Question

How to covert ethyl cyanide to ethanoic acid ??????????????

Answer 1

First up would be to get rid of the Nitrogen, and convert it to an acid.
Treating methyl cyanide with dilute acid and water results in its hydrolysis, which yields ethanoic acid with the evolution of ammonia.
CH3-CN + 2H2O ---> CH3COOH + NH3
Now, we can treat it with Red P/Br2 to give the bromo derivative. This is called the Hell-Volhard-Zelinsky Reaction.
CH3COOH + Br2 --> CH2Br-COOH + HBr