Question

Which one of the following reagent(s) is/are used for the conversion of ketone into hydrocarbons?
A) $ LiAl{H_4} $
B) $ {N_2}{H_4}/{H_2}{O_2} $
C) $ Mg/Hg,{H_2}O $
D) $ Na/Hg,HCl $

Answer 1

Hint: The process of conversion of ketones to hydrocarbons is a reduction process. Firstly, the reduction of ketones will give alcohol, and further removal of the hydroxyl group will give us Hydrocarbons. Commonly, Clemmensen Reduction is used for this reduction.

Complete answer:
Let us see the reactions of the given reagents on ketones one by one:
1. $ LiAl{H_4} $ : Lithium Aluminium Hydride is one of the most useful reducing agents in organic chemistry. It serves as a source of Hydride i.e. $ {H^ - } $ . The negative charge is due to the Hydrogen being more electronegative than Aluminium. The reaction of $ LiAl{H_4} $ on Ketones gives Secondary Alcohols. Hence option A is incorrect.
2. $ {N_2}{H_4}/{H_2}{O_2} $ : $ {N_2}{H_4}/{H_2}{O_2} $ is a strong reducing agents and used for the reduction of Alkenes and Alkynes. The hydrogen is added in a syn fashion to reduce the multiple bonds. $ {N_2}{H_4}/KOH $ is used in the Wolff-Kirshner reduction, which reduces carbonyls to alkanes. Option B is incorrect.
3. $ Mg/Hg,{H_2}O $ : The reaction of ketones with Mg-Hg is known as Pinacol Coupling reaction. It is a free radical process. The C-C bonds are formed between carbonyl groups of ketones. Leads to the formation of diols. Option C is incorrect.
4. $ Na/Hg,HCl $ : Sodium Amalgam (Na-Hg) along with HCl is a strong reducing reagent used for reduction of ketones to alkanes (hydrocarbons). If Zn-Hg is used it is known as Clemmensen Reduction. Option D is correct. The Reaction can be given as:

The correct answer is Option D.

Note:
Other reducing agents used for converting Carbonyls to Hydrocarbons are: Wolff-Kishner Reduction ( $ {N_2}{H_4}/KOH $ ), Clemmensen Reduction (Zn-Hg/ conc. HCl). Sodium Amalgams are also used in place of Zinc Amalgams.