Reaction Mechanisms: Free Radical Substitution

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Presentation transcript:

Reaction Mechanisms: Free Radical Substitution 1

Monochlorination of methane CH4 + Cl2 → CH3Cl + HCl methane chloromethane

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

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

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

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

Monochlorination of ethane C2H6 + Cl2 → C2H5Cl + HCl ethane chloroethane

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

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

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

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