A preparation method of 5,6-dimethyl-5-heptene-2-one

Abstract

The present invention discloses a method for preparing 5,6-dimethyl-5-heptene-2-one. The method comprises the following steps: under the action of a catalyst prepared in situ by organoaluminum and phosphorus oxide compounds, 5,6-dimethyl-5-heptene-2-one is prepared by pinacol and alkoxypropylene. The synthetic route of the present invention is novel, with pinacol and 2-alkoxypropylene as starting materials, a one-pot reaction process is adopted, and a 5,6-dimethyl-5-heptene-2-one intermediate is prepared simply and efficiently, and the intermediate can be used in the preparation of precious spices irone; compared with the 5,6-dimethyl-5-heptene-2-one synthesis method in the prior art, the present invention only needs one-step reaction. Secondly, the present invention uses phosphorus oxide compounds and organoaluminum for synergistic catalysis, and a small amount of catalyst completes the dehydration and rearrangement reaction of pinacol, simplifies the operation, and improves the yield and route atom economy.

Description

Technical Field

[0001] The invention belongs to the field of fine chemicals, and specifically relates to a method for preparing 5,6-dimethyl-5-heptene-2-one in one pot by using pinacol and alkoxypropylene as raw materials. The intermediate is a key intermediate for synthesizing the precious fragrance irone. Background Art

[0002] Irisone is a very precious spice. It has three isomers: α-, β- and γ-. There are also cis-trans and optical isomers among the three isomers. The fragrance and threshold of each isomer are slightly different, but basically they all have characteristic aromas similar to iris and violet. Irisone is the main aroma source of iris oil, and the products currently on the market are mainly α-irone. α-irone has a soft sweet fragrance and a pure aroma. It can be used in the preparation of high-grade floral fragrances such as iris, violet, and wisteria. These fragrances are used in daily products such as food, cosmetics, soaps, and cigarettes. According to known reports, there are only a few manufacturers in Switzerland and Japan that produce irone, and the production capacity is small, which cannot meet market demand and the price remains high.

[0003] There are many methods for producing irone. It can be extracted from plants containing irone, and there are also reports on the synthesis of irone by biological fermentation. However, the cost of these two methods is relatively high and they are rarely used in actual production. Chemical synthesis is currently the most commonly used method for preparing irone. Depending on the starting materials, the chemical synthesis methods of irone include the pseudoionone method and the 2,3-dimethyl 1,3-butadiene method. The pseudoionone method uses pseudoionone as a raw material and obtains irone through epoxidation, reduction, methylation, cyclization and other reactions. The starting raw materials of this method are relatively expensive, and it takes multiple steps to obtain irone, so its practical application value is poor.

[0004]

[0005] The 2,3-dimethyl-1,3-butadiene method uses 2,3-dimethyl-1,3-butadiene as a raw material, first reacts with hydrogen bromide to obtain a bromide, then reacts with methyl acetoacetate, saponifies and decarboxylates to obtain the key intermediate 5,6-dimethyl-5-heptene-2-one, which is then subjected to reactions such as acetylation, rearrangement, and cyclization to finally obtain irone. This route has simple starting materials and certain advantages. The main disadvantage is that hydrogen bromide needs to be introduced before alkylation, saponification, and decarboxylation can be performed to obtain 5,6-dimethyl-5-heptene-2-one. The waste salts and wastewater generated during the alkylation and saponification decarboxylation process can be optimized and simplified if the relevant processes can be simplified. This route can be made more competitive (L. Ruzicka, H. Schinz, Helv. Chim. Acta 1940, 23, 959).

[0006]

[0007] In summary, 5,6-dimethyl-5-heptene-2-one is a key intermediate for the synthesis of irone. The current main synthesis method is to use 2,3-dimethyl-1,3-butadiene as a raw material and obtain it through bromination, alkylation, saponification and decarboxylation. The process flow is relatively complicated and the yield is poor. In order to prepare irone products more economically and cheaply, it is necessary to develop a new 5,6-dimethyl-5-heptene-2-one synthesis route, starting from low-cost raw materials, to prepare 5,6-dimethyl-5-heptene-2-one efficiently and in a green and environmentally friendly manner. Summary of the invention

[0008] The object of the present invention is to provide a method for preparing 5,6-dimethyl-5-heptene-2-one, which is obtained by a one-pot process using readily available pinacol and alkoxypropylene as raw materials. The method of the present invention is simple, has mild conditions, and uses cheap and readily available raw materials, and has good application value.

[0009] In order to achieve the above objectives and the above technical effects, the present invention adopts the following technical solutions:

[0010] A method for synthesizing 5,6-dimethyl-5-heptene-2-one comprises the following steps: preparing 5,6-dimethyl-5-heptene-2-one from pinacol and alkoxypropylene under the action of a catalyst prepared in situ from an organic aluminum and a phosphorus oxide compound.

[0011] The reaction formula is as follows:

[0012]

[0013] The 5,6-dimethyl-5-heptene-2-one described in the present invention is a key synthesis intermediate of irone.

[0014] The possible reaction mechanism is shown in the following formula: pinacol is dehydrated under the action of a catalyst to obtain a 2,3-dimethyl 3-butene-2-ol intermediate, which then undergoes a Saucy-Marbet rearrangement reaction with alkoxypropylene to ultimately obtain 5,6-dimethyl-5-heptene-2-one.

[0015]

[0016] In the present invention, the catalyst is prepared in situ by organic aluminum and phosphorus oxide, and the reaction formula is as follows:

[0017]

[0018] In the present invention, the pinacol is 2,3-dimethyl-2,3-butanediol.

[0019] The alkoxypropylene of the present invention includes, but is not limited to, one or more of 2-methoxypropylene, 2-ethoxypropylene, 2-propoxypropylene, and 2-butoxypropylene, preferably 2-methoxypropylene and / or 2-ethoxypropylene.

[0020] The amount of alkoxypropylene used in the present invention is 300-500 mol% of pinacol.

[0021] As a preferred embodiment, in the present invention, the catalyst is prepared in situ from organoaluminum and phosphorus oxide in alkoxypropane.

[0022] Preferably, the organoaluminum of the present invention includes but is not limited to one or more of methylaluminum chloride, dimethylaluminum chloride, diethylaluminum chloride, diethylaluminum chloride, aluminum isopropoxide, trimethylaluminum, triethylaluminum, preferably dimethylaluminum chloride and / or diethylaluminum chloride.

[0023] In the present invention, the amount of the organic aluminum is 1.0-5.0 mol% of pinacol.

[0024] Preferably, the phosphorus oxide compound may be, but is not limited to, one or more of phosphoric acid, diphenyl phosphate, dibenzyl phosphate, dimethyl phosphate, diethyl phosphate, ditolyl phosphate, diisooctyl phosphate, tris(oxalato)phosphoric acid, preferably diphenyl phosphate and / or ditolyl phosphate.

[0025] Preferably, the amount of the phosphorus oxide compound used in the present invention is 2.0-5.5 mol% of pinacol.

[0026] Preferably, the alkoxypropane may be, but is not limited to, 2,2-dimethoxypropane, 2,2-diethoxypropane, 2,2-dipropoxypropane, 2,2-dibutoxypropane, and the like.

[0027] As a preferred solution, in the present invention, introducing a small amount of silver salt into the reaction system can further increase the catalyst activity, and the silver salt is one or more of silver nitrate, silver perchlorate, silver tetrafluoroborate, silver hexafluorophosphate, etc.

[0028] Preferably, the amount of the silver salt used in the present invention is 1.0-2.0 mol% of pinacol.

[0029] In the present invention, the reaction of the present invention is preferably carried out under solvent-free conditions. If a solvent is to be used, an aprotic solvent is preferably used, including but not limited to one or more of n-hexane, toluene, xylene, ether, tetrahydrofuran, methyl tert-butyl ether, dichloromethane, dichloroethane, etc.

[0030] In the present invention, the reaction process of the present invention can be batch, semi-batch or continuous, preferably batch, with all materials added at once.

[0031] Preferably, the reaction time of the present invention is 3 to 8 hours.

[0032] Preferably, the reaction temperature of the present invention is 110-160°C.

[0033] In the present invention, after the reaction is completed, the reaction liquid is distilled to recover excess alkoxypropylene and alkoxypropane, and then de-weighted and separated to obtain 5,6-dimethyl-5-heptene-2-one.

[0034] In the present invention, the 5,6-dimethyl-5-heptene-2-one is obtained by reacting pinacol and alkoxypropylene through dehydration, Saucy-Marbet rearrangement and the like, and can be used as a key intermediate for the synthesis of irone.

[0035] The present invention adopts the above technical solution and has the following positive effects:

[0036] (1) The method has a novel synthetic route, and the raw materials used, pinacol and methoxypropylene, are simple, easy to obtain, and inexpensive. The conversion is completed in one pot, and the reaction yield is high, which has great potential application value.

[0037] (2) The present invention innovatively uses an in-situ prepared phosphorus oxide-aluminum catalyst, and the Lewis basic P=O and Lewis acidic aluminum synergistically catalyze, so that the catalyst has good catalytic activity and can efficiently complete the conversion.

[0038] (3) The present invention also found that introducing a small amount of silver salt into the reaction system to precipitate chloride ions can further enhance the catalyst activity. DETAILED DESCRIPTION

[0039] The present invention is described in detail below by examples, but the present invention is not limited to the following examples.

[0040] The main raw material information is as follows:

[0041] 2-Methoxypropylene, 2-ethoxypropylene, 2-propoxypropylene, homemade, 99%; pinacol, industrial pure, Aladdin reagent; dimethylaluminum chloride n-hexane solution (2M), diethylaluminum chloride n-hexane solution (2M), ethylaluminum dichloride n-hexane solution (2M), diethylaluminum n-hexane solution (2M), aluminum isopropoxide, J&K reagent, purity 98-99%; dimethyl phosphate, diphenyl phosphate, di-p-tolyl phosphate, tri(oxalato)phosphoric acid, Alfa Aesar, purity 99%.

[0042] Silver tetrafluoroborate, silver hexafluorophosphate, purity 99%, 2,2-dimethoxypropane, 2,2-diethoxypropane, 2,2-dipropoxypropane, homemade, >99%.

[0043] The gas chromatography test conditions of the present invention are as follows:

[0044] Instrument model: Agilent 8890B; Chromatographic column: Capillary column HP-5 (30m×0.30mm×0.25μm); Initial temperature 80℃, raised to 100℃ at a rate of 5℃ / min; then raised to 200℃ at a rate of 10℃ / min, maintained for 5.0min. Carrier gas high-purity nitrogen, split ratio 30:1, split flow 42mL / min. Carrier gas saving: 19mL / min, start waiting time 5.0min. Injection temperature 250℃, detector FID, detector temperature 250℃, air flow 350mL / min, hydrogen flow 30mL / min, tail gas flow 60mL / min, injection volume 0.2μL.

[0045] Embodiment 1:

[0046] In the glove box, add dimethyl phosphate (3.78g, 30.0mmol) to a 100mL single-mouth bottle equipped with a magnetic stirrer, then add 2,2-dimethoxypropane (20.0mL), mix the two evenly, slowly add dimethylaluminum chloride n-hexane solution (2M, 9.0mL) to the mixture, stir and react for 10 minutes to obtain a catalyst solution. Seal the 100mL single-mouth bottle, take it out of the glove box, strictly protect it with nitrogen, and set it aside. In the air, add pinacol (70.9g, 0.6mol) and 2-methoxypropylene (173.1g, 2.4mol) to a 500mL autoclave at room temperature, seal the autoclave, and carefully and slowly replace it with nitrogen 3 times to completely replace the air in the reactor. Finally, the nitrogen pressure in the reactor is maintained at normal pressure. The autoclave was stirred (600 rpm) and heated by the jacket. When the temperature inside the autoclave reached 150°C, the catalyst solution prepared in advance was quickly pumped into the autoclave using a horizontal flow pump. After the catalyst was fed, the timing was started, and the reaction was kept warm and stirred for 4 hours. The reaction liquid was sampled through the bottom tube of the reactor, and GC analysis showed that the raw material pinacol was completely converted, and the selectivity of the product 5,6-dimethyl-5-heptene-2-one was 97.0%.

[0047] Embodiment 2:

[0048] In the glove box, add dimethyl phosphate (1.39g, 11.0mmol) to a 100mL single-mouth bottle equipped with a magnetic stirrer, then add 2,2-dimethoxypropane (20.0mL), mix the two evenly, slowly add dimethylaluminum chloride n-hexane solution (2M, 2.8mL) to the mixture, stir and react for 10 minutes to obtain a catalyst solution. Seal the 100mL single-mouth bottle, take it out of the glove box, strictly protect it with nitrogen, and set it aside. In the air, add pinacol (65.0g, 0.55mol) and 2-methoxypropylene (198.3g, 2.75mol) to a 500mL autoclave at room temperature, seal the autoclave, and carefully and slowly replace it with nitrogen 3 times to completely replace the air in the reactor. Finally, the nitrogen pressure in the reactor is maintained at normal pressure. The autoclave was stirred (600 rpm) and heated by the jacket. When the temperature inside the autoclave reached 160°C, the catalyst solution prepared in advance was quickly pumped into the autoclave using a horizontal flow pump. After the catalyst feeding was completed, the timing was started, and the reaction was kept warm and stirred for 8 hours. The reaction liquid was sampled through the bottom tube of the reactor, and GC detection and analysis showed that the raw material pinacol was completely converted, and the selectivity of the product 5,6-dimethyl-5-heptene-2-one was 89.3%.

[0049] Embodiment 3:

[0050] In the glove box, add dimethyl phosphate (4.23g, 33.6mmol) to a 100mL single-mouth bottle equipped with a magnetic stirrer, then add 2,2-dimethoxypropane (20.0mL), mix the two evenly, slowly add dimethylaluminum chloride n-hexane solution (2M, 15.3mL) to the mixture, stir and react for 10 minutes to obtain a catalyst solution. Seal the 100mL single-mouth bottle, take it out of the glove box, strictly protect it with nitrogen, and set it aside. In the air, add pinacol (72.1g, 0.61mol) and 2-methoxypropylene (132.0g, 1.83mol) to a 500mL autoclave at room temperature, seal the autoclave, and carefully and slowly replace it with nitrogen 3 times to completely replace the air in the reactor. Finally, the nitrogen pressure in the reactor is maintained at normal pressure. The autoclave was stirred (600 rpm) and heated by the jacket. When the temperature inside the autoclave reached 130°C, the catalyst solution prepared in advance was quickly pumped into the autoclave using a horizontal flow pump. After the catalyst feeding was completed, the timing was started, and the reaction was kept warm and stirred for 5 hours. The reaction liquid was sampled through the bottom tube of the reactor, and GC detection and analysis showed that the raw material pinacol was completely converted, and the selectivity of the product 5,6-dimethyl-5-heptene-2-one was 94.9%.

[0051] Embodiment 4:

[0052] In the glove box, add dimethyl phosphate (3.63g, 28.8mmol) to a 100mL single-mouth bottle equipped with a magnetic stirrer, then add 2,2-dimethoxypropane (20.0mL), mix the two evenly, slowly add diethylaluminum chloride n-hexane solution (2M, 10.8mL) to the mixture, stir and react for 10 minutes to obtain a catalyst solution. Seal the 100mL single-mouth bottle, take it out of the glove box, strictly protect it with nitrogen, and set it aside. In the air, add pinacol (85.1g, 0.72mol) and 2-methoxypropylene (207.7g, 2.88mol) to a 500mL autoclave at room temperature, seal the autoclave, and carefully and slowly replace it with nitrogen 3 times to completely replace the air in the reactor. Finally, the nitrogen pressure in the reactor is maintained at normal pressure. The autoclave was stirred (600 rpm) and heated by the jacket. When the temperature inside the autoclave reached 150°C, the catalyst solution prepared in advance was quickly pumped into the autoclave using a horizontal flow pump. After the catalyst was fed, the timing was started, and the reaction was kept warm and stirred for 4 hours. The reaction liquid was sampled through the bottom tube of the reactor, and GC detection and analysis showed that the raw material pinacol was completely converted, and the selectivity of the product 5,6-dimethyl-5-heptene-2-one was 98.0%.

[0053] Embodiment 5:

[0054] In the glove box, add dimethyl phosphate (3.66g, 29.0mmol) to a 100mL single-mouth bottle equipped with a magnetic stirrer, then add 2,2-dimethoxypropane (20.0mL), mix the two evenly, slowly add ethyl aluminum dichloride n-hexane solution (2M, 5.8mL) to the mixture, stir and react for 10 minutes to obtain a catalyst solution. Seal the 100mL single-mouth bottle, take it out of the glove box, strictly protect it with nitrogen, and set it aside. In the air, add pinacol (68.5g, 0.58mol) and 2-methoxypropylene (167.3g, 2.32mol) to a 500mL autoclave at room temperature, seal the autoclave, and carefully and slowly replace it with nitrogen 3 times to completely replace the air in the reactor. Finally, the nitrogen pressure in the reactor is maintained at normal pressure. The autoclave was stirred (600 rpm) and heated by the jacket. When the temperature inside the autoclave reached 150°C, the catalyst solution prepared in advance was quickly pumped into the autoclave using a horizontal flow pump. After the catalyst was fed, the timing was started, and the reaction was kept warm and stirred for 5 hours. The reaction liquid was sampled through the bottom tube of the reactor, and GC detection and analysis showed that the raw material pinacol was completely converted, and the selectivity of the product 5,6-dimethyl-5-heptene-2-one was 93.8%.

[0055] Embodiment 6:

[0056] In the glove box, add dimethyl phosphate (2.77g, 22.0mmol) to a 100mL single-mouth bottle equipped with a magnetic stirrer, then add 2,2-dimethoxypropane (20.0mL), mix the two evenly, slowly add aluminum isopropoxide (4.49g, 22.0mmol) to the mixture, stir and react for 10 minutes to obtain a catalyst solution. Seal the 100mL single-mouth bottle, take it out of the glove box, strictly protect it with nitrogen, and set it aside. In the air, add pinacol (65.0g, 0.55mol) and 2-methoxypropylene (158.6g, 2.2mol) to a 500mL autoclave at room temperature, seal the autoclave, and carefully and slowly replace it with nitrogen 3 times to completely replace the air in the reactor. Finally, the nitrogen pressure in the reactor is maintained at normal pressure. The autoclave was stirred (600 rpm) and heated by the jacket. When the temperature inside the autoclave reached 160°C, the catalyst solution prepared in advance was quickly pumped into the autoclave using a horizontal flow pump. After the catalyst feeding was completed, the timing was started, and the reaction was kept warm and stirred for 6 hours. The reaction liquid was sampled through the bottom tube of the reactor, and GC detection and analysis showed that the raw material pinacol was completely converted, and the selectivity of the product 5,6-dimethyl-5-heptene-2-one was 92.7%.

[0057] Embodiment 7:

[0058] In the glove box, add dimethyl phosphate (3.23g, 25.6mmol) to a 100mL single-mouth bottle equipped with a magnetic stirrer, then add 2,2-diethoxypropane (20.0mL), mix the two evenly, slowly add triethylaluminum n-hexane solution (2M, 12.8mL) to the mixture, stir and react for 10 minutes to obtain a catalyst solution. Seal the 100mL single-mouth bottle, take it out of the glove box, strictly protect it with nitrogen, and set it aside. In the air, add pinacol (75.6g, 0.64mol) and 2-ethoxypropylene (220.5g, 2.56mol) to a 500mL autoclave at room temperature, seal the autoclave, and carefully and slowly replace it with nitrogen 3 times to completely replace the air in the reactor. Finally, the nitrogen pressure in the reactor is maintained at normal pressure. The autoclave was stirred (600 rpm) and heated by the jacket. When the temperature inside the autoclave reached 150°C, the catalyst solution prepared in advance was quickly pumped into the autoclave using a horizontal flow pump. After the catalyst was fed, the timing was started, and the reaction was kept warm and stirred for 4 hours. The reaction liquid was sampled through the bottom tube of the reactor, and GC analysis showed that the raw material pinacol was completely converted, and the selectivity of the product 5,6-dimethyl-5-heptene-2-one was 96.5%.

[0059] Embodiment 8:

[0060] In the glove box, add diphenyl phosphate (5.20g, 20.8mmol) to a 100mL single-mouth bottle equipped with a magnetic stirrer, then add 2,2-dipropoxypropane (25.0mL), mix the two evenly, slowly add diethylaluminum chloride n-hexane solution (2M, 10.4mL) to the mixture, stir and react for 10 minutes to obtain a catalyst solution. Seal the 100mL single-mouth bottle, take it out of the glove box, strictly protect it with nitrogen, and set it aside. In the air, add pinacol (61.5g, 0.52mol) and 2-propoxypropylene (208.3g, 2..08mol) to a 500mL autoclave at room temperature, seal the autoclave, and carefully and slowly replace it with nitrogen 3 times to completely replace the air in the reactor. Finally, the nitrogen pressure in the reactor is maintained at normal pressure. The autoclave was stirred (600 rpm) and heated by the jacket. When the temperature inside the autoclave reached 160°C, the catalyst solution prepared in advance was quickly pumped into the autoclave using a horizontal flow pump. After the catalyst feeding was completed, the timing was started, and the reaction was kept warm and stirred for 5 hours. The reaction liquid was sampled through the bottom tube of the reactor, and GC detection and analysis showed that the raw material pinacol was completely converted, and the selectivity of the product 5,6-dimethyl-5-heptene-2-one was 94.4%.

[0061] Embodiment 9:

[0062] In the glove box, add di-p-toluene phosphate (5.23g, 18.8mmol) to a 100mL single-mouth bottle equipped with a magnetic stirrer, then add 2,2-dimethoxypropane (25.0mL), mix the two evenly, slowly add dimethylaluminum chloride n-hexane solution (2M, 9.4mL) to the mixture, stir and react for 10 minutes to obtain a catalyst solution. Seal the 100mL single-mouth bottle, take it out of the glove box, strictly protect it with nitrogen, and set it aside. In the air, add pinacol (55.5g, 0.47mol) and 2-methoxypropylene (135.6g, 1.88mol) to a 500mL autoclave at room temperature, seal the autoclave, and carefully and slowly replace it with nitrogen 3 times to completely replace the air in the reactor. Finally, the nitrogen pressure in the reactor is maintained at normal pressure. The autoclave was stirred (600 rpm) and heated by the jacket. When the temperature inside the autoclave reached 150°C, the catalyst solution prepared in advance was quickly pumped into the autoclave using a horizontal flow pump. After the catalyst was fed, the timing was started, and the reaction was kept warm and stirred for 4 hours. The reaction liquid was sampled through the bottom tube of the reactor, and GC detection and analysis showed that the raw material pinacol was completely converted, and the selectivity of the product 5,6-dimethyl-5-heptene-2-one was 97.2%.

[0063] Embodiment 10:

[0064] In the glove box, add tri(oxalato)phosphoric acid (8.88g, 30.0mmol) to a 100mL single-mouth bottle equipped with a magnetic stirrer, then add 2,2-dimethoxypropane (30.0mL), mix the two evenly, slowly add dimethylaluminum chloride n-hexane solution (2M, 12.0mL) to the mixture, stir and react for 10 minutes to obtain a catalyst solution. Seal the 100mL single-mouth bottle, take it out of the glove box, strictly protect it with nitrogen, and set it aside. In the air, add pinacol (70.9g, 0.6mol) and 2-methoxypropylene (173.1g, 2.4mol) to a 500mL autoclave at room temperature, seal the autoclave, and carefully and slowly replace it with nitrogen 3 times to completely replace the air in the reactor. Finally, the nitrogen pressure in the reactor is maintained at normal pressure. The autoclave was stirred (600 rpm) and heated by the jacket. When the temperature inside the autoclave reached 160°C, the catalyst solution prepared in advance was quickly pumped into the autoclave using a horizontal flow pump. After the catalyst was fed, the timing was started, and the reaction was kept warm and stirred for 6 hours. The reaction liquid was sampled through the bottom tube of the reactor, and GC analysis showed that the raw material pinacol was completely converted, and the selectivity of the product 5,6-dimethyl-5-heptene-2-one was 98.4%.

[0065] Embodiment 11:

[0066] In the glove box, dimethyl phosphate (2.92g, 23.2mmol) was added to a 100mL single-mouth bottle equipped with a magnetic stirrer, and then 2,2-dimethoxypropane (20.0mL) was added. After the two were mixed evenly, silver tetrafluoroborate (1.13g, 5.8mmol) and dimethylaluminum chloride in n-hexane solution (2M, 8.7mL) were slowly added to the mixture. After stirring for 30 minutes, the silver chloride precipitate was filtered to obtain a catalyst solution. The 100mL single-mouth bottle was sealed, taken out of the glove box, strictly protected by nitrogen, and set aside. In the air, pinacol (68.5g, 0.58mol) and 2-methoxypropylene (167.3g, 2.32mol) were added to a 500mL autoclave at room temperature, the autoclave was sealed, and nitrogen was carefully and slowly replaced 3 times to completely replace the air in the reactor. Finally, the nitrogen pressure in the reactor was maintained at normal pressure. The autoclave was stirred (600 rpm) and heated by the jacket. When the temperature inside the autoclave reached 110°C, the catalyst solution prepared in advance was quickly pumped into the autoclave using a horizontal flow pump. After the catalyst was fed, the timing was started, and the reaction was kept warm and stirred for 3 hours. The reaction liquid was sampled through the bottom tube of the reactor, and GC analysis showed that the raw material pinacol was completely converted, and the selectivity of the product 5,6-dimethyl-5-heptene-2-one was 99.7%.

[0067] Embodiment 12:

[0068] In the glove box, add diphenyl phosphate (5.40g, 21.6mmol) to a 100mL single-mouth bottle equipped with a magnetic stirrer, then add 2,2-dimethoxypropane (30.0mL), mix the two evenly, slowly add lithium silver hexafluorophosphate (1.37g, 5.4mmol) and dimethylaluminum chloride in n-hexane solution (2M, 8.1mL) to the mixture, stir and react for 30 minutes, filter and remove the silver chloride precipitate to obtain a catalyst solution. Seal the 100mL single-mouth bottle, take it out of the glove box, strictly protect it with nitrogen, and set it aside. In the air, add pinacol (63.8g, 0.54mol) and 2-methoxypropylene (155.8g, 2.16mol) to a 500mL autoclave at room temperature, seal the autoclave, and carefully and slowly replace it with nitrogen 3 times to completely replace the air in the reactor. Finally, the nitrogen pressure in the reactor is maintained at normal pressure. The autoclave was stirred (600 rpm) and heated by the jacket. When the temperature inside the autoclave reached 120°C, the catalyst solution prepared in advance was quickly pumped into the autoclave using a horizontal flow pump. After the catalyst feeding was completed, the timing was started, and the reaction was kept warm and stirred for 3 hours. The reaction liquid was sampled through the bottom tube of the reactor, and GC detection and analysis showed that the raw material pinacol was completely converted, and the selectivity of the product 5,6-dimethyl-5-heptene-2-one was 99.3%.

[0069] Comparative Example 1:

[0070] In the glove box, dimethyl phosphate (3.78 g, 30.0 mmol) was added to a 100 mL single-mouth bottle equipped with a magnetic stirrer, and then 2,2-dimethoxypropane (20.0 mL) was added. After the two were mixed evenly, the catalyst solution was obtained after stirring for 10 minutes. The 100 mL single-mouth bottle was sealed, taken out of the glove box, strictly protected by nitrogen, and set aside. In the air, pinacol (70.9 g, 0.6 mol) and 2-methoxypropylene (173.1 g, 2.4 mol) were added to a 500 mL autoclave at room temperature, the autoclave was sealed, and nitrogen was carefully and slowly replaced 3 times to completely replace the air in the reactor. Finally, the nitrogen pressure in the autoclave was maintained at normal pressure. The autoclave was stirred (600 rpm) and the jacket was heated. When the internal temperature of the reactor reached 150 ° C, the catalyst solution prepared in advance was quickly pumped into the autoclave with a horizontal flow pump. After the catalyst feeding was completed, the timing was started, and the reaction was kept warm and stirred for 4 hours. The reaction liquid was sampled through a bottom tube of the reactor and analyzed by GC. The raw material pinacol was completely converted and the selectivity of the product 5,6-dimethyl-5-heptene-2-one was 67.0%.

[0071] Comparative Example 2:

[0072] In the glove box, add the n-hexane solution of dimethylaluminum chloride (2M, 9.0mL) to a 100mL single-mouth bottle equipped with a magnetic stirrer, then add 2,2-dimethoxypropane (20.0mL), mix the two evenly, and slowly stir the reaction for 10 minutes to obtain a catalyst solution. Seal the 100mL single-mouth bottle, take it out of the glove box, strictly protect it with nitrogen, and set it aside. In the air, add pinacol (70.9g, 0.6mol) and 2-methoxypropylene (173.1g, 2.4mol) to a 500mL autoclave at room temperature, seal the autoclave, and carefully and slowly replace it with nitrogen 3 times to completely replace the air in the reactor. Finally, the nitrogen pressure in the autoclave is maintained at normal pressure. Turn on the autoclave stirring (600rpm) and jacket heating. When the internal temperature of the reactor reaches 150℃, use a horizontal flow pump to quickly pump the prepared catalyst solution into the autoclave. After the catalyst feeding is completed, start the timing, keep warm, and stir the reaction for 4 hours. The reaction liquid was sampled through a bottom tube of the reactor and analyzed by GC. The raw material pinacol was completely converted and the selectivity of the product 5,6-dimethyl-5-heptene-2-one was 54.0%.

[0073] Comparative Example 3:

[0074] In a glove box, dimethyl phosphate (3.78 g, 30.0 mmol) was added to a 100 mL single-mouth bottle equipped with a magnetic stirrer, and a n-hexane solution of dimethylaluminum chloride (2 M, 9.0 mL) was slowly added, and the reaction was stirred for 10 minutes to obtain a catalyst solution. The 100 mL single-mouth bottle was sealed, taken out of the glove box, and strictly protected with nitrogen for standby use.

[0075] In the air, add pinacol (70.9g, 0.6mol) and 2-methoxypropylene (173.1g, 2.4mol) to a 500mL autoclave at room temperature, seal the autoclave, and replace the air in the reactor carefully and slowly with nitrogen three times to completely replace the air in the reactor. Finally, the nitrogen pressure in the reactor is kept at normal pressure. Turn on the autoclave stirring (600rpm) and jacket heating. When the temperature inside the reactor reaches 150°C, use a horizontal flow pump to quickly pump the prepared catalyst solution into the autoclave. After the catalyst feeding is completed, start the timing, keep warm, stir and react for 4 hours. The reaction liquid is sampled through the bottom tube of the reactor, and the GC detection and analysis show that the raw material pinacol is completely converted, and the selectivity of the product 5,6-dimethyl-5-heptene-2-one is 64.0%.

Claims

1. A method for preparing 5,6-dimethyl-5-heptene-2-one, comprising the following steps: Under the action of a catalyst prepared in situ by an organic aluminum and a phosphorus oxide compound, pinacol and alkoxypropylene are used to prepare 5,6-dimethyl-5-heptene-2-one; the organic aluminum comprises one or more of methyl aluminum chloride, dimethyl aluminum chloride, diethyl aluminum chloride, diethyl aluminum chloride, aluminum isopropoxide, trimethyl aluminum, and triethyl aluminum; and the phosphorus oxide compound comprises one or more of phosphoric acid, diphenyl phosphate, dibenzyl phosphate, dimethyl phosphate, diethyl phosphate, ditolyl phosphate, diisooctyl phosphate, and tri(oxalato)phosphoric acid.

2. The method according to claim 1, characterized in that The pinacol is 2,3-dimethyl-2,3-butanediol; the alkoxypropylene includes one or more of 2-methoxypropylene, 2-ethoxypropylene, 2-propoxypropylene, and 2-butoxypropylene.

3. The method according to claim 1, characterized in that The amount of the organic aluminum used is 1.0-5.0 mol% of pinacol.

4. The method according to claim 1, characterized in that: The amount of phosphoric acid used is 2.0-5.5 mol% of pinacol.

5. The method according to claim 1, characterized in that The catalyst is prepared in situ from organic aluminum and phosphorus oxide in alkoxypropane; the alkoxypropane includes one or more of 2,2-dimethoxypropane, 2,2-diethoxypropane, 2,2-dipropoxypropane and 2,2-dibutoxypropane.

6. The method according to claim 1, characterized in that A silver salt is introduced into the reaction system, wherein the silver salt is one or more of silver nitrate, silver perchlorate, silver tetrafluoroborate, and silver hexafluorophosphate.

7. The method according to claim 1, characterized in that The reaction is carried out with or without a solvent, wherein the solvent includes one or more of n-hexane, toluene, xylene, ether, tetrahydrofuran, methyl tert-butyl ether, dichloromethane and dichloroethane.

8. The method according to claim 1, characterized in that The reaction process is batch, semi-batch or continuous.

9. The method according to claim 1, characterized in that: The reaction time is 3 to 8 hours; and / or the reaction temperature is 110 to 160°C.

10. The method according to claim 1, characterized in that After the reaction is completed, the reaction solution is distilled to recover excess alkoxypropylene, and then de-weighted and separated to obtain 5,6-dimethyl-5-heptene-2-one.

11. The method according to claim 1, characterized in that: The amount of the alkoxypropylene used is 300-500 mol% of the pinacol.

12. The method according to claim 6, characterized in that The amount of the silver salt used is 1.0-2.0 mol% of pinacol.

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