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Reaction Mechanisms: Free Radical Substitution

Reaction Mechanisms: Free Radical Substitution. Monochlorination of methane. CH 4 + Cl 2 → CH 3 Cl + HCl methane chloromethane. Initiation. Ultraviolet light causes splitting of chlorine molecules into chlorine atoms Cl - Cl → Cl ● + Cl ●

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Reaction Mechanisms: Free Radical Substitution

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  1. Reaction Mechanisms: Free Radical Substitution

  2. Monochlorination of methane • CH4 + Cl2→ CH3Cl + HCl methane chloromethane

  3. Initiation • Ultraviolet light causes splitting of chlorine molecules into chlorine atoms Cl - Cl → Cl● + Cl● Chlorine Chlorine atoms molecule (free radicals)

  4. Propagation CH4 + Cl● = CH3● + HCl methane Methyl radicalHydrogen chloride CH3● + Cl2 = CH3Cl+ Cl ● Chloromethane Chlorine atom free to react with another methane molecule

  5. Termination Cl● + Cl● = Cl2 CH3● + Cl ●= CH3Cl CH3● + CH3● = C2H6

  6. Evidence for this mechanism Use of ultraviolet light even for a very short period causes a chain reaction Formation of trace quantities of ethane Reaction speeded up by sources of free radicals such as tetraethyl lead

  7. Monochlorination of ethane • C2H6 + Cl2→ C2H5Cl + HCl ethane chloroethane

  8. Initiation • Ultraviolet light causes splitting of chlorine molecules into chlorine atoms Cl - Cl → Cl● + Cl● Chlorine Chlorine atoms molecule

  9. Propagation C2H6 + Cl● = C2H5● + HCl ethane ethyl radicalhydrogen chloride C2H5● + Cl2 = C2H5Cl+ Cl ● Chloroethane Chlorine atom free to react with another ethane molecule

  10. Termination Cl● + Cl● = Cl2 C2H5● + Cl ●= C2H5Cl C2H5● + C2H5● = C4H10

  11. Evidence for this mechanism Use of ultraviolet light even for a very short period causes a chain reaction Formation of trace quantities of butane Reaction speeded up by sources of free radicals such as tetraethyl lead

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