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. $\endgroup$– permeakraCommented Jun 25, 2014 at 22:14
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5$\begingroup$ 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 ! $\endgroup$– PepriaCommented Jun 25, 2014 at 23:25
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1$\begingroup$ 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 $\endgroup$– chipbusterCommented Jun 26, 2014 at 0:06
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2$\begingroup$ @permeakra Please share your wisdom. I tried finding it on google (for a good while) and managed nothing. And frankly, I find your attitude a little disturbing. $\endgroup$– Martin - マーチン ♦Commented Jun 26, 2014 at 3:12
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1$\begingroup$ @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. $\endgroup$– DissenterCommented Jun 26, 2014 at 3:43
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1 Answer
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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. $\endgroup$ Commented Jun 26, 2014 at 6:53
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$\begingroup$ Thanks for pointing that out, I meant reduction potential. I'm not my best at one in the morning! $\endgroup$ Commented Jun 26, 2014 at 15:05
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2$\begingroup$ 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? $\endgroup$– CharlesCommented Jul 13, 2015 at 10:14