- Created by: James
- Created on: 08-05-13 11:42
Amines and Amides
Organic derivatives of ammonia, they have alkyl groups attached to N instead of hydrogen. The lone pair of electrons allows them to act as bases, ligands and nucleophiles.
A primary amine has a N atom bonded to one alkyl group. Secondary amine is bonded to two, tertiary amine is bonded to three. When naming, name the carbon chain followed by amine, or use the prefix amino (NH2) followed by the alkane.
Amines dissolve in water forming weakly alkaline solutions. They also accept a H+ ion from water or from an acid.
Primary amides have general formula R-C=O-NH2.
Secondary amides have general formula R'-C=O-N-HR.
When amides are hydrolysed, C-N bond breaks. Acid hydrolysis makes carboxylic acid and alkylammonium ion. Alkaline hydrolysis makes carboxylate ion and an amine (both reflux).
Polymer properties by design
Condensation polymerisation: Two different monomers join together forming a condensation polymer. A small molecule is eliminated (usually water or hydrogen chloride).
Condensation polymers: Polyamides (nylons) and polyesters.
Polyamides: Condensing diamines and dicarboxylic acids. Polyesters: Condensing diols and dicarboxylic acids.
At room temperature: Most polymers have crystalline regions (highly ordered chains) and amorphous regions (randomly arranged chains). Cooling polymers gives higher % of crystalline regions.
Eventually, glass transition temperature (Tg) is reached and the polymer becomes brittle/glass like. As a polymer warms up, chains slide over each other making it flexible. Continue to heat melts the polymer and it becomes liquid.
Nylon chains are held together by hydrogen bonding. Polyesters held together by PDPDs. The longer the chain, the stronger the polymer (more intermolecular bonds).
Plasticisers lower the Tg. They are molecules that sit inbetween chains allowing them to slide. Cold drawing increases strength of polymers (stretching it).
Green chemistry and recycling
Most rubbish goes to landfill, some of which is plastics.
An alternative to burying them is to recycle the plastics, but identifying and sorting them is expensive. Many thermoplastics are made of copolymers and can only be remoulded.
Another approach is to turn polymers back by cracking.
Third option is to degradable plastics. In the future, we could use biopolymers, biodegradable plastics or photodegradable plastics. All of these break down in the environment.
Burning plastics releases energy (but causes problems such as increased CO2 emissions).
Life cycle assessments measure emissions during the extraction of raw materials, the manufacturing process, the distribution to customers and its disposal. This 'cradle to grave' approach allow chemists to evaluate the impact of producing such a material.
Green chemistry involves designing chemical processes that reduce or eliminate waste and the use of hazardous materials.