chapter 14 - alcohols

• physical properties of alcohols:

  • polar bonds between O-H groups
  • very weak London forces, but strong hydrogen bonds between O-H groups
• alcohols - volatility and boiling points

  • in liquid state, intermolecular hydrogen bonds require more energy to be broken down then london forces
  • so alcohols have a lower volatility then alkenes with the same amount of carbons
• alcohols - solubility in water

  • alcohols can form hydrogen bonds with water, so is soluble
  • hydrogen bonds form between the polar O-H groups and the water molecules
• Primary alcohols:

  • -OH group is attached to a carbon atom that is attached to 2 hydrogen atoms and 1 alkyl group
• Secondary alcohols:

  • -OH group is attached to a carbon atom that is attached to 1 hydrogen atom and 2 alkyl groups
• Tertiary alcohols:

  • -OH group is attached to a carbon atom that is attached to no hydrogen atoms and 3 alkyl groups
• Oxidation of alcohols

  Primary and secondary alcohols can be oxidised by an oxidising agent
• Oxidising mixture

  Solution of potassium dichromate (VI), acidified with dilute sulfuric acid
• Oxidation of alcohol

  Orange solution containing dichromate (VI) ions is reduced to a green solution containing chromium(III) ions
• Oxidation of primary alcohols

  Primary alcohols can be oxidised to either aldehydes or carboxylic acids
• Preparation of aldehydes

  On gentle heating of primary alcohols with acidified potassium dichromate, an aldehyde is formed
• Preparation of aldehydes

  1. Aldehyde is distilled out of the reaction mixture as it forms

  2. This prevents any further reaction with the oxidising agent

  3. Dichromate (VI) ions change colour from orange to green
• Preparation of carboxylic acids

  1. A primary alcohol is heated strongly under reflux, with an excess of acidified potassium dichromate (VI)

  2. A carboxylic acid is formed

  3. Use of an excess of the acidified potassium dichromate (VI) ensures that all of the alcohol is oxidised

  4. Heating under reflux ensures that any aldehyde formed initially in the reaction also undergoes oxidation to the carboxylic acid
• When preparing the aldehyde, use distillation to remove the aldehyde from the reaction mixture
• When preparing the carboxylic acid, heat the alcohol under reflux
• Oxidation of secondary alcohols

  1. Secondary alcohols are oxidised to ketones

  2. It is not possible to further oxidise ketones using acidified dichromate (VI) ions

  3. To ensure the reaction goes to completion, the secondary alcohol is heated under reflux with the oxidising mixture

  4. The dichromate (VI) ions once again change colour from orange to green
• Dehydration


  Any reaction in which a water molecule is removed from the starting material
• Dehydration of alcohols

  1. Alcohol is heated under reflux in the presence of an acid catalyst

  2. The product of the reaction is an alkene
• Elimination reaction


  A reaction that involves the removal of a small molecule from a molecule, resulting in two products
• Alcohols react with hydrogen halides to form haloalkanes
• Preparing a haloalkane

  1. The alcohol is heated under reflux with sulfuric acid and a sodium halide

  2. The hydrogen halide is formed in situ

  3. The hydrogen halide reacts with the alcohol to produce the haloalkane