Carboxylic Acids: Types of Reactions
Carboxylic acid exhibits a number of reactions depending on the involvement of a specific part of the -COOH group. It mainly includes nucleophilic acyl substitution reaction, in which a hydroxy group of -COOH is replaced by another nucleophile, and the acidic behavior of carboxylic acids, which is due to the cleavage of O-H bond in -COOH group. The former reaction leads to the conversion of carboxylic acid into a variety of different derivatives/categories of organic compounds, whereas the latter converts it into salts which find applications in many industries, like soap and detergent synthesis and pharmaceutical industries. Other important types of chemical reactions involve reduction of -COOH group, decarboxylation, electrolysis and substitution reactions in the hydrocarbon part at α-carbon atom.
Identify the correct product of the following reaction:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Adipic acid
Hot acidified potassium permanganate is a vigorous oxidising agent that breaks a C=C double bond completely. Each carbon of the double bond is oxidised according to what it carries:
a carbon with one hydrogen (–CH=) becomes a –COOH group;
a carbon with no hydrogen (>C=) becomes a ketone group;
a terminal =\( \ce{CH2} \) becomes \( \ce{CO2} \).
In cyclohexene, each carbon of the double bond carries one hydrogen. Breaking the double bond opens the ring, and both ends become –COOH groups. The six-carbon ring becomes a straight six-carbon chain with a carboxyl group at each end:
\( \displaystyle \ce{C6H10 + 4[O]} \xrightarrow[\text{heat}]{\ce{KMnO4/H2SO4}} \ce{HOOC-(CH2)4-COOH} \)
This is hexanedioic acid, known as adipic acid.
Why the other options are incorrect
Option (1) Phthalic acid — Incorrect. Benzene-1,2-dicarboxylic acid is aromatic and has eight carbons. It comes from the oxidation of o-xylene, not from cyclohexene.
Option (2) Terephthalic acid — Incorrect. Benzene-1,4-dicarboxylic acid comes from the oxidation of p-xylene.
Option (3) Glutaric acid — Incorrect. Pentanedioic acid has only five carbons, so it would come from cyclopentene.
NCERT (2026-27 edition):
Methods of Preparation of Carboxylic Acids – …
