Question

In Wurtz reaction alkyl halide reacts with:
(A) Sodium in ether
(B) Sodium in dry ether
(C) Sodium only
(D) Alkyl halide in ether

Answer 1

Hint: When two alkyl halides combine together to form a larger alkane group, it is a Wurtz reaction. The reagent used here contains an element that is also found in the table salt. But incase of tertiary alkyl halide, it will give alkenes due to steric hindrance.

Complete Solution :
-Wurtz is a famous name reaction in organic chemistry.
-When two alkyl halides combine together in the presence of sodium in dry ether, it forms a bigger alkane, it is called as Wurtz reaction.
Let us now understand the mechanism of this reaction with the help of an example.
-The reaction has an alkyl halide, from which there is a halogen-metal exchange. This involves the radical species that results in a nucleophilic substitution reaction.
\[R - X + M \to {R^ \bullet } + {M^ + }{X^ - }\]
-One electron from the metal is transferred to the halogen to produce a metal halide and an alkyl radical.
-After accepting the electron, it forms an alkyl ion. This intermediate is explained in the next step.
\[{R^ \bullet } + M \to {R^ - }{M^ + }\]
-The nucleophilic carbon of the alkyl anion then displaces the halide in a SN2 reaction forming a new carbon-carbon covalent bond.
\[{R^ - }{M^ + } + R - X \to R - R + {M^ + }{X^ - }\]
Thus, it creates the R-R alkane group. This is the complete mechanism of Wurtz reaction.
Now, the reason why we use sodium in dry ether as the reagent.
-Na metal is highly reactive, so we need a solvent that will not start a reaction with sodium.
-If dry ether is not used then, the sodium will react with the water to form hydroxides, thus disturbing the target reaction.
-Thus, ether also acts as a catalyst to fasten the production of intermediates.
So, the correct answer is “Option B”.

Note: The alkyl halides should not be bulky in nature, especially at the halogen end, there is a greater amount of alkene formed. Methane cannot be synthesized via the Wurtz reaction since the product of an organic coupling reaction must have at least two carbon atoms. This becomes the limitation of Wurtz Reaction.