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Ethanol reacts with $\mathrm{PCl_5}$ to give which set of products?
A$\mathrm{CH_3CH_2Cl} + \mathrm{POCl_3} + \mathrm{HCl}$
B$\mathrm{CH_3CH_3} + \mathrm{H_2O}$
C$\mathrm{CH_3CH_2OH \cdot HCl}$ (complex salt)
D$\mathrm{CH_3CHO} + \mathrm{H_2}$
Answer & Solution
Correct answer: A. $\mathrm{CH_3CH_2Cl} + \mathrm{POCl_3} + \mathrm{HCl}$
1. NCERT §7.4 (Reactions of alcohols — halogenation): $\mathrm{PCl_5}$ is a strong chlorinating agent that converts alcohols to alkyl chlorides.
2. Generic equation: $\mathrm{R{-}OH} + \mathrm{PCl_5} \to \mathrm{R{-}Cl} + \mathrm{POCl_3} + \mathrm{HCl}$.
3. For ethanol: $\mathrm{CH_3CH_2OH} + \mathrm{PCl_5} \to \mathrm{CH_3CH_2Cl} + \mathrm{POCl_3} + \mathrm{HCl}$.
4. All three by-products are formed: ethyl chloride (the substitution product), phosphoryl chloride (from $\mathrm{PCl_5}$ losing $\mathrm{Cl}$ and gaining $\mathrm{O}$), and HCl gas.
5. Option B describes a different reaction. Option C is a salt that doesn't form. Option D is dehydrogenation, not happening here.
_Source: NCERT Class 12 Chemistry Part 2, Ch 7, §7.4 (Conversion of alcohols to alkyl halides — $\mathrm{PCl_5}$, $\mathrm{PCl_3}$, $\mathrm{SOCl_2}$), p. 12–13._
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