Naming & Characteristics
Amines resemble ammonia but with alkyl groups replacing some of the H atoms.
Primary amine = amines with one alkyl group
Secondary = have two alkyl groups
Tertiary = have three alkyl groups
Higher homologues named with prefix 'amino' eg 2-aminopropane
Diamine = amines with two amino groups attached
Low molecular mass = gas / volatile liquid - strong smells
Most properties due to the lone pair of electrons on the N atom, responsible for;
> Very soluble in water > A base > A ligand > A nucleophile
Solubility of amines
Can form H bonds to water. Amines with larger alkyl groups are less soluble because alkyl groups disrupt the H bonding in water.
Amines as bases
Lone pair on N can form dative covalent bonds. When electron pair donated to a H+ > acts as a H+ acceptor therefore a base.
NH3 + H2O --> NH4+ + OH-
Ammonium ion = NH4+. Amines act in the same way = proton acceptor - solution contains OH so is alkaline.
Amines also react with acids = H3O+ = strong proton donor - reaction goes to completion
Ligands, Nucleophiles & Amide formation
Lone pair of electrons on N atom can bond to metal ions.
Lone pair on N atom attacks electrophiles.
Undergo substitution reactions with halogenoalkanes to form secondary / tertiary amines
Undergo acylation (acyl group added to an amine) > amide formed
eg Ethanoyl Chloride + Ammonia --> Ethanamide (primary amide)
Very vigorous reaction even at room temp (acyl chlorides v reactive). Can react violently with water to form carboxylic acids = ANHYDROUS conditions must be used
Primary amine + an acyl chloride --> secondary amide + HCl
Amides & their hydrolysis
Primardy amides formed from ammonia & acyl chloride
Secondary amides formed from an amine & an acyl chloride
The C-N bond is broken.
Heat amide under reflux with mod conc aq acid or alkali
If acid catalyst used --> product contains ammonium ions
If alkali catalyst used --> carboxylic acid loses an H+, product contain carboxylate ions
Condensation polymers involving NH2 group
NH2 group react with COOH or -CO-Cl --> secondary amide formed = Condensation reaction: two molecules react together to form a larger molecule with the elimination of a small molecule.
Condensation polymerisation: when diamines and dicarboxylic acids which have reactive groups in two places - can form polymer chains. Monomer units linked by amide groups. These polymers are polyamides or Nylons.
Proteins: also condensation polymers, with peptide links and monomers are amino acids.