Question

In the reaction sequence shown below, what is the mass (in grams) of product (C) formed?

Hint:

When the given mass equals molar mass, the substance is exactly one mole — product mass equals its molar mass if stoichiometry is 1:1.

Answer 1

Correct Answer: 228

Concept:

Sn/HCl reduces a nitro group (\(NO_2\)) to an amine (\(NH_2\)).
Acetic anhydride acetylates the amine group to form an amide.
\(NHCOCH_3\) and \(CH_3\) are ortho–para directing groups.
Bromination occurs at the most activated available position.
Step 1: Identify compound (A). Compound (A) is p-nitrotoluene. Molar mass of p-nitrotoluene: \[ C_7H_7NO_2 = 137\ \text{g mol}^{-1} \] Given mass \(=137\ \text{g}\Rightarrow 1\ \text{mol}\)
Step 2: Formation of compound (B). \[ \text{Sn/HCl reduces } NO_2 \rightarrow NH_2 \] Thus, (B) is p-toluidine: \[ C_7H_9N \]
Step 3: Acetylation of (B). \[ NH_2 \xrightarrow{(CH_3CO)_2O} NHCOCH_3 \] Compound formed is p-methylacetanilide: \[ C_9H_{11}NO \]
Step 4: Bromination. Both \(CH_3\) and \(NHCOCH_3\) are ortho–para directing groups. Para positions are already occupied, so bromination occurs at one ortho position. Final compound (C): \[ C_9H_{10}BrNO \]
Step 5: Calculate molar mass of (C). \[ 9\times12 + 10\times1 + 14 + 16 + 80 \] \[ =108 + 10 + 14 + 16 + 80 = 228\ \text{g mol}^{-1} \]
Step 6: Mass of product formed. Since starting compound is \(1\) mole and reactions are \(1{:}1\): \[ \boxed{ \text{Mass of (C)} = 228\ \text{g} } \]