Question

Convert ethyl bromide to ethane.

Answer 1

Hint: For the preparation of ethane from ethyl bromide, you will have to convert ethyl bromide into ethane by (i) using reducing agent like lithium aluminum hydride $LiAl{H_4}$ in ether (ii) by using Grignard Reagent- A Grignard reagent is an organomagnesium compound which can be described by the chemical formula ‘$R - Mg - X$’ where $R$ refers to an alkyl or aryl group and $X$ refers to a halogen.

Complete answer:
(i) Ethyl bromide is a primary alkyl halide in which the halide group is bromine and the alkyl group is ethane. We have studied that primary alkyl halides can be reduced to alkanes by Lithium aluminum hydride $LiAl{H_4}$ in dry ether.
$C{H_3}C{H_2}Br\xrightarrow[{Dry{\text{ ether}}}]{{LiAl{H_4}}}C{H_3}C{H_3}$
OR
(ii) Alkyl Halides react with magnesium in dry ether to form Alkyl Magnesium halides, commonly known as Grignard reagent. Grignard reagents form alkanes when treated with cold water or dilute acid.
$C{H_3}C{H_2}Br + Mg\xrightarrow{{{\text{Dry ether}}}}C{H_3}C{H_2}MgBr$
$C{H_3}C{H_2}MgBr + {H_2}O \to C{H_3}C{H_3} + Mg(OH)Br$

Note:
The hydride ion in $LiAlH_4$ is very basic. For this reason, $LiAlH_4$ reacts violently with water and therefore must be used in dry solvents such as anhydrous ether and THF. Like many other strong bases, the hydride ion in $LiAlH_4$ is a good nucleophile, and LiAlH4 contains its own “built-in” Lewis acid, the lithium ion.
The order of reactivity of the halogens in haloalkanes is I > Br > CI > > F. Organofluorides are so unreactive that they are never used to prepare Grignard reagents. Organohalogen compounds containing bromine and chlorine are readily available, and are commonly used to prepare Grignard reagents. Grignard reagents are used synthetically to form new carbon–carbon bonds.