mixture was extracted with ethyl acetate (3X 10 mL), and the combined organic phases were extracted with anhydrous Na 2 SO 4 Drying, concentrating under reduced pressure, and separating and purifying by petroleum ether/ethyl acetate column chromatography to obtain the target product 1-naphthoic acid shown in formula (II-k), wherein the yield is 93%, and the HPLC purity is 97.2%. 1 H NMR(400MHz,DMSO-d 6 )δ13.16(s,1H),8.87(d,J＝8.6Hz,1H),8.21–8.13(m,2H),8.03(d,J＝8.1Hz,1H),7.70–7.53(m,3H)； 13 C NMR(101MHz,DMSO-d 6 )δ169.1,133.9,133.4,131.1,130.3,129.1,128.2,128.0,126.6,126.0,125.3.
EXAMPLE 18 4-Benzoylbenzoic acid
In a 20mL reaction flask, 4-methylbenzophenone (98 mg,0.5 mmol), 6-bromobenzothiazole (11 mg,0.05 mmol), trifluoroacetic acid (23 mg,0.2 mmol) and tetrabutylammonium chloride (56 mg,0.2 mmol) were added to the mixture, acetonitrile (2 mL) was added, the mixture was exposed to air and was reacted under 25W of violet light at 60℃for 24 hours with stirring, the reaction solution was further washed with saturated brine, the mixture was extracted with ethyl acetate (3X 10 mL), and the mixture was combinedAnhydrous Na for organic phase of (2) 2 SO 4 Drying, concentrating under reduced pressure, and separating and purifying by petroleum ether/ethyl acetate column chromatography to obtain the target product 4-benzoyl benzoic acid shown as formula (II-l), wherein the yield is 79%, and the HPLC purity is 97.6%.
1 H NMR(600MHz,DMSO-d 6 )δ13.36(s,1H),8.10(d,J＝8.0Hz,2H),7.82(d,J＝8.2Hz,2H),7.76(d,J＝7.6Hz,2H),7.70(t,J＝7.4Hz,1H),7.57(t,J＝7.6Hz,2H)；
13 C NMR(151MHz,DMSO-d 6 )δ195.8,167.1,141.0,137.0,134.5,133.6,130.2,130.1,129.9,129.1.
EXAMPLE 19 Aspirin
In a 20mL reaction flask, o-tolylacetate (75 mg,0.5 mmol), 6-bromobenzothiazole (11 mg,0.05 mmol), concentrated hydrochloric acid (36 wt%,25mg,0.25 mmol) and acetonitrile (2 mL) were added to the mixture, the mixture was exposed to air and irradiated with 25W of violet light, stirred at 30℃for 24 hours, the reaction mixture was washed with saturated brine, the mixture was extracted with ethyl acetate (3X 10 mL), and the combined organic phases were extracted with anhydrous Na 2 SO 4 Drying, concentrating under reduced pressure, and separating and purifying by petroleum ether/ethyl acetate column chromatography to obtain the target product benzoic acid shown as formula (II-m), wherein the yield is 56%, and the HPLC purity is 98.1%. 1 H NMR (600MHz,DMSO-d 6 )δ13.07(brs,1H),7.93(dd,J＝7.8,1.8Hz,1H),7.64(td,J＝7.8,1.2Hz,1H),7.38(td,J＝7.8,1.2Hz,1H),7.20(dd,J＝7.8,1.2Hz,1H)2.25(s,3H)； 13 C NMR(151MHz,DMSO-d 6 )δ169.6,166.1,150.6,134.3,131.8,126.5,124.5,124.2,21.3.
Example 20 felbinac
In a 20mL reaction flask, 2-methyl-4' - (trifluoro) was addedMethyl) -1,1' -biphenyl (118 mg,0.5 mmol), 6-bromobenzothiazole (11 mg,0.05 mmol), concentrated hydrochloric acid (36 wt%,25mg,0.25 mmol), acetonitrile (2 mL) was added to the mixture, the mixture was exposed to air and was reacted under 25W of violet light at 50℃for 24 hours with stirring, the reaction solution was further washed with saturated brine, the mixture was extracted with ethyl acetate (3X 10 mL), and the combined organic phases were washed with anhydrous Na 2 SO 4 Drying, concentrating under reduced pressure, and separating and purifying by petroleum ether/ethyl acetate column chromatography to obtain the target product benzoic acid shown as formula (II-n), wherein the yield is 63%, and the HPLC purity is 98.8%.
1 H NMR(400MHz,DMSO-d 6 )δ12.88(brs,1H),7.84(dd,J＝7.7,1.2Hz,1H),7.77(d,J＝8.1Hz,2H),7.63(td,J＝7.5,1.4Hz,1H),7.57–7.50(m,3H),7.41(dd,J＝7.6,1.0Hz,1H)； 13 C NMR(100MHz,DMSO-d 6 )δ169.3,145.8,140.5,132.2,131.7,131.0,130.0,129.6,128.5,128.1(q,J＝31.7Hz),125.3(q,J＝3.8Hz),124.9(q,J＝271.9Hz).

Claims (7)

1. The method for preparing the aromatic acid by metal-free photocatalytic oxidation is characterized by comprising the following steps of: adding a compound shown in a formula (I), a photocatalyst and an additive into a solvent, exposing the mixture to air or oxygen, stirring the mixture at 25-60 ℃ under the irradiation of a light source for reaction, and after the reaction is finished, carrying out post-treatment on the reaction solution to obtain an aromatic acid compound shown in a formula (II), wherein the reaction equation is as follows:
，
wherein Ar is benzene ring, furyl, thienyl, naphthyl or benzophenone, and H on Ar group is R 1 Monosubstituted, substituent R 1 Is alkyl, substituted hydroxy, aldehyde or substituted alkyl, H on Ar group is replaced by R 2 Substituted or unsubstituted, R being the substituent 2 Is monosubstituted or polysubstituted, n=1 to 2, n is an integer, and substituent R 2 Is alkyl, alkoxy, halogen, trifluoromethyl, aryl substituted aryl or substituted phenolic hydroxyl;
the structure of the photocatalyst is shown as a formula (III), wherein H on the benzene ring is substituted or not substituted by a substituent R, R is halogen, methyl, alkoxy, trifluoromethoxy, nitro or acetyl when substituted,
；
the solvent is acetonitrile, dichloromethane, 1, 2-dichloroethane, ethyl acetate or acetone; the additive is one or a mixture of more of hydrochloric acid, sulfuric acid, sodium hydrogen bromide, potassium chloride, tetrabutylammonium chloride and trifluoroacetic acid; the light source is blue light, white light or purple light.
2. The method of claim 1, wherein the substituent R 1 is-CH 3 、-CH 2 OH、-CHO、-CH 2 Cl, or-CH 2 OCH 3 Substituent R 2 Is methyl, methoxy, chlorine, fluorine, trifluoromethyl, benzene ring, trifluoromethyl phenyl or acetyl substituted phenolic hydroxyl.
3. The process of claim 1, wherein the reaction temperature is 50-60 ℃.
4. The process according to claim 1, wherein the mass ratio of the compounds of formula (I), the catalyst and the additives is 1:0.1 to 0.5:0.2 to 1.
5. The method of claim 1, wherein the reaction time is from 6 to 48 hours.
6. The method of claim 1, wherein the post-processing is performed by: the reaction mixture was quenched with saturated brine, extracted with ethyl acetate, the organic layer was separated, dried over anhydrous sodium sulfate and concentrated under reduced pressure, and finally purified on a silica gel column with petroleum ether/ethyl acetate or dichloromethane/methanol.
7. The process according to claim 1, wherein the mass ratio of the compound of formula (I), the catalyst and the additive is 1:0.1-0.2:0.4-0.5.
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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108276270A (en) * 2018-02-05 2018-07-13 浙江工业大学 A kind of catalysis oxidation synthetic method of aryl formate
CN111018708A (en) * 2019-11-22 2020-04-17 浙江工业大学 Synthesis method of difluoroalkyl substituted aromatic ketone compound under photocatalysis
CN113277936A (en) * 2021-05-24 2021-08-20 西安交通大学 Method for preparing aromatic acid by oxidation reaction of 1, 2 and 3-stage alkyl substituted aromatic compounds under catalysis of iron

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108276270A (en) * 2018-02-05 2018-07-13 浙江工业大学 A kind of catalysis oxidation synthetic method of aryl formate
CN111018708A (en) * 2019-11-22 2020-04-17 浙江工业大学 Synthesis method of difluoroalkyl substituted aromatic ketone compound under photocatalysis
CN113277936A (en) * 2021-05-24 2021-08-20 西安交通大学 Method for preparing aromatic acid by oxidation reaction of 1, 2 and 3-stage alkyl substituted aromatic compounds under catalysis of iron

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