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Strong and Weak Reductants

Oxidation and reduction are opposite reactions. Just like there are “strong” and “weak” oxidants, there are also strong and weak reductants.

Let’s look at the “oxidation ladder” again.

Remember that when we go up rungs of the “ladder” we are oxidizing, and when we go “down” we are reducing.

Weak reductants (common example: sodium borohydride, NaBH4) go down one rung in the oxidation ladder, from aldehydes to primary alcohols or ketones to secondary alcohols. (But they don’t reduce carboxylic acids or esters).

Strong reductants (common example: lithium aluminum hydride, LiAlH4) go down two rungs in the oxidation ladder, from carboxylic acids to primary alcohols or from esters to primary alcohols. They will also reduce aldehydes and ketones to alcohols, just like NaBH4.

Tomorrow: How to make alcohols into good leaving groups.

Thanks for reading! James

PS – further reading – reduction of carboxylic acids to alcohols using LiAlH4
reagent friday: sodium borohydride