7. Write the equations involved in the following reactions:
(i) Cannizzaro reaction
(ii) Aldol condensation
(iii) Hell-Volhard-Zelinsky reaction
Solution:
(i) Cannizzaro reaction:
The Cannizzaro reaction is a chemical reaction that involves the base-induced disproportionation of two molecules of a non-enolizable-aldehyde to give primary alcohol and a carboxylic acid. The Cannizzaro reaction is a redox reaction in which two molecules of an aldehyde are reacted to produce primary alcohol and a carboxylic acid using a hydroxide base. The reaction begins with a hydroxide attack on the carbonyl carbon followed by deprotonation to give a dianion. This unstable intermediate releases a hydride anion which attacks another molecule of aldehyde. In this process, the dianion converts to a carboxylate anion and the aldehyde to an alkoxide. The alkoxide then picks up a proton from water to provide the alcohol final product, while the carboxylate is converted to the carboxylic acid product after acid work-up
(ii) Aldol condensation
The aldol condensation is a reaction between a ketone and an aldehyde and an enol or enolate, leading to the formation of a new C-C double bond, along with the release of a water molecule. The condensation happens if the aldol addition produt is heated for prolonged a prolonged period. Because of the release of a water molecule, this reaction is called a "condensation" reaction.
In this reaction, a β−hydroxyaldehyde or a β−hydroxyketone is formed, which gets dehydrated to form an enal or enone.
(iii) Hell Volhard Zelinsky reaction
(i) Cannizzaro reaction:
The Cannizzaro reaction is a chemical reaction that involves the base-induced disproportionation of two molecules of a non-enolizable-aldehyde to give primary alcohol and a carboxylic acid. The Cannizzaro reaction is a redox reaction in which two molecules of an aldehyde are reacted to produce primary alcohol and a carboxylic acid using a hydroxide base. The reaction begins with a hydroxide attack on the carbonyl carbon followed by deprotonation to give a dianion. This unstable intermediate releases a hydride anion which attacks another molecule of aldehyde. In this process, the dianion converts to a carboxylate anion and the aldehyde to an alkoxide. The alkoxide then picks up a proton from water to provide the alcohol final product, while the carboxylate is converted to the carboxylic acid product after acid work-up
(ii) Aldol condensation
The aldol condensation is a reaction between a ketone and an aldehyde and an enol or enolate, leading to the formation of a new C-C double bond, along with the release of a water molecule. The condensation happens if the aldol addition produt is heated for prolonged a prolonged period. Because of the release of a water molecule, this reaction is called a "condensation" reaction.
In this reaction, a β−hydroxyaldehyde or a β−hydroxyketone is formed, which gets dehydrated to form an enal or enone.
(iii) Hell Volhard Zelinsky reaction
That carboxylic acid which has alpha hydrogen, when heated with halogens, gives alpha halo acid. Such reactions are called H.V.Z. reaction.
