9 grams of urea nitrate, was added in small portions to 32 mLof ice cold (-3 C) concentrated sulfuric acid at such a rate that the temperature did not
exceed 5 C. Total time for addition was approximately one-half hour, after which the mixture was poured on 75 grams of ice. The white precipitate was
filtered, washed with ice cold water, just sufficient to cover it, and air dried. Material obtained weighed 5.3 grams and melted with decomposition at
157-158 C.
20g of nitrourea, 65g of zinc dust and 10 mL pure methanol (without water) are mixed in mortar and ground into a thick paste. A glass beaker is filled
with 12 ml of glacial acetic acid and 15 mL pure methanol, then placed into an ice water bath. The cold nitrourea and zinc paste is added in small
portions with gentle stirring. The reaction will give off much heat, so the initial portions should be smaller, and added over longer intervals of
time, so the mixture does not overheat. The rate of addition should be adjusted to keep the temperature from rising too much, ideally around 10 degC.
Do not allow the temperature at any time to rise to 35C. If the mixture becomes too thick or the temperature rises too rapidly, cold methanol should
be added (no more than 50g). The additions to the paste should be done over a time of around 3 hours.
After completion, the beaker containing the reaction mixture should be allowed to stand in ice water bath for another hour. The beaker is then removed
from bath and allowed to warm slowly to normal temperature. The final volume of the mixture should be around 130 mL. After one hour at room
temperature, the mixture is placed on water bath, heated to 25 degC, and stirred for 30 minutes, then heated to 32-35C, and stirred for 30 more
minutes, finally being heated to 40 degC and stirred at this temperature for another 15 minutes.
When the reduction reaction is complete, the solution is immediately filtered using a vacuum funnel, and filtering the solid product dry. The solid is
washed with 90 mL of water, then filtered. The solids left over are discarded. The filtrates (solution that dissolved out the semicarbazide and passed
through the filter paper) are combined. The solution will contain around 10g of dissolved semicarbazide. The yield for the reaction of nitrourea to
semicarbazide at this point is 60%)
Dilute sulfuric acid (5% solution) is added to the solution until the pH just reaches 6.5. It is important that the resulting solution not be too
acidic or contain excess acid. It may be helpful to pre-cool the acid solution.
9.2g of Sodium Nitrite is separately dissolved in 125 mL water, and this solution is reacted with the semicarbazide sulfate solution (which contains
the equivalent of 10g semicarbazide). The addition should be slowly done, over the period of roughly ten minutes, the temperature should be kept below
20 degC, but ideally 10 degC is good. The reaction may give off some poisonous vapors so do it outside or in a fumehood. After this reaction,
immediately proceed to the final step, which is to gradually add a pre-chilled concentrated solution of sodium hydroxide.
The resulting solution contains dissolved sodium azide, along with byproducts of sodium carbamate, and sodium sulfate (much of it will precipitate out
as solid crystals on the bottom below 15 degC).
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I was
reading about hydrazine generation by semicarbazide and liquid ammonia and dilute acids under pressure. Why not semicarbazide and sodium nitrite
with an acid? ANyone have thoughts on this?