The hydroxyl group of an alcohol can be replaced by a halogen atom. The reaction is often known as halogenation.Chlorination of primary and secondary alcohols is carried out using phosphorus (V) chloride PCl5 at room temperature.Chlorination of tertiary alcohols is done by mixing the alcohol with concentrated hydrochloric acid at room temperature.Bromination is carried out by reacting the alcohol with 50% sulfuric acid and potassium bromide.Iodination is carried out using red phosphorus and iodine.