Diisobutylaluminium hydride

Diisobutylaluminium Hydride (DIBAL-H or DIBAL) is a chemical reagent used extensively in organic chemistry for the reduction of esters, carboxylic acids, and nitriles to aldehydes, as well as in the reduction of certain types of ketones to alcohols. It is a complex organoaluminium compound with the formula (i-Bu₂AlH)₂, where i-Bu represents isobutyl groups. This reagent is highly selective and is particularly useful in synthetic chemistry for the partial reduction of compounds sensitive to over-reduction.

Properties and Structure

Diisobutylaluminium hydride is a colorless, pyrophoric liquid at room temperature. It is soluble in hydrocarbons such as hexanes and toluene, which are commonly used as solvents for its applications. The structure of DIBAL-H consists of two isobutyl groups bonded to an aluminium centre, along with a hydride ion. This structure is responsible for its reactivity and selectivity in organic synthesis.

Applications in Organic Synthesis

DIBAL-H is widely used in organic synthesis for the selective reduction of various functional groups:

• Ester Reduction: It reduces esters to aldehydes under controlled conditions, avoiding further reduction to alcohols.
• Nitrile Reduction: Nitriles are reduced to aldehydes, providing a useful method for the synthesis of aldehydes from more readily available nitriles.
• Ketone Reduction: Certain ketones can be selectively reduced to secondary alcohols using DIBAL-H.
• Amide Reduction: Under specific conditions, amides can be reduced to aldehydes or alcohols.

Mechanism of Action

The mechanism of action of DIBAL-H involves the transfer of a hydride ion from the aluminium to the electrophilic carbon of the functional group being reduced. This process typically occurs through a six-membered transition state, which helps explain the selectivity of DIBAL-H for certain reductions.

Safety and Handling

Due to its pyrophoric nature, DIBAL-H must be handled with extreme care. It can spontaneously ignite upon exposure to air and react violently with water, producing flammable gases. Therefore, it is typically handled under an inert atmosphere in a dry solvent.

Environmental and Health Considerations

While DIBAL-H is a valuable tool in synthetic organic chemistry, its handling and disposal require careful consideration due to its reactivity and potential environmental impact. Proper safety protocols, including the use of personal protective equipment and fume hoods, are essential when working with this reagent.

See Also

• Organometallic chemistry
• Reduction (chemistry)
• Aldehyde
• Alcohol (chemistry)