Alcohol

• Alcohols


  Molecules with a hydroxyl functional group 'OH' attached somewhere to a hydrocarbon chain
• Hydroxy group


  The OH group named as a side chain, rather than ending the molecule name in 'ol'
• Carbonyl compounds


  • Aldehydes
  • Ketones
  • Carboxylic acids
• Aldehydes


  Carbonyl bonded to at least one H atom, given the suffix 'al'
• Ketones


  Carbonyl bonded to two C atoms, given the suffix 'one'
• Carboxylic acids


  Carbonyl bonded to an OH group, given the suffix 'oic acid'
• Combustion of alcohols


  1. Alcohol + excess oxygen → carbon dioxide + water

  2. Incomplete combustion can lead to carbon monoxide or carbon particles
• Petrol now contains 10% ethanol
• Balancing alcohol combustion reactions

  Go in alphabetical order: C, H, O
• Alcohol combustion reactions

  • Combustion of pentan-2-ol in excess oxygen

  2. Combustion of 2-methylpropanol to form black particles (C)

  3. Combustion of octan-3-ol to produce a poisonous gas (CO)
• Direct hydration


  Mechanism, uses H2O, conc. H3PO4 catalyst, high temperature (200-450 °C), high pressure (50-100 atm)
• Fermentation


  Converts glucose to ethanol using yeast catalyst, no air, temperature of 30-40 °C
• Neither a low temperature nor a high temperature is suitable for fermentation
• Photosynthesis → Fermentation → Combustion


  Demonstrates how bio-ethanol can be considered carbon-neutral
• Reasons bio-ethanol is not really carbon-neutral

  • Planting
  • Harvesting
  • Transport
  • Extracting sugar
  • Distilling ethanol solution
  • Fertiliser production
• Advantages of fermentation


  • Glucose is renewable source
  • Lower temperatures require less energy
  • Simpler equipment required is cheaper
• Disadvantages of fermentation


  • Land used to grow crops is not available for food crops
  • Ethanol is impure and must be distilled to purify
  • Low yield
  • Rate is slow
  • Batch production method is difficult to automate
• Advantages of direct hydration

  • High-purity ethanol produced
  • Continuous production
  • Fast rate of reaction
• Disadvantages of direct hydration

  • Crude oil is not renewable
  • High temperature and pressure requires a lot of energy (expensive)
  • Hi-tech equipment required (expensive)
• Elimination of alcohols


  Dehydration reaction, elimination mechanism, using hot conc. H2SO4 as catalyst
• Mechanism for elimination of butan-2-ol


  Can give more than one elimination product
• Solvent extraction


  Using a separating funnel to remove impurities from the product of a reaction
• Stages of separation


  Add sodium hydrogen carbonate solution to impure organic liquid

  2. Shake the separating funnel

  3. Release any pressure buildup

  4. Allow layers to separate

  5. Remove the pure organic layer
• Separating funnel

  Apparatus used to remove impurities from a reaction product
• Stages of Separation


  1. Place impure organic liquid in separating funnel

  2. Add sodium hydrogen carbonate solution

  3. Shake

  4. Allow layers to separate

  5. Remove aqueous layer

  6. Add drying agent

  7. Decant liquid
• Sodium hydrogen carbonate solution

  Reacts with and neutralises any unreacted acid catalyst
• Reaction of sodium hydrogen carbonate with acid

  2H+ + CO32- → H2O + CO2
• Releasing pressure is important after shaking the mixture
• Cyclohexanol is the impurity removed
• Removing cyclohexanol by re-distillation

  1. Cyclohexene has lower boiling point than cyclohexanol

  2. Cyclohexene will boil off first and be collected as distillate
• Alcohol classification


  Primary, secondary, tertiary
• Alcohols


  • Primary and secondary alcohols can be oxidised
  • Tertiary alcohols cannot be oxidised
• Oxidation of primary alcohols

  1. Primary alcohol → Aldehyde

  2. Aldehyde → Carboxylic acid
• Oxidation of secondary alcohols

  Secondary alcohol → Ketone
• Tertiary alcohols cannot be oxidised
• Oxidation equation summary


  • Primary alcohol 1[O] 1H2O Aldehyde Distillation
  • Aldehyde 1[O] 0 Carboxylic acid Reflux
  • Primary alcohol 2[O] 1H2O Carboxylic acid Reflux, excess oxidising agent
  • Secondary alcohol 1[O] 1H2O Ketone Distillation or Reflux
• Condenser


  Cools hot vapour and condenses it to liquid
• Anti-bumping granules prevent large bubbles and unsafe 'bumping'
• Reflux apparatus


  1. Condenser positioned vertically above reaction mixture

  2. Prevents reactant vapour from escaping

  3. Allows complete oxidation to carboxylic acid
• Distillation apparatus


  1. Condenser positioned horizontally above reaction mixture

  2. Allows aldehyde vapour to escape and be collected, preventing further oxidation