Appearance Colorless liquid | ||
 | ||
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.
Contents
Structure
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.
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 by this route.
6 iBu3 + 2 Al + 3 H2 → 6 iBu2AlHIn the second step isobutylene adds to the diisobutylaluminium to give TiBA.
6 iBu2AlH + 6 (C4H8) → 6 iBu3AlReactions
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 iC4H8Like most organoaluminium compounds, TiBA reacts violently with water and air and must be handled with care.