Alcohols

• General formula alcohols


  CnH2n+1OH
• Naming Alcohols


  • Have the ending -ol and if necessary the position number for the OH group is added between the name stem and the –ol
  • If the compound has an –OH group in addition to other functional groups that need a suffix ending then the OH can be named with the prefix hydroxy-)
• Alcohols


  • butan-2-ol
  • 2-hydroxypropanoic acid
  • ethane-1,2-diol
  • propane-1,2,3-triol
• Different types of alcohols

  • Primary (1 carbon attached to the carbon adjoining the oxygen)
  • Secondary (2 carbons attached to the carbon adjoining the oxygen)
  • Tertiary (3 carbons attached to the carbon adjoining the oxygen)
• Bond angles in Alcohols

  • H-C-H bonds and C-C-O are 109.5o (tetrahedral shape)
  • H-O-C bond is 104.5o (bent line shape)
• Alcohols have relatively low volatility and high boiling points due to their ability to form hydrogen bond between alcohol molecules
• Smaller alcohols can dissolve in water because they can form hydrogen bonds to water molecules
• Oxidation Reactions of the Alcohols


  1. Partial Oxidation of Primary Alcohols (primary alcohol -> aldehyde)

  2. Full Oxidation of Primary Alcohols (primary alcohol -> carboxylic acid)

  3. Oxidation of Secondary Alcohols (secondary alcohol -> ketone)

  4. Tertiary alcohols cannot be oxidised
• Aldehydes


  Name ends in –al, always has the C=O bond on the first carbon of the chain
• Ketones


  Name ends in -one, when 5C's or more in a chain then a number is needed to show the position of the double bond
• Distillation


  1. Separation technique to separate an organic product from its reacting mixture

  2. Collect the distillate at the approximate boiling point of the desired aldehyde and not higher
• Distillation apparatus


  • Round bottomed flask
  • Liebig condenser
  • Thermometer
  • Water in at bottom, out at top
  • Electric heaters often used
• Reflux


  1. Used when heating organic reaction mixtures for long periods

  2. Condenser prevents organic vapours from escaping

  3. Anti-bumping granules added to prevent vigorous, uneven boiling
• Reflux apparatus


  • Round bottomed flask
  • Condenser with water in and out openings
  • No sealed top on condenser
• Distinguishing between Aldehydes and Ketones

  1. Tollens' Reagent test (aldehydes form silver mirror, ketones no change)

  2. Fehling's Solution test (aldehydes reduce solution, ketones no change)
• Dichromate ion (Cr2O7^2-)


  Reduces to the green Cr^3+ ion
• Tertiary alcohols cannot be oxidised at all by potassium dichromate
• Aldehydes


  Can be further oxidised to carboxylic acids
• Ketones


  Cannot be further oxidised
• Tollens' Reagent test


  1. Mix aqueous ammonia and silver nitrate

  2. Heat gently

  3. Aldehydes are oxidised to carboxylic acid, silver(I) ions are reduced to silver atoms

  4. Observation: Silver mirror forms with aldehydes, no visible change with ketones
• Fehling's Solution test


  1. Reagent contains blue Cu^2+ ions

  2. Heat gently

  3. Aldehydes are oxidised to carboxylic acid, copper(II) ions are reduced to copper(I) oxide

  4. Observation: Blue Cu^2+ ions change to red precipitate of Cu2O with aldehydes, no reaction with ketones
• The presence of a carboxylic acid can be tested by addition of sodium carbonate, it will fizz and produce carbon dioxide
• Dehydration Reaction


  1. Alcohol -> Alkene

  2. Reagents: Concentrated sulfuric or phosphoric acids

  3. Conditions: Warm (under reflux)

  4. Role of reagent: Dehydrating agent/catalyst

  5. Type of reaction: Acid catalysed elimination
• Alcohols that can give more than one alkene product

  • 2° and 3° alcohols
• Producing alkenes from alcohols provides a possible route to polymers without using monomers derived from oil
• Acid catalysed elimination mechanism for dehydration of alcohols


  H+ comes from conc H2SO4 or conc H3PO4
• Fermentation


  • Glucose -> Ethanol + Carbon dioxide
  • Conditions: Yeast, no air, 30-40°C
  • Optimum temperature around 38°C
• Fermentation


  • Batch process, slow, high production costs
  • Ethanol made is not pure and needs purifying
  • Depletes land used for growing food crops
• Industrial formation of ethanol from ethene

  1. Reagent: Ethene from cracking of crude oil fractions

  2. Conditions: High temperature 300°C, high pressure 70 atm, strong acidic catalyst of conc H3PO4

  3. Type of reaction: Hydration/addition
• Industrial formation of ethanol from ethene

  • Faster reaction, purer product, continuous process
  • High technology equipment needed, high energy costs
• Ethanol produced from fermentation is a biofuel
• Ethanol as biofuel


  Any CO2 given off when burned would have been extracted from the air by photosynthesis when the plant grew, so no net CO2 emission
• The term "carbon neutral" refers to an activity that has no net annual carbon (greenhouse gas) emissions to the atmosphere