Question

uestions for Discussion 1. Discuss the use of excess acetic anhydride and the function of phosphoric acid. 2. What reaction is involved in the decomposition of excess acetic anhydride with water? 3. Explain the separation of the aspirin product from phosphoric acid and the decomposition product of excess acetic anhydride. mass of empty= 2.977 0.913 x 100 =49.1 boat he canada 3.89

the lab of synthesis of acetylsalicylic acid

Answer 1

1. Reaction of salicylic acid with excess acetic anhydride in presence of strong acid as a catalyst results in the formation of acetylsalicylic acid i.e. Aspirin. Here, acetic anhydride acts as acetylating agent while strong acid catalyses the reaction.

2. Acetic anhydride decomposes on reaction with water and forms acetic acid. As the name suggests acetic anhydride, it is formed by dehdration of two acetic acid molecule so on reaction with water it again converts into acetic acid which is completely soluble in water.

(CH₃CO)₂O + H₂O → 2 CH₃COOH

3. On completion of the reaction excess cold water is added to the reaction mixture so the product i.e. aspirin precipitates out as white product and remaining acetic anhydride decomposes to acetic acid which is miscible in water as well as phosphoric acid which was used as catalyst also solublises in the water.