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Addition of LiAlH4 to aldehydes to give primary alcohols

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

Notes: The choice of specific acid is unimportant, so long as it gives the neutral alcohol in the end.


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 aldehyde (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 here isn’t crucial.