Write the reaction equation: Octane-butane-methane-bromomethane-ethane

Let’s write down the chain of transformations:
C8H18 – C4H10 – CH4 – CH3Br – C2H6.
Let’s compose the equations for organic substances:
1. С8Н18 = С4Н10 + С4Н8 – octane decomposition reaction, butane and butene were obtained;
2. С4Н10 = СН4 + С3Н6 – cracking of butane, methane and propylene were formed;
3. CH4 + Br2 = CH3Br + HBr – substitutions, bromomethane is released;
4. СН3Br + 2Na = C2H6 + 2NaBr – ethane was obtained in the course of the Wurtz reaction.
The above reactions show the relationship between the homologues of saturated hydrocarbons for the example of octane and methane. The reaction products are of practical importance, for example, bromomethane is used as a solvent.