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Dibal-h

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Dibal-h

Diisobutylaluminium hydride
Identifiers
CAS number 1191-15-7 YesY
ChemSpider 10430352 YesY
Jmol-3D images Image 1
Properties
Molecular formula C16H38Al2 (dimer)
Molar mass 142.22 (monomer)
Appearance colorless liquid
Density 0.798 g/cm3
Melting point

–80 °C

Boiling point

116–118 °C/1 mmHg

Solubility in water hydrocarbon solvents
Hazards
Main hazards ignites in air
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Diisobutylaluminium hydride (DIBALH, DIBAL, DIBAL-H or DIBAH, ) is a reducing agent with the formula (i-Bu2AlH)2, where i-Bu represents isobutyl (-CH2CH(CH3)2). This organoaluminium compound was investigated originally as a co-catalyst for the polymerization of alkenes.[1]

Properties

Like most organoaluminum compounds, the compound’s structure is probably more than that suggested by its empirical formula. A variety of techniques, not including X-ray crystallography, suggest that the compound exists as a dimer and a trimer, consisting of tetrahedral aluminium centers sharing bridging hydride ligands.[2] Hydrides are small and, for aluminium derivatives, are highly basic, thus they bridge in preference to the alkyl groups.

DIBALH can be prepared by heating triisobutylaluminium (itself a dimer) to induce beta-hydride elimination:[3]

(i-Bu3Al)2 → (i-Bu2AlH)2 + 2 (CH3)2C=CH2

Although DIBALH can be purchased commercially as a colorless liquid, it is more commonly purchased and dispensed as a solution in an organic solvent such as toluene or hexane.

Use in organic synthesis

DIBALH is useful in organic synthesis for a variety of reductions, including converting esters and nitriles to aldehydes. DIBALH efficiently reduces α-β unsaturated esters to the corresponding allylic alcohol.[4] By contrast, LiAlH4 reduces esters and acyl chlorides to primary alcohols, and nitriles to primary amines [use Feiser work-up procedure]. DIBALH reacts slowly with electron-poor compounds, and more quickly with electron-rich compounds. Thus, it is an electrophilic reducing agent whereas LiAlH4 can be thought of as a nucleophilic reducing agent.

Safety

DIBAH, like most alkylaluminium compounds, reacts violently with air and water, potentially leading to fires.

References

External links

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