PYX

     PYX, a code name for 3,5-dinitro-N,N'-bis(2,4,6-trinitrophenyl)- 2,6-pyridinediamine, is a powerful insensitive high explosive with similar properties and usefulness as RDX or HMX. Other names include 3,5-dinitro-2,6-bis(2,4,6-trinitroanilino)-pyridine; and 2,6-Bis(picrylamino)-3,5-dinitropyridine. Its resistance to high temperatures is a valuable property that has found a use in oil wells, the aerospace industry, and in nuclear technology. PYX’s ability to withstand temperatures up to 315 C for over 10 hours earns it the title of the most heat stable explosive known.

CHEMICALS	APPARATUS
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     Step 1 In a small beaker, prepare a solution of 100 mL of water and 10.9 g of 2,6-diaminopyridine. In a 1000-mL round-bottom Florence flask, prepare a solution of 400 g of isopropyl alcohol (100%) and 55 g of picryl chloride. Stir well to dissolve some of the chloride and then add 8.4 g of magnesium carbonate. Heat both the beaker and the flask to 28 C while stirring. Continue stirring until the picryl chloride completely dissolves in the alcohol and the diaminopyridine is mixed with the water. Configure the flask for reflux with addition and add the water-diaminopyridine mix to the flask of alcohol solution slowly over a 30 minute period while maintaining a gentle reflux. The addition will generate some CO2 waste, so control the addition accordingly to regulate the reaction. After the addition, continue refluxing for about 5 hours. At the end of the refluxing period, pour the hot solution over a filter to collect the crystals of the intermediate compound 2,6-bis(picrylamino)pyridine. Wash this compound several times with small portions of water. Yield is about 96%. Step 2 Add 825 parts by weight of 98% nitric acid to a 1000-mL round-bottom Florence flask. Slowly add 100 parts by weight of wet 2,6-bis(picrylamino)pyridine as prepared above to the flask at such a rate as to keep the acid between 0 C and 30 C. Having an ice water bath handy may help if the temperature rises too much. After the addition, set the flask up for reflux and heat the flask to the reflux temperature of the nitric acid (about 76 C) while stirring. Continue to reflux the flask for about 5 hours. Afterwards, discontinue cooling the reflux condenser and heat the flask (about 84 C) to distill off about 20% of the nitric acid. Allow the acid mix to cool to about 27 C and the solid product to settle. Decant off as much acid as possible and vacuum filter the remaining contents to collect the solid product. An acid resistant filter paper is advised, or the acid can be diluted with a large quantity of water before pouring on the filter paper. Wash the obtained product of PYX several times with water to remove all traces of acid. The wet product is placed in an oven and heated at 38 C until a constant weight is obtained. Yield is about 80 based on the mass of the intermediate. Optionally, PYX of increased sensitivity can be prepared. As PYX is rather difficult to detonate reliably, it is sometimes advantageous to make it more sensitive. Into a small beaker add 1 part by weight (for example 50 g) of PYX prepared above to 5 parts by weight of DMSO (about 250 mL). Heat the beaker to 80-85 C while stirring until all of the PYX dissolves. Slowly pour the hot solution into another beaker containing 100 parts by weight (4 L) of acetone. It is important to add the solution to the acetone, not the acetone to the solution. Stir the mixture slightly to mix it. Quickly add 40 parts by weight (2 L) of cold water to the solution to precipitate the PYX. Collect the crystals by filtration and wash them with 20 parts (1 L) of acetone. Allow to dry at reduced pressure. This process alters the crystal structure of PYX to obtain a more sensitive form.

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