Reduction of Carboxylic Acids by Lithium Aluminum Hydride

REDUCTION OF CARBOXYLIC ACIDS BY LITHIUM ALUMINUM HYDRIDE 

Lithium aluminum hydride is capable of reducing carboxyhc acids all the way to the corresponding primary alcohols, which are obtained upon aqueous acidic work-up. 

Although the exact mechanism of this transformation is not completely understood, it is clear that the hydride reagent first acts as a base, forming the lithium salt of the acid and hydrogen gas. Carboxylate salts are generally resistant to attack by nucleophiles. Yet, despite the negative charge, lithium aluminum hydride is so reactive that it is capable of 

Propose synthetic schemes that produce compound B from compound A. 

In Summary The nucleophilic reactivity of lithium aluminum hydride is sufQciently great to effect the reduction of carboxylates to primary alcohols. 

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Another nucleophilic addition to the carboxylate group is in the reduction of carboxylic acids by lithium aluminum hydride. 

Reduction of carboxylic acids by lithium aluminum hydride, followed by hydrolysis, gives the corresponding primary alcohols (Fig. 17.52). There is no unanimity on the details of the reaction mechanism, but the first step must be formation of the carboxylate anion and hydrogen. Anion formation is foUowed by addition of hydride to the carbonyl group. The result is another dianion. In this case, the aluminum is undoubtedly tightly bound to one of the oxygen anions. 

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