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Prelab 18 - lab work
Organic Chemistry Lab II (CHEM201401)
Boston College
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Prelab 18
Synthesis of cholesteryl benzoate
Caution: Pyridine is toxic liquid. Use only in the fume hood and avoid contact with skin. Benzoyl chloride is a lachrymator (tear gas) and is moisture sensitive. Work with this liquid in a hood. Acetic anhydride is corrosive avoid skin.
Obtain dry 50 mL Erlenmeyer flask. Put 1 g of cholesterol. 3 mL of pyridine to flask and swirl to dissolve the cholesterol.
Syringe and Pasteur pipet and measure 0 mL of benzoyl chloride and put into flask. Heat on steam bath for 10 minutes.
Cool flask by swirling in a beaker of cold water. Dilute mixture with 15 mL of methanol. Collect solid (cholesteryl benzoate) vacuum filtration. Rinse and wash with methanol.
Recrystallize cholesteryl benzoate by heating on steam bath with 20 mL of ethyl acetate until all solid dissolves. However, if there are solids leftover than you need to filter hot solution by gravity==(Small amount of ethyl acetate in the receiving flask and place the flask on steam bath. Line a stemless funnel with a fluted filter paper, allow the ethyl acetate vapors to warm the funnel before filtering the hot solution).
Let ethyl acetate solution of product to cool to r. and then put on ice. Get a beaker of ice and cool ethyl acetate. Collect through vacuum. Wash with cold ethyl acetate. Leave vacuum on for a while so crystals can dry. Weigh them. Mix equal amounts of the product (few crystals each) and cholesterol. Obtain melting points of the purified product and mixture with cholesterol.
Grab a lamp and bring to hood.
0 g of cholesteryl benzoate on one end of a glass microscope slide. Rest this end of the slide on a hot plate and turn the plate to high setting. When the solid melts, it will turn a cloudy liquid and then into a clear liquid. Once the clear liquid appears, use test tube holder to grab the end of the slide with no material. Lift slide off plate. Use the lamp and shine light at the slide from the side as the sample cools and record observations. Repeat the heating and cooling many times if you want.
Synthesis of acetylsalicylic acid
- 400 mL beaker with 150 mL of water and heat to boiling point on hot plate. 2 g of salicylic acid and put into 125 mL Erlenmeyer flask. Dispense 5 mL of acetic anhydride from the dispensing buret into flask. Add 5 drops of 85% phosphoric acid. Swirl flask to mix. Clamp into the boiling water bath. Heat 8 minutes. Remove flask from hot water bath and turn off plate. Cautiously, add 2 mL of deionized water to flask. Water will react vigorously with any unreacted acetic anhydride if left over. Once subsided, add 40 mL of water to flask. Let it cool at r. for 10 mins and place flask in ice. Stir with glass rod
Prelab 18
every once in a while, when cooling. Collect solid by vacuum and wash with ice-cold water. Set aside small portion (spatula-tip full, 20-30 mg) of crude acetyl-salicylic acid.
Recrystallize by transferring it into a 125 mL Erlenmeyer flask and add 6 mL of 95% ethanol. Heat slowly the flask on hot plate until aspirin completely dissolves.
As soon as it has all dissolved, remove flask from hot plate and add water to the solution in 5 mL portions, swirling after each addition, until total of 25 mL has been added.
Place flask in ice bath for 10 minutes. Collect aspirin by vacuum. Wash crystals with ice cold water. Leave vacuum on for few minutes so aspirin can dry. Once finish vacuuming, press crystals between two pieces of filter paper to dry them.
Test solubility of acetylsalicylic acid in toluene and in hot water. Then see what happens when aqueous solution is cooled and when it is rubbed against the tube with a stirring rod.
Test the solubility of product in 1 M sodium hydroxide. And then add equal amount of 1 M hydrochloric acid. Record what you see.
Test the solubility of an aspirin tablet in toluene and hot water and compare with product. Obtain melting point of a bit of tablet.
Observe and record and compare what happens to the tablet in the melting point capillary and product when melting.
Prepare 5 clean, small test tubes (they don’t have to be dry). Place a spatula-tip amount of following in test tubes:
a. 1. Salicylic acid
b. 2. Crude product
c. 3. Purified product
d. 4. Same as 3
e. 5. Empty (control)
Add 5-10 drops of water to test tubes 1-3 and 5. Add 5-10 drops of 0 M HCl solution to test tube 4 and heat it in a beaker of boiling water for 5 mins.
Then add 1-2 drops of 1% ferric chloride solution to each of the five test tubes. Record observations.
Save the purified aspirin product in drawer and obtain mass and melting point next week.
Prelab 18 - lab work
Course: Organic Chemistry Lab II (CHEM201401)
University: Boston College
