Chemical reactions of alkanes are discussed

1. Chemical Reactions of Alkanes
by
Dr. Nidhi Gupta
M.M. College of Pharmacy
Mullana, Ambala, Haryana, India

6. 1. The reaction is initiated in step I by the homolytic fission of the chlorine
molecule due to the action of heat or light resulting in the production of
chlorine free radicals.
2. In step (2), the chlorine free radical attacks a molecule of methane to form a
stable molecule of HCI and a methyl free radical. In step (3) the methyl free
radical reacts with chlorine molecule to yield methyl chloride and a chlorine
free radical.
3. The chlorine free radical can again attack another molecule of methane as in
step (2). The sequence of reactions in steps (2) and (3) is repeated over and
over again, and thus the chain reaction is propagated.
4. The chain reaction taking place by steps (2) and (3) comes to a halt if a
chlorine free radical meets another chlorine free radical to from a chlorine
molecule in step (4); or if a chlorine free radical meets a methyl radical to
produce a molecule of methyl chloride as in step (5): or two methyl radicals
combine to give ethane as shown in step 6.
5. The steps 4, 5 and 6 which form stable terminal products are referred to as the
'Termination steps’.

8. • When the concentration of methyl chloride produced as a result of chain
propagation steps increases sufficiently, then it can combine with a chlorine
free radical to produce chloromethyl radical and HCI. This radical participates
further in chain reaction to form dichloromethane
and chlorine free radical which can continue the chain by reacting with another
molecule of CH3CI.