Oxidation of primary alcohols to carboxylic acids requires reflux

Steps:

• Primary alcohols oxidize to aldehydes, then carboxylic acids with excess dichromate(VI).
• Aldehydes are volatile and can escape if distilled early, halting at aldehyde stage.
• Reflux condenses vapors, keeping intermediates in mixture for complete oxidation.
• Excess oxidant ensures both steps occur, yielding carboxylic acid.

Why D is correct:

• Heating under reflux retains the intermediate propanal, allowing reaction 2 to form propanoic acid, as per standard oxidation procedure for carboxylic acids.

Why the others are wrong:

• A: Excess dichromate is used but alone doesn't prevent aldehyde loss; reflux is also needed.
• B: Sulfuric acid catalyzes but excess concentrated isn't specifically required for this oxidation.
• C: Immediate distillation isolates propanal after reaction 1, preventing further oxidation to acid.

Final answer: D