3.3.5 - Alcohols

• Distillation: A separation technique used to separate an organic product from it's reacting mixture
• Electric heaters are used to heat organic chemicals because organic chemicals are highly flammable and could set a fire with a naked flame.
• Reflux: an apparatus that involves the continuous evaporation and condensation of organic reaction mixtures for long periods.
• Tertiary alcohols cannot be oxidised by potassium dichromate because there is no hydrogen atom bonded to the carbon with the -OH group
• What substance causes alcohol to oxidise?

  • Potassium dichromate
  • K2Cr2O7 is an oxidising agent that causes alcohols to oxidise
• Key difference between aldehydes and ketones:

  • Aldehydes can be further oxidised to carboxylic acids
  • ketones cannot be further oxidised
  • chemical basis for tests
• Describe the reaction of alcohols with dehydrating agents:

  • Reagent: Concentrated sulphuric or phosphoric acid
  • Reaction: Alcohol -> Alkene
  • Conditions:
  • Warm (under reflux)
• What are two ways of forming ethanol:

  • fermentation
  • hydration of ethene
• Formation of ethanol from ethene:

  • Reaction: Hydration
  • Reagent: Ethene
  • Conditions:
  • High temp - 300 degrees c
  • High pressure - 70 atm
• What are the conditions for fermentation?

  • yeast is present
  • air is absent
  • temperatures 30 - 40 degrees celsius
• Fermentation is done in the absence of air to prevent further reactions occurring as these can oxidise ethanol to produce ethanoic acid
• The optimum temperature for fermentation is around 38 degrees because:

  • at lower temperatures reactions are too slow
  • higher temperatures the yeast die and enzymes denature
• What is a biofuel? Fuel produced from plants
• What does carbon neutral mean? An activity that has no net annual carbon emissions to the atmosphere
• Disadvantages of the use of crops for the production of ethanol:

  • Growth is subject to the environment
  • Reduces land available for food growth
  • Requires the use of fossil fuels
  • Not carbon neutral
  • Requires significant processing after production to separate the ethanol from water
• Bromine is an electrophile - a lone pair acceptor.
• Advantages of the fermentation of glucose method for making ethanol:

  • Low-tech
  • Cheap equipment
  • Renewable resources only
• Advantages of the hydration of ethene method for making ethanol:

  • Faster reaction
  • Purer product
  • Continuous process
• Name the product of this reaction:

  partial oxidation of a primary alcohol = aldehyde + water
• Name the product of this reaction

  
  

  full oxidation of a primary alcohol = carboxylic acid + water
• Name the products of this reaction:

  full oxidation of a secondary alcohol = ketone + water
• What is the functional group of an alcohol?

  Hydroxyl group -OH
• What is the general formula of an alcohol?

  
  

  C n H2n+1OH
• What kind of intermolecular forces do alcohols have? Why?

  • Hydrogen bonding
  • because of the electronegativity difference in the OH bond
• What makes an alcohol primary? C bonded to OH is bonded to one other C atom
• What makes an alcohol secondary? C bonded to OH is bonded to two other C atoms
• What makes an alcohol tertiary? C bonded to OH is bonded to three other C atoms
• How can ethanol be made by fermentation? Plant carbohydrates broken down and fermented by enzymes in yeast → ethanol
• What conditions are needed for fermentation to take place?

  • Enzymes in yeast as catalyst
  • 35 °C
  • anaerobic conditions
• Equation for production of alcohol by fermentation:

  
  

  C6H12O6 (aq) → 2C2H5OH + 2CO2
• Write an equation for the combustion of ethanol. C2H5OH (l) + 3O2 (g) → 2CO2 (g) + 3H2O (l)
• Elimination reaction: The removal of a smaller molecule from a larger one
• What forms if you partially oxidise a primary alcohol? An aldehyde
• What conditions are needed to partially oxidise a primary alcohol?

  • Dilute sulphuric acid
  • potassium dichromate (VI)
  • distill product as it’s produced, gentle heating
• What forms if you fully oxidise a primary alcohol? A carboxylic acid
• What forms if you oxidise a secondary alcohol? A ketone
• What is an aldehyde? What is its functional group? Molecule with C=O group at the end of a carbon chain, carbonyl functional group (C=O)
• What is a ketone? What is its functional group? Molecule with C=O group around the middle of a carbon chain, carbonyl functional group (C=O)
• What does the Tollens’ test give a positive result for? aldehydes
• What does Fehling’s solution give a positive test result for? aldehydes