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Monday, July 04, 2005

Esterification: The Synthesis of Aspirin (ASA)

The most common medical ester is aspirin (ASA; acetyl salicylic acid). Other drugs such as Worm Guard (anti-wormer), Maxicaine (local anesthetic), Malathion (organophosphate), Mebendazole (antihelmenthic), Demerol (narcotic analgesic) and Equinil (sedative) are also esters.
The starting reactants for this experiment are salicylic acid and acetic anhydride (structures are shown above).

Salicylic acid reacts better with acetic anhydride than acetic acid, so acetic acid will provide the acetyl group which will react with the alcoholic -OH group on the salicylic acid. (The reaction is on the top of the post.)

Chemicals needed for the reaction: Salicylic acid, Acetic anhydride, and Concentrated sulfuric acid.

Equipment: 250 mL Erlenmeyer flask, Hot water bath, Ice bath, Buchner funnel and filter paper, Glass stirring rod, and Electronic pan balance and weighing boat.

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  • I cannot accept this entry.
    1) you must use a peer-reviewed article using at least one CiteULike reference (you can have other links for additional info)
    2) you cannot copy reactions or text from the internet. Redraw the single step of interest in ChemSketch and summarize in your own words.
    3) any entry that I graded "full marks" in the comments can be used as a example of how to do this assignment (e.g. first post on reduction of an ester to an alcohol)

    By Blogger Jean-Claude Bradley, at 6:13 AM  

  • First deadline is here. Since you have another post within the deadline, I will not count this one. Lets leave it in as an example of what errors to avoid.

    By Blogger Jean-Claude Bradley, at 6:46 AM  

  • What is the role of acetic anhydride and salicylic acid in the synthesis of ASA

    By Anonymous Anonymous, at 10:16 AM  

  • Acetic anhydride is the acylating agent. It adds the CH3CO group.

    By Blogger Jean-Claude Bradley, at 10:27 AM  

  • why is the ASA crystalized from alcohol/water instead of just water

    By Anonymous Anonymous, at 8:15 PM  

  • why is the ASA crystalized from alcohol??

    By Anonymous Anonymous, at 8:17 PM  

  • why is the ASA crystalized from alcohol??

    By Anonymous Anonymous, at 8:17 PM  

  • The choice of the solvent mixture in recrystalization is based on high solubility at high temperature and low solubility when it cools. Pure water was not optimal for this apparently and so water/ethanol was chosen by trial and error.

    By Blogger Jean-Claude Bradley, at 6:15 AM  

  • What is the role of the sulfuric acid?

    By Anonymous Anonymous, at 8:20 PM  

  • It is a catalyst

    By Blogger Jean-Claude Bradley, at 5:20 AM  

  • What would happen if a base such as NaOH were used instead of sulphuric acid?

    By Anonymous Anonymous, at 11:21 AM  

  • what would haven if a solid remains after the addition of NaHCO3?

    By Anonymous Anonymous, at 11:23 AM  

  • sir,is their is any other way to synthesis ASA which can be demonstrated to school students

    By Blogger raja, at 5:05 AM  

  • Raja - I am sure there are simple lab experiments that can be done but I don't teach the lab. You should be able to find something on Google.

    By Blogger Jean-Claude Bradley, at 6:25 AM  

  • sir, on addition of ferric chloride drops, what colour shows the presence of salicyclic acid?

    By Anonymous Anonymous, at 5:12 AM  

  • no ferric chloride in this experiment

    By Blogger Jean-Claude Bradley, at 8:38 AM  

  • If you add ferric chloride to the salicylic acid it should turn a purple/violet color.

    By Anonymous Anonymous, at 11:37 PM  

  • what is the kinetics constant for this syntesis?

    By Anonymous Anonymous, at 5:23 PM  

  • Don't know the kinetic details

    By Blogger Jean-Claude Bradley, at 5:47 PM  

  • hello,
    Why is acetic anhydride used opposed to acetic acid in the synthesis of acetaminophen?

    By Anonymous Anonymous, at 4:21 PM  

  • Acetic acid must be activated (to an anhydride or acid chloride, etc.) to react with an alcohol.

    By Blogger Jean-Claude Bradley, at 9:49 AM  

  • Why do you use H2SO4 instead of HCl?

    By Anonymous Anonymous, at 6:00 AM  

  • Anhydrous sulfuric acid is a liquid while anhydrous HCl is a gas, which is inconvenient

    By Blogger Jean-Claude Bradley, at 4:35 PM  

  • who is supposed to take the proton from sulfuric acid? i think the oxygen of the carbonyl group of acetic anhydride would, am i right?
    will you please show me the mechanism of this esterification with sulfuric acid catalyst? (in this post, i cant see the using of catalyst)
    thank you so much!

    By Anonymous Anonymous, at 9:17 PM  

  • Yes the acid would protonate the carbonyl group of the anhydride and thus activate it. I don't have a link handy for the full mechanism but you should be able to find one on Google.

    By Blogger Jean-Claude Bradley, at 10:58 AM  

  • why is acetic anhydride added in excess in the synthesis of aspirin?in?

    By Anonymous Anonymous, at 2:03 PM  

  • just to make sure the reaction goes to completion

    By Blogger Jean-Claude Bradley, at 3:41 PM  

  • In reduction of carbonyl group to alcohol, why does Lithium aluminium hydride has more reducing ability than the rest of the metal hydride?

    By Anonymous Anonymous, at 4:59 AM  

  • Lithal is a stronger reducing agent compared to borohydride derivatives probably because aluminum is more electropositive than boron

    By Blogger Jean-Claude Bradley, at 10:27 AM  

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