decomposes at 260 °C
HNIW is an acronym for hexanitrohexaazaisowurtzitane, other names include CL-20; octahydro-1,3,4,7,8,10-hexanitro-5,2,6-(iminomethenimino)-1H-imidazo[4,5-b]pyrazine; 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.05,9.03,11]dodecane; and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane. HNIW is a new kid on the block, it was first prepared by A.T. Nielsen in 1987, and has since been proposed as a propellent for bullets and as a blasting explosive. There are actually 6 crystalline isomers of HNIW, this lab will prepare the beta form, although some of the alpha form will probably be made. The other isomers are made by heating the crystals to its decomposition point, the alpha and beta forms are the most stable. This explosive will most likely be the standard workhorse of the 21st century, it is currently still in testing for useful applications. HNIW is a symmetric polyazacyclic nitramine, itself a type of caged polynitramine, a promising new series of compounds. HNIW is similar to RDX and HMX in structure and explosive properties. This is a two part lab, the first synthesizing a derivative called tetraacetyldibenzylhexaazaisowurtzitane (TADB), then from that, HNIW.
|acetic anhydride||500-mL Florence flask|
Prepare a solution of 129 mL of N,N-dimethylformamide and 65 mL of acetic anhydride in a round-bottomed 500-mL Florence flask. Add to the flask, with stirring, 43.2 g of HBIW, 0.8 mL of bromobenzene, and 4.7 g of Pearlman's catalyst. Purge the flask by bubbling hydrogen gas in the liquid ,this will displace the air. Continue to bubble hydrogen gas into the flask and stir. If possible, maintain a pressure of 50 psi. Over a short period of time, the temperature may rise to about 50 °C, at this temperature begin cooling the flask with a cold water or salt-ice bath to keep it under 50 °C. The total reaction time needed is 24 hours. Since it is undesirable to bubble hydrogen gas through the flask for this length of time, as much would be wasted, a pressure is maintained. During the reaction, stop cooling if the temperature drops below 35 °C, always keep it between 35-50 °C. Stir the contents of the flask for the entire 24 hours. Purge the flask by bubbling nitrogen gas into it to displace any remaining hydrogen. Filter the contents of the flask to collect the solid material and the catalyst. Wash with 130 mL of denatured ethyl alcohol, this should leave behind a gray solid of Pearlman's catalyst and TADB. The TADB can be separated from the catalyst by dissolving the solid in boiling chloroform, and filtering to remove the remaining solid catalyst. Boil the chloroform down to recrystallize the TADB. The yield is about 85%.
Prepare a solution of 15.5 g of the above prepared TADB, 1.1 mL of water, and 300 mL of sulfolane in a round bottomed 500-mL Florence flask on a salt-ice bath. Add 10.5 g of nitrosyl tetrafluoroborate to the flask over a period of 30 minutes, keeping the temperature below 25 °C. After the addition, stir the mixture for 1 hour at 25 °C, then for 1 hour at 55-60 °C. Allow the solution, which should be a yellow-orange color, to cool to 25 °C. After cooling, rapidly add 47.8 g of nitrosyl tetrafluoroborate, keeping the temperature below 25 °C. Stir the mixture at 25 °C for 2 hours, then at 55-60 °C for 2 hours. Cool the mixture to below 10 °C with a salt-ice bath, then dump the contents, solid precipitate and all, into a large bucket. Slowly add 4.5 L of water to the mixture in the bucket, keeping the temperature below 25 °C, the color of the solution should change from green to yellow, some brown fumes may be evolved. Maintain the temperature at 25 °C with continuous stirring for 18 hours, a white precipitate should form. Filter to collect this crude HNIW, and wash several times with water to yield about 12 g of hydrated product. To purify the HNIW, dissolve it in 40 mL of ethyl acetate, chromatographically filter the solution through a short column of silica get, and wash with ethyl acetate. Pour the filtered solution into 500 mL of chloroform to precipitate the HNIW in its anhydrous beta form. The chromatographic filtration can be skipped. If pale yellow crystals are obtained as the crude product, it is the wrong stuff. Heat these crystals in 15 mL of water per 1 g of product at 95 °C with stirring for 10 minutes, then cool to 0 °C. After standing for 6 hours, filter and wash the crude product as above, it should be HNIW now. You will need a graduated cylinder for measuring liquids, a stirring rod or magnetic stirrer for mixing, and a thermometer to monitor the temperature.
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