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.

Let’s look at some chemical structures:
One problem occurs with aspirin is that it has a destructive effect on the blood vessel walls and inhibit the synthesis of prostacyclin. To resolve this problem, we can use potential anti-platelet agents including the O-acyl esters which are synthesized from salicylic acid and diflunisal. Those agents work by acylation of cyclooxygenase and have a higher extraction than aspirin. That makes them yield a greater selectivity in their effect on platelet inhibition relative to prostacyclin inhibition on vessel walls.

The actual reaction is shown on the top.