An organic compound ‘A’ with molecular formula CH4O reacts with HI to give an alkyl iodide, which then reacts with potassium cyanide to produce ‘B’. Compound ‘B’ on reduction followed by reaction with HNO2 gives an alcohol, which on oxidation gives ‘C’. Compound ‘C’ reacts with CH3MgBr to give ‘D’, which on hydrolysis gives compound ‘E’, which is also an alcohol.
In the reaction sequence given in the passage, what is the compound ‘B’?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Acetonitrile
In the passage, A (\( \ce{CH4O} \)) is methanol, which has one carbon atom. HI converts it to methyl iodide:
\( \displaystyle \ce{CH3OH + HI -> CH3I + H2O} \)
KCN is ionic and gives cyanide ions, which attack the carbon of \( \ce{CH3I} \) through their carbon atom. The product is an alkyl cyanide (nitrile), \( \ce{CH3CN} \), acetonitrile (ethanenitrile):
\( \displaystyle \ce{CH3I + KCN -> CH3CN + KI} \)
This fits the rest of the passage: reduction of \( \ce{CH3CN} \) gives ethylamine, which with nitrous acid gives ethanol.
Why the other options are incorrect
Option (2) Ethyl cyanide — Incorrect. \( \ce{CH3CH2CN} \) has three carbon atoms; it would come from an ethyl halide, but A has only one carbon.
Option (3) Methyl isocyanide — Incorrect. An isocyanide (\( \ce{CH3NC} \)) forms when the attack is through nitrogen, which happens with AgCN, not with ionic KCN.
Option (4) Ethyl isocyanide — Incorrect. It has both the wrong number of carbon atoms and the N-linked group that KCN does not give.
NCERT (2026-27 edition):
Example 6.5 – “Haloalkanes react with KCN to form alkyl cyanides as main product while AgCN forms isocyanides as the chief product. Explain.”
“KCN is predominantly ionic and provides cyanide ions in solution. Although both carbon and nitrogen atoms are in a position to donate electron pairs, the attack takes place mainly through carbon atom and not through nitrogen atom since C—C bond is more stable than C—N bond.”