Preparing amines and diazonium dyesEdexcel International A Level Chemistry: Subtopic test

1. 1
   A chemist wishes to make butylamine, CH₃CH₂CH₂CH₂NH₂, starting from 1-bromopropane, CH₃CH₂CH₂Br. Two different routes to primary amines are being considered.

   (a)

   Which reagents and conditions would convert 1-bromopropane into butylamine in two steps?

   [1 mark]

   • AExcess ethanolic ammonia heated in a sealed tube
   • BNaOH(aq), heated under reflux; then LiAlH₄ in dry ether
   • CKCN dissolved in ethanol, heated under reflux; then heated with dilute hydrochloric acid
   • DKCN dissolved in ethanol, heated under reflux; then LiAlH₄ in dry ether

   (b)

   Why is a large excess of ammonia used when a halogenoalkane is converted into a primary amine?

   [1 mark]

   • ASo that the amine formed is unlikely to meet and react with more halogenoalkane
   • BAmmonia acts as a catalyst and is not used up
   • CIt oxidises the halogenoalkane to the amine
   • DIt makes the reaction exothermic so heating is not needed

   (c)

   Write an equation for the reaction of 1-bromopropane with excess ammonia, using structural formulae, and state the conditions used.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Phenylamine is prepared in a school laboratory from nitrobenzene, C₆H₅NO₂ (Mr = 123). In one preparation, 12.3 g of nitrobenzene is reduced to phenylamine, C₆H₅NH₂ (Mr = 93), and the percentage yield is 60%.

   (a)

   Nitrobenzene is heated under reflux with tin and concentrated hydrochloric acid. Which organic species is present in the flask at the end of the reflux?

   [1 mark]

   • AC₆H₅NH₂
   • BC₆H₅N₂⁺
   • CC₆H₅NH₃⁺
   • DC₆H₅NO₂

   (b)

   What mass of phenylamine is obtained?

   [1 mark]

   • A9.30 g
   • B5.58 g
   • C3.35 g
   • D7.38 g

   (c)

   Write an equation for the reduction of nitrobenzene to phenylamine, using [H] to represent the reducing agent, and explain why the reaction mixture is finally made alkaline.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student prepares benzenediazonium chloride from phenylamine and then uses the solution straight away to make an azo dye.

   (a)

   Describe how benzenediazonium chloride is prepared from phenylamine. Give the reagents, the temperature and an equation.

   [3 marks]

   (b)

   The cold diazonium solution is added to a cold solution of phenol in sodium hydroxide. State what is seen, give an equation for the coupling reaction, and explain why the mixture is kept below 10 °C and why the phenol is dissolved in alkali.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Azo dyes are made from aromatic amines. A dye chemist is asked to plan the synthesis of the azo dye 4-hydroxyazobenzene, HOC₆H₄N=NC₆H₅, and to explain its properties.

   (a)

   Outline a synthesis of 4-hydroxyazobenzene starting from nitrobenzene. Give the reagents and conditions and the product of each stage.

   [6 marks]

   (b)

   Explain why 4-hydroxyazobenzene is coloured, and why the diazonium salt solution must be kept below 10 °C.

   [6 marks]

   Total for question 4: 12 marks

End of questions