Fundamentals of Organic ChemistryChemistryAldehydes and Ketones
A chemist attempted to reduce the compound shown below with NaBH ₄ , but could not isolate the desired product, 4-hydroxybutanoic acid. Which of the following best explains this observation?
Options
- AAn intermediate was formed that reacted to give a cyclic ester.
- BNaBH ₄ is not reactive enough to reduce either the carboxylic acid or the aldehyde.
- CAn intermediate was formed that reacted to give a cyclic acetal.
- DNaBH ₄ reduced both the carboxylic acid and the aldehyde.
Correct answer
A. An intermediate was formed that reacted to give a cyclic ester.
Step-by-step solution
The given compound is 4-oxobutanoic acid, which contains both an aldehyde group ( - CHO ) and a carboxylic acid group ( - COOH ). Sodium borohydride ( NaBH ₄ ) is a mild reducing agent. It selectively reduces aldehydes and ketones to their corresponding alcohols, but it is not a strong enough reducing agent to reduce carboxylic acids or esters. When the compound is treated with NaBH ₄ , only the aldehyde group is reduced to a primary alcohol, forming 4-hydroxybutanoic acid ( HO - CH ₂- CH ₂- CH ₂- COOH ) as an inte