Chemical Properties of Alkanes::
Alkanes being saturated compounds mostly show substitution reactions. Their oxidation is very difficult thus even strong oxidizing agents like KMnO4, K2Cr2O7 etc cannot oxidize them.
Halogenation:
Halogens replace hydrogen from alkanes and it is called halogenation of alkanes. The order of reactivity of halogens with alkanes is
F2>Cl2>Br2>I2
Fluorine shows a reaction to explosive violence. The reaction of iodine is slow and reversible.
Halogenation is a substitution reaction and it proceeds through the free radical mechanism.
- In dark no reaction occurs CH4 + Cl2 -> No reaction
- In direct sunlight reaction occurs with explosive violence and carbon soot is produced
- CH4 + 2Cl2 —> C + 4 HCl
- In diffused sunlight a chain reaction occurs.
CH4 + Cl2 —> CH3Cl + HCl
CH3Cl + Cl2 —> CH2Cl2 + HCl
CH2Cl2 + Cl2 —> CHCl3 + HCl
CHCl3 + Cl2 —> CCl4 + HCl
If Cl2 is taken in excess then tetra chloromethane will be major product. If methane is taken in excess then chloromethane will be the major product.
Mechanism:
It is a free radical substitution reaction. Its steps are divided into three categories.
Step-I Initiation Reaction:
Reaction Initiating Step: The step in which molecule splits and free radical is generated and due to which then reaction starts is called initiation step.

Step-II Reaction Propagation Step:
The step in which one free-radical gives birth to another free radical is called propagation. Following are reaction propagation steps.







Step-III Reaction Terminating Step
The step in which two free radicals combine to give a molecule is called the termination step.

Oxidation:
- Combustion:
Alkanes on heating strongly in air start burning. A combustion reaction is an oxidation reaction.
Alkanes on burning in sufficient supply of air produce carbon dioxide and water vapours and heat is liberated.
CH4 + 2O2 → CO2 + 2H2O + 891kJ
But in limited supply of air carbon monoxide and water vapours is produced and less heat is liberated.
2CH4 + 3O2 → 2CO + 4H2O + Heat
And in very little supply of air carbon soot and water are produced and least heat is liberated.
CH4 + O2 → C + 2H2O + Heat
Ethane or burning also produce same products.
2C2H6 + 7O2 → 4CO2 + 6H2O ΔH = – 3081 KJ or -1540.5 KJ/mol
- Catalytic Oxidation:
Lower alkanes on heating in air in presence of copper catalyst and applying pressure, oxidize to mixture of useful products.
Alkanes first oxidize to corresponding alcohols

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