Amines

• What is the equilibrium reaction for methylamine in water?

  CH3NH2 + H2O ⇌ CH3NH3+ + OH-
• Why do primary aliphatic amines act as Bronsted-Lowry bases?

  They can accept protons due to lone pair.
• Why are primary aliphatic amines considered weak bases?

  They produce low concentrations of hydroxide ions.
• How do primary aliphatic amines compare to ammonia in base strength?

  They are stronger due to electron-releasing alkyl groups.
• Why do primary aromatic amines like phenylamine not form basic solutions?

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

  Acids
• 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 base strength?

  They are stronger due to more alkyl groups.
• Why is the trend of tertiary amines being the strongest amine base not valid?

  They are less soluble in water than secondary amines.
• What is the overall order of base strength for amines?

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

  Acids
• What is the reaction for forming a primary amine from halogenoalkanes?

  CH3CH2Br + 2NH3 → CH3CH2NH2 + NH4Br
• What is the role of ammonia in the nucleophilic substitution reaction?

  It acts as the initial nucleophile.
• What is the first step in the mechanism for forming a primary amine?

  The nucleophile attacks the halogenoalkane.
• 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 one maximize the amount of primary amine formed?

  By using an excess of ammonia.
• What occurs when forming a tertiary amine from a secondary amine?

  The same reaction mechanism occurs with 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 chloride reacts with a primary amine?

  Acyl chloride to secondary amide.
• What is the change in functional group when acid anhydride reacts with a primary amine?

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

  1. Convert halogenoalkane to nitrile using KCN.
  2. Reduce nitrile to amine using LiAlH4 or H2 with Ni catalyst.
• What are the overall reactions for forming amines from halogenoalkanes?

  • Primary amine: CH3CH2Br + 2NH3 → CH3CH2NH2 + NH4Br
  • Secondary amine: CH3CH2NH2 + CH3Br → CH3CH2NHCH3 + NH4Br
  • Tertiary amine: CH3CH2NHCH3 + CH3Br → (CH3)3N + NH4Br
  • Quaternary ammonium salt: (CH3)3N + CH3Br → (CH3)4N+ + Br-
• What are the differences in base strength among different types of amines?

  • Aromatic amines: Weakest
  • Ammonia: Weak
  • Primary amines: Stronger
  • Secondary amines: Strongest
  • Tertiary amines: Less strong than secondary