阅读说明：本技术 一种高纯度覆盆子酮的合成方法 (Synthesis method of high-purity raspberry ketone ) 是由 阎圣刚 廖鸿儒 曾令贵 于 2021-09-14 设计创作，主要内容包括：本发明属于香料及精细化工技术领域,具体涉及一种高纯度覆盆子酮的合成方法。本发明合成方法以2,6-二叔丁基苯酚为原料,在酸性催化剂a催化条件下,与丁烯酮或4-羟基丁酮进行烷基化反应,生成2,6-二叔丁基-4-羟基苄基丙酮,然后经过酸性催化剂b催化脱叔丁基,得到覆盆子酮。本发明先以2,6-位占位保护的苯酚2,6-二叔丁基苯酚为原料,与丁烯酮或4-羟基丁酮烷基化反应可以100％定位于对位,得到的2,6-二叔丁基-4-羟基苄基丙酮,收率高；然后经过脱叔丁基过程,得到高收率、高纯度的覆盆子酮；该方法工艺简单,反应时间短,产品纯度高,反应副产物可以回收再利用,催化剂可循环使用,成本低,适合于工业化生产。(The invention belongs to the technical field of spices and fine chemical engineering, and particularly relates to a synthesis method of high-purity raspberry ketone. The synthesis method comprises the steps of taking 2, 6-di-tert-butylphenol as a raw material, carrying out alkylation reaction with butenone or 4-hydroxy butanone under the catalysis of an acidic catalyst a to generate 2, 6-di-tert-butyl-4-hydroxybenzyl acetone, and then removing tert-butyl through catalysis of an acidic catalyst b to obtain the raspberry ketone. According to the invention, 2, 6-position occupying protected phenol 2, 6-di-tert-butylphenol is taken as a raw material, and is subjected to alkylation reaction with butenone or 4-hydroxybutyl ketone to be positioned at para position by 100%, so that the obtained 2, 6-di-tert-butyl-4-hydroxybenzyl acetone has high yield; then, obtaining raspberry ketone with high yield and high purity through a tert-butyl removing process; the method has the advantages of simple process, short reaction time, high product purity, recyclable reaction by-products, recyclable catalyst and low cost, and is suitable for industrial production.)

1. A synthesis method of high-purity raspberry ketone is characterized in that 2, 6-di-tert-butyl phenol is used as a raw material and is subjected to alkylation reaction with butenone or 4-hydroxy butanone under the catalysis of an acidic catalyst a to generate 2, 6-di-tert-butyl-4-hydroxybenzyl acetone, and tert-butyl is removed through catalysis of an acidic catalyst b to obtain raspberry ketone.

2. The method for synthesizing high-purity raspberry ketone according to claim 1, is characterized by comprising the following steps:

(1) preparation of raspberry ketone precursor compound: dissolving 2, 6-di-tert-butylphenol by using an aprotic solvent A, adding the solution into a reactor, adding an acidic catalyst a, stirring, heating to 0-120 ℃, dropwise adding butenone or 4-hydroxybutanone dissolved in the aprotic solvent A within 1-5h, continuously reacting for 3-5h, cooling to room temperature, filtering, adjusting the pH value of the filtrate to be neutral, recovering the aprotic solvent A at normal pressure, and carrying out reduced pressure distillation to obtain a raspberry ketone precursor 2, 6-di-tert-butyl-4-hydroxybenzylacetone;

(2) preparing raspberry ketone: adding an acidic catalyst B and an aprotic solvent B into a reactor, mixing, heating to 90-150 ℃, then dropwise adding 2, 6-di-tert-butyl-4-hydroxybenzyl acetone dissolved in the aprotic solvent B, reacting for 1.5-5h, collecting generated isobutene gas, cooling to room temperature after the reaction is finished, filtering out a solid catalyst, adjusting the pH value of the filtrate to be neutral, recovering the protic solvent B at normal pressure, and carrying out reduced pressure distillation to obtain the raspberry ketone.

3. The method for synthesizing high-purity raspberry ketone according to claim 2, further comprising:

(3) preparation of 2, 6-di-tert-butylphenol: and (3) freezing and collecting the reaction product isobutene in the step (2), and reacting the isobutene with phenol under the action of a catalyst to obtain the 2, 6-di-tert-butylphenol.

4. The method for synthesizing raspberry ketone according to claim 1 or 2, wherein said acidic catalyst a is any one of inorganic acid, organic acid, acidic resin and solid acid.

5. The method for synthesizing raspberry ketone according to claim 4, wherein said inorganic acid is any one of sulfuric acid, phosphoric acid or hydrochloric acid; the organic acid is any one of p-toluenesulfonic acid, methanesulfonic acid, trifluoromethyl sulfonic acid, dodecyl sulfonic acid or hexadecyl sulfonic acid; the acidic resin is Amberlyst series acidic resin or perfluorosulfonic acid resin; the solid acid is acidic diatomite or acidic alumina; amberlyst series acidic resins are preferred.

6. The method for synthesizing raspberry ketone of claim 2, wherein in step (1), the aprotic solvent a is aromatic hydrocarbon or polar solvent a; the aromatic hydrocarbon comprises toluene, xylene, dioxane or tetraethylene glycol dimethyl ether; the polar solvent a comprises acetonitrile, N-dimethylformamide or N, N-diethylacetamide; toluene is preferred.

7. The method for synthesizing raspberry ketone according to claim 1 or 2, wherein said acidic catalyst b is any one of Lweis acid, inorganic acid, organic acid and acidic resin, and said Lweis acid is any one of aluminum trichloride, zinc chloride, tin tetrachloride and titanium chloride; the inorganic acid is sulfuric acid or phosphoric acid; the organic acid is any one of methylbenzenesulfonic acid, methanesulfonic acid and trifluoromethanesulfonic acid; the acidic resin is perfluorosulfonic acid resin.

8. The method for synthesizing raspberry ketone of claim 2, wherein in step (2), said aprotic solvent B is a high boiling aromatic hydrocarbon or a polar solvent B; the aromatic hydrocarbon is any one of toluene, xylene, decane or dodecane; the polar solvent b is dimethyl sulfoxide, sulfolane, N-dimethylformamide or N, N-diethylformamide.

9. The method for synthesizing raspberry ketone of claim 8, wherein said aprotic solvent B is decane or dodecane.

10. The method for synthesizing high-purity raspberry ketone according to claim 1, wherein in step (3), the catalyst is an acidic resin.

Technical Field

The invention belongs to the technical field of spices and fine chemical engineering, and particularly relates to a synthesis method of high-purity raspberry ketone.

Background

The raspberry ketone has the chemical name of 4-p-hydroxyphenyl-2-butanone (4-p-hydroxyphenylly) -2-butanone), is the main aroma component of raspberry fruits, and has the characteristic sweet fruit aroma and aroma. The raspberry ketone is a synthetic spice which is internationally recognized, is safe and widely applied, and has elegant fruit fragrance and flavor enhancement and sweetening effects. The latest edition of food additive health standard (GB2760-2014) in China stipulates that raspberry ketone is the permitted edible spice (FEMA code: 2588). The raspberry ketone is used for preparing essence of raspberry, grape, pineapple, peach, plum, strawberry, raspberry, jasmine, gardenia, tuberose and the like, can keep fragrance for a long time, and is used as a modifier or a fixing agent for a large amount of daily spice, food spice, daily chemical essence and tobacco essence. Raspberry ketone has certain whitening effect and anti-inflammatory effect, and is widely used for blending cosmetics. The acetic ester of raspberry ketone is used as a high-efficiency insect attractant (cue lure ketone) in agriculture. Recent research shows that the basin ketone has alpha-glucosidase inhibitory activity and PPAR-alpha agonistic activity, and shows the application prospect in the field of metabolic disease treatment. Therefore, the raspberry ketone is a fine chemical with good development value and high added value.

The natural products of raspberry ketone exist in the juice of raspberry (raspberry), raspberry and the like, but the content is very rare, only about 0.1-0.2ppm in raspberry juice, which was found as early as 18 centuries, and it was confirmed in 1957 as the main flavor substance in raspberry. Because the content is extremely low and the raspberry ketone is difficult to separate, the raspberry ketone can be commercially produced in a large scale by being developed to the utmost extent at present. The chemical synthesis methods of raspberry ketone are more, including condensation and reduction methods of p-hydroxybenzaldehyde and acetone, alkylation synthesis methods of phenol and 4-hydroxy-2-butanone Friedel-Crafts, alkylation synthesis methods of phenol and methyl vinyl ketone Friedel-Crafts, condensation, reduction and hydrolysis synthesis methods of p-alkoxy benzaldehyde and acetone, and esterification reactions of phenyl acetate and methyl vinyl ketone Friedel-Crafts and hydrolysis synthesis methods.

The raspberry ketone synthesis methods are discussed in detail in two recent documents (crown, perfume and essence cosmetics, 2017, NO4, 14-20; Zhang Heng, acetaldehyde acetic acid chemical industry, 2014, 9 th, 12-18), and the methods are all thousands of years, but most of the methods have the problems of long working procedures, multiple synthesis steps, complex process, long reaction time, multiple byproducts, low yield and the like.

Disclosure of Invention

The invention aims to provide a synthesis method of high-purity raspberry ketone, which adopts a two-step method, firstly takes 2, 6-position occupying protected phenol (2, 6-di-tert-butylphenol) as a raw material, and can be positioned at para position by 100% through alkylation reaction with butenone or 4-hydroxybutyl ketone, so that the obtained 2, 6-di-tert-butyl-4-hydroxybenzyl acetone has high yield; then obtaining the raspberry ketone with high purity and high quality through the process of removing tert-butyl, and the method has the advantages of simple process, short reaction time, high product purity and low cost, and is suitable for industrial production.

The invention provides a synthesis method of high-purity raspberry ketone, which adopts a Friedel-Crafts alkylation reaction method, takes 2, 6-di-tert-butylphenol as a raw material, and performs alkylation reaction with butenone or 4-hydroxy butanone under the catalysis of an acidic catalyst a to generate 2, 6-di-tert-butyl-4-hydroxybenzyl acetone, and then removes tert-butyl through the catalysis of an acidic catalyst b to obtain the high-purity raspberry ketone.

Friedel-Crafts alkylation is a reaction in which an aromatic hydrocarbon is reacted with an alkylating agent under the catalytic action of an acid, and the hydrogen on the aromatic ring is replaced by an alkyl group.

In the technical scheme, phenol (2, 6-di-tert-butylphenol) protected by 2, 6-tert-butyl is used as a raw material, Friedel-Crafts alkylation reaction is carried out on the phenol and butenone or 4-hydroxy butanone with electrophilic groups, 100% of the phenol can be positioned at the para position, the obtained raspberry ketone precursor compound (2, 6-di-tert-butyl-4-hydroxybenzyl acetone) is high in yield, then an isobutene protective agent is added in the presence of an acidic catalyst, high-purity raspberry ketone is obtained through distillation, and a byproduct isobutene can be recovered and used for synthesizing 2, 6-di-tert-butylphenol, so that recycling is realized.

Further, the method specifically comprises the following steps:

(1) preparation of raspberry ketone precursor compound: dissolving 2, 6-di-tert-butylphenol by using an aprotic solvent A, adding the solution into a reactor, adding an acidic catalyst a, stirring, heating to 0-120 ℃, dropwise adding butenone or 4-hydroxybutanone dissolved in the aprotic solvent A within 1-5h, continuously reacting for 3-5h, cooling to room temperature, filtering, adjusting the pH value of the filtrate to be neutral, recovering the aprotic solvent A at normal pressure, and carrying out reduced pressure distillation to obtain a raspberry ketone precursor 2, 6-di-tert-butyl-4-hydroxybenzylacetone;

(2) preparing raspberry ketone: adding an acidic catalyst B and an aprotic solvent B into a reactor, mixing, heating to 90-150 ℃, then dropwise adding 2, 6-di-tert-butyl-4-hydroxybenzyl acetone dissolved in the aprotic solvent B, reacting for 1.5-5h, collecting generated isobutene gas, cooling to room temperature after the reaction is finished, filtering out a solid catalyst, adjusting the pH value of the filtrate to be neutral, recovering the protic solvent B at normal pressure, and carrying out reduced pressure distillation to obtain the raspberry ketone.

Specifically, the reactor is provided with a thermometer, a reflux condenser tube and a constant-pressure dropping funnel, so that the temperature, the dropping speed and the pressure can be controlled conveniently; meanwhile, the upper end of the reflux condenser pipe is connected with a gas guide pipe to lead out isobutene gas generated in the reaction process, so that the recovery of isobutene serving as a reaction byproduct is facilitated.

Further, the technical scheme also comprises (3) preparation of 2, 6-di-tert-butylphenol: and (3) freezing and collecting the reaction product isobutene in the step (2), and reacting the isobutene with phenol under the action of a catalyst to obtain the 2, 6-di-tert-butylphenol. The 2, 6-di-tert-butylphenol obtained in the technical scheme can be used as a raw material for synthesizing a covered plate and recycled.

Further, in the above technical solution, the acidic catalyst a is any one of an inorganic acid, an organic acid, an acidic resin and a solid acid.

Further, in the above technical scheme, the inorganic acid is any one of sulfuric acid, phosphoric acid or hydrochloric acid; the organic acid is any one of p-toluenesulfonic acid, methanesulfonic acid, trifluoromethyl sulfonic acid, dodecyl sulfonic acid or hexadecyl sulfonic acid; the acidic resin is Amberlyst series acidic resin or perfluorosulfonic acid resin; the solid acid is acidic diatomite or acidic alumina; preferably Amberlyst series acidic resins

Specifically, from environmental and safety considerations, the preferred catalyst is Amberlyst series acidic resin, which can be utilized more than 10 times with an additional 10% addition of fresh resin per use.

Specifically, when the perfluorosulfonic acid resin is used, the catalyst has high activity, the reaction is completed after the dropwise addition is completed, and the resin can be added or not added after the repeated use.

Specifically, when trifluoromethanesulfonic acid is used, the reaction is completed after the completion of the dropwise addition, and the activity is high. Specifically, when the acidic diatomite is used, the product can be used only three times because the reusability of the diatomite is poor, and the product yield is reduced to about 30 percent.

Further, in the above technical scheme, the aprotic solvent a is an aromatic hydrocarbon or a polar solvent a; the aromatic hydrocarbon comprises toluene, xylene, dioxane or tetraethylene glycol dimethyl ether; the polar solvent a comprises acetonitrile, N-dimethylformamide or N, N-diethylacetamide. Specifically, toluene series aromatic hydrocarbons are preferable as the reaction solvent for the sake of more convenient purification of the product.

Further, in the step (2) in the above technical solution, the acidic catalyst b is any one of an lweiss acid, an inorganic acid, an organic acid and an acidic resin, and the lweiss acid is any one of aluminum trichloride, zinc chloride, tin tetrachloride and titanium chloride; the inorganic acid is sulfuric acid or phosphoric acid; the organic acid is any one of methylbenzenesulfonic acid, methanesulfonic acid and trifluoromethanesulfonic acid; the acidic resin is perfluorosulfonic acid resin.

Further, in the step (2) in the above technical scheme, the aprotic solvent B is a high-boiling aromatic hydrocarbon or a polar solvent B; the aromatic hydrocarbon is any one of toluene, xylene, decane or dodecane; the polar solvent b is any one of dimethyl sulfoxide, sulfolane, N-dimethylformamide or N, N-diethylformamide. In the technical scheme, because the removed tert-butyl has the existence of acid during the removal reaction, alkylation reaction can be carried out on aromatic hydrocarbon, and therefore, hydrocarbons such as decane, dodecane and other inert solvents can be preferably used for recycling isobutene.

Further, in the step (3) of the above technical solution, the catalyst is an acidic resin.

Compared with the prior art, the method has the beneficial effects that:

1. the method adopts 2, 6-position occupying protected phenol 2, 6-di-tert-butylphenol as a raw material, can be positioned at para position by 100 percent through alkylation reaction with butenone, and obtains the 2, 6-di-tert-butyl-4-hydroxybenzyl acetone, which has high yield; the raspberry ketone with high yield and high purity can be obtained through the process of removing tert-butyl;

2. the reaction by-product isobutene obtained by the method can be recovered and used as a raw material for synthesizing 2, 6-di-tert-butylphenol, and the cost can be saved;

3. the invention further saves the production cost by selecting the recyclable catalyst;

4. the two-step reaction of the invention is conventional chemical operation, and has the advantages of simple process, short reaction time, high product purity and low cost, and is suitable for industrial production.

Drawings

FIG. 1 is a flow diagram of the synthesis of raspberry ketone and the recovery of isobutylene in the present invention.

Detailed Description

The technical features of the present invention described above and those described in detail below (as an embodiment) can be combined with each other to form a new or preferred technical solution, but the present invention is not limited to these embodiments, and the embodiments also do not limit the present invention in any way.

The experimental procedures in the following examples are conventional unless otherwise specified. The formulations according to the following examples are all commercially available products and are commercially available, unless otherwise specified.

The invention is described in further detail below with reference to the figures and examples:

FIG. 1 is a flow chart of the synthesis of raspberry ketone and the recovery of isobutene of the present invention, which includes three steps, the first step is the reaction of 2, 6-di-tert-butylphenol and butenone to produce 2, 6-di-tert-butyl-4-hydroxybenzyl acetone; the second step is that the 2, 6-di-tert-butyl-4-hydroxybenzyl acetone is heated and decomposed under the action of an acid catalyst to obtain raspberry ketone and isobutene serving as target products; and the third step is that isobutene and phenol are catalyzed by acid resin to obtain 2, 6-di-tert-butylphenol, and the 2, 6-di-tert-butylphenol can participate in the reaction to obtain a target product, so that the cyclic utilization of byproducts is realized.

Example 1

Adding 300mL of toluene and 51.6g of 2, 6-di-tert-butylphenol into a 500mL three-neck flask with a thermometer, a reflux condenser and a constant-pressure dropping funnel, adding 10g of Amberlyst15 resin into a reaction bottle, starting electromagnetic stirring, slowly raising the temperature of the reaction bottle to 90 ℃, then dropwise adding 17.5g of butenone dissolved in 50mL of toluene into the reaction bottle (dropwise adding is completed within 2 h), continuing to react for 3h after dropwise adding, cooling the reaction dissolved mixture to room temperature, filtering out the Amberlyst15 resin by using a sand core filtering funnel, adjusting the pH of the filtrate to be neutral by using a drop of saturated sodium carbonate solution, transferring the reaction solution into a 500mL single-neck flask, recovering toluene at normal pressure, distilling under reduced pressure to obtain 65.1g of a raspberry ketone precursor compound (chemical name: 2, 6-di-tert-butyl-4-hydroxybenzylacetone), the yield is 94.0%, the purity is 99%, boiling point: 170 ℃ and 174 ℃/1-2mmHg, crystallization after standing, melting point: 80-90 ℃.

Wherein the resin catalyst can be used for more than 10 times, and 1g of new resin is additionally added each time the resin catalyst is used.

Example 2

Adding 100mL of toluene into a 250mL three-neck flask with a thermometer, a reflux condenser tube and a constant-pressure dropping funnel, freezing the toluene to below 0 ℃ by using a cooling bath, taking 2g of 98% sulfuric acid, slowly dropping the sulfuric acid into the toluene, stirring for 20min, adding 12.6g of 2, 6-di-tert-butylphenol into a reaction bottle, starting electromagnetic stirring, slowly dropping 4.5g of butenone dissolved in 50mL of toluene into the reaction bottle at about 0 ℃ (dropping is completed within 1 h), continuing to react for 3h after dropping is completed, cooling the reaction dissolved mixture to room temperature, adjusting the pH to be neutral by using a sodium carbonate saturated solution, separating out a water layer, drying an organic layer by using magnesium sulfate, recovering the toluene at normal pressure, distilling under reduced pressure to obtain 13.1g of a product raspberry ketone precursor compound (2, 6-di-tert-butyl-4-hydroxybenzylacetone), wherein the yield is 77.3%, the purity was 98%.

Example 3

Adding 120mL of toluene and 5g of p-toluenesulfonic acid into a 250mL three-necked flask with a thermometer, a reflux condenser and a constant-pressure dropping funnel, heating the reaction mixture to 80 ℃, stirring for 10min, adding 18.2g of 2, 6-di-tert-butylphenol into the reaction flask, starting electromagnetic stirring, slowly dropping 8.17g of 4-hydroxy butanone dissolved in 40mL of toluene into the reaction flask at 80 ℃ (dropping is completed within 2.5 h), continuing to react for 4h after dropping is completed, cooling the reaction dissolved mixture to room temperature, adding 20mL of water into the reaction solution to dissolve p-toluenesulfonic acid into the water layer, separating the water layer, adjusting the pH of the organic layer to be neutral by using a sodium carbonate saturated solution, then discharging the water layer, drying the organic layer by using magnesium sulfate, recovering toluene at normal pressure, distilling under reduced pressure to obtain 22.3g of a raspberry ketone precursor compound (2, 6-di-tert-butyl-4-hydroxy benzyl acetone), the yield was 91.7% and the purity 98%.

Example 4

Adding 500mL of toluene and 30g of acidic diatomite (dried at 300 ℃) into a 1000mL three-neck flask with a thermometer, a reflux condenser tube and a constant-pressure dropping funnel, heating the mixture to 100 ℃, stirring for 30min, adding 126.2g of 2, 6-di-tert-butylphenol into a reaction bottle, starting electromagnetic stirring, slowly dropping 43.4g of butenone dissolved in 100mL of toluene into the reaction bottle at 100 ℃ (dropping is completed within 5 h), continuing to react for 5h after dropping is completed, cooling the reaction dissolved mixture to room temperature, performing suction filtration by using a Buchner funnel, filtering out a catalyst of diatomite, adding a small amount of saturated solution of sodium carbonate into the reaction solution to be neutral, then discharging a water layer, drying an organic layer by magnesium sulfate, recovering toluene under normal pressure, distilling under reduced pressure to obtain 136.8g of a raspberry ketone precursor compound (2, 6-di-tert-butyl-4-hydroxybenzylacetone), the yield was 79.1% and the purity 98%.

Wherein, the repeated applicability of the acidic diatomite is poor, and the activity of the acidic diatomite is lost after the acidic diatomite is used for only three times.

Example 5

200mL of decane and 50g of acidic sulfonic acid resin (resistant to temperature of 150 ℃) are added into a 500mL three-neck flask with a thermometer, a reflux condenser pipe (wherein the upper end of the reflux condenser pipe is connected with an air guide pipe to lead out isobutene gas generated in the reaction process) and a constant pressure dropping funnel, 56.1g of raspberry ketone precursor compound (2, 6-di-tert-butyl-4-hydroxybenzylacetone) dissolved in 100mL of decane is slowly dripped into reaction liquid at 120 ℃ from the dropping funnel, isobutene gas is immediately discharged, generated isobutene is introduced into a freezing steel cylinder through a connecting pipe, the steel cylinder is frozen by dry ice, dripping is finished for about 3h, the dripping speed is controlled according to the speed of effluent gas, the flow rate of medium gas is controlled to ensure that all the reacted isobutene is collected into the steel cylinder, and the reaction is carried out until no gas overflows, after about 5h of reaction, cooling the reaction liquid to room temperature, filtering out the acidic sulfonic acid resin catalyst, adjusting the pH of the reaction liquid to be neutral, recovering decane at normal pressure, and distilling under reduced pressure to obtain 29.6g of raspberry ketone, wherein the yield is 89.0%, the purity is 99%, and the melting point is as follows: 83-84 ℃, boiling point: 176 and 179 ℃ at 4-5 mmHg.

Example 6

Adding 400mL of decane and 80g of Nafion perfluorosulfonic acid resin NR50 into a 1000mL three-neck flask with a thermometer, a reflux condenser (wherein the upper end of the reflux condenser is connected with an air duct to lead out isobutene gas generated in the reaction process) and a constant-pressure dropping funnel, slowly heating the mixed solution to 100 ℃, slowly adding 125.6g of raspberry ketone precursor compound (2, 6-di-tert-butyl-4-hydroxybenzylacetone) dissolved in 200mL of decane slowly dropwise into the reaction solution at 100 ℃ from the dropping funnel, immediately discharging the isobutene gas, introducing the generated isobutene into a freezing steel cylinder through a connecting pipe, freezing the steel cylinder by using dry ice to ensure that the isobutene is completely condensed for about 4h, controlling the dropping speed according to the speed of the discharged gas to ensure that the isobutene obtained by reaction is completely collected into the steel cylinder, immediately after the dropwise addition, no gas overflows, cooling the reaction liquid to room temperature, filtering out a resin catalyst, adjusting the pH of the reaction liquid to be neutral, recovering decane at normal pressure, and distilling under reduced pressure to obtain raspberry ketone, wherein 67.8g is obtained, the yield is 91.0%, the purity is 99%, and the melting point is as follows: 83-84 ℃.

The resin catalyst can be repeatedly used for a plurality of times, and is different from other catalysts in that only a little new resin is added when the resin catalyst is repeatedly used for the 6 th time.

Example 7

40mL of decane and 2.0g of trifluoromethanesulfonic acid are added into a 100mL three-neck flask provided with a thermometer, a reflux condenser tube (wherein the upper end of the reflux condenser tube is connected with an air guide tube to lead out isobutene gas generated in the reaction process) and a constant-pressure dropping funnel, the mixed solution is slowly heated to 90 ℃, 12.5g of raspberry ketone precursor compound (2, 6-di-tert-butyl-4-hydroxybenzylacetone) dissolved in 20mL of decane is slowly dropped into a reaction solution at 90 ℃ from the dropping funnel, isobutene gas is immediately discharged, the generated isobutene is introduced into a freezing steel cylinder through a connecting tube, the steel cylinder is frozen by dry ice to ensure that the isobutene is completely condensed, the dropping is completed within about 1.5h, the catalytic activity of the trifluoromethanesulfonic acid in the perfluorosulfonic acid resin is basically equivalent, the reaction is completed after the dropping, the reaction solution is cooled to room temperature, adjusting pH to neutral with sodium carbonate saturated solution, separating water layer, drying organic layer with magnesium sulfate, recovering decane under normal pressure, and distilling under reduced pressure to obtain raspberry ketone 6.4g with yield 86.0%, purity 99%, melting point: 83-84 ℃.

In conclusion, the synthesis method adopts a two-step method, in examples 1-4, 2, 6-di-tert-butylphenol subjected to 2, 6-position space-occupying protection is used as a raw material, and 100% of phenol can be positioned at para position in the alkylation reaction with butenone, so that the obtained 2, 6-di-tert-butyl-4-hydroxybenzyl acetone has the yield up to 94%; in examples 5 to 7, 2, 6-di-tert-butyl-4-hydroxybenzylacetone obtained in examples 1 to 4 was dissolved in a solvent and added to an acidic catalyst, and the raspberry ketone obtained through the tert-butyl removal process had a yield of 91% and a purity of 99%.

Finally, it should be emphasized that the above-described preferred embodiments of the present invention are merely examples of implementations, rather than limitations, and that many variations and modifications of the invention are possible to those skilled in the art, without departing from the spirit and scope of the invention.