Hexamine production

Multiple arylations of polybromobenzenes have been conducted to generate electron-rich arylamines. Tribromotriphenylamine and 1,3,5-tribromobenzene all react cleanly with A-aryl piperazines using either P(o-tolyl)3 or BINAP-ligated catalysts to form hexamine products [107]. Reactions of other polyhalogenated arenes have also been reported [108]. Competition between aryl bromides and iodides or aryl bromides and chlorides has been investigated for the formation of aryl ethers [109], and presumably similar selectivity is observed for the amination. In this case bro-mo, chloroarenes reacted preferentially at the aryl bromide position. This selectivity results from the faster oxidative addition of aryl bromides and is a common selectivity observed in cross-coupling. Sowa showed complete selectivity for amination of the aryl chloro, bromo, or iodo over aryl-fluoro linkages [110]. This chemistry produces fluoroanilines, whereas the uncatalyzed chemistry typically leads to substitution for fluoride. 

Multiple arylations of polybromobenzenes were also conducted to generate electron-rich arylamines. Tribromotriphenylamine and 1,3,5-tribromobenzene all react cleanly with iV-aryl piperazines using either P(o-tolyl)3 or BINAP-ligated catalysts to form hexamine products [107]. Reactions of other polyhalogenated arenes have also been reported [108]. 

Urea - formaldehyde polymers. Formalin and urea (usually in the molecular proportions of 3 2) condense in the presence of ammonia, pyridine or hexamine to give urea - formaldehyde polymers, known commercially as Bedle or Plaskon, and are widely used as moulding powdens. It is believed that the intermediate products in the condensation are methylol-urea and dimethylol-urea ... 

If the crystals are opaque white and do not deliquesce quickly in air of average humidity (65% rh), they may be contaminated with some Hex amine. Washing 100g of the crude product with lOOmL of Chloroform by stirring in a beaker then filtering, repeated as many times as necessary, will remove Hex amine. Methylamine HCI is insoluble in Chloroform whereas Hexamine Is at the rate of 1g to 10mL. 

Hexamethylenetetramine. Pure hexamethylenetetramine [100-97-0] (also called hexamine and HMTA) is a colorless, odorless, crystalline sohd of adamantane-like stmcture (141). It sublimes with decomposition at >200° C but does not melt. Its solubiUty in water varies Htde with temperature, and at 25°C it is 46.5% in the saturated solution. It is a weak monobase aqueous solutions are in the pH 8—8.5 range (142). Hexamethylenetetramine is readily prepared by treating aqueous formaldehyde with ammonia followed by evaporation and crystallisation of the soHd product. The reaction is fast and essentially quantitative (142). 

A number of disinfectants apparentiy owe their activity to formaldehyde, although there is argument on whether some of them function by other mechanisms. In this category, the dmg with the longest history is hexamethylenetetramine (hexamine, urotropin) [100-97-0] which is a condensation product of formaldehyde and ammonia that breaks down by acid hydrolysis to produce formaldehyde. Hexamine was first used for urinary tract antisepsis. Other antimicrobials that are adducts of formaldehyde and amines have been made others are based on methylolate derivations of nitroalkanes. The apphcations of these compounds are widespread, including inactivation of bacterial endotoxin preservation of cosmetics, metal working fluids, and latex paint and use in spin finishes, textile impregnation, and secondary oil recovery (117). 

Similar products from natural rubber may be made by fluxing a cresol novolak containing hexamine with the rubber at 150°C. 

The cationic polymerization of cardanol under acidic conditions has been referred to earlier [170,171], NMR studies [16] indicated a carbonium ion initiated mechanism for oligomerization. PCP was found to be highly reactive with aldehydes, amines, and isocyates. Highly insoluble and infusible thermoset products could be obtained. Hexamine-cured PCP showed much superior thermal stability (Fig. 12) at temperatures above 500°C to that of the unmodified cardanol-formaldehyde resins. However, it was definitely inferior to phenolic resins at all temperatures. The difference in thermal stability between phenolic and PCP resins could be understood from the presence of the libile hydrocarbon segment in PCP. 

The FR characteristics of PCP and Anorin-38 were improved substantially by introducing bromine. When five bronine atoms were introduced by controlled bromi-nation, the resin (the product obtained was still fluid in nature and could be crosslinked by hexamine to get hard partially brominated PCP-PBPCP) showed excellent FR characteristics exhibiting self-extinguishing property and UL 94 V-0 grade when blended with polyethylene, NR, etc. There was excellent compatibility with polyolefins as well as with other polymers such as cellulose, polyurethane, etc. Table 13 shows the FR properties of NR-PBPCP. 

In the former Soviet Union much use is made of industrial by-products to prepare acid inhibitors. The PB class is obtained by treating technical butyraldehyde with ammonia and polymerising the resulting aldehyde-ammonia. PB-5, for example, with O-Ol-O-15% of an arsenic salt is used in 20-25% HCl. A mixture of urotropine (hexamethyleneimine, hexamine) with potassium iodide, a regulator and a foaming agent is the ChM inhibitor. BA-6 is prepared from the condensation product of hexamine with aniline. A more recent development is the Katapin series which consists of /7-alkyl benzyl pyridine chlorides Katapin A, for example, is the /7-dodecyl compound. 

From this process, the yield of HMX/RDX is approx 90% of theory (based on Hexamine molecule), and 85% of this mixt is HMX The tracer expts conducted to study the mechanism of nitrolysis and product formation in the above process are briefly outlined in... 

During the first stage in the addition of reactants and aging, all of the original Hexamine and p-CH20 is consumed and DPT is the major product isolated. The quantity of DPT isolated is approx doubled when p-CH20 is included. 

In conclusion, there appears to be some supporting evidence, other than these tracer studies, that the synthesis of HMX and RDX molecules can be accomplished thru a build-up from single methylene-containing spedes or other small molecules, and that this route can also take place via a total degradation and resynthesis from molecules such as Hexamine. However, die development of an economical process for the large scale production of these expl nitramines, in particular HMX, via a method precluding the use of Hexamine, is vet to be accomplished... 

Recent years, the authors have innovatively proposed a method by using the aqueous ammonia liquor containing hexamine cobalt (II) complex to scrub the NO-containing flue gases[6-9], since several merits of this complex have been exploited such as (1) activation of atmospheric O2 to a peroxide to accelerate the O2 solubility, (2) coordination of NO, as NO is a stronger ligand than NH3 and H2O of Co( II) complexes to enhance the NO absorption and (3), catalysis of NO oxidation to further improve the absorption both of O2 and NO. Thus, a valuable product of ammonium nitrate can be obtained. 

Evidently this is a hydrogenation and the source of the hydrogen is benzylamine as indicated by the production of benzaldehyde and ammonia in equivalent amounts presumably the benzylamine is dehydrogenated to the imine C,HjCH =NH, which is then hydrolysed. In the absence of hexamine, the maximum yield of benzaldehyde is 50 per cent. When hexamine is added to the reaction mixture, the yield of aldehyde is increased and that of methylbenzylamine is decreased, and methyl-amine is present at the end of the reaction. Hexamine reacts as the methylene derivative of ammonia, CH2=NH, which is hydrogenated to methylamine. The fundamental stage of the Sommelet reaction may be written as ... 

Somewhat unanticipated applications can arise. For example, a process for the production of ultrapure hydrogen peroxide for the electronics industry has been patented recently,1425 which uses the macrobicyclic hexamine complex (29) supported on an inert material for dioxygen... 

It is made by the nitration of hexamine (hexamethylenetetramine), itself prepared from formaldehyde and ammonia. Hexamine was originally nitrated with a large excess of concentrated nitric acid at temperatures below 30°C and the product recovered by adding the reaction liquor to an excess of chilled water. Later the yield was improved by adding ammonium nitrate to the reaction as this reacts with the liberated formaldehyde. A much-used process converts the hexamine first to its dinitrate, which is then reacted with ammonium nitrate, nitric acid and acetic anhydride (the last reagent being re-formed from the product by use... 

Reduction of dibenzothiophene with sodium in liquid ammonia has been shown to be sensitive to the experimental methods employed however, the major product is usually 1,4-dihydrodibenzothiophene. 27 -28i The electrochemical reduction of dibenzothiophene in ethylene-diamine-lithium chloride solution has been shown to proceed via stepwise reduction of the aromatic nucleus followed by sulfur elimination. In contrast to the reduction of dibenzothiophene with sodium in liquid ammonia, lithium in ethylenediamine, or calcium hexamine in ether, electrolytic reduction produced no detectable thiophenol intermediates. Reduction of dibenzothiophene with calcium hexamine furnished o-cyclohexylthiophenol as the major product (77%). Polaro-graphic reduction of dibenzothiophene 5,5-dioxide has shown a four-electron transfer to occur corresponding to reduction of the sulfone group and a further site. ... 

The importance of cyclic nitramines as military explosives has meant that an enormous amount of research has been conducted in this area. Only some of the rich array of products and by-products obtainable from hexamine nitrolysis are discussed in this section. For mechanistic smdies and detailed analysis of these reactions the primary research papers should be consulted. " ... 

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. 

The nitrolysis of hexamine with 40 equivalents of a 25 % solution of dinitrogen pentoxide in absolute nitric acid in carbon tetrachloride at —20 °C is reported to give a 57 % yield of RDX. The product is free from HMX as determined by NMR (>95 % pure)." ... 

The presence of HMX as an impurity in RDX is not a problem when the product is used as an explosive. However, the need for an analytical sample of RDX makes other more indirect methods feasible. One such method involves the oxidation of 1,3,5-trinitroso-1,3,5-triazacyclohexane (109) ( R-salt ) with a mixture of hydrogen peroxide in nitric acid at subambient temperature and yields analytical pure RDX (74%) free from HMX." The same conversion has been reported in 32 % yield with three equivalents of a 25 % solution of dinitrogen pentoxide in absolute nitric acid. l,3,5-Trinitroso-l,3,5-triazacyclohexane (109) is conveniently prepared from the reaction of hexamine with nitrous acid at high acidity. ... 

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. 

Other nitramine products from the nitrolysis of hexamine... 

Proceeding from a precursor polyaza-caged structure, which may be different from the desired product, but includes the final structure within the cage. Although not a caged compound the synthesis of RDX from the nitrolysis of hexamine would fit this category. 

Dagley and co-workers reported the synthesis of 2-nitrimino-5-nitrohexahydro-1,3,5-triazine (100) from the Mannich condensation of nitroguanidine (98), formaldehyde and t-butylamine, followed by nitrolysis of the t-butyl group of the resulting product, 2-nitrimino-5-fert-butylhexahydro-l,3,5-triazine (99). The triazine (100) has also been synthesized from the reaction of nitroguanidine and hexamine in aqueous hydrochloric acid, followed by nitration of the resulting product (97) with a solution of nitric acid in acetic anhydride. ... 

When ammonia gas is passed over anhydrous nickel chloride the product is an ammoniate, hexamine nickel chloride, NiCb GNHs. Ammoniate also can be prepared in solution by dissolving nickel chloride hexahydrate in an aqueous solution of ammonia. 

The final product of the action of nitric acid on hexamine or hexamine dinitrate is RDX see Vol 3, p C614. At low temps, however a number of other compounds are produced (Ref 2). Dilution of the hexamine dinitrate-nitric acid reaction mixture at low temperatures with ethyl ether and subsequent treatment of the gum so obtained with methyl and ethyl alcohols and water severally leads to l-alkoxy-3 5-dinitro-l 3 5-triazacyclohexane (IV), l 3-di-nitro-l 3 5-triaza-n-pentane 5-nitrate (V), and methylenedi-1 -(3 5-dinitro-1 3 5-triaza-cyclo-hexane) (VI). Dilution of the reaction mixture with methyl and ethyl alcohol produces mainly 3 5-dinitro-1 3 5-triazacyclohexane nitrate (II). 

Hexamethylenetetramine Explosive. A powerful solid explosive was claimed to have been prepd by oxidizing hexamine with a solution of hydrogen peroxide, treating the resulting product with nitric acid and then, reoxidizing with H202 (Ref 1). After drying, this was mixed with AN, castor oil and turpentine (Ref 2)... 

HDN is one of the intermediate products obtained during preparation of Cyclonite from hexamine. It has also been proposed for use in the manufacture of an explosive, tentatively considered to be 1,3,5-trinitrohexahydro-s- triazine (Ref 7). Its use in an AN-slurry expl has been patented (Ref 12)... 

Note If instead of treating the free hexamine with peroxide, its salts are used (such as the citrate), or if hexamine is treated with peroxide in the presence of substantial quantities of acid, the resulting product is Hexanjethylene-triperoxide diamine (qv)... 

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