Green Synthesis Experiment Report of Adipic Acid
1. To understand the disadvantages of traditional synthesis methods and the advantages of green synthesis methods through the preparation of adipic acid; 2. Familiar with the recycling of catalysts without the need for recovery.
2、 Experimental principle: Adipic acid, commonly known as fatty acid, has the molecular formula GHiQ. The most widely used production process for adipic acid worldwide is the nitric acid oxidation process using cyclohexanone or cyclohexanone as raw materials (Figure 1). In this production route, strong oxidizing nitric acid is used, which severely corrodes equipment, and the N20 gas generated during the production process is considered one of the reasons for global warming and ozone depletion, causing great pollution to the environment. Ryoji Noyon published a green synthesis method for adipic acid in Science in 1998, proposing a green preparation route using water as a solvent, H2O2 as an oxidant, tungsten as a catalyst, and potassium bisulfate (KHSO4) as a phase transfer catalyst with methyl trioctyl ammonium chloride (aliquat 336) as the catalyst.
This route does not require strong acids, does not produce harmful gases such as N2O, uses water as a solvent does not produce waste liquid, and the catalyst can be directly recycled without recycling. Subsequently, researchers have discovered that without the need for a phase transfer catalyst, using water as the solvent and H2O2 as the catalyst, a coordination catalyst synthesized in situ from sodium tungstate oxalic acid can also be used to synthesize adipic acid (Figure 2).
O OH
Figure 1: Preparation of Adipic Acid NaWO · 2H2O-H2Q by Traditional Synthesis Method
O 1. Instrument: Magnetic heating stirrer, condenser tube, round bottom flask, beaker, drying tube, surface dish, basic burette, melting point analyzer, three necked flask, vacuum pump, analytical flask.
.
2、 Sodium tungstate (AR), cyclohexanol (AR), cyclohexene (AR), concentrated nitric acid (AR), potassium bisulfate (AR),
OH
KHSO, W! OqU2lt3fO6
HO O
Figure 2 Two different green synthesis methods for preparing succinic acid
H2C2O4-2H2O-H2O2
HO
.
O OH O
4. Experimental steps
1. Traditional preparation method
Add 2ml of concentrated nitric acid to a 10mL round bottom flask, place it in a stirring magnet, and install a condenser tube. The device diagram is shown below (see Figure 3). Heat up to 80 ° G in a ventilated cabinet (with N2O gas released), then slowly drip 1mL of cyclohexanol from above the condenser into a round bottom flask through a dropper. During the drip process, try to avoid contact between cyclohexanol and the inner wall of the condenser. The acceleration of the drip should be controlled at around 1 drop/min, and the drip process should last for 30-40 minutes. After dropwise addition, maintain 80 ° C and continue the reaction for 2 hours, then cool to
room temperature and cool in an ice water bath to precipitate crystals. Filter with a Buchner funnel, wash with a small amount of ice water, then wash with a small amount of ethanol, and try to dry the crystals as much as possible. Collect drugs and dry them in a drying oven to determine their melting point.
15min， Weigh and calculate the yield, take less for mass production
Figure 3 Traditional preparation method device diagram
2. Green preparation method - sodium tungstate oxalic acid as catalyst
Add sodium tungstate, oxalic acid,
% H2O2, and magnetic particles to a 100mL three necked flask.
. After stirring at room temperature for 15-20 minutes, add cyclohexene. Set up the reflux device (see figure
4), continue to stir rapidly and vigorously, and heat until reflux occurs. During the reaction process, the reflux temperature will gradually increase. After reflux, pour the hot reaction solution into a 100mL beaker, cool it with cold water to near room temperature, and then cool it in an ice bath for 20 minutes. Filter with a Buchner funnel, wash with 5mL of ice water, and then wash with 5mL of ethanol to dry the crystals as much as possible. Dry the product to a balance, weigh it, record the mass of adipic acid, calculate the yield, and take a small amount of product to determine the melting point.
Figure 4 Green preparation method device diagram
3. Determination of adipic acid content
The content of adipic acid is determined by acid-base titration method.
. Accurately weigh two experimental products (accurate to) into a 250ml conical flask, add 50mL of hot distilled water, and stir to dissolve the sample. Add 1 drop of phenolphthalein indicator and titrate with L-1 sodium hydroxide standard solution until it turns slightly red. The endpoint is when the color does not fade within 30 seconds. Titrate 2 portions each. Calculate the percentage content of adipic acid in the sample.
Product
Product Quality
Initial Reading/mL Endpoint Reading
NaOH Concentration Percentage Content
/g
/mL
/mol • L -/%
1
Traditional Method Preparation Green Method Preparation
V. Results and Discussion
Preparation Method
Raw Material Quality
Theoretical Yield Actual Yield
/g
Traditional methods
Green methods can be seen from the table above that the yield of products prepared by traditional methods is higher than that of green methods, but the pollution is greater
Color preparation methods have a slight advantage and can be said to have their own advantages and disadvantages.
.
6、 Experimental thinking
Melting point/oC
Purity/%
; In terms of purity, in this experiment, due to the premature addition of raw materials in the green preparation, the reaction proceeded earlier, resulting in lower yield and longer melting process.
