Triethylborane

Chemical Properties

Clear colourless to light amber solution. Miscible with most organic solvents; immiscible with water.

Uses

Reagent in organic syntheses blocking agent and radical initiator.

Uses

Triethylborane reacted with 8-hydroxyquinoline to synthesize three 8--hydroxyquinolato (q) boron compounds B(C2H5)2q (1), BPh2q (2), and B(2-naph)2q (3).

Uses

It is used in mixtures with triethylaluminumas hypergolic igniters in rocket propulsionsystems.

Preparation

Triethylborane is prepared by reacting triethylaluminium with boron halides or by reacting diborane with ethylene: 
(C₂H₅)₃Al + BCl₃ → (C₂H₅)₃B + AlCl₃
B₂H₆ + CH₂=CH₂ → (C₂H₅)₃B

Synthesis Reference(s)

The Journal of Organic Chemistry, 51, p. 427, 1986 DOI: 10.1021/jo00354a002

Hazard

Flammable, dangerous fire risk, ignites spontaneously in air. Reacts violently with water and oxidizing materials. Toxic by inhalation, strong irritant.

Health Hazard

Triethylboron is a toxic substance. The toxicsymptoms from chronic exposure to thiscompound are not reported. Skin contact canburn tissues.

Fire Hazard

Triethylborane is a pyrophoric substance, igniting spontaneously on exposure to air, chlorine, or bromine. Explosion may result when mixed with oxygen. Contact with ozone, peroxides and other oxidants can cause explosion. Its concentrated solutions can be pyrophoric. Flash point of 1 M solution in hexane is －23°C ( －9°F), while that in tetrahydrofuran is －17°C (1°F) (Aldrich 1996). It decomposes explosively when mixed with water.

Flammability and Explosibility

Pyrophoric

reaction suitability

reagent type: reductant

Safety Profile

Poison by ingestion and intraperitoneal routes. Mildly toxic by inhalation. Animal experiments show that the vapor is a poison which causes pulmonary irritation and convulsions. A very dangerous fire hazard by spontaneous chemical reaction with oxichzers. Spontaneously flammable in air. Explodes in oxygen atmospheres. Hypergolic reaction with triethylaluminum. Ignites on contact with chlorine, bromine, or other halogens. Will react with water or steam to produce toxic and flammable vapors. To fight fire, do NOT use halogenated extinguishing agents. When heated to decomposition or upon contact with air it emits toxic acrid smoke and irritating fumes. See also BORANES and BORON COMPOUNDS.

Purification Methods

It distils at 56-57o/220mm. It can also be purified via its ammonia addition complex which is distilled in a high vacuum, decomposed with dry HCl, and the Et3B is distilled out. It is commercially available as a 15% solution in hexane or as 1M solution in hexane. [Brown J Am Chem Soc 67 376 1945, Bamford et al. J Chem Soc 471 1946, Lin et al. J Organomet Chem 312 277 1986, Beilstein 4 III 1957, 4 IV 4359.]