Amines, Amino acids and polymers

• Amines are organic compounds, derived from ammonia, NH3, in which one or more hydrogen atoms in ammonia have been replaced by a carbon chain or ring
• In an aliphatic amine: the nitrogen atom is attached to at least one straight or branched carbon chain (alkyl group, R). e.g. methylamine
• In an aromatic amine: the nitrogen atom is attached to an aromatic ring (aryl group, Ar) e.g. phenylamine
• Classifying amines: primary, secondary, tertiary - based on the number of alkyl or aryl groups attached to the nitrogen atom
• Amines occur commonly in nature with many being well known for their effects on the body
• Serotonin acts as a neurotransmitter, responsible for the control of appetite, sleep, memory and learning, temperature regulation, muscle contraction and depression
• Pseudoephedrine is an active ingredient in decongestion medications such as nose drops and in cold remedies. It works by shrinking nasal membranes and inhibiting nasal secretions
• There are many different ways of naming amins.
• One way to name a primary amine, with the NH2 group on the end of the chain, is by adding the suffix -amine to the name of the alkyl chain
• Where a primary amine contains an amine group on any other carbon, but carbon-1, the amine is named using the prefix amino- and a number is added to indicate the positions of the amine group along the chain.
• In secondary and tertiary amines, containing the same alkyl grouo, the prefixes di- or tri- are used to indicate the number of alkyl groups attached to the nitrogen atom e.g. (CH3)2NH is dimethylamine
• When two or more different groups are attached to a nitrogen atom, the compound is named as a N-substituted derivative of the large group e.g. CH3NHCH2CH2CH3 is N-methylpropylamine and CH3N(CH2CH3)CH2CH2CH3 is N-ethyl-N-methylpropylamine
• The smell of a decomposing organism is made up of all sorts of compounds, but amines and compounds of sulfur give the characteristic smell of decay. Most of the amines come from the breakdown of proteins, and two of the amines have such unpleasant odours that they have been named putrescine (1,4-diaminobutane) after the process of putrefaction and cadaverine (1,5-diaminopentane), after the Latin-derived word for a corpse - cadaver
• Putrescine and cadaverine are also components of bad breath - putrescine has an industrial use - it is a raw material for producing some polymers
• Amines behave as bases in their chemical reactions as the lone pair of electrons on the nitrogen atom can accept a proton
• When an amine accepts a proton, a dative covalent bond is formed between the lone pair of electrons on the nitrogen atom and the proton
• Amines are bases and they neutralise acids to make salts.
• Formation of primary amines: ammonia has a lone pair of electrons on the nitrogen atom which allows ammonia to act as a nucleophile in a substitution reaction with a haloalkane. The product of this reaction is an ammonium salt. Aqueous alkali is then added to generate the amine from the salt
• e.g. formation of propylamine from 1-chloropropane and ammonia:

  salt formation:

  CH3CH2CH2Cl + NH3 = CH3CH2CH2NH3+CL-

  1-chloropropane propylammonium chloride (salt)

  amine formation:

  CH3CH2CH2NH3+CL- + NaOH = CH3CH2CH2NH2 + NaCl + H2O

  propylammonium chloride propylamine
• Essential conditions for this reaction:

  1. ethanol is used as the solvent. This prevents any substitution of the haloalkane by water to produce alcohols
  2. Excess ammonia is used. This reduces further substitution of the amine group to form secondary and tertiary amines
• HOWEVER - this reaction is unsuitable for making a pure primary amine. The product still contains a lone pair of electrons on the nitrogen atom that can react further with a haloalkane to form a secondary amine. The product of this reaction is again called an ammonium salt
• CH3CH2CH2Cl + CH3CH2CH2NH2 = (CH3CH2CH2)2NH2+Cl-

  propyl amine dipropylammonium chloride (salt)

  The secondary amine is obtained from the salt by reacting the product with sodium hydroxide