Addition of NaBH4 to ketones to give secondary alcohols

by James

Description:  Addition of sodium borohydride (NaBH4) to ketones gives secondary alcohols (after addition of acid) [private_ReactionGuide]

Notes: The precise type of acid isn’t crucial for this reaction; H2O, H+, H3O(+) or other acids might be used.


Notes:  Again, many different acids can be used in the last step. It’s not crucial which specific acid is used, just that something is present that can donate a proton to form the alcohol.

Mechanism:  NaBH4 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: Again, the choice of H2O /H2SO4 as acid isn’t crucial.


{ 4 comments… read them below or add one }





Does nabh4 also give conjugated nucleophillic addition reaction with alpha beta unsaturated ketone?



It can; you might find this to be somewhat textbook dependent. In practice, it can go either way. To get addition to occur exclusively on the carbonyl carbon, sometimes cerium trichloride is used. Google “Luche reduction”



Is it true that NaH cannot reduce ketones and aldehydes? If so, I wonder what is the reason.


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