Amines

• What is the equilibrium reaction for methylamine in water?

  CH3NH2 + H2O ⇌ CH3NH3+ + OH-
• What is the equilibrium reaction for ammonia in water?

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

  Because the lone pair of electrons on nitrogen can form a dative covalent bond with H+
• Why are primary aliphatic amines considered weak bases?

  They produce only a low concentration of hydroxide ions
• How do primary aliphatic amines compare to ammonia in terms of base strength?

  They are stronger bases than ammonia
• What effect do alkyl groups have on the base strength of primary aliphatic amines?

  Alkyl groups are electron releasing and increase the availability of the lone pair on nitrogen
• Why do primary aromatic amines like phenylamine not form basic solutions?

  The lone pair on nitrogen delocalizes with the benzene ring
• What do amines react with to form ammonium salts?

  Amines react with acids
• What is the reaction of methylamine with hydrochloric acid?

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

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

  Because of the strong ionic interactions
• Why are secondary amines stronger bases than primary amines?

  They have more alkyl groups that push electron density onto nitrogen
• Why is the trend of tertiary amines being the strongest bases not observed?

  Tertiary amines are less soluble in water, making them weaker bases
• What is the overall order of base strength among amines?

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

  Acids
• What is the reaction of a primary amine with a halogenoalkane?

  It forms a secondary amine and ammonium salt
• What is the mechanism for forming a primary amine from halogenoalkanes?

  A nucleophilic substitution reaction occurs
• What is the first step in the mechanism for forming a primary amine?

  The nucleophile attacks the halogenoalkane to form an intermediate
• What happens in the second step of the mechanism for forming a primary amine?

  A second ammonia removes a proton from the intermediate
• How can using excess ammonia affect the formation of primary amines?

  It can limit further reactions and maximize primary amine yield
• What is the reaction mechanism for forming a tertiary amine?

  The same nucleophilic substitution mechanism occurs as with secondary amines
• What promotes the formation of quaternary ammonium salts?

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

  They are used as cationic surfactants
• How do surfactants affect the surface tension of liquids?

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

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

  Reduce nitrile to amine using LiAlH4 or H2 with a Ni catalyst
• What is the disadvantage of reducing nitroarenes to aromatic amines?

  It is a two-step reaction that may have a low yield
• What reagents can reduce nitro groups to amine groups?

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

  It forms phenylammonium chloride
• How can phenylamine be obtained from phenylammonium chloride?

  By reacting it with NaOH
• What is the reaction of amines with acyl chlorides and acid anhydrides?

  They form amides in a nucleophilic addition-elimination reaction
• What is the change in functional group when a primary amine reacts with an acyl chloride?

  It changes to a secondary amide
• What are the conditions for the reaction of primary amines with acid anhydrides?

  Room temperature
• What is the reaction of acyl chloride with primary amine?

  RCOCl + 2CH3NH2 → RCONHCH3 + CH3NH3+Cl-
• What is the reaction of acid anhydride with primary amine?

  (RCO)2O + 2CH3NH2 → RCONHCH3 + [CH3NH3]+[RCO2]-
• What is the product of the reaction between acyl chloride and primary amine?

  Secondary amide
• What is the product of the reaction between acid anhydride and primary amine?

  Secondary amide