The synthesis of aspirin acetylsalicylic acid from salicylic acid and acetic anhydride follows a simple stoichiometric reaction:C7H6O3 salicylic acid + C4H6O3 acetic anhydride C9H8O4 aspirin + C2H4O2 acetic acid From the balanced equation, we can see that the optimal molar ratio of salicylic acid to acetic anhydride is 1:1. This means that one mole of salicylic acid reacts with one mole of acetic anhydride to produce one mole of aspirin and one mole of acetic acid.In practice, a slight excess of acetic anhydride is often used to ensure the complete conversion of salicylic acid to aspirin. However, the optimal theoretical ratio for the highest yield remains 1:1.