Question

To make a dihalo-olefin from an alkyne, should the halogen be added to the alkyne, or vice versa?

Answer 1

Clearly, the bromine should be ADDED to the alkyne.

Explanation:

An alkyne could potentially react with 2 equiv of halogen. A priori, we would predict that a reaction where the alkyne was in excess (i.e. the bromine added to bulk alkyne) was the preferred method.

In the reverse addition, more than the 1 equiv of `X_2` might be added to the alkyne.