Which of the following is the most suitable requirement for the dehydration of ethanol to form an ether?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Sulphuric acid at 413 K
Alcohols are dehydrated by protic acids such as \( \ce{H2SO4} \), and the product depends on the temperature. At 413 K one ethanol molecule attacks another protonated ethanol molecule, and water is lost between two molecules to give the ether, ethoxyethane:
\( \displaystyle \ce{2C2H5OH} \xrightarrow[\text{413 K}]{\ce{H2SO4}} \ce{C2H5-O-C2H5 + H2O} \)
Why the other options are incorrect
Option (2) Sulphuric acid at 443 K — Incorrect. At this higher temperature water is lost from one molecule, and the main product is ethene, not the ether.
Option (3) Sodium hydroxide at 413 K — Incorrect. NaOH is a base, not a protic acid; it cannot protonate the –OH group, so ethanol is not dehydrated.
Option (4) Sodium hydroxide at 443 K — Incorrect. A base does not bring about dehydration of an alcohol at any temperature; an acid is needed.
NCERT (2026-27 edition):
7.6.1 Preparation of Ethers – “1. By dehydration of alcohols
Alcohols undergo dehydration in the presence of protic acids (H2SO4, H3PO4). The formation of the reaction product, alkene or ether depends on the reaction conditions. For example, ethanol is dehydrated to ethene in the presence of sulphuric acid at 443 K. At 413 K, ethoxyethane is the main product.”