VSEPR_VOID
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Nitric Acid Purification
I have prepared ~500 ml of by the distillation of a mixture of potassium nitrate and sulfuric acid. This acid was then made clear by bubbling dried
air through it. Density shows it to be between 68% and 70% pure.
RDX is on my 'chemical bucket list' due to its importance as a high explosive and extreme stability (not even detonating under stall arms fire). I
also already have purified Hexamethylenetetramine set aside just for this purpose. All the procedures I have seen for its synthesis call for white
fuming (WF) nitric acid having a concentration of about 98%.
WF nitric acid in "Handbook of Preparative Inorganic Chemistry" is prepared using phosphorus pentoxide as a drying agent along with vacuum
distillation.
I. Acid of the highest possible concentration
is distilled; then an inert,
dust-free gas stream, preferably
preheated, is passed through toremove
the nitrogen oxides. It is ultimately
distilled over P2O5.
II. By distillation with H3SO4. The
starting material is acid of the
highest possible concentration...The apparatus
is connected to an aspirator
via a safety trap.
It is also recommended that a stream of oxygen containing some
ozone be passed through the highly concentrated acid and that it be
distilled under aspirator vacuum.
I lack both phosphorus pentoxide and a vacuum distillation apparatus sadly and can not produce it by this method. Does anyone have a procedure for
preparing WF nitric acid without the equitment/reagents listed above? Many thanks.
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ninhydric1
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You don't need a vacuum distillation apparatus. If you have 90+% sulfuric acid, you can just react it with a nitrate salt and distill carefully at 83
degrees Celsius to prevent nitric acid decomposition. This will produce fuming nitric acid as long as you don't add water to the original reaction
mixture.
NileRed did it without a vacuum:
https://www.youtube.com/watch?v=8YWVBBGSxZ8
The philosophy of one century is the common sense of the next.
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NeonPulse
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The problem is without a vacuum you will get NO2 contamination so this just adds the extra step of blowing dry air through it a second time. I found
that even much over the temp requirement for distillation will create at least some decomposition. Distilled from P2O5 will create some N2O5 which is
also a potent nitration agent but if you only want HNO3 then a second distillation over H2SO4 after the initial run will concentrate the acid
sufficiently to be useful in RDX and other things. If you started from HDN then the acid required can be less than 98% concentration and you will
still get decent yield.
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Vosoryx
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I've heard from various sources that (carefully) mixing azeotropic nitric acid with azeotropic sulphuric acid and then distilling at 83 degrees will,
if repeated a few times and done on an arid day, produce WFNA. (Once the dissolved gasses are boiled out) This works even better if you start from
Azeotropic sulphuric (instead of just straight 92% drain cleaner, which is what I start from for my nitric) and dry the nitrate salt beforehand.
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VSEPR_VOID
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I have heard there is a method that involves urea. Is there a method that does not involve distillation?
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Sulaiman
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Why purify in this case ?
Why would you not use azeptropic HNO3 with dissolved NO2 for nitration.
Or RFNA instead of WFNA ?
What problem would the dissolved NOx cause ?
CAUTION : Hobby Chemist, not Professional or even Amateur
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VSEPR_VOID
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The synthesis of RDX requires WF nitric acid in all of the methods I have seen so RF nitric acid or azotropic nitric acid will not due. If I can not
find a way to make it without distillation I will have to ask someone on the forum to make it for me and send it to me.
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Fulmen
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Correct. This is called extractive distillation, the optimal ratio seems to be equal volumes of 67% nitric and 98% sulfuric acid. With weaker acids
you should calculate the amounts so that you end up with the same concentration sulfuric acid after distillation. The FNA produced will be appr. half
the volume of the initial NA.
The product will be somewhat contaminated with NOx unless distilled under vacuum, but IIRC a small amount of urea will remove this. I can't recall if
I did this or not, but it did produce RDX in good yield by direct nitration of hexamine.
The only other method for making FNA I can recall that doesn't use distillation is to react anhydrous calcium nitrate with conc. sulfuric acid. The
problem is that you end up with a gypsum paste saturated with FNA, and separating would a PITA to put it mildly. I've only tried it once and ended up
dumping the entire batch.
It might be possible to wash out the NA using excess SA to produce a mixed acid for other nitration reactions though.
We're not banging rocks together here. We know how to put a man back together.
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XeonTheMGPony
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there was one methode for producing pure nitric by reacting nitrate salt with sulfuric acid, then adding small amount of water then extracting with
DCM
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Deathunter88
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WFNA can easily be made by doing a solvent extraction of 68% (or lower concentration as well) nitric acid with dichloromethane. Nitric acid is very
soluble in DCM, but water is not. I don't have the exact procedure handy but I do remember there being a SM thread on it, and following the procedure
i successfully produced 5ml of WFNA as a proof of concept. It's really just like any other solvent extraction. Additionally, if you are willing to
evaporate off the DCM instead of distilling it, you don't even need to distill anything.
Apologies I didn't see XeonTheMGPony post, but I hope mine will still give this procedure some credibility for just how easy it is.
[Edited on 29-4-2018 by Deathunter88]
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VSEPR_VOID
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That might work! I will have to look into it and purchase some DCM
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