Amines and Amides
The NH2 group is called the AMINO group. The lone pair on on the N atom is responsible for amines being bases, nucleophiles and ligands.
CH3CH2CH2CH2CH2NH2 is either aminopentane or pentylamine
A base is a proton acceptor.
Amines dissolve in water and acids forming weak alkaline solutions, creating an alkylammonium ion and another expelled ion (usually OH-)
The lone pair on the nitrogen atom forms a dative covalent bond with the hydrogen ion.
A nucleophile is an electron pair donor.
Primary amines react with halogenoalkanes to form secondary amines, then they react with halogenoalkanes to form tertiary amines.
Amines and Amides 2
The primary amine acts as a nucleophile, attacking the positive carbon in the halogenoalkane.
Successive hydrogen groups are replaced by alkyl groups- alkylation reaction.
Amines react with acyl chlorides (COCl) to form secondary amides- Acylation reaction
When the hydrogen is replaced by an ethanoyl group (CH3CO) then it's Ethanoylation.
Primary amides have the structural formula -CONH2.
Secondary amides have the structural formula -CONH-
A polyamide has 2 amide groups on either side of the molecule.
Hydrolysis of Amides
The C-N bond in an amide is broken.
Amines and Amides 3
In an acid hydrolysis:
- Moderately concentrated HCl acid is used under reflux.
- Carboxylic acid and ammonium ion is formed.
In an alkaline hydrolysis:
- Moderately concentrated alkali NaOH is used under reflux.
- Amine and carboxylate anion is formed.
Amides are neutral.
Amides are dehydrated using P4O10, and leaves a CN group in the place of the NH2.
Polyamides, Nylon and Kevlar
In Nylon, the repeating unit contains chains of carbon atoms.
Nylon 6,6 contains 2 monomers, a carboxylic acid and an amine. They react together in a CONDENSATION POLYMERISATION reaction.
Due to the slow reaction between a diamine and a dicarboxylic acid, an acyl chloride derivative of the acid is used.
Naming- The first number is the No, of carbons in the diamine and the second number is the No. of carbons in the dicarboxylic acid.
Nylon is strong, tough, rigid and abrasion resistant in addition to chemical unreactiveness. Nylon also repels water.
Polyamides, Nylon and Kevlar 2
- Was the first polymeric aromatic amide (aramid) made from a diamine and a dicarboxylic acid.
- Insoluable in water, so concentrated sulfuric acid used to dissolve it
- Fire resistant,
- extremely strong- linear molecules are packed together parallel, held by hydrogen bonds. Sheets stack regularly around the axis to give a perfectly ordered structure.
- low density (made from light atoms eg. C, O, N, H)
- used for bulletproof vests, aeroplane wings, boat constructions.
During condensation polymerisation, two monomers join together forming a condensation polymer while a small molecular (usually water or HCl) is expelled.
Polyamides are formed from diamines and dicarboxylic acids
Polyesters are formed from dicarboxylic acids and diols.
At room temperature, polymers have crystalline regions (highly ordered chains) and amorphous regions (randomly arranged chains). The higher the percentage of crystalline regions the stiffer the polymer. Cooling the polymer gives more crystalline regions.
At Tg, the Glass Transition Temperature is reached, and the polymer becomes brittle or glass like. The polymer chains begin to slide over each other making it more flexible.
At Tm, the melting temperature is reached and the polymer becomes liquid.
Polymer Properties 3- Bonding
The longer the polymer chains the stronger the polymer.
Hydrogen bonding holds nylon chains together.
Permanent Dipole- Permenant Dipole bonds hold Polyester chains together.
Instanteneous Dipole- Induced Dipole bonds hold Polyethene chains together.
Both nylons and polyesters form linear polymer chains making them ideal as fibres.
Polymer Properties 4- Modification
- Introducing monomers with larger side groups which push the polymer chains further apart weakening intermolecular bonds.
- They lower Tg, as the plasticisers go between chains, allowing them to slide more freely.
- Stretching a polymer to form a 'neck' where all polymer chains are lined up creating a crystalline area, giving more opportunities for intermolecular bonding.
Green Chemistry- Recycling Polymers
- Plastic Process Scrap Recyling
- Post- Use Plastic Recycling- plastics recycled which have undergone a lifetime of service. (sorting is expensive)
- Chemical or Feedstock Recycling- breaking polymers into monomers (cracking)
- Bioplastics- biopolymers, synthetic biodegradable plastics or photodegradable plastics.
- Recycling other materials.
- Reducing CO2 emissions through recycling.
The 'Life Cycle Assessment' is used to calculate the carbon emissions of a plastic over it's entire life cycle.