From Sciencemadness Wiki
Jump to: navigation, search
IUPAC name
Other names
Boron hydride
Diboron hexahydride
Molar mass 27.67 g/mol
Appearance Colorless gas
Odor Repulsive and sweet
Density 1.131 g/L
Melting point −92.49 °C (−134.48 °F; 180.66 K)
Boiling point −164.85 °C (−264.73 °F; 108.30 K)
Solubility Reacts with alcohols
Slightly soluble in diethyl ether, diglyme
Vapor pressure 39.5 atm (16.6 °C)
232.1 J·mol-1·K-1
36.4 kJ/mol
Lethal dose or concentration (LD, LC):
40 ppm (rat, 4 h)
29 ppm (mouse, 4 h)
40–80 ppm (rat, 4 h)
159–181 ppm (rat, 15 min)
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Diborane is the inorganic chemical compound consisting of boron and hydrogen with the formula B2H6. It is a toxic, colorless and pyrophoric gas with a repulsively sweet odor, with a variety of uses in chemistry and industry.



Diborane reacts exothermically with oxygen to form boron trioxide and water:

2 B2H6 + 6 O2 → 2 B2O3 + 6 H2O

Diborane reacts violently with water to form hydrogen and boric acid:

B2H6 + 6 H2O → 2 B(OH)3 + 6 H2

It reacts similarly with alcohols, but yields borate esters instead of free acid. Reaction with methanol for example, gives hydrogen and trimethylborate:

B2H6 + 6 MeOH → 2 B(OMe)3 + 6 H2

Pyrolysis of diborane gives hydrogen and diverse boron hydride clusters. This method can be used to produce a variety of heavier boranes, like decaborane.

Treating diborane with sodium amalgam gives NaBH4 and Na[B3H8].

When diborane is treated with lithium hydride in diethyl ether, lithium borohydride is formed:

B2H6 + 2 LiH → 2 LiBH4

Diborane reacts with anhydrous hydrogen chloride or hydrogen bromide gas to give a boron halohydride:

B2H6 + HX → B2H5X + H2 (X = Cl, Br)

Treating diborane with carbon monoxide at 470 K and 20 bar gives borane carbonyl (H3BCO).

Diborane readily reduces carboxylic acids to the corresponding alcohols, whereas ketones react only sluggishly.


Diborane is a colorless gas with a terrible odor, which can be pyrophoric in air and will react with water and alcohols.


Diborane is not sold by lab suppliers, and usually has to be made in situ. Industrial companies may sell the compound in gas tanks, to other companies.


A very accessible route relies on the direct reaction of borohydride salts with a non-oxidizing acid, such as phosphoric acid or dilute sulfuric acid.

2 BH4 + 2 H+ → 2 H2 + B2H6

Similarly, oxidation of borohydride salts has been demonstrated and remains convenient for small-scale preparations. For example, using iodine as an oxidizer:

2 NaBH4 + I2 → 2 NaI + B2H6 + H2

The industrial synthesis of diborane involves the reduction of boron trifluoride with strong reducing agents, such as sodium hydride, lithium hydride or lithium aluminium hydride:

8 BF3 + 6 LiH → B2H6 + 6 LiBF4

Two laboratory methods start from boron trichloride with lithium aluminium hydride or from boron trifluoride ether solution with sodium borohydride. Both methods result in as much as 30% yield:

4 BCl3 + 3 LiAlH4 → 2 B2H6 + 3 LiAlCl4
4 BF3 + 3 NaBH4 → 2 B2H6 + 3 NaBF4


  • Demonstration of pyrophoricity
  • Make green fire
  • Reagents for hydroboration
  • Make borane–tetrahydrofuran adduct
  • Synthesis of decaborane



Diborane is toxic, pyrophoric and reacts with water.


Should not be stored for long. Can be kept dissolved in an inert solvent, under argon gas.


Should be burned outside.


Relevant Sciencemadness threads