Selective oxidation of primary alcohols to aldehydes

Steps:

• Identify the reaction type: oxidation of a primary alcohol to an aldehyde, requiring a mild oxidizing agent.
• Recall that acidified dichromate(VI) oxidizes primary alcohols to aldehydes under controlled conditions (e.g., distillation to prevent further oxidation).
• Evaluate options: A matches mild oxidation; B uses permanganate, which is less selective; C is too harsh for aldehydes; D is not an oxidant.
• Confirm A by its standard use in organic chemistry for partial oxidation.

Why A is correct:

• Acidified K2Cr2O7 selectively oxidizes R-CH2OH to R-CHO, as the orange Cr(VI) reduces to green Cr(III), with the reaction: 3RCH2OH + Cr2O7^2- + 8H+ → 3RCHO + 2Cr^3+ + 7H2O.

Why the others are wrong:

• B: Dilute acidified MnO4- oxidizes to carboxylic acids, not stopping at aldehydes.
• C: Hot concentrated acidified MnO4- causes complete oxidation to CO2 and H2O for many substrates.
• D: H2SO4 dehydrates alcohols to alkenes, not oxidizes them.

Final answer: A