Question

With regards to a Cannizzaro Reaction Lab: Post-lab Question #1: A student in your class prepared his prelab correctly. In his prelab procedure, he had written to add 2.5 mL of concentrated HCl (that is added to the aqueous layer in the last paragraph of the procedure) to the reaction mixture after it was refluxed and transferred to a separatory funnel.

a) In regards to chemical reactions, explain what the consequence of this change will be. (1.5 points)

b) During the rest of the procedure, what product(s) go into which solutions, and what will ultimately be isolated from what solutions if the rest of the steps of the procedure from this point onward are done correctly?

Answer 1

(a). In the cannizzaro reaction, HCl is added to the reaction mixture after it was refluxed and transferred to a separatory funnel. It is because, the product obtained after the reaction is not resistant to acid. If HCl is added before extraction, the alcohol present in the product mixture will get protonated and a water molecule will be elliminated from the protonated alcohol. Now the positively charged species undergo charge delocalization and we get a combination of different resonance structures. Finally, the different resonance structures will get proton from water and will give different alcohols in the reaction mixture.

(b). During the rest of the procedure, carboxylate and alcohol products will go into ether solution and a carboxylic acid is isolated from the water and brine solution.