Question

Why did this synthesis of Aspirin fail?

The method used was:
1. Add 2.5 g of salicylic acid(about 2494 mg), 3.0 ml of acetic anhydride, and 5 drops of concentrated(85%) phosphoric acid to a 50-mL Erlenmeyer flask.
2. Heat the flask with a hot water bath at about 70°C for 5 minutes. The solution should be transparent after the reaction.
3. Add 2 mL of distilled water to the flask. After a minute, take off the flask from the water bath and add 20 ml of distilled water to the flask. Then put the flask in an ice bath and get crystals.
4. Collect the aspirin crystals by vacuum filtration. Use a Buchner funnel and dry filter papers. Scrape out the solid in the flask with a glass rod and dump on the filter paper. Rinse it with 5 mL of distilled water.
5. Dry the aspirin in 110°C oven for 5 minutes. I get about 2556 mg of aspirin.
6. Take 1 g of aspirin and follow a process similar to 1-5. Add 15 mL of diethyl ether and 1 g of aspirin to a 50-mL Erlenmeyer flask. Then heat the reaction with a hot water bath at about 50°C. Take off the flask and add 15 mL of petroleum ether to the flask. Put the flask in an ice bath and get white needle shaped crystals. Collect the crystals by vacuum filtration. Rinse it with petroleum ether. Finally dry the crystals in 110°C oven. (Recrystallization)
When I took them out after 5 minutes, they was slightly less dry. (now I get about 311 mg) I wanted to use a melting point apparatus, so I continued heating a little more. However, it melted...It seems that new substances have been formed instead of aspirin. Especially, at the point where there were filter holes, black powder like something created. I wonder what these could be.

When I was synthesizing aspirin (at method 3), crystals formed unexpectedly because the temperature of the hot water bath slowly decreased. However, since the solution was already transparent enough, I believed it would not have a significant impact. Additionally, the aspirin was not finely powered but rather in chunk form.

Answer 1

The synthesis of aspirin failed due to incorrect temperature maintenance, use of chunked salicylic acid, and potentially flawed recrystallization process.

Step-by-step explanation:

The synthesis of aspirin failed due to a few factors:

1. The temperature during the reaction was not maintained at the correct range. The reaction should have been heated at around 70°C, but it seems that the temperature slowly decreased, leading to unexpected crystal formation.
2. The salicylic acid used was not finely powdered, which could affect the reaction kinetics and the formation of aspirin crystals.
3. Additionally, the recrystallization process might not have been executed properly, as indicated by the decreased dryness of the crystals after being heated in the oven.

The black powder-like substance that formed at the filter holes could be impurities or by-products of the reaction.