STUDIES ON RDX AND RELATED COMPOUNDS: I. THE DIRECT NITROLYSIS OF HEXAMINE TO RDX

Maximum yields, of about 40%, of RDX were obtained with nitric acid of all concentrations down to 88%, providing the molar ratio of nitric acid to hexamine was sufficiently high. The rate of nitrolysis increased rapidly as the molar ratio of nitric acid to hexamine was increased and continued to do so after the molar ratio was raised above that required for maximum yields. The initial rate was shown to have an upper limit, however, at very high molar ratios. An intermediate in the nitrolysis reaction was isolated and identified as 3,5-dinitrocyclotrimethylenetriamine-1-nitrate (I). (I) was formed rapidly in sufficient quantities of 85 to 91% nitric acid at 0 °C., but had a high rate of decomposition which was independent of both acid concentration and ratio of nitric acid to (I) with 80 to 90% nitric acid. Under nitrolysis conditions some of the hexamine was converted to products not capable of giving RDX, owing apparently to hydrolysis of precursors to (I). The activation energy for the conversion of (I) to RDX was found to be identical with that for the rate controlling step of the conversion of hexamine to RDX. This fact, together with the general kinetic behavior of (I), provided evidence that (I) was a true intermediate and that its reaction to RDX was the rate controlling step in the direct nitrolysis of hexamine. The mechanism of the over-all reaction is discussed in relation to published information concerning the constitution of concentrated nitric acid. Nitracidium ion is believed to be the active nitrolyzing agent.