Lithium Borohydride Ester Reduction Mechanism

Lithium borohydride (LiBH4) is a commonly used reducing agent in organic chemistry. When esters are treated with LiBH4, the reduction proceeds via a nucleophilic addition-elimination mechanism.

In the first step, the LiBH4 is activated by the presence of a catalyst such as iodine or titanium tetrachloride. This activation allows for the formation of hydride ions (H-) which serve as the reducing agents.

The second step involves the attack of the hydride ion on the carbonyl group of the ester, forming an intermediate alkoxide. This intermediate is unstable and quickly decomposes to form an alkoxyborohydride and an alcohol.

In the final step, the alkoxyborohydride is reduced by a second hydride ion to form a borate ester and a new molecule of alcohol. The borate ester is generally considered to be the main product of the reaction.

Overall, the LiBH4 ester reduction mechanism proceeds through a series of nucleophilic additions and eliminations, resulting in the formation of a borate ester and an alcohol.