Triisobutylaluminium (TiBA) is an
organoaluminium compound with the formula Al(CH
2CH(CH
3)
2)
3. This colorless
pyrophoric
A substance is pyrophoric (from grc-gre, πυροφόρος, , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolith ...
liquid is mainly used to make linear primary
alcohol
Alcohol most commonly refers to:
* Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom
* Alcohol (drug), an intoxicant found in alcoholic drinks
Alcohol may also refer to:
Chemicals
* Ethanol, one of sev ...
s and
α-olefin
In organic chemistry, alpha-olefins (or α-olefins) are a family of organic compounds which are alkenes (also known as olefins) with a chemical formula , distinguished by having a double bond at the primary or alpha (α) position.''Petrochemical ...
s.
[Michael J. Krause, Frank Orlandi, Alfred T. Saurage, Joseph R. Zietz Jr. "Aluminum Compounds, Organic" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. ]
Structure
Triisobutylaluminium exists in equilibrium with its
dimer
Dimer may refer to:
* Dimer (chemistry), a chemical structure formed from two similar sub-units
** Protein dimer, a protein quaternary structure
** d-dimer
* Dimer model, an item in statistical mechanics, based on ''domino tiling''
* Julius Dimer ( ...
. The equilibrium constant, K
D, is 3.810 at 20 °C.
: 2Al(CH
2CH(CH
3)
2)
3 2CH(CH3)2)3">l(CH2CH(CH3)2)3sub>2
In the dimer, the bridging carbon-aluminium bond is elongated and exhibits evidence of restricted rotation. For the sake of simplicity, TiBA is written as the monomer in this article.
Synthesis
Trialkylaluminium compounds are available industrially through the reactions of aluminium powder, hydrogen gas, and the desired alkenes. The synthesis of TiBA requires two steps; the first step produces
diisobutylaluminium hydride (written as a monomer):
:6CH
2=C(CH
3)
2 + 2Al + 3H
2 → 6HAl(CH
2CH(CH
3)
2)
2
In the second step
isobutylene
Isobutylene (or 2-methylpropene) is a hydrocarbon with the chemical formula . It is a four-carbon branched alkene (olefin), one of the four isomers of butylene. It is a colorless flammable gas, and is of considerable industrial value.
Producti ...
adds to the diisobutylaluminium to give TiBA:
:CH
2=C(CH
3)
2 + HAl(CH
2CH(CH
3)
2)
2 → Al(CH
2CH(CH
3)
2)
3
Reactions
α-olefins are readily eliminated from β-branched trialkylaluminium compounds. Trialkylaluminium compounds are used in the industrial production of polymers. In the most common of these compounds, TIBA, a substantial level of Al – H bonds are present at equilibrium. The greater stability of unbranched trialkylaluminium compounds relative to branched trialkylaluminium compounds in TIBA forms the basis for a general synthesis of triethyl- and higher linear trialkylaluminium materials from triisobutylaluminium.
:Al(CH
2CH(CH
3)
2)
3 + 3RCH=CH
2 → Al(CH
2CH
2R)
3 + 3CH
2=C(CH
3)
2
Safety
Like most organoaluminium compounds, TiBA reacts violently with water and air.
[
]
References
Further reading
*Keisuke Suzuki, Tetsuya Nagasaws, Encyclopedia of Reagents for Organic Synthesis, Triisobutylaluminum, 2009
{{Aluminium compounds
Organoaluminium compounds