The addition of sodium or potassium iodide catalyzes many SN2 reactions of alkyl chlorides or bromides. Explain. I think the reason why it catalyzes many SN2 reactions, has to do with the fact that it is the best leaving group of all the alkyl halides. But why else? Also, is the potassium and sodium the group that brings the iodide into the solution? Or do we use them, because they are cheaper than lets say lithium. Ignore my tangent, and please explain my initial question.