Organic synthesisAQA A-Level Chemistry: Topic test

1. 1
   A chemist wants to make propylamine, CH₃CH₂CH₂NH₂, from bromoethane, CH₃CH₂Br, in two steps, using only reactions from the A Level specification.

   (a)

   Which reagent and conditions should be used for the first step?

   [1 mark]

   • APotassium cyanide in aqueous ethanol, heated under reflux
   • BAqueous sodium hydroxide, heated under reflux
   • CConcentrated ammonia in ethanol, heated in a sealed tube
   • DPotassium hydroxide in ethanol, heated

   (b)

   What is the intermediate compound formed in the route?

   [1 mark]

   • APropylamine
   • BEthylamine
   • CPropanoic acid
   • DPropanenitrile

   (c)

   Explain why the chemist cannot make propylamine by heating bromoethane with excess ammonia, and how the route used overcomes this problem.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A chemist plans to make butan-2-one, CH₃COCH₂CH₃, from but-1-ene, CH₂=CHCH₂CH₃, in three steps via 2-bromobutane and butan-2-ol.

   (a)

   Step 1 is the reaction of but-1-ene with hydrogen bromide. What is the major product?

   [1 mark]

   • A1-bromobutane, CH₂BrCH₂CH₂CH₃
   • B1,2-dibromobutane
   • C2-bromobutane, CH₃CHBrCH₂CH₃
   • Dbutan-2-ol

   (b)

   Which reagent and conditions should be used for step 3, to convert butan-2-ol into butan-2-one?

   [1 mark]

   • ASodium tetrahydridoborate(III), NaBH₄, at room temperature
   • BAcidified potassium dichromate(VI), heated
   • CPotassium cyanide in ethanol
   • DConcentrated sulfuric acid, heated

   (c)

   Give the reagent and conditions for step 2 and name the type of reaction.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Cyclohexene, C₆H₁₀, is made by heating cyclohexanol, C₆H₁₁OH (Mᵣ = 100.0), with concentrated phosphoric acid, which acts as a catalyst. The cyclohexene (Mᵣ = 82.0) is distilled off as it forms. No solvent is used. Water is the only other product.

   (a)

   Write an equation for the reaction and calculate the percentage atom economy for making cyclohexene.

   [3 marks]

   (b)

   Explain why chemists aim to design processes that use no solvent and that have a high percentage atom economy.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A chemist devises a three-step route to make 2-hydroxypropanoic acid, CH₃CH(OH)COOH (Mᵣ = 90.0), from ethanol, CH₃CH₂OH, using only reactions from the A Level specification. In a trial of the route, the yields of the three steps were 85.0%, 90.0% and 80.0%.

   (a)

   Devise the three-step synthesis. For each step give the reagents and conditions and the organic product, and explain why the product of the first step is distilled off as it forms.

   [6 marks]

   (b)

   Calculate the overall percentage yield of the route and the mass of 2-hydroxypropanoic acid made from 0.500 mol of ethanol. Evaluate the route against the aims of designing production methods with fewer steps and non-hazardous starting materials.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   Phenylamine, used to make dyes, is made from benzene in two steps. In the first step benzene is converted to nitrobenzene. In the second step the nitrobenzene is converted to phenylamine.

   (a)

   Which reagents and conditions are used for the first step?

   [1 mark]

   • ADilute nitric acid at room temperature
   • BConcentrated nitric acid and concentrated sulfuric acid, below 50 °C
   • CNitrogen dioxide gas with an aluminium chloride catalyst
   • DAqueous sodium nitrite at room temperature

   (b)

   Why is the temperature of the first step kept below 50 °C?

   [1 mark]

   • ATo prevent more than one nitro group substituting into the ring
   • BTo prevent the nitrobenzene from being reduced
   • CTo make the reaction go faster
   • DTo prevent hydrolysis of the nitrobenzene

   (c)

   State the reagents used for the second step and explain why the mixture is made alkaline at the end of the second step.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A flavour company makes the ester propyl ethanoate, CH₃COOCH₂CH₂CH₃ (Mᵣ = 102.0), from propan-1-ol (Mᵣ = 60.0). Route 1: heat propan-1-ol with ethanoic acid (Mᵣ = 60.0) using concentrated sulfuric acid as a catalyst. Route 2: react propan-1-ol with ethanoyl chloride, CH₃COCl (Mᵣ = 78.5), at room temperature.

   (a)

   Which compound is the by-product in Route 2?

   [1 mark]

   • AWater
   • BEthanoic acid
   • CHydrogen gas
   • DHydrogen chloride

   (b)

   Which statement about Route 1 is correct?

   [1 mark]

   • AThe reaction goes to completion because sulfuric acid is a strong acid
   • BThe sulfuric acid is used up in the reaction
   • CThe reaction is reversible, so the yield is limited by the position of equilibrium
   • DHydrogen chloride is released as a by-product

   (c)

   Calculate the percentage atom economy for each route.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A chemist wants to convert propan-1-ol, CH₃CH₂CH₂OH, into propan-2-ol, CH₃CH(OH)CH₃, in three steps via propene and 2-bromopropane.

   (a)

   State the reagent and conditions for each of the three steps.

   [3 marks]

   (b)

   Explain why 2-bromopropane is the major product of step 2, and why this affects the overall yield of the route.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A chemist devises a three-step route from benzene to phenylethene, C₆H₅CH=CH₂ (Mᵣ = 104.0), the monomer for poly(phenylethene). The route uses only reactions from the A Level specification. In a trial the yields of the three steps were 76.0%, 90.0% and 85.0%.

   (a)

   Devise the three-step synthesis. For each step give the reagent and conditions and the organic product.

   [6 marks]

   (b)

   Calculate the overall percentage yield and the mass of phenylethene made from 39.0 g of benzene (Mᵣ = 78.0). Explain why chemists aim to design routes with fewer steps and with non-hazardous reagents, with reference to this route.

   [6 marks]

   Total for question 8: 12 marks

End of questions