Amines & Amides

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  • Created by: J.E.C.
  • Created on: 12-04-14 15:23

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

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Properties

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

Neutralisation reaction

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Ligands, Nucleophiles & Amide formation

As ligands

Lone pair of electrons on N atom can bond to metal ions.

As nucleophiles

Lone pair on N atom attacks electrophiles. 

Undergo substitution reactions with halogenoalkanes to form secondary / tertiary amines

Amide Formation

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

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Amides & their hydrolysis

Primardy amides formed from ammonia & acyl chloride

Secondary amides formed from an amine & an acyl chloride

Hydrolysing amides

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

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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.

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