July 20, 2019, 12:45:51 PM
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Topic: Acetylation or Esterification to get Aspirin?  (Read 248 times)

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Offline sharbeldam

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Acetylation or Esterification to get Aspirin?
« on: June 01, 2019, 10:54:54 AM »
As I read about the synthesis of aspirin (Acetyl salicylic acid) from salicylic acid, usually they react the salicylic acid with acetic anhydride to get an Aspirin and this is called acetylation of the alcohol group in aspirin.
my question is, why they dont react the salicyclic acid with a carboxylic acid via an esterification process to get the aspirin? is it only because the acetic anhydride is more reactive? and is there a link that shows what groups can the acetic anhydride react with?

thanks alot.

Offline AWK

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Re: Acetylation or Esterification to get Aspirin?
« Reply #1 on: June 01, 2019, 11:04:50 AM »
There are many methods for obtaining esters. In the pharmaceutical industry, the most important factors determining the choice of the process are the costs and the ease of obtaining a clean product or its purification. Normal esterification (acid and alcohol) is an equilibrium reaction. The use of acetic anhydride or acetyl chloride bypasses the equilibrium process.
AWK

Offline sharbeldam

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Re: Acetylation or Esterification to get Aspirin?
« Reply #2 on: June 02, 2019, 02:10:44 AM »
thx AWK!

Offline hollytara

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Re: Acetylation or Esterification to get Aspirin?
« Reply #3 on: June 03, 2019, 02:00:40 AM »
Acetate esters in particular are often best made via acetic anhydride.  While reaction with acetyl chloride is also favorable, it requires an equivalent of base (usually pyridine or trimethylamine) to remove the HCl byproduct.  With acetic anhydride, once can use sodium acetate as the base.  This is milder, less toxic, and can be used catalytically (0.1 equivalent or so).  Other anhydrides are not commercially available and inexpensive (as acetic anhydride is), so this method is not as attractive for making butanoates and so forth. 

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