Synthesis of Chloroalkanes

• What are chloroalkanes?

  Alkanes with hydrogen replaced by chlorine
• Why is it important to understand the synthesis of chloroalkanes?

  They are significant to chemists' work
• What initiates photochemical reactions with alkanes?

  Ultraviolet (UV) light
• What type of reaction occurs when halogens react with alkanes?

  Free radical substitution reaction
• What is a free radical?

  A particle with an unpaired electron
• How do free radicals form?

  When a covalent bond splits equally
• How is a free radical represented in a mechanism?

  With a dot next to it
• What happens when a mixture of methane and chlorine is exposed to UV light?

  It reacts to form chloromethane
• What is the overall equation for the synthesis of chloromethane?

  CH₄ + Cl₂ → CH₃Cl + HCl
• What are the three stages in the synthesis of chloromethane?

  • Initiation
  • Propagation
  • Termination
• What occurs during the initiation step of chloromethane synthesis?

  Free radicals are produced from Cl-Cl bonds
• What is photodissociation?

  Breaking Cl-Cl bonds using sunlight energy
• What happens during the propagation step of chloromethane synthesis?

  Free radicals are used up and created
• What is the first reaction in the propagation stage of chloromethane synthesis?

  Cl• + CH₄ → •CH₃ + HCl
• What happens to the methyl free radical during propagation?

  It attacks another Cl₂ molecule
• What occurs when chlorine is in excess during chloromethane synthesis?

  Hydrogen atoms on methane are replaced
• What are the products formed when chlorine replaces all hydrogen in methane?

  Dichloromethane, trichloromethane, tetrachloromethane
• What happens in the termination step of chloromethane synthesis?

  Free radicals combine to form stable molecules
• What are some possible termination reactions in chloromethane synthesis?

  •CH₃ + •Cl → CH₃Cl
• What are chlorofluorocarbons (CFCs)?

  Halogenoalkanes with all hydrogen replaced
• How does ozone protect the Earth?

  It absorbs ultraviolet radiation from the Sun
• What is the reaction that forms ozone from oxygen molecules?

  O₂ + •O → O₃
• What happens to CFCs in the upper atmosphere?

  C-Cl bonds break down by ultraviolet radiation
• How do chlorine free radicals affect ozone molecules?

  They react to destroy multiple ozone molecules
• What is the overall reaction for ozone destruction by chlorine free radicals?

  2O₃(g) → 3O₂(g)
• Why were CFCs banned?

  They caused damage to the ozone layer
• What are some alternatives to CFCs?

  HCFCs and HFCs are used as alternatives
• What changes have been made to aerosol products since the ban on CFCs?

  Many now use pump spray systems
• What is a common coolant gas used in industrial fridges now?

  Ammonia or hydrocarbons
• What are the environmental problems associated with CFCs?

  • Damage to the ozone layer
  • Contribute to global warming
  • Long atmospheric lifetime