A TiO2 / NaBr photocatalytic system for selective oxidation of primary alcohols to produce acids under mild conditions

Abstract

The present invention relates to the field of photocatalytic alcohol oxidation, and more particularly to a TiO2 / NaBr photocatalytic system for selectively oxidizing primary alcohols to produce acids under mild conditions. The present invention utilizes TiO2 as a primary catalyst and a halide salt as a co-catalyst. In an organic solvent, a primary alcohol raw material is added, and the system is developed in situ under oxygen and blue LED visible light. This photocatalytic system can efficiently complex with primary alcohol compounds. At room temperature, under the pressure of an oxygen balloon, and using ethyl acetate as the reaction solvent, it can oxidize the hydroxyl groups in aromatic and aliphatic primary alcohols to the corresponding acids. This method offers the advantages of good product selectivity, high conversion efficiency, and mild conditions. Furthermore, the catalyst is easily recyclable and the production cost is low. This method is a successful example of the photocatalytic oxidation of the biomass alcohol platform compound n-butanol to n-butyric acid.

Description

Technical Field

[0001] The present invention relates to the field of photocatalytic alcohol oxidation, and in particular to a TiO2 / NaBr photocatalytic system method for selectively oxidizing primary alcohols under mild conditions to prepare acids. Background Art

[0002] The catalytic conversion of primary alcohols to their corresponding carboxylic acids is an important reaction in the synthesis of pharmaceutical intermediates, pesticides, and fragrances. Aliphatic primary alcohols such as n-butanol are often converted to butyric acid via selective oxidation for further fine chemical synthesis, such as butyrates and cellulose butyrate. However, conventional thermal catalytic oxidation of butanol typically requires precious metal catalysts and strong chemical oxidants such as hydrogen peroxide or tert-butyl hydroperoxide, which not only require high reaction temperatures and oxygen pressures but also cause serious environmental pollution. Compared with thermal catalysis, photocatalysis is a method that is not subject to thermodynamic constraints, can bypass equilibrium limitations, and has high catalytic activity at low temperatures.

[0003] The photocatalyst TiO2 is widely used as a photocatalytic material due to its low cost, chemical stability, non-toxicity, and band gap of 3.0–3.3 eV. TiO2-based photocatalytic materials have been developed as a promising approach for photocatalytic oxidation reactions. Typically, TiO2 exhibits photocatalytic activity only under ultraviolet irradiation but does not respond to visible light unless it is modified with organic dyes or complexed with heteroatoms such as O, N, and S. In the prior art, alcohol compounds can be efficiently and selectively oxidized to carboxylic acids under visible light irradiation using a binary catalyst system. However, MOFs are unstable under strong oxidizing conditions and have poor recycling performance.

[0004] Based on this, the present invention uses TiO2 as a semiconductor photocatalyst and adds co-catalysts such as NaBr to construct a TiO2-based binary photocatalytic alcohol oxidation system, which can significantly improve the activity of the catalyst in the selective oxidation of alcohols and solve the above-mentioned photocatalyst deactivation problem in the catalytic cycle. Summary of the Invention

[0005] The purpose of the present invention is to address the problems existing in the background technology and propose a method for a TiO2 / NaBr photocatalytic system for selectively oxidizing primary alcohols to prepare acids under mild conditions, thereby solving the technical problems of high production cost, poor product selectivity caused by the use of strong oxidants, and low conversion efficiency in the traditional thermal catalytic oxidation process of primary alcohols. The high-efficiency primary alcohol catalytic oxidation system using TiO2 as a photocatalyst and NaBr as a co-catalyst achieves the goal of highly selectively oxidizing primary alcohols to prepare acid compounds under mild, light-irradiated conditions, and solves the problem of photocatalyst deactivation in the catalytic cycle.

[0006] The technical solution of the present invention is a method for selectively oxidizing primary alcohols under mild conditions to prepare acids using a TiO2 / NaBr photocatalytic system, comprising the following steps:

[0007] S1, using TiO2 as main catalyst, halide salt as co-catalyst, adding organic solvent, and obtaining TiO2 / NaBr catalytic system in situ;

[0008] S2, adding a primary alcohol raw material to the mixed solution obtained in S1;

[0009] S3. Oxygen is introduced into the mixed solution to which the primary alcohol raw material is added, and sampling is performed after illumination to obtain an acid compound.

[0010] Preferably, the type of TiO2 in S1 is anatase.

[0011] Preferably, the halide salt in S1 is one or more of NaBr, NaCl, NaF, LiBr, and KBr.

[0012] Preferably, the organic solvent in S1 is one of acetonitrile, ethyl acetate, cyclohexane, and 1,4-dioxane.

[0013] Preferably, the primary alcohol raw material in S2 is an aromatic primary alcohol raw material or an aliphatic primary alcohol raw material.

[0014] Preferably, the aromatic primary alcohol raw material is benzyl alcohol, p-bromobenzyl alcohol, p-methoxybenzyl alcohol, p-chlorobenzyl alcohol, or p-chlorobenzyl alcohol.

[0015] Preferably, the aliphatic primary alcohol raw materials are n-butanol and 1-heptanol.

[0016] Preferably, the oxygen pressure introduced in S3 is 1 balloon pressure.

[0017] Preferably, the wavelength of light in S3 is one of 420nm, 450nm, 520nm, 590nm, and 630nm.

[0018] Preferably, the illumination time in S3 is 0-8 hours.

[0019] Optionally, TiO2 may be directly purchased commercial anatase TiO2 or synthetic anatase TiO2;

[0020] Furthermore, in this method, the halide salt used is NaBr, and the organic solvent used is ethyl acetate.

[0021] Furthermore, in this method, the aromatic primary alcohol raw materials are benzyl alcohol, p-bromobenzyl alcohol, p-methoxybenzyl alcohol, p-chlorobenzyl alcohol, and p-chlorobenzyl alcohol; the aliphatic primary alcohol raw materials are n-butanol and 1-heptanol.

[0022] Furthermore, in this method, the illumination condition adopted is blue light LED with a wavelength of 450nm.

[0023] Furthermore, in this method, the illumination time used is 4h, 5h, or 6h.

[0024] Compared with the prior art, the present invention has the following beneficial technical effects:

[0025] With TiO2 as the main catalyst, NaBr as the co-catalyst, the organic solvent ethyl acetate and primary alcohol raw materials were added, and a TiO2 / NaBr method for the efficient and selective photocatalytic oxidation of primary alcohols into acids was developed under the conditions of oxygen and visible light with a wavelength of 420nm.

[0026] This method has the advantages of good product selectivity, high conversion efficiency, mild conditions, easy catalyst recycling, and low production cost. It is a successful example of the photocatalytic oxidation of the biomass alcohol platform compound n-butanol to n-butyric acid, achieving the goal of highly selective oxidation of primary alcohols to acid compounds under mild, light conditions, and solving the problem of photocatalyst deactivation in the catalytic cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a performance relationship diagram of the catalyst cycle experiment of the TiO2 / NaBr binary photocatalytic system of the present invention on benzyl alcohol under visible light. DETAILED DESCRIPTION

[0028] Examples 1-4

[0029] 5 mg of anatase TiO2, 0.06 mmol of NaBr, 0.2 mmol of 1-heptanol, 8 ml of solvent, an O2 balloon, and a 450 nm blue LED were added to a normal pressure reaction vessel. The reaction system was kept at room temperature under 450 nm illumination in an O2 atmosphere. After 4 hours, a sample was taken and centrifuged, and the supernatant was determined by gas chromatography with a flame ionization detector (GC-FID).

[0030] Table 1 shows the conversion rate of 1-heptanol and the yield of 1-heptanoic acid under different solvent conditions

[0031]

[0032] Examples 5-9

[0033] 5 mg of anatase TiO2, 0.06 mmol of NaBr, 0.2 mmol of n-butanol, 8 ml of ethyl acetate, an O2 balloon, and LED illumination conditions of different wavelengths were added to a normal pressure reaction vessel. The reaction system was kept at room temperature and illuminated under LED illumination of different wavelengths in an O2 atmosphere for 4 hours. After that, the sample was centrifuged and the supernatant was determined by gas chromatography and flame ionization detector (GC-FID).

[0034] Table 2 shows the conversion rate of n-butanol and the yield of n-butyric acid under LED light of different wavelengths

[0035]

[0036] Examples 10-15

[0037] 5 mg of anatase TiO2, 0.06 mmol of halide, 0.2 mmol of n-butanol, 8 ml of ethyl acetate, an O2 balloon, and LED illumination conditions of different wavelengths were added to a normal pressure reaction vessel. The reaction system was kept at room temperature under 450 nm illumination conditions in an O2 atmosphere. After 4 hours, the sample was centrifuged and the supernatant was determined by gas chromatography and flame ionization detector (GC-FID).

[0038] Table 3 shows the conversion rate of n-butanol and the yield of n-butyric acid under different halide conditions

[0039]

[0040]

[0041] Examples 16-22

[0042] 5 mg of anatase TiO2, 0.06 mmol of NaBr, 0.2 mmol of primary alcohol, 8 ml of ethyl acetate, an O2 balloon, and LED illumination conditions of different wavelengths were added to a normal pressure reaction vessel. The reaction system was kept at room temperature under 450 nm illumination conditions in an O2 atmosphere. After several hours, the sample was centrifuged and the supernatant was determined by gas chromatography with a flame ionization detector (GC-FID).

[0043] Table 4 shows the conversion rate of different primary alcohol raw materials and the yield of product acid

[0044] Example Primary alcohol time Primary alcohol conversion rate (%) Product acid yield (%) 16 Benzyl alcohol 4 99 95 17 4-Bromobenzyl alcohol 5 99 98 18 p-Anisylbenzyl alcohol 4 99 98 19 4-Chlorobenzyl alcohol 6 99 94 20 Chlorobenzyl alcohol 6 99 92 21 n-Butanol 4 99 97 22 1-Heptanol 4 99 96

[0045] Combining the above embodiments and Figure 1 , that is, the relationship between the conversion rate of raw material benzyl alcohol and the yield of product benzoic acid and the number of catalyst cycles. Catalytic conditions: room temperature, under 450nm LED light, when 25mg TiO2, 0.3mmol NaBr and 1mmol benzyl alcohol are added to 40mL ethyl acetate, the product selectivity is good, the conversion efficiency is high, and the catalyst is easy to recycle, achieving the goal of highly selective oxidation of primary alcohols to prepare acid compounds under mild and light conditions, and solving the problem of photocatalyst deactivation in the catalytic cycle.

[0046] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited thereto. Various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A TiO2 / NaBr photocatalytic method for selectively oxidizing primary alcohols to produce acids under mild conditions, characterized in that: The specific steps include: S1, using TiO2 as the main catalyst and NaBr as the co-catalyst, adding ethyl acetate to obtain the TiO2 / NaBr catalytic system in situ; S2. Adding a primary alcohol raw material to the mixed solution obtained in S1; wherein the primary alcohol raw material is an aromatic primary alcohol raw material or an aliphatic primary alcohol raw material; the aromatic primary alcohol raw material is benzyl alcohol, p-bromobenzyl alcohol, p-methoxybenzyl alcohol, p-chlorobenzyl alcohol, or o-chlorobenzyl alcohol; the aliphatic primary alcohol raw material is n-butanol or 1-heptanol; S3, introducing oxygen into the mixed solution with the primary alcohol raw material, maintaining the reaction system at room temperature and irradiating it in an O2 atmosphere, and then sampling to obtain an acid compound; The wavelength of light in S3 is 420nm or 450nm.

2. The method of claim 1 for selectively oxidizing primary alcohols to prepare acids using a TiO2 / NaBr photocatalytic system under mild conditions, wherein: The type of TiO2 in S1 is anatase.

3. The method of claim 1 for selectively oxidizing primary alcohols to prepare acids using a TiO2 / NaBr photocatalytic system under mild conditions, wherein: The photoperiod in S3 is 4h, 5h or 6h.

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