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WaveFront
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Concentration of ortophosphoric acid?
Hi,
I have found ortophosphoric acid as a rust remover. I am thinking to boil it, to get some more concentrated form that could be used as dehydrating
agent. Well i don't think that I can achieve P2O5... but who knows? I am a bit worried about formation of of acidic fumes. Any suggestion? 
Edit of title by chemoleo: it is phosphoric acid
[Edited on 26-2-2009 by chemoleo]
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Sauron
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Brauer's book (in forum library) has details on concentrating orthophosphoric acid all the way to anhydrous.
That is not P2O5/P4O10 but 100$ H3PO4
Not a dehydrating agent.
What do you want to dehydrate?
Do you merely want to dry something or do you want to abstract the elements of water from a compound?
For example, an amide to a nitrile.
Sic gorgeamus a los subjectatus nunc.
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WaveFront
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Well, I was thinking to dehydrate nitric acid to achieve some nitrations from diluted nitric. Since it is not worth for dehydrate, maybe I must
forget it. I will read the reference to the Brauer´s book.
Thanks
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Sauron
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You want to obtain conc HNO3 from dil HNO3 to perform nitrations? Then what you want to do is to distill HNO3 with conc H2SO4, the cheapest
dehydrating agent there is.
Or, prepare HNO3 from conc H2SO4 and KNO3 - you can either use the mixture to nitrate your substrate in many cases or you can distill the HNO3 from
the mixture.
Again instructions are in Brauer.
Be careful as this is nothing to fool around with carelessly.
Sic gorgeamus a los subjectatus nunc.
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WaveFront
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I was looking for a shorcut to convert HMTD to RDX, mixing HMTD, nitric, ammonium nitrate and "dehydrating agent", so I wanted to avoid the
sulfuric, as is destroys RDX.
As you said, maybe the easiest way in the distillation.
Thanks again for your safety advice. Though I´m pretty coward already 
[Edited on 24-2-2009 by WaveFront]
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Sauron
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I.m afraid there are no shortcuts such as you describe, which appears to be some bastardized form of the Bachman process sans Ac2O. The Bachman
process is tricky and often fumes off in inexpert hands, so, I advise you to stick to the simpler methods.
[Edited on 25-2-2009 by Sauron]
Sic gorgeamus a los subjectatus nunc.
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WaveFront
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Well, after all maybe there is still a small possibility...
I should try to heat the ortophosphoric in the microwave oven and see what happens... 
http://www.springerlink.com/content/70r0r1108t918174/
[Edited on 24-2-2009 by WaveFront]
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Sauron
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Put H3PO4 in a microwave and you get hot H3PO4.
A good way to ruin a microwave.
You are starting to sound like a walking disaster.
Sic gorgeamus a los subjectatus nunc.
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WaveFront
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Ok, I am not expert in Chemistry, as you have noticed.
The link says they get metha-phosphoric, that should be solid. It is not for the microwaves themselves, but for the heating, and the microwaves is a
comfortable method to heat in an inert vessel like glass.
A good method to protect a microwave is to have inside certain amount of water, (in other glass, for example).
I am new here and I guess I should stop my thread at this point.
Anyway, thanks for your interest.
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DJF90
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Having a glass of water will only theoretically stop the microwave from overloading. This will do nothing to prevent corrosion of the microwave cause
by the acid phophoric acid fumes that will be produced to some degree. Bear in mind that hot conc. phosphoric acid also etches glass if I remember
correctly.
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panziandi
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Glass is not INERT to hot conc H3PO4 ...
I would not like to go heating ortho-phosphoric acid to dehydrate it to pyrophosphoric or metaphosphoric. I used to heat ammonium hydrogen phosphate
to get the concentrated acid, it's very difficult to drive off all of the ammonia and my beaker eventually broke!
Make nitric acid from KNO3 and H2SO4 and distill it out of the mixture. You can achieve highly pure and highly concentrated nitric acid.
If you are truely insane perhaps try acetyl nitrate.... I AM JOKING!
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DJF90
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Concentrating the nitric acid using conc. sulfuric acid is the easiest way to do this, and if you UTSFE I'm sure you will find plenty of threads
detailing the production of concentrated nitric acid. Make sure that you use something suitable to heat the mixture in a flask (NOT an oil or water
bath... sand is most likely to be best). If you distill the nitric acid under reduced pressure ("vacuum") make sure you use a suckback trap and
appropriate scrubber depending on type of vacuum pump you use (so as to not damage the pump with the acidic vapors).
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WaveFront
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Definitely, i will not concentrate the phosforic... at least at this point of knowledge
I prefer the advice of panzianzi and maybe use the ketene route, hot and confinated (Joking).
About sulfuric, I have a fridge compressor as a vacuum pump, maybe when I have time (not at this moment) I prepare an appropiate setup.
Thanks everybody
[Edited on 25-2-2009 by WaveFront]
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Sauron
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It is neither necessary nor advisable to do the distillation of HNO3 under vacuum. At the minimum this would mean adding a serious cold trap (Dewar,
liquid N2 or dry ice-acetone slurry) as well as suckback protection and you need none of that when operating at normal pressure. Keeep it simple,
stupid was the rule long befoe this forum started.
Sic gorgeamus a los subjectatus nunc.
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PHILOU Zrealone
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To me the dehydration of H3PO4 is a good idea...but polyphosphoric acid is only reached after a long time slow reflux boiling of H3PO4 in the
open...polyphosphoric acid is indeed a sort of anhydride because it displays anhydride bonds P-O-P and therefore it is valuable as alternative to P2O5
what might be difficult to find or get for some of us...
HO-P(OH)(=O)-OH + HO-P(OH)(=O)-OH --> (HO-)2P(=O)-O-P(=O)(-OH)2 + H2O
Etc. to higher polymers with loss of water.
It would be a serious loss of energy to put it with diluted HNO3...I would as suggested by others first make a preconcentration step to 69% the
azeotropic conc HNO3-H2O and then use a heat recylcable dehydrating stuf like anhydrous MgSO4 or Mg(NO3)2 for a further distillation or decantation of
the 69% conc HNO3 to higher %.
The use of polyphosphoric acid as dehydrator for nitration is known but in your case, I think it might be a trouble because of the viscosity of the
stuff what would render you mix less heat diffusionable and thus less heat controlable and favourise hotspots --> runnaway in the case of RDX
Also is it really a good idea to start with HMTD ( if you mean hexamethylenediamine triperoxyde)?
[Edited on 25-2-2009 by PHILOU Zrealone]
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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Sauron
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I would guess he means hexamethylenetetramine dinitrate, but he really ought to have been explicit, the over-use of acronyms is a constant source of
confusion and error.
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WaveFront
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Nop, I wanted to say the peroxide, one of the few things I can do with my scarce reactives. I was thinking the shortest way from my HMTD to RDX.
Later I would have try a more direct route; maybe adding H2O2 to the mix, the HMTD could be an intermediate product in the reaction thus catalysing
the formation of RDX. I hope not have said any sort of stupidity (I am electronic, not chemic)
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Sauron
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Well, you have been advised against thst foolishness and I can only agree, and wash my hands oh this self destructive idiocy.
Sic gorgeamus a los subjectatus nunc.
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PHILOU Zrealone
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| Quote: | Originally posted by WaveFront
Nop, I wanted to say the peroxide, one of the few things I can do with my scarce reactives. I was thinking the shortest way from my HMTD to RDX.
Later I would have try a more direct route; maybe adding H2O2 to the mix, the HMTD could be an intermediate product in the reaction thus catalysing
the formation of RDX. I hope not have said any sort of stupidity (I am electronic, not chemic) |
-H2O2 and HMTD are not suitable initial product to go to RDX...Hexamethylene tetramine (HMTA) (used to get HMTD) is on the other hand much better
starting material.
I see two reasons not to use the peroxyde:
1°) It is explosive, sensitive to friction and heat...what you get by definition if you want to mix your reactant mix and keep the heat reaction
cool.
2°) You will have to oxydise much more CH2-O moeties than with HMTA and much more rearrangement of the N and CH2 to get the sym-triazine ring...thus
this means much more exothermic (thus much less control of heat and gas evolution (CO2)) and much lower yield...
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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WaveFront
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I trust what Philou says is true. The (probably wrong) idea came to me for two reasons:
--In Urbanski vol 3, it is briefly mentioned a route from HMTD to RDX, with conc. nitric acid and ammonium nitrate. The ammonium nitrate would
increase the yield giving some NH2+ (???) groups to the reaction. (I am travelling and don´t have access to the book now)
--A long time ago I tried to "nitrate" HMTD with an small amount of 70% nitric.... but it failed and just decomposed, giving probably hexamine
dinitrate (?) or maybe nothing. But the reaction was fast, so a light turned on on my mind when I got the ortophosphoric....
If I were to do that, i would add the HMTD in tiny amounts to avoid any kind of runaway. But finally I will not make this, have other less dangerous
things in mind
Just that... if reactives were easy
to adquire, everything would be easier and I would not complicate the things...
[Edited on 25-2-2009 by WaveFront]
[Edited on 25-2-2009 by WaveFront]
[Edited on 25-2-2009 by WaveFront]
[Edited on 25-2-2009 by WaveFront]
[Edited on 25-2-2009 by WaveFront]
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Ebao-lu
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| Quote: | | Well, I was thinking to dehydrate nitric acid to achieve some nitrations from diluted nitric. |
H3PO4 will not work as a dehydrating agent, but you can try to heat your H3PO4 with a salpeter to get conc(and probably, fuming) nitric acid distilled
off. Maybe even dihydrophosphates would work, but it higher temperatures.
| Quote: | | The link says they get metha-phosphoric, that should be solid. |
it is indeed an interesting route to
metaphosphoric acid, but you can realy spoil the microwave. H3PO4 tends to overheat and it will make a big "BUBBLE" once, and get out from the
vessel(besides glass is known to be not resistant, and metall can't be used). Besides metaphosphoric acid is poisonous.
| Quote: |
Later I would have try a more direct route; maybe adding H2O2 to the mix, the HMTD could be an intermediate product in the reaction thus catalysing
the formation of RDX. I hope not have said any sort of stupidity (I am electronic, not chemic) |
The route from HMTD and ammonium nitrate+HNO3 is possible, because HMTD is like a dehydrating agent there, allowing to use less HNO3 and somewhat
replace it with NH4NO3 that provides N atoms that HMTD molecule lecks to become a cycle with 3 CH2 and 3 NH. H2O2 can not be used as a catalyst there
(especially an aqueous solution of one, that will only further inhibit NO2+ formation).
This method seems to be very dangerous - HMTD can easily explode under conc HNO3. The original procedure probably must be using low temperatures.
Besides, i highly reccomend you to avoid all the physical manipulations with the reacion at any step(better to use some distant method for adding all
the reagents, maybe made from alarm clock or a remote console), even if they are stated in the procedure as made by hands. That also concerns the
scale and the load of HMTD, if it is not specially mentioned in the procedure. As for HNO3, in this case it should not contain traces of metal
ions(that can react with H2O2), and be colourless if possible. WaveFront, i dont reccomend you to do RDX that way anyway(only if completely distant)
[Edited on 25-2-2009 by Ebao-lu]
[Edited on 25-2-2009 by Ebao-lu]
as for concentration, there was some thread in prepublication
https://sciencemadness.org/talk/viewthread.php?tid=7370
[Edited on 25-2-2009 by Ebao-lu]
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WaveFront
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As you say the mix HMTD +nitric , is inadmisible risk. My hope was that, added is small amounts, the HMTD dissapears very fast by the action of the
nitric.
Anyway, as I said, I will not assume the risk. If somebody more skilled and with better equipment wants to try, please, tell to us.
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panziandi
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LOL! You are crazy :p
Anyway... I said Acetyl Nitrate which can be used as an "exotic" nitrating agent but you would have to be rather daft to make it pure much more common
to prepare in situ. I never mentioned ketene :s
Anyway this is a little k3wl for my tastes
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Ebao-lu
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I think main danger is coming from HMTD itself, not from the mixture of HMTD+HNO3. But RM can undergo a vigourous red-ox reaction with heat
production, and cause the detonation either of dissolved, or unreacted part of solid HMTD. So better to add hmtd to acid, non contrary(there should
be no solid). For example, you can devide your hmtd to many small parts, keep them in remoteness of the reaction vessel, and add carefully to the RM
one by one, after the previous is consumed(even you need to run away before next part of HMTD falls into RM).
What is there in Urbanski procedure concerning cooling?
[Edited on 25-2-2009 by Ebao-lu]
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WaveFront
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| Quote: |
What is there in Urbanski procedure concerning cooling?
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Nothing in Vol. 3
For the procedure, it just points to reference:
56. T. VRBANSKI and K. SZYC-LEWANSKA, Bull. Acad. Polon. Sci., ser. chim. 6, 165 (1958).
[Edited on 26-2-2009 by WaveFront]
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