# Why is there a color change when ethene reacts with bromine?

Nov 2, 2016

Because neither ethylene nor ethyl bromide have a characteristic colour.

#### Explanation:

On the other hand, bromine has a characterstic red-orange colour. When bromine reacts with an olefin (which are typically colourless), the orange colour dissipates as it reacts with the bromine.

Typically, we use orange-coloured bromine water, and the reaction gives an halohydrin:

$R C H = C {H}_{2} + B {r}_{2} \left(a q\right) \rightarrow R C H \left(O H\right) C {H}_{2} B r + H B r \left(a q\right)$

Bromine is the electrophile, i.e. ""^(delta+)Br-Br^(delta-), and it reacts to give a ${2}^{\circ}$ carbocation. This carbocation then reacts with the most abundant nucleophile, which of course is water in aqueous solution.

Bromine is the one of the most corrosive substances you can handle in a laboratory. You treat this as you would treat your girlfriend/boyfriend, i.e. with care and respect.