Monday, April 30, 2012

Dissolving lithium in anhydrous ammonia


Here's an interesting reaction where lithium metal is dissolved in anhydrous ammonia. I placed a couple small pieces of lithium in a test tube, then connected the tube to a larger flask of ammonium hydroxide via silicone tubing. Upon heating the flask, gaseous ammonia will be produced which is condensed in the test tube by cooling it with a bath of alcohol and dry ice. The resulting solution is brilliant bronze in color, but at lower lithium concentrations, the solution is deep blue -- a very beautiful reaction.

6 comments:

Sean Michael Ragan said...

As you probably already know, this reaction is called the "Birch Reduction." The blue color is commonly attributed to "solvated electrons," i.e. the solution of alkali metal in liquid ammonia is kind of like a beaker full of dissolved electrons in the same way that, say, hydrogen chloride dissolved in water is like a beaker full of dissolved protons. You may also be aware that the garage version of this reaction using lithium from coin cells is somewhat infamous as a common reduction operation in the illegal manufacture of methamphetamine from pseudoephedrine.

Jonathan said...

Why do the drug lords have to go ruining beautiful chemical reactions?

Mark said...

Try drying the ammonia prior to liquefaction using a drying column packed with calcium chloride or Drierite. Cheers, Mark

Mark said...

Try drying the ammonia gas by passing it through a column of desiccant (e.g. calcium chloride, Drierite) before the cold trap. Cheers, Mark

Anonymous said...

It's not a "Birch reaction". Li+NH3 is only a reactive to do a Birch reaction

Th' Gaussling said...

Lithium is prone to reaction with atmospheric nitrogen to form a nitride coating on the surface. This coating passivates the lithium and renders it less reactive. Storage under argon is recommended to keep the lithium fresh. The low atomic weight of lithium means that relatively small amounts of it can generate a good deal of hydrogen on contact with water. The LiOH residual is quite caustic and justifies eye protection when handling.

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