6.3.3 - Preparation of Halogenoalkanes

• making halogenoalkanes using alkanes

  free radical substitution (halogenation)

  alkane + chlorine/bromine -> halogenoalkane

  conditions: heating or exposure to UV
• making halogenoalkanes from alkenes

  electrophilic addition

  alkene + hydrogen halide -> halogenoalkane with one halogen atom

  alkene + halogen -> halogenoalkane with two halogen atoms
• making halogenoalkanes using alcohols

  alcohol + phosphorous halide/hydrogen halide -> halogenoalkane + water

  substitution reaction

  purify via distillation
• making chloroalkanes using phosphorous pentachloride

  ROH + PCl5 -> RCl + HCl + POCl3
• making chloroalkanes using hydrochloric acid

  ROH + HCl -> RCl + H2O

  room temperature

  used to make tertiary halogenoalkanes because HCl reacts fastest with tertiary alcohols and slowest with primary
• making bromoalkanes using alcohol

  react alcohol with a mixture of sodium or potassium bromide and concentrated sulfuric acid

  produces hydrogen bromide that reacts with alcohol to forms a bromoalkane and water
• making iodoalkanes using alcohols

  1. make phosphorous triiodide in situ under reflux with the alcohol, red phosphorous and iodine
  2. react it with alcohol: 3ROH + PI3 -> 3RI + H3PO3