Name the reagent required to convert cyclohexene into hexane-1,6-dioic acid.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → KMnO4/H2SO4, Δ
Hot acidified potassium permanganate is a strong oxidising agent that cleaves the C=C double bond completely. In cyclohexene each doubly bonded CH carbon is oxidised to a –COOH group; because the double bond is inside a ring, cleavage opens the ring and gives a six-carbon chain with a carboxyl group at each end:
\( \displaystyle \ce{C6H10 + 4[O]} \xrightarrow{\ce{KMnO4/H2SO4},\ \Delta} \ce{HOOC(CH2)4COOH} \)
The product is hexane-1,6-dioic acid (adipic acid).
Why the other options are incorrect
Option (2) Tollens’ reagent — Incorrect. A mild oxidising agent that oxidises only the –CHO group of aldehydes; it does not cleave a C=C bond.
Option (3) Grignard reagent — Incorrect. RMgX is a nucleophile that adds to C=O groups; it is not an oxidising agent and does not react with an isolated C=C bond.
Option (4) KCN — Incorrect. \( \ce{CN^{-}} \) is a nucleophile used to make nitriles from alkyl halides; it cannot oxidise an alkene to an acid.
NCERT (2026-27 edition):
From Alkylbenzenes – “Aromatic carboxylic acids can be prepared by vigorous oxidation of alkyl benzenes with chromic acid or acidic or alkaline potassium permanganate. The entire side chain is oxidised to the carboxyl group irrespective of length of the side chain. Primary and secondary alkyl groups are oxidised in this manner while tertiary group is not affected. Suitably substituted alkenes are also oxidised to carboxylic acids with these oxidising reagents.”