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Author: Subject: Attempted synthesis of KN3 with methanol: failed, but interesting observation
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[*] posted on 20-9-2016 at 12:44
Attempted synthesis of KN3 with methanol: failed, but interesting observation

I read about synthesizing KN3 from an organic nitrite (e.g. isopropyl nitrite or butyl nitrite), KOH and hydrazine hydrate, with pure ethanol as solvent.

I do not have pure ethanol, not the 96%, nor anhydrous ethanol, because of the very high taxes on this. I did not want to use my denatured ethanol, as this contains some oily stuff with a fruity odour. I decided I give it a try with pure methanol instead. This does not work, but the observation is interesting.

I did the following:

Dissolve as much of KOH in some methanol. Allow white solid matter to settle at the bottom and decant the resulting clear colorless liquid from the remaining solid matter.
Add a little pure hydrazine hydrate (64% hydrazine by weight, corresponding to N2H4.H2O) to the solution of KOH in methanol and swirl: A colorless liquid is obtained. This clear liquid is called A.

In another test tube, mix appr. 1 volume of isopropyl nitrite with three volumes of methanol: a pale yellow liquid is obtained. This clear pale yellow liquid is called B.

Add a few drops of solution B to liquid A: When this is done, a big bubble of gas is produced, but this immediately dissolves in the liquid again. The top part of the liquid becomes orange, but remains clear. On shaking, the entire liquid becomes yellow.
Slowly add all of liquid B to liquid A while swirling constantly: The resulting liquid becomes quite hot and becomes beautiful orange/yellow. It remains clear.
The temperature remains high for quite some time, apparently there is some exothermic reaction going on for a few minutes. Slowly, colorless crystals appear in the liquid. The crytals settle at the bottom and also on the glass wall crystals appear.

Take apart a small amount of the clear orange/yellow liquid and add dilute H2SO4 to it: A lot of gas is produced, the orange color disappears, a white precipitate is formed (this must be hydrazine bisulfate, which is nearly insoluble in cold water). When a flame of a cigarette lighter is kept near the gas, then it quickly burns with a pale bluish/greyish flame.

Allow the remaing part of the yellow/orange liquid to stand for a hour and let it cool down: A fairly thick layer of crystals has formed on the bottom, the liquid still is orange/yellow.
The liquid does not produce any gas on acidification with dilute H2SO4, it does produce a white precipitate though (excess hydrazine, giving hydrazine bisulfate).

The crystals are rinsed twice with diethyl ether. After rinsing they are off-white, very pale tan. The ether quickly is evaporated and the result is a fairly dry crystalline solid.

Next I did some tests:
- Heat some of the solid in a test tube: It melts, giving a colorless liquid, which on cooling down solidifies to a white solid again.
- Put some of the solid on a small spatula and keep it in a flame. It melts and starts to fizzle somewhat. On stronger heating all of it seems to evaporate. No fire, no explosion. This certainly is not azide (a test with commercial NaN3 shows that this burns with a loud crackling noise and spraying orange sparks around).
- Dissolve some of the solid in water. It dissolves quite well. Add a little solution of copper sulfate. The result is formation of a brown precipitate. The brown precipitate disappears again and a white solid is formed (probably some copper(I) compound). On acidification with a large excess amount of dilute H2SO4 the white solid seems to remain. Some gas is produced as well, the white solid moves upward and forms a foamy mess on/near the surface of the liquid.

I repeated the experiments with 1-propanol instead of methanol. With this no orange/yellow color is obtained. Apparently, methanol does something very specific in this reaction.

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[*] posted on 20-9-2016 at 13:12

Maybe using KOH/methanol some transesterfication of the isopropylnitrite to methyl nitrite takes place, which is a gas far below room temperature and would explain the bubble of gas formed as well as the flamability of the gas. According to this reference ( methyl nitrite and hydrazine hydrate should be able to produce sodium azide, though maybe conditions need to be very different and some reduction products of hydrazine and methyl nitrite were formed instead, maybe an (N/O)alkylhydroxylamine? Hydroxylamine itself decomposes using a copper(II) salt pretty quicly IIRC.

[Edited on 20-9-2016 by nitro-genes]
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[*] posted on 24-9-2016 at 22:34

Very interesting observations. We tried this reaction with isopropyl nitrite using ethanol and also using isopropanol as solvents, and using both sodium and potassium hydroxide, and all combinations worked (although NaOH requires more solvent due to lower solubility). The only catch with using IPA as a solvent is that if any of the IPA has been oxidised to acetone (e.g. over-exposure to air) then this will stuff things up because your hydrazine will rapidly react with the ketone. Ethanol is therefore somewhat more reliable.

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[*] posted on 25-9-2016 at 06:12

I also did this reaction many years back. Used anhydrous ethanol , sodium/potassium hydroxide and hydrazine hydrate 80%. My version was i used methyl nitrite prepared directly in situ (nitrite sol.+methanol and add dilute h2so4) and bubbled through mixture hydrazine/na/koh/etOH - for me more convenient no handling with nitrites which makes headache. For some time beautiful crystals azide came out - potassium or sodium , washing with ether, after couple of years still nice and white.
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