Question

(a) What is inorganic benzene ? Why is it so called? How will you get it from diborane?

(b) Identify A, B, C and D in the following sequence of reactions. 

Metal (A) + N₂ → (B) + C (white ppt.) + D (g) White ppt. (C) dissolves in NaOH solution while gas (D) gives white fumes with HCl.

Answer 1

(a) Borazine or borazole is known as inorganic benzene because its structure is similar to that of benzene. It is also iso-electronic or isostructural with y benzene. Like carbon in benzene, both N and B, in d borazine are sp² hybridized. Each N has a p-orbital which is perpendicular to the sigma bonding orbital and contain a lone pair of electron. In contrast, each B has an empty p-orbital which is also perpendicular to plane of the ring. Thus, the pi-bonding in borazine is dative and it arises from the sidewise overlapping of fully filled orbitals of N and empty orbitals of B.

(b) (i) since gas (D) gives white fumes with HCl it must be ammonia (NH₃). 

(ii) Since metal (A) on heating reacts with nitrogen to form compound B, which on hydrolysis with water gives white ppt.(C) which dissolves in NaOH along with evolution of NH₃ (D) p therefore, metal (A) must be Al, (B) must be it aluminium nitride (AIN) and (C) must be p aluminium hydroxide Al(OH)₃.

2Al + N₂ → 2AIN 

AIN + 3H₂O → Al(OH)₃ + NH₃ 

AK(OH)₃ + NaOH  → NaAlO₂ + 2H₂O 

NH₃ + HCl →  NH₄Cl