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Saturday, October 29, 2016

Diborane Structure

Preparation:
  • 4BH3 + 3LiALH4 → 2B2H6 + 3LiF + 3AlF3
  • 2NaBH4 +I→ B2H+ 2NaI + H2
  • 2BF3 + 6NaH → B2H6 + 6NaF
Structure:
  • Diborane contains four terminal and two bridging hydrogen atoms
  • The terminal H atoms and B atoms lie in one plane. The bridging H atoms lie above and below the plane
Properties:
  • Colourless highly toxic gas
  • B.P : 180 K
  • Catches fire instantly in air
  • Burns in oxygen releasing energy 
    B₂H₆ + 3 O₂ → B₂O₃ + 3 H₂O; ΔcHΘ = -1976 kJ/ mol
  • Hydrolyze in water to give boric acid  
    B₂H₆ + 6H₂O → 2B(OH)₃ + 6 H₂
  • Borane adducts: 
    B₂H₆ + 2NMe₃ → 2BH₃.NMe₃
    B₂H₆ + 2CO → 2BH₃.CO
  • On reaction with ammonia and subsequent heating, gives borazine also known as inorganic benzene
    3B₂H₆ + 6NH₃ → 3[BH₂(NH₃)₂]+[BH₄]- → 2B₃N₃H₆ + 12H₂
                                                                      Borazine


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