Triisobutylaluminium

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Triisobutylaluminium
Triisobutylaluminum.svg
Monomeric form
Identifiers
CAS number 100-99-2 YesY
Jmol-3D images Image 1
Properties[1]
Molecular formula C12H27Al
Molar mass 198.32 g mol−1
Appearance Colorless liquid
Density 0.786 g/mL at 25 °C
Melting point 4 to 6 °C (39 to 43 °F; 277 to 279 K)
Boiling point 86 °C (187 °F; 359 K)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Triisobutylaluminium (TiBA) is an organoaluminium compound with the formula Al(CH2CH(CH3)2)3. This colorless pyrophoric liquid is mainly used to make linear primary alcohols and α-olefins.[2]

Structure[edit]

Triisobutylaluminium was thought to be exclusively monomeric, however, it was discovered to exist in equilibrium with its dimer. To allow for the dimer to form, there is an appreciable increase in the length of the bonds between Al and the bridging alkyl ligand. There is also evidence of restricted rotation of the bridging isobutyl groups in the dimer. The equilibrium constant, KD, is 3.810 at 20 °C.[3]

Synthesis[edit]

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 by this route.

6 iBu3 + 2 Al + 3 H2 → 6 iBu2AlH

In the second step isobutylene adds to the diisobutylaluminium to give TiBA.

6 iBu2AlH + 6 (C4H8) → 6 iBu3Al

Reactions[edit]

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.

(iC4H9)3Al + 3 RCH=CH2 → (RCH2CH3)3Al + 3 iC4H8

Like most organoaluminium compounds, TiBA reacts violently with water and air and must be handled with care.[1]

References[edit]

  1. ^ a b http://www.sigmaaldrich.com/catalog/product/aldrich/257206?lang=en&region=US Triisobutylaluminum] at Sigma-Aldrich
  2. ^ 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. doi:10.1002/14356007.a01_543
  3. ^ Martin B. Smith, Journal of Organometallic Chemistry, The Monomer-Dimer Equilibria of Liquid Ammonium Alkyls II Triisobutylaluminum Journal of Organometallic Chemistry, Volume 22, Issue 2, April 1970, Pages 273-281. doi:10.1016/S0022-328X(00)86043-X

Further reading[edit]

  • Keisuke Suzuki, Tetsuya Nagasaws, Encyclopedia of Reagents for Organic Synthesis, Triisobutylaluminum, 2009