Synthesis of 2-butyne from 2-butene

[jfeyen]

Homework Statement

I'm having a hard time deciding exactly what the mechanism would be for
CH₃CH=CHCH₃→CH₃C\equivCCH₃

Homework Equations

The Attempt at a Solution

My professor only explained half of the mechanism quickly assuming the rest would be obvious, so I know that it will start with a halogenation breaking the double bond before reforming the triple bond. My problem is whether only one equivalent of Br₂ is needed or two before you are able to dehalogenate and form the triple bond. I'm also having a hard time figuring out why the bromines have be be added in the first place only to be taken off again. Also it seems that after the bromination there is a second step adding a catalyst (?) of either Zn or something that looks like +o^- (t-butoxide?). Does this have any effect on the whether we need 2 or 4 bromines on the molecule before reducing? And what exactly makes the bromines come off to form the triple bond?

 

[Infinitum]

See the mechanism here http://www.chemistry.ccsu.edu/glagovich/teaching/311/content/alkyne/synthesis/alkynemake2.html

 

[jfeyen]

Thanks