Question

\[B{F_3}\] reacts with NaH at 450 K to form NaF and X. When X reacts with LiH in diethyl ether. Y is formed. What is Y?
A. \[LiB{O_2}\]
B. \[L{i_2}{B_4}{O_7}\]
C. \[LiB{H_4}\]
D. \[{B_2}{H_6}.LiH\]

Answer 1

Hint: The compounds containing boron atoms and hydrogen atoms connected to each other are called boranes. Compound X shows unstability at room temperature and is sweet in odour.

Complete Step by Step Solution:
When boron trifluoride reacts with sodium hydride at 450k diborane, sodium fluoride is formed. Here X is diborane.
The reaction between boron trifluoride and sodium hydride is shown below.:
\[2B{F_3} + 6NaH \overset{450K}{\rightarrow}{B_2}{H_6}(X) + 6NaF\]

In the above reaction, two mole of boron trifluoride reacts with six mole of sodium hydride at a temperature of 450K to form one mole of diborane and 6 mole of sodium fluoride.
When diborane reacts with lithium hydride in presence of diethyl ether, lithium boron hydride is formed. Here, diethyl ether act as a solvent. So, compound Y is lithium boron hydride.
\[{B_2}{H_6} + 2LiH \overset{diethyl ether}{\rightarrow}2LiB{H_4}(Y)\]

In the above reaction, one mole of diborane reacts with two moles of lithium hydride to give two moles of lithium boron hydride.
Therefore, the correct option is C.

Additional information: Lithium boron hydride is used as a strong reducing agent. It is used in the reduction of ester compounds to alcohol. Lithium boron hydride also reduces primary amides to amines. It is also used to synthesise another borohydride.

Note: Lithium boron hydride is also known as lithium borohydride. Sodium hydride is an alkaline metal hydride used as a base in organic synthesis.