Amines

• What is the reaction of methylamine with water?

  CH3NH2 + H2O ⇌ CH3NH3+ + OH-
• What is the reaction of ammonia with water?

  NH3 + H2O ⇌ NH4+ + OH-
• Why do primary aliphatic amines act as Bronsted-Lowry bases?

  The lone pair on nitrogen accepts protons
• Why are primary aliphatic amines considered weak bases?

  They produce a low concentration of hydroxide ions
• How do alkyl groups affect the basicity of primary aliphatic amines?

  They push electrons towards nitrogen, enhancing basicity
• Why do primary aromatic amines like phenylamine not form basic solutions?

  The lone pair on nitrogen delocalizes with the benzene ring
• What do amines form when they react with acids?

  Ammonium salts
• What is the reaction of methylamine with hydrochloric acid?

  CH3NH2 + HCl → CH3NH3+Cl-
• What happens when NaOH is added to an ammonium salt?

  It converts the salt back to the amine
• Why are ionic salts formed from amines soluble in acids?

  Due to strong ionic interactions
• How do secondary amines compare to primary amines in terms of basicity?

  Secondary amines are stronger bases than primary amines
• Why are tertiary amines not the strongest bases?

  They are less soluble in water
• What is the overall order of base strength among amines?

  Aromatic amines < ammonia < primary < tertiary < secondary
• What do all amines react with to form ammonium salts?

  Acids
• What is the reaction of diethylamine with an acid?

  (CH3CH2)2NH + H+ → (CH3CH2)2NH2+
• How can primary amines be formed from halogenoalkanes?

  By nucleophilic substitution with ammonia
• What is a disadvantage of forming primary amines through nucleophilic substitution?

  Further reactions lead to secondary and tertiary amines
• What is the first step in forming a primary amine from a halogenoalkane?

  Attack by ammonia to form an intermediate
• What happens in the second step of the nucleophilic substitution mechanism?

  Ammonia removes a proton from the intermediate
• How can a tertiary amine be formed from a secondary amine?

  By reacting with a halogenoalkane
• What promotes the formation of a quaternary ammonium salt?

  Using an excess of halogenoalkane
• What are quaternary ammonium salts used for?

  As cationic surfactants
• How do surfactants affect surface tension?

  They reduce the surface tension of liquids
• What is the first step in preparing amines from nitriles?

  Convert halogenoalkane to nitrile using KCN
• What is the second step in preparing amines from nitriles?

  Reduce nitrile to amine using LiAlH4
• What reagents can reduce nitroarenes to aromatic amines?

  Sn and HCl or Fe and HCl
• What is formed when nitrobenzene is reduced?

  Phenylamine and an ionic salt
• What is a disadvantage of reducing nitroarenes to aromatic amines?

  It is a two-step reaction with low yield
• How do aliphatic amines and phenylamine react with acyl chlorides?

  They form amides in nucleophilic addition-elimination reactions
• What is the change in functional group when acyl chlorides react with primary amines?

  Acyl chloride to secondary amide
• What is the change in functional group when acid anhydrides react with primary amines?

  Acid anhydride to secondary amide
• What are the steps to prepare amines from nitriles?

  1. Convert halogenoalkane to nitrile using KCN in aqueous ethanol (heat under reflux).
  2. Reduce nitrile to amine using LiAlH4 or H2 with a Ni catalyst.
• What is the overall scheme of reactions for amine formation?

  • Use excess ammonia to maximize primary amine.
  • Use excess halogenoalkane to promote quaternary salt formation.