Preparation of Adipic Acid

Preparation of Adipic Acid
1. Experimental Objective: To learn the principle and method of preparing adipic acid by oxidation of cyclohexanol; 2. Mastering operational skills such as concentration, filtration, and recrystallization
2. Experimental principle
KMnO4 can oxidize cyclohexanol to adipic acid under acidic, neutral, and alkaline conditions. KMnO4 has the strongest oxidation ability under acidic conditions, which can cause excessive oxidation and reduce the quality of adipic acid, and manganese salts are difficult to recover.
. KMnO4 can be reduced to MnO2 under neutral or weakly alkaline conditions, and the oxidation rate of organic compounds by KMnO4 is faster under alkaline conditions than under acidic conditions. Therefore, KMnO4 is more suitable as an oxidant for the oxidation of cyclohexanol under alkaline conditions.
Using NaOH solution to provide alkaline conditions, KMnO4 is reduced to MnO2, making it easy to recover and utilize after washing and drying. Especially under alkaline conditions, potassium permanganate has good selectivity in the reaction, and the generated adipate is easy to separate, with simple operation, stable reaction, and fast reaction rate.
3、 Experimental and Pharmaceutical Instruments: Three necked flasks, beakers, thermometers, constant pressure dropping funnels, spherical condenser tubes, conical flasks, alcohol lamps, asbestos nets, Buchner funnels, suction filter bottles, etc. Pharmaceutical Instruments: 0.3mol/L NaOH solution (50ml), KMnO4 solid (6g), cyclohexanol (2.1ml), sodium bisulfite, concentrated hydrochloric acid, etc. Experimental Steps: Add 50ml of 0.3mol/L NaOH solution to a 250ml beaker, place it on a magnetic stirrer, and dissolve 6g of KMnO4 into the NaOH solution while stirring. Transfer the stirred solution to a three necked flask and install the experimental instrument as shown in the figure. Add 2.1ml of cyclohexanol to the constant pressure dropping funnel and use it during the experiment.
After installing the experimental setup, conduct the experiment by adding 2.1ml of cyclohexanol dropwise to the above solution using a dropper, maintaining the temperature of the reactants at 43-47 ℃. When the alcohol dropwise addition is complete and the temperature of the reaction mixture drops to around 43 ℃, the boiling water bath heats the mixture to coagulate the manganese dioxide. Place a small droplet of the mixture on a flat filter paper to test if the reaction is complete. If there is no purple color present, it indicates that KMnO4 is no longer present. If a purple color is observed in the test solution, a small amount of solid sodium bisulfite can be used to remove excess potassium permanganate.
Filter the liquid in the three necked flask while it is hot, and wash the manganese dioxide residue with a small amount of hot water three times (2 mL each time), squeezing out the water in the residue as much as possible each time. Combine the filtrate and wash solution, and acidify with 4ml concentrated hydrochloric acid to pH 2.0. Transfer the liquid to a small beaker, carefully heat and evaporate to concentrate the solution to around 10 ml, then stop heating and allow it to cool naturally, crystallize, and separate the precipitated adipic acid. Weigh the mass of adipic acid obtained and calculate the yield.
【 Operation points and precautions 】
1. KMnO4 should be finely ground to facilitate its full reaction. two Cyclohexanol is a viscous liquid at room temperature, which can be added with an appropriate amount of water and stirred, making it easy to use a dropper to add 3 Drip addition: This experiment is a strongly exothermic reaction, so the rate of adding cyclohexanol should not be too fast (1-2 drops/second), otherwise, due to the strong exothermic reaction, the temperature will rise sharply and cause an explosion. 4. Strictly control the reaction temperature and stabilize it between 43-47 ℃. This reaction is exothermic and will cause the mixture to exceed 45 ° C. If the temperature of the mixture cannot rise to 45 ° C after 5 minutes of reaction at room temperature, it can be carefully warmed to 40 ° C to initiate the reaction. five To improve the yield, it is best to cool the solution with ice water to reduce the solubility of adipic acid in water.
5、 Experimental data processing
1. Product characteristics: 2 Theoretical yield: 3 Actual output: 4 Yield Calculation:
VI. Experimental Summary