PrimoPyro - 20-10-2002 at 06:47
Tired.......
Detailed explanation to come in a couple hours, after some sleep. Wanted to get this far before bed at least.
Here is the mechanism for the reaction of hydrazine with sodium nitrite in acidic medium, to form sodium azide upon alkaline workup. Sorry you had to
wait so long, Nick. It's been a very busy week for me.
PrimoPyro
Shit
PrimoPyro - 20-10-2002 at 06:49
Man, my fatigue is making me stupid, lol. I forgot to link the picture, doh!
It would really be nice if the edit function worked. Wink, wink, madscientist and Polverone.
Nick F - 20-10-2002 at 12:29
Thanks, much appreciated 
Ah well, I got it wrong when I tried working it out! I didn't know that the reaction started between N2H4 and NOCl. Would I be right in thinking that
NOCl is formed in small amounts in the reaction between NaNO2 and HCl, in cold dilute aqueous solution?
Hmm... if this is the case then is it necessary to make the more dangerous hydrazine hydrate, could you simply use the much safer hydrazine chloride
and NaNO2?
Strangely, I haven't actually been able to find a written method for producing azides using alkali metal nitrites. Does anyone have one?
Acidic Medium
PrimoPyro - 20-10-2002 at 17:20
Yes, as was shown in my mechanism for diazotization thread, O=N-Cl is made by protonation and dehydration of nitrous acid, and is in equilibrium with
nitrous acid and NO+ ion.
Hydrazine hydrochloride would be the major preference to be used. The problem as I see it right now is that this reaction requires acidic medium in
order to progress. However, the acidic medium will ensure that HN3 predominates in solution over N3-, which is a serious health risk.
Madscientist, I suspect that this is why your own experiments with this method went sour. In a basic environment, or even just neutral, the reactions
have immense difficulty proceeding. Indeed the first reaction, the protonation(s) of nitrous ion would not occur at all. OH is not as good a leaving
group as Cl, and O- ion is not a leaving group at all. On the contrary, it would prevent any leaving because of an electron pushing effect on the
nitrogen, when an electron withdrawing effect is needed for the desired pathway. It is a fact that protons are necessary, but perhaps a little
solubility chemistry could be exploited?
Say for example, doing the reaction in a two-pot partition of sorts. Prepare the nitrosyl chloride seperately from NaNO2 + 2HCl, and add the other
reactants afterwards, those being hydrazine acetate, acetic acid, water, and lead acetate.
I *think* the same reaction would ocur, except with the deviation being that lead azide would precipitate upon formation, removing it from the
reaction medium entirely. What are your thoughts?
PrimoPyro
madscientist - 20-10-2002 at 17:39
It might work - but I'm worried that having such a large quantity of acetic acid present might prevent much, if any, lead azide from precipitating.
Considering that there would be three moles of acetate anions for every mole of azide anions, it's hard to imagine much lead azide precipitating..
Nick F - 21-10-2002 at 04:03
And you'd get at least some lead chloride ppting too, I would imagine.
HN3 is a serious health risk. I thought about doing it in a closed vessel, but that'd increase the concentration of HN3 vapour in the air, and it
could get up to levels that are dangerously explosive...
Since HCl is reformed in the reaction, maybe you'd be able to use just a tiny amount of it, and have a slower reaction?
rikkitikkitavi - 21-10-2002 at 08:08
I wouldnt worry to much about HN3 formation:
HN3 = (H)+ + (N3)- pkA = 4,74
HClO = (H)+ + ClO- pkA = 7,52
Thus ClO- is almost 1000 stronger base than (N3)- which means that any free H+ forms HClO instead of HN3.
The coupled equlibrium
HClO + (N3)- = ClO- + HN3 has a eq. constant of 0,0016. Fex starting with 0,2 M of both HClO and (N3)- gives about 0,0075 M HN3. And HN3 is very
soluble in water and weak solutions are stable.
/rickard
ClO- ?
PrimoPyro - 21-10-2002 at 13:17
Where are you getting hypochlorite ions in solution from? Am I missing something?
For the synthesis outlined, no hypochlorite would be formed, only chloride. Do you have similar figures for chloride ion?
PrimoPyro
rikkitikkitavi - 21-10-2002 at 21:48
me/ so wasted. Total syntax error.
forget my previous post.
/rickard
synthesis
Anni - 28-10-2002 at 11:35
Are you sure, it`s not a obscure reaction ?
N2H4 + NaNO2 ----> NaN3 + 2H2O ?
I dont understand
PrimoPyro - 28-10-2002 at 15:07
I dont understand your question. Could you re-word it please?