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14.20: Esters to Alcohols: Hydride Reductions

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Organic Chemistry

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Esters to Alcohols: Hydride Reductions

14.20: Esters to Alcohols: Hydride Reductions

Esters are reduced to primary alcohols when treated with a strong reducing agent like lithium aluminum hydride. The reaction requires two equivalents of the reducing agent and proceeds via an aldehyde intermediate.

Lithium aluminum hydride is a source of hydride ions and functions as a nucleophile. The mechanism proceeds in three steps. Firstly, the nucleophilic hydride ion attacks the carbonyl carbon of the ester to form a tetrahedral intermediate. Subsequently, the carbonyl group re-forms, and the alkoxide ion departs as the leaving group, generating an aldehyde. Lastly, a second nucleophilic attack by the hydride ion at the carbonyl carbon of the aldehyde yields an alkoxide ion, which gives a primary alcohol as the final product upon protonation.


However, in case the desired product is an aldehyde, it is possible to stop the reaction at the aldehyde intermediate by using a milder reducing agent like diisobutylaluminum hydride or lithium tri(t-butoxy) aluminum hydride, at a lower temperature.


Esters Alcohols Hydride Reductions Strong Reducing Agent Lithium Aluminum Hydride Primary Alcohols Aldehyde Intermediate Nucleophile Mechanism Tetrahedral Intermediate Alkoxide Ion Leaving Group Final Product Milder Reducing Agent Diisobutylaluminum Hydride Lithium Tri(t-butoxy) Aluminum Hydride Lower Temperature

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