Excerpt from Different Sources for Synthesis of Aspirin

The Esterification Process
Aspirin can be made by using a process called esterification. Esterification occurs when a carboxylic acid and an alcohol combine in a reaction to produce an ester. This reaction can be used to synthesize aspirin from salicylic acid. In the lab, the carboxylic acid alcohol mixture is heated in the presence of H2SO4, sulfuric acid, which acts as a catalyst. During the reaction process, a molecule of water splits off and the remaining carboxylic acid and alcohol fragments become attached producing an ester.
General Reaction of Esterification

Esterification of Aspirin Usng Acetic Acid

What We Are Doing In The Lab
You start by weighing out a sample of salicylic acid into an Erlenmeyer flask. To the sample you will add acetic anhydride. We are using acetic anhydride instead of acetic acid because acetic anhydride has a faster reaction time. The catalyst concentrated H2SO4 is added to speed up the reaction. The flask containing this solution is then heated in a boiling water bath for about 15 minutes. This process is called esterifcation.
Esterification of Aspirin In Our Lab Using Acetic Anhydride
The flask is then removed and allowed to cool. Ice cold distilled water is slowly added to the flask to decompose any unreacted acetic annhydride.

Decomposition of Unreacted Acetic Anhydride
Ice cold distilled water is added to the flask again. The flask is then chilled in an ice-water bath for about 10 minutes until crystallization of the aspirin is complete. The aspirin crystals are collected on a Buchner funnel and washed with additional ice cold distilled water. You are using ice cold distilled water instead of room temperature distilled water because aspirin is insoluble in cold water and you would not be dissolving any of your aspirin product. The acetic acid and H2SO4 are water soluble, in any temperature water, and can be removed by washing the aspirin with the chilled water. Salicylic acid is only slightly soluble in water and...