Chemistry > p Block Elements > 3.0 Compounds of boron
p Block Elements
1.0 Group $13$ – The Boron Family
2.0 Boron
3.0 Compounds of boron
4.0 Compounds of Aluminium
5.0 Group $14$ – The Carbon family
6.0 Allotropes of Carbon
7.0 Compounds of Carbon
8.0 Properties of Silicon
9.0 Group $15$-The Nitrogen Family
10.0 Oxides of nitrogen
10.1 Nitrogen Oxide $N_2O$ or Laughing gas (Neutral)
10.2 Nitric Oxide $NO$ (Neutral)
10.3 Nitrogen trioxide $N_2O_3$
10.4 Nitrogen dioxide or Di-nitrogen tetroxide $NO_2$ or $N_2O$
10.5 Nitrogen pentaoxide $N_2O_5$
11.0 Oxyacids of Nitrogen
11.1 Nitric acid $HNO_3$
11.2 Oxidation of Metalloid and Inorganic compounds by Nitric acid
11.3 Action of Metals & Proteins
12.0 Phosphorus
13.0 Oxygen
14.0 Sulphur
3.3 Diborane ($B_2H_6$)
10.2 Nitric Oxide $NO$ (Neutral)
10.3 Nitrogen trioxide $N_2O_3$
10.4 Nitrogen dioxide or Di-nitrogen tetroxide $NO_2$ or $N_2O$
10.5 Nitrogen pentaoxide $N_2O_5$
11.2 Oxidation of Metalloid and Inorganic compounds by Nitric acid
11.3 Action of Metals & Proteins
The simplest boron hydride known is diborane in which boron atom is $sp^3$ hybridised.
It is a colourless and high toxic gas with a boiling point of $180\ K$.
It contains two different set of $B-H$ bonds. Two bridged $H$ atoms are in a plane perpendicular to the rest of the molecule. Terminal $B-H$ bonds are shorter than bridged $B-H$ bonds.
Its structure is unique and involves two electrons three centre bond. Here the bridged $H$ is connected with two boron atoms through two electrons three center bond. (DIAGRAM)
Preparation:
1. By treating boron trifluoride with $LiAlH_4$ in diethyl ether. $$4B{F_3} + 3LiAl{H_4} \to 2{B_2}{H_6} + 3LiF + 3Al{F_3}$$
2. By the oxidation of sodium borohydride with iodine. $$2NaB{H_4} + {I_2} \to {B_2}{H_6} + 2NaI + {H_2}$$
3. Diborane is produced on an industrial scale by the reaction of $BF_3$ with sodium hydride. $$2B{F_3} + 6NaH\mathop \to \limits^{450K} {B_2}{H_6} + 6NaF$$
Properties:
1. Stable at low temperature only.
2. ${B_2}{H_6} + 6{H_2}O \to 2{H_3}B{O_3} + 6{H_2}$
3. ${B_2}{H_6} + 6C{l_2}\mathop \to \limits^{25^\circ C} 2BC{l_3} + 6HCl$
4. ${B_2}{H_6} + 3{O_2} \to {B_2}{O_3} + 3{H_2}O$
5. Diborane undergoes cleavage reactions with lewis bases $(L)$ to give borane adducts, $BH_3.L$ $${B_2}{H_6} + 2NM{e_3} \to 2B{H_3}.NM{e_3}$$
6. Reaction of ammonia with diborane gives initially $B_2H_6.2NH_3$ which is formulated as ${\left[ {B{H_2}{{\left( {N{H_3}} \right)}_2}} \right]^ + }{\left[ {B{H_4}} \right]^ - }$, further heating gives borazine, $B_3N_3H_6$ known as “inorganic benzene” in view of its ring structure with alternate $BH$ and $NH$ groups.
$${B_2}{H_6} + N{H_3}\mathop \to \limits^{excessN{H_3}} {B_2}{H_6}.2N{H_3}$$
$${B_2}{H_6} + N{H_3}\mathop \to \limits_{{\text{high temp}}{\text{.}}}^{{\text{excess }}N{H_3}} {(BN)_x}\left\{ {{\text{Boron nitride }}\left( {{\text{graphite like structure}}} \right)} \right\}$$
$${B_2}{H_6} + N{H_3}\mathop \to \limits_{{\text{high temp}}{\text{.}}}^{{\text{ratio }}2N{H_3}:1{B_2}{H_6}} {B_3}{N_3}{H_6}\left\{ {{\text{Borazine }}\left( {{\text{Inorganic Benzene}}} \right)} \right\}$$
