Hexamethylenetetramine Dinitrate

     Hexamethylenetetramine dinitrate, also called HDN, is a rather weak high explosive made from a quite simple reaction between methenamine and a nitrating mixture forming a quaternary ammonium salt. It is fairly stable to heat, shock, and friction but it is somewhat hygroscopic. This explosive is a close cousin to the far superior RDX, but HDN does not really stand out as anything exceptional from a military perspective. The reaction is quite simple and straightforward for the improvisational chemist. Two different methods of preparation are presented here and the molar ratios may be scaled up or down as required.

CHEMICALS	APPARATUS
acetone	250-mL beaker
ammonium nitrate	desiccator
hydrochloric acid	graduated cylinder
methenamine	stirrer/stirring rod
nitric acid	thermometer
water

     Dissolve 14 g (0.1 mol) of methenamine in 50 mL of warm water in a 250-mL beaker. Place the beaker of solution into a salt-ice bath and cool it to 5 °C or less. Measure out 20 mL (0.314 mol) of 70% nitric acid into a small test-tube or beaker and cool the acid in the ice bath as well. It is not necessary to use 70% acid as long as the proper molar amount is added, just limit the amount of water the methenamine is dissolved in accordingly if dilute acid is used. Slowly add the nitric acid, with stirring, to the methenamine solution at such a rate as to keep the temperature below 5 °C. The addition of the acid should cause the immediate precipitation of product. Continue stirring a minute after all of the acid has been added to insure complete precipitation, and then pour the mixture over a vacuum filter to collect the crystals. Hexamethylenetetramine dinitrate can be decomposed by water into formaldehyde in short order, so no extra time should be taken. Wash the crystals with several portions of dry acetone or anhydrous ethyl alcohol to remove any last trace of acid and to accelerate drying. Place the crystals in a desiccator to dry. Store in a tightly closed vial to protect from moisture.     You will need a graduated cylinder for measuring liquids, a stirring rod or magnetic stirrer for mixing, and a thermometer to monitor the temperature.

     An alternative to using nitric acid in this synthesis is to use a nitrate salt and hydrochloric acid. The yields may be a bit less, but the result is the same. Instead of preparing a hexamine solution, prepare a nitrating solution by dissolving 28 g (0.35 mol) of ammonium nitrate in 80 mL (0.8 mol) of 31.45% hydrochloric acid in a 250-mL beaker. Cool this solution in a salt-ice bath to 0 degrees. Again, it is not necessary to use the specified concentration of hydrochloric acid as long as the proper molar amount is added. Dissolve 14 g (0.1 mol) of methenamine in a minimum amount of water (about 21 mL). Quickly add this solution to the nitrating mix with rapid stirring; a precipitate should soon form. Filter and wash the crystals as above. One could substitute sodium nitrate or potassium nitrate of the same molar mass in place of ammonium nitrate.

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