Explain electrophilic addition reactions of ethylene with mechanism.

Explanation

1) Addition of halogens : Ethylene combines with halogens at room temp.in an inert solvent medium, to give a vicinal dihalide.
Ex : Bromination.
`underset("Ethylene")(CH_(2)=CH_(2)+Br_(2))tounderset("((Vicinal dihalide)")underset("(1, 2- dibromoethane)")(CH_(2).Br-CH_(2)Br)`
Mechanism : It involves 2 steps.
Step (I) : The `pi`- electrons of the double bond attack the halogen molecule. Then a loose `pi` complex (cyclic bromonium ion), with a 3- membered ring is formed.

Step (II): The negative bromide ion attacks the cyclic bromonium Ion from the backside.

This is called, 'trans' addition of halogens.
2) Addition of hydrogen halide: Ethylene reacts with hydrogen halide (HX) to give ethyl halide.
Ex : `underset("Ethylene")(CH_(2)=CH_(2)+HXtounderset("Ethylhalide")(CH_(3)CH_(2)X)`
Mechanism : This mechanism is quite similar to that of the halogen addition, involving 2 steps.
Step : 1
3) Addition of hypohalous acid to ethylene : Ethylene reacts with hypochlorous acid to give ethylene chlorohydrin.
`underset("Ethylene")(CH_(2)=CH_(2)+HOCl)tounderset("Ethylene chlorohydrin")(underset(OH)underset(|)CH_(2)-underset(Cl)underset(|)CH_(2))`
Mechanism : `HOClto(HO)^(-)+Cl'`
The same mechanism as in the case of addition of HX.
`HXtoH^(+)+X^(-)`
In HOCl, the Cl' adds first. Then `OH^(-)` adds to the carbon atom.