Acetylsalicylic acid is therefore, along with acetic acid, one of the products of the esterification of salicylic acid with acetic anhydride. Once an aspirin tablet is ingested and enters the small intestine, the acetylsalicylic acid undergoes a hydrolysis reaction, where acetylsalicylic acid reacts with water to break the ester bond and produce salicylic acid and acetic acid, as shown in Figure 1 .