Sciencemadness Discussion Board

Using dark red tinted or even black sulfuric acid for nitrations

dangerous amateur - 24-6-2015 at 02:28

I wonder if sulfuric acid that was stored in plastic vessels to long is OK to use for nitroesters like ETN.
Most technical grade stuff is reddish even when it's fresh delivered.
Mine is black. Concentration is still OK.

It's obvious that this has something to do with the PE canister. Same stuff stored in glass is absolutely clear.

I usually get rid of any discolorations after the second recrystalisation, but I wonder if those contaminants could have any adverse effects I'm not aware of.

diggafromdover - 24-6-2015 at 05:49

Quote: Originally posted by dangerous amateur  
I wonder if sulfuric acid that was stored in plastic vessels to long is OK to use for nitroesters like ETN.
Most technical grade stuff is reddish even when it's fresh delivered.
Mine is black. Concentration is still OK.

It's obvious that this has something to do with the PE canister. Same stuff stored in glass is absolutely clear.

I usually get rid of any discolorations after the second recrystalisation, but I wonder if those contaminants could have any adverse effects I'm not aware of.


Other way around - the contaminants are remnants of the manufacturing process, closely coupled to where they got the Sulfur Dioxide for the Contact Process. Glass, which is more expensive, is used for top shelf acid.

aga - 24-6-2015 at 11:07

If you wish to go anywhere near EM it would be safer and generally Better (for you and others nearby) to use pure reagents.

Any question hanging over any reagent could mean the difference between life or widely scattered, severely mangled and generally very juicy death.

Loptr - 24-6-2015 at 11:19

I have seen clear concentrated sulfuric acid turn dark after being stored in a plastic bottle for a while. Mine came from Elemental Scientific, and it is now very dark.

I would say just try it, and make sure you have very good cooling.

[Edited on 24-6-2015 by Loptr]

aga - 24-6-2015 at 11:30

i think they call that a 'reaction'.

Loptr - 24-6-2015 at 11:35

Quote: Originally posted by aga  
i think they call that a 'reaction'.


Yes, but the intention is that a bottles content doesn't react with the bottle. :)

dangerous amateur - 26-6-2015 at 02:37

They guy who gave it to me say it was clear when he bought it years ago.

He wanted to throw it away, so I salvaged it.

These contaminants are NOT from the manufacturing process, if that helps narrowing it down a little.
Something organic, leached from the plastic?

Even if it acts as a sensitizer, in case I get rid of the stuff by recrystallization it wont be a problem. As long as it does not cause runaways...?

Loptr - 26-6-2015 at 05:41

Again, a small scale experiment would be best here. You could also likely decolorize it using activated charcoal. I used a chromatography column packed with fine activated charcoal with my hardware store sulfuric acid because it had a slight discoloration. I used the positive end of my vacuum pump to push the sulfuric acid through the column pretty quickly with good results.

If you get a runaway with a small scale, you surely can expect one with anything larger.


Also, what would be an example of an impurity within sulfuric acid that would cause a runaway? I am not into energetics that much, and don't really understand how an impurity within the acid could cause one.


[Edited on 26-6-2015 by Loptr]

diggafromdover - 26-6-2015 at 05:48

Well, if the stuff was clear to begin with, then it must be reaction with either the container or something within it. The overwhelming tendency of Concentrated Sulfuric Acid (CSA) is to dehydrate the neighborhood. The end result - from carbohydrate like a lab towel or a finger - is Carbon, which is black. Like the color is due to suspended Carbon.

I think Loptr has an excellent suggestion.

As a side thought, you might reserve the CSA saturated activated charcoal and use it in a situation where an acid catalyst is needed.

[Edited on 26-6-2015 by diggafromdover]

Praxichys - 26-6-2015 at 06:21

Add some hydrogen peroxide to the acid and boil it back up to its original concentration. This will remove pretty much all organic contaminants, even suspended carbon. You can also boil it with a little nitric acid added but the fumes are nastier and it takes longer.

If your reaction tolerates metal ions, boiling with persulfates will also work. Both ammonium and sodium persulfate are sold as PCB etchants. Your acid will have some sodium or ammonium (bi)sulfate contamination afterward though - not really a problem for most EM applications.

EDIT:

By the way, I find that the usual source of contamination is the degradation of the foil-lined fiber seal in the cap. Everything else is basically impervious to the acid.

[Edited on 26-6-2015 by Praxichys]