Method for synthesizing carvacrol by using byproduct carvacrol ether as raw material

Abstract

The invention belongs to the technical field of organic synthesis, and particularly discloses a method for synthesizing carvacrol by taking a byproduct carvacrol ether as a raw material, which comprises the following steps: S1, dissolving the raw material carvacrol ether in a solvent, and carrying out heating reaction under the action of a catalyst in a hydrogen atmosphere to generate carvacrol, tetrahydrocarvone and tetrahydrocarvacrol; and S2, after the reaction is finished, filtering, recovering the catalyst, and carrying out vacuum rectification on the filtrate to obtain a carvacrol finished product, tetrahydrocarvone and tetrahydrocarvacrol. Compared with the prior art, the method has the advantages that the synthetic route is short, the production conversion rate is high, the selectivity is good, the combined yield of the carvacrol, the tetrahydrocarvacrol and the tetrahydrocarvone can reach 70%, filtering separation and catalyst recovery are performed after the reaction, and the filtrate can be directly rectified to obtain carvacrol with the content of 99%; the by-products tetrahydrocarveol and tetrahydrocarvone can be dehydrogenated to be continuously converted into carvacrol, so that the maximum utilization of the products is realized, the production cost can be reduced, three industrial wastes are reduced, and the economic benefit is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, relates to the synthesis of an organic product carvacrol, and specifically relates to a method for synthesizing carvacrol using a by-product carvacrol ether as a raw material. Background Art

[0002] Carvacrol is an isomer of thymol, and its aroma is similar to thymol, so it is also called isothymol. Carvacrol is a colorless to light yellow thick oily liquid with the smell of thymol. As a commonly used food additive and fragrance, it has the characteristics of low toxicity and naturalness. Carvacrol is mainly used to prepare flavors such as dill, cloves, mint and vanilla, and is used in toothpaste, tooth powder, oral products, talcum powder, soap and daily industrial products. It is used as a local anesthetic in medicine. In addition, carvacrol can kill bacteria and intestinal parasites and can be used as a disinfectant and bactericide. Therefore, the industrial production of carvacrol has important applications and economic value.

[0003] There are three main routes for synthesizing carvacrol at present. One is to use carvone / isodihydrocarvone as raw materials and synthesize carvacrol by intramolecular rearrangement under the action of strong acid. For example, CN101475448A reported that organic acid or inorganic acid was used as the main catalyst, and PEG-600 or PEG-400 was used as an auxiliary agent to promote the intramolecular rearrangement of carvone to synthesize carvacrol; Patent CN107867975A reported that isodihydrocarvone was obtained by acidic rearrangement after alkaline epoxidation to obtain carvacrol; the catalyst used in the acidic rearrangement method is cheap, and the process does not require high equipment, so it is widely used in industrial production. However, this reaction is accompanied by a side reaction of two molecules of carvacrol being dehydrated to form carvacrol ether.

[0004]

[0005] The second method uses dihydrocarvone / isodihydrocarvone as raw materials, and undergoes dehydrogenation isomerization to synthesize carvacrol under the action of a metal catalyst. For example, patent CN105481657A dissolves isodihydrocarvone and a catalyst in a solvent, and heats them to undergo a dehydrogenation and oxidation reaction to generate carvacrol; patent CN107365247A uses dihydrocarvone as a raw material, and uses Cu / Cr to catalyze the dehydrogenation and isomerization of dihydrocarvone to synthesize carvacrol; patent CN109206300A reports that isodihydrocarvone and a carbon-based composite catalyst are dissolved in a solvent, and heated to undergo a dehydrogenation and oxidation reaction to generate carvacrol; the reaction used in the above method is a dehydrogenation reaction, which has high requirements for equipment and a high reaction temperature, often higher than 200°C, which poses a great safety hazard, so it is currently less industrialized.

[0006]

[0007] The third method uses o-methylphenol as a raw material and synthesizes carvacrol through a Friedel-Crafts reaction with isopropanol or 2-halopropane. For example, patent CN 1488615 reported the use of aluminum chloride or ferric chloride to promote the reaction of o-methylphenol with 2-chloropropane to synthesize carvacrol; this method will produce a large amount of aluminum salt and iron salt solid waste, causing environmental pollution, and the Friedel-Crafts reaction has poor selectivity and high production cost, which limits its further application in production.

[0008]

[0009] Among the above three methods, the acidic rearrangement method uses a cheap catalyst and has low requirements on equipment, so it is widely used in industrial production. However, when applied to industrial production, the carvacrol ether produced by it affects the reaction yield, increases the reaction kettle liquid rate, and brings more economic losses. Therefore, if the by-product carvacrol ether can be comprehensively utilized, it will be beneficial to promote the industrial production of carvacrol. Summary of the invention

[0010] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for synthesizing carvacrol using by-product carvacrol ether as raw material. The present invention uses by-product carvacrol ether produced in the process of preparing carvacrol by acidic rearrangement as raw material, and through the screening of solvents, catalysts, auxiliary agents, temperature and hydrogen pressure, carvacrol is synthesized with high selectivity. Tetrahydrocarvone and tetrahydrocarveol produced in the reaction process can be converted into carvacrol by dehydrogenation.

[0011] The present invention is achieved through the following technical solutions: A method for synthesizing carvacrol using carvacrol ether as a byproduct as a raw material comprises the following steps: S1: dissolving the raw material carvacrol ether in a solvent, and reacting at elevated temperature in the presence of a catalyst and hydrogen to generate carvacrol, tetrahydrocarvone, and tetrahydrocarveol. The reaction equation of the process is as follows:

[0012] S2: After the reaction is completed, the catalyst is recovered by filtering, and the filtrate is subjected to vacuum distillation to obtain the carvacrol product and tetrahydrocarvone and tetrahydrocarveol; The solvent is one or a mixture of two or more of water, methanol, ethanol, isopropanol, toluene, xylene and cyclohexane; The catalyst is one or a mixture of two or more of Pd / C, Pd / Al2O3, Pt / C or Raney Ni.

[0013] During the reaction, GC was used to monitor the progress of the reaction. When the content of carvacrol ether in the raw material was detected to be lower than 1%, the reaction was stopped.

[0014] A further improvement of the present invention is: The catalyst is Pd / C or Pt / C or a mixture of the two.

[0015] Furthermore, an auxiliary agent is added during the reaction process, and the auxiliary agent is one or a mixture of two or more of sodium methoxide, sodium tert-butoxide, potassium tert-butoxide, sodium hydroxide, potassium hydroxide, barium hydroxide, lithium hydroxide, cesium carbonate, sodium carbonate, potassium carbonate, DBU (1,8-diazacyclo[5,4,0]undecene-7), and TMEDA (tetramethylethylenediamine).

[0016] Preferably, the auxiliary agent is one or a mixture of two or more of potassium tert-butoxide, sodium tert-butoxide or sodium methoxide.

[0017] Furthermore, the mass ratio of the auxiliary agent to the raw material is 0.01~5:100.

[0018] Furthermore, the solvent is water or a mixed solvent consisting of water and one or more of methanol, ethanol, isopropanol, toluene, xylene, and cyclohexane.

[0019] Furthermore, the mass ratio of the organic solvent to water in the mixed solvent is 1-100:100.

[0020] Furthermore, in S1, the hydrogen pressure is 5-80 bar, the temperature of the temperature-raising reaction is 100° C.-200° C., and the time is 2-12 h.

[0021] Furthermore, the mass ratio of the catalyst to the raw material is 0.01-5:100; the mass ratio of the solvent to the raw material is 0.5-10:1.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following obvious advantages: The invention has a short synthesis route, a high conversion rate and good selectivity. The combined yield of carvacrol, tetrahydrocarveol and tetrahydrocarvone can reach 70%. The reaction is filtered and separated, and the catalyst is recovered. The filtrate can be directly distilled to obtain carvacrol with a content of 99%. The by-products tetrahydrocarveol and tetrahydrocarvone can be further converted into carvacrol through dehydrogenation.

[0023] The raw material carvacrol ether of the invention mainly comes from the foot oil of carvone / isodihydrocarvone acid rearrangement, and the carvacrol ether is comprehensively utilized to be converted into carvacrol with utilization value, and the by-products tetrahydrocarveol and tetrahydrocarvone can also be further dehydrogenated and converted into carvacrol, so that the product can be utilized to the maximum extent, the production cost can be reduced, the three industrial wastes can be reduced, and the economic benefit can be improved. DETAILED DESCRIPTION

[0024] The present invention is described in detail below.

[0025] Example 1 500g of carvacrol ether was added to the reactor, followed by 5g of Pd / C and 5g of sodium tert-butoxide, followed by 500g of water, nitrogen replacement, and then hydrogen was introduced to 40 bar, the temperature was raised to 150°C, and the reaction was continued for 8h until the GC content of the raw material was less than 1%, and the reaction was stopped. After the reaction was completed, the crude product was filtered out and then distilled to obtain 230g of carvacrol, 105g of tetrahydrocarvone, and 36g of tetrahydrocarveol, with a combined yield of 71%.

[0026] Example 2 500g of carvacrol ether was added to the reactor, followed by 5g of Pt / C and 5g of sodium hydroxide, and then 500g of a mixed solvent, in which the weight ratio of methanol to water was 1:10, and nitrogen was replaced. Then hydrogen was introduced to 80 bar, and the temperature was raised to 200°C. The reaction was continued for 4 hours until the GC content of the raw material was less than 1%, and the reaction was stopped. After the reaction was completed, the crude product was filtered out and then distilled to obtain 200g of carvacrol, 89g of tetrahydrocarvone, and 40g of tetrahydrocarveol, with a combined yield of 63.6%. Example 3

[0027] 500g of carvacrol ether was added to a reactor, followed by 5g of Pd / Al2O3 and 5g of potassium hydroxide, and then 250g of a mixed solvent, wherein the weight ratio of cyclohexane to water was 1:5, and nitrogen was replaced, and then hydrogen was introduced to 20 bar, and the temperature was raised to 180°C, and the reaction was carried out for 10 hours until the GC content of the raw material was less than 1%, and then the reaction was stopped. After the reaction was completed, the crude product was filtered out and then distilled to obtain 156g of carvacrol, 85g of tetrahydrocarvone, and 75g of tetrahydrocarveol, with a combined yield of 61.4%.

[0028] Example 4 500g of carvacrol ether was added to the reactor, and 5g of Pt / C was added without adding an auxiliary agent. Then 250g of water was added, and nitrogen was replaced. Then hydrogen was introduced to 40bar, and the temperature was raised to 180°C. The reaction was carried out for 8h. The reaction was stopped when the GC content of the raw material was less than 1%. After the reaction was completed, the crude product was filtered out and then distilled to obtain 210g of carvacrol, 110g of tetrahydrocarvone, and 65g of tetrahydrocarveol. The combined yield of the three was 67.4%.

[0029] Example 5 500g of carvacrol ether was added to a reactor, followed by 5g of Raney Ni and 5g of sodium methoxide, and then 500g of a mixed solvent, wherein the weight ratio of isopropanol to water was 1:10, and nitrogen was replaced, and then hydrogen was introduced to 60 bar, and the temperature was raised to 150°C, and the reaction was carried out for 8 hours until the GC content of the raw material was less than 1%, and then the reaction was stopped. After the reaction was completed, the crude product was filtered out, and then the crude product was distilled to obtain 170g of carvacrol, 140g of tetrahydrocarvone, and 40g of tetrahydrocarveol, with a combined yield of 68.2%.

[0030] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for synthesizing carvacrol using carvacrol ether as a by-product as a raw material, characterized in that: The following steps are involved: S1: dissolving the raw material carvacrol ether in a solvent, and reacting at elevated temperature in the presence of a catalyst and a hydrogen atmosphere to generate carvacrol, tetrahydrocarvone, and tetrahydrocarveol; S2: After the reaction is completed, the catalyst is recovered by filtering, and the filtrate is subjected to vacuum distillation to obtain the carvacrol product and tetrahydrocarvone and tetrahydrocarveol; The solvent is one or a mixture of two or more of water, methanol, ethanol, isopropanol, toluene, xylene and cyclohexane; The catalyst is one or a mixture of two or more of Pd / C, Pd / Al2O3, Pt / C or Raney Ni.

2. A method for synthesizing carvacrol using by-product carvacrol ether as raw material according to claim 1, characterized in that: During the reaction, GC was used to monitor the progress of the reaction. When the content of carvacrol ether in the raw material was detected to be lower than 1%, the reaction was stopped.

3. A method for synthesizing carvacrol using by-product carvacrol ether as raw material according to claim 1, characterized in that: The catalyst is Pd / C or Pt / C or a mixture of the two.

4. A method for synthesizing carvacrol using carvacrol ether as a by-product as claimed in claim 1, characterized in that: An auxiliary agent is added during the reaction process, and the auxiliary agent is one or a mixture of two or more of sodium methoxide, sodium tert-butoxide, potassium tert-butoxide, sodium hydroxide, potassium hydroxide, barium hydroxide, lithium hydroxide, cesium carbonate, sodium carbonate, potassium carbonate, DBU, and TMEDA.

5. A method for synthesizing carvacrol using by-product carvacrol ether as raw material according to claim 4, characterized in that: The auxiliary agent is one or a mixture of two or more of potassium tert-butoxide, sodium tert-butoxide or sodium methoxide.

6. A method for synthesizing carvacrol using by-product carvacrol ether as raw material according to claim 5, characterized in that: The mass ratio of the auxiliary agent to the raw material is 0.01-5:

100.

7. A method for synthesizing carvacrol using by-product carvacrol ether as raw material according to claim 1, characterized in that: The solvent is water or a mixed solvent consisting of water and one or more of methanol, ethanol, isopropanol, toluene, xylene and cyclohexane.

8. A method for synthesizing carvacrol using by-product carvacrol ether as raw material according to claim 7, characterized in that: The mass ratio of the organic solvent to water in the mixed solvent is 1-100:

100.

9. A method for synthesizing carvacrol using by-product carvacrol ether as raw material according to claim 1, characterized in that: In S1, the hydrogen pressure is 5-80 bar, the temperature of the heating reaction is 100°C-200°C, and the time is 2-12 hours.

10. The method for synthesizing carvacrol using carvacrol ether as a by-product as claimed in claim 1, characterized in that: The mass ratio of the catalyst to the raw material is 0.01-5:100; the mass ratio of the solvent to the raw material is 0.5-10:1.

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