A method for synthesizing leaf alcohol

Abstract

The invention discloses a method for synthesizing leaf alcohol, comprising the following steps: (1) adding crotonaldehyde and a catalyst to a high-pressure reactor, stirring, filling with nitrogen, adding acetaldehyde at 50-80°C, reacting, and obtaining an intermediate 2,4-hexadienal; (2) adding a catalyst, an intermediate and isopropanol to the high-pressure reactor, introducing hydrogen under stirring, and reacting to obtain leaf alcohol; the catalyst of the method of the invention is easy to prepare, low in price and easy to recycle, the catalytic process conditions are mild, and the requirements for equipment are low. The invention has high atomic utilization rate, high yield, high purity, less three wastes, and is suitable for industrial production. Compared with the original acetaldehyde crotonaldehyde method of Akimichi Furuhata, the invention reduces the original three-step reaction to two steps; eliminates the use of reducing agent sodium borohydride, greatly improving the total yield of leaf alcohol; reduces the temperature and pressure required for the reaction, and is more energy-saving, safer and more environmentally friendly than the original reaction.

Description

Technical Field

[0001] The invention relates to the field of chemical synthesis, and in particular to a method for synthesizing leaf alcohol. Background Art

[0002] Leaf alcohol (chemical name: cis-3-hexen-1-ol) is a very important spice with the natural fragrance of fresh grass. Leaf alcohol and its derivatives are one of the most popular precious fragrances in the world and are also a symbol of the green revolution in the world's spice industry.

[0003] Leaf alcohol exists in almost all green plants. However, due to its low boiling point and high water solubility, the production of leaf alcohol extracted from nature is extremely small and the production cost is high, so biochemical and chemical synthesis processes are more commercially valuable.

[0004] Patent CN1762941A discloses a method for synthesizing leaf alcohol, which uses butene-1 as raw material, undergoes bromination, and debromination under alkaline conditions to obtain butyne-1, then butyne-1 and bromoalkane form acetylene anions under the action of Grignard reagent, and then undergoes ring opening with ethylene oxide to obtain 3-hexyne-1-ol; then, incomplete hydrogenation is performed under normal temperature and pressure to obtain the product leaf alcohol, with a purity of more than 99%. However, this method has long synthesis steps, low yield, harsh reaction conditions, and high cost.

[0005] Patent CN106631687A discloses "a method for synthesizing leaf alcohol using a silane-Lewis acid catalytic system". Methylpyran (6-methyl-3,6-dihydro-2H-pyran) is used as a raw material. In a silane-Lewis acid system, a one-pot reaction is carried out at a temperature of 20 to 70°C and a reaction time of 20 to 80 minutes. Methylpyran is ring-opened to generate leaf alcohol, and the finished leaf alcohol is obtained by distillation. In this method, the catalyst is recovered and reused by applying the heavy component method, but the use of Lewis acid has high requirements for the corrosion protection of the equipment.

[0006] Patent CN101875599A discloses a "new method for synthesizing leaf alcohol" using 1-pentene and formaldehyde, paraformaldehyde, trioxymethylene or formalin as raw materials, and preparing leaf alcohol through a one-step reaction catalyzed by Lewis acid. This method reacts at -40 to 20°C, consumes a lot of energy, and is difficult to achieve industrial mass production.

[0007] Patent CN101928203A discloses "a method for supercritical synthesis of leaf alcohol". The raw materials n-pentene and formaldehyde are mixed evenly in a solvent and then enter a coil reactor, and condensation reaction is continuously carried out under supercritical conditions, and then enter the flash evaporator through a high-pressure valve. The low-boiling products flashed out are cooled to below 40°C by a condenser and flow into the light component receiver, and the remaining flow flows into the heavy component receiver, and then the products are separated by distillation. This method has the disadvantages of complex process, low yield, harsh reaction conditions, high corrosion to equipment, and low raw material safety.

[0008] Patent CN114540428A discloses a method for producing natural leaf alcohol by temperature-variable fermentation of tea leaves. Fresh tea leaves are put into a fermentation tank and fermented by temperature-variable fermentation. The leaf alcohol content in the tea leaves can be significantly increased by treating the tea leaves by temperature-variable fermentation, and the leaf alcohol content can be increased from 2% to more than 28%; the total yield of leaf alcohol after distillation after post-treatment extraction of tea oil is greater than 85%. However, the raw material tea leaves of the biochemical synthesis method are relatively expensive and have limited output, while the corresponding leaf alcohol content of the tea leaves is actually only 28%, which leads to a relatively high production cost of the biochemical synthesis method.

[0009] Yuan Dongmei used sorbic acid as raw material, sorbic acid was esterified with anhydrous ethanol in benzene, and the esterification product was esterified with NaBH in absolute anhydrous ether. 4 The reduction was carried out at 20℃~30℃ for about 10min, and then the reduction product dienol was reacted with Mo(CO) 6 The product is obtained by selective hydrogenation in a high pressure reactor at 120°C to 140°C for 3h to 6h with a yield of 74.8%. This method has a higher yield, but the synthesis steps are long and NaBH is used. 4 Reduction, high cost and high pressure are required.

[0010] Akimichi Furuhata developed the acetaldehyde-crotonaldehyde method to synthesize leaf alcohol. Acetaldehyde and crotonaldehyde undergo aldol condensation under the catalysis of 50% morpholine-phosphoric acid solution (molar ratio 3:1) to obtain the intermediate 2,4-hexadienal, which is then reacted with NaBH 4 The intermediate 2,4-hexadienol was reduced and then heated at 190-200°C and 5 MPa H 2 The method has many steps, low yield, harsh reaction conditions, and uses NaBH 4 Reduction and high cost. The reaction route is as follows:

[0011] Summary of the invention

[0012] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for synthesizing leaf alcohol with a simple, efficient, green and safe preparation process.

[0013] The technical solution of the present invention is summarized as follows:

[0014] A method for synthesizing leaf alcohol comprises the following steps:

[0015] (1) Add crotonaldehyde I and the first catalyst to a high-pressure reactor, start stirring, fill with nitrogen to make the reaction pressure reach 0.1-2 MPa, add acetaldehyde II at 50-80° C., add the entire amount within 1.5-2 hours, and continue to react at 0.1-2 MPa and 50-80° C. for 1-1.5 hours to obtain the intermediate 2,4-hexadienal III;

[0016] (2) Add the second catalyst, the intermediate 2,4-hexadienal III and isopropanol into a high-pressure reactor, introduce hydrogen to 1.0-5.0 MPa under stirring, raise the temperature to 120-200° C., and react for 4-12 hours to obtain leaf alcohol IV;

[0017] The reaction formula is as follows:

[0018]

[0019] Preferably, the first catalyst is tetraethylammonium hydroxide, tetrabutylammonium hydroxide or hexadecyltrimethylammonium hydroxide.

[0020] Preferably, the second catalyst is at least one of chromium hexacarbonyl, molybdenum hexacarbonyl, tungsten hexacarbonyl and iron pentacarbonyl.

[0021] Advantages of the present invention:

[0022] (1) The catalyst of the method of the present invention is easy to prepare, inexpensive and easy to recycle, the catalytic process conditions are mild, and the equipment requirements are low.

[0023] (2) The present invention has high atomic utilization rate, high yield, high purity, less three wastes, and is suitable for industrial production.

[0024] (3) Compared with the original acetaldehyde crotonaldehyde method of Akimichi Furuhata, the present invention reduces the original three-step reaction to two steps; eliminates the use of reducing agent sodium borohydride, greatly improving the total yield of leaf alcohol; reduces the temperature and pressure required for the reaction, and is more energy-saving, safer, and more environmentally friendly than the original reaction. DETAILED DESCRIPTION

[0025] The present invention is further explained below in conjunction with specific embodiments. However, it should be noted that the protection scope of the present invention is not limited by these specific implementation methods and principle explanations, but is determined by the claims.

[0026] Example 1

[0027] A method for synthesizing leaf alcohol comprises the following steps:

[0028] (1) Add 56 g of crotonaldehyde I and 5 mL of 10% tetraethylammonium hydroxide (first catalyst) ethanol solution into a 500 ml autoclave, start stirring, charge nitrogen to make the reaction pressure reach 0.1 MPa, and the reaction temperature is 50°C; slowly pump in 44 g of acetaldehyde II, and the pumping is completed in 2 hours, and the reaction is continued at 0.1 MPa and 50°C for 1 hour; collect the reaction liquid, distill and separate the solvent, filter, remove the tetraethylammonium hydroxide solid, and obtain 2,4-hexadienal III after vacuum distillation of the filtrate, with a crotonaldehyde conversion rate of 91.50%, a product selectivity of 99.5%, and a purity of 99.4%.

[0029] (2) 1.25 g of hexacarbonyl chromium (the second catalyst), 25 mL of the intermediate 2,4-hexadienal III and 75 mL of isopropanol were added to a 500 ml high-pressure reactor. Under stirring, hydrogen was introduced to 2 MPa, the temperature was raised to 160°C, and the reaction was carried out for 8 hours. The product was subjected to vacuum distillation to obtain leaf alcohol IV with a conversion rate of 86.60%, a selectivity of 95.38% and a purity of 99.6%.

[0030] The synthetic route is as follows:

[0031]

[0032] Table 1 Comparison between the method of the present invention (Example 1) and the Akimichi Furuhata method

[0033] Example 1 Akimichi Furuhata method Total yield of leaf alcohol 75.2％ 29.41％ Reaction steps Two-step method Three-step approach Reaction temperature 160℃ 190℃ Reaction pressure 2MPa 5MPa Carbonyl hydrogenation Catalytic hydrogenation Reducing agent reduction

[0034] Example 2

[0035] A method for synthesizing leaf alcohol comprises the following steps:

[0036] (1) Add 56 g of crotonaldehyde I and 5 mL of 10% tetrabutylammonium hydroxide (first catalyst) ethanol solution into a 500 ml autoclave, start stirring, charge nitrogen to make the reaction pressure reach 2 MPa, and the reaction temperature is 80°C; slowly pump in 44 g of acetaldehyde II, and the pumping is completed within 1.5 h. Continue to react at 2 MPa and 80°C for 1.5 h, collect the reaction liquid, distill and separate the solvent, filter, remove the tetrabutylammonium hydroxide solid, and obtain 2,4-hexadienal III after vacuum distillation of the filtrate. The crotonaldehyde conversion rate is 96.80%, the product selectivity is 59.1%, and the purity is 99.4%.

[0037] (2) 1.25 g of molybdenum hexacarbonyl (the second catalyst), 25 ml of the intermediate 2,4-hexadienal III and 75 ml of isopropanol were added to a 500 ml high-pressure reactor. Under stirring, hydrogen was introduced to 1 MPa, the temperature was raised to 200°C, and the reaction was carried out for 4 hours. The product was subjected to vacuum distillation to obtain leaf alcohol with a conversion rate of 70.11%, a selectivity of 90.59% and a purity of 99.7%.

[0038] Example 3

[0039] A method for synthesizing leaf alcohol comprises the following steps:

[0040] (1) Add 56 g of crotonaldehyde I and 5 mL of 10% hexadecyltrimethylammonium hydroxide (first catalyst) ethanol solution into a 500 ml autoclave, start stirring, charge nitrogen to make the reaction pressure reach 1 MPa, and the reaction temperature is 60°C; slowly pump in 44 g of acetaldehyde II, and the pumping is completed within 1.8 h, and continue to react at 1 MPa and 60°C for 1.2 h; collect the reaction liquid, distill and separate the solvent, filter, remove the hexadecyltrimethylammonium hydroxide solid, and obtain 2,4-hexadienal III after vacuum distillation of the filtrate, with a crotonaldehyde conversion rate of 92.55%, a product selectivity of 92.5%, and a purity of 99.4%.

[0041] (2) 1 g of hexacarbonyl tungsten and 0.25 g of hexacarbonyl iron (the second catalyst), 25 ml of the intermediate 2,4-hexadienal III and 75 ml of isopropanol were added to a 500 ml high-pressure reactor. Under stirring, hydrogen was introduced to 5 MPa, the temperature was raised to 120°C, and the reaction was carried out for 12 hours. The product was subjected to vacuum distillation to obtain leaf alcohol IV with a conversion rate of 73.90%, a selectivity of 54.49% and a purity of 99.5%.

Claims

1. A method for synthesizing leaf alcohol, characterized in that The steps include: (1) Add crotonaldehyde (I) and the first catalyst to a high-pressure reactor, start stirring, fill with nitrogen to make the reaction pressure reach 0.1-2 MPa, add acetaldehyde (II) at 50-80°C, add the addition within 1.5-2 hours, continue to react at 0.1-2 MPa and 50-80°C for 1-1.5 hours; obtain the intermediate 2,4-hexadienal (III); (2) Add the second catalyst, the intermediate 2,4-hexadienal (III) and isopropanol into a high-pressure reactor, introduce hydrogen to 1.0-5.0 MPa under stirring, raise the temperature to 120-200° C., and react for 4-12 hours to obtain leaf alcohol (IV); The reaction formula is as follows: The second catalyst is at least one of chromium hexacarbonyl, molybdenum hexacarbonyl, tungsten hexacarbonyl and iron pentacarbonyl.

2. The method according to claim 1, characterized in that The first catalyst is tetraethylammonium hydroxide, tetrabutylammonium hydroxide or hexadecyltrimethylammonium hydroxide.

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