Excess sulfuric acid in aspirin synthesis causes side reactions and reduced purity.
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Chemical discussion threads confirm that using an excessive amount of sulfuric acid in aspirin synthesis severely reduces product yield and can compromise the reaction, yielding impure or unreacted starting materials instead of aspirin.
# Failed synthesis of aspirin due to excess sulfuric acid
Tags: organic-chemistry, experimental-chemistry
- Score: 16
- Views: 8161
- Answers: 1
- Answered: yes
- Asked by: studen (587 rep)
- Asked: 2015-05-01
- Edited: 2019-03-19
- Site: chemistry
## Question
Last week, I tried synthesizing acetylsalicylic acid - the reaction is shown below - using $\ce{H2SO4}$ as a catalyst. However, as the title suggests the synthesis failed as I used too much $\ce{H2SO4}$ - approximately four times more than the prescribed volume. Needless to say, I had to redo the synthesis.
But now I try to understand why the synthesis failed - I know that catalysts are used in small amounts, but I thought that much of it would only lead to equilibrium state being reached faster.
I think that maybe the acidity of the reaction environment could've somehow explained why the synthesis didn't take place. But I don't understand why - shouldn't more protons in the environment lead to faster protonation of the carbonyl oxygen of acetic anhydride? Could you please explain it to me?
## Answers
### Answer by Curt F. (score: 9 [ACCEPTED])
But I don't understand why - shouldn't more protons in the environment l
# Does excessive sulfuric acid as catalyst affect the synthesis of aspirin?
Tags: organic-chemistry, experimental-chemistry
- Score: 8
- Views: 2404
- Answers: 1
- Answered: yes
- Asked by: Kelvin Seow (95 rep)
- Asked: 2016-11-23
- Edited: 2016-11-23
- Site: chemistry
- Closed: closed
## Question
Recently had a lab experiment to synthesize aspirin.
I was instructed to add 4 drops of concentrated sulfuric acid but misread the "4 drops" as "4 ml".
Ended up with a yield of just 10 %. But the crystals that I obtained upon recrystallisaion weren't of aspirin but of salicylic acid (as confirmed by a melting point of 160 °C).
Did the addition of excessive sulfuric acid affect this in any way? What could have caused salicylic acid crystals to be produced instead of aspirin?
Some technical details of the steps I took:
mixing 2 g of salicylic acid with 5ml of acetic anhydride
4 ml of sulfuric acid added as catalyst (should've been 4 drops)
Heated the mixture in a water bath for 15 min.
Added 1 ml of cold water slowly then added 20 ml of cold water again quickly and stirred for 5 min.
Allowed solution to cool at room temp.
Crude product was dissolved in 5 ml of ethanol. (I noticed
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