totse.com | Preparation of Octogen (HMX)

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Octogen (HMX) is formed in the nitration of hexamethylenetetramine (`hexamine') and is a by-product of production of cyclonite (RDX) as it was pointed out in Vol. III, p. 90. However, the statement given in Vol. III needs to be corrected. On the basis of our present knowledge, octogen which accompanies cyclonite does not reduce the power of cyclonite. On the contrary, owing to a higher velocity of detonation octogen can increase the strength of cyclonite.

W. E. Bachmann and Sheehan [ 158 ] developed a method of preparing RDX containing a small quantity of HMX. The method involved nitrolysis of hexamine with ammonium nitrate-nitric acid solution and acetic anhydride. By varying parameters of temperature and acid concentration, ammonium nitrate and acetic anhydride it was shown that the ratio RDX/HMX can be altered. These results led Bachmann and co-workers to prepare mixture rich in HMX. The optimum yield obtained was 82% conversion of hexamine to HMX/RDX mixture containing up to 73% HMX.

Low acidity and the presence of NH4NO3 (and paraformaldehyde - [162]) favours the formation of octogen. Without ammonium nitrate the linear compound was formed. Higher acidity helps to obtain RDX (159]. Bell and Dunstan [162] nitrated DPT at -20øC. After warming the solution to 30øC HMX resulted in a low yield.

By using 15 NH4 N03 W. E. Bachmann and co-workers [ 159] established that only 15% of nitrogen from NH4 enters octogen, and much more (ca. 37%) enters hexogen. Castorina and co-workers [160,161] used C labelled hexamine, DPT and paraformaldehyde, and found that all these compounds contribute to the formation of octogen. They obtained HMX with 15% of RDX. They isolated pure HMX by dissolving all in acetone, evaporating to form a precipitate and cooling to 25øC. The crystalline solid is HMX. The presence of RDX in the substance can be detected by acting with sodium nitroso ferricyanide on the acetone solution. A blue colour reveals the presence of RDX (reaction of S. B. Wright according to [161 ) ).

It has been found by Picard [162] that the addition of paraformaldehyde to the mixture of ammonium nitrate-nitric acid-acetic acid-acetic anhydride increases the yield of octogen.

The following is the method described by Fedoroff and Sheffield [127] as apparently used in U.S.A.

To a 6-10 l. flask equipped with a stirrer and three dropping funnels add 785 g acetic acid,13 g acetic anhydride and 17 g of paraformaldehyde keeping the temperature at 44 ñ 1øC. Add over 15 min a solution of 101 g of hexamine in 165 g acetic acid, 320 g of acetic anhydride and 180 g of ammonium nitrate-nitric acid solution prepared by dissolving 840 g of ammonium nitrate in 900 g of nitric acid (99% concentration). The hexamine and nitric acid are added continuously in correct proportions. The mixture is stirred for 15 min. After that are added: 320 g of acetic anhydride and 271 g of nitric acid-ammonium nitrate solution in that proportion and then 160 g of acetic anhydride are added in bulk. The mixture is stirred for 60 min., 350 g of hot water are added and refluxed for 30 min. The content is cooled to 20øC by adding ice, the precipitate is collected and washed with three portions of cold water. The yield of á-HMX is 95% of the theoretical and the purity 90%. A similar method of obtaining á-HMX was given by Robbins and Boswell [163]. The composition of the product was 77.5% HMX and 22.5% RDX. The yield of HMX was 87.5%. A method was also described for nitrating hexamine with nitric acid in the presence of BF3. A yield of 96% was claimed [164].

Preparation of Octogen from DPT (3,7-dinitro-1,3,5,7 tetraazabicyclo [3,3,1] nonane) (Vol. III, p. 90, formula XII)

There are methods of obtaining octogen in two steps by forming DPT as the first step, followed by acting on DPT with nitric acid or nitric acid with ammonium nitrate or nitric acid, ammonium nitrate and acetic anhydride. However the yield of DPT is not very high. The best method of obtaining DPT consists in introducing hexamine dinitrate to 90% sulfuric acid at 8-15øC. After 45 min. all is poured on ice and the solution is filtrated. The filtrate is neutralized with 28% ammonia to pH = 5.5-6.5 DPT precipitated [165].

Another method of making octogen from DPT (1 mole) consists in acting with NH4NO3 (1.6 mole) and nitric acid (3.2 mole) at 60-65øC for one hour. Water is then added and all is heated for 12 hours in a steam-bath. The yield was 75% of the theoretical (according to [5] ).

The description of the industrial manufacture of octogen in Hungary has been given [166). In the first step DPT was obtained from hexamine, acetic anhydride, paraformaldehyde and a solution of ammonium nitrate in nitric acid. After that the rest of the reagents were added.

5-7 moles of nitric acid (min. 98%),
3-S moles ammonium nitrate,
10-1 I moles acetic anhydride and
0.27-0.54 moles of paraformaldehyde

After that water was added and the temperature was raised to 98øC by injecting live steam. All was cooled and the product filtered. It contained 60-70% octogen and 30-40% hexogen.

To obtain pure á-form the product is dissolved in acetone and refluxed for 45 min. All forms of octogen pass into the solution. Also unstable products decompose on boiling.

If pure octogen free of cyclonite is required, octogen can be obtained due to lower solubility in acetone. By warming the product with a three times larger quantity of acetone at 40-50øC, all cyclonite passes into the solution.

The commercial grade of HMX produced in France seems to contain ca. 2.25% RDX [179].

The quantity of octogen is determined by treating an 0.2 g sample with 100 ml of 1,2-dichloroethane saturated with HMX. The insoluble matter is pure octogen.

The octogen should consist of á-polymorph by examination of a 5% mull of the sample in hexachlorobutadiene or tetrachloroethylene in a sodium chloride cell. Another sample of pure á-polymorph is placed in a compensating cell. The absorption is observed between 14.0 and 14.3 æ.