14. Alcohols

• functional group: R-OH, where R is an alkyl group, bond angle 104.5 (2 lone pairs)
• position of OH group is denoted by including the number of the carbon it is attached to
• primary alcohol: 1 carbon bonded to the carbon adjacent to the oxygen
• secondary alcohol: 2 carbons bonded to the carbon adjacent to the oxygen
• tertiary alcohol: 3 carbons bonded to the carbon adjacent to the oxygen
• alcohols have higher boiling points than the parent alkanes due to hydrogen bonds which are stronger than London Forces. alcohols are also soluble in water
• • the carbon-oxygen bond and the oxygen-hydrogen bond are polar bonds, due to the difference in electronegativity in the atoms
  • the delta positive carbon bond attracts nucleophiles which attack the carbon bond
• combustion of alcohols:

  • alcohols always combust completely
• oxidation of alcohols:

  • primary alcohols -> aldehydes -> carboxylic acids
  • secondary -> ketones
• alcohols are oxidised by acidified potassium dichromate, which is reduced itself
• 1o alcohol -> aldehyde:

  • distillation apparatus is used
  • aldehydes have lower boiling points than the alcohols so they evaporate and condense
  • the aldehyde is thus removed from the oxidising agent and is not oxidised further
• 1o alcohol -> carboxylic acid:

  • reflux apparatus is used
  • the aldehyde is not removed from the round bottom flask so it continues to oxidise into a carboxylic acid
• reflux:

  • used when heating volatile organic reagents that would evaporate if heated openly
  • the vertical condenser cools products which drip back into the round bottom flask
  • anti-bumping granules are added to ensure smooth boiling and allow smaller bubbles to form
  • the round bottom flask allows for even distribution of heat
• 2o alcohols -> ketone:

  • heat under reflux
• acidified potassium dichromate turns from orange to green when reduced in oxidation of alcohols
• substitution of alcohols to haloalkanes:

  • alcohols react with hydrogen halides to form haloalkanes
  • the hydrogen halide is formed in situ from heating sulfuric acid and a sodium halide
  • heat the alcohol, sulfuric acid and soidum halide in reflux apparatus
• dehydration of alcohols:

  • alcohol -> alkene
  • elimination reaction
  • reagent: conc. acid e.g. phosphoric acid
  • conditions: heat