ALCOHOLS

• Alcohols contain an -OH group and follow the general formula CnH2n+1OH
• Alcohols can be produced via two main methods: hydration and fermentation
• Hydration method:

  • Alcohols are produced from alkenes in the presence of an acid catalyst
  • Phosphoric acid is commonly used as the catalyst under aqueous conditions at 300°C and high pressures
  • Very high percentage yield as ethanol is the only product, favored as an industrial process
• Fermentation method:

  • Enzymes break down starch from crops into sugars which can be fermented to form alcohol
  • Cheaper than hydration, can be carried out at a lower temperature
  • Fermented in batches, slower process with a lower percentage yield
  • Ethanol is a common biofuel produced in this way, considered carbon neutral
• Alcohols can be primary (1o), secondary (2o), or tertiary (3o)

  • 1o and 2o alcohols can be oxidised to produce various products
  • 3o alcohols are not easily oxidised
• 1o alcohols can be heated in the presence of acidified potassium dichromate and distilled to produce aldehydes

  • When heated further under reflux conditions, 1o alcohols oxidise further to produce carboxylic acids
• 2o alcohols can be oxidised when heated in the presence of acidified potassium dichromate to produce ketones
• Potassium Dichromate (K2Cr2O7) is used in the oxidation of alcohols as the oxidising agent

  • It is reduced as the alcohol is oxidised, observed as a colour change from orange to green
• Alkenes can be formed from the dehydration of alcohols, where a molecule of water is removed from the molecule

  • Excess of hot sulfuric acid is added and aluminium oxide is used as a catalyst
• H+ acidic ions are reformed in the reaction showing how they act as a catalyst

  • Addition polymers can be produced from fermentation without the need for crude oil, a nonrenewable resource
  • Fermentation produces the primary alcohol which is then dehydrated to produce an alkene used in the production of addition polymers