alcohols

• Alcohols


  Smaller alcohols (up to 3 carbons) are soluble in water because they can form hydrogen bonds with water. The longer the hydrocarbon chain the less soluble the alcohol.
• Alcohols have relatively low volatility due to their ability to form hydrogen bond between alcohol molecules
• Uses of alcohols


  • Ethanol is 'alcohol' in alcoholic drinks. Ethanol is commonly used as a solvent in the form of methylated spirits.
  • Methanol is used as a petrol additive to improve combustion and is increasing important as a feedstock in the production of organic chemicals
• General formula alcohols


  CnH2n+1OH
• Classifying Alcohols


  • Primary alcohols are alcohols where 1 carbon is attached to the carbon adjoining the oxygen
  • Secondary alcohols are alcohols where 2 carbon are attached to the carbon adjoining the oxygen
  • Tertiary alcohols are alcohols where 3 carbon are attached to the carbon adjoining the oxygen
• Complete Combustion of alcohols

  CH3CH2OH (l) + 3 O2(g) 2CO2(g) + 3 H2O(l)
• Partial Oxidation of Primary Alcohols

  1. 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
• An aldehyde's name ends in –al and it always has the C=O bond on the first carbon of the chain so it does not need an extra number
• Full Oxidation of Primary Alcohols


  1. primary alcohol carboxylic acid

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

  3. Conditions: use an excess of dichromate, and heat under reflux: (distil off product after the reaction has finished)
• Reflux


  Reflux is used when heating organic reaction mixtures for long periods. The condenser prevents organic vapours from escaping by condensing them back to liquids.
• Oxidation of Secondary Alcohols

  1. secondary alcohol ketone

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

  3. Conditions: heat under reflux
• Ketones


  Ketones end in -one. When ketones have 5C's or more in a chain then it needs a number to show the position of the double bond. E.g. pentan-2-one
• Tertiary alcohols cannot be oxidised at all by potassium dichromate: This is because there is no hydrogen atom bonded to the carbon with the OH group
• Reaction of alcohols with dehydrating agents

  1. Alcohol Alkene

  2. Reagents: Concentrated sulfuric or phosphoric acid

  3. Conditions: warm (under reflux)

  4. Role of reagent: dehydrating agent/catalyst

  5. Type of reaction: acid catalysed elimination
• Substitution reactions of Alcohols to form Haloalkanes


  1. Alcohol Haloalkane

  2. Reagents: Concentrated sulfuric and sodium halide