Bachmann process

The Bachmann process, used in the United States and in some European countries, is a simplification of a series of complex reactions. In this process, a solution of one part hexamine in 1.65 parts acetic acid, and a solution of 1.50 parts ammonium nitrate dissolved in 2.0 parts nitric acid and 5.20 parts acetic anhydride are used. The reaction may be summarized as ... 

In the Bachmann process an 80—84% yield is obtained, ca 10% of which is cyclotetramethylenetetranitramine (HMX). The Woolwich process gives a 70—75% yield containing only a trace of HMX. 

The material balance for the Bachmann process is similar to that of the KA process... 

RDX. Gilpin Winkler (Ref 38b) measured a heat of nitration of — 88.0kcal/mole of hexa-mine for the reaction of hexamine with 97.5% nitric acid. They also obtained a value of — 140kcal/mole of hexamine for the formation of RDX from hexamine and Bachmann reagents (acetic anhydride, acetic acid, ammonium nitrate and nitric acid). Incidentally, Gilpin Winkler interpret their results to mean that hexamine dinitrate is an intermediate in the direct nitrolysis of hexamine to give RDX, while hexamine mononitrate is an intermediate in the Bachmann process of producing RDX... 

The McGill workers postulated that, in their process, methylene nitramine (CH2=N—N02) is formed as an intermediate, which then tri-merizes to RDX. However, the existence of methylene nitramine has never been proven. Werner Bachmann (Ref 2) of the University of Michigan, during WWII, conceived of a combination process in which the Hale nitrolysis of Hexamine would occur first, and the remaining methylene would be converted to RDX by the Ross-Schiessler route. Using three feed streams Ac20, Hexamine In acetic acid, and AN in nitric acid, the Bachmann process results in an 80% yield of RDX (two moles from one of Hexamine), including a small amount of HMX. 

While the present industrial synthesis of RDX via the Bachmann process has many faults, it is high yielding and would be difficult to match by an alternative synthesis. Even so, Gilbert and co-workers reported on a study investigating the nitrolysis of a series of 1,3,5-trisubstituted-... 

Variations in the conditions used for the nitrolysis of hexamine have a profound effect on the nature and distribution of isolated products, including the ratio of RDX to HMX. It has been shown that lower reaction acidity and a reduction in the amount of ammonium nitrate used in the Bachmann process increases the amount of HMX formed at the expense of Bachmann and co-workers ° were able to tailor the conditions of hexamine nitrolysis to obtain an 82 % yield of a mixture containing 73 % HMX and 23 % RDX. Continued efforts to provide a method for the industrial synthesis of HMX led Castorina and co-workers to describe a procedure which produces a 90 % yield of a product containing 85 % HMX and 15 % RDX. This procedure conducts nitrolysis at a constant reaction temperature of 44 °C and treats hexamine, in the presence of a trace amount of paraformaldehyde, with a mixture of acetic acid, acetic anhydride, ammonium nitrate and nitric acid. Bratia and co-workers ° used a three stage aging process and a boron trifluoride catalyst to obtain a similar result. A procedure reported by Picard " uses formaldehyde as a catalyst and produces a 95 % yield of a product containing 90 % HMX and 10 % RDX. 

Gilbert and co-workers showed that the nitrolysis of 1,3,5-triacyl-1,3,5-triazacyclohexanes offered little benefit over the conventional synthesis of RDX via the nitrolysis of hexamine. This is not the case for HMX where its synthesis via the Bachmann process is far from perfect. This process and its modifications are expensive, requiring large amounts of acetic anhydride. The rate of production is slow and the maximum attainable yield is 75 %. In fact, HMX is five times as expensive as RDX to produce by this process and this prevents the widespread use of this high performance explosive. Many efforts have focused on finding more economical routes to HMX. 

SNPE, France, produced reduced sensitivity RDX (RS-RDX) by the Woolwich synthesis by employing a proprietary recrystallization process. This RS-RDX displayed reduced sensitivity to shock initiation. Subsequently, some other manufacturers also claimed to produce some form of RDX that exhibits reduced sensitivity to shock compared with the conventional RDX produced by the Bachmann process. EURENCO has also developed a process to mass-manufacture a variety of low sensitive Hexogen (RDX), called I-RDX. 

During World War II W. E. Bachmann et al. [62, 63, 64] worked out a process of cyclonite manufacture identical in principle to the above. Bachmann s idea was to combine Ross s E-method with hexamine nitration. A semi-plant scale equipment based upon the new combined Bachmann process came into operation at the end of 1941. After the procedure for cyclonite production had been worked out, the problem of the regeneration of acetic acid was solved in the United States cyclonite was produced mainly by this method. 

Bachmann s products were known as Type B RDX and contained a constant impurity level of 8-12%. The explosive properties of this impurity were later utilized and the explosive HMX, also known as Octogen, was developed. The Bachmann process was adopted in Canada during World War II, and later in the USA by the Tennes-see-Eastman Company. This manufacturing process was more economical and also led to the discovery of several new explosives. A manufacturing route for the synthesis of pure RDX (no impurities) was developed by Brockman, and this became known as Type A RDX. 

Lastly, the KA-process (Bachmann process) is based on the reaction between hexamethylenetetramine dinitrate and ammonium nitrate with a small amount of nitric acid in an acetic anhydride solution. The chemical reaction is presented in Reaction 7.15. 

Various uses of acetic acid are discussed in Refs 5 7- Its principal use in explosives industry is the manuf of cyclonite(RDX) by the Bachmann process. It can also be used for the prepn of high-nitrogen(ca 14%N) nitrocellulose. US specification JAN-A-465, covers the requirements for acetic acid used in Ordnance (see Acetic Acid, Analytical Procedures)... 

As a group, many other researchers were working on new processes for prepg RDX both in the USA (Refs 24, 27,28,30,32,34,36,37, 38, 42 60i and in Canada (Refs 78,86,87,88,89,90,92 and others). The Bachmann process was applied industrially during WWII at one plant in Canada and later in the US by the Torinessee-Eastman Co (Holston Ordnance Works, Kingsport, Tenn). It not only made the manuf of RDX more economical... 

Properties of RDX. As described above, there are two types of US technical grade RDX, depending on the method of manif Type A, mp 202-203° prepd fcy the nitric acid-process and Type B, mp 192 93° (decomp with si evolution of fumes ), prepd by the acetic anhydride, combination or Bachmann processes... 

RDX , OSRD Rept 159 (Oct 1941) 28) F.C. Whitmore, "Recovery of Acetic Acid and Ammonium Nitrate from the Bachmann Process for Preparing RDX , OSRD Rept 393 (Feb 1942)... 

Western Cartridge Co, "Engineering Laboratory Investigation of Cyclonite Process , OSRD Rept 612 (June 1942) 31) J-R- Johnson, "The Sensitivity of RDX, HMX, and RDX-HMX Mixtures , OSRD Rept 797 (Aug 1942) 32) J.R. Johnson, "Studies Relating to the Bachmann Process", OSRD Rept 800 (Aug 1942) 33) W.E. Bachmann, "Studies on the Preparation and Properties of RDX , OSRD Rept 820 (Aug 1942)... 

B4 = mixture 60-70% trinitroanisol and 30-40% aluminum (italy) Bachmann process (RDX-Synthesis) 70... 

The compound is formed as a by-product from the manufacture of Cyclonite by the Bachmann process (from hexamethylenetetramine, ammonium nitrate, nitric acid, and acetic anhydride). It is obtained as the sole product, when 1,5-methylene-3,7-dinitro-1,3,5,7-tetrazacy-clooctane is treated with acetic anhydride, ammonium nitrate, and nitric acid. 

A modification of the Bachmann process used to make RDX with the same starting materials and in similar equipment is employed for the manufacture of HMX. The reaction temperature is lower (44 1°C as compared to 68°C for RDX) and the raw materials are mixed in a two-step process. The yield of HMX per mole of hexamine is about 55 to 60 percent, as compared to 80 to 85 percent in the manufacture of RDX. 

It is made by any of several processes, none of which is as immediately obvious as the straightforward nitrations we have mentioned so far. The Henning, Schnurr, Knoffler, Apel, and Bachmann processes all use an aliphatic ring compound, hexamethylenetetramine, as the basic starting material, which is reacted with concentrated nitric acid under various conditions and with other various additives. In these processes, three of the methylene groups and one of the amine groups are split off the parent molecule and lost. In the Eble and Wolfram processes, the ring is built up from short radicals that bond to each other. For the Eble process, the reactants are paraformaldehyde and ammonium nitrate mixed in acetic anhydride. 

Johnson. "Studies Relating to the Bachmann Process , OSRD Rept 800 (Aug 1942) 33) W.E. 

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