A process for the preparation of 2,6-di-tert-butyl-4-methylphenol

Abstract

This invention uses 2,6-di-tert-butylphenol and formaldehyde as main raw materials. An etherification reaction is carried out in the presence of an alcohol solvent and the catalyst triethylamine. The solvent and catalyst are then recovered by distillation and returned to the next batch of reaction. The resulting etherified product is dissolved in a hydrocarbon solvent and hydrogenated in the presence of a nickel-copper-titanium composite catalyst to obtain 2,6-di-tert-butyl-4-methylphenol. This invention innovatively uses triethylamine as a catalyst to obtain an intermediate through etherification, followed by hydrogenation to obtain 2,6-di-tert-butyl-4-methylphenol in high yield. This avoids the high losses and environmental odor problems associated with using dimethylamine as a reactant.

Description

Technical Field

[0001] This invention relates to a method for preparing 2,6-di-tert-butyl-4-methylphenol, specifically a method for preparing 2,6-di-tert-butyl-4-methylphenol by etherification and hydrogenation reduction of 2,6-di-tert-butylphenol with formaldehyde under the action of a catalyst. Background Technology

[0002] 2,6-Di-tert-butyl-4-methylphenol is used as a food additive and is known as the antioxidant BHT. In the petrochemical industry, it is called antioxidant and anti-scorching agent T501. It is a multi-purpose, world's most widely used phenolic non-coloring antioxidant. It is an excellent antioxidant and anti-gumming agent for oils, especially lubricating oils, and is also a general antioxidant for synthetic rubbers such as butadiene, styrene-butadiene, chloroprene, and nitrile butadiene, as well as synthetic resins and plastics such as polyethylene, polystyrene, polypropylene, and ABS resin. Food-grade antioxidant BHT is used to prevent rancidity of animal and vegetable oils, and is also used as an antioxidant in oil-containing foods and cosmetics, as well as in food-grade plastics and packaging synthetic materials that come into contact with food.

[0003] The main synthesis processes for 2,6-di-tert-butyl-4-methylphenol include the p-cresol method, the (m- and p-)mixed cresol method, and the phenol method.

[0004] The p-cresol process involves the alkylation of p-cresol, produced by the sulfonation and alkaline fusion of high-purity toluene, with isobutylene under an acidic catalyst. Following distillation and crystallization, high-purity 2,6-di-tert-butyl-4-methylphenol is obtained. However, this process suffers from high raw material costs and difficulties in sourcing raw materials.

[0005] The (meta- and para-)mixed cresol process uses mixed cresols, a byproduct of coal tar, as raw material. Under the action of an acidic catalyst, it reacts with isobutylene through alkylation. Then, after complex distillation and crystallization, 2,6-di-tert-butyl-4-methylphenol is obtained. The product of this process has a complex composition of impurities, making it difficult to meet food-grade standards. The equipment also suffers from severe corrosion and pollution.

[0006] In recent years, domestic and international reports (Chinese Patent CN108250047A, US Patent US4122287) have described a novel process for synthesizing 2,6-di-tert-butyl-4-methylphenol from phenol. Phenol reacts with isobutylene under a catalyst to yield mono-tert-butylphenol, 2,4-di-tert-butylphenol, and 2,6-di-tert-butylphenol, which are then separated to obtain high-purity individual products. Specifically, 2,6-di-tert-butylphenol undergoes a Mannich reaction with formaldehyde and dimethylamine in an alcoholic medium (such as ethanol or methanol) to form a Mannich base, which is then subjected to pressurized catalytic hydrogenation at 120°C to produce 2,6-di-tert-butyl-4-methylphenol, with a yield of 98.7% (based on 2,6-di-tert-butylphenol). The reaction principle is as follows: .

[0007] The aforementioned patent can yield products with high yield and high purity, but it also has certain drawbacks. The dimethylamine used in the reaction has a low boiling point, and its aqueous solution is generally used, which will generate wastewater. At the same time, due to the special properties of dimethylamine, it is easy to volatilize during the reaction and recovery process, resulting in high losses and producing a foul odor in the air, which is not environmentally friendly. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the technical problem to be solved by this invention is to provide a high-yield, low-cost, and environmentally friendly method for preparing 2,6-di-tert-butyl-4-methylphenol.

[0009] This invention uses 2,6-di-tert-butylphenol and polyoxymethylene as the main raw materials. An etherification reaction is carried out in the presence of an alcohol solvent and a triethylamine catalyst. The solvent and catalyst are then recovered by distillation and returned to the next batch of reaction. The resulting ether is dissolved in a hydrocarbon solvent and hydrogenated in the presence of a nickel-copper-titanium composite catalyst to obtain 2,6-di-tert-butyl-4-methylphenol.

[0010] The reaction principle of this invention is as follows: .

[0011] According to the present invention, the molar ratio of 2,6-di-tert-butylphenol to formaldehyde is 1:1-1.7, preferably 1:1.2.

[0012] According to the present invention, the mass ratio of 2,6-di-tert-butylphenol to the catalyst triethylamine is 1:0.5-1.0, preferably 1:0.9.

[0013] According to the present invention, the solvent used in the reaction is methanol, ethanol, isopropanol, isobutanol or a mixture thereof in any proportion, and the ratio of solvent to 2,6-di-tert-butylphenol is 1-3:1, preferably 2:1.

[0014] According to the present invention, the temperature of the etherification reaction is 70-150°C, optimized to 120-130°C, and the reaction time is 1-5 hours, preferably 2-3 hours.

[0015] According to the present invention, the hydrogenation catalyst is a modified composition of nickel-copper-titanium, and the amount of catalyst used is 5-15% of the weight of the ether.

[0016] According to the present invention, the nickel-copper-titanium composition ranges in the hydrogenation catalyst are 40-60%, 30-50%, and 5-10%, respectively.

[0017] According to the present invention, the hydrocarbon solvent for the hydrogenation reaction is heptane, decahydronaphthalene, or a mixture thereof in any proportion.

[0018] According to the present invention, the hydrogenation pressure is 1-4 MPa, preferably 2-3 MPa.

[0019] According to the present invention, the hydrogenation temperature is 100-150℃, preferably 120-130℃.

[0020] This invention innovatively uses triethylamine as a catalyst to obtain an intermediate through etherification, followed by hydrogenation to obtain 2,6-di-tert-butyl-4-methylphenol in high yield, thus avoiding the high losses and environmental odor problems caused by using dimethylamine as a reaction raw material. Detailed Implementation

[0021] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims. Example 1

[0022] Etherification reaction: Add 100 ml of methanol to a 250 ml reactor equipped with a stirrer and thermometer. While stirring, add 38.3 g of paraformaldehyde (1.2 mol, 94% purity). Heat to 60-70°C, then add 125 ml of triethylamine dropwise over 30 minutes. After the addition is complete, maintain the temperature for 60 minutes to allow for complete depolymerization. After depolymerization, cool to room temperature and pour into a dropping funnel for later use. Simultaneously, add 400 ml of methanol to another 1 L reactor. While stirring, add 206 g (1 mol) of 2,6-di-tert-butylphenol, maintaining stirring until the solid is completely dissolved. Then, add the above formaldehyde-methanol-catalyst solution dropwise to this reactor at room temperature over 20-30 minutes. After the addition is complete, maintain the temperature for 60 minutes, then heat to 120-130°C and continue the reaction for 2 hours. After the reaction is complete, evaporate the solvent and catalyst for reuse in the next batch reaction, yielding 236.2 g of the product with a purity of 94.2% and a yield of 98%. Example 2

[0023] Hydrogenation reaction: 100 g of a nickel-copper-titanium catalyst (containing 60% nickel, 35% copper, and 5% titanium) was charged into a fixed-bed reactor. The temperature was raised to 130°C, and hydrogen gas was introduced. The reactor pressure was maintained at 3 MPa. Simultaneously, the above solid was added to 700 g of heptane and dissolved with stirring. The solution was then pumped at a rate of 0.5 hr / min using a metering pump. -1 The hydrogenation reaction was carried out in the reactor at a space velocity. The solvent was removed from the reactants under vacuum to obtain 236 grams of crude 2,6-di-tert-butyl-4-methylphenol with a purity of 94% and a yield of 98.8%. The crude product was then recrystallized from ethanol to obtain pure 2,6-di-tert-butyl-4-methylphenol with a melting point of 69.8-70℃. Example 3

[0024] Same as Example 1, except that the amount of paraformaldehyde used was 32 grams (1 mol, content 94%), and 231 grams of crude product were obtained with a content of 93% and a yield of 94.6%. Example 4

[0025] Similar to Example 1, except that the nickel-copper-titanium catalyst composition is 40% nickel, 50% copper, and 10% titanium, 100 grams yields 220 grams of finished product with a content of 90% and a yield of 87.2%. Example 5

[0026] Similar to Example 1, except that the reaction duration was 5 hours, yielding 230.6 grams of finished product with a purity of 92.2% and a yield of 93.6%. Example 6

[0027] Same as Example 1, except the reaction temperature was 70℃, yielding 200 grams of finished product with a content of 85% and a yield of 74.8%. Example 7

[0028] Same as Example 1, except the reaction temperature was 150℃, yielding 218 grams of finished product with a content of 90% and a yield of 86.4%. Example 8

[0029] Same as Example 2, except that the hydrogenation temperature was 100℃, yielding 235 grams of crude 2,6-di-tert-butyl-4-methylphenol with a purity of 88%. Example 9

[0030] Same as Example 2, except that the hydrogenation temperature was 150℃, yielding 230 grams of crude 2,6-di-tert-butyl-4-methylphenol with a purity of 92%. Example 10

[0031] Similar to Example 2, except that the solvent was decahydronaphthalene, 236 grams of crude 2,6-di-tert-butyl-4-methylphenol were obtained with a purity of 93.8%. Example 11

[0032] Same as Example 2, except that the hydrogenation pressure was 4 MPa, yielding 230 grams of crude 2,6-di-tert-butyl-4-methylphenol with a purity of 92%. Example 12

[0033] Similar to Example 2, except that the solvent was a mixture of heptane and decahydronaphthalene in a mass ratio of 1:1, 235 g of crude 2,6-di-tert-butyl-4-methylphenol was obtained with a purity of 93.8%.

[0034] Based on the data from the above embodiments, the present invention uses triethylamine as an etherification catalyst, avoiding the use of trimethylamine raw material, which is volatile and produces a foul odor, and then obtains 2,6-di-tert-butyl-4-methylphenol in high yield through continuous hydrogenation reaction.

Claims

1. A method for preparing 2,6-di-tert-butyl-4-methylphenol, characterized by using... 2,6-Di-tert-butylphenol and polyoxymethylene are used as the main raw materials. The reaction is carried out in the presence of an alcohol solvent and a catalyst, triethylamine. The solvent and catalyst are then recovered and returned to the next batch of reaction. The resulting etherified product is dissolved in a hydrocarbon solvent and continuously hydrogenated in the presence of a hydrogenation catalyst to obtain 2,6-di-tert-butyl-4-methylphenol.

2. The preparation method according to claim 1, characterized in that... The molar ratio of 1,2,6-di-tert-butylphenol to formaldehyde is 1:1-1.7, preferably 1:1.

2.

3. The preparation method according to claim 1, characterized in that... The molar ratio of 1,2,6-di-tert-butylphenol to the catalyst triethylamine is 1:0.5-1.0, preferably 1:0.

9.

4. The preparation method according to claim 1, characterized in that... The solvent used in the etherification reaction is methanol, ethanol, isopropanol, isobutanol or a mixture thereof in any proportion, and the ratio of solvent to 2,6-di-tert-butylphenol is 1-3:1, preferably 2:

1.

5. The preparation method according to claim 1, characterized in that... The etherification reaction temperature is 70-150℃, optimized to 120-130℃, and the reaction time varies with the reaction temperature.

6. The preparation method according to claim 1, characterized in that... The catalyst for the hydrogenation reaction is a modified nickel-copper-titanium composition, and the amount of catalyst used is 5-15% of the weight of the ether.

7. The preparation method according to claim 6, characterized in that... The nickel-copper-titanium composition ranges in the hydrogenation catalyst are 40-60%, 30-50%, and 5-10%, respectively.

8. The preparation method according to claim 1, characterized in that... The hydrocarbon solvent used in the hydrogenation reaction is heptane, decahydronaphthalene, or a mixture thereof in any proportion.

9. The preparation method according to claim 1, characterized in that... The hydrogenation pressure is 1-4 MPa, preferably 2-3 MPa.

10. The preparation method according to claim 1, characterized in that... The hydrogenation temperature is 100-150℃, preferably 120-130℃.