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Instead of generating anhydrous ammonia as a liquid using either pressure or cryogenic freezing, I would like to avoid the hassle entirely by using anhydrous ammonia generated as a gas. Is there a way to use a gaseous form of ammonia for the birch reduction that doesn't generate sodium amide? I'm a hobbyist chemist so I don't have access to a ton of glassware or specialty equipment.

And before someone asks me if I'm making meth- No. I like my freedom and this is just a hobby of mine. Mostly why I'm trying the birch is because I have heard the color of the solvated electron is quite beautiful. Chemistry is a wonderful science and I wish simply showing an interest in it wasn't considered so unusual!

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    $\begingroup$ The wiki mentions Birch-like reactions in THF and liquid amines. I guess, that mixture of dry tetramethylethyleneamine and some primary/secondary amine should work. That said, it would require an argon line and I wouldn't do it without a fume hood. However. Some aromatic compounds demonstrate quite significant affinity to electron, and can form stable in solution carbanions. This suggests, that at least for naphtalene and heavier aromatics something can be worked in dry THF with proton donor added by drops. The products, however, may be unexpected. $\endgroup$ – permeakra Jan 17 '16 at 10:40
  • $\begingroup$ I saw that on Wikipedia but I don't have the equipment available to safely try that as far as I can figure. I found this PDF (goo.gl/MT9Q8i) which identifies a specialized product sold by the SiGNa company which allows ammonia free "birch" reductions which takes place in a solution of tetrahydrofuran and the special sodium they symbolized as Na-SG(I). The reaction they detail takes place at 0 deg C and produces reduced phenanthrene at 60% yield. However, since I'm not actually attempting to reduce something, simply learn and see the classical birch, that is not helpful. $\endgroup$ – Emily M Jan 17 '16 at 17:23
  • $\begingroup$ @permeakra Can you identify what products would be produced by the dry THF reaction added dropwise? I'm quite curious. $\endgroup$ – Emily M Jan 17 '16 at 18:55
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    $\begingroup$ Naphtalene (and some other aromatics) produce radical-anions in THF with sodium. Such radical-anions are strong reducing agents, but also may be protonated. The radical produced may pair, dispropotionate or reduce further. $\endgroup$ – permeakra Jan 17 '16 at 20:39
  • $\begingroup$ Lower molecular weight alkyl amines can be used in place of anhydrous ammonia for a birch reduction, if your just wanting to observe the blue colour this might be a more practicle alternative. $\endgroup$ – Technetium Jan 18 '16 at 1:31
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A word of caution: pure ammonia, in either its gaseous or liquified form is extremely dangerous to handle, especially in the context of your 'hobby' where, in your own words you "don't have access to a ton of glassware or specialty equipment." Any ammonia that escapes from your reaction and isn't ventilated properly will cause severe burns to anything it comes into contact with, including completely trashing the lining of your nose and lungs etc. In an attempt to relieve your curiosity, a photograph of a birch reduction showing the characteristic blue is shown below:

enter image description here

That said, the question is an interesting one in the context of laboratory chemistry.

Is there a way to use a gaseous form of ammonia for the birch reduction that doesn't generate sodium amide?

Yes and No. The most common way of performing these reactions on a small scale in a lab context is to essentially pass the gas over your reaction as illustrated below:

enter image description here

Practically, you're not actually making liquid ammonia and then transferring it to your reaction, but rather your passing it over your reaction flask which is fitted with a condenser which will cause in-situ liquefaction of the gaseous ammonia. Even a simple dry ice condenser is sufficient to do this, and the formation of the active reagent is easily observed by the appearance of the characteristic blue/green colour. Any gas not liquified is then passed to the back of the fume cupboard, or, ideally, bubbled through a solution of something to neutralise it and hence stop it being released.

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  • $\begingroup$ Thank you for that answer. So if I were to use a cold finger I could condense the gas immediately before the reaction, and that would only take some cheap dry ice? Also your picture of the dissolved reducing metal/ ammonia solution shows a solution with a ton of free e-; it seems almost black instead of blue. Also I am well aware of the dangers of ammonia. I have a respirator which is rated for ammonia that I purchased online in preparation for this reaction. I also made an airtight setup for the reaction using ptfe tape and stainless steel pipes for the connections. $\endgroup$ – Emily M Jan 16 '16 at 20:59
  • $\begingroup$ Yes. A cold finger with dry ice/acetone is sufficient to cause the ammonia to condense into the reaction flask. One issue you will have if you;re generating the ammonia yourself, however, is that you're unlikely to generate a useful pressure of ammonia. You may also have issues keeping it sufficiently dry. $\endgroup$ – NotEvans. Jan 16 '16 at 21:00
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    $\begingroup$ You'd need a pressure gauge/flow regulator $\endgroup$ – NotEvans. Jan 16 '16 at 21:18
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    $\begingroup$ Let us continue this discussion in chat. $\endgroup$ – NotEvans. Jan 16 '16 at 21:19
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    $\begingroup$ @EmilyM just to add some numbers to NotNicolaou's excellent answer, the boiling point of ammonia is -33 C. A dry ice/acetone (or isopropanol) bath is -78 C, so sufficiently cold to condense ammonia. $\endgroup$ – jerepierre Jan 16 '16 at 21:29

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