Preparation of Pure Ammonia

by Eleusis

As stated before, this is only for the truly insane. Please consult all relevant toxicology sources, lab technique manuals, and common sense before attempting this procedure. It is mildly amusing when it works, but a major lethal pain in the ass if, say, you run out of dry ice. Kid's, don't try this at home, really.

There are no good ways to efficiently make ammonia without extensive industrial equipment. Even worse, due to it's low boiling point and corrosive/poisonous nature, there are no good ways to really store it in the home lab either. But, if you need pure ammonia, there is little other choice but to use the following procedure.

Assemble the following glassware or an equivalent in stainless steel:


     ---------     -----------------   
     | ----- |     |  ------------ | 
     ||     ||     | |            ||
    /||\    ||    -- --          8||
    ||||    ||    |xxx|           ||
1  -||||    ||    |xxx|           ||
   -||||    ||    |xxx|           ||
    ||||    ||    |xxx|           ||
  2 ||||    ||    |xxx|           | --------     -
    ||||   5||   6|xxx|           --------| |   | |
   -||||    ||    |x7x|                   | | 10| |9
3  -||||    ||    |xxx|                   | |   | |
    ||||    ||    |xxx|                   | |   | |
    \||/    ||    |xxx|                   |  ---  |
     ||     ||    |xxx|                    \     /
     /\     ||    |xxx|                     -- --
  ---  ---  ||    |xxx|                       ||
  |      |  ||    -- --               |   ----  ----   |
  |  4   |  ||     | |                |   |   11   | 10|12
  |      |  | -----  |                |   |        |   |
  |      |  ----------                |   ----------   |
  --------                             ----------------

(1) is the Supply connection for ice water for the condenser (2) which serves to condense much of the evolved water. (3) is the return line for the cooling water. (4) is the boiling flask where 3% Ammonia solution is placed to boil gently. (5) is glass or teflon tubing. (6) is a glass cylinder or Hempel fractionation column which is packed with (7) Calcium Oxide or Soda Lime to remove remaining water from the ammonia vapor. (8) is teflon tubing to connect the column to the (9) Cold Finger condenser which is charged with (10) a dry ice/acetone slush. (11) is the receiver flask to hold condensed liquid ammonia. (12) is a bowl that contains (10) dry ice/acetone slurry to keep the condensed ammonia in the liquid state.

3% or 28% (if you are *really* lucky to get it) Ammonium Hydroxide solution is placed into a glass container and an equinormal amount of concentrated (31.45% ok) Hydrochloric acid is added to make ammonium chloride. This mixture is then concentrated to about 15% of the original volume by boiling off the excess water (*).

The ammonium chloride/water solution is placed in a flask and chilled to 0C using an ice/salt bath. An equinormal amount of Sodium Hydroxide solution is then added to convert the ammonium chloride into ammonia and salt. You should add enough water such that the ammonia concentration will be less than 40% (it saturates around 47% at 0C and allowance must be made for the dissolved salt). Now, the flask contents are gently boiled to liberate ammonia as a gas. The water vapor which comes along is condensed back into the flask and the boiling continues until no more ammonia comes off the cold finger condenser. At this point, the boiling flask can be recharged to continue distillation. The collected ammonia should ideally be used immediately by disconnecting the cold finger from the receiver and performing the reaction requiring liquid ammonia in situ (eg - a Birch Reduction). The collected ammonia will be anhydrous, any water being removed first by the reflux condenser, next by the CaO drier and third by forming ice on contact with the cold finger.

Keep in mind that if you need, say, .5 liter of ammonia, you will have to distill 17 liters of 3% Ammonia solution to get it. This will require a *lot* of dry ice, so get a styrofoam cooler-full ahead of time.

(*) Thanks to Jason Kennerly for reminding me that making the ammonium salt will improve the volumetric efficiency of the process greatly!


- eleusis@netcom.com - Ammonia Preparation Doc - 09/03/95 -