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Synthesis of Paracetamol by Acetylation of 4-Aminophenol watch

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    Hi, i'll be doing this experiment using 4-aminophenol and acetic anhydride as well as triethylamine. I'm not sure what the purpose of triethylamine is, maybe to soak up the by-product which is ethanoic acid? So ethanoic acid + TEA --> triethylammonium acetate.

    I cant find anything online, most experiments i found didnt even need TEA, they mainly used water.

    Thank you!
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    (Original post by xal)
    Hi, i'll be doing this experiment using 4-aminophenol and acetic anhydride as well as triethylamine. I'm not sure what the purpose of triethylamine is, maybe to soak up the by-product which is ethanoic acid? So ethanoic acid + TEA --> triethylammonium acetate.

    I cant find anything online, most experiments i found didnt even need TEA, they mainly used water.

    Thank you!
    The triethylamine acts as a nucleophilic catalyst.

    The amine group on 4-aminophenol is slow to attack because its lone pair is stabilised by delocalisation around the aromatic ring, this makes the rate of reaction slow.

    Triethylamine improves the rate by attacking the anhydride to give CH3CON(Et)3 +
    with the charge on the Nitrogen atom. This charged species is unstable and is therefore a better electrophile, so the 4-aminophenol attacks it more readily, reproducing the tertiary amine.

    (note a secondary or primary amine could lose a proton after reaction with the anhydride and would thus become a stable amide, but with tertiary amines there is no proton to lose)

    This sort of nucleophilic catalyst is quite common, probably the most common reagent to carry out the role is pyridine.
 
 
 

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