Hexamine

Hexamine MSDS

Hexamine is a white crystaline powder with a smell that some say resembles fish. It is used as a fuel for emergency stoves and is also used as a fuel in the pyrotechnical world in some star formulas. The word hexamine is a shortened name for hexamethylenetetramine. It is made by reacting aqueous formaldehyde with aqueous ammonia.

6HCHO(aq) + 4NH3(aq) ----> C6H12N4(aq) + 6H2O(l)

Materials Equipment
Formaldehyde, 37% solution 250ml flask
10% ammonia solution Centigrade thermometer
  Ice bath
  Evaporation dish

 

Into a 250ml flask, pour 45mls of a 37% formaldehyde solution. Place this in an ice bath and toss a thermometer in. Measure out 100mls of a 10% ammonia soluiton in a graduated cylinder (you can use the same one you used for the formaldehyde). When the formaldehyde in the flask reaches 5C, you can begin additions of ammonia. Add the ammonia solution by holding the graduated cyilinder against the thermometer and pouring so that the ammonia water pours down the thermometer. When the temperature jumps up to 15C, stop the addition (you can go over, I'm just giving a good stopping point). Swirl the flask in the ice bath and bring it back down around 5C. If you can't wait until it gets to 5C (like me) just add it at whatever temperature until it gets to 15C. Once all the ammonia solution is added, swirl the flask some more then remove the thermometer. Pull the flask out of the ice bath and stopper it. Set it in a room temp location and leave it there over-night. It would be wise to secure the stopper in some fashion but not neccesary. Gas will not be generated but it would be wise to fasten it because the liquid will expand as temperature rises and may be enough to force the stopper out. When you open the flask after it has finished reacting, lightly smell it. It should still smell of ammonia. If it does not, add more ammonia solution and repeat the last step. Once it has obtained an amoniacle smell permanently, it is time to get your hexamine out of this solution.

Set the flask on a hot plate and bring it up to boil. The temperature of the contents will not go straight to 100C. It will go to a lower temperature and begin releasing ammonia gas from the solution. It will continue this until it gets to 100C (or whatever the boiling point of water is at your elevation). Boil this down to around 50mls and pour the solution into a 200ml evaporating dish. Evaporate this over steam until there is no longer a puddle of water (stir often). There should be lumps of crystals in the evaporating dish that look like they have a small ammount of water in them. Put this dish in an oven at 100C (about 215F) and leave it there for 2 hours or longer if it needs it. When you take it out, you should have an off white solid. This is your crude hexamine. The theoretical yeild is 14.03 grams. I got 15.6 grams which comes out to a 111% yeild. This could mean one of three things; The formaldehyde solution I used was more than 37%, There are 1.57grams of impurities in this hexamine, or I am God. The last one I know for a fact isn't true, the second one is highly unlikely because there aren't many places that a sample can pick up that much impurities. The first one seems most probable, since my formaldehyde is actually called "~37%" not "37.0000%". I'm sure impurities account for some of the weight in this. You can purify your hexamine or use it as is. Me being the purity freak that I am, I decided to purify it.

To purify, recrystalize this from ethanol. You should be able to dissolve all the hexamine with about 150-160ml of hot, 96% ethanol. It would be best to use anhydrous ethanol because some impurities will dissolve in the water thats in the ethanol (about 6mls 150ml 96% ethanol). By the way, when I say hot I mean anything above 70C. You should be able to tell when the hexamine dissolves and the impurities are left. There will be a different looking crystal structure (or different color if a bug or something fell in). While this is still hot, filter it into a 200ml evaporating dish. Make sure the dish is on a stable surface as this will fill the dish pretty high. Place a cover over the evaporating dish to keep other stuff from falling in.

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