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Learn7405Paper 2 · Paper 2: Organic chemistryOrganic synthesisMulti-step synthesis
Organic synthesis · Subtopic 2 of 2

Multi-step Synthesis

A2 synthesis combines aliphatic and aromatic reactions. Key aromatic links: benzene → (conc. HNO₃/H₂SO₄) nitrobenzene → (Sn/HCl, NaOH) phenylamine → (NaNO₂/HCl < 10 °C) diazonium → (phenol/NaOH) azo dye, or (warm water) phenol. Benzene → (RCl/AlCl₃) alkylbenzene → (KMnO₄/OH⁻, heat) benzoic acid. Benzene → (RCOCl/AlCl₃) aryl ketone → (NaBH₄) secondary alcohol. Acyl chlorides make esters and amides. Plan by retrosynthesis, give reagents and conditions, and recognise each step's reaction type. Purify solids by recrystallisation and check purity by melting point.

Cambridge 9701 Paper 4Edexcel YCH11 WCH15AQA 7405 Paper 2≈ 50 minRevision 1 · updated 2026-11-01
Section 1 of 14

Learning objectives

  • Recall aromatic reaction routes.
  • Plan syntheses of up to four steps.
  • Name reaction types for each step.
  • Describe purification and purity checks.
Pause and think

How could you make benzoic acid from benzene in two steps?

Section 2 of 14

Core idea

Start hereDesigning a route

A drug chemist starts with cheap benzene and ends with a medicine. Each step is a reaction you already know.

The big idea

Put groups onto the ring by electrophilic substitution, then change them with familiar aliphatic chemistry. Fewer, higher-yield steps are better.

Aromatic reaction map

Key links between aromatic compounds.

Worked exampleOverall yield

Four steps: 90%, 80%, 75%, 60%. Overall yield?

Goal
%.
Strategy
Multiply.
  1. 0.90×0.80=0.720.90\times0.80=0.72
    Two steps.
  2. 0.72×0.75×0.60=0.3240.72\times0.75\times0.60=0.324
    All four.
Answer32.4%.
✓ CheckBelow the worst step ✓.
Exam tipPurity Recrystallise from minimum hot solvent; a sharp melting point matching data shows purity.

Summary

  • Ring first, side chain second.
  • Give reagents, conditions, intermediates.
  • Recrystallise and test melting point.
Key words
Recrystallisation
Purifying a solid by dissolving in hot solvent and cooling.
HistoryWoodward. Robert Burns Woodward synthesised quinine, cholesterol and vitamin B₁₂ (with Eschenmoser, over 100 steps), earning the 1965 Nobel Prize.
Fun factIbuprofen's greener route. The BHC process cut ibuprofen manufacture from six steps to three, raising atom economy from about 40% to nearly 80%.
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