A process for the preparation of methyl heptenone

Abstract

This invention provides a method for preparing methylheptenone via the Saucy-Marbet reaction of 2-methyl-3-buten-2-ol and 2-methoxypropylene. By controlling the content of key impurities tert-amyl alcohol and water in the raw materials, a reaction conversion rate of ≥99.5% and a reaction selectivity of ≥98.5% can be achieved. The catalyst used in this invention is inexpensive and readily available, the reaction conditions are mild, the operation is simple, and the reaction yield is high. This method solves the problems of existing processes, such as excessive waste, complex side reactions, and difficulties in product purification.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a method for preparing methylheptenone by reacting 2-methyl-3-buten-2-ol and 2-methoxypropylene via a Saucy-Marbet reaction. Background Technology

[0002] Methylheptenone, possessing aromas of lemongrass, isobutyl acetate, and fresh fruit, is a permitted food flavoring under national standards and can be used to formulate banana, pear, and berry flavorings. Methylheptenone is also a very important synthetic intermediate, used in the synthesis of flavorings such as linalool, citral, and pseudoionone. Currently, methods for preparing methylheptenone mainly include the acetylene-acetone method, the isobutylene-formaldehyde method, the isoprene method, and the Saucy-Marbet method.

[0003] The acetylene-acetone method was the earliest industrialized method for producing methylheptenone (patents DE2126356, GB788301, GB888999, DE1137433, CN1218792A). This method uses acetone as the starting material. Acetylene adds to acetone to obtain an alkynyl alcohol intermediate, which is then partially hydrogenated to obtain an allyl alcohol intermediate. The allyl alcohol intermediate undergoes a Carroll rearrangement reaction with ethyl acetoacetate to yield the methylheptenone product. This route requires a large amount of calcium carbide to produce acetylene, generating a significant amount of calcium carbide waste. The Carroll reaction also produces an equivalent amount of ethanol as a byproduct. The synthetic route has poor atom economy and generates a considerable amount of waste.

[0004] The isoprene method uses isoprene as the starting material, which is added with hydrogen chloride to obtain isopentenyl chloride. The isopentenyl chloride then condenses with acetone to yield methylheptenone. The main challenge of this route lies in the condensation reaction. Current literature reports primarily employ phase transfer catalysis (patents JP40-22251, JP56-115734, JP56-61319, CN1762955A, CN1772722A, CN103664556A). Selecting a suitable phase transfer catalyst is crucial for the condensation reaction of chloroisoprene with acetone. A significant drawback of existing technologies is the difficulty in catalyst recovery. Overall, the isoprene method for preparing methylheptenone exhibits poor selectivity, generally low yields, generates substantial amounts of waste, and faces difficulties in recovering the phase transfer catalyst, hindering industrial production. This process has since been phased out.

[0005] BASF patents report a one-pot synthesis of 6-methyl-6-hepten-2-one from isobutylene, formaldehyde, and acetone. The resulting product is then subjected to hydroisomerization to yield methylheptenone (patents DE1277848B, DE1267682B). Although the synthetic route is concise, the first step involves harsh reaction conditions: high temperature and high pressure. Furthermore, the reaction selectivity is poor (40-50% product selectivity), accompanied by the formation of numerous byproducts, making product purification by distillation difficult.

[0006] The Saucy-Marbet method for preparing methylheptenone uses 2-methyl-3-buten-2-ol and 2-methoxypropene as raw materials. Under the action of an acid catalyst, a Saucy-Marbet rearrangement reaction occurs to produce methylheptenone (patents DE1193490, DE19649564, CN1539 807A, CN1914143, CN108299171A, CN1228757, CN102197014). While the Saucy-Marbet method offers high atom utilization and is environmentally friendly, it uses a weak acid catalyst, resulting in poor reactivity and requiring high reaction temperatures and long reaction times to complete the reaction. Conversely, using strong acid catalysts such as phosphoric acid or sulfonic acid provides better reactivity, but the reaction selectivity is poor, and the starting material 2-methyl-3-buten-2-ol undergoes dehydration to form diene byproducts, affecting separation.

[0007] In summary, there are currently multiple methods for synthesizing methylheptenone, and some synthetic routes have been industrialized. However, these synthetic routes generally suffer from drawbacks such as generating a lot of waste, complex side reactions, and difficulties in product purification. Therefore, it is still necessary to develop new methods for synthesizing methylheptenone in a more efficient, environmentally friendly, and atom-economical manner. Summary of the Invention

[0008] To address the problems of excessive waste, complex side reactions, and difficult product purification in existing methods for preparing methylheptenone, this invention provides a method for preparing methylheptenone by reacting 2-methyl-3-buten-2-ol and 2-methoxypropylene via a Saucy-Marbet reaction. By controlling the content of the impurity tert-amyl alcohol in 2-methyl-3-buten-2-ol, and simultaneously controlling the water content in both 2-methyl-3-buten-2-ol and 2-methoxypropylene, a reaction conversion rate of ≥99.5% and a reaction selectivity of ≥98.5% can be achieved.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing methylheptenone, comprising:

[0011] 2-Methyl-3-buten-2-ol and 2-methoxypropylene undergo a Saucy-Marbet reaction in the presence of a catalyst to produce methylheptenone.

[0012] We were surprised to find that the content of tert-amyl alcohol and water in the feedstock had a significant impact on the conversion rate and selectivity of the reaction. The content of the impurity tert-amyl alcohol in the 2-methyl-3-buten-2-ol was controlled at 200-3000 ppm, while the water content in both 2-methyl-3-buten-2-ol and 2-methoxypropylene was controlled at 100-2000 ppm. The impurity tert-amyl alcohol is the main byproduct of the hydrogenation of 2-methyl-3-butyn-2-ol and has a boiling point close to that of 2-methyl-3-buten-2-ol, therefore it cannot be completely removed. To reduce the content of the impurity tert-amyl alcohol, a very high theoretical plate number or a large rectification reflux ratio is usually required for its separation, but this also results in a significant increase in energy consumption. Furthermore, water exists in an azeotropic relationship with both the feedstock 2-methyl-3-buten-2-ol and 2-methoxypropylene, and therefore cannot be completely removed either. Methods to reduce the content of tert-amyl alcohol include distillation and improving the selectivity of hydrogenation of 2-methyl-3-butyn-2-ol. Methods to reduce the water content include drying, azeotropic distillation, and extractive distillation. As long as the relevant contents are adjusted to the range of this invention, there are no special requirements for the methods.

[0013] As a preferred embodiment, the catalyst may be one or more of the following: organic amine sulfonates (preferably ethanolamine sulfonate, more preferably diethanolamine methanesulfonate, triethanolamine methanesulfonate, diethanolamine p-toluenesulfonate and triethanolamine p-toluenesulfonate), phosphate diesters (preferably diphenyl phosphate, naphthol phosphate and dibenzyl phosphate and more than one or more), and phosphite diesters (preferably dimethyl phosphite, diphenyl phosphite and diethyl phosphite and more than one or more).

[0014] In one specific embodiment, the molar ratio of the catalyst to 2-methyl-3-buten-2-ol is 0.005 to 0.1%, preferably 0.01 to 0.05%;

[0015] In one specific embodiment, the ethanolamine sulfonate is prepared by reacting an organic amine (diethanolamine, triethanolamine) with a sulfonic acid (methanesulfonic acid, p-toluenesulfonic acid) in a 1:1 molar ratio, a conventional acid-base neutralization reaction. Both the organic phosphodiester catalyst and the organic phosphite catalyst are commercially available.

[0016] In one specific embodiment, the temperature of the Saucy-Marbet reaction is 100-200°C, preferably 140-160°C.

[0017] In one specific embodiment, the residence time of the Saucy-Marbet reaction is 2 to 6 hours, preferably 3 to 4 hours.

[0018] In one specific embodiment, the molar ratio of 2-methyl-3-buten-2-ol to 2-methoxypropylene is 1:2 to 5, preferably 1:2.5 to 3.

[0019] In one specific embodiment, the purity of 2-methyl-3-buten-2-ol and 2-methoxypropylene is above 99%, preferably above 99.5%.

[0020] In one specific embodiment, the Saucy-Marbet reaction has a selectivity of ≥98.5% and a conversion rate of ≥99.5%.

[0021] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0022] The method reported in this invention controls the content of key impurities tert-amyl alcohol and water in the raw materials, and can achieve a reaction conversion rate of ≥99.5%, a reaction selectivity of ≥98.5%, less waste, less catalyst usage, and the catalyst is inexpensive and readily available. The operating conditions are mild and suitable for industrial-scale production. Detailed Implementation

[0023] To better understand the technical solution of the present invention, the following embodiments will further illustrate the method provided by the present invention. However, the present invention is not limited to the listed embodiments, but should also include any other known modifications within the scope of the claims of the present invention.

[0024] The main reagent sources for each embodiment and comparative example are as follows:

[0025] 2-Methyl-3-buten-2-ol, purity ≥99.5%; 2-methoxypropylene, purity ≥99.5%

[0026] Diethanolamine, triethanolamine, methanesulfonic acid, p-toluenesulfonic acid, diphenyl phosphate, naphthol phosphate, and dimethyl phosphite were purchased from Aladdin Reagent, with a purity ≥99%.

[0027] Methanol and acetone, purity ≥99.5%, Xilong Chemical.

[0028] In the examples, 2-methyl-3-buten-2-ol with a tert-amyl alcohol content of 200 ppm can be obtained by optimizing the number of trays and the reflux ratio in the distillation process. Then, by adding tert-amyl alcohol, 2-methyl-3-buten-2-ol with different tert-amyl alcohol contents can be formulated. Furthermore, 2-methyl-3-buten-2-ol and 2-methoxypropylene can be dried using molecular sieves to control the water content below 100 ppm, and then water can be added to formulate 2-methyl-3-buten-2-ol and 2-methoxypropylene with different water contents.

[0029] The gas chromatography testing conditions used in this invention are as follows:

[0030] Instrument model: Agilent 8890B;

[0031] Injection volume: 0.5 μL;

[0032] Inlet temperature: 250℃;

[0033] Flow split ratio: 30 / 1;

[0034] Column: Agilent INNOWAX, 30m × 250μm × 0.25μm;

[0035] Column flow rate: 1.5 mL / min;

[0036] Temperature program: Start at 35℃, hold for 5 minutes, then increase the temperature to 250℃ at a rate of 10℃ / min, and hold for 10 minutes.

[0037] Detector temperature: 250℃; air flow rate: 400mL / min; hydrogen flow rate: 40mL / min; nitrogen flow rate: 25mL / min.

[0038] Example 1

[0039] Diethanolamine (0.0105 g, 0.1 mmol) and p-toluenesulfonic acid (0.0172 g, 0.1 mmol) were added to a 0.5 L high-pressure reactor. Then, 86.565 g (1 mol) of 2-methyl-3-buten-2-ol (purity 99.527%, tert-amyl alcohol content 300 ppm, water content 2000 ppm) and 218.515 g (3 mol) of 2-methoxypropylene (purity 99.515%, water content 2000 ppm) were added. The reactor was closed, and the air inside was replaced three times with 0.5 MPaG nitrogen. The nitrogen was then purged, and the reactor was opened and heated. Timing began when the temperature inside the reactor reached 140 °C. The reaction was maintained at this temperature for 4 hours, and samples were taken. GC analysis showed a conversion rate of 99.615% and a reaction selectivity of 98.531%.

[0040] Example 2

[0041] Triethanolamine (0.0746 g, 0.5 mmol) and p-toluenesulfonic acid (0.0861 g, 0.5 mmol) were added to a 0.5 L high-pressure reactor, followed by 86.565 g (1 mol) of 2-methyl-3-buten-2-ol (purity 99.525%, tert-amyl alcohol content 1000 ppm, water content 2000 ppm) and 182.096 g (2.5 mol) of 2-methoxypropylene (purity 99.517%, water content 2000 ppm). The reactor was closed, and the air inside was replaced three times with 0.5 MPaG nitrogen. The nitrogen was then purged, and the reactor was opened and heated. Timing began when the temperature inside the reactor reached 100 °C. The reaction was maintained at this temperature for 2 hours, and samples were taken. GC analysis showed a conversion rate of 99.575% and a reaction selectivity of 98.699%.

[0042] Example 3

[0043] Triethanolamine (0.0746 g, 0.5 mmol) and methanesulfonic acid (0.0481 g, 0.5 mmol) were added to a 0.5 L high-pressure reactor, followed by 86.565 g (1 mol) of 2-methyl-3-buten-2-ol (purity 99.526%, tert-amyl alcohol content 2000 ppm, water content 1000 ppm) and 145.677 g (2 mol) of 2-methoxypropylene (purity 99.516%, water content 2000 ppm). The reactor was closed, and the air inside was replaced three times with 0.5 MPaG nitrogen. The nitrogen was then purged, and the reactor was opened and heated. Timing began when the temperature inside the reactor reached 160 °C. The reaction was maintained at this temperature for 3 hours, and samples were taken. GC analysis showed a conversion rate of 99.511% and a reaction selectivity of 98.513%.

[0044] Example 4

[0045] Diethanolamine (0.0053 g, 0.05 mmol) and methanesulfonic acid (0.0048 g, 0.05 mmol) were added to a 0.5 L high-pressure reactor. Then, 86.565 g (1 mol) of 2-methyl-3-buten-2-ol (purity 99.531%, tert-amyl alcohol content 500 ppm, water content 100 ppm) and 364.192 g (5 mol) of 2-methoxypropylene (purity 99.515%, water content 100 ppm) were added. The reactor was closed, and the air inside was replaced three times with 0.5 MPaG nitrogen. The nitrogen was then purged, and the reactor was opened and heated. Timing began when the temperature inside the reactor reached 200 °C. The reaction was maintained at this temperature for 6 hours, and samples were taken. GC analysis showed a conversion rate of 99.623% and a reaction selectivity of 98.897%.

[0046] Example 5

[0047] Triethanolamine (0.0448 g, 0.3 mmol) and methanesulfonic acid (0.0288 g, 0.3 mmol) were added to a 0.5 L high-pressure reactor, followed by 86.565 g (1 mol) of 2-methyl-3-buten-2-ol (purity 99.528%, tert-amyl alcohol content 2000 ppm, water content 1000 ppm) and 182.096 g (2.5 mol) of 2-methoxypropylene (purity 99.516%, water content 1000 ppm). The reactor was closed, and the air inside was replaced three times with 0.5 MPaG nitrogen. The nitrogen was then purged, and the reactor was opened and heated. Timing began when the temperature inside the reactor reached 150 °C. The reaction was maintained at this temperature for 4 hours, and samples were taken. GC analysis showed a conversion rate of 99.538% and a reaction selectivity of 98.693%.

[0048] Example 6

[0049] Diphenyl phosphate (0.125 g, 0.5 mmol) was added to a 0.5 L high-pressure reactor, followed by 86.565 g (1 mol) of 2-methyl-3-buten-2-ol (purity 99.528%, tert-amyl alcohol content 2000 ppm, water content 2000 ppm) and 218.515 g (3.0 mol) of 2-methoxypropylene (purity 99.526%, water content 1000 ppm). The reactor was closed, and the air inside was replaced three times with 0.5 MPaG nitrogen. The nitrogen was then purged, and the reactor was opened and heated. Timing began when the temperature inside the reactor reached 140 °C. The reaction was maintained at this temperature for 3 hours, and samples were taken. GC analysis showed a conversion rate of 99.527% and a reaction selectivity of 98.533%.

[0050] Example 7

[0051] In a 0.5L high-pressure reactor, 0.174 g (0.5 mmol) of naphthol phosphate was added, followed by 86.565 g (1 mol) of 2-methyl-3-buten-2-ol (99.531% purity, 500 ppm tert-amyl alcohol, 1000 ppm water) and 218.515 g (3.0 mol) of 2-methoxypropylene (99.526% purity, 1000 ppm water). The reactor was closed, and the air inside was purged three times with 0.5 MPaG nitrogen. The nitrogen was then purged, and the reactor was opened and heated. Timing began when the temperature reached 140°C. The reaction was maintained at this temperature for 3 hours, and samples were taken. GC analysis showed a conversion rate of 99.626% and a selectivity of 98.554%.

[0052] Example 8

[0053] Dimethyl phosphite (0.110 g, 1 mmol) was added to a 0.5 L high-pressure reactor, followed by 86.565 g (1 mol) of 2-methyl-3-buten-2-ol (purity 99.543%, tert-amyl alcohol content 200 ppm, water content 200 ppm) and 218.515 g (3.0 mol) of 2-methoxypropylene (purity 99.535%, water content 200 ppm). The reactor was closed, and the air inside was replaced three times with 0.5 MPaG nitrogen. The nitrogen was then purged, and the reactor was opened and heated. Timing began when the temperature inside the reactor reached 160 °C. The reaction was maintained at this temperature for 6 hours, and samples were taken. GC analysis showed a conversion rate of 99.512% and a reaction selectivity of 98.623%.

[0054] Comparative Example 1

[0055] Triethanolamine (0.0448 g, 0.3 mmol) and methanesulfonic acid (0.0288 g, 0.3 mmol) were added to a 0.5 L high-pressure reactor, followed by 86.565 g (1 mol) of 2-methyl-3-buten-2-ol (purity 99.525%, tert-amyl alcohol content 3500 ppm, water content 1500 ppm) and 182.096 g (2.5 mol) of 2-methoxypropylene (purity 99.514%, water content 1500 ppm). The reactor was closed, and the air inside was replaced three times with 0.5 MPaG nitrogen. The nitrogen was then purged, and the reactor was opened and heated. Timing began when the temperature inside the reactor reached 150 °C. The reaction was maintained at this temperature for 4 hours, and samples were taken. GC analysis showed a conversion rate of 99.312% and a reaction selectivity of 96.165%.

[0056] Comparative Example 2

[0057] Triethanolamine (0.0448 g, 0.3 mmol) and methanesulfonic acid (0.0288 g, 0.3 mmol) were added to a 0.5 L high-pressure reactor, followed by 86.565 g (1 mol) of 2-methyl-3-buten-2-ol (purity 99.531%, tert-amyl alcohol content 2000 ppm, water content 2500 ppm) and 182.096 g (2.5 mol) of 2-methoxypropylene (purity 99.515%, water content 2500 ppm). The reactor was closed, and the air inside was replaced three times with 0.5 MPaG nitrogen. The nitrogen was then purged, and the reactor was opened and heated. Timing began when the temperature inside the reactor reached 150 °C. The reaction was maintained at this temperature for 4 hours, and samples were taken. GC analysis showed a conversion rate of 99.234% and a reaction selectivity of 96.593%.

Claims

1. A method for preparing methylheptenone, comprising: 2-Methyl-3-buten-2-ol and 2-methoxypropylene undergo a Saucy-Marbet reaction in the presence of a catalyst to produce methylheptenone; characterized in that the tert-amyl alcohol content in 2-methyl-3-buten-2-ol is 200-3000 ppm, and the water content in both 2-methyl-3-buten-2-ol and 2-methoxypropylene is 100-2000 ppm.

2. The method according to claim 1, characterized in that, The catalyst is selected from organic amine sulfonates, phosphate diesters, and phosphite diesters.

3. The method according to claim 2, characterized in that, The organic amine sulfonate is ethanolamine sulfonate, the phosphate diester is selected from one or more of diphenyl phosphate, naphthol phosphate and dibenzyl phosphate, and the phosphite diester is selected from one or more of dimethyl phosphite, diphenyl phosphite and diethyl phosphite.

4. The method according to claim 3, characterized in that, The ethanolamine sulfonate is selected from one or more of diethanolamine methanesulfonate, triethanolamine methanesulfonate, diethanolamine p-toluenesulfonate, and triethanolamine p-toluenesulfonate.

5. The method according to claim 1 or 2, characterized in that, The molar ratio of the catalyst to 2-methyl-3-buten-2-ol is 0.005–0.1%.

6. The method according to claim 5, characterized in that, The molar ratio of the catalyst to 2-methyl-3-buten-2-ol is 0.01–0.05%.

7. The method according to claim 1, characterized in that, The molar ratio of 2-methyl-3-buten-2-ol to 2-methoxypropylene is 1:2 to 5.

8. The method according to claim 1, characterized in that, The molar ratio of 2-methyl-3-buten-2-ol to 2-methoxypropylene is 1:2.5 to 3.

9. The method according to any one of claims 1-4, characterized in that, The reaction temperature is 100-200℃.

10. The method according to claim 9, characterized in that, The reaction temperature is 140-160℃.

11. The method according to any one of claims 1-4, characterized in that, The reaction residence time is 2 to 6 hours.

12. The method according to claim 11, characterized in that, The reaction residence time is 3-4 hours.