Question

Consider the following reaction sequence: 

Given: Compound (x) has percentage composition \(76.6%\ \text{C}\), \(6.38%\ \text{H}\) and vapour density \(=47\). Compound (y) develops a characteristic colour with neutral \(\mathrm{FeCl_3}\) solution. Identify the {INCORRECT statement.}

• A. Compound \(y\) will dissolve in \(\mathrm{NaHCO_3}\) and evolve a gas.
• B. Both compounds \(x\) and \(y\) will burn with sooty flame.
• C. Compound \(x\) is more acidic than compound \(y\).
• D. Both compounds \(x\) and \(y\) will dissolve in \(\mathrm{NaOH}\).

Hint:

Carboxylic acids are always stronger acids than phenols, and the Kolbe–Schmitt reaction is a key test reaction for phenol.

Answer 1

The Correct Option is C

Step 1: Identify compound \(x\) Given vapour density: \[ \text{Molecular mass} = 2 \times 47 = 94 \] Let the molecular formula be \( \mathrm{C_xH_yO_z} \). From percentage composition: \[ \frac{12x}{94} \times 100 = 76.6 \Rightarrow x \approx 6 \] \[ \frac{y}{94} \times 100 = 6.38 \Rightarrow y \approx 6 \] Thus: \[ \text{Compound } x = \mathrm{C_6H_6O} \] The most common aromatic compound with formula \(\mathrm{C_6H_6O}\) is phenol.
Step 2: Identify compound \(y\) The reaction conditions:
\(\mathrm{CO_2 + NaOH}\), high pressure and temperature
Followed by acidification This is the {Kolbe–Schmitt reaction}, where phenol is converted into salicylic acid. \[ \text{Phenol} \xrightarrow{\text{Kolbe–Schmitt}} \text{Salicylic acid} \] Salicylic acid gives a characteristic violet colour with neutral \(\mathrm{FeCl_3}\), confirming the identity of compound \(y\).
Step 3: Evaluate each statement Statement (A): Salicylic acid contains a \(-\mathrm{COOH}\) group and reacts with \(\mathrm{NaHCO_3}\) to release \(\mathrm{CO_2}\). \[ \Rightarrow \text{Correct} \] Statement (B): Both phenol and salicylic acid are aromatic compounds and hence burn with a sooty flame. \[ \Rightarrow \text{Correct} \] Statement (C): Phenol is {less acidic} than salicylic acid. Salicylic acid has both \(-\mathrm{COOH}\) and phenolic \(-\mathrm{OH}\), making it significantly more acidic. \[ \Rightarrow Incorrect \] Statement (D): Both phenol and salicylic acid dissolve in \(\mathrm{NaOH}\) due to formation of phenoxide and salicylate ions. \[ \Rightarrow \text{Correct} \] Final Conclusion: \[ \boxed{\text{Statement (C) is incorrect}} \]