14.14:
Acid Halides to Alcohols: Grignard Reaction
In addition to lithium aluminum hydride, organomagnesium halides, known as Grignard reagents, convert acid halides to alcohols.
Unlike the first approach, where the final product is a primary alcohol, reduction with the Grignard reagent yields a tertiary alcohol.
The reaction requires two equivalents of the Grignard reagent and proceeds via a ketone intermediate.
Since the alkyl–magnesium bond is highly polar, the alkyl carbon acquires a carbanionic character and functions as a nucleophile.
The first step of the mechanism begins with a nucleophilic attack by the Grignard reagent at the carbonyl carbon, forming a tetrahedral intermediate.
In the second step, the carbon–oxygen double bond is reconstructed, and the halide ion departs as a leaving group to yield a ketone.
Next, the ketone is attacked by another equivalent of the Grignard reagent, generating an alkoxide intermediate.
Lastly, protonation of the alkoxide drives the reaction to completion, forming a tertiary alcohol as the final product.
14.14:
Acid Halides to Alcohols: Grignard Reaction
Organomagnesium halides, commonly known as Grignard reagents, convert acid halides to tertiary alcohols. The reaction requires two equivalents of the Grignard reagent and proceeds via a ketone intermediate.
Grignard reagents are a source of carbanions and function as nucleophiles. The mechanism begins with the nucleophilic attack by the carbanion at the carbonyl carbon of the acid halide to form a tetrahedral intermediate. Next, the carbonyl group is re-formed, and the halide ion departs, forming a ketone. The addition of another equivalent of the carbanion generates a tertiary alkoxide ion. Protonation of the alkoxide gives a tertiary alcohol as the final product.
