JEE Main 2021 · 24 February · morning · Single correct · +4 / −1
Which of the following reagent is used for the following reaction ?
CH₃ CH₂ CH₃ →(?) CH₃ CH₂ CHO
- (a) Molybdenum oxide
- (b) Manganese acetate
- (c) Copper at high temperature and pressure
- (d) Potassium permanganate
Answer and solution
Answer (a) Molybdenum oxide
Solution
Chemistry ma’am · 3 steps
Alkane to aldehyde in one controlled step: think of the NCERT trio and pick the molybdenum oxide catalyst.
- What changes. Propane becomes propanal. One terminal CH₃ becomes CHO and the carbon chain stays intact. This is controlled oxidation, not combustion, so the reagent must be a catalyst with O₂ that stops at a particular product.
- Recall the catalysts. NCERT lists three controlled oxidations of alkanes. Each catalyst gives its own kind of product.
Reagent Example Product type Cu, 523 K, 100 atm CH₄ → CH₃OH alcohol Mo₂O₃ (molybdenum oxide) CH₄ → HCHO aldehyde (CH₃COO)₂Mn C₂H₆ → CH₃COOH carboxylic acid KMnO₄ (CH₃)₃CH → (CH₃)₃COH tertiary alcohol, attacks only 3° C–H - So. The product here is an aldehyde, so the reagent is molybdenum oxide with O₂: option (a).
The idea to keep. For controlled oxidation of alkanes, match the catalyst to the product: Cu gives alcohol, Mo₂O₃ gives aldehyde, manganese acetate gives acid, KMnO₄ gives a tertiary alcohol.
Answer from the NTA final answer key. Solution by PrepWiser.