A method for preparing p-tert-butylbenzaldehyde by low-temperature oxidation

Abstract

This invention provides a method for the low-temperature oxidation preparation of p-tert-butylbenzaldehyde. The method involves using p-tert-butyltoluene as a starting material in an acidic organic solvent at 10-30°C, under the action of a catalyst and initiator, and by introducing oxygen to oxidize and obtain p-tert-butylbenzaldehyde. This method suppresses side reactions, exhibits high selectivity, and utilizes a low reaction temperature, thereby improving the reaction yield and reducing production costs. In practical production, it offers advantages such as safety and high efficiency.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a method for preparing p-tert-butylbenzaldehyde by low-temperature oxidation. Background Technology

[0002] p-tert-butylbenzaldehyde is an important organic chemical raw material and intermediate with wide applications in pharmaceuticals, dyes, pesticides, food additives, fragrances, and flavorings. Currently, methods for synthesizing p-tert-butylbenzaldehyde include benzyl brine hydrolysis, hydrogenation, and oxidation.

[0003] The process of preparing p-tert-butylbenzaldehyde by chlorination and hydrolysis of p-tert-butyltoluene is complex and highly polluting. The product contains residual chlorine that is difficult to remove, making it unsuitable for use in pharmaceuticals and their intermediates.

[0004] Chinese patent CN1944368A discloses a method for preparing p-tert-butylbenzaldehyde by hydrogenation reaction of methyl p-tert-butylbenzoate as raw material under the catalysis of a catalyst at atmospheric pressure and high temperature. This method is complex, has a high reaction temperature, and a low yield, making it unsuitable for industrialization.

[0005] Oxidation methods include chemical oxidation, oxygen (air) oxidation, and electrochemical oxidation. Among these, oxygen (air) liquid-phase oxidation is currently the most interesting method, as it does not consume expensive oxidants, has a large production capacity, and causes minimal environmental pollution, making it a promising method for future development. However, this method involves very high reaction temperatures, and the product, p-tert-butylbenzaldehyde, is easily further oxidized to p-tert-butylbenzoic acid.

[0006] Therefore, further research and optimization of the preparation method of p-tert-butylbenzaldehyde are needed to reduce side reactions, increase yield, and reduce production costs. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method for the low-temperature oxidation preparation of p-tert-butylbenzaldehyde. This method uses p-tert-butyltoluene as a starting material and oxidizes it at 10-30°C to obtain p-tert-butylbenzaldehyde. It suppresses side reactions, exhibits high selectivity, and utilizes a low reaction temperature, thereby improving the reaction yield and reducing production costs. In practical production, it offers advantages such as safety and high efficiency.

[0008] The purpose of this invention is to provide a method for preparing p-tert-butylbenzaldehyde by low-temperature oxidation. The method involves using p-tert-butyltoluene as a raw material at 10-30°C, in an acidic organic solvent, under the action of a catalyst and an initiator, and by introducing oxygen to oxidize and prepare p-tert-butylbenzaldehyde.

[0009] The catalyst is selected from one or more cobalt-containing compounds, preferably one or more cobalt carboxylate compounds, and more preferably cobalt acetate.

[0010] The initiator is selected from one or more bromine-containing substances, preferably one or more of elemental bromine, hydrogen bromide and metal bromide salts, and more preferably HBr.

[0011] The acidic organic solvent is selected from one or more carboxylic acid solvents, preferably one or more alkyl carboxylic acid solvents, and more preferably acetic acid.

[0012] The oxygen pressure is 20-45 bar, preferably 25-40 bar, and more preferably 30-35 bar.

[0013] Another objective of this invention is to provide p-tert-butylbenzaldehyde prepared by the aforementioned low-temperature oxidation method.

[0014] The present invention has the following beneficial effects:

[0015] (1) In this invention, p-tert-butylbenzaldehyde is prepared by one-step reaction using tert-butyltoluene as the starting material. The process is simple, easy to control, and conducive to stable production to obtain the target product.

[0016] (2) In this invention, a cobalt-containing compound is used as a catalyst and an initiator is introduced, especially an aqueous solution of hydrogen bromide, which improves the reaction activity and allows the reaction to be carried out at low temperature (10-30℃).

[0017] (3) The process temperature in this invention is 10-30℃, which avoids high-temperature reactions, effectively inhibits the occurrence of side reactions, reduces by-products, and improves selectivity and yield. Attached Figure Description

[0018] Figure 1 The GC analysis diagram of the tert-butylbenzaldehyde product in Example 1 of the present invention is shown.

[0019] Figure 2 The GC analysis chromatogram of p-tert-butylbenzaldehyde prepared in Comparative Example 1 of the present invention is shown.

[0020] Figure 3 The GC analysis chromatogram of p-tert-butylbenzaldehyde prepared in Comparative Example 2 of the present invention is shown. Detailed Implementation

[0021] The present invention will now be described in detail through specific embodiments, and the features and advantages of the present invention will become clearer and more explicit with these descriptions.

[0022] This invention provides a method for preparing p-tert-butylbenzaldehyde by low-temperature oxidation. The method involves using p-tert-butyltoluene as a raw material in an acidic organic solvent at 10-30°C, with oxygen introduced in the presence of a catalyst and an initiator, to oxidize and prepare p-tert-butylbenzaldehyde.

[0023] The preferred reaction temperature is 15-25℃, more preferably 15-20℃. Within this temperature range, the reaction exhibits high selectivity and yield for the product p-tert-butylbenzaldehyde; excessively high temperatures result in lower selectivity, lower yield, and the generation of impurities. Furthermore, operating at 15-25℃ is more conducive to safer production, as the reaction is less hazardous than at higher temperatures. Low temperatures offer greater safety for oxidation reactions compared to high temperatures. The solvents used in this invention have low flash points (e.g., acetic acid and propionic acid have flash points of 39℃ and 54℃ respectively under standard atmospheric pressure); flash points increase with pressure, and since this invention involves a low-temperature reaction, with the reaction temperature significantly lower than the solvent's flash point, it offers better safety and greater industrial potential compared to other processes.

[0024] The catalyst is selected from one or more cobalt-containing compounds, preferably one or more cobalt carboxylate compounds, and more preferably cobalt acetate. The catalyst is 1 wt% to 11 wt% of p-tert-butyltoluene, preferably 1.5 wt% to 9 wt%, and more preferably 2 wt% to 7 wt%.

[0025] The initiator is selected from one or more bromine-containing substances, preferably one or more of elemental bromine, hydrogen bromide, and metal bromide salts, more preferably hydrogen bromide, such as an aqueous solution of hydrogen bromide. The initiator accounts for 10wt% to 80wt% of the catalyst mass, preferably 14wt% to 70wt%, more preferably 18wt% to 60wt%. Insufficient initiator dosage results in slow initiation (long initiation time, or even no initiation), while excessive initiator dosage will leave a small amount of residue during product separation, affecting product quality.

[0026] When the initiator is an aqueous solution of hydrogen bromide, its concentration is 20wt% to 50wt%, preferably 25wt% to 45wt%, and more preferably 30wt% to 40wt%. The initiation rate of the above-mentioned concentrations of aqueous hydrogen bromide is slower at higher concentrations, and excessively high concentrations can affect the catalyst's lifetime.

[0027] The acidic organic solvent is selected from one or more carboxylic acid solvents, preferably one or more alkyl carboxylic acid solvents containing 2-5 carbon atoms, and more preferably acetic acid. The mass ratio of the acidic organic solvent to p-tert-butyltoluene is (70-130):40, preferably (80-120):40, and more preferably (90-110):40. The product selectivity decreases with increasing carbon chain length of the organic carboxylic acid.

[0028] The oxygen pressure is 20–35 bar, preferably 25–35 bar, and more preferably 30–35 bar. If the oxygen pressure is too low (less than 20 bar), the reaction is slow or even nonexistent; if the oxygen pressure is too high (greater than 35 bar), the reaction has no obvious benefit and instead increases the risk; the reaction achieves better results when the reaction pressure is 30–35 bar.

[0029] The reaction time is 4-9 hours, preferably 5-8 hours, and more preferably 6-7 hours.

[0030] The present invention also provides p-tert-butylbenzaldehyde prepared by the method for preparing p-tert-butylbenzaldehyde using the aforementioned low-temperature oxidation.

[0031] Example

[0032] Example 1

[0033] 100g of acetic acid, 40g of p-tert-butyltoluene, and 1.8g of cobalt acetate were added sequentially to a high-pressure reactor. The mixture was stirred while maintaining the reactor temperature at 17℃ and the stirring speed at 200-300 rpm. After mixing, 1.0g of 35wt% hydrogen bromide aqueous solution was added to the reactor, and oxygen was introduced to pressurize the mixture to 30-35 bar. The reaction was carried out for 6-7 hours, with the reactor pressure controlled at 30-35 bar during the reaction. After the reaction was completed, the pressure was released, and 300g of water was added to the reactor. After stirring for 30 minutes, the reaction solution was allowed to stand for oil-water separation to obtain the product p-tert-butylbenzaldehyde, with a molar yield of 94.74%.

[0034] The obtained p-tert-butylbenzaldehyde product was analyzed by gas chromatography (GC), and the test results are as follows: Figure 1 As shown.

[0035] Comparative Example

[0036] Comparative Example 1

[0037] p-tert-butylbenzaldehyde was prepared according to the method in Example 1, with the only difference being that the reactor temperature was 34°C. The molar yield was 87.06%. The product chromatogram is shown below. Figure 2 As shown.

[0038] Comparative Example 2

[0039] p-tert-butylbenzaldehyde was prepared according to the method in Example 1, with the only difference being that the reactor temperature was 56°C. The molar yield was 69.12%. The product chromatogram is shown below. Figure 3 As shown.

[0040] The present invention has been described in detail above with reference to specific embodiments and / or exemplary examples, as well as the accompanying drawings. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for preparing p-tert-butylbenzaldehyde by low-temperature oxidation, comprising: using p-tert-butyltoluene as a raw material, in an acidic organic solvent, under the action of a catalyst and an initiator, oxidizing the raw material with oxygen to obtain p-tert-butylbenzaldehyde at 10-25°C. The catalyst is cobalt acetate, the initiator is an aqueous solution of hydrogen bromide, and the acidic organic solvent is acetic acid. The catalyst is 1 wt% to 11 wt% of p-tert-butyltoluene. The initiator is 10wt%~80wt% of the catalyst mass. The concentration of the hydrogen bromide aqueous solution is 20wt%~50wt%. The mass ratio of the acidic organic solvent to p-tert-butyltoluene is (70-130):

40. The oxygen pressure is 20-35 bar.

2. The method according to claim 1, characterized in that, The mass ratio of the acidic organic solvent to p-tert-butyltoluene is (80-120):

40.

3. The method according to claim 2, characterized in that, The mass ratio of the acidic organic solvent to p-tert-butyltoluene is (90-110):

40.

4. The method according to claim 1, characterized in that, The catalyst is 1.5 wt% to 9 wt% of p-tert-butyltoluene.

5. The method according to claim 4, characterized in that, The catalyst is 2 wt% to 7 wt% of p-tert-butyltoluene.

6. The method according to claim 1, characterized in that, The initiator is 14wt% to 70wt% of the catalyst mass.

7. The method according to claim 6, characterized in that, The initiator is 18wt% to 60wt% of the catalyst mass.

8. The method according to claim 1, characterized in that, The concentration of the hydrogen bromide aqueous solution is 25wt%~45wt%.

9. The method according to claim 8, characterized in that, The concentration of the hydrogen bromide aqueous solution is 30wt%~40wt%.

10. The method according to claim 1, characterized in that, The oxygen pressure is 25-35 bar.

11. The method according to claim 10, characterized in that, The oxygen pressure is 30-35 bar.

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