Convert but-2-yne to 2,2,3-trichlorobutane

[KurtWagner]

Homework Statement

Show by means of equations how you could convert but-2-yne to 2,2,3-trichlorobutane

The Attempt at a Solution

So, as far as I know, to make 2,3-dichlorobutane, all that is required is the addition of one mole of Cl₂ in the presence of an organic solvent.

My query is how to add just one more Cl to the structure.

My first thought is to use 1.5 moles of Cl₂ for each mole of but-2-yne:

2 C4H6 + 3Cl2 → C4H7Cl3

Is this the correct way to do this?

 

[Borek]

No, you will get 2,2,3,3-tetrachlorobutane mixed with 2,3-dichlorobut-2-ene this way.

 

[Saitama]

So, as far as I know, to make 2,3-dichlorobutane, all that is required is the addition of one mole of Cl₂ in the presence of an organic solvent.

No, you would get 2,3-dichlorobut-2-ene if you do that with but-2-yne. Now you need to add an H-atom and Cl-atom across the double bond. Can you think of a reaction which does that?

 

[KurtWagner]

No, you would get 2,3-dichlorobut-2-ene if you do that with but-2-yne. Now you need to add an H-atom and Cl-atom across the double bond. Can you think of a reaction which does that?

So I need one mole of Cl₂ and one of HCl?

Oh, and yeah I should have said 'ene', thanks.

 

[Saitama]

So I need one mole of Cl₂ and one of HCl?

Only one mole of HCl. :)

 

[KurtWagner]

Thanks

 

[epenguin]

One reaction then another. Impeccable! The easy part is done! But is there a best order, and if so which?

 

[KurtWagner]

Does the answer to the order have to do with electronegativity?

 

[Saitama]

Does the answer to the order have to do with electronegativity?

I think so. If HCl addition is done first, the vinyl cation being formed is less stable. Cl2 addition should be done first.

 

[epenguin]

I don't know answers, my first question would be whether reactions conveniently stop after the first bond opening.