The sodium fusion test done in the lab for the systematic identification of a given organic compound is basically fusing sodium metal in a fusion tube, and then adding the compound in a small quantity, then gently heating the compound and then after the completion of initial reaction, strongly heating to red heat and then plunging it into water.

I found that Sodium naphthalenide can be produced by the direct reaction of sodium naphthalenide with THF as the solvent. It is used for the solubilisation of sodium metal and is used as a reagent in place of just sodium metal as it is more effective.

So, the question is whether sodium naphthalenide will form in the fusion tube? If yes, why? If no, why not?

I asked a professor who said it is very unlikely to form due to the presence of oxygen (open to the atmosphere) and without the solvent. I did not get it exactly.

If the reaction does take place, then I think naphthalenide anion will probably undergo oxidation due to the oxygen, but no evidence of oxygen is specifically found. So, the reaction probably doesn't take place. Another evidence pointing towards the "no reaction takes place" side is that the contents of the fusion tube remain colourless (except for the piece of sodium metal) till we start heating it strongly, and the excess naphthalene in the tube vaporises and catches fire, blackening the tube from the outside.

Also, if it is possible, in the comments section, or in an answer, please include the energy difference between naphthalene and naphthalenide radical anion.

So, why does the reaction not take place in the absence of solvent?

  • $\begingroup$ Under the conditions for the sodium fusion test naphthalene should either evaporate or burn. I suppose it is possible that some sodium naphthalenide is transiently formed sometime during the process. However, even if it did survive until the end of the testing procedure, it would be returned to the naphthalene form upon the water quenching step. $\endgroup$ – BiggChemT Nov 11 '16 at 16:43
  • $\begingroup$ @BiggChemT That is sort of what I was thinking, that naphthalene (fused) serves as the solvent for the transient sodium naphthalenide (if formed). However, the naphthalenide radical anion would undergo disproportionation on quenching with water. $\endgroup$ – Eashaan Godbole Nov 12 '16 at 17:42

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