The nitrolysis of hexamine 245is much more efficient than method 5.15.1.1 and works on the principle that one mole of
hexamine can produce two moles of RDX. However, hexamine is deficient in nitrogen for this
to occur, so in this process, ammonium nitrate is used as a reagent to supplement nitrogen and
allow the reaction to follow Equation (5.23).
(CH 2 ) 6 N 4 .2HNO 3 + 2 HNO 3 + 2 NH 4 NO 3 + 6 Ac 2 O 2 RDX + 12 AcOH
(Eq. 5.23)Figure 5.100An unusual feature of the KA-process is that the reaction is conducted at 60–80◦C. Solutions
of nitric acid in acetic anhydride are known to be prone to dangerous ‘fume off’ at temperatures
above ambient. However, a saturated solution of ammonium nitrate in fuming nitric acid can be
added to warmed acetic anhydride without such danger. In fact, these reactions are commonly
conducted at 60–80◦C as a matter of safety by preventing a build-up of unreacted starting
material. The hexamine used in these reactions is in the form of the dinitrate salt, which
is formed as a crystalline salt on addition of a saturated aqueous solution of hexamine to
concentrated nitric acid below 15◦C. The use of hexamine dinitrate in this process reduces the
amount of nitric acid needed for the nitrolysis.
The order and timing of the addition of reagents in the KA-process is varied but in a typical
procedure three reagents, namely, acetic anhydride, a solution of ammonium nitrate in nitric
acid, and solid hexamine dinitrate, are added slowly, in small portions and in parallel, into
the reaction vessel which is preheated to 60–80◦C. On completion the reaction mixture is
often cooled to 50–60◦C and the RDX filtered and sometimes washed with acetic acid. This
process produces a product which melts over a 2◦C range but the RDX still contains up to
10 % HMX as a by-product. Dilution of the reaction mixture with water before removing the
RDX produces a very impure product containing numerous unstable linear nitramine-nitrates.
Based on the assumption that one mole of hexamine dinitrate produces two mole of RDX the
KA-process commonly yields 75–80 % of RDX.
5.15.1.3 Nitrolysis of hexamine with ammonium nitrate – nitric acid
(CH 2 ) 6 N 4 + 2 NH 4 NO 3 + 4 HNO 3 2 RDX + 6 H 2 O (Eq. 5.24)Figure 5.101This method is known as the K-process after its discoverer K ̈offler.^201 Like method 5.15.1.2 it
uses ammonium nitrate to compensate for the nitrogen deficiency in hexamine and works to
Equation (5.24) where two moles of RDX are produced per mole of hexamine. As observed
with method 5.15.1.2, the addition of ammonium nitrate to nitric acid appears to prevent
dangerous oxidation reactions from occurring. In fact, this nitrolysis reaction only occurs at
elevated temperature and so a constant temperature of 80◦C is usually maintained throughout
the reaction. Yields of approximately 90 % are attainable based on one mole of hexamine
producing two moles of RDX.