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What is a possible mechanism for the Beilstein test for halogens ? I can't seem to find a arrow pushing mechanism for this reaction.

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  • $\begingroup$ You can easily find it if you dig google enough. I do know the answer, but not going to write one and recommend to search it yourself, it is easy. $\endgroup$ – permeakra Jun 25 '14 at 22:14
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    $\begingroup$ Please, I tried a Google search but I could not find one. If writing the mechanism is too much work, please give me a link. Thank You ! $\endgroup$ – Pepria Jun 25 '14 at 23:25
  • $\begingroup$ I was under the impression that the goal of a stack exchange was so that, when you googled a question, the top result would be a stack exchange result. This was the stated goal on Stack Overflow; I'm not sure if it's extended to all sites on the stack exchange network $\endgroup$ – chipbuster Jun 26 '14 at 0:06
  • $\begingroup$ hmm..well its listed as the fourth result. Maybe if someone helped me figure out the mechanism, it might become the first result... $\endgroup$ – Pepria Jun 26 '14 at 0:28
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    $\begingroup$ @permeakra I agree with Martin; I would like to add that you usually have useful contributions, and I would like to hear them even if answers are readily found online. It's always great getting a second opinion. $\endgroup$ – Dissenter Jun 26 '14 at 3:43
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When you heat the copper wire in a flame, it is oxidized on the surface to copper (II) oxide:

$$\ce{2Cu(s) + O2(g) -> 2CuO(s)}$$

Then when you mix it with the halide and heat it, the higher reduction potential makes it displace the oxygen.

Here's an example with sodium chloride:

$$\ce{CuO(s) + 2NaCl(s) -> CuCl2(g) + Na2O}$$

Copper halides are volatile (except for fluorides); the gas is hot enough to push some electrons into an excited state, and as they cool a tiny bit, the electrons drop back into their rest state and emit the excess energy in the form of a photon with a wavelength corresponding to the color green.

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  • $\begingroup$ Chlorine, however, is less electronegative than oxygen. $\endgroup$ – Dissenter Jun 26 '14 at 6:53
  • $\begingroup$ Thanks for pointing that out, I meant reduction potential. I'm not my best at one in the morning! $\endgroup$ – prooffreader Jun 26 '14 at 15:05
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    $\begingroup$ I heard that even before mixing the halide, when you are heating the copper wire, a green colour flame might be seen. So you must wait till that colour disappears before you mix the halide. This is probably due to impurities of halides in the environment or on the wire. So what do these halides convert into - considering the green colour disappears after some time? $\endgroup$ – Charles Jul 13 '15 at 10:14

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