Addition of LiAlH4 to ketones to give secondary alcohols

by James

Description: Addition of lithium aluminum hydride to ketones leads to formation of secondary alcohols (after addition of acid) [private_ReactionGuide]

Notes: The precise identity of the acid is not generally important

Examples:

Notes: Lots of different acids can be used in the last step. It’s not important which specific acid is used, just that something is present that can form the alcohol.

Mechanism: LiAlH4 is a source of hydride (H–) and the reaction begins with 1,2-addition of hydride to the carbonyl of the ketone (Step 1, arrows A and B). Upon addition of acid, the oxygen is protonated (Step 2, arrows C and D) to give the neutral alcohol.

Notes:  The choice of H2O / H2SO4 as acid isn’t crucial here. Any strong acid will do.

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{ 2 comments… read them below or add one }

Joseph Delaune December 9, 2013 at 11:55 pm

LiAlH4 seems to function in the same alcohol reduction reactions as the reagent, NaBH4. If LiAlH4 achieves the same products as NaBH4, what is the point of having to remember NaBH4 as a reagent?

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Jason Mathias March 23, 2014 at 9:47 pm

On stereochemistry – Since this is a flat structure before AlH3, does this produce equal amounts of enantiomers if there is a stereocenter at the Carbon?

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