Organic synthesis routesAQA A-Level Chemistry: Subtopic test

1. 1
   A pharmaceutical company is redesigning the production of a drug intermediate. The existing process has five steps, is carried out in a chlorinated organic solvent and starts from a toxic compound. The company wants a greener process.

   (a)

   Which is the main reason chemists try to design processes that do not need a solvent?

   [1 mark]

   • AIt increases the percentage atom economy of the reaction
   • BIt reduces waste and the hazards of flammable or toxic solvents
   • CIt increases the activation energy of the reaction
   • DIt guarantees that the product is pure without further purification

   (b)

   A redesigned process has only four steps, each with a yield of 80%. What is the overall percentage yield?

   [1 mark]

   • A80%
   • B64%
   • C32%
   • D41%

   (c)

   Explain why chemists aim to design processes that use no solvent and that start from non-hazardous materials.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Ethanol can be made by two routes. Route A: hydration of ethene with steam, C₂H₄ + H₂O → C₂H₅OH. Route B: hydrolysis of bromoethane with aqueous sodium hydroxide, C₂H₅Br + NaOH → C₂H₅OH + NaBr. Relative atomic masses: H = 1.0, C = 12.0, O = 16.0, Na = 23.0, Br = 79.9.

   (a)

   Which statement about the atom economy of the two routes is correct?

   [1 mark]

   • ARoute A has 100% atom economy because ethanol is the only product
   • BRoute B has 100% atom economy because all the reactants are used up
   • CRoute B has the higher atom economy because it uses sodium hydroxide
   • DBoth routes have the same atom economy because both make ethanol

   (b)

   What is the percentage atom economy of Route B for making ethanol?

   [1 mark]

   • A69.1%
   • B46.0%
   • C30.9%
   • D100%

   (c)

   Use the atom economies to justify why a chemist would prefer Route A to Route B.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A research chemist plans to make organic compounds from simple starting materials. Only reactions from the A Level specification are to be used, and each synthesis may have up to four steps.

   (a)

   Devise a two-step synthesis of propan-1-amine, CH₃CH₂CH₂NH₂, from bromoethane. For each step, give the reagents and conditions and the name or formula of the organic product.

   [3 marks]

   (b)

   Devise a three-step synthesis of propanone, CH₃COCH₃, from propene, CH₃CH=CH₂. For each step, give the reagents and conditions and the organic product. Explain why the first step gives the product needed for this synthesis.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A company manufactures an intermediate for a pain-relief drug. The existing route has five steps, uses an organic solvent and a toxic starting material, and has an atom economy of 28%. A new route has two steps, needs no solvent, uses non-hazardous starting materials and has an atom economy of 85%. The company also makes aromatic products from benzene, which it converts into phenylamine and then into N-phenylethanamide.

   (a)

   Evaluate the new route compared with the existing route, explaining why chemists aim for the features of the new route.

   [6 marks]

   (b)

   Devise a three-step synthesis of N-phenylethanamide, C₆H₅NHCOCH₃, from benzene. For each step give the reagents and conditions and the organic product, and name the mechanism of the first step.

   [6 marks]

   Total for question 4: 12 marks

End of questions