# Homework Help: Convert but-2-yne to 2,2,3-trichlorobutane

1. Jul 10, 2014

### KurtWagner

1. The problem statement, all variables and given/known data

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

3. 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?

2. Jul 10, 2014

### Staff: Mentor

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

3. Jul 10, 2014

### Saitama

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?

4. Jul 10, 2014

### KurtWagner

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

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

5. Jul 10, 2014

### Saitama

Only one mole of HCl. :)

6. Jul 10, 2014

### KurtWagner

Thanks

7. Jul 10, 2014

### epenguin

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

8. Jul 10, 2014

### KurtWagner

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

9. Jul 10, 2014

### Saitama

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

10. Jul 11, 2014

### epenguin

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