The Polymer Revolution

Addition Reactions of Alkenes
1. Adding hydrogen to C=C bonds produces alkanes.
  1. e.g. Ethene will react with hydrogen gas to produce ethene but only with a nickel catalyst, 150 degrees and high pressure/platinum catalyst at room temp and pressure.
  2. The C=C bond opens up and hydrogen atoms join on to give an alkane.
2. Bromine water can be used to test for C=C bonds.
  1. When you shake an alkane with bromine water it decolourises - becomes colourless - and forms a dibromoalkane.
  2. Adding bromine is the test for unsaturation. Saturated compounds don't react.
3. Electrophilic Addition
  1. The bromine is an example of electrophilic addition.
    1. During electrophilic addition reactions, the double bonds open up and atoms are added to the carbons.
    2. They happen because the bond has got plenty of electrons and is easily attacked by electrophiles.
      1. Electrophiles are electron-pair acceptors - they usually don't have enough electrons so they're are attracted to areas where there's a lot of them about.
      2. The double bond is nucleophilic - it's attracted to places that don't have enough electrons.
  2. Hydrogen Halides
    1. Alkenes also undergo addition reactions with hydrogen bromide - to form bromoalkanes.
    2. If the HBr adds to an unsymmetrical alkene, like propene, there are two possible products.
  3. Reacting Alkenes with Water and an H2SO4 Catalyst Makes Alcohols
    1. 1. H2C=CH2 + H2SO4 --> CH3CH2OSO2OH
      2. Ethene + Sulphuric Acid --> Ethyl H Sulfate
4. Ethanol is manufactured by steam hydration.
  1. It is hydrated by steam at 300 degrees and a pressure of 60atm. This reaction is reversible and the reaction yield is low but the unreacted ethene gas is recyclable.
Alcohols and Other Organic Compounds
1. Alcohols
  1. The alcohol homologous series has the general formula CnH2n+1OH.
  2. In a primary alcohol, the carbon with the -OH is attached to one other carbon.
  3. In a secondary alcohol, the carbon with the -OH is attached to 2 other carbons.
  4. In a tertiary alcohol, the carbon with the -OH is attached to three other carbons.
  5. They can be dehydrated to form alkenes. C2H5OH --> CH2=CH3 + H2O
    1. Ethanol vapour can be passed over a hot catalyst of pumice stone or aluminium oxide, Al2O3.
    2. It can also be heated by reflux with excess concentrated sulfuric acid at 170 degrees. The ethene produced is then collected over water.
      1. In this method, the sulfuric acid acts as the dehydrating agent in the elimination reaction.
  6. Alcohols can be Oxidised
    1. Using an Oxidising Agent
      1. Complete oxidation forms carbon dioxide and water. This is a combustion reaction.
    2. By Burning Them
      1. Primary alcohols are oxidised to aldehydes then carboxylic acid.
      2. Secondary alcohols are oxidised to ketones only
    3. Whether a primary alcohol is oxidised into a aldehyde or a carboxylic acid depends on the reaction conditions.
      1. Gently heating ethanol with potassium dichromate(VI) solution and sulfuric acid in a test tube produces apple smelling ethanal (aldehyde). However it usually oxidises to form vinegar smelling ethanoic acid.
        To just get an aldehyde it needs to be taken out of the oxidising solution as soon as it's formed.
      2. To produce a carboxylic acid, the alcohol has to be vigorously oxidised. The alcohol is mixed with excess oxidising agent and heated under reflux.
2. Aldehydes and Ketones
  1. Their general formula is CnH2nO
  2. Aldehydes have their carbonyl group at the END of the carbon chain.
  3. Ketones have their carbonyl group anywhere in the MIDDLE of the carbon chain.
  4. They both contain a double-bonded oxygen.
3. Carboxylic Acids
  1. They contain a -COOH functional group.
Hydrogen Bonding
1. Hydrogen bonding is the strongest intermolecular force.
  1. It only occurs when hydrogen is covalently bonded to fluorine, nitrogen or oxygen because they are very electronegative so they draw the bonding electrons away from the hydrogen atom.
    1. Water and ammonia both have hydrogen bonding.
2. Density of Water and Ice
  1. There is the max no. of hydrogen bonds in ice which forms a lattice structure. As the ice melts some of the hydrogen bonds break and the lattice breaks down which allows molecules to fill the spaces.
3. Boiling Points
  1. Hydrogen bonding is quite a strong intermolecular force, so it has a lot of effect on the properties of substances.
    1. Substances that form hydrogen bonds have higher boiling points and melting points because they require extra energy to break the bonds.
      1. This is the case with water and ammonia.
4. Polymers Can Dissolve
  1. Polymers have incredibly long chains so ones with -OH groups can form hydrogen bonds with water molecules, allowing it to dissolve.
  2. Polymer molecules can also bond to each other by hydrogen bonds.
    1. If the polymer has loads of -OH groups, the hydrogen bonding will be very strong.
    2. If the polymer has very few -OH groups, there won't be many hydrogen bonds formed with water molecules and the polymer will be insoluble.
    3. If the polymer has not too many hydrogen bonds and not too few then it'll be soluble.
Polymers
1. Addition Polymers
  1. The double bonds in alkenes can open up and join together to make long chains called polymers.
    1. This is called addition polymerisation.
      1. For example, poly(ethene) is made by the addition polymerisation of ethene.
  2. Copolymers are made from more than one type of monomer, they join in a random order.
    1. For example, ethene can be combined with propene to produce a polymer with different properties from either poly(ethene) or poly(propene).
2. Monomers
  1. To find the monomer used to form an addition polymer, take the repeated unit and add a double bond.
  2. Because of the loss of the double bond, poly(alkenes) are unreactive.
3. Cross-Linking
  1. Thermoplastic Polymers
    1. They don't have cross-linking between chains, it's only weak intermolecular forces that hold the chains together.
    2. These forces are easy to overcome so it's super easy to melt the plastic. They can be melted and remoulded.
  2. Thermosetting Polymers
    1. e.g. Bakelite
    2. They have covalent cross links which hold the chains together in a 3D giant covalent structure.
    3. The polymer doesn't soften when it's heated, though, heated too much it can char. They are strong, hard and insoluble.
4. Properties and Uses
  1. Poly(chloroethene) is durable and flexible so it can be used for water pipes, insulation and building material.
  2. Poly(tetrafluorioethene) is chemically inert and has non-stick properties. This makes it ideal for coating frying pans.
  3. Polystyrene is cheap and can be made into expanded polystyrene which is a good, light insulator.
  4. Perspex is transparent and pretty strong so it can be used in place of glass for certain things.
E/Z Isomerism
1. Rotation
  1. Single bond allow atoms to rotate freely.
  2. Atoms can't rotate around C=C bonds and this is what causes E/Z isomerisation.
2. Stereoisomerism
  1. Stereoisomers have the same structural formula but a different spacial arrangement.
  2. This happens when the 2 double bonded carbon atoms each have different atoms or groups attached to them.
  3. When the same groups are across the double bond then it's the E-isomer.
  4. When the same groups are both above or both below the double bond then it's the Z-isomer.
3. Cis-Trans Isomers
Infrared Spectroscopy

Next up

The Polymer Revolution

Description

Resource summary

Media attachments

Similar

	Created by gordonbrad almost 11 years ago