Hexamethylene tetramine compounds

Phenolic antioxidants in rubber extracts were determined indirectly photometrically after reaction with Fe(III) salts which form a red Fe(II)-dipyridyl compound. The method was applicable to Vulkanox BKF and Vulkanox KB [52]. Similarly, aromatic amines (Vulkanox PBN, 4020, DDA, 4010 NA) were determined photometrically after coupling with Echtrotsalz GG (4-nitrobenzdiazonium fluoroborate). For qualitative analysis of vulcanisation accelerators in extracts of rubbers and elastomers colour reactions with dithio-carbamates (for Vulkacit P, ZP, L, LDA, LDB, WL), thiuram derivatives (for Vulkacit I), zinc 2-mercaptobenzthiazol (for Vulkacit ZM, DM, F, AZ, CZ, MOZ, DZ) and hexamethylene tetramine (for Vulkacit H30), were mentioned as well as PC and TLC analyses (according to DIN 53622) followed by IR identification [52]. 8-Hydroquinoline extraction of interference ions and alizarin-La3+ complexation were utilised for the spectrophotometric determination of fluorine in silica used as an antistatic agent in PE [74], Also Polygard (trisnonylphenylphosphite) in styrene-butadienes has been determined by colorimetric methods [75,76], Most procedures are fairly dated for more detailed descriptions see references [25,42,44],... 

The compound, precipitated by interaction of hexamethylene tetramine and acidic 30% hydrogen peroxide, is a heat- and shock-sensitive powerful explosive when dry, much more shock sensitive than mercury fulminate. It explodes in contact with bromine or sulfuric acid. 

Two-stage resins (novolacs) are produced by the acid-catalyzed reaction of phenol and a portion of the required formaldehyde. Tire resin product is brittle at room temperature. It can be melted, but it will not crosslink. Novolacs can only be cured by the addition of a hardener, almost always formaldehyde supplied as hexamethylene tetramine. Upon heating, the latter compound decomposes to yield ammonia and formaldehyde. 

Hydrogen peroxide reacts with some acids (sulphuric acid for instance) and forms peroxy-acida, and with some bases [such as Ca(OH2), Ba(OH)2, Mg(OH)2, Zn(OH)2] and forms peroxides. Oxides of the IV and VI group of the periodic system (i. e. oxides of Ce, Ti, V, Nb, Ta, Cr, Mo, W, U) also react with hydrogen peroxide to form peroxides, peroxy-acids and persalts. Many additive compounds of hydrogen peroxide are known such as with sodium metaborate, urea and hexamethylene-tetramine. 

SAFETY PROFILE Most cured resins have little or no toxicity. If curing is incomplete there may be residues of highly toxic curing agents such as the organic amines m-phenylene diamine, diethylene triamine, tetraethylene pentamine, and hexamethylene tetramine, as well as phthalic anhydride and related compounds. When heated to decomposition they emit highly toxic fumes. See also various epoxy hardeners and POLYMERS, INSOLUBLE. 

With hexamethylene tetramine, or urotropine, an addition compound of the following formula is obtained ... 

An additive compound is also formed with hexamethylene tetramine this consists of crystals melting at 122° C. (Nef). 

Pure nitric acid free of nitrogen dioxide, so called white fuming nitric acid (WFNA). is in use as an oxidizer and for nitration of some compounds (e.g. hexamethylene tetramine [hexamine], Vol. Ill, p. 87). 

To overcome the objectionable reoxidation of formaldehyde and decomposition at the temperature of the reaction zone in the oxidation of methane, it has been proposed to react the formaldehyde as fast as formed with some substance to give a compound more stable under the conditions of the reaction and thus to increase the yields obtainable. It is claimed 101 that a reaction between the newly formed formaldehyde and annnonia to form a more stable compound, hexamethylene-tetramine, is possible under certain conditions, so that the formaldehyde is saved from destruction and can be obtained in a technically satisfactory yield. The hexamethylenetetramine is prepared by oxidizing methane with air in the presence of ammonia gas. A mixture consisting of six volumes of methane, twelve volumes of oxygen, and four volumes of ammonia gas is passed through a constricted metal tube which is heated at the constriction. The tube is made of such a metal as copper, silver, nickel, steel, iron, or alloys of iron with tin, zinc, aluminum, or silicon or of iron coated with one of these metals. Contact material to act as a catalyst when non-catalytic tubes are used in the form of wire or sheets of silver, copper, tin, or alloys may be introduced in the tube. At atmospheric pressure a tube temperature... 

Novolaks cannot undergo a spontaneous curing, because they are polyfunctional phenols cross-linked by methylene bridges. Therefore the curing agents must be at least bifunctional compounds. Curing can be carried out without the elimination of water with compounds that are easily converted into methylene carbonium ions for example, hexamethylene tetramine, which is widely used commercially (Urotropin, Hexa). Dihydroxy-benzyl amine and trihydroxybezyl amine structures are also formed with the elimination of ammonia, e.g.. 

Thus, urea formaldehyde resins are particularly suitable as rapid-setting (curing, hardening) molding materials. Aniline formaldehyde resins are hardened with compounds such as paraformaldehyde, hexamethylene tetramine, or furfurol, since as no polycondensation reactions occur in the absence of acid catalysts, pre-cross-linked products have to be used for this purpose. Aniline resins therefore cannot be used as rapid-setting molding materials (cf. Section 12.2.2). 

Another interesting cage compound is 1,3,5 triazaphospha-adamantane. It is made by reacting the cage molecule hexamethylene tetramine with formaldehyde and phosphine (7.293). The oxide, with 4-coordinated P, is easily obtained by room temperature oxidation with hydrogen peroxide, and the sulphide by addition of sulphur. A related cage stracture can be obtained from formaldehyde and a hydrazide [26]. 

For different applications, there are different U/F ratios and B-stage oligomers. They can be stabilized by hexamethylene tetramine to keep them alkaline, or they can be reversibly etherifled with methanol or butanol to make them stable and soluble in organic solvents (Fig. 3.10). They may be compounded and processed in water or organic solution or as solid powders for different applications. For final cnre, they are compounded with latent acid catalysts such as ammonium sulfamate, ammonium phenoxyacetate, ethylene sulfite, and trimethyl phosphate and generally heated to accelerate the cross-hnking reaction. 

To achieve cure, therefore, a hardener has to be added to the adhesive formulation. Suitable compounds are hexamethylene tetramine (hexamine) and paraformaldehyde as both are formaldehyde donors. In the case of the hexamine, thermal breakdown, in the presence of the water produced by the phenol/formaldehyde condensation reaction, not only yields more formaldehyde but also ammonia, which can help catalyse the reaction. 

Phenolic resins are prepared by a step-growth polymerisation of formaldehyde and phenol or phenol derivative using an acid or a base catalyst. The product type and the quality largely depend on the ratio of the reactants used and the nature of the catalyst. Phenolic resins are available in two varieties 1) novolac, which is a thermoplastic type and can be used as it is or can be cured with hexamethylene tetramine (HMTA) to get a crosslinked structure. This can also be viewed as a reactive intermediate, and can be transformed into other groups so different types of structures can be generated and 2) resole, which is a multifunctional reactive compound and can be cured thermally without a catalyst or an acid catalyst. 

This compound also uses Neoprene W type polychloroprene rubber. The compound, though coloured black with a few parts of carbon black is mainly filled with silica, which is a reinforcing mineral filler. The silica also helps to bond the rubber to the steel cords other ingredients added for this purpose include cobalt naphthenate. A commonly used system for this purpose is one comprising resorcinol and hexamethylene tetramine (HMT) which acts as a formaldehyde donor to form a phenolic resin in situ, but this is not suitable for Neoprene compounds because resorcinol is a fast accelerator for Neoprene vulcanization and interferes with its processing safety. 

Generally the activity of formaldehyde releasing compounds is reduced in alkaline media containing ammonia, because of the formation of inactive hexam-ethylene tetramine (Section 3.3.1). In the case of MCA, however, the hexamethylene tetramine formed reacts with MCA or CA to give quaternary hexaminium salts (Sections 3.3.5 and 3.3.6) which are effective, as they release formaldehyde widely independent of pH (see Section 3.3). 

Many rubber composites require that the rubber adheres permanently to a substrate such as steel, brass, textiles or other media. There are a number of established proprietary additives, which may be added to the rubber compound, which function in this capacity. The resorcinol-formaldehyde-silica (RFS) system is commonly used to achieve adhesion to metals. This system relies on the interaction of resorcinol (or a resorcinol donor), a methylene donor snch as hexamethylene tetramine and precipitated silica. Other systems that may rely on cobalt complexes or blocked isocyanates may also be used. 

Resin systems have been employed extensively for many years in applications such as the bonding of textiles to rubber, in hoses and belts where they have been used as tackifiers, reinforcers, curing agents and adhesion promoters. The addition of resin and/or cobalt depends upon the application and performance requirements of the rubber article that is to be bonded. Traditionally, resorcinol in combination with a methylene donor such as hexamethylene tetramine (HMT Figure 7.6) was utilised either alone or in compounds containing cobalt salts. On heating, HMT decomposes to produce ammonia and formaldehyde that reacts with the resorcinol to produce a stable, highly crosslinked polymeric network. 

As stated previously, precipitated silica is being used to replace the carbon black filler in so-called green tyres where it has been shown to reduce rolling resistance [43-46], and so help to reduce fuel consumption. Since the late 1960s, silica has been used in combination with resin systems and at that time PPG introduced a system that consisted of HI-SIL hydrated silica, resorcinol and hexamethylene tetramine (HRH). Initially it was used chiefly for bonding various rubbers to textiles, but such systems have found increasing use in wire coat and belt compounds. 

To improve mechanical, physical, chemical, electrical, optical, thermal, or molding performance, additives may be combined with the resin matrix. Reaction catalysts include hexamethylene tetramine for phenolics. Mica, alumina, and silica provide electrical arcing resistance. Halogenated compounds are fire retardants while zinc stearate and wax-Uke materials improve part release from the mold cavity. The molding process is improved through solvent-Uke additives that reduce the charge s viscosity. Wetting... 

Also obtained from the addition compound (SM) of 3,4-diacetoxy-a-chloroace-tophenone and hexamethylene tetramine in chloroform at r.t. for 24 h (40%). SM in ethanolic solution was treated with 38% hydrochloric acid at r.t. for 3 days [4597]. 

In addition, a third class of chemical additives is used in the HRH rubber formulations. This third additive is known as a methylene donor because it actually reacts with the resorcinol formaldehyde resin during the mixing in the rubber compound. The most common methylene donor used by the rubber industry today is hexamethoxymethylmelamine (HMMM). However, sometimes another chemical, hexamethylene tetramine (HMT), may be used. 

Ammonia is reacted with formaldehyde to produce hexamethylene tetramine, which is used as a methylene donor in the HRH adhesion system for rubber. It is also used to cure novolac phenolic resins in rubber compounds to increase hardness. 

The resulting novolak resins do not contain reactive methylol groups and so will not self-cross-link on heating. Instead, novolaks are compounded with reactants capable of forming methylene bridges at elevated cure temperatures and usually under alkaline conditions, e.g. hexamethylene tetramine ( hexa ), or paraform. A novolak resin is predominantly tri-functional, being open to cross-link formation at the o- and p-positions. 

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