3.3.5 Alcohols

• Alcohol production:

  Ethanol can be made by two processes:

  > Direct hydration of ethene

  > Fermentation
• Alcohol production:

  Ethene + Steam -> Ethanol

  Direct hydration of ethene conditions:

  Temperature: 300 degrees

  Pressure: 6.5 x 10^3 kPa

  Phosphoric acid catalyst
• Alcohol production:

  Glucose -> Ethanol + Carbon Dioxide

  Fermentation conditions:

  Temperature: 35 degrees

  Anaerobic conditions

  Yeast
• Alcohol production: Fermentation vs Hydration

  Raw Materials:

  >Fermentation - Sugar from plants (Renewable)

  >Hydration - Ethene form oil (non-renewable)

  Speed of reactions:

  >Fermentation - Slow

  >Hydration - Fast

  Yield:

  >Fermentation - Low (15%)

  >Hydration - High (95%)

  Quality of product:

  >Fermentation - Impure ethanol needs distilling

  >Hydration - Pure ethanol
• Alcohol production: Fermentation vs Hydration

  Atom economy:

  >Fermentation - Low, 51.1%

  >Hydration - High, 100%

  Type of process:

  >Fermentation - Batch (stop start) expensive on manpower

  >Hydration - Continuous (24hrs) cheap on manpower

  Equipment:

  >Fermentation - Cheap

  >Hydration - Expensive

  Energy used:

  >Fermentation - Low (35 degrees and atmospheric pressure)

  >Hydration - High (300 degrees and 6500 kPa)
• Biofuel is a fuel produced from renewable living things such as plants
• Carbon neutral is when there is no change in the total amount /level of carbon dioxide present in the atomsphere
• Carbon neutral - the carbon dioxide released when the fuel is burnt is the same as the carbon dioxide taken in from the air by the plants by photosynthesis.
• Equations to prove ethanol made by fermentation is carbon neutral:

  Carbon dioxide taken in:

  >Photosynthesis

  6CO2 + 6H2O -> C6H12O6 + 6O2

  therefore 6 molecules of CO2 taken in

  
  

  Carbon dioxide released :

  >Fermentation produces ethanol

  C6H12O6 -> 2C2H5OH + 2CO2

  > Combustion of ethanol

  C2H5OH + 3O2 -> 2CO2 + 3H20

  2C2H5OH + 6O2 -> 4CO2 + 6H20

  therefore 6 molecules of CO2 released
• Oxidation of primary alcohol:

  [O] - acidified potassium dichromate (VI)

  primary alcohol are first oxidised to aldehydes then carboxylic acids

  Equations:

  Ethanol + [O] -> Ethanal + Water (removes 2 H)

  Ethanal + [O] -> Ethanoic acid (Adds one O )

  Reflux changes the primary alcohol to carboxylic acid
• Oxidation of secondary alcohol:

  Secondary alcohol are oxidised to Ketones

  Propan-2-ol + [O] -> Propanone + Water
• Oxidation of tertiary alcohols:

  Tertiary alcohols CANNOT be oxidised by acidified potassium dichromate (VI)
• Alkenes can be formed from alcohols through dehydration/ acidic elimination

  Conditions:

  Temperature - 180 degrees

  Conc H2SO4/H3PO4
• Acidic Elimination ( Alcohol -> alkene )


  Conditions: 180 °C , Reflux

  Reagent: Conc Sulfuric acid/ phosphoric acid
• Oxidation of primary and secondary alcohols

  Condition: Warm Distillation

  Reagent: acidified potassium dichromate (VI) / [O]

  Forms: 1° -> Aldehyde , 2° -> Ketone.

  Refluxing

  Condition: Hot reflux.

  Reagent: acidified potassium dichromate (VI)/ [O]

  Forms: 1° -> carboxylic acid
• Esterification

  Condition: conc H2SO4 , reflux

  Reagent: Carboxylic acid

  Forms: Ester