(a) Describe the following giving linked chemical equations: 

 (i) Cannizzaro reaction 

 (ii) Decarboxylation 

(b) Complete the following chemical equations: 

 

(i) Cannizaro reaction 

In this reaction, the aldehydes which do not have a -hydrogen atom, undergo self-oxidation and reduction (disproportionation) reaction on treatment with a concentrated alkali. 
Example: 

(ii) Decarboxylation 

The decarboxylation reaction can be carried out either by using soda lime or by electrolysis 

Using soda lime: Sodium salts of carboxylic acids when heated with soda lime (NaOH + CaO) in the ratio 3:1)  undergo decarboxylation reaction to yield alkanes. 

Electrolytic decarboxylation: Electrolysis of aqueous solutions of sodium or potassium salts of carboxylic acids give alkanes having twice the number of carbon atoms present in the alkyl group of acid. 

 This is known as Kolbe’s decarboxylation. 

 2RCOONa--> 2RCOO^- + 2Na⁺

 H₂O-->2OH^- + 2H⁺

 
At Anode:-

2RCOO^- - 2e^---> CO₂ + R - R

At Cathode:-

 2H⁺ + 2e^----> H₂

b)