Reduction [LiAlH4] Definition:
Addition of lithium aluminum hydride (LiAlH4) to carboxylic acids leads to the formation of primary alcohols (after addition of acid).
Reduction [LiAlH4] Explained:
Lithium aluminum hydride abbreviated LAH, is capable of reducing carboxylic 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, the first step is likely a proton transfer. Lithium aluminum hydride is a powerful nucleophile and a strong base which may deprotonate carboxylic acid.
One of the possibilities for the rest of the mechanism is a reaction of the carboxylate ion with AlH3 followed by elimination to form an aldehyde.
This aldehyde cannot be isolated and it is further attacks by LAH to form an alkoxide ion, which is then protonated.