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DIBORANE

DIBORANE. It is prepared by treating boron Trifluoride with LiAlH4 in diethyl ether 4BF 3 + 3LiAlH 4 2B 2 H 6 +3LiF + 3ALF 3 In a laboratory the diborane is prepared by the oxidation of sodium borobhydride with iodine

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DIBORANE

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  1. DIBORANE

  2. It is prepared by treating boron Trifluoride with LiAlH4 in diethyl ether 4BF3 + 3LiAlH4 2B2H6 +3LiF + 3ALF3 • In a laboratory the diborane is prepared by the oxidation of sodium borobhydride with iodine 2NaBH4 + I2 B2H6 +2NaI +H2 • In industry it is prepared by the reaction of BF3 with sodium hydride 2 BF3 + 6 NaH 450 K B2H6 + 6 NaF Methods Of Preparetion

  3. 1) Diborane is a colorless, highly toxic gas. It has boiling point ok 180 K 2) Diborane catches fire spontaneously when it is exposed to atmospheric air it burns with oxygen. The reaction is exothermic releasing a lager amount of energy B2H6 + 3O2 B2O3 + 3H2O ΔH= - 1976 K J mol-1 3) it is readily hydrolyzed by water to form boric acid B2H6 + 6H2O 2B(OH)3 + 6H2 Properties

  4. With Lewis bases, diborane first undergoes cleavage (breaking) to form borane (BH3) which then reacts to form adducts B2H6 + 2NMe 2BH3 . NMe B2H6 + 2CO 2BH3 . CO 5) with ammonia an addition product B2H6.NH3 which then decomposes on heating at 473K to give a volatile compound called borazole (Borazine) B2H6 + NH3 B2H6.NH3 3 B2H6 + 6NH3 473K 2B3N3H6 + 12H2 ( borazole) B2H6 + 6NH3 (BN) n Boron nitride

  5. Structure H H H B B H H H B in GS ES H 2s 2p 1S Sp3 B undergoes sp3 hybridization and 3 hybridized orbitals have one electron each and one orbital is vacant. Each Boron form two sigma bonds by overlapping with s orbital of H and a normal 2e2c covalent bond is formed. These are coplanar. Two more bonds are formed by overlapping of one boron sp3 orbital with one electron, one hydrogen s orbital with one electron and another boron sp3 with no electron. Thus a 2e3c bond is formed , also called banana or tau bond.

  6. Structure of Higher Boranes Types of Bonds in Boranes • 1. Normal covalent bonds -2c-2e- B-H • 2. Normal covalent bonds - 2c-2e- B-B • 3. Bridge bonds -3c-2e- B-H-B • 4. Bridge bonds - 3c-2e- B-B-B • 5. Closed bridge bonds - 3c-2e- • B • B B

  7. Structure of Higher Boranes 1. Tetraborane – B 4H10 • Bonds – • Four bridging (3c-2e) B-H-B bonds viz, B1 –H-B3 , B2-H –B3, B1-H-B4 and B2- H-B4 • One direct (2c-2e) B-B bond (B1-B2 bond) • Six terminal (2c-2e) B-H bonds namely B3-H, B3-H, B2-H, B2-H, B4-H and B4-H bonds.

  8. 2.Pentaborane – B5H9 Bonds – 1. Five terminal B-H bonds (viz., B1-H, B4-H, B2-H, B3-H and B5-H bonds) 2.Four bridging B-H-B bonds (namely B1-H-B2, B2-H-B3, B3-H-B4, and B4-H-B1 bonds), 3. Two B-B bonds (B1-B5 and B5-B4 bonds) 4.One closed (3c-2e) B5-B3-B2 bonds.

  9. 3. Decaborane – B10H14 Bonds – 1.Four bridging (3c-2e) B-H-B bonds namely B5-H-B6, B6-H-B7, B8-H-B9 and B9-H-B10. 2. Each of B-atoms is linked with one H-atom by terminal B-H bonds. Thus the molecule has ten terminal B-H bonds viz., B1-H, B2-H, B3-H, B4-H, B5-H, B6-H, B7-H, B8-H, B9-H and B10-H bonds. 3.Four B-B bonds (B2-B5, B2-B7, B4-B8, B4-B10) 4.Four closed (3c-2e) B-B-B bonds (B1-B2-B3, B1-B3-B4, B1-B5-B10 and B3-B7-B8 bonds) +

  10. BORAZINE – BORAZOLE – INORGANIC BENZENE (HBNH)3

  11. PREPARATION

  12. PROPERTIES

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