JEE Main 2021 · 22 July · evening · Single correct · +4 / −1
In the chemical reactions given above A and B respectively are :
- (a) H₃PO₂ and CH₃CH₂Cl
- (b) CH₃CH₂OH and H₃PO₂
- (c) H₃PO₂ and CH₃CH₂OH
- (d) CH₃CH₂Cl and H₃PO₂
Answer and solution
Answer (a) H₃PO₂ and CH₃CH₂Cl
Solution
Chemistry ma’am · 3 steps
First remove the diazo group to get benzene, then put an ethyl group on it by Friedel-Crafts.
- Find A. The diazonium group is replaced by H, and the product is plain benzene. Hypophosphorous acid does this reduction, so A is H₃PO₂.
C₆H₅N₂⁺Cl⁻ + H₃PO₂ + H₂O → C₆H₆ + N₂ + H₃PO₃ + HCl
- Find B. Benzene becomes ethylbenzene with anhydrous AlCl₃. This is Friedel-Crafts alkylation, which needs an alkyl halide. AlCl₃ pulls off the chloride and leaves an ethyl electrophile, so B is CH₃CH₂Cl.
- So. A is H₃PO₂ and B is CH₃CH₂Cl, which is option (a).
The idea to keep. H₃PO₂ (or ethanol) swaps -N₂⁺ for H. Friedel-Crafts alkylation with anhydrous AlCl₃ needs an alkyl halide, not an alcohol.
Answer from the NTA final answer key. Solution by PrepWiser.