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Author: Subject: Nitroglycerin discoloration
killswitch
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[*] posted on 26-12-2011 at 13:37
Nitroglycerin discoloration




I don't think this is what is meant by "clear, colorless product." Nearly all of the occluded water had been removed by the time that picture was taken, but that has only caused the discoloration to intensify. As to what's causing it, my preliminary guess would be the formation of acrolein compounds, but I have no idea where they could have come from.

The nitration was performed in 98% H2SO4 and NH4NO3 from the Walgreens store brand cold packs (no sand in this brand, so I used it without recrystallization).
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[*] posted on 26-12-2011 at 14:04


Have you tried neutralizing the NG with soda?



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[*] posted on 26-12-2011 at 14:30


Yeah, I always neutralize before I dehydrate, since acid is the more potent hazard.

I added some more NaHCO3 after reading your post; there was no detectable evolution of CO2. No clue what's going on.

Edit:

"Acrolein tends to polymerize when left at room temperature, leaving a gummy yellowish residue with a putrid odor." -Wikipedia.

Uh-oh. That describes my product pretty well, although it isn't particularly viscous.

There *is* a source of NO- radicals, since skin contact produced a noticeable vasodilatory headache, but I'm not sure how much acrolein or other contaminants are present.

[Edited on 26-12-2011 by killswitch]

[Edited on 26-12-2011 by killswitch]
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[*] posted on 26-12-2011 at 16:01


Quote:

There *is* a source of NO- radicals, since skin contact produced a noticeable vasodilatory headache,


Errm, no. NG is a powerful vasodilant itself. And how would acrolein end up in your NG? It's not like you've been boiling your reaction mixture up to the point where glycerin starts to carbonize...




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[*] posted on 26-12-2011 at 23:25


Quote: Originally posted by vulture  


Errm, no. NG is a powerful vasodilant itself.


Yes, because it is a source of NO- radicals, which the body uses as a signaling mechanism.

Quote: Originally posted by vulture  
And how would acrolein end up in your NG? It's not like you've been boiling your reaction mixture up to the point where glycerin starts to carbonize...


Exactly. I have no clue as to the nature of the discolorant and am merely hypothesizing. It may well be something else entirely. That's why I'm asking.
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[*] posted on 27-12-2011 at 04:22


From COPAE:
"Dynamite glycerin is a distilled product of high purity, density 1.262 or higher, and contains at least 99% of glycerin and less than 1% of water.
It varies in color from pale yellow to dark brown, generally has a faint odor resembling that of burnt sugar, and yields a nitroglycerin of a pale yellow or pale brown color."


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[*] posted on 27-12-2011 at 07:43


I have never been able to get "water clear" glyceryl trinitrate either. Even with reagent grade reactants. Always a little yellow.



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[*] posted on 27-12-2011 at 08:38


Some time ago I tried to make some colorless NG and I finally got some after lots and lots of purifications. I mean, I lost over half of my crude NG to get perfectly colorless one.
The worst in this story is that after two months in a clear test tube it turn back to a pale orange. I don't know if it react with light or it is some product decomposition.
The properties of the NG have almost no difference between the clear and the pale orange one. So you don't have to worry about it, but be sure that your NG is completly neutral.
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[*] posted on 27-12-2011 at 08:46


Yeah, and the greater the cross-section of the beaker, the more that tint will show up!


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[*] posted on 27-12-2011 at 14:04


A slight yellowish tint is normal for NG that has been synthesized using OTC reagents. You should be more concerned about the pH of the liquid, as residual acids will cause decomposition of your product over time. If it's neutral or very close to it, there is nothing to worry about.
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[*] posted on 28-12-2011 at 01:57


I manage to get perfectly clear NG. NG is a #$*@ to remove all the acid from. I made a setup like this and use a solution with 5% salt and then maximum dissolved sodium carbonate. Let it run for a couple days at 60-70F and you will get high quality acid free NG.

http://www.youtube.com/watch?v=-KBZtIX4-7o
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[*] posted on 28-12-2011 at 02:09


On a side-note, nitroglycol can easily be mistaken for water - viscosity in nitroglycol is only marginally higher and it's quite colourless . . .


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