Identify the two reagents used to convert ethanol to butane.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Phosphorus pentachloride, sodium.
Ethanol has two carbon atoms and butane has four, so the conversion needs two steps: replace –OH by a halogen, then join two ethyl groups.
Alcohol to alkyl halide: the –OH group of an alcohol is replaced by chlorine with \( \ce{PCl5} \), \( \ce{PCl3} \), \( \ce{SOCl2} \) or HCl/\( \ce{ZnCl2} \).
Wurtz reaction: an alkyl halide heated with sodium in dry ether gives an alkane with double the number of carbon atoms.
\( \displaystyle \ce{C2H5OH + PCl5 -> C2H5Cl + POCl3 + HCl} \)
\( \displaystyle \ce{2C2H5Cl + 2Na} \xrightarrow{\text{dry ether}} \ce{C2H5-C2H5 + 2NaCl} \)
So the two reagents are phosphorus pentachloride (to make chloroethane) and sodium (to couple two ethyl groups into butane).
Why the other options are incorrect
Option (1) Sulphuryl chloride, sodium — Incorrect. Sulphuryl chloride (\( \ce{SO2Cl2} \)) chlorinates alkanes by a free radical reaction; it is not the reagent for replacing the –OH of an alcohol. Thionyl chloride (\( \ce{SOCl2} \)) is the one used for alcohols.
Option (3) Phosphorus trichloride, aniline — Incorrect. \( \ce{PCl3} \) does give chloroethane, but aniline cannot join two ethyl groups; it would only give N-ethylaniline.
Option (4) Aniline, anhydrous aluminium chloride — Incorrect. Neither reagent converts ethanol into an alkyl halide, and aniline forms a salt with \( \ce{AlCl3} \), so no carbon–carbon bond is formed.