Green synthesis method of 2, 6-dihydroxytoluene

Abstract

The invention provides a green synthesis method of 2, 6-dihydroxytoluene. According to the synthesis method, 2, 6-diaminotoluene is taken as a raw material, 2, 6-dihydroxytoluene can be directly obtained through one-step hydrolysis reaction, a sulfuric acid aqueous solution is matched with copper sulfate in the reaction process, and the problems that coking is serious and the yield is low when sulfuric acid is independently used are solved. Sodium sulfate, especially solid waste sodium sulfate, is utilized to saturate a solution in the post-treatment process, so that the extraction rate is improved, and the unit consumption of ethyl acetate is reduced. The synthesis method disclosed by the invention is high in efficiency, low in cost, less in three wastes, green and environment-friendly, and suitable for industrially producing the 2, 6-dihydroxytoluene.

Description

Technical Field

[0001] The present invention belongs to the field of chemical synthesis. Specifically, the present invention relates to a green synthesis method for synthesizing 2,6-dihydroxytoluene. Background Art

[0002] 2,6-Dihydroxytoluene, also known as 2-methylresorcinol, is an important chemical raw material with many important physical and chemical properties. It can be applied to multiple fields such as synthetic resins, pharmaceuticals, pesticides, pigments, dyes, agrochemicals, photosensitive materials, and explosives. 2,6-Dihydroxytoluene can not only be used as an intermediate, but also due to its good disinfection and sterilization function, it has been widely used in products such as shampoos and skin care products in recent years, showing a very strong market demand.

[0003] There are many synthesis methods for 2,6-dihydroxytoluene. Starting from different raw materials, 2,6-dihydroxytoluene can be synthesized through different routes. For example, using glutaric acid as the starting material, it reacts with acetyl chloride under the catalysis of nitrobenzene and aluminum chloride to form 2-methyl-1,3-cyclohexanedione, then reacts with acetic anhydride to obtain 2,6-diacetoxytoluene, and finally hydrolyzes to get 2,6-dihydroxytoluene; this method has a complex synthesis route, many by-products, large environmental pollution, and the total yield is only 50%. Using p-toluic acid as the raw material, sulfonation is carried out to introduce sulfonic acid groups at the 2,6-positions, then hydrolysis generates phenols at the 2,6-positions, and finally decarboxylation is carried out to obtain 2,6-dihydroxytoluene; this method uses a large amount of acid and base, is difficult to post-treat, has relatively serious environmental pollution, and the total yield is only about 50%. Using resorcinol as the raw material, it reacts with methanol in ammonium chloride-methanol to obtain the product, or first introduces tert-butyl groups at the 4,6-positions, then methylates with methanol or iodomethane, and finally removes the tert-butyl groups to obtain the product; the said method has many steps, high cost, relatively low total yield, and poor economy. Using 2,6-diaminotoluene as the raw material, hydrolysis is carried out to obtain 2,6-dihydroxytoluene. Regarding this method, US3933925 discloses that using NH4HSO4 as the catalyst, the molar ratio of 2,6-diaminotoluene to NH4HSO4 is 1:6, and the molar ratio to water is 1:60. Hydrolysis is carried out in an autoclave at 220 °C for 5 h to obtain the product 2,6-dihydroxytoluene, and the yield is 60.1%; this method has a large amount of catalyst used, low yield, and poor economy. CN103304381A discloses that under the catalysis of a composite solid acid catalyst, 2,6-diaminotoluene is hydrolyzed to 2,6-dihydroxytoluene in a steam reactor; however, in this method, the preparation of the composite solid acid catalyst is difficult, the operation of the steam reactor is complex and the temperature is as high as 300-350 °C, and the crude product of 2,6-dihydroxytoluene needs to be purified by vacuum distillation, and the practical value is not high. CN103626638A discloses that 2,6-diaminotoluene is dissolved in water, the pH value is adjusted to 1-3 with sulfuric acid, a NaNO2 solution is added at 0 °C, and then the temperature is raised to 40-80 °C for reaction to obtain 2,6-dihydroxytoluene. The role of NaNO2 is not disclosed in this document, nor is the yield of the reaction. CN103694087A discloses a method similar to CN103626638A, the only difference being that a Lewis acid is used instead of sulfuric acid. CN114085132A discloses that 2,6-diaminotoluene is hydrolyzed to 2,6-dihydroxytoluene in the presence of phosphoric acid and a catalyst. The amount of phosphoric acid used is 6-7 times the molar amount of 2,6-diaminotoluene, and the catalyst is ferric chloride, ferrous chloride, copper chloride, cuprous chloride, and the amount used is 0.01-0.06 times the molar amount of 2,6-diaminotoluene, and the yield can reach 90-95%; this method also requires the use of a very large amount of phosphoric acid, is difficult to post-treat, and has large environmental pollution.

[0004] In summary, the existing methods for synthesizing 2,6-dihydroxytoluene have disadvantages such as high cost, large pollution, low yield, and long process steps. There is an urgent need to develop a method that can synthesize 2,6-dihydroxytoluene more efficiently and environmentally friendly. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention provides a green synthesis method of 2,6-dihydroxytoluene, which is obtained by hydrolyzing 2,6-diaminotoluene in one step using sulfuric acid and copper sulfate as catalysts.

[0006] The synthesis method of 2,6-dihydroxytoluene according to the present invention comprises:

[0007] 2,6-diaminotoluene is hydrolyzed in an aqueous sulfuric acid solution in the presence of copper sulfate to obtain 2,6-dihydroxytoluene.

[0008] In one embodiment, the method comprises adding 2,6-diaminotoluene and an aqueous sulfuric acid solution to an autoclave, then adding copper sulfate, replacing with an inert gas, sealing the reaction kettle, heating the autoclave to 200-250 °C, with a pressure of 2-5 MPa, holding the reaction, cooling to 50-100 °C, adding a sulfate, discharging, cooling to below 40 °C, extracting with ethyl acetate, concentrating the organic layer to dryness, adding water, heating to dissolve clearly and then adding toluene and stirring, allowing the aqueous phase material to cool slowly and crystallize after layering, and separating to obtain 2,6-dihydroxytoluene.

[0009] In one embodiment, the mass concentration of the aqueous sulfuric acid solution is 10-30%, preferably 15-20%. The amount of the aqueous sulfuric acid solution used is 2-4 times the mass of 2,6-dihydroxytoluene, preferably 2.5-3.5 times. The amount of the aqueous sulfuric acid solution used can make both sulfuric acid and water within an appropriate range.

[0010] In one embodiment, the amount of copper sulfate used is 1-10% of the mass of 2,6-dihydroxytoluene, preferably 4-8%.

[0011] In one embodiment, the inert gas includes at least one of nitrogen, argon, and helium.

[0012] In one embodiment, the inert gas replacement is carried out multiple times to make the oxygen content < 0.05%.

[0013] In one embodiment, the reaction temperature is 220-240 °C and the pressure is 3-4 MPa. If the reaction temperature is too low, the conversion rate of 2,6-diaminotoluene is insufficient, and if the reaction temperature is too high, there is a risk of coking.

[0014] In one embodiment, the reaction time is 2-12 h, preferably 4-10 h.

[0015] In one embodiment, the temperature is lowered to 50 - 80 °C and then sulfate is added. Adding sulfate can increase the saturation of the solution, which is beneficial for extracting the product from water, thereby reducing the amount of solvent used. The sulfate can be sodium sulfate or potassium sulfate. The sulfate can be commercially available industrial pure or solid waste sulfate recovered from other reactions. The solid waste sulfate has relatively more impurities, but basically does not affect the purity of the final 2,6 - dihydroxytoluene product. The amount of sulfate used can be 0.1 - 0.3 times the mass of the sulfuric acid aqueous solution, preferably 0.12 - 0.2 times.

[0016] In one embodiment, the discharged material is cooled to below 30 °C or to room temperature, and then extracted with ethyl acetate.

[0017] In one embodiment, the amount of ethyl acetate used is 0.4 - 2 times the mass of the sulfuric acid aqueous solution, preferably 0.6 - 1 times.

[0018] In one embodiment, after the organic layer is concentrated to dryness, 0.5 - 2 times the mass of water based on the residue is added, and heated to above 45 °C to dissolve it clearly. Preferably, 1 - 1.5 times the mass of water based on the residue is added, and heated to 45 - 55 °C.

[0019] In one embodiment, after dissolving clearly, 0.3 - 0.6 times the mass of toluene based on the water added is added, preferably 0.5 times the mass of toluene based on the water added.

[0020] In one embodiment, the aqueous phase material is slowly cooled to - 5 - 10 °C for crystallization, and the crystallization time is 10 - 120 min. Preferably, the aqueous phase material is cooled to - 5 - 5 °C for crystallization.

[0021] Advantages of the present invention: The present invention provides a green synthesis method of 2,6 - dihydroxytoluene. The synthesis method of the present invention directly obtains 2,6 - dihydroxytoluene from 2,6 - diamino - toluene in one - step reaction. Sulfuric acid aqueous solution and copper sulfate are used in the reaction process, effectively reducing coking and improving the atom utilization rate; in the post - treatment process, sodium sulfate is used to form a saturated solution and then extracted, improving the extraction rate and reducing the unit consumption of ethyl acetate, and the sodium sulfate can be solid waste generated from other processes and can be fully utilized. Water crystallization is adopted, and water and toluene can be reused repeatedly, reducing sewage discharge and being beneficial to environmental protection. In short, the synthesis method of the present invention is highly efficient, low - cost, has less three - wastes, is green and environmentally friendly, and is suitable for industrial production of 2,6 - dihydroxytoluene. Detailed embodiments

[0022] The present invention is described in more detail below to facilitate understanding of the present invention.

[0023] The experimental methods in the following examples are all conventional methods unless otherwise specified. For those without specific technologies or conditions indicated in the examples, they are carried out according to the technologies or conditions described in the literature in this field or according to the product specifications.

[0024] Example 1: Add 100 g of 2,6-diaminotoluene and 300 g of 15% sulfuric acid aqueous solution into an autoclave, then add 5 g of copper sulfate. Replace with nitrogen three times, and detect that the oxygen content < 0.05%. Seal the reaction kettle. Heat the autoclave to 220 - 230 °C, with a pressure of 3 MPa, and keep the temperature for reaction for 6 hours. Cool down to 50 °C, add 50 g of solid waste sodium sulfate, discharge the material, cool down to room temperature, extract with 200 g of ethyl acetate, separate the layers to obtain the organic layer. Concentrate the organic layer to dryness first under normal pressure and then under reduced pressure. Add water with a mass 1 time that of the kettle residue, stir and dissolve it clearly at 45 - 55 °C, then add toluene with a mass 0.5 times that of the kettle residue, and stir for 1 hour to separate the layers. Slowly cool down the aqueous phase material to crystallize until the temperature in the kettle is 0 - 5 °C, keep the temperature for 30 minutes, and centrifuge to obtain 94.7 g of white crystal 2,6-dihydroxytoluene, with a yield of 93.2%, a purity of 99.8%, a melting point of 119 - 120 °C, and ESI-MS: 124.1[M+H] + 。

[0025] Example 2: Add 100 g of 2,6-diaminotoluene and 300 g of 20% sulfuric acid aqueous solution into an autoclave, then add 5 g of copper sulfate. Replace with nitrogen three times, and detect that the oxygen content < 0.05%. Seal the reaction kettle. Heat the autoclave to 220 - 230 °C, with a pressure of 3 MPa, and keep the temperature for reaction for 5 hours. Cool down to 70 °C, add 50 g of solid waste sodium sulfate, discharge the material, cool down to room temperature, extract with 200 g of ethyl acetate, separate the layers to obtain the organic layer. Concentrate the organic layer to dryness first under normal pressure and then under reduced pressure. Add water with a mass 1 time that of the kettle residue, stir and dissolve it clearly at 45 - 55 °C, then add toluene with a mass 0.5 times that of the kettle residue, and stir for 1 hour to separate the layers. Slowly cool down the aqueous phase material to crystallize until the temperature in the kettle is 0 - 5 °C, keep the temperature for 30 minutes, and centrifuge to obtain 95.3 g of white crystal 2,6-dihydroxytoluene, with a yield of 93.8%, a purity of 99.7%, and a melting point of 119 - 120 °C.

[0026] Example 3: Add 100 g of 2,6-diaminotoluene and 300 g of 20% sulfuric acid aqueous solution into an autoclave, then add 7.5 g of copper sulfate, displace with nitrogen three times, detect that the oxygen content is <0.05%, seal the reaction kettle, heat the autoclave to 220 - 230 °C, with a pressure of 3 MPa, keep the temperature for reaction for 5 hours, cool down to 60 °C, add 50 g of solid waste sodium sulfate, discharge the material, cool down to room temperature, extract with 200 g of ethyl acetate, separate the layers to obtain the organic layer. First concentrate the organic layer to dryness under normal pressure and then under reduced pressure, add water with a mass 1 time that of the kettle residue, stir and dissolve clearly at 45 - 55 °C, then add toluene with a mass 0.5 times that of the kettle residue, stir for 1 hour and separate the layers. Slowly cool down the aqueous phase material to crystallize, until the temperature in the kettle is -5 - 0 °C, keep the temperature for 30 minutes, and centrifuge to obtain 94.2 g of white crystal 2,6-dihydroxytoluene, with a yield of 92.7%, a purity of 99.8%, and a melting point of 119 - 120 °C.

[0027] Example 4: Add 100 g of 2,6-diaminotoluene and 300 g of 15% sulfuric acid aqueous solution into an autoclave, then add 5 g of copper sulfate, displace with nitrogen three times, detect that the oxygen content is <0.05%, seal the reaction kettle, heat the autoclave to 230 - 240 °C, with a pressure of 4 MPa, keep the temperature for reaction for 4 hours, cool down to 80 °C, add 50 g of sodium sulfate, discharge the material, cool down to room temperature, extract with 200 g of ethyl acetate, separate the layers to obtain the organic layer. First concentrate the organic layer to dryness under normal pressure and then under reduced pressure, add water with a mass 1 time that of the kettle residue, stir and dissolve clearly at 45 - 55 °C, then add toluene with a mass 0.5 times that of the kettle residue, stir for 1 hour and separate the layers. Slowly cool down the aqueous phase material to crystallize, until the temperature in the kettle is -5 - 0 °C, keep the temperature for 30 minutes, and centrifuge to obtain 95.5 g of white crystal 2,6-dihydroxytoluene, with a yield of 94.0%, a purity of 99.9%, and a melting point of 119 - 120 °C.

[0028] Comparative Example 1: Add 100 g of 2,6-diaminotoluene and 300 g of 20% sulfuric acid aqueous solution into an autoclave, displace with nitrogen three times, detect that the oxygen content is <0.05%, seal the reaction kettle, heat the autoclave to 220 - 230 °C, with a pressure of 3 MPa, keep the temperature for reaction for 10 hours, cool down to 70 °C, add 50 g of solid waste sodium sulfate, discharge the material, and there is a large amount of tar adhering to the bottom of the kettle and the stirring shaft; cool down to room temperature, extract with 200 g of ethyl acetate, separate the layers to obtain the organic layer. First concentrate the organic layer to dryness under normal pressure and then under reduced pressure, add water with a mass 1 time that of the kettle residue, stir and dissolve clearly at 45 - 55 °C, then add toluene with a mass 0.5 times that of the kettle residue, stir for 1 hour and separate the layers. Slowly cool down the aqueous phase material to crystallize, until the temperature in the kettle is 0 - 5 °C, keep the temperature for 30 minutes, and centrifuge to obtain 18.7 g of grayish-white 2,6-dihydroxytoluene, with a yield of 18.4%, a purity of 98.3%, and a melting point of 114 - 117 °C.

[0029] Comparative Example 2: Add 100 g of 2,6-diaminotoluene and 300 g of 20% sulfuric acid aqueous solution into an autoclave, then add 5 g of copper chloride, displace with nitrogen three times, detect that the oxygen content < 0.05%, seal the reaction kettle, heat the autoclave to 220 - 230 °C, the pressure is 3 MPa, keep the temperature for reaction for 5 hours, cool down to 70 °C, add 50 g of solid waste sodium sulfate, discharge the material, cool down to room temperature, extract with 200 g of ethyl acetate, separate the layers to obtain the organic layer. Concentrate the organic layer to dryness first under normal pressure and then under reduced pressure, add water with a mass 1 time that of the kettle residue, stir and dissolve clearly at 45 - 55 °C, then add toluene with a mass 0.5 times that of the kettle residue, stir for 1 hour and separate the layers. Slowly cool down the aqueous phase material to crystallize, until the temperature in the kettle is 0 - 5 °C, keep the temperature for 30 minutes, and centrifuge to obtain 78.6 g of white crystal 2,6-dihydroxytoluene, with a yield of 77.4%, a purity of 99.2%, and a melting point of 118 - 119 °C.

[0030] Comparative Example 3: Add 100 g of 2,6-diaminotoluene and 300 g of 15% sulfuric acid aqueous solution into an autoclave, then add 5 g of copper sulfate, displace with nitrogen three times, detect that the oxygen content < 0.05%, seal the reaction kettle, heat the autoclave to 220 - 230 °C, the pressure is 3 MPa, keep the temperature for reaction for 6 hours, cool down to room temperature and discharge the material, extract with 200 g of ethyl acetate, separate the layers to obtain the organic layer. Concentrate the organic layer to dryness first under normal pressure and then under reduced pressure, add water with a mass 1 time that of the kettle residue, stir and dissolve clearly at 45 - 55 °C, then add toluene with a mass 0.5 times that of the kettle residue, stir for 1 hour and separate the layers. Slowly cool down the aqueous phase material to crystallize, until the temperature in the kettle is 0 - 5 °C, keep the temperature for 30 minutes, and centrifuge to obtain 81.7 g of white crystal 2,6-dihydroxytoluene, with a yield of 80.4%, a purity of 99.9%, and a melting point of 119 - 120 °C.

[0031] It can be seen from the experimental results that the synthesis method of the present invention can prepare 2,6-dihydroxytoluene with high purity in high yield. In Comparative Example 1, due to the absence of the catalyst copper sulfate, the reaction coked severely, a large amount of tar adhered to the bottom of the kettle and the stirring shaft, the post-treatment was difficult, and the product yield was very low; in Comparative Example 2, although copper chloride was used as the catalyst, the coking problem was not completely solved, and the reaction yield was still insufficient; in Comparative Example 3, due to the absence of sodium sulfate, the extraction efficiency of ethyl acetate was insufficient, and at least one more extraction was required to reach the level of the present invention.

[0032] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the method of the present invention, several improvements and supplements can still be made, and these improvements and supplements should also be regarded as the protection scope of the present invention.

Claims

1. A method for synthesizing 2,6-dihydroxytoluene, characterized in that: The method comprises: 2,6-Diaminotoluene is hydrolyzed in a sulfuric acid aqueous solution in the presence of copper sulfate to obtain 2,6-dihydroxytoluene; wherein the mass concentration of the sulfuric acid aqueous solution is 10-30%, the amount of the sulfuric acid aqueous solution is 2-4 times the mass of the 2,6-dihydroxytoluene, and the amount of copper sulfate is 1-10% of the mass of the 2,6-dihydroxytoluene.

2. The method according to claim 1, characterized in that The method comprises the following steps: adding 2,6-diaminotoluene and a sulfuric acid aqueous solution into an autoclave, then adding copper sulfate, replacing with an inert gas, sealing the autoclave, heating the autoclave to 200-250°C and a pressure of 2-5MPa, keeping the temperature for reaction, cooling to 50-100°C, adding sulfate, discharging, cooling to below 40°C, extracting with ethyl acetate, concentrating the organic layer to dryness, adding water, heating to dissolve, then adding toluene and stirring, and after separation, slowly cooling the aqueous phase material for crystallization to obtain 2,6-dihydroxytoluene.

3. The method according to claim 1 or 2, characterized in that: The mass concentration of the aqueous sulfuric acid solution is 15-20%, and the amount of the aqueous sulfuric acid solution used is 2.5-3.5 times the mass of 2,6-dihydroxytoluene.

4. The method according to claim 1 or 2, characterized in that: The amount of copper sulfate used is 4-8% of the mass of 2,6-dihydroxytoluene.

5. The method according to claim 1 or 2, characterized in that: The reaction temperature is 220~240℃ and the pressure is 3~4MPa.

6. The method according to claim 2, characterized in that Cool down to 50~80℃ and then add sulfate; the amount of sulfate used is 0.1~0.3 times the mass of the sulfuric acid aqueous solution.

7. The method according to claim 2, characterized in that: The amount of ethyl acetate used is 0.4 to 2 times the mass of the aqueous sulfuric acid solution.

8. The method according to claim 2, characterized in that: After the organic layer is concentrated to dryness, add 0.5 to 2 times the mass of water of the residue and heat to above 45°C to make the solution clear.

9. The method according to claim 8, characterized in that After the solution is dissolved, add toluene in an amount 0.3 to 0.6 times the mass of water.

10. The method according to claim 9, characterized in that The aqueous phase material is slowly cooled to -5~10°C for crystallization, and the crystallization time is 10~120min.