sodium azide synthesis

[Moltar]

Anyone made some sodium azide from sodium nitrate and sodium amide?

1 mol of powdered sodium nitrate and 3 mol of sodium amide is mixed in beaker and this is molten at 175 degree centigrade. The mix is heated until no ammonia is bubble off and the cooled mass will give a mix of sodium azide and sodium hydroxide.

NaNO3 + 3 NaNH2 -> NaN3 + 3 NaOH + NH3

How can you remove the sodium hydroxide from the cooled mass ?

By the way, a much better method to obtain sodium azide is when dinitrogen monoxide is passed over heated sodium amide at 180 degree centigrade.

NaNH2 + N2O -> NaN3 + H2O

Dinitrogen monoxide is formed when ammonium nitrate is slight heated above the melt point. A Distilling Column will help.

NH4NO3 -> NH3 + HNO3 -> N2O + 2 H2O

Any reply is more than helpful.

[sprocket]

This is a very dangerous procedure, which I'm about to make even more dangerous. Good temperature control and protection is essential.

To separate sodium azide from sodium hydroxide you can convert the azide to hydrazoic acid (highly unstable) by acidification. The hydrogen azide is then distilled off (bp 30°C). The heat of neutralization should be more than enough to evaporate the hydrogen azide, so add the acid slowly. It's probably a good idea to have some water in the receiving flask to dilute the distilled hydrogen azide as it's fairly stable in low concentrations.

Pure sodium azide is then obtained upon neutralization of the hydrazoic acid.

Obtaining pure nitrous oxide from ammonium nitrate can be tricky. A temperature of 180-200°C must be maintained and the stream of gas thoroughly dried. At temperatures above 230°C other nitrogen oxides form.

Keep in mind that sodium amide reacts with water to form sodium hydroxide and ammonia. If you do not dry the nitrous oxide you will end up using even more sodium amide than with the sodium nitrate reaction.

With drying of the nitrous oxide the reaction would be:
2 NaNH2 + N2O --> NaN3 + NaOH + NH3

[sprocket]

Found a couple of nice procedures in Handbook of Preparative Inorganic Chemistry, Volume 1 • Second Edition by Georg Brauer.

A solution of NaN3 is mixed with a small amount of litmus and sulfuric acid ( 2 : 1 diluted with H2O) is slowly added. When an excess of acid is present, the mixture is slowly distilled. By repeated fractionation one obtains 91% acid, which can be made anhydrous by distillation over CaCl2. However, extraordinarily violent explosions sometimes occur with this procedure. According to Gunther and Meyer, HN3 can be prepared in a relatively safe fashion by replacing the sulfuric acid with stearic acid. Pure NaN3 is mixed in a round-bottom flask with stearic acid; a trap cooled to —40°C is fused directly to this flask. The reaction flask is evacuated and heated. The HN3 is then purified by distillation at —50 to 80°C.


SOLUTIONS OF HYDRAZOIC ACID
Because of the very high danger of explosion with pure HN3, it is expedient to work only with its relatively harmless solutions.
I. Aqueous solution: A solution of NaN3 (15 g.) and NaOH (5 g.) is prepared in 150 ml. of water in a 250-ml. distillation flask equipped with an addition funnel and a high-efficiency condenser. The end of the condenser is connected by means of an adapter to a 500-ml. suction flask, which contains 100 ml. of water. The suction outlet of the flask is connected to a tube leading directly to the hood. The contents of the flask are heated to boiling (very important!), and 90 ml. of 40% H2SO4 is added dropwise. The distillation is continued until about 50 ml. of the solution remains in the flask. In this manner one obtains a solution containing about 3% HN3 (0.6-0.7N). The initial addition of NaOH is a precautionary measure which definitely precludes too high a concentration of HN3 in the cold solution.

II. Anhydrous Ether Solution: Since the distribution of HN3 between water and ether is approximately 1:7, one can extract an aqueous solution of HN3 with ether. However, even in this case it is preferable to use a distillation method: NaN3 (30 g.) is dissolved in 100 ml. of water, 150 ml. of ether is added, and the mixture is placed in a 500-ml., round-bottom flask. The latter is equipped with an adapter fitted to a condenser, followed by a suitable icecooled receiver flask containing 100 ml. of ether. The roundbottom flask is also equipped with an addition funnel, the tip of which is immersed in the liquid and through which 30 ml. of concentrated H2SO4 is slowly added. The bulk of the ether and HN3 distill off during the addition of the H2SO4. The remainder is driven off by heating on a steam bath. The ether distillate is dried over CaCl2 and then distilled from this desiccant.

[lacrimachemist]

If this method using hydrazoic acid is used, be EXTREMELY careful. Not only is it highly explosive, but it is extremely poisonous. Hopefully you know this, but just in case...

[meyer25]

Prepare a solution of 40g (1,0mol) NaOH in 50-60mL distilled water. Cool down and adjust the volume to 100mL (10M conc.). Add 62g (1,0mol) 80% hydrazine hydrate and cool down to 0-5°C. Under temperature control of 0-5°C (ice bath) and stirring, add dropwise 90g isopropyl nitrite over an hour. After adding all isopropyl nitrite, stirr by 0-5°C for additional 15minutes, then stop stirring and let the mixture warm up to room temperature. After this is done, evaporate almost all volatile parts under vacuum. You may evaporate the reaction mixture by heating it gently, but avoid open flame or similar because of the isopropanol and traces of isopropyl nitrite boiling off the mixture. Avoid also exposure to iPrONO, as it is toxic. After evaporating all liquids, the solid rest is fairly pure sodium azide. Do not dry the solid substance by heat! Just put it in an desiccator and let it dry by normal teperature. Keep in mind that it is a violent poison.