- Created by: Kyra Mullarney
- Created on: 22-04-19 15:18
- When comparing alcohols with alkanes containing the same number of carbon atoms alcohols are less volatile, have higher melting points and greater water solubility than the corresponding alkanes.
- Differences become much smaller as the length of the carbon chain increases.
- Alcohols have polar O-H bonds because of the difference in the electronegativity of the oxygen and hydrogen atoms therefore the alcohols are polar.
- The intermolecular forces will be very weak but there will also be much stronger hydrogen bonds.
- Hydrogen bonds require large amounts of energy to overcome them so alcohols have high melting points.
- Alcohols are soluble in water as the polar OH group can form hydrogen bonds with the water molecule.
Combustion of alcohols
- Alcohols burn completely in a plentiful supply of oxygen to produce carbon dioxide and water.
- The reaction is exothermic releasing a large quantity of energy in the form of heat.
C2H5OH + 3O2 ---> 2CO2 + 3H2O
Oxidation of primary alcohols
- On gentle heating of alcohols under distillation with acidified potassium dichromate, an aldehyde is formed.
- If the primary alcohol is heated strongly under reflux with an excess of potassium dichromate a carboxylic acid is formed.
C4H9OH + [O] ---> C4H8O + H2O
Butan-1-ol + oxidising agent ---> butanal + water
C4H9OH + 2[O] ---> C3H7COOH + H2O
Butan-1-ol + oxidising agent ---> butanoic acid + water
Oxidation of secondary alcohols
- Secondary alcohols are heated under reflux to form ketones.
- It is not possible to further oxidise ketones using acidified potassium dichromate.
C3H7OH + [O] ---> C3H6O + H2O
Propan-2-ol + oxidising agent ---> Propanone
Dehydration of alcohols
- Alcohols are heated under reflux in the presence of an acid catalyst such as concentrated sulfuric acid or concentrated phosphoric acid.
- Produces an alkene.
- It is an example of an elimination reaction.
Substitution reactions of alcohols
- Alcohols react with hydrogen halides to form haloalkanes.
- The alcohol is heated under reflux with sulfuric acid and a sodium halide.
C3H7OH + HBr ---> C3H7Br + H2O
Propan-2-ol + hydrogenbromide ---> 2-bromopropane + water