How do you knock off a halogen from a hydrocarbon chain?

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Discussion Overview

The discussion revolves around the process of removing a halogen from a hydrocarbon chain without introducing other atoms or double bonds, specifically focusing on replacing the halogen with a hydrogen atom. The scope includes theoretical and practical aspects of organic chemistry reactions.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that dehydrohalogenation can remove the halogen, leading to the formation of a double bond between adjacent carbon atoms.
  • Another participant agrees and notes that the subsequent hydrogenation of the double bond can convert it back to a single bond, requiring a catalyst for the reaction.
  • A third participant confirms the need for catalytic hydrogenation to reduce the double bond and mentions specific catalysts such as Ni, Pd, Pt, and Rh.
  • Another approach is proposed involving the treatment of the hydrocarbon with alkali metals like Na, K, or Li, followed by a workup with water, which is suggested as a viable alternative, particularly for larger quantities.

Areas of Agreement / Disagreement

Participants generally agree on the necessity of two separate reactions to achieve the desired outcome, but multiple methods for accomplishing the task are discussed, indicating a lack of consensus on the best approach.

Contextual Notes

The discussion does not resolve the effectiveness or efficiency of the proposed methods, nor does it clarify the conditions under which each method would be preferable.

Simfish
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Without introducing any other atoms or double bonds into the chain? (just replace the halogen with a hydrogen atom). Assume for now that the halogen was introduced in the middle of the carbon chain.
 
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Okay I think I solved it.

Dehydrohalogenation removes the halogen and the attached carbon forms a double bond with another carbon. But then hydrogenation of this double bond into a single bond is spontaneous (it just needs a catalyst to speed up).
 
Last edited:
Pretty much. Yes, it's going to be two separate reactions. Next, you need to reduce the double bond somehow, as by catalytic hydrogenation: i.e., high pressure H2 + a suitable transition metal (Ni, Pd, Pt, Rh, etc).
 
That's one way. Another is to treat with Na or K or Li and work up with water. Your way is better for large quantities.
 

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