Alcohols

• Alcohol


  A compound containing the hydroxyl (OH) functional group
• Making ethanol


  1. Fermentation

  2. Hydration of ethene
• Fermentation


  • Requires yeast
  • Anaerobic environment
  • Temperature 30-40°C
• Fermentation


  Converts glucose to ethanol and carbon dioxide
• Hydration of ethene


  • Requires catalyst (H3PO4 or H2SO4)
  • Temperature 300°C
  • Pressure 70 atm
• Ethanol can be used as a biofuel
• Carbon neutral


  No net release of CO2 when using ethanol as a fuel
• Ethanol as a biofuel is not truly carbon neutral as it does not account for CO2 emissions from transport and machinery used in production
• Photosynthesis occurs where we take in carbon dioxide and give out oxygen, but this does not account for carbon dioxide produced from transport and machinery used in crop harvesting
• Photosynthesis and fermentation of planting material


  Produces carbon dioxide
• Combustion


  Produces carbon dioxide
• The assumption of carbon neutrality does not account for carbon dioxide produced from transport and machinery used in crop harvesting
• Ethanol produced as a biofuel may not be truly carbon neutral when accounting for the emissions from its production
• Primary alcohol


  Alcohol with one alkyl group attached to the carbon with the OH group
• Secondary alcohol


  Alcohol with two alkyl groups attached to the carbon with the OH group
• Tertiary alcohol


  Alcohol with three alkyl groups attached to the carbon with the OH group
• Oxidation of alcohols


  1. Primary alcohols can be oxidized to aldehydes and then carboxylic acids

  2. Secondary alcohols can be oxidized to ketones

  3. Tertiary alcohols cannot be oxidized
• Oxidizing agent


  Acidified potassium dichromate (K2Cr2O7)
• Oxidizing agent (acidified potassium dichromate)


  Changes colour from orange to green when oxidation occurs
• Producing ethanol


  Distill off ethanol before it can be further oxidized to ethanoic acid
• Producing carboxylic acids from alcohols

  Heat under reflux to ensure complete oxidation
• Oxidation of secondary alcohols


  Produces ketones
• Oxidation by heating on the reflux

  1. Drive oxidation from primary alcohol ethanol to carboxylic acid

  2. Heat under reflux
• You are not expected to be able to draw reflux apparatus
• Heating under reflux allows you to go right through to the carboxylic acid
• Stopping oxidation at the aldehyde


  Do a bit of distillation
• Secondary alcohol


  Oxidised to a ketone
• The ketone is the final oxidation product when there is no hydrogen to slip the oxygen into
• Oxidation products


  • Aldehyde
  • Carboxylic acid
  • Ketone
• The colour change with acidified potassium dichromate is very important to observe
• If given a molecular formula for an alcohol, you may need to rearrange it to draw an isomer that is a secondary alcohol
• Tests to determine the organic product

  1. Add a carbonate to test for the acid

  2. Use Tollens' reagent (ammonia silver nitrate) - aldehyde gives silver mirror, ketone gives no visible change

  3. Use acidified potassium dichromate - primary/secondary alcohols oxidise, tertiary alcohol does not
• Dehydration of alcohols


  1. Lose the OH group and the hydrogen from the adjacent carbon

  2. Requires acid catalyst like conc. H2SO4

  3. Classified as an elimination reaction
• Dehydration cannot occur if the adjacent carbon has no hydrogen