Organolithium compounds are made by an oxidative insertion reaction from lithium metal and alkyl halides. Each inserting reaction requires two atoms of lithium and generates one equivalent of lithium halide salt.

$\mathrm{RX}\frac{\mathrm{Li}}{\text{ THF or Hexane }}\mathrm{RLi}+\mathrm{LiX}$

Now these organolithiums are used to remove halogen atoms from alkyl and aryl halides in a reaction known as halogen–metal exchange.

$\begin{array}{l}\mathrm{R}\text{'}\mathrm{X}\underset{\mathrm{THF}}{\overset{\mathrm{RLi}}{\to }}\mathrm{R}\text{'}\mathrm{Li}+\mathrm{RX}\\ \mathrm{ArX}\underset{\mathrm{THF}}{\overset{\mathrm{RLi}}{\to }}\mathrm{ArLi}+\mathrm{RX}\end{array}$