DennyDevHE77
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What's inside the dry fuel tablets
I ran out of chemically pure urotropine (for HMTD), had to go to a fishing store and buy dry fuel.
When I decided to burn one to test it, I found out that after burning there was a black sponge of something unclear. (pictured).
A google search indicated that usually dry fuel tablets are pressed with a small amount of paraffin or wax. But when you try to dissolve the tablet in
water, it dissolves without residue. So I think that it can be a black residue when burning.....
And what do you think, if HMTD is so badly soluble in everything, is it possible to make it from such tablets, and then successively wash with acetone
and gasoline? Maybe that would remove all the unnecessary stuff.
  
[Edited on 28-12-2023 by DennyDevHE77]
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Microtek
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I would recommend purifying the hexamine (if that is what it is) before using it in a synthesis. You could precipitate it as a salt, and then freebase
it if you couldn't use the salt directly such as when using HDN in RDX synthesis.
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RustyShackleford
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i would just buy another brand of tablets. Doesnt seem worthwhile to purify if it dissolves in water.
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OneEyedPyro
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You could do a small test extraction with chloroform or MeOH and see if whatever impurity is in there might be insoluble in those solvents I suppose.
95% of what's out there for fuel tabs is trioxane these days which is also water soluble. Are you certain its hexamine to begin with?
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Sir_Gawain
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While the popular Esbit brand contains trioxane and possibly other contaminants, the Coghlans brand is nearly pure hexamine. I’ve used them without
purification to make RDX, and got a good yield. You may be able to purify your tablets by recrystallizing from water. Hexamine has retrograde
solubility, so dissolve in cold water and warm it to precipitate the hexamine.
“Alchemy is trying to turn things yellow; chemistry is trying to avoid things turning yellow.” -Tom deP.
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Etanol
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This is not a trioxan. Trioxan does not leave carbon when burning.
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