Jor - 20-9-2009 at 13:25
I will soon obtain 100mL of 55% hydrazine hydrate (35% hydrazine). I really wanted this, but took the somewhat safer 55% concentration, instead of
100% hydrazine hydrate (65% hydrazine). I will use some for reductions, for the luminol synthesis (I have my 3-nitrophthalic acid crystallising right
now), and I was thinking of other things to use it for.
One thing that came into mind is making HI.
I was thinking the following reaction would likely occur:
N2H4 + 2 I2 --> N2 + 4 HI
This would make an extremely efficient reaction, if you take just a slight excess of iodine, add a very small crystals of thiosulfate, and distill. Or
one can also take a very small excess hydrazine, and accept the very small hydrazine contamination in the final product.
And it would require small amounts of hydrazine. 2 moles of I2, about 500 grams, would require only a little more than 90mL of the 55% hydrazine
hydrate (or 50mL 100% hydrazine hydrate). So I could make about 51mL of 57% HI from just 9mL my hydrazine and 50g of iodine (I have plenty of iodine,
about 350g).
So do you guys see any complications in this reaction? I don't see why it won't work. the only thing I am scared of is that some sort of explosive
compound is formed, just like in the case of ammonia+iodine, something like N2I4 (just a guess). Do you know if any of these compounds exist?
I need HI for a few inorganic synthesis.
JohnWW - 20-9-2009 at 14:44
If done in the aqueous liquid phase, it would be much safer and easier to handle than by simply trying to react H2 gas with I2.
Jor - 20-9-2009 at 15:18
H2 and I2 react only slowly. And H2 just bubbles out of solution, wasting lots of HI.
I just read that HI is actually made industrially using hydrazine:
http://www.absoluteastronomy.com/topics/Hydrogen_iodide
So I am going to try this method when I get my hydrazine.
chemrox - 20-9-2009 at 21:41
seem like another explanation of why HI (aq) is so expensive.
woelen - 21-9-2009 at 09:12
You don't need free hydrazine base. Just use the sulfate salt, which is much easier and safer to handle. Add I2 to a solution of this and distill off
the liquid (HI + water). Somewhat easier is first mixing hydrazine sulfate with NaOH (use slight excess hydrazine sulfate), because hydrazine sulfate
is only sparingly soluble while hydrazine sulfate + NaOH leads to much more concentrated solutions, from which Na2SO4 can be crystallized before you
have to evaporate the HI from the solution.
If you have hydrazine chloride, then this also works, but then you have the complication that HCl is left behind instead of H2SO4 and that is much
more difficult to separate from HI, so the sulfate is preferrable.
Using the free base hydrazine might be risky, because freebase hydrazine tends to disproportionate in many reactions (side reaction, occurring when
the liquid heats up): 3N2H4 --> 4NH3 + N2 and the NH3 in turn can react to form NI3.NH3, an explosive adduct of nitrogen triiodide and ammonia. You
can see whether this side reaction occurs or not. If you add iodine to an excess amount of hydrazine and the liquid does not become totally clear,
then you have NI3.NH3. This material is dark grey, like iodine and does not dissolve.
[Edited on 21-9-09 by woelen]
Ephoton - 22-9-2009 at 01:08
I think I might be having a wetdream