Alcohols

• Alkenes formed via mechanism of DEHYDRATION from alcohol


  1. Lone pairs of oxygen attach to H+ ion from the catalyst

  2. Positive charge forms on oxygen, curly arrow from C-O to Oxygen

  3. Removal of H2O and C-H curly arrow to C-C bond to lose the H+ ion

  4. Alkene is formed with H2O and H+
• Hydration of alkenes to form alcohols: using steam and acid catalyst


  1. Curly arrow from double bond to H+ ion, H ion then joins molecules

  2. Lone pair from oxygen from the H2O curly arrow to positive carbon

  3. H2O joins molecule, curly arrow from O-H bond (in H2O) to + oxygen

  4. H+ Lost from water and Alcohol and H+ ion formed
• Making Cyclohexene via distillation, separation and purification


  1. DISTILLATION: Add sulfuric/phosphoric acid and cyclohexanol into a round bottom flask. Add anti bumping granules

  2. Use a heating mantle to warm up the flask to 83 degrees (boiling point of cyclohexanol)

  3. Chemicals with lower boiling points that 83 degrees will evaporate enter condenser, cools and condenses back into liquid

  4. Products collected in conical flasks may still have impurities such as unreacted cyclohexanol and water

  5. SEPARATION AND PURIFICATION: Add products from previous distillation into separating funnel and add water to dissolve soluble impurities creating an aqueous solution

  6. 2 layers will form, Top = impure cyclohexene Bottom = Aqueous layer with water soluble impurities (Drain this off, remove stopper)

  7. Take impure cyclohexene and add to round bottomed flask and add anhydrous calcium chloride (Dehydrating agent) will remove aqueous substance still remaining aqueous solution, invert flask and leave for 20 minutes
• Fermentation of ethanol: An alternative to making ethanol rather than ethene and steam


  1. Uses yeast ( an enzyme converting glucose to carbon dioxide and ethanol)in anaerobic conditions and is an exothermic reaction

  2. Rate of reaction is dependent on temperature
• Fermentation


  • Requires little equipment and is renewable so it is cheap
  • The biggest cost is fractional distillation (used to obtain pure ethanol) at the end which requires energy and time
• Biofuels


  Made from dead biological matter, sigar (like sugarcane) fermented to produce ethanol
• Advantages of biofuels

  • Biofuels are renewable and more sustainable
  • Biofuels produce CO2 when burnt but classed as carbon neutral as CO2 is absorbed again for photosynthesis as sugarcane is still growing
• Disadvantages of biofuels

  • Expensive to convert existing petrol engines to take fuel with higher concentrations of ethanol
  • Land used to grow food is used to grow sugarcane for fuel= causing a foot shortage in countries growing a lot of sugarcane e.g. (Brazil and india)
• Biofuels are seen as almost carbon neutral: biofuels made from sugar cane fermented to produce ethanol, when ethanol is burned the greenhouse gas, CO2 is produced but used up by growing plants in photosynthesis
• Fossil fuels are burnt to transport biofuels across the country also fossil fuels used to make more fertilisers to put on crops
• To oxidise primary alcohol (ethanol) to an aldehyde - CH3CH2OH (l) + [ O ] --> CH3CHO (g) + H2O (l)

  
  

  
  

  1. Mixture heated gently in distillation apparatus

  2. Receiver cooled in ice to reduce evaporation of the product

  3. Ethanal (aldehyde) vaporises as soon as it is formed and distils off

  4. This stops it from oxidising further to ethanoic acid
• Oxidising ethanol to ethanoic acid CH3CH2OH (l) + [O] -> CH3COOH (g) + H2O

  
  

  
  

  1. Excess dichromate used

  2. Mixture is refluxed in reflux apparatus

  3. Reflux meaning vapour condenses and drips back into the reaction flask, SO while mixture is refluxing any ethanol or ethanal vapour will condense and drip back into the flask

  4. Eventually it is oxidised to the acid

  5. After refluxing for 20 mins you can distil the ethanoic acid off (boiling temp 118 degrees)
• Reflux

  Allows strong heating without loss of volatile reactants or products
• Oxidation by potassium dichromate (K2Cr2O7)


  Mild oxidising agent so reduced itself turning orange (Cr2O7 2- dichromate ion) to green (Cr3+ chromium ion)
• Fehling's solution

  • Blue as it contains Cu2+ ions
  • Added to warm aldehyde = Blue to a brick red precipitate
  • Ketones remain Blue
• Tollens (Ag[Nh3]2)


  • Added to warm aldehyde = Tollens reduced to silver mirror coated around the flask
  • Ketones = no silver precipitate forms
• State a simple chemical test that distinguishes the propanoic acid from the propan-1-ol.

  Propanoic acid: effervescence / bubbles

  Propan-1-ol no (visible) change/reaction