Reactions of alcohols

• Combustion

  Alcohols burn completely in a plentiful supply of oxygen to produce carbon dioxide and water, this reaction is exothermic releasing a large quantity of energy in the form of heat.
• Oxidation of alcohol

  Primary and secondary alcohols can be oxidized by an oxidizing agent. The usual oxidising mixture is a solution of potassium dichromate (VI)$K_2Cr_2O_7$ acidified with dilute sulfuric acid$H_2SO_4$. If that alcohol is oxidized the orange solution containing dichromate (VI) ions is reduced to a green solution containing chromium (III) ions.
• Oxidation of primary alcohols

  Primary alcohols can be oxidized to either aldehydes or carboxylic acids. The product of the oxidation depends on the reaction conditions used because aldehydes are themselves also oxidised to carboxylic acids.
• Preparation of aldehydes

  On gentle heating of primary alcohols with acidified potassium dichromate, an aldehyde is formed. To ensure that the aldehyde is prepared rather than the carboxylic acid the aldehyde is distilled out of the reaction mixture as it forms this prevents any further reaction with the oxidizing agent. The dichromate (VI) ions change colour from orange to green.
• Preparation of carboxylic acids

  If a primary alcohol is heated strongly under reflux, with an excess of acidified potassium dichromate (VI), a carboxylic acid is formed. Use of an excess of the acidified potassium dichromate (VI) ensures that all of the alcohol is oxidized. Heating under reflux ensures that any alcohol formed initially in the reaction also undergoes oxidation to the carboxylic acid.
• Oxidation of secondary alcohols

  Secondary alcohols are oxidised to ketones. To ensure the reaction goes to completion, the secondary alcohol is heated under reflux with the oxidizing mixture the dichromate (VI) ions change colour from orange to green.
• Oxidation of tertiary alcohols

  Tertiary alcohols do not undergo oxidation reactions. The acidified dichromate (VI) remains orange when added to a tertiary alcohol.
• Dehydration

  An alcohol is heated under reflux in the presence of an acid catalyst such as concentrated sulfuric acid or concentrated phosphoric acid. The product of the reaction is an alkene. Dehydration of an alcohol is an example of an elimination reaction.
• Substitution

  Alcohols react with hydrogen halides to form haloalkanes. To form a haloalkane, the alcohol is heated under reflux with sulfuric acid and a sodium halide. The hydrogen halide is formed in situ. A hydrogen halide formed reacts with the alcohol to produce a haloalkane.