Read the passage carefully and answer the Questions.
Ethers with the general formula \( C_nH_{2n+2}O \) and functional group C-O-C may be divided as symmetrical and unsymmetrical. Lower symmetrical ether may be obtained by the dehydration of alcohols at low temperatures in the presence of protic acids, such as \( H_2SO_4 \) and \( H_3PO_4 \) whereas at high temperature intramolecular dehydration takes place. Formation of ether from primary alcohols is also accompanied by the formation of small amount of alkenes. Due to the steric hindrance, secondary and tertiary alcohols undergo elimination reaction rather than substitution reaction yielding alkene as major product. Ethers can also be obtained by heating alkyl halides with sodium or potassium alkoxides. Substituted Ethers (secondary & tertiary) can also be prepared using this method. If primary halides are replaced with secondary and tertiary halides, alkenes are the major products.
The major product in the following reaction is
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Ethers
Heating an alcohol with concentrated sulphuric acid removes water, and the temperature decides the product. At the lower temperature, about 413 K (140 °C), with the alcohol in excess, two molecules lose one molecule of water between them (intermolecular dehydration) and an ether is formed. At the higher temperature, about 443 K, one molecule loses water internally and an alkene is formed.
The acid protonates one alcohol molecule; a second alcohol molecule attacks it as a nucleophile (\(S_N2\)) and pushes out water; loss of a proton then gives the ether:
\( \displaystyle \ce{R-OH + H-O-R} \xrightarrow[\text{140}\,^\circ\text{C}]{\ce{H2SO4}} \ce{R-O-R + H2O} \)
For ethanol this gives ethoxyethane. So the major product is an ether.
Why the other options are incorrect
Option (1) Alkenes — Incorrect. Alkenes are the main product at the higher temperature (443 K for ethanol), or from secondary and tertiary alcohols.
Option (3) Carboxylic acids — Incorrect. These need oxidation of a primary alcohol by an oxidising agent such as acidified \( \ce{KMnO4} \) or \( \ce{K2Cr2O7} \); dehydration does not oxidise.
Option (4) Aldehydes — Incorrect. These come from controlled oxidation of a primary alcohol (for example with PCC, or dehydrogenation over copper at 573 K), not from dehydration.
NCERT (2026-27 edition):
Preparation of Ethers – …
