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Author: Subject: Nitromethane extraction
xwinorb
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[*] posted on 12-4-2006 at 10:38
Distilling nitromethane from RC fuel


SWIX has a question on distilling nitromethane from RC fuel.

Technique used :

Aproximately 800 ml of RC fuel was washed with 200 ml water, twice, water poured carefully over fuel to avoid emulsion. Top water layer separated. Bottom layer dried with CaCl2 ( this dessicant is used in an Organic Synthesis method for making nitromethane ).

Distilled at RT. Main nitromethane fraction collected at 90 - 101 C. Got 250 g. Compared weight of same volume of water, got 221 g. This yields density = 1.13.

Question :

I have done this twice, both times I noticed some strange yellow byproduct forming on the side of the boiling flask during distillation. Not sure if it is nitromethane decomposing, castor oil decomposing or nitromethane reacting with other ingredient in the RC fuel.

Does someone knows what this is ?

Does this happens when distilling pure nitromethane ?

Any danger ?


This time, I have also extracted the top water layer with DCM, combined with main fraction. But, the DCM BP is raised by the nitro / oil mix, so it does not separate cleanly from the main nitro fraction. I think I would distill it separately next time.

Any suggestions or comments welcome.
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daeron
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[*] posted on 12-4-2006 at 12:29


it doesnt happen with the pure nitromethane...i doubt that its some byproduct forming, prolly some of the impurities w lower density and higher surface tension. when exactly does this start to happen, on the begining, during the whole or at the end?

if nitromethane was decomposing you would know about it, trust me




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xwinorb
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[*] posted on 12-4-2006 at 14:23
Impurity


It happens in the middle of the distillation. Started seeing some yellow spots, slowly increasing, a fairly large ammount at the end. Washed away easily with 70 % IPA and soap.

I prefer washing the MeOH with water, then drying the RC fuel before distilling as outlined, because the yields seem better. Otherwise a lot of nitro just evaporates away with the MeOH at the start.

I don't think there is any problem using water, but what about CaCl2 as dessicant ? It is indeed recomended in the Organic Synthesis for nitromethane.
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praseodym
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[*] posted on 13-4-2006 at 04:31


Shouldn't be a problem since CaCl2 is suitable for drying alkyl and aryl halides, most esters, saturated and aromatic hydrocarbons as well as ethers.



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Tacho
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[*] posted on 13-4-2006 at 08:52


xwinorb, I would be VERY CAREFUL with those byproducts.

Reading your post, I remembered something I read long ago in the usenet groups (google.groups). Doing a search with +nitromethane +explosive +salts +distillation I found this:

"Distillation of Nitromethane
Todas as 24 mensagens no tópico - exibir como árvore
De: Dave Klein - ver perfil
Data: Sex 15 mar 2002 19:47
E-mail: dpkl...@hotmail.com (Dave Klein)
Grupos: sci.chem
<snip>

My group here at Iowa State has run into some problems with the drying of
nitromethane by distillation. Hopefully someone can help us out....

A while back (>10 yrs) we had an explosion of the contents of a
nitromethane still. After refluxing on Calcium Hydride overnight, it was
noticed that a yellowish sludge was forming inside the flask. The
distillation was stopped, and the nitromethane was decanted from the
sludge. The flask was placed in the back of a hood, overnight, the flask
detonated and turned the flask into sand.


Recently, we used calcium chloride as the drying agent instead of calcium
hydride (300ml CH3NO2 over 2.5 g CaCl2). However, it was noticed that a
yellow sludge was again forming. Upon further reflux, the solution turned
maroon, then to black.


So my question is: Does anyone have any personal experience with this sort
of problem? and if so: How did you dispose of it?


Thanks For Your Time


Dave Klein



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<snip>
-

Nitromethane is acidic and salts of the aci-nitro tautomer are
explosive. Try drying over activated 4A molecular sieves followed by
reduced pressure distillation.

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As I said before in this thread, the Merck index says nitromethane forms explosive salts.

Therefore, I believe the extraction of nitromethane with an alkali is not a good idea.

[Edited on 13-4-2006 by Tacho]
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neutrino
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[*] posted on 13-4-2006 at 17:32


These salts are known as nitronates. Search this forum and RS (www.roguesci.org) for more information about them.



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[*] posted on 13-4-2006 at 17:47


Yes, but the nitronates form under alkaline conditions. Doesn't look like alkaline conditions were employed here. I suggest that if you *must* use CaCl2, add some HCl to it to keep it acidic. Keep adding it during destillation. Although I seem to remember that NM is unstable both in alkaline and acidic conditions, but for the latter, I couldn't figure out why.
As I suggested before, possibly a route to purification is to form the nitronate first (witha base), purify this (clean in water), and react with dilute H2SO4 to form NM again, which should form an insoluble layer.
Nonetheless, distillation should be safe if no extreme temperatures, or base/acid additions are used. There's a prep on orgsyn for this, dealing with the destillation.




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[*] posted on 13-4-2006 at 22:59


Nitronate is not stable in the presence of water, so this route does not work. If you want to make nitronate salts from nitromethane, then you need a strong base in non-aqueous solvent (e.g. CH3CH2ONa in CH3CH2OH). Even NaOH in CH3CH2OH is not suitable. The water formed in the reaction then slowly destroys your nitronate salt.

I don't know what the precise decomposition products are of nitronate/water. The material first becomes brown and then a dark, almost black, insoluble crap is produced. This crap still contains quite some nitro-groups, it can be made to decompose violently, but it surely is not useful for any other purpose than for making a bang.




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xwinorb
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[*] posted on 14-4-2006 at 14:40


I have just run a small experiment :

I added a small ammount of CaCl2 to distilled water, measured the pH with my electronic pH meter ( it is a good meter and I trust it ), I am getting right now 10.38

Looks like I might have formed nitronates whithout knowing it ( ? )


Question :

I have combined all the nitro I have after the described distillation. It is slighly yellow. Would it be safe to wash with diluted HCl and see if that removes the yellow color ?

Would this be safe to distill at RT ?


Further comments :

Also, I have once ( before this try ) distilled the pure RC fuel, I have the impression the yellow spots did not showed up, but I am not sure about it.

If that is really the case, I might end up dumping this one and distilling the RC again whithout drying this time. I am also trying to find 99 % nitro.

I am putting this on hold for now, maybe in one week or two. As I have said before, I might through away the yellow tinted one I got right now.
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xwinorb
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[*] posted on 18-4-2006 at 18:06
Problem seen at re-distillation


SWIX decided to try to re-distill the nitromethane, after testing a small ammount on a test tube.

Distillation initially OK, I started collecting at 90 C, because again looked like there was still some DCM mixed in. After a while, started noticing small bubbles forming at side of boiling flask, on localized spots. It started showing up more and more. Finnaly, small solid yellow spots started appearing at the previous bubble locations. Then I decided I was not liking it and stopped the distillation.

It is possible I could have finished it whithout problem, have done it before, but I did not know about nitronates at that time.

The distiiled fraction ( got some 70 g ) looks clear like water. After a while, staying in fridge, it is turning cloudy ( not yellowish like the input, though ). I think it still has some DCM and / or water mixed in. Probably it will clear and water will float to the top, have seen it before.

After turning off the heat, the yellow solids re-dissolved in the initial nitromethane fraction.

Any way I can test this to see if it is really nitronate ? Will it burn easier ? I tried to wash first fraction ( from previous distillation ) with HCl, it is still yellow.

Whatever this is, it is separable by distillation, most of it stays in the input fraction, but I believe part of it was carried over to distilled fraction.

If someone knows more about this please post. It seems to correlate with drying with CaCl2, I got more of the impurity this time, as described in first post. I have dried it more, and also combined with the DCM extraction ( bad idea ).

The RC fuel I used is PowerMaster, 50 %. I think it has castor oil and synthetic oil also.

I guess I will go back to distilling the RC fuel without drying or washing.
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xwinorb
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[*] posted on 18-4-2006 at 18:16


Would like to add this :

I tried to burn the two samples, after dripping in a piece of paper towel. The yellow one burned faster and more energetically.

The re-distilled nitro burned slower, easier to put down flame.
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[*] posted on 18-4-2006 at 23:36


I know a fellow that used 80% nitro boat fuel as is in a mdma reductive amination synth and ended up with decent yeilds.
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[*] posted on 4-2-2012 at 22:02


I am surprised that nobody here has bothered to check the Material Safety Data Sheet on CH3NO2 to find out the answers to a lot of the questions here...

http://www.mallchem.com/msds/englishhtml/N5740.htm

nitromethane is in fact impact sensitive and is made more impact sensitive by contact with certain other compounds/elements. for example, if aluminium particles are mixed into CH3NO2 it becomes much more impact sensitive, to the point that in racing engines, it can cause preignition by the shock of the surrounding cylinder combustion events.

it is strongly advised NOT to distill nitromethane. it is an unnecessary process. Just call your local Drag Racing strip and ask where you can buy it from in 100%. Also, the ratio of cost per cc is strongly in the favour of just buying it outright not to mention not having to expose yourself to uneccesary risk.

Also it is not classed as an explosive [unless combined with sensitizers] and as the MSDS states,

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[*] posted on 6-2-2012 at 07:18


a quick google search brought me to 100% nitromethane .
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[*] posted on 14-2-2012 at 04:44


yeah I just bought 4ltrs of 99.99% for $70 in Australia of all places from a hobby shop.
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[*] posted on 15-2-2013 at 21:12


Would the base extraction method also be applicable to recovering the methanol? So I'm thinking...

1. Add saturated NaOH solution to 92:8 MeOH nitromethane mixture
(Would an excess of base solution hurt anything?)
2. Put in freezer for a while
3. Vacuum filter off the nitro precipitate
4. Flush remaining MeOH with equal volume of water
5. Distill off and collect MeOH

Any obvious flaws in that my chem illiterate self is unaware of? Thanks.
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[*] posted on 16-2-2013 at 01:52


Use more water with the NaOH, about 1/4 of the volume of the MeOH/MeNO2.
Pre-chil the MeOH/MeNO2 in the freezer first as it will get very hot and let it stand until it all cools down, filter and distill.
It would need an additional distillation as there is some ammonia/amine formed contaminating the distillate.
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[*] posted on 16-2-2013 at 10:51


When you say use more water do you mean a less saturated NaOH solution? Also, forgot to mention everything should be pre-chilled, good idea. I'm guessing multiple distillations won't be needed if it is distilled fractionally after the nitro has been filtered off?

[Edited on 17-2-2013 by luckybot]
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[*] posted on 16-2-2013 at 12:58


Yes, I say less saturated partly due to perhaps an irrational fear of distilling salts of potentially explosive compounds and wanting to keep the solids dissolved. It also helps moderate the exothermic reaction due to the high specific heat capacity of water.

Excess of NaOH is no problem.

the amine contaminant is produced during the distillation and so can only be removed on the 2nd distillation.

When/if I next travel in this direction I would attempt identification of this amine but since you're heading down here maybe you can take the fore-run of the 2nd distillation and neutralize with HCl, evaporate to dryness and characterize the residue e.g. MP or other physical properties.
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[*] posted on 16-2-2013 at 15:03


you klotz's, why not pick up a gallon of the pure?
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[*] posted on 16-2-2013 at 15:30


Well if I can get it out of the same OTC mix I got my nitromethane for no extra cost with only a little fuss I would imagine it's worth it. Not to mention I haven't yet sourced a supplier of methanol.

[Edited on 16-2-2013 by luckybot]
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[*] posted on 17-2-2013 at 07:33


Okay I took a liter of the chilled 92:8 MeOH nitromethane mixture and added more than an equal volume of near saturated NaOH solution. I made the NaOH solution by dropping lye into water with stirring until it stopped dissolving and made a cloudy white mixture, after that I added some more water to bring it back to being clear. The MeOH/NaOH/Nitromethane proceeded to warm up slightly and first turn a pale yellow, then as it cooled towards room temp it turned a very dark brown/black, like used motor oil or dark cola. I put it in the freezer overnight and the next morning it was in the same state. I'm guessing I have screwed up somehow? I can see no precipitate since the mixture is so dark. Perhaps there is not enough water and things are staying dissolved in the methanol, the mixture did not freeze.

Filtering does nothing. I was imagining I would see a precipitate in my mostly still clear methanol, filter that and then re distill, this is looking much messier than I thought.

[Edited on 17-2-2013 by luckybot]
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[*] posted on 17-2-2013 at 13:12


Turning black is normal.
But you used a lot more water than I did so nothing precipitated, you can proceed with the 1st distillation.
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[*] posted on 17-2-2013 at 13:28


So the filtering isn't even necessary? I guess the dissolved nitro stuff is going to stay behind in the distillation flask?
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[*] posted on 17-2-2013 at 13:31


Yes, if you use a lot of water but I like to keep the volume down due limited flask sizes.
You should distill this preferably with a fractionating column and a black, maybe somewhat viscous mess will be left behind but poses no cleaning problems.
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