woelen
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Preparation of dilute hydrazine from N2H4.2HCl
I have a decent amount of hydrazine dihydrochloride (300 grams or so) and I would like to use part of this for making a dilute (let's say 20%)
solution of hydrazine in water. With 100 grams of this I can make 30 grams hydrazine, allowing me to make approximately 150 ml of a 20% solution.
I want to do the following:
- Take 100 grams of N2H4.2HCl
- Add 50 ml of water
- Slowly, while stirring add 75 grams of crunched solid NaOH.
This results in a slurry of NaCl and a liquid, which also is saturated in NaCl and contains the free hydrazine base. This step I already tried on a
testtube scale with the same proportions of chemicals and it works quite well. You simply have to add the NaOH slowly, due to the production of heat.
When 75 grams of NaOH is added, then this is just below the amount needed to neutralize all HCl. So, with this amount, no excess hydroxide remains,
while certainly 95% of all hydrazine will be released as free base.
I want to filter the slurry of NaCl and then boil off the clear liquid to get all water and hydrazine in this. What remains is a chunk of left-over
NaCl. I plan to do this distillation in my all-glass with ground joints distillation setup, at normal pressure and boiling range 100 .. 120 C, until
an almost dry slurry of mainly HaCl remains. With this procedure I expect that I certainly can have a 90% yield.
My problem is that I read in many places that hydrazine attacks glass when it is distilled. I don't want to spoil my precious all-glass distillation
setup with this.
Now I am not using excess NaOH, but just enough to almost neutralize both HCl's in the N2H4.2HCl. If that is done, then hardly any free hydroxide will
be present in the liquid. Is this safe with the glassware or does this still lead to attack of the glass? I hardly can imagine that hydrazine attacks
glass, I suspect it is the hydroxide which is bad.
Any advice on this is highly welcomed. Next weekend I want to try this, but only if I am convinced that the glassware is not attacked.
If there are any other risks, which I overlook, then I also like to know about that (I know of the toxicity of hydrazine and that the vapor is
carcinogenic).
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PHILOU Zrealone
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Just as NaOH corrodes glass upon heating, so does N2H4...
Note that only the concentrated warm N2H4 will corrode the glass.
I had pure 80% hydrazine solution (hydrazine monohydrate) at home in a plastic PE bottle. When placed in glass testubes, I never noticed any
corrosion...
Personnally I would avoid distillating the stuf in glasware since when concentrated, the risk of explosion is high owing to the endothermic heat of
formation of N2H4...it is hypergolic.
From this you see that cold distillation (enventually with reduced pressure) is the best. I would make a distillation settup with an enclosed system
consiting of two flasks (hard PE plastic or glass) and a plastic pipe between the two.
First flask would be your reactor where you can put the NaOH and the N2H4.HCl or N2H4.2HCl...
The heat of reaction and the surrounding would serve as heat source! The second flask will be put into a freezer (or freezing bath)...
N2H5OH being volatile (like water is), it will slowly evaporate from the reaction flask and condense into the freezing flask, without any risk of
explosion. Eventually, at the end, help the process by gentle warming of the reaction flask; neutralisation heat will not last forever
Beware to the cleaningness of your glasware and reactants...
Traces of heavy metals are very bad for hydrazine (catalytical decomposition)...
Iron into the NaOH, Chromium onto your glasware (H2SO4/K2Cr2O7 cleaning), or other heavy metals that you like most from what I can see out of your
website 
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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Formatik
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| Quote: | Originally posted by woelen My problem is that I read in many places that hydrazine attacks glass when it is distilled. I don't want to spoil
my precious all-glass distillation setup with this.
Now I am not using excess NaOH, but just enough to almost neutralize both HCl's in the N2H4.2HCl. If that is done, then hardly any free hydroxide will
be present in the liquid. Is this safe with the glassware or does this still lead to attack of the glass? I hardly can imagine that hydrazine attacks
glass, I suspect it is the hydroxide which is bad. |
Just use some metal vessels for heating, all of the older procedures I've seen use silver apparatuses, but it seems that copper works too since Gmelin
mentions a process for N2H5OH that uses N2H4 sulfate which is mixed with powdery KOH and a bit H2O which was distilled in a copper retort, and the
condenser made of glass. I would also clean the metal beforehand with thiourea solutions (commonly available as anti-tarnish).
I don't know about iron itself. Rusting metals should be avoided. The autoignition of N2H4 is at about 23ºC in contact with iron rust, 132º in with
black iron, 156º in contact with stainless steel, and 270º in contact with glass (Hazardous Chemicals, Desk Reference, 3rd ed.). And N2H4 can ignite
with porous materials also (wood, cloth, oil).
The Merck Index, 14th ed., says N2H4 can be stored for years sealed in glass, in a cool, dark area. N2H5OH doesn't attack stainless V2A steel,
Allegheny stainless 304 and 347 steel, where Mo-based stainless steels should be avoided. The Merck Index also says N2H4 explodes if it is distilled
while traces of air are present.
Cork and rubber also get attacked (anhydrous and the hydroxide both attack those). For anhydrous N2H4 you can work with (distill in) glass, only if it
is under reduced pressure, the same with N2H5OH. Note also that you can use anhydrous CaO with the hydrochloride to get your N2H5OH.
[Edited on 5-2-2009 by Formatik]
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woelen
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Thanks for your responses. It now is clear to me that simple distillation at 100..120 C of this compound is not wise. It will eat the glass and may
even lead to explosion. So, I should find some metal flask, in which to do the distillation, or use vacuum at lower temperature. I have no experience
yet with the latter, I'll first try with water at 60 C or so. I do have a vacuum pump (up to now I used it for other things only, such as filtering
and physics experiments).
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DJF90
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Would forming a silver mirror on the inside of the flask protect it from the hydrazine? The silver could be removed by nitric acid once the procedure
is completed.
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Panache
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i know not whether the plumbing industry is as advanced (perhaps it is more so) in the Netherlands as it is in Australia, however i will comment
assuming it is.
In australia there are two kinds of polyolefin tubing available that serve excellently for dealing with caustic or phosphoric solutions at temperature
(up to 70C) and under vacuum. One is of polypropylene construction the other of polybutylene construction.
The polybutylene tubing is used for hot water systems, it is a snap and lock system, of recent deployment, and specified for hot water up to 70C and
120PSI, quite remarkable and super convenient, i have never had it under vacuum.
The polypropylene tubing is used for alcohol delivery systems in large hospitality businesses (casino's etc), and is rated similarly (its wall
thickness however is notably larger and it comes in a range or colours, whereas the polybutylene tubing is available in depressing light grey only).
Notably though this system is also specified for suction and caustic ( to allow cleaning of the lines). I can also report that with very limited
skills i have successfully welded this tubing, using a cool alcohol flame, onto the polypropylene stoppers commonly used for volumetric flasks,
(having the same taper gradient as ground glass labware). Greater success no doubt would come using a heat gun (must buy one eventually). I have used
this system extensively and have never had a failure.
I state these facts within this thread less so as a practical response to your query Woelen, as your volumes are small, but more so in an effort to
encourage SM members to realise the availability of very practical polymer solutions to problems pertaining to glassware.
Polyolefin's are our future, go Shell!
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watson.fawkes
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| Quote: | Originally posted by Panache
The polybutylene tubing is used for hot water systems, it is a snap and lock system, of recent deployment, and specified for hot water up to 70C and
120PSI, quite remarkable and super convenient, i have never had it under vacuum. |
Polybutylene was rated for
household plumbing in the US a while ago, then derated because of formulation and reliability problems. There's a second generation of PB out that is
evidently much better. My warning is to check the manufacture date of the material. Basically, don't buy new old-stock (NOS) tubing or fittings.
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Formatik
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| Quote: | Originally posted by woelen
Thanks for your responses. It now is clear to me that simple distillation at 100..120 C of this compound is not wise. It will eat the glass and may
even lead to explosion. So, I should find some metal flask, in which to do the distillation, or use vacuum at lower temperature. I have no experience
yet with the latter, I'll first try with water at 60 C or so. I do have a vacuum pump (up to now I used it for other things only, such as filtering
and physics experiments). |
Some of the distillation procedures given for N2H5OH preparation are done with a vacuum and some at regular atmospheric pressure. Though I haven't
looked at any of the procedures to see what, if any precautions were taken. I will get you the general references later, then you can see what I'm
talking about.
I've also looked through Gmelin to find more on hazards of distillation. Looking at behavior to air. In CO2-free air, N2H5OH decomposes slowly at 25
to 30 deg. forming N2 (normally it absorbs CO2 out of the air). At 150 to 160 deg. in the presence of air also the following reaction occurs: N2H5OH +
O2 = 3 H2O + N2 (A. Scott, J. chem. Soc. 85 [1904] 917). Some oxides react explosively with N2H5OH, e.g. HgO, CrO3 (oxidizers, of course).
N2H4 itself: N2H4 can be heated without any signs of decomposing, first after higher temperatures it decomposes - namely over 300º according to C.A.
Lobry de Bruyn (Ber. 28 [1895] 3085; Rec. Trav. chim. 15 [1896] 180). In the presence of air decomposition is to NH3 and N2 at 183º, in the presence
of H2O in a N2-atmosphere N2H4 is stable at 300º (A. Scott, J. chem. Soc. 85 [1904] 913; A. Stähler, Ber. 42 [1909] 3019). Hg-, Cu- and Pb-oxide
react very violently (C.A. Lobry de Bruyn, Rec. Trav. chim. 15 [1896] 183).
Although N2H4 doesn't explode when heated in a flame, but burns with a hissing yellow flame (C.A. Lobry de Bruyn, Rec. Trav. chim. 13 [1894] 439),
distillation of larger amounts (however, not in a H2-atmosphere) causes an extraordinarily violent detonation (R. Stollé, K. Hofmann, Ber. 37 [1904]
4524).
I'm not sure what the scale is, Stollé and Hofmann ref is talking about, but it seems to me the precautionary of Merck might apply to industrial
scale quantities. Which sometimes is the case for this kind of knowledge when drawing out of references, laboratory scale knowledge gets mixed in with
the industrial, and then this becomes "general knowledge", e.g. like those on the MSDS. But it never hurts to be precautious. That all should give
some more saftey background on those.
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chemrox
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Formatik: What apparatus made of what material(s) did the workers cited above use? If not glass they must have discussed the issue in the
reports....?
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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S.C. Wack
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Stolle and Hofmann may have been doing something that someone else is unlikely to do.
http://www.rsc.org/delivery/_ArticleLinking/DisplayArticleFo...
An abstract is on page 28.
If you really need anhydrous hydrazine (!) safer alternatives are known (see Vogel) and are discussed in the relevant thread.
The bad reactions of hydrazine can be found in the usual places such as Bretherick's, Mellor, Ullmann's, K-O, and probably that hydrazine pdf from a
while back.
Hurd and Bennett, in making 95-96% hydrazine hydrate from dilute solution with toluene and xylene azeotropes in 1928, (see Vogel again) used glass
flasks and fractionating columns, and corks covered with tinfoil.
[Edited on 7-2-2009 by S.C. Wack]
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Formatik
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| Quote: | Originally posted by chemrox
Formatik: What apparatus made of what material(s) did the workers cited above use? If not glass they must have discussed the issue in the
reports....? |
I don't know regarding citations in my previous post. But concerning the hydrate preparation procedures where Cu or Ag was used as the apparatus is
where distillation was done at regular atmospheric pressures, otherwise reduced pressures and this is all that is mentioned in Gmelin concerning this.
Nothing mentioned of any inert atmosphere (if the authors even used one).
| Quote: | Originally posted by S.C. Wack
Stolle and Hofmann may have been doing something that someone else is unlikely to do.
http://www.rsc.org/delivery/_ArticleLinking/DisplayArticleFo...
An abstract is on page 28.
If you really need anhydrous hydrazine (!) safer alternatives are known (see Vogel) and are discussed in the relevant thread. |
From that link you've given us it seems hydrazine might not be on the main menu. Probably mentioned as precaution as a side.
| Quote: | | Hurd and Bennett, in making 95-96% hydrazine hydrate from dilute solution with toluene and xylene azeotropes in 1928, (see Vogel again) used glass
flasks and fractionating columns, and corks covered with tinfoil. |
Raschig also used to wrap cork stoppers with the Sn foil to protect against the anhydrous.
Anyways, right here is what I was talking about, woelen. The boiling points might also be useful.
[Edited on 7-2-2009 by Formatik]
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woelen
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Formatik, thanks for the PDF-file. It is very informative.
It is amazing to see how many practical difficulties exist in isolating such a simple base from its salts. Before I can proceed, I need additional
apparatus. I'll go for the vacuum distillation route at 60 C or so. I tried vacuum distillation with water, where the water is heated in a water-bath,
kept at 60 C. It worked well, but I need a cold-trap. Without a cold-trap, a lot of water vapor was sucked into the pump (droplets of water were
formed in the transparent rubber tube, going to the vacuum allonge to the vacuum pump). I have a membrane pump, but I don't want to have any
hydrazine-containing vapor in it.
I could use an erlenmeyer as cold-trap, but I am afraid that it might implode (thin glass and not a spherical shape).
According to Formatik's PDF-link, storage of hydrazine-hydrate may be another risk, which I did not think of. It slowly decomposes under many
conditions, giving N2, which may lead to pressure buildup.
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chloric1
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Woelin sounds like you got a interesting method here I would love to know the outcome.
| Quote: |
According to Formatik's PDF-link, storage of hydrazine-hydrate may be another risk, which I did not think of. It slowly decomposes under many
conditions, giving N2, which may lead to pressure buildup.
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Yeh well if the vacuum distillation method works out OK for you and it is not terribly time consuming, I would only make hydrazine hydrate as needed.
It is rocket fuel by the way. You could take whatever ou don't use and change it back to N2H4 2HCl if you like. That would be the safest approach.
Fellow molecular manipulator
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