Question

A mono-substituted aromatic compound P decolourizes bromine water, gives a purple red colour with aqueous FeCl$_3$ and is also soluble in aqueous NaOHCompound P undergoes acetylation with reagent Q in the presence of a base to give R as the major productReagent Q displays two characteristic bands at 1830 cm$^{-1}$ and 1750 cm$^{-1}$ in its IR spectrumP, Q and R are

• A. A
• B. B
• C. C
• D. D

Hint:

FeCl$_3$ colour test and NaOH solubility strongly indicate phenolAcid anhydrides show two carbonyl IR bands near 1830 cm$^{-1}$ and 1750 cm$^{-1}$

Answer 1

The Correct Option is C

Step 1: Identify compound P from bromine water test.
Compound P decolourizes bromine waterThis indicates that the aromatic ring is highly activated towards electrophilic substitutionPhenol gives this test because the $-OH$ group strongly activates the benzene ring

Step 2: Identify compound P from FeCl$_3$ test.
Compound P gives purple red colour with aqueous FeCl$_3$This is a characteristic test of phenolic compoundsTherefore, P must contain a phenolic $-OH$ group

Step 3: Confirm P from NaOH solubility.
Phenol is acidic enough to dissolve in aqueous NaOH by forming sodium phenoxide
\[ \text{C}_6\text{H}_5\text{OH} + \text{NaOH} \rightarrow \text{C}_6\text{H}_5\text{ONa} + \text{H}_2\text{O} \]
Thus, compound P is phenol

Step 4: Identify reagent Q from IR data.
Reagent Q shows two characteristic IR absorption bands at 1830 cm$^{-1}$ and 1750 cm$^{-1}$Such two carbonyl stretching bands are characteristic of acid anhydrides

Step 5: Match Q with given options.
Among the given reagents, acetic anhydride contains two carbonyl groups and shows two strong carbonyl stretching frequenciesTherefore, Q is acetic anhydride
\[ \text{Q} = (\text{CH}_3\text{CO})_2\text{O} \]

Step 6: Acetylation of phenol.
Phenol undergoes acetylation with acetic anhydride in the presence of baseThe hydrogen of phenolic $-OH$ is replaced by acetyl group to form phenyl acetate
\[ \text{C}_6\text{H}_5\text{OH} + (\text{CH}_3\text{CO})_2\text{O} \rightarrow \text{C}_6\text{H}_5\text{OCOCH}_3 \]

Step 7: Conclusion.
Therefore, P is phenol, Q is acetic anhydride, and R is phenyl acetateThis combination is shown in option (C)
\[ \boxed{\text{C}} \]