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Metal hydrides such as ${\mathbf{NaBH}}_{\mathbf{4}\mathbf{}}\mathbf{and}\mathbf{}{\mathbf{LiAIH}}_{\mathbf{4}}$are powerful reducing agents that reduce an aldehyde into primary alcohol and a ketone into secondary alcohol.

${\mathrm{LiAIH}}_4$is more powerful than${\mathrm{NaBH}}_4$ . It can also reduce other powerful functional groups like carboxylic acid and its derivatives into alcohols.

In the case of$\mathrm{LiAIH}{\left[\mathrm{OC}{\left({\mathrm{CH}}_3\right)}_3\right]}_3$ , as the electron-withdrawing groups are attached with aluminum, the reducing nature gets decreased and the reaction occurs only at the aldehyde stage.

The functions of the metal hydrides are shown below:-

The M-H is polar, and the hydride present in M-H acts as a nucleophile. As a result, it can readily attack the carbonyl carbon center to yield alcohol.

Representation of the mechanism of M-H