Module 4.2.1- Alcohols

• Naming Alcohols (IUPAC) example


  butan-2,3-diolremember the 'di' to mark 2 alcohol functional groups

  
• Reasoning for alcohol properties

  Alcohols have a polar O-H bond, therefore, making the molecule polar with strong Hydrogen bonds

  The alkane chain contain non-polar bonds which are very weak London forces

  
• Alcohol- water solubility


  Due to the polar O-H bond in the alcohol molecule, it is able to form hydrogen bonds with water
• Alcohol- boiling point


  High due to the strong hydrogen bonds and so more energy is required to overcome the intermolecular forces
• Alcohol- volatility


  Lower volatility (than alkanes) since boiling point is higher due to the strong hydrogen bonds
• Compounds with low boiling points are more volatile than those with higher because...


  they are easily converted from a liquid to a gas
• As the hydrocarbon chain length increases...


  ...solubility decreases since the influence of the O-H bond becomes relatively smaller
• Primary alcohol


  An alcohol in which the OH group is attached to a carbon atom that is attached to two or three hydrogen atoms.

  
• Secondary alcohol


  An alcohol in which the -OH group is attached to a carbon atom that is attached to two carbon chains and one hydrogen atom.

  
• Tertiary alcohol


  An alcohol in which the -OH group is attached to a carbon atom that is attached to three carbon atoms and no hydrogen atoms.

  
• Combustion of alcohols

  Alcohols combust with oxygen in the air to produce carbon dioxide and waterBalance Carbons first, then Hydrogens and then the Oxygens

  
• What type of alcohols can be oxidised


  primary and secondary only

  not tertiary
• Oxidising agent [O]


  Potassium dichromate (VI) acidified with dilute sulfuric acid

  K2Cr2O7/ H2SO4
• Oxidation of primary alcohols

  primary alcohol -> aldehyde -> carboxylic acid
• Oxidation of secondary alcohols

  secondary alcohol -> ketone
• Primary alcohol + [O] -> aldehyde (preparation)


  aldehyde is distilled out of the reaction mixture as it is formed preventing any further reaction with the oxidising agent

  
• Colour change in oxidation of alcohols

  Orange to green
• Primary alcohol + 2[O] -> carboxylic acid (preparation)


  primary alcohol is heated strongly under reflux
• Secondary alcohol + [O] -> ketone (preparation)


  secondary alcohol is heated strongly under reflux and cannot go any further
• Oxidation of tertiary alcohols

  No
• Dehydration of alcohols (alcohol to alkene)

  When an alcohol is heated under reflux in the presence of a hot acid catalyst (e.g H2SO4 or H3PO4) a water molecule is eliminated, forming an alkene
• Alcohol + hydrogen halide


  Haloalkane + waterheated under reflux with sulfuric acid and sodium halide

  
• How is a hydrogen halide formed (in situ) to react with alcohol


  e.g. NaBr + H2SO4 -> NaHSO4 + HBr
• Distillation apparatus set up

  heat

  thermometer

  distillation flask

  condenser

  flask

  
• Reflux apparatus set up


  heat

  pear-shaped flask

  condenser