Amines (DONE) Flashcards
How can aliphatic primary amines be prepared from halogenoalkanes?
- Conditions and Reagents (explain why certain reagents and conditions are used) (2 marks)
- Reaction mechanism (1 mark)
REAGENTS
- Excess ammonia dissolved in ethanol (excess to prevent amine formed reacting with halogenoalkane)
CONDITIONS
- Sealed tube (as ammonia is a gas) and heat
Nucleophilic Substitution
Give the simple and detailed versions of the preparation of aliphatic amines from halogenoalkanes, take bromomethane as an example.
Hint: The question will ask why excess NaOH is used in this reaction
(3 marks)
SIMPLE
- Bromomethane + ammonia -> methylamine + HBr
DETAILED
- Ammonia + HBr -> Ammonium bromide
or Methylamine + HBr -> Methylammonium bromide salt
- Salt + NaOH (aq) -> methylamine + Water + NaBr
How can primary aliphatic amines be produced from nitriles?
- Reagents (1 mark)
- Type of reaction (1 mark)
- Lithium aluminium hydride
- Reduction
How can primary aromatic amines be prepared from nitrobenzene?
- Conditions (1 mark)
- Reagents (2 marks)
- How is the end product achieved
- Reducing agent of Tin and concentrated hydrochloric acid
- Heat under reflux
- Steam distillation
Give the simple and detailed versions of the preparation of phenylamine from nitrobenzene
(3 marks)
SIMPLE
Nitrobenzene + 6[H] -> Phenylamine + 2H₂O
DETAILED
- Phenylamine + HCl -> Phenylammonium chloride salt
- Phenylammonium ion + Hydroxide ion -> Phenyl ammonia + 2H₂O
Describe briefly how amines are weak bases
(2 marks)
- They have a lone pair of electrons on the nitrogen
- This can be used to accept a proton by means of co-ordinate bonding
Explain why primary aliphatic amines (methylamine) are stronger bases than ammonia
(3 marks)
- The alkyl groups ‘push’ electrons towards/ release the electrons slightly towards the nitrogen atom (positive inductive effect)
- Making it more electron-rich/electron density of the nitrogen lone pair than the nitrogen in ammonia
- Thus increasing its availability to form a coordinate bond to a proton
Explain why primary aliphatic amines (methylamine) are stronger bases than phenylamine
(3 marks)
- The lone pair of electrons on the nitrogen of phenylamine
- Interacts with the delocalised pi electron system
- Therefore it is less likely to accept a proton
Describe the reaction of amines with ethanoyl chloride (ethanoylation)
- Reaction mechanism (3 different answers)
- Products formed
- Condensation/Elimination/Nucleophilic addition
- Amide and HCl
Describe the reaction of primary aliphatic amines with nitric acid/nitrous acid
- Show how nitric (III) acid is obtained
- General formula equation
- Conditions
- Observations
IN SITU
- NaNO₂ + dil. HCl -> HNO₂ + NaCl
Reaction
- R-NH₂ + HNO₂ -> R-OH + N₂ -> H₂O
- Between 0 and 10 degrees, ideally 5
- Effervescence of nitrogen gas
Describe the reaction of primary aromatic amines with warm nitric acid/nitrous acid
- General formula equation
- Conditions
- Observations
- C₆H₅NH₂ + HNO₂ -> C₆H₅OH + N₂ -> H₂O
- Room temperature (>10)
- Effervescence of nitrogen gas
Describe the reaction of primary aromatic amine with cold nitrous acid to form the diazonium salt
- The full balanced equation
- Conditions
- Phenylamine + HCl + HNO₂ (or NaNO₂ with HCl) -> Benzenediazonium chloride/C₆H₅-Cl⁻N⁺≡N + 2H₂O
- 5 degrees/ below 10
Show how the formation of the Azo Dye via coupling reactions. Give:
- The full balanced equation
- Observation
- Type of reaction
- What the azo group is
- Conditions
- Benzenediazonium chloride + Phenol + NaOH -> C₆H₅-N=N-H₄C₆OH + NaCl + H₂O
- Coupling/Electrophilic substitution
- Yellow orange precipitate
- N=N is the azo group
- 5 degrees
What is a chromophore?
(2 marks)
- Group of atoms/structural unit responsible for absorption of visible light or ultraviolet radiation
- Responsible for colour when absorption is in the visible region
How does colour appear?
- The chromophore absorbs all the colour of white/visible light apart from orange
- Orange is then reflect (solid) or transmitted (solution)
