Home / AS & A Level Chemistry 33.3 Acyl chlorides: Exam Style Questions Paper 4

AS & A Level Chemistry 33.3 Acyl chlorides: Exam Style Questions Paper 4

A Level Chemistry Paper 4 - All Chapters
Question

Methyl red can be synthesised as shown in Fig. 7.1.

(a) (i) Give the systematic name of P.

(ii) P can be synthesised as shown in Fig. 7.2.

Suggest reagents and conditions for this reaction.
(iii) A student attempts to synthesise P by an alternative route, as shown in Fig. 7.3. Compound T is the major product in this reaction rather than P.

Explain why T is the major product in this reaction.

(b) S reacts in a similar way to phenol in step 3.
(i) Draw the structures of Q, R and S in the boxes in Fig. 7.1. 
(ii) Suggest reagents and conditions for steps 1 and 2 in Fig. 7.1.

▶️ Answer/Explanation
Solution

(a)(i)

Answer: 2-nitrobenzoic acid OR 2-nitrobenzenecarboxylic acid.

Explanation: The systematic name of P is derived from the parent structure benzoic acid with a nitro group at the 2-position (ortho to the carboxyl group).

(a)(ii)

Answer: Hot/reflux conditions with acidified/alkaline \( KMnO_4 \) (potassium permanganate).

Explanation: The oxidation of a methyl group (\( -CH_3 \)) to a carboxyl group (\( -COOH \)) requires a strong oxidising agent like \( KMnO_4 \) under heating or reflux.

(a)(iii)

Answer: The carboxyl group is electron-withdrawing and meta-directing, favouring nitration at the 3- and 5-positions (T) over the 2-position (P).

Explanation: Electron-withdrawing groups like \( -COOH \) deactivate the benzene ring and direct electrophilic substitution (nitration) to the meta positions, making T the major product.

(b)(i)

Answer: Structures of Q, R, and S

Explanation: Q is the diazonium salt formed from P, R is the intermediate after coupling, and S is the final methyl red structure (as shown in the image).

(b)(ii)

Answer: Step 1: \( NaNO_2 \) and dilute HCl at 0–5 °C (diazotisation).
Step 2: \( N,N \)-dimethylaniline in acidic/alkaline medium (coupling reaction).

Explanation: Step 1 converts the amine to a diazonium salt, while Step 2 involves an azo coupling reaction with \( N,N \)-dimethylaniline to form methyl red.

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