Preparation method of menthol

Abstract

The invention belongs to the technical field of organic synthesis, and particularly discloses a preparation method of menthol, which comprises the following steps: (1) carrying out rearrangement reaction on 1-methyl-4-isopropenyl-cyclohex-2-ene-1-ol under the catalysis of a transition metal catalyst to generate 3-methyl-6-isopropenyl-cyclohex-2-ene-1-ol; and (2) carrying out hydrogenation reaction on the 3-methyl-6-isopropenyl-cyclohex-2-ene-1-ol under the catalysis of a hydrogenation catalyst to generate the menthol. According to the invention, 1-methyl-4-isopropenyl-cyclohex-2-ene-1-alcohol is taken as a raw material, and the raw material is a by-product of numerous carvone production enterprises, so that waste can be turned into wealth, the problem of environmental protection in production is solved, and new economic benefits and social benefits are created.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of organic synthesis, and relates to the synthesis of a perfume, in particular to a preparation method of menthol. BACKGROUND

[0002] Menthol is also known as menthol, menthol ice, with a melting point of 42-43 DEG C, a boiling point of 216 DEG C, a specific optical rotation of-51 DEG-45 DEG, a flash point of 93 DEG C, and a relative density of 0.8810 g / ml. It is a cyclic terpene alcohol flavor, which appears as colorless needle or shuttle columnar crystal or white crystalline powder. It has a cool, fresh, pleasant mint characteristic aroma, and a sweet and cool taste. Menthol is easily soluble in ethanol, chloroform, petroleum ether, diethyl ether, liquid paraffin or volatile oil, and is slightly soluble in water.

[0003] Menthol has the effects of relieving itching, pain, corrosion, stimulation, anesthesia, cooling and anti-inflammatory, and can be used for treating headache, neuralgia, itching, respiratory inflammation, atrophic rhinitis, hoarseness and the like. Menthol can be used as a food flavoring agent, a flavor enhancer, and can be used in candies (mint candies, gum), beverages, ice cream and the like, and is widely used in cigarettes, cosmetics, toothpaste, perfume, floral water and the like.

[0004]

[0005] The existing methods for synthesizing menthol are as follows: (1) CN 10160265 A reports a method for synthesizing menthol, which comprises the following steps: performing an amination reaction on ethylenediamine and myrcene to obtain geraniamine, performing isomerization on the geraniamine under the catalysis of a chiral catalyst to obtain an intermediate enamine, performing hydrolysis on the enamine in an acidic medium to obtain an intermediate D-citronellal, generating L-isomenthol under the catalysis of a Lewis acid catalyst and an organic solvent, and generating L-menthol after hydrogenation of the L-isomenthol. The method has complicated process steps, and a large amount of wastewater is generated in the post-treatment process, which is not environmentally friendly.

[0006]

[0007] (2) CN 105461516 B reports a method for synthesizing D,L-menthol by hydrogenation of thymol at 50-300 DEG C, then synthesizing D,L-menthol and benzoic acid to obtain D,L-menthyl benzoate, and then performing rectification and repeated recrystallization to obtain D-menthyl benzoate and L-menthyl benzoate, and then performing ester exchange to obtain D-menthol and L-menthol. The method has complex process steps, needs repeated recrystallization, and has low single yield.

[0008] (3) CN 105254475 B reports a kind of with citronellol as raw material, in solvent, at a certain temperature, by the action of oxide free radical initiator, it occurs intramolecular free radical addition reaction, and obtains racemic menthol;The raw material citronellol used in this method is relatively expensive, there is no economic benefit, not conducive to industrial production.

[0009]

[0010] From the above patents, it can be seen that there are many methods for synthesizing menthol reported at present, but all have problems such as complicated process steps, poor environmental protection, low economic benefit and so on, which are not conducive to industrial production. SUMMARY

[0011] In view of the deficiencies of the prior art, the purpose of the present application is to provide a preparation method of menthol with mild conditions and simple operation, and the catalyst used in the present application can be recycled;The present application uses 1-methyl-4-isopropenyl-cyclohex-2-en-1-ol as raw material, which is a by-product of many spearmint oil production enterprises, using this as raw material not only turns waste into treasure, solves the environmental problem faced in production, but also creates new economic and social benefits.

[0012] The present application is realized by the following technical solutions: A preparation method of menthol, comprising the following steps: (1) making 1-methyl-4-isopropenyl-cyclohex-2-en-1-ol undergo rearrangement reaction under the catalysis of transition metal catalyst to generate 3-methyl-6-isopropenyl-cyclohex-2-en-1-ol; (2) making 3-methyl-6-isopropenyl-cyclohex-2-en-1-ol undergo hydrogenation reaction under the catalysis of hydrogenation catalyst to generate menthol.

[0013] The reaction route is as shown below:

[0014] Further improved schemes of the present application are: The transition metal catalyst is ammonium metavanadate.

[0015] Further, the mass ratio of 1-methyl-4-isopropenyl-cyclohex-2-en-1-ol to transition metal catalyst is 1: (0.0005-0.01).

[0016] Further, the temperature of the rearrangement reaction is 130-180℃, and the rearrangement reaction is stopped when the conversion of the raw material is 40%-60%.

[0017] Further, the hydrogenation catalyst is selected from Raney Ni, palladium on carbon or copper on carbon.

[0018] Further, the mass ratio of the 3-methyl-6-isopropenyl-cyclohex-2-en-1-ol to the hydrogenation catalyst is 1: (0.005-0.03).

[0019] Further, the temperature of the hydrogenation reaction is 80-150℃, the pressure is 10-60 bar, and the time is 4-8h.

[0020] Further, the steps (1) and (2) further comprise the operation of separation and purification.

[0021] Compared with the prior art, the present application has the following beneficial effects: The rearrangement reaction in the preparation method of the present application has high selectivity, the catalyst used is cheap and environmentally friendly, and can be recycled; the entire preparation process has mild conditions and simple and convenient operation.

[0022] The present application uses 1-methyl-4-isopropenyl-cyclohex-2-en-1-ol as a raw material, which is a by-product of many spearmint oil production enterprises. Using this as a raw material not only turns waste into treasure, solves the environmental problem faced in production, but also creates new economic and social benefits. DETAILED DESCRIPTION

[0023] The present application will be described in detail below in combination with specific examples.

[0024] Example 1

[0025] (1) 1-methyl-4-isopropenyl-cyclohex-2-en-1-ol 500 g, ammonium metavanadate 1.5 g, were added to a reaction kettle, stirred uniformly, heated to 150℃, then kept at 150℃ for 3h, until the conversion of the raw material was 50%-60%, the reaction was stopped, then vacuum distillation was carried out to obtain 223 g of 3-methyl-6-isopropenyl-cyclohex-2-en-1-ol, and the raw material 225 g was recovered, the conversion rate was 55%, and the selectivity was 81%.

[0026] (2) 223 g of 3-methyl-6-isopropenyl-cyclohex-2-en-1-ol was added to a hydrogenation kettle, 2.2 g of Raney Ni catalyst was added, stirred uniformly, the hydrogenation kettle was replaced with nitrogen for 3 times, then replaced with hydrogen for 3 times, then 30 bar of hydrogen was filled, heated to 130℃, kept for 4h, until the content of the raw material was less than 1%, the reaction was stopped, and vacuum distillation was carried out to obtain menthol 195 g.

[0027] Example 2

[0028] (1) Into a reactor, 1-methyl-4-isopropenyl-cyclohex-2-en-1-ol 500 g, ammonium metavanadate 0.5 g were added, stirred uniformly, heated to 150°C, then kept at 150°C for 5h, until the conversion of raw material was 40%-50%, stopped the reaction, then reduced pressure distillation to get 168 g 3-methyl-6-isopropenyl-cyclohex-2-en-1-ol, and recovered 282 g raw material, conversion rate: 43.6%, selectivity: 77%.

[0029] (2) Into a hydrogenation reactor, 168 g 3-methyl-6-isopropenyl-cyclohex-2-en-1-ol was added, then 1.7 g 5% palladium-carbon catalyst was added, stirred uniformly, the hydrogenation reactor was replaced with nitrogen for 3 times, then replaced with hydrogen for 3 times, then filled with 30 bar hydrogen, heated to 130°C, kept for 8h, until the content of raw material was less than 1%, stopped the reaction, reduced pressure distillation to get menthol 145 g.

[0030] Example 3

[0031] (1) Into a reactor, 1-methyl-4-isopropenyl-cyclohex-2-en-1-ol 500 g, ammonium metavanadate 5 g were added, stirred uniformly, heated to 130°C, then kept at 130°C for 3h, until the conversion of raw material was 50%-60%, stopped the reaction, then reduced pressure distillation to get 211 g 3-methyl-6-isopropenyl-cyclohex-2-en-1-ol, and recovered 220 g raw material, conversion rate: 56%, selectivity: 75%.

[0032] (2) Into a hydrogenation reactor, 211 g 3-methyl-6-isopropenyl-cyclohex-2-en-1-ol was added, then 2.2 g copper-carbon catalyst was added, stirred uniformly, the hydrogenation reactor was replaced with nitrogen for 3 times, then replaced with hydrogen for 3 times, then filled with 30 bar hydrogen, heated to 130°C, kept for 6h, until the content of raw material was less than 1%, stopped the reaction, reduced pressure distillation to get menthol 183 g.

[0033] Example 4

[0034] (1) Into a reactor, 1-methyl-4-isopropenyl-cyclohex-2-en-1-ol 500 g, ammonium metavanadate 1.5 g were added, stirred uniformly, heated to 150°C, then kept at 150°C for 3h, until the conversion of raw material was 50%-60%, stopped the reaction, then reduced pressure distillation to get 219 g 3-methyl-6-isopropenyl-cyclohex-2-en-1-ol, and recovered 223 g raw material, conversion rate: 55.4%, selectivity: 79%.

[0035] (2) 219 g of 3-methyl-6-isopropenyl-cyclohex-2-en-1-ol was added into a hydrogenation kettle, and the recovered Raney Ni catalyst of Example 1 was added, stirred uniformly, the hydrogenation kettle was replaced with nitrogen for 3 times, replaced with hydrogen for 3 times, then filled with 30 bar hydrogen, heated to 130°C, and kept for 4 h until the content of the raw material was less than 1%, the reaction was stopped, and menthol 188 g was obtained by vacuum rectification.

[0036] The above description of the embodiments is only for illustrating the technical concept and characteristics of the present application, and its purpose is to enable those skilled in the art to understand the content of the present application and to implement it. Those skilled in the art can easily make various modifications to these embodiments, and apply the general principles described herein to other embodiments without creative labor, therefore, the above embodiments cannot limit the protection scope of the present application. Any improvements and modifications made by those skilled in the art according to the disclosure of the present application without departing from the scope of the present application shall be covered within the protection scope of the present application.

Claims

1. A method for preparing menthol, characterized in that: The following steps are involved: (1) allowing 1-methyl-4-isopropenyl-cyclohex-2-en-1-ol to undergo rearrangement reaction under the catalysis of a transition metal catalyst to produce 3-methyl-6-isopropenyl-cyclohex-2-en-1-ol; (2) 3-methyl-6-isopropenyl-cyclohex-2-en-1-ol is subjected to a hydrogenation reaction in the presence of a hydrogenation catalyst to produce menthol.

2. The method for preparing menthol according to claim 1, wherein: The transition metal catalyst is ammonium metavanadate.

3. The method for preparing menthol according to claim 1, wherein: The mass ratio of the 1-methyl-4-isopropenyl-cyclohex-2-en-1-ol to the transition metal catalyst is 1:(0.0005-0.01).

4. The method for preparing menthol according to claim 1, wherein: The temperature of the rearrangement reaction is 130-180° C., and the rearrangement reaction is stopped when the raw material conversion is 40%-60%.

5. The method for preparing menthol according to claim 1, wherein: The hydrogenation catalyst is selected from Raney Ni, palladium carbon or copper carbon.

6. The method for preparing menthol according to claim 1, wherein: The mass ratio of the 3-methyl-6-isopropenyl-cyclohex-2-en-1-ol to the hydrogenation catalyst is 1:(0.005-0.03).

7. The method for preparing menthol according to claim 1, wherein: The hydrogenation reaction temperature is 80-150° C., the pressure is 10-60 bar, and the time is 4-8 hours.

8. The method for preparing menthol according to claim 1, wherein: Steps (1) and (2) also include separation and purification operations.

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