Preparation method of 1,2-hexanediol

A common method for preparing 1,2-hexanediol is through the epoxidation reaction of hexene, using peracetic acid as the oxidant, and reacting in a suitable organic solvent such as dichloromethane. The reaction temperature is controlled at 0-10 ℃ and the reaction time is about 2-4 hours. 1,2-epoxyhexane is then subjected to ring opening hydrolysis with water under the action of an acidic catalyst such as sulfuric acid, and the hydrolysis temperature is maintained at 50-70 ℃. After several hours of reaction, 1,2-hexanediol can be obtained.
Starting from hexanal, hexanal is first reacted with ethylene glycol to form an aldehyde under the catalysis of p-toluenesulfonic acid. The reaction is carried out under reflux in toluene solvent at a reflux temperature of 110-115 ℃ for about 35 hours. Then, the aldehyde is reduced under the action of reducing agents such as lithium aluminum hydride. The reduction reaction is carried out at a low temperature in anhydrous ether, controlled at around -78 ℃, and finally hydrolyzed to obtain 1,2-hexanediol. Using microbial transformation method to prepare 1,2-hexanediol and screening specific microbial strains with reducing ability, such as certain yeast strains. Adjust the culture medium containing carbon sources (such as glucose), nitrogen sources (such as yeast extract), etc. to an appropriate pH value (generally pH 6.5-7.5), introduce the cultured microbial strains, and then add diethyl adipate as a substrate. Cultivate in a shaker at around 30 ℃ for several days of fermentation conversion, and obtain 1,2-hexanediol through subsequent treatments such as extraction and distillation. Using 1-hexene as the raw material, it reacts with oxygen and hydrogen in a catalytic system composed of titanium tetrachloride and aluminum alkyl. The reaction pressure is controlled at 2-5 MPa and the temperature is between 80-100 ℃. The corresponding alcohol intermediate is then subjected to a hydrogenation reduction step using palladium carbon catalyst. The hydrogen pressure is 13 MPa and the temperature is between 50-60 ℃, resulting in the production of 1,2-hexanediol. 1,2-Hexanediol can also be prepared by hydrolysis reaction of halogenated hexane. For example, 1-bromo-2-hexanol reacts with sodium hydroxide aqueous solution under heating conditions, with a reaction temperature controlled at 70-90 ℃ and a reaction time of 3-6 hours. A nucleophilic substitution reaction occurs, and the bromine atom is replaced by a hydroxyl group. After separation and purification, the target product 1,2-hexanediol can be obtained.
Using electrochemical synthesis method to prepare 1,2-hexanediol, starting from adipic acid, in a specific electrolyte system (such as a solution of propylene carbonate containing tetrabutylammonium bromide), graphite electrode and platinum electrode are used to apply a certain voltage (such as 2-4V) for electrolytic reaction. The electrolysis temperature is maintained at 20-30 ℃. After a certain period of electrolysis, 1,2-hexanediol is obtained through post-treatment. Firstly, 1-hexyne and water undergo an addition reaction catalyzed by mercuric salt. The addition reaction is carried out in a dilute sulfuric acid solution at a temperature of 40-60 ℃ with 2-hexanone. Then, 2-hexanone is reduced using a reducing agent such as sodium borohydride. The reduction reaction is carried out in ethanol solvent at room temperature, and finally, 1,2-hexanediol is obtained through further treatment. Separate and prepare 1,2-hexanediol from a mixture of isomers of hexanediol. Using distillation method to separate different isomers based on their boiling point differences. The boiling point of 1,2-hexanediol is about 209-211 ℃. By precisely controlling the temperature and reflux ratio of the distillation tower (such as controlling the reflux ratio at 5-10), high-purity 1,2-hexanediol can be separated from the mixture. Using adipic acid monoester as raw material, hydrogenation reaction is carried out under the action of hydrogenation catalyst (such as Raney nickel). The hydrogenation reaction is carried out in a high-pressure reactor with hydrogen pressure of 5-10 MPa and reaction temperature of 150-180 ℃. 1,2-hexanediol and corresponding alcohol are separated by distillation and other separation methods to obtain pure 1,2-hexanediol.
Preparation of 1,2-hexanediol using the formatting reagent method. First, prepare the ethyl magnesium bromide reagent, react magnesium shavings with bromoethane in anhydrous ether, maintain the reaction temperature at 30-40 ℃, and then react it with ethylene oxide. After the reaction is complete, hydrolysis is carried out using dilute sulfuric acid solution. Finally, 1,2-hexanediol is obtained through conventional separation and purification operations.