Which oxidation condition would convert a primary alcohol to an aldehyde rather than to a carboxylic acid?

• A. Jones oxidation
• B. Hydrogenation
• C. PCC oxidation
• D. Ozonolysis

Answer: (C)

Selective oxidation of a primary alcohol to an aldehyde is achieved with PCC, pyridinium chlorochromate. PCC is a milder, anhydrous oxidant, so it removes two hydrogens from the alcohol to form the aldehyde but doesn’t push the oxidation further to the carboxylic acid. In contrast, Jones oxidation uses a strongly acidic, aqueous chromium(VI) reagent and typically converts primary alcohols all the way to carboxylic acids. Hydrogenation would reduce rather than oxidize. Ozonolysis targets alkenes and doesn’t convert simple alcohols to carbonyls. So the condition that best gives the aldehyde from a primary alcohol is PCC oxidation.