Ethanol is treated separately with the reagents given in List-I. Match each reagent with the main organic product in List-II.
| List-I (Reagent) | List-II (Main organic product) |
|---|---|
| (A) Sodium metal | (I) Ethene |
| (B) Ethanoic acid with a small amount of concentrated H2SO4 | (II) Bromoethane |
| (C) Phosphorus tribromide | (III) Ethyl ethanoate |
| (D) Concentrated H2SO4 at 443 K | (IV) Sodium ethoxide |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → A-IV, B-III, C-II, D-I
Ethanol reacts either by breaking its O–H bond (with sodium, with a carboxylic acid) or its C–O bond (with phosphorus tribromide, with hot concentrated acid).
(A) Sodium metal — This matches (IV) Sodium ethoxide. An active metal replaces the hydrogen of the O–H group and hydrogen gas is given off:
\( \displaystyle \ce{2C2H5OH + 2Na -> 2C2H5ONa + H2} \)
(B) Ethanoic acid with a small amount of concentrated H2SO4 — This matches (III) Ethyl ethanoate. This is esterification, a reversible reaction:
\( \displaystyle \ce{CH3COOH + C2H5OH} \overset{\ce{H+}}{\rightleftharpoons} \ce{CH3COOC2H5 + H2O} \)
(C) Phosphorus tribromide — This matches (II) Bromoethane. The –OH group is replaced by bromine:
\( \displaystyle \ce{3C2H5OH + PBr3 -> 3C2H5Br + H3PO3} \)
(D) Concentrated H2SO4 at 443 K — This matches (I) Ethene. On heating with the acid, ethanol loses a molecule of water (dehydration):
\( \displaystyle \ce{C2H5OH} \xrightarrow[\text{443 K}]{\ce{H2SO4}} \ce{CH2=CH2 + H2O} \)
NCERT (2026-27 edition):
7.4.4 Chemical Reactions – “(i) Reaction with metals: Alcohols and phenols react with active metals such as sodium, potassium and aluminium to yield corresponding alkoxides/phenoxides and hydrogen.”
“2. Esterification … Alcohols and phenols react with carboxylic acids, acid chlorides and acid anhydrides to form esters.” … “The reaction with carboxylic acid and acid anhydride is carried out in the presence of a small amount of concentrated sulphuric acid.”
“2. Reaction with phosphorus trihalides: Alcohols are converted to alkyl bromides by reaction with phosphorus tribromide…”
“3. Dehydration: … Ethanol undergoes dehydration by heating it with concentrated H2SO4 at 443 K.”