I'm preparing for a chem prac on reduction of a ketone group (in particular, the C=O in benzoin) using a nucleophilic addition reaction.

In the experimental method, all we do is react benzoin with $\ce{NaBH4}$, the nucleophile. The solvent we're using is a mix of ethanol/water. From what I've learned, the reaction forms a $\ce{C-O^-}$ alkoxide group which then needs to grab a proton from something to form the alcohol.

In the procedure, we mix ethanol/water, and that's it - no addition of dilute acid to then protonate the alkoxide. We're told to add hot water. Am I right in saying that addition of hot water provides a source of protons to protonate the alkoxide?

Thanks :)


1 Answer 1


The nucleophile is the H-, a hydride. In your SP3 ketone, the tiny Hydride will have no issue producing a high yield of the alkoxide.

The heat will simply make the reaction faster and drive the equilibrium further.

Ethanol + water is a mild acid, so no issue with protons to complete your alcohol, and the heat makes that mix slightly more active as a proton donor.

You end up with a new equilibrium of your 2 alcohols competing for the proton, however with plenty of methanol and some careful washing with hexane or toluene you should be able to get your alcohol out of that mixture...


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