Amines, amino acids, and proteins

• Aliphatic amines


  Amines without aromatic rings present
• Preparing primary aliphatic amines

  1. React ammonia with a halogenoalkane

  2. X = an electronegative species e.g. Cl, Br

  3. CH3CH2CH2Cl + NH3 Æ CH3CH2CH2NH3Cl

  4. CH3CH2CH2NH3Cl + NH3 Æ CH3CH2CH2NH2 + NH4Cl
• The second reaction is reversible so excess ammonia will push the equilibrium to the right
• Substitution of hydrogen atoms on nitrogen


  • Primary amines
  • Secondary amines
  • Tertiary amines
  • Quaternary ammonium salts (R4N+Cl- where R = any alkyl chain)
• Preparing aromatic amines


  1. Reduce nitroarenes such as nitrobenzene, refluxed at 100°C using a reducing agent of tin and concentrated HCl

  2. The tin and concentrated HCl react to form hydrogen
• Amines as Lewis bases

  The nitrogen atom on an amine has a lone pair of electrons which it can donate to a Lewis acid
• Amines as Brønsted-Lowry bases


  The nitrogen atom on an amine can accept a proton
• Reaction of amines with dilute inorganic acids

  1. Form alkylammonium salts

  2. CH3CH2NH2 + HCl Æ CH3CH2NH3+Cl-
• Amides


  A group of nitrogen-containing organic compounds that contain both an amine group and an acyl group
• Forming primary (1°) amides

  React acyl chlorides with ammonia
• Forming secondary (2°) amides


  Mix acyl chlorides with primary amines
• Forming tertiary (3°) amides


  Mix acyl chlorides with secondary amines
• α–amino acids


  Contain both the amine functional group and the carboxylic acid functional group (carboxyl group) attached to the same carbon atom
• Amino acids


  Amphoteric, meaning they have both acidic and basic properties and can exist as zwitterions, having no charge overall
• Isoelectric point


  The pH at which the overall charge of a molecule is zero
• Reactions of amino acids


  • Carboxylic acid group reacts with: metal oxides, alkalis, carbonates, alcohols
  • Amine group reacts with: inorganic acids e.g. HCl
• Optical isomers


  Species which are non-superimposable mirror images of each other. One isomer rotates plane-polarised light clockwise, and the other rotates it anticlockwise
• Optical isomerism


  A form of stereoisomerism that occurs as a result of chirality in molecules
• Chiral centre


  A carbon atom with 4 different groups attached (it is asymmetric). Denoted by an asterisk
• Amino acids have a chiral centre provided the R group is not just -H, -COOH or -NH2
• A 50:50 mix of the enantiomers (a racemic mixture) will have no overall effect on plane-polarised light as the effects from the two enantiomers cancel out
• Amines


  Weak bases
• Primary amines


  The lone pair of electrons on the N atom is readily donated due to the extra electron density from the alkyl groups
• Aryl amines


  The lone pair of electrons on the nitrogen atom is attracted into the benzene ring, so the electron pair is less easily donated
• Amines as nucleophiles


  The lone pair of electrons on the nitrogen atom allows them to act as nucleophiles
• Nucleophilic substitution of haloalkanes with ammonia

  Forms amines
• Nucleophilic substitution of haloalkanes with primary amines


  Forms secondary amines
• Reaction of haloalkanes with secondary amine

  Forms tertiary amines
• Reaction of haloalkanes with tertiary alkanes

  Forms quaternary ammonium salts
• Quaternary ammonium salts


  Contain a large alkyl group and are often used as cationic surfactants. They have one long non–polar hydrocarbon chain and a charged end.
• Nucleophilic addition–elimination reactions of ammonia and primary amines


  With acyl chlorides and acid anhydrides
• When ammonia reacts, the product formed is a primary amide
• Primary amines react by the same mechanism, but the product formed is an N–substituted (secondary) amide