P-Block Elements: Diborane

P-Block Elements

• P-block elements have their last electron in P-orbitals.

Boron Family (Group IIIA)

Diborane (B2H6)

• Diborane, a significant boron hydride, exhibits unique properties and reactions.
• Preparation Methods:
  • Reacting boron halides with reducing agents such as sodium borohydride (NaBH4) or Lithium Aluminium Hydride (LAH).
  • Reducing B2O3 with H2 at high temperature and pressure using Al+AlCl3 as a catalyst.
• Properties:
  • Stable in absence of moisture; flammable and decomposes when in contact with water.
  • Burns in oxygen to produce boron oxide, releasing heat.
  • Reacts with ammonia at high temperatures to form borazole and at low temperatures to create an additive product.
• Structure & Bonding:
  • Contains 8 atoms and 7 bonds, requiring 14 electrons, but has only 12.
  • Electron-deficient due to the absence of 2 electrons.
  • Each boron atom undergoes sp3 hybridization, forming sigma (σ) bonds with hydrogen and three-centered two-electron bonds.

Borazole (B3N3H6)

• Known as inorganic benzene due to its structural similarity to benzene.
• Preparation:
  • Formed by the reaction of diborane with ammonia at elevated temperatures.
• Properties:
  • Exists as a colorless liquid, more reactive than benzene.
  • Hydrolysis yields boric acid; reacts with HCl to form B3N3H9Cl3.
• Structure:
  • Planar configuration with SP2 hybridized B and N atoms; π-bonding involves dative overlap between boron and nitrogen.

Boron Trihalides

• Contains BF3, BCl3, BBr3, and BI3; acidity increases with electronegativity of halogen.
• Ranking of acidity: BF3 < BCl3 < BBr3 < BI3 due to the presence of partial double bond character in BF3 enhancing resonance.

Boron Nitride (BN)

• Synthesized by heating nitrogen with boron or via reaction of boric oxide with carbon.
• Exhibits a structure akin to graphite, comprising alternating boron and nitrogen atoms in hexagonal layers.

Carbon Family (Group IV)

Carbides

• Formed when carbon reacts with other elements and categorized into ionic, covalent, and interstitial types.
• Ionic Carbides:
  • Yield hydrocarbons upon hydrolysis; subdivided into methanides, acetalides, and allylides based on products formed.
• Covalent Carbides:
  • Includes substances like B4C3 and SiC (carborundum).
• Interstitial Carbides:
  • Formed when carbide ions occupy interstitial sites in metal lattices.

Silicones

• Organosilicon polymers characterized by Si-O-Si bonds.
• Preparation Methods:
  • Direct Si process and aromatic silylation involving reactions with alkyl halides or benzene.
• Types:
  • Linear Silicones: Derived from hydrolysis of dimethyl dichloro silane.
  • Cyclic Silicones: Formed from linear silicones through the elimination of water.
  • Cross-linked Silicones: Result from polymerization of hydrolyzed alkyl trichlorosilane.
• Properties:
  • Heat stability up to 2000°C, non-toxic, and water-repellent.

Hydroxylamine (NH2OH)

• Synthesized via the hydrolysis of sodium nitrite in acidic conditions.
• Properties:
  • Colorless, poisonous, soluble in various solvents, and decomposes at 200°C to yield ammonia and nitrogen.
• Reactivity:
  • Reduces halogens and reacts with carbonyl compounds to form oximes.
• Applications:
  • Used in analytical chemistry to identify carbonyl compounds, producing nylon-6, estimating metal ions, and synthesizing dimethyl glyoxime.