A method for catalytic oxidation to produce p-methoxybenzaldehyde and the catalyst used

Abstract

The present invention belongs to the field of compound preparation, and particularly relates to a method for catalytic oxidation to produce p-methoxybenzaldehyde and the catalyst used. The preparation method of the catalyst of the present invention comprises the following steps: dissolving a mixed salt composed of a soluble cobalt salt, a soluble manganese salt and a soluble trivalent metal salt in deionized water to obtain a mixed salt solution; dissolving sodium carbonate and sodium hydroxide in deionized water to obtain a mixed alkali solution; mixing the mixed salt solution and the mixed alkali solution in a dropping manner and then aging, and then filtering the aged product by suction, and calcining the obtained catalyst precursor to obtain a catalyst for catalytic oxidation to produce p-methoxybenzaldehyde. The present invention also simultaneously provides a method for catalytic oxidation to produce p-methoxybenzaldehyde, using p-methylanisole as a raw material and using the catalyst obtained above. The method for catalytic oxidation to produce p-methoxybenzaldehyde of the present invention does not use a cocatalyst, and the catalyst used can be reused.

Description

Technical Field

[0001] The present invention belongs to the field of compound preparation, and particularly relates to a method for catalytic oxidation of p-methylanisole (p-methoxytoluene) to prepare p-methoxybenzaldehyde and a catalyst used therefor. Background Art

[0002] p-Methoxybenzaldehyde, also known as anisaldehyde, has the molecular formula C 8 H 8 O 2 . It is a colorless or light yellow liquid at room temperature, with a persistent hawthorn aroma. It is a spice with high added value and is widely used in the preparation of fragrance raw materials. p-Methoxybenzaldehyde is also an intermediate in the pharmaceutical industry and can be used to prepare drugs such as the antimicrobial amoxicillin, the vasodilator diltiazem hydrochloride, and the choleretic agent drotaverine. p-Methoxybenzaldehyde is also used in polymer materials and can be used to prepare polyferrocene-p-methoxybenzaldehyde.

[0003] At present, there are many synthetic methods for synthesizing p-methoxybenzaldehyde from p-methylanisole, which are as follows:

[0004] 1. Electrooxidation method: Electrochemical oxidation methods are divided into direct and indirect electrooxidation methods. Currently, most domestic and foreign literature reports use the indirect electrooxidation method. This method has high selectivity and yield, but the electrochemical method has high energy consumption and large equipment investment.

[0005] 2. Gas-phase catalytic oxidation method: This method mainly uses a supported catalyst to catalytically oxidize p-methylanisole to synthesize p-methoxybenzaldehyde at high temperature. However, this method has problems such as too high reaction temperature (about 300 °C), easy over-oxidation of raw materials to CO x , easy deactivation of the catalyst and troublesome preparation.

[0006] 3. Liquid-phase catalytic oxidation method: This method is widely used and is one of the most common methods reported for preparing p-methoxybenzaldehyde at present.

[0007] In this type of method for catalytically oxidizing p-methylanisole as a raw material to produce p-methoxybenzaldehyde, the main products are p-methoxybenzaldehyde and p-methoxybenzyl acetate, and also contain a small amount of p-methoxybenzyl alcohol as a by-product. The boiling point of p-methoxybenzaldehyde (248 °C) and p-methoxybenzyl acetate (270 °C) differ greatly, so p-methoxybenzaldehyde can be easily rectified and purified from the reaction product (reaction mother liquor). p-Methoxybenzyl acetate is an intermediate for important industrial and pharmaceutical chemicals and can also react with strong bases to obtain p-methoxybenzyl alcohol.

[0008] For example, it includes the following schemes:

[0009] Chinese Patent CN111253227A reported that a solution containing p-methylanisole was passed into a capillary column loaded with an active component. This method has high selectivity, but there are problems such as low conversion rate, troublesome preparation of the capillary column with the active component, and difficulty in recovery after deactivation. The Hong Long research group used a metal porphyrin / metal salt catalyst to catalytically oxidize p-methylanisole to prepare p-methoxybenzaldehyde (Guangdong Chemical Industry, 2015, 42, 9-10). This method has a low conversion rate, and the homogeneous catalyst cannot be reused. A large amount of p-methoxybenzyl alcohol by-products are generated during catalytic oxidation, and its boiling point is close to that of p-methoxybenzaldehyde, making it difficult to separate and purify. The Du Xi research group used copper acetate and cobalt acetate as catalysts, potassium bromide and sodium carbonate as co-catalysts, and hydrogen peroxide as the oxygen source to catalytically oxidize p-methylanisole to prepare p-methoxybenzaldehyde (Journal of Anhui Agricultural Sciences, 2010, 38, 18657-18660). This method has relatively high selectivity, but the main catalyst and co-catalyst are homogeneous catalysts and cannot be reused, resulting in more three wastes after the reaction.

[0010] The invention of CN115850044B, "A method for synthesizing p-methoxybenzaldehyde", discloses that using p-hydroxybenzaldehyde and dimethyl carbonate as raw materials, methylation reaction is carried out in the presence of a catalyst to generate p-methoxybenzaldehyde. The catalyst is a supported catalyst, including a carrier and a metal oxide supported on the carrier; the metal oxide is selected from one or a combination of more than one of zinc oxide, manganese oxide, magnesium oxide, barium oxide, calcium oxide, lithium oxide, sodium oxide, potassium oxide, and rubidium oxide. The supported catalysts are respectively denoted as Mg-Na 2 CO 3 -0.05-H 3 BO 3 / Y, K-NaOH-0.05-H 3 BO 3 / Y, Ba-NaOH-0.05-H 3 BO 3 / Y, Cu-NaOH-0.05-H 3 BO 3 / Y, Fe-NaOH-0.05-H 3 BO 3 / Y, Ag-NaOH-0.05-H 3 BO 3 / Y, Ca-NaOH-0.05-H 3 BO3 / Y, Co-NaOH-0.05-H 3 BO 3 / Y. The raw material p-hydroxybenzaldehyde used in CN115850044B has a relatively high price, usually 15,000 - 25,000 yuan / ton higher than the market price of p-methylanisole. Preparing p-methoxybenzaldehyde from p-hydroxybenzaldehyde has poor economy; moreover, the reaction pressure is high, reaching 2 MPa.

[0011] The invention of CN109456152B, "A Method for Catalytic Oxidation of p-Methoxytoluene to Prepare p-Methoxybenzaldehyde", discloses that using p-methoxytoluene (i.e., p-methylanisole) as the substrate and a transition metal salt and a nitrogen-containing ligand as the catalyst, catalytic selective oxidation is carried out under mild conditions to prepare p-methoxybenzaldehyde. The transition metal salts used are one or more of cobalt nitrate, cobalt acetate, cobalt chloride, cobalt sulfate, cobalt acetylacetonate, cobalt isooctanoate, cobalt oleate, cobalt neodecanoate, copper nitrate, copper acetate, copper chloride, copper sulfate, copper acetylacetonate, copper isooctanoate, copper oleate, copper neodecanoate, manganese nitrate, manganese acetate, manganese chloride, manganese sulfate, manganese acetylacetonate, manganese isooctanoate, manganese oleate, manganese neodecanoate. CN109456152B uses a homogeneous catalyst, and the catalyst is difficult to be reused; the conversion rate of p-methylanisole is relatively low (not exceeding 50%).

[0012] The invention of CN103936568B, "A Method for Preparing p-Methoxybenzyl Alcohol from p-Methoxytoluene", discloses that p-methoxytoluene, catalyst I and a solvent are added to an oxidation reaction kettle, and oxygen is introduced at a certain temperature. After reacting for a certain time, the reaction is stopped. Catalyst I is a transition metal salt, preferably acetate, such as cobalt acetate, manganese acetate, nickel acetate, cerium acetate, chromium acetate, zinc acetate, iron acetate, copper acetate, cobalt nitrate, manganese nitrate, copper nitrate, cobalt chloride, cobalt bromide, cobalt acetylacetonate, iron acetylacetonate, cobalt stearate, manganese stearate, cobalt naphthenate, palladium acetate, palladium chloride, etc., or a composite catalyst composed of several of these catalysts in a certain molar ratio, preferably one of cobalt acetate, manganese acetate, chromium acetate, cerium acetate, palladium acetate, iron acetate, copper acetate, etc., or a composite catalyst composed of them in a certain molar ratio. Although CN103936568B uses a homogeneous catalyst to achieve the reuse of the catalyst, the reuse steps are cumbersome. According to the environmental impact report of the technical transformation project of fine chemical production (phase III) of Kelsi Chemical in 2015, for the recovery and reuse of the catalyst, most of the acetic acid and water are distilled out at 140 °C, and then 10 times the amount of water of the catalyst is added to the obtained distillation residue for washing and liquid separation to wash out the water-soluble catalyst (cobalt acetate, chromium acetate, cerium acetate) from the organic matter; then the water phase containing the catalyst is filtered to filter out the organic solid waste, and the filtrate is heated to 105 - 112 °C under normal pressure to distill out the water vapor containing acetic acid, and the distillation residue is the catalyst; finally, the catalyst in the distillation residue is dissolved in acetic acid at 70 - 90 °C and reused after dissolution. The recovery and reuse of the homogeneous catalyst in this patent consumes a large amount of energy, and some catalyst, raw materials and products will inevitably be lost during the liquid separation, washing and distillation stages. Summary of the Invention

[0013] The technical problem to be solved by the present invention is to provide a method for catalytic oxidation to produce p-methoxybenzaldehyde using a heterogeneous catalyst.

[0014] To solve the above technical problem, the present invention provides a method for preparing a catalyst (high-efficiency catalyst) for catalytic oxidation to produce p-methoxybenzaldehyde, comprising the following steps:

[0015] 1), Dissolve a mixed salt composed of a soluble cobalt salt (divalent), a soluble manganese salt (divalent), and a soluble trivalent metal salt in deionized water to obtain a mixed salt solution (Solution A);

[0016] (Cobalt + Manganese): Trivalent metal = (4 ± 0.1): 0.8 - 2 molar ratio;

[0017] Cobalt: Manganese = (1 - 3): (3 - 1) molar ratio;

[0018] The trivalent metal is aluminum or cerium;

[0019] 2), Dissolve sodium carbonate and sodium hydroxide in deionized water to obtain a mixed alkali solution (Solution B); in the mixed alkali solution, the total concentration of sodium ions is 2.8 ± 0.2 mol / L, and the molar ratio of sodium hydroxide: sodium carbonate = (3 ± 0.2): 1;

[0020] 3), Control the temperature in the reaction vessel to be 50 - 70 °C (preferably 60 ± 5 °C), and under stirring conditions, add the mixed salt solution dropwise into the reaction vessel. The dropping time is 20 - 50 minutes (preferably 30 - 40 minutes). During the dropping of the mixed salt solution, simultaneously add the mixed alkali solution into the reaction vessel (forming a reaction system), so as to control the pH of the reaction system in the reaction vessel to be 8.5 - 9.0;

[0021] After the dropping of the mixed salt solution is completed, continue to add the mixed alkali solution dropwise into the reaction vessel (still maintaining the temperature of 50 - 70 °C and stirring conditions) until the pH of the reaction system in the reaction vessel is 9.5 - 10; then raise the temperature in the reaction vessel to 75 - 90 °C (preferably 80 ± 5 °C), and age for 22 - 26 hours under stirring conditions to obtain an aged product;

[0022] Note: During the simultaneous dropping of the mixed salt solution and the mixed alkali solution, a coprecipitation occurs in the reaction system in the reaction vessel to obtain a layered metal hydroxide (in a hydrotalcite structure);

[0023] 4), Filter the aged product obtained in step 3) by suction filtration, and wash the filter cake with water (deionized water) until the filter cake is neutral after washing. Then dry the washed filter cake (dry it in an oven) to obtain a catalyst precursor (cobalt-manganese-aluminum catalyst precursor or cobalt-manganese-cerium catalyst precursor);

[0024] 5), Heat the catalyst precursor obtained in step 4) to 350 - 450 °C at a rate of 10 - 20 °C per minute and then calcine for 3 - 5 hours (preferably calcine at 400 ± 5 °C for 4 h), and then naturally cool to room temperature to obtain a catalyst for catalytic oxidation to produce p-methoxybenzaldehyde (cobalt-manganese-aluminum composite metal oxide or cobalt-manganese-cerium composite metal oxide).

[0025] The above calcination can be carried out in a muffle furnace.

[0026] As an improvement to the preparation method of the catalyst for catalytic oxidation to produce p-methoxybenzaldehyde in the present invention:

[0027] In the mixed salt solution, the sum of the concentrations of cobalt, manganese, and trivalent metal is 0.7 - 1.2 mol / L (preferably 0.8 - 1 mol / L).

[0028] As a further improvement to the preparation method of the catalyst for catalytic oxidation to produce p-methoxybenzaldehyde in the present invention:

[0029] The molar ratio of cobalt:manganese:trivalent metal is 1:3:1.9.

[0030] As a further improvement to the preparation method of the catalyst for catalytic oxidation to produce p-methoxybenzaldehyde in the present invention:

[0031] The soluble cobalt salt is Co(NO 3 ) 2 ·6H 2 O; the soluble manganese salt is Mn(NO 3 ) 2 ·4H 2 O;

[0032] The soluble trivalent metal salt is Al(NO 3 ) 3 ·9H 2 O, Ce(NO 3 ) 3 ·6H 2 O.

[0033] As a further improvement to the preparation method of the catalyst for catalytic oxidation to produce p-methoxybenzaldehyde in the present invention:

[0034] The drying in step 4): temperature 90 - 110 °C, time 6 - 10 hours.

[0035] As a further improvement to the preparation method of the catalyst for catalytic oxidation to produce p-methoxybenzaldehyde in the present invention:

[0036] The stirring speed in step 3) is 400 - 800 rpm.

[0037] As a further improvement to the preparation method of the catalyst for catalytic oxidation to produce p-methoxybenzaldehyde in the present invention:

[0038] In step 4): After drying, it is crushed (through a 100-mesh sieve) to obtain the catalyst precursor.

[0039] The present invention also simultaneously provides a method for catalytic oxidation to produce p-methoxybenzaldehyde. Using p-methylanisole as the raw material and the catalyst (cobalt-manganese-aluminum composite metal oxide or cobalt-manganese-cerium composite metal oxide) prepared by any of the above methods, it includes the following steps:

[0040] Load the catalyst, acetic acid as the solvent, and p-methylanisole as the raw material into a gas-connected reactor. Introduce oxygen as the reaction gas into the reactor. Control the reaction pressure of the reactor at 0.2 - 0.4 Mpa (the reaction pressure can be controlled by controlling the opening of the oxygen pressure reducing valve, preferably 0.3 Mpa). Under the catalytic action of the catalyst, p-methylanisole and oxygen react. The reaction temperature is 90 - 120 °C (preferably 110 ± 10 °C), and the reaction time is 4 - 8 h; thus, p-methoxybenzaldehyde is prepared and obtained;

[0041] Catalyst : p-methylanisole = 0.15 - 0.38 g / 1 ml, and the dosage of acetic acid is 4 - 20 times the volume of p-methylanisole.

[0042] The reaction equation is:

[0043] .

[0044] Note: After the reaction ends, the reaction product in the reactor consists of the solvent, the catalyst, p-methoxybenzaldehyde as the main product, and by-products, etc.;

[0045] Filter / centrifuge the reaction product. The solid obtained by filtration / centrifugation is the recyclable catalyst and can be reused (the recovered catalyst can be directly reused. In the present invention, in order to exclude the influence of other substances on the content detection, the catalysts are all washed and then reused in the experiment);

[0046] The liquid obtained by filtration / centrifugation contains p-methoxybenzaldehyde as the main product. The product content can be measured by gas chromatography, and p-methoxybenzaldehyde can be obtained by a conventional distillation method. This distillation method is common knowledge in this industry, so it will not be elaborated in detail.

[0047] In the method for catalytic oxidation to produce p-methoxybenzaldehyde according to the present invention, since the catalyst (cobalt-manganese-aluminum composite metal oxide or cobalt-manganese-cerium composite metal oxide) is insoluble in the reaction system, it belongs to a heterogeneous catalyst, and the catalytic reaction occurs on the surface of the catalyst. Therefore, the catalyst can be easily separated after the reaction, so as to achieve reuse.

[0048] The catalyst of the present invention has the technical advantages of high activity, strong selectivity and reusability. The solvent used in the present invention is acetic acid which is cheap and easily available. In the existing similar technologies, the catalysts used are homogeneous catalysts that cannot be reused, and most of the existing similar technologies use relatively expensive solvents.

[0049] The method for catalytic oxidation to produce p-methoxybenzaldehyde according to the present invention does not use a cocatalyst, and the catalyst used can be reused. The method for catalytic oxidation to produce p-methoxybenzaldehyde according to the present invention has a fast reaction rate, high conversion rate, and high yield and easy separation of the obtained p-methylbenzaldehyde. Specific Embodiments

[0050] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto:

[0051] Example 1-1: Preparation of Co-Mn-Al composite metal oxide as a catalyst, the following steps are carried out in sequence:

[0052] 1), Preparation of mixed salts:

[0053] The mixed salt Co-Mn-Al is composed of 0.02 mol (5.82 g) of Co(NO 3 ) 2 ·6H 2 O, 0.06 mol (14.70 g) of Mn(NO 3 ) 2 ·4H 2 O, 0.017 mol (6.38 g) of Al(NO 3 ) 3 ·9H 2 O;

[0054] Dissolve the mixed salt Co-Mn-Al in 120 mL of deionized water to obtain a mixed salt solution (solution A) accordingly; in the mixed salt solution, the sum of the concentrations of the three metal elements Co, Mn, and Al is 0.81 mol / L.

[0055] 2), Preparation of alkali solution:

[0056] Dissolve 0.2 mol of NaOH and 0.067 mol of Na 2 CO 3Dissolve it in 120 mL of deionized water to prepare a mixed alkali solution; in the mixed alkali solution, the total sodium ion concentration is 2.78 mol / L. The molar ratio of NaOH:Na 2 CO 3 ≈3:1.

[0057] 3), respectively load the mixed salt solution (solution A) and the mixed alkali solution (solution B) into 200 mL constant pressure funnels, and place the constant pressure funnels on the four-necked flask; simultaneously drip solution A and solution B into the four-necked flask, specifically as follows:

[0058] Control the temperature in the four-necked flask to 60 °C. Under stirring conditions, uniformly drip solution A into the four-necked flask within 30 - 40 minutes. During the dripping process of solution A, simultaneously drip solution B into the four-necked flask to control the pH of the reaction system in the four-necked flask to 8.5 - 9.0. After the dripping of solution A is completed, continue to drip solution B under stirring conditions until the pH of the reaction system in the four-necked flask is controlled at 9.5 - 10; then raise the temperature to 80 °C and age for 24 hours under stirring conditions to obtain an aged product.

[0059] The rotation speeds of the stirring during the above dripping process and the stirring during the aging process are both 600 - 800 rpm.

[0060] Note: During the simultaneous dripping of the mixed salt solution and the mixed alkali solution, a coprecipitation occurs in the reaction system in the reaction vessel.

[0061] 4), filter the aged product obtained in step 3) by suction filtration. Wash the filter cake (precipitate) obtained by suction filtration with deionized water until it is neutral. After washing, put the filter cake into an oven and dry it at 100 °C for 8 hours, and grind it into powder (pass through a 100-mesh sieve) to obtain a Co-Mn-Al catalyst precursor.

[0062] 5), place the Co-Mn-Al catalyst precursor in a programmed temperature muffle furnace, start heating from room temperature at a heating rate of 15 °C per minute to 400 °C, and then keep it at a constant temperature (400 °C) and calcine for 4 hours.

[0063] Subsequently, naturally cool it to room temperature in the muffle furnace to obtain a Co-Mn-Al0.85 composite metal oxide named, where 0.85 is the molar proportion of Al in Co.

[0064] Examples 1-2 to 1-4: Compared with Example 1-1, change Al(NO 3 ) 3 ·9H 2The dosage of O (as described in Table 1 below), and the rest is the same as that of Example 1-1. Thus, Co-Mn-Al composite metal oxides (Co-Mn-Al1, Co-Mn-Al1.4, Co-Mn-Al1.9) are obtained.

[0065] Table 1

[0066]

[0067] Example 2-1: Preparation of Co-Mn-Ce composite metal oxide as a catalyst. Compared with Example 1-1, the following changes are made:

[0068] 1), Prepare the mixed salt:

[0069] The mixed salt Co-Mn-Ce is composed of 0.02 mol (5.82 g) of Co(NO 3 ) 2 ·6H 2 O, 0.06 mol (14.70 g) of Mn(NO 3 ) 2 ·4H 2 O, and 0.017 mol (7.38 g) of Ce(NO 3 ) 3 ·6H 2 O.

[0070] Dissolve the mixed salt Co-Mn-Ce in 120 mL of deionized water to obtain a mixed salt solution (Solution A); in the mixed salt solution, the sum of the concentrations of the three metal elements Co, Mn, and Ce is 0.81 mol / L;

[0071] The rest is the same as that of Example 1-1.

[0072] In this Example 2-1, the product obtained in step 4) is named Co-Mn-Ce catalyst precursor; the product obtained in step 5) is named Co-Mn-Ce0.85 composite metal oxide, and 0.85 is the molar ratio of Ce to Co.

[0073] Examples 2-2 to 2-4: Compared with Example 2-1, change the dosage of Ce(NO 3 ) 3 ·6H 2 O in step 1) (as described in Table 2 below), and the rest is the same as that of Example 2-1. Thus, Co-Mn-Ce composite metal oxides (Co-Mn-Ce1, Co-Mn-Ce1.4, Co-Mn-Ce1.9) are obtained.

[0074] Table 2

[0075]

[0076] Example 3 series. Compared with Examples 1-2, the molar amount of Al(NO 3 ) 3 ·9H 2 O is kept unchanged at 0.02 mol, and the total molar amount of Co(NO 3 ) 2 ·6H 2 O and Mn(NO 3 ) 2 ·4H 2 O is kept unchanged at 0.08 mol. Only the molar ratio of Co(NO 3 ) 2 ·6H 2 O and Mn(NO 3 ) 2 ·4H 2 O is changed, as specifically described in Table 3 below; the rest is the same as Examples 1-2.

[0077] Table 3

[0078]

[0079] Example 4 series. Compared with Examples 2-2, the molar amount of Ce(NO 3 ) 3 ·6H 2 O is kept unchanged at 0.02 mol, and the total molar amount of Co(NO 3 ) 2 ·6H 2 O and Mn(NO 3 ) 2 ·4H 2 O is kept unchanged at 0.08 mol. Only the molar ratio of Co(NO 3 ) 2 ·6H 2 O and Mn(NO 3 ) 2 ·4H 2 O is changed, as specifically described in Table 4 below; the rest is the same as Examples 2-2.

[0080] Table 4

[0081]

[0082] Experiment 1 series. A method for preparing p-methoxybenzaldehyde from p-methylanisole (for catalyst performance evaluation):

[0083] The Co-Mn-Al and Co-Mn-Ce composite metal oxides obtained from Example 1 series to Example 2 series were respectively subjected to the following operations:

[0084] Put 0.75 g of Co-Mn-Al or Co-Mn-Ce composite metal oxide as a catalyst into a 300 mL gas-connected reactor, and then add 2 mL of p-methylanisole and 40 mL of acetic acid. The reactor was connected to an oxygen cylinder, and the gas pressure in the reactor was controlled at 0.3 MPa. Under the catalytic action of the catalyst, p-methylanisole and oxygen reacted at a reaction temperature of 110 °C for 4 h.

[0085] After the reaction was completed, the reaction product in the reactor was put into a centrifuge for centrifugation (rotation speed: 8000 rpm, centrifugation time: 5 minutes). The solid obtained by centrifugation was the reusable catalyst.

[0086] The centrifuged liquid was detected for the component content by gas phase area normalization method, and the obtained reaction results are shown in Table 5 below. Among them, Co-Mn-Al 1.9 and Co-Mn-Ce 1.9 had high conversion rates and high yields of p-methoxybenzaldehyde.

[0087] It should be noted that: The Co-Mn-Al and Co-Mn-Ce composite metal oxides in Example 1 series to Example 2 series did not dissolve in the reaction system of the above Experiment 1.

[0088] Table 5 Comparison table of the catalytic oxidation effects of catalysts with different Al and Ce contents

[0089]

[0090] Note: The conversion rate and selectivity of the present invention were obtained by gas phase area normalization method.

[0091] Conversion rate of p-methylanisole (%) = 100 - percentage of peak area of p-methylanisole;

[0092] Yield of p-methoxybenzaldehyde (%) = percentage of peak area of p-methoxybenzaldehyde;

[0093] Yield of p-methoxybenzyl alcohol (%) = percentage of peak area of p-methoxybenzyl alcohol;

[0094] Yield of p-methoxybenzyl acetate (%) = percentage of peak area of p-methoxybenzyl acetate.

[0095] Experiment 2 series:

[0096] Compared with Experiment 1, the catalysts obtained by using the Series of Example 3 and the Series of Example 4 were adopted to investigate the influence of different Co and Mn contents on the catalytic performance; the rest was the same as Experiment 1.

[0097] The reaction results were compared with Co-Mn-Al 1 (i.e., Co1-Mn3-Al1) and Co-Mn-Ce1 (i.e., Co1-Mn3-Ce1) in Experiment 1 as shown in Table 6. It can be known from Table 6 that Co1-Mn3-Al1 is a catalyst with the second highest conversion rate among the Co-Mn-Al1 series catalysts, but the highest yield of p-methoxybenzaldehyde. Co1-Mn3-Ce1 is a catalyst with the highest conversion rate and the highest yield of p-methoxybenzaldehyde among the Co-Mn-Ce1 catalysts.

[0098] It should be noted that the Co-Mn-Al and Co-Mn-Ce composite metal oxides in the Series of Example 3 to the Series of Example 4 will not dissolve in the reaction system of the above Experiment 2.

[0099] Table 6 Influence of different Co and Mn contents on the catalytic performance

[0100]

[0101] Series of Experiment 3:

[0102] Compared with the catalysts in Experiment 1 being "Co-Mn-Al1.9, Co-Mn-Ce1.9", the dosage of the catalyst, the addition amount of p-methylanisole, and the reaction time were changed; the amount of acetic acid solvent was kept unchanged, and the rest was the same as Experiment 1.

[0103] Specifically as follows:

[0104] 1 g / 1.5 g of Co-Mn-Al1.9 or Co-Mn-Ce1.9 catalyst was put into a 300 mL gas-connected reaction kettle, and then 4 mL / 8 mL of p-methylanisole and 40 mL of acetic acid were added respectively. The reaction kettle was connected to an oxygen cylinder, the gas pressure was controlled at 0.3 MPa, the reaction temperature was 110 °C, and the reaction was carried out for 8 h. The reaction results are shown in Table 7.

[0105] It should be noted that the catalysts used in the Series of Experiment 3 will not dissolve during the reaction process.

[0106] Table 7 Influence of increasing the amount of p-methylanisole on the catalytic reaction

[0107]

[0108] Series of Experiment 4: Catalyst reuse experiment:

[0109] First time (i.e., the number of applications is 0 times): Put 1.5 g of Co-Mn-Al1.9 or Co-Mn-Ce1.9 catalyst into a 300 mL gas-connected reactor, and then add 8 mL of p-methylanisole and 40 mL of acetic acid respectively. Connect the reactor to an oxygen cylinder (introduce oxygen as the reaction gas into the reactor), control the gas pressure at 0.3 MPa, the reaction temperature at 110 °C, and react for 8 h. After the reaction, put the reaction product into a centrifuge for centrifugation (rotation speed 8000 rpm, centrifugation time 5 minutes). The solid obtained by centrifugation is washed with ethanol 3 times and dried at 100 °C to constant weight, and it is a recyclable catalyst (about 1.2 - 1.4 g).

[0110] Number of applications is 1 time: Use the recovered catalyst above and add fresh Co-Mn-Al1.9 or Co-Mn-Ce1.9 catalyst accordingly until the total amount of the catalyst is still 1.5 g; repeat the above reaction;

[0111] And so on, so as to obtain cases under different numbers of applications, as shown in Table 8 below.

[0112] With the increase of the number of repeated applications of Co-Mn-Al1.9, its catalytic activity also decreases. However, Co-Mn-Ce1.9 does not show an obvious attenuation of catalytic activity with the increase of the number of applications. After repeating the application 3 times, there is still a conversion rate of more than 70% and a yield of p-methoxybenzaldehyde of more than 23%.

[0113] Table 8 Experimental results of repeated application of the catalyst

[0114]

[0115] Comparative experiment 1:

[0116] Replace the trivalent metals Al and Ce in Example 1-2 "Co-Mn-Al1 (Co1-Mn3-Al1)" and Example 2-2 "Co-Mn-Ce1 (Co1-Mn3-Ce1)" with Cr and Fe, and other catalyst preparation conditions are similar; thus, Co1-Mn3-Cr1 or Co1-Mn3-Fe1 are obtained respectively.

[0117] Detect 0.75 g of Co1-Mn3-Cr1 or Co1-Mn3-Fe1 according to the method described in Experiment 1, and the reaction results are shown in Table 9. It can be known that when the trivalent metals are replaced with Fe and Cr, both the catalyst conversion rate and the product yield decline significantly.

[0118] Table 9 Influence of different trivalent metals on the catalytic activity of the catalyst

[0119]

[0120] Comparative experiment 2:

[0121] Relative to Example 1-2, Mn is replaced with one or more metal element combinations of Ce, Cr, and Mn (the amounts remain unchanged), and other catalyst preparation conditions are similar to those of Example 1-2; thereby obtaining Co1-Ce3-Al1, Co1-Ce2-Cr1-Al1, and Co1-Mn2-Ce1-Al1, respectively.

[0122] 0.75 g of Co1-Ce3-Al1, Co1-Ce2-Cr1-Al1, and Co1-Mn2-Ce1-Al1 were tested according to the method described in Experiment 1. The reaction results are shown in Table 10. When Mn was replaced by Ce or a combination of Ce and Cr, the catalytic oxidation effect was poor. If Mn was replaced by Mn and Ce to form Co1-Mn2-Ce1-Al1 catalyst, although the conversion rate of p-methyl anisole was high, the yield of p-methoxybenzaldehyde was low.

[0123] Table 10 Effect of different catalyst combinations on the catalytic effect of catalysts

[0124]

[0125] Finally, it should be noted that the above examples are only some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. A method for producing p-methoxybenzaldehyde by catalytic oxidation, using p-methylanisole as a raw material, characterized in that: Using a catalyst comprises the following steps: A catalyst, acetic acid as a solvent, and p-methylanisole as a raw material are loaded into a gas-connected reactor, oxygen as a reaction gas is introduced into the reactor, and the reaction pressure of the reactor is controlled to be 0.2-0.4 MPa. Under the catalytic action of the catalyst, p-methylanisole and oxygen react, the reaction temperature is 90-120° C., and the reaction time is 4-8 hours; thereby p-methoxybenzaldehyde is prepared; Catalyst: p-methyl anisole = 0.15~0.38g / 1mL, the amount of acetic acid used is 4~20 times the volume of p-methyl anisole; The preparation method of the catalyst comprises the following steps: 1) Dissolving a mixed salt consisting of a soluble cobalt salt, a soluble manganese salt and a soluble trivalent metal salt in deionized water to obtain a mixed salt solution; (Cobalt + Manganese): trivalent metal = (4 ± 0.1): 0.8~2 molar ratio; Cobalt: manganese = (1~3): (3~1) molar ratio; The trivalent metal is aluminum or cerium; 2) Sodium carbonate and sodium hydroxide are dissolved in deionized water to obtain a mixed alkaline solution; in the mixed alkaline solution, the total concentration of sodium ions is 2.8±0.2 mol / L, and the molar ratio of sodium hydroxide: sodium carbonate is (3±0.2):1; 3) Control the temperature in the reaction container to 50-70°C, and add the mixed salt solution to the reaction container under stirring for 20-50 minutes. During the process of adding the mixed salt solution, add the mixed alkali solution to the reaction container to control the pH of the reaction system in the reaction container to 8.5-9.0; After the mixed salt solution is added dropwise, the mixed alkali solution is continued to be added dropwise into the reaction container until the pH of the reaction system in the reaction container is 9.5-10; then the temperature in the reaction container is increased to 75-90° C., and the mixture is aged for 22-26 hours under stirring conditions to obtain an aged product; 4) Filter the aged product obtained in step 3) by suction, and wash the filter cake with water until the filter cake is neutral after washing. Then the washed filter cake is dried to obtain a catalyst precursor; 5) The catalyst precursor obtained in step 4) is heated to 350-450° C. at a rate of 10-20° C. per minute, calcined for 3-5 hours, and then naturally cooled to room temperature to obtain a catalyst.

2. The method for producing p-methoxybenzaldehyde by catalytic oxidation according to claim 1, characterized in that: In the mixed salt solution, the sum of the concentrations of cobalt, manganese and trivalent metals is 0.7~1.2 mol / L.

3. The method for producing p-methoxybenzaldehyde by catalytic oxidation according to claim 2, characterized in that: The molar ratio of cobalt: manganese: trivalent metal = 1:3:1.

9.

4. The method for producing p-methoxybenzaldehyde by catalytic oxidation according to any one of claims 1 to 3, characterized in that: The soluble cobalt salt is Co(NO3)2·6H2O; the soluble manganese salt is Mn(NO3)2·4H2O; The soluble trivalent metal salts are Al(NO3)3·9H2O and Ce(NO3)3·6H2O.

5. The method for producing p-methoxybenzaldehyde by catalytic oxidation according to claim 4, characterized in that: The drying in step 4) is carried out at a temperature of 90 to 110° C. and a time of 6 to 10 hours.

6. The method for producing p-methoxybenzaldehyde by catalytic oxidation according to claim 5, characterized in that: The stirring speed in step 3) is 400-800 rpm.

7. The method for producing p-methoxybenzaldehyde by catalytic oxidation according to claim 6, characterized in that In the step 4), the catalyst precursor is obtained by drying and then crushing.

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