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

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Discussion Overview

The discussion revolves around the chemical conversion of but-2-yne to 2,2,3-trichlorobutane, exploring the necessary reactions and conditions for achieving this transformation. Participants examine the addition of chlorine and hydrogen atoms, as well as the implications of reaction order and stability of intermediates.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested
  • Exploratory

Main Points Raised

  • One participant suggests using 1.5 moles of Cl2 to convert but-2-yne to 2,2,3-trichlorobutane, proposing the equation 2 C4H6 + 3Cl2 → C4H7Cl3.
  • Another participant counters that this approach would yield a mixture of 2,2,3,3-tetrachlorobutane and 2,3-dichlorobut-2-ene instead.
  • It is noted that to produce 2,3-dichlorobutane, one mole of Cl2 is needed in the presence of an organic solvent, but this would lead to 2,3-dichlorobut-2-ene when starting with but-2-yne.
  • Participants discuss the need to add an H-atom and Cl-atom across the double bond, questioning whether one mole of HCl is also required.
  • There is a suggestion that the order of reactions may be influenced by electronegativity, with one participant proposing that Cl2 addition should occur before HCl addition due to stability concerns of the vinyl cation formed.
  • A participant expresses uncertainty about whether reactions stop after the first bond opening, indicating a lack of clarity on the reaction mechanisms involved.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best method for achieving the conversion, with multiple competing views on the appropriate reactions and their order remaining unresolved.

Contextual Notes

There are uncertainties regarding the stability of intermediates and the specifics of reaction mechanisms, as well as the potential for side reactions leading to undesired products.

KurtWagner
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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?
 
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No, you will get 2,2,3,3-tetrachlorobutane mixed with 2,3-dichlorobut-2-ene this way.
 
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KurtWagner said:
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?
 
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Pranav-Arora said:
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.
 
KurtWagner said:
So I need one mole of Cl2 and one of HCl?

Only one mole of HCl. :)
 
Thanks
 
One reaction then another. Impeccable! The easy part is done! But is there a best order, and if so which?
 
Does the answer to the order have to do with electronegativity?
 
KurtWagner said:
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.
 
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I don't know answers, my first question would be whether reactions conveniently stop after the first bond opening.
 

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