Question

How is nitromethane prepared from
(i) $\alpha -$chloro sodium acetate
(ii) $\alpha -$nitro isobutylene?

Answer 1

Nitroalkanes can be obtained by treating alkyl halides with silver nitrate in alcoholic solution. Hydrolysis of $\alpha -$nitro alkene can produce nitromethane.

Complete step by step solution:
When $\alpha-$ chloro sodium acetate is treated with silver nitrate, the chlorine gets replaced by the nitro group and $\alpha -$nitro sodium acetate is formed, which undergoes hydrolysis to give nitro methane and sodium bicarbonate as a by-product.
This reaction is a nucleophilic substitution reaction. Since silver nitrite is predominantly covalent, only nitrogen pairs are available for bond formation. Hence, on adding $AgN{O_2}$, the attack of $NO_2^-$ takes place mainly through nitrogen and a nitroalkane is obtained as the major product.

$\alpha -$nitro isobutylene undergoes hydrolysis in an acidic medium to give nitromethane and acetone.

Note: When $\alpha -$ chloro sodium acetate is treated with silver nitrate, some alkyl nitrate is also formed ($20-30\%$) in the reaction along with nitroalkane. This is because$NO_2^-$ ion is an ambident nucleophile and can attack the alkyl halide through nitrogen as well as through oxygen. If $\alpha -$ chloro sodium acetate is treated with $NaN{O_2}$ or $KN{O_2}$ in place of $AgN{O_2}$, the main product will be alkyl nitrite. Nitroalkenes do not undergo hydrolysis in the basic medium to form nitromethane.