Question

aspirin synthesis: A) Describe why it is necessary to cool down the reaction mixture slowly after heating for 5 minutes? What is this process and why is it happening?

B.) what would happen if the cooling occurred too quickly?

Answer 1

1.The synthesis of Acetylsalicylic acid(ASA) from salicylic acid is esterification.The first step is create suspension of acetic anhydride and salicylic acid.H₃PO₄ donates H⁺ to bind the reaction complex.As the reaction proceeds,salicylic acid disappeares.once all salicylic acid is disappeared the reaction is complete.Product acetylsalicylic acid remain dissolved in hot solution.Now at this point we are cooling the solution by adding distilled water.At the starting of reaction we have taken excess acetic anhydride .This excess acetic anhydride must be hydrolyzed to acetic acid.Now this acetic anhydride is very reactive towards water that is why hydrolysis must be done very slowly.that is why water added vey slowly,dropwise.once the hydrolysis is complete more water is added.Then the flask is kept in an ice bath to lower the solubility of acetylsalicylic acid. Then we get the precipitate of ASA.so the process is hydrolysis and in order to do this hydrolysis the mixture is cooling very slowly(water is added slowly).

2.Acetic anhydide is highly reactive to water and the hydrolysis of acetic anhydride is exothermic reaction.If we add more water it is dangerous i.e lab accident can occur