alcohols

• Naming Alcohols


  1. Have the ending -ol

  2. If necessary the position number for the OH group is added between the name stem and the –ol

  3. 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
• Primary alcohols


  Alcohols where 1 carbon is attached to the carbon adjoining the oxygen
• Secondary alcohols


  Alcohols where 2 carbon are attached to the carbon adjoining the oxygen
• Tertiary alcohols


  Alcohols where 3 carbon are 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)
• Hydrogen bonding in alcohols

  Alcohols have relatively low volatility and high boiling points due to their ability to form hydrogen bonds between alcohol molecules
• Solubility of alcohols


  Smaller alcohols can dissolve in water because they can form hydrogen bonds to water molecules
• Oxidation Reactions of Alcohols

  1. Potassium dichromate K2Cr2O7 is an oxidising agent that causes alcohols to oxidise

  2. The exact reaction depends on the type of alcohol (primary, secondary, tertiary) and the conditions
• Partial Oxidation of Primary Alcohols

  1. Reaction: primary alcohol → aldehyde

  2. Reagent: potassium dichromate (VI) solution and dilute sulfuric acid

  3. Conditions: use a limited amount of dichromate, warm gently and distil out the aldehyde as it forms
• Aldehydes


  • An aldehyde's name ends in –al
  • It always has the C=O bond on the first carbon of the chain so it does not need a number in its name
• Distillation


  1. Used as a separation technique to separate an organic product from its reacting mixture

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


  • Liebig condenser with water in at the bottom and out at the top
  • Thermometer bulb at the T junction to measure boiling point
  • Round bottomed flask heated by electric heater
• Full Oxidation of Primary Alcohols


  1. Reaction: primary alcohol → carboxylic acid

  2. Reagent: potassium dichromate(VI) solution and dilute sulfuric acid

  3. Conditions: use an excess of dichromate, heat under reflux
• Carboxylic acids


  The name ends in -oic acid
• Reflux


  • Used when heating organic reaction mixtures for long periods
  • Condenser prevents organic vapours from escaping
  • Anti-bumping granules added to prevent vigorous boiling
• Oxidation of Secondary Alcohols

  1. Reaction: secondary alcohol → ketone

  2. Reagent: potassium dichromate(VI) solution and dilute sulfuric acid

  3. Conditions: heat under reflux
• Ketones


  • The name ends in -one
  • If 5C's or more in the chain, a number is needed to show the position of the double bond
• Tertiary alcohols cannot be oxidised at all by potassium dichromate
• Distinguishing aldehydes and ketones

  • Aldehydes can be further oxidised to carboxylic acids whereas ketones cannot be further oxidised
• Tollens' Reagent test


  1. Reagent: Tollens' reagent formed by mixing aqueous ammonia and silver nitrate

  2. Reaction: aldehydes are oxidised by Tollens' reagent into a carboxylic acid, forming a silver mirror

  3. Ketones result in no visible change
• Fehling's solution test


  1. Reagent: Fehling's solution containing blue copper(II) ions

  2. Reaction: aldehydes are oxidised, reducing the copper(II) ions to red copper(I) oxide

  3. Ketones result in no visible change
• Oxidation of the ketone


  Under these conditions
• Aldehydes


  Can be further oxidised to carboxylic acids
• Ketones

  Cannot be further oxidised
• Tollens' Reagent


  Formed by mixing aqueous ammonia and silver nitrate, the active substance is the complex ion of [Ag(NH3)2]+
• Tollens' Reagent test


  1. Heat gently

  2. Aldehydes only are oxidised into a carboxylic acid

  3. Silver(I) ions are reduced to silver atoms

  4. With aldehydes, a silver mirror forms coating the inside of the test tube

  5. Ketones result in no visible change
• Fehling's solution


  Contains blue Cu 2+ ions
• Fehling's solution test


  1. Heat gently

  2. Aldehydes only are oxidised into a carboxylic acid

  3. Copper(II) ions are reduced to copper(I) oxide

  4. Aldehydes: Blue Cu 2+ ions in solution change to a red precipitate of Cu2O

  5. Ketones do not react
• The presence of a carboxylic acid can be tested by addition of sodium carbonate. It will fizz and produce carbon dioxide.
• Dehydration Reaction


  Removal of a water molecule from a molecule
• Dehydration of alcohols


  1. Reagents: Concentrated sulfuric or phosphoric acids

  2. Conditions: Warm (under reflux)

  3. Role of reagent: Dehydrating agent/catalyst

  4. Type of reaction: Acid catalysed elimination
• Some 2o and 3o alcohols can give more than one product, when the double bond forms between different carbon atoms
• Dehydration of butan-2-ol


  • but-1-ene
  • but-2-ene
• But-2-ene could also exist as E and Z isomers
• Producing alkenes from alcohols provides a possible route to polymers without using monomers derived from oil.
• Acid catalysed elimination mechanism for dehydration of alcohols

  1. The H+ comes from the conc H2SO4 or conc H3PO4

  2. Forming ethanol
• Fermentation


  Conversion of glucose to ethanol and carbon dioxide
• Conditions for fermentation

  1. Yeast

  2. No air

  3. Temperatures 30 –40oC

  4. Optimum temperature around 38oC
• Hydration


  Addition of water to a molecule