Reactions of alcohols

• Alcohols combust completely to produce carbon dioxide and water. This reaction is exothermic. As the number of carbon atoms in the alcohol increases, the quantity of heat released per mole also increases.
• Primary and secondary alcohols can be oxidised by an oxidising agent.

  The usual oxidising mixture is a solution of potassium dichromate(VI) acidified with dilute sulfuric acid.
• When an alcohol is oxidised by acidified potassium dichromate, the orange solution containing the dichromate(VI) ions is reduced to a green solution containing chromium(III) ions.
• Primary alcohols can be oxidised to either aldehydes or carboxylic acids. The product of the oxidation depends on the conditions used because aldehydes are themselves also oxidised to carboxylic acids
• On gentle heating of primary alcohols with acidified potassium dichromate, an aldehyde is formed.

  To ensure an aldehyde is prepared rather than carboxylic acid, the aldehyde is distilled out of the mixture as it forms

  This prevents further reaction with the oxidising agent
• If a primary alcohol is heated strongly under reflux, with an excess of acidified potassium dichromate, a carboxylic acid is formed.

  The excess of acidified potassium dichromate(VI) ensures all of the alcohol is oxidised.

  Heating under reflux ensures that any aldehyde formed initially in the reaction also undergoes oxidation to the carboxylic acid
• Secondary alcohols are oxidised to ketones.

  It isn't possible to further oxidise ketones using acidified dichromate(VI) ions.

  To ensure the reaction goes to completion, the secondary alcohol is heated under reflux with the oxidising mixture
• Tertiary alcohols do not undergo oxidation reactions. The acidified dichromate(VI) remains orange
• Dehydration is any reaction in which a water molecule is removed from the starting material
• An alcohol is heated under reflux in the presence of an acid catalyst (e.g. sulfuric acid or concentrated phosphoric acid) the product is an alkene. This the dehydration of the alcohol, an example of an elimination reaction.
• Alcohols react with hydrogen halides to produce haloalkanes.

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

  Sodium halide reacts with sulfruic acid

  This forms the hydrogen halide which then reacts with alcohol to form the haloalkane.

  This is a substitution reaction.