Preparation of aminesAQA A-Level Chemistry: Subtopic test

1. 1
   A student prepares butylamine, CH₃CH₂CH₂CH₂NH₂, from 1-bromobutane, CH₃CH₂CH₂CH₂Br. The 1-bromobutane is added to a large excess of ammonia dissolved in ethanol, and the mixture is heated in a sealed tube.

   (a)

   Which reagent and conditions are used to convert a halogenoalkane into a primary amine in this way?

   [1 mark]

   • AExcess ethanolic ammonia, heated in a sealed tube
   • BAqueous sodium hydroxide, heated under reflux
   • CTin and concentrated hydrochloric acid, heated under reflux
   • DLithium tetrahydridoaluminate in dry ether

   (b)

   Why is a large excess of ammonia used?

   [1 mark]

   • ATo increase the boiling point of the mixture
   • BTo act as a solvent in place of ethanol
   • CTo stop the ammonia from acting as a base
   • DTo reduce the chance of the butylamine formed reacting with more 1-bromobutane

   (c)

   Write an equation for the formation of butylamine and explain why two moles of ammonia are needed for each mole of 1-bromobutane.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Propylamine, CH₃CH₂CH₂NH₂, is prepared in industry from propanenitrile, CH₃CH₂CN. The propanenitrile is itself made by heating bromoethane with potassium cyanide in ethanol. The nitrile is then reduced to the primary amine.

   (a)

   Which reagent and solvent can be used to reduce propanenitrile to propylamine?

   [1 mark]

   • ADilute hydrochloric acid, heated under reflux
   • BLithium tetrahydridoaluminate (LiAlH₄) in dry ether
   • CExcess ethanolic ammonia
   • DAcidified potassium dichromate(VI)

   (b)

   How does the number of carbon atoms in propylamine compare with the number in the bromoethane from which the nitrile was made?

   [1 mark]

   • AOne fewer
   • BThe same
   • COne more
   • DTwo more

   (c)

   Write an equation for the reduction of propanenitrile using [H] to represent the reducing agent, and suggest one advantage of making a primary amine by this route rather than from a halogenoalkane and ammonia.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student reduces nitrobenzene, C₆H₅NO₂ (Mr = 123.0), to phenylamine, C₆H₅NH₂ (Mr = 93.0), by heating it under reflux with tin and concentrated hydrochloric acid. After the reaction the student adds excess sodium hydroxide solution and extracts the phenylamine. From 12.3 g of nitrobenzene the student isolates 6.51 g of phenylamine.

   (a)

   Write an equation for the reduction of nitrobenzene using [H], and explain why sodium hydroxide is added at the end of the reaction.

   [3 marks]

   (b)

   Calculate the percentage yield of phenylamine.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A pharmaceutical company needs the primary aliphatic amine ethylamine, CH₃CH₂NH₂, of high purity. Two routes are available: heating bromoethane with ammonia, or reducing ethanenitrile, CH₃CN. A dye company separately needs phenylamine, which is made from benzene.

   (a)

   Explain why heating bromoethane with ammonia gives a mixture of products, and why reducing ethanenitrile is a better route to a pure primary amine.

   [6 marks]

   (b)

   Describe how phenylamine is prepared from benzene in two stages, giving the reagents, conditions and equations, and state one use of phenylamine.

   [6 marks]

   Total for question 4: 12 marks

End of questions