Which reagent would you use to reduce an aldehyde to a primary alcohol?

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Multiple Choice

Which reagent would you use to reduce an aldehyde to a primary alcohol?

The key idea is reducing the carbonyl group by delivering a hydride (H–) to the carbonyl carbon. When an aldehyde receives a hydride, the C=O bond is converted to a C–O–, which after work-up gives a primary alcohol. Reagents that provide hydride, such as sodium borohydride (NaBH4) or lithium aluminium hydride (LiAlH4), are classic and reliable for this transformation. NaBH4 is milder and often selective for aldehydes and ketones, while LiAlH4 is stronger and can reduce a broader range of groups, but both will take an aldehyde to a primary alcohol. The other options are not reducing agents for this purpose. A strong oxidizing environment (dichromate in acid) would oxidize an aldehyde further to a carboxylic acid rather than reduce it. Thionyl chloride converts alcohols to alkyl chlorides, not carbonyls to alcohols. Acidic hydrolysis typically affects acetals or esters, not convert aldehydes to alcohols.

The key idea is reducing the carbonyl group by delivering a hydride (H–) to the carbonyl carbon. When an aldehyde receives a hydride, the C=O bond is converted to a C–O–, which after work-up gives a primary alcohol. Reagents that provide hydride, such as sodium borohydride (NaBH4) or lithium aluminium hydride (LiAlH4), are classic and reliable for this transformation. NaBH4 is milder and often selective for aldehydes and ketones, while LiAlH4 is stronger and can reduce a broader range of groups, but both will take an aldehyde to a primary alcohol.

The other options are not reducing agents for this purpose. A strong oxidizing environment (dichromate in acid) would oxidize an aldehyde further to a carboxylic acid rather than reduce it. Thionyl chloride converts alcohols to alkyl chlorides, not carbonyls to alcohols. Acidic hydrolysis typically affects acetals or esters, not convert aldehydes to alcohols.

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