Hexamethylene Tetramine HMT

There are other methylene donors that can be used in HRH. Hexamethylene tetramine (HMT) is the second most common choice for use in HRH. However, the resulting adhesion characteristics will be different when HMT is used in place of HMMM. 

Tight Supply Situations in the Past and Future Supply Outlook 

There are a limited number of producers in the world for HMMM. 

Historically, HMT was the first methylene donor used in the HRH adhesion system. However, over the years, HMMM has replaced much of the HMT used in HRH. HMT is still used to some extent in HRH adhesion. 

HMT is also sometimes used in HRH systems for good adhesion. It is probably the second most commonly used methylene donor, which reacts with the resorcinol component of the HRH to achieve the desired adhesion. 

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Davey and Rutti (1976) studied the effeet of polyerystals growth on agglomeration of hexamethylene tetramine (HMT). Regular six member elusters were... 

N-Nitration. RDX, 5, is a cyclic nitramine obtained by the nitration of hexamethylene tetramine (HMT) in the presence of an excess of concentrated nitric acid. RDX is formed by the nitration of the three outside nitrogen atoms of HMT with removal of the internal nitrogen and methylene (-CH2-) groups. RDX is produced along with ammonium nitrate (NH4NO3) and formaldehyde (HCHO) as by-products. However, another molecule of RDX can be produced by adding NH4NO3, HCHO, and acetic acid (Eqs. 12.8 and 12.9) [1]. 

In the improved synthesis of Ifetroban described previously, environmental concerns due to special handling of copper bromide waste and hazards associated with hexamethylene tetramine (HMT) on manufacturing scale led to further perfection of the synthesis. Mechanistic considerations suggested that an oxidized form of aminoamide B (Scheme 4) would eliminate the necessity for a late-stage copper-mediated oxidation. This was indeed accomplished. The cyclization-elimination sequence was initiated by a Lewis add and completed by base-mediated elimination to afford the Ifetroban penultimate. In addition to eliminating the need for... 

Figure 3.41 Comparison of the growth rate of hexamethylene tetramine (HMT) crystals from water and ethanol solutions. (Reproduced with permission from Davey 1982a.)...

TABLE 3.3 Growth of Hexamethylene Tetramine (HMT) from Ethanol and Water Solvents... 

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. 

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. 

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. 

Hexamethylene tetramine" (methenamine urotropin, HMT) Limited prophylactic effect no convincing benefit after exposure Yes None N/A... 

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