Phenol hexamine

The historical link between the use of HMT to alleviate or prevent the effects of phosgene is a long one. In designing respirators to defend against phosgene during WWI, a range of compounds was examined. For example, soda lime (a mixture of sodium hydroxide and calcium hydroxide) proved effective, while phenol and sodium phe-nolate were also effective and British Phenolate Helmet (P Helmet) was first used on December 15, 1915. This was followed by the Phenolate Hexamine Helmet (PH Helmet) from early 1916 onwards. The PH Helmets comprised a flannel sack which had been dipped in a mixture of... 

A glassy carbon fiber can be produced from a melt spun phenol-hexamine thermoset resin [296,297] or a cured novalac [296,298], without the requirement of a stabilization stage. 

During the past four decades phenolic resins have become of increased significance in rubber compounding. For example, the resin based on cashew nut shell liquid, which contains phenolic bodies such as anacardic acid (Figure 23.23), may, when blended with hexamine, be incorporated into nitrile rubber (butadiene-acrylonitrile rubber). 

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. 

One of the interesting properties of PBPCP [187] was its fast heat dissipation characteristics and so it was tested by the well-known oxy-acetylene panel test (ASTM 285-70) for ablative materials. Figure 13 shows the survival of a flower for 100 s. kept on the 6.35-mm asbestos fiber-reinforced hexamine-cured panel. The ablation rate value of this material was 3.2 x 10 in/s in comparison with 3.6 x 10 in/s for asbestos-phenolic. As the char content of PBPCP was only 27% compared with 60% for conventional phenolics, mechanisms involving transpiration processes rather than heat blocking by char formation might be playing a greater role in this case [188]. 

Hexamine is a cross-linking agent for phenolic resins. 

The acid-catalyzed reaction occurs by an electrophilic substitution where formaldehyde is the electrophile. Condensation between the methylol groups and the benzene rings results in the formation of methylene bridges. Usually, the ratio of formaldehyde to phenol is kept less than unity to produce a linear fusible polymer in the first stage. Crosslinking of the formed polymer can occur by adding more formaldehyde and a small amount of hexamethylene tetramine (hexamine. 

An estimate five (5) million pounds per year of hexamine are consumed to make commercial explosives. Hexamine demand from the phenolic resin segment has declined due to increased competition from formaldehyde-free resins and other resins that offer performance advantages. 

Production. Production has declined from 48 million pounds in 1995 to 32 million pounds in 2001. The decline is mainly due to a decline in the use of phenolic resins that contain hexamine.252 Hexamine is produced as a granular and free-flowing powder as well as a 42.5 percent solution. The solution is shipped in tank trucks, railcars, and drums. Solids are packed in bags, fiber drums, and super sacks. Hexamine is sensitive to moisture. Therefore it should be stored in an atmosphere with a relative humidity below 60 percent.126... 

Formylation of Phenols (or Amines) with Hexamine (Duff)... 

This reaction is readily accomplished by heating the phenolic compound at 150-160 for 10 to 30 minutes with a mixture of glycerol, boric acid, and hexamine. The phenolic aldehyde is liberated by acidification and steam distillation. By this general procedure, sixteen phenolic aldehydes have been prepared. Although the yields are only 15-20%, the method requires little time and furnishes a reasonably pure product which is the ortho isomer (cf. method 143). 

Duff reaction. Hexamine condenses with a phenol in the ortho position to give a Schiff base which on hydrolysis yields the o-hydroxy aldehyde ... 

Duff heated glycerol with boric acid at 170° until no more water was eliminated) added 25 g. each of a phenol and hexamine, heated at 170° for 15 min., and isolated the chelated o-hydroxy aldehyde by steam distillation. For several phenols, yields were in the range 2-8.5 g. Pyrogallol-1,3-dimethyl ether is substituted in the para position to give syringic aldehyde (I) in 31-32% yield. W. Baker applied to... 

Hexamethylene tetramine is an important chemical. Its most important application is as a source of formaldehyde for crosslinking phenolic molding powders, shell molding resins, and two-step curing resins for chip board. Quatemization of HMTA with an alkyl chloride (R-Cl) gives a family of bactericides (developed by Dow) for use in latex paints and as a dermatitis preventative in water-soluble cutting oil. Hexamine is used in pharmaceutical formulations to combat urinary tract infections and also as an intermediate in the production of chloramphenicol. 

PF is made by the condensation polymerisation of phenol and formaldehyde. Due to the volatile and toxic/irritant nature of formaldehyde, this is usually fixed with ammonia giving hexamine. Polymerisation of hexamine and phenol not only produces phenol formaldehyde but may release residues of phenol, formaldehyde or ammonia. In certain cases some residues may remain in the moulding and be released into the product. As with UF, PF is mainly used for closures but due to the fact that the material is naturally dark, it is used for dark or deep colours. PF is generally more resistant to heat and moisture than UF. Both UF and PF are used with a range of fillers, e.g. wood flour, synthetic fibre. Density 1.25-1.45. General pharmaceutical applications have now reduced. 

These may be wood, paper or flour filled, but be alert to possible release of ammonia, phenol, or formaldehyde residues from the moulding process. PF can be made by reacting phenol with hexamine (made from formaldehyde+ammonia). 

HEXAMINE (100-97-0 100-97-0) Combustible solid (flash point 482°F/250°C). Incompatible with acids, l-bromopentaborane(9), organic anhydrides, isocyanates, vinyl acetate, acrylates, substituted allyls, alkylene oxides, epichlorohydrin, iodine, iodoform, ketones, aldehydes, alcohols, glycols, phenols, cresols, caprolactam solution, sodium peroxide, strong oxidizers. Attacks aluminum, copper, lead, tin, zinc, and their alloys, and some plastics, rubber, and coatings. 

PENTAETHYLENE HEXAMINE (4067-16-7) Combustible liquid (flash point 347 -405°F/175°-207°C cc). Incompatible with strong oxidizers, oiganic anhydrides, acrylates, alcohols, aldehydes, alkylene oxides, substituted allyls, cellulose nitrate, cresols, caprolactam solution, epichlorohydrin, ethylene dichloride, isocyanates, ketones, glycols, nitrates, phenols, vinyl acetate. Exothermic decomposition with maleic anhydride. Increases the explosive sensitivity of nitromethane. Attacks chemically active metals. 

The cardol present in CNSL, if in high proportion can lead to an exothermic reaction with formaldehyde and also It appears desirable for the phenolic components to have a high proportion of triene in order for the first acid-catalysed side chain oligomerisation stage to proceed. CNSL-formaldehyde polymers have greater flexibility than those from phenol-formaldehyde, due to internal plasticising, they are also more soluble in solvents, and due to their hydrophobicity they have resistance to water penetration, and hence acidic and alkaline media. For some applications highly methylolated cardanol is useful and this can be formed with formaldehyde, by the use of adipic or succinic acid as catalysts, and subsequently rapidly cured with hexamine (ref. 245). 

Phosphoric acid, or more commoifly ammonium chloride, is used as a hardener for UF resin adhesives. Ammonium chloride reacts with formaldehyde to produce hexamine and hydrochloric acid, and the latter catalyzes the curing of the resin. In the manufacture of plywood a resin (with U/F molar ratio typically 1 1.8) mixed with hardener is applied to wood veneers, which are then plied together and pressed at 95-110°C under a pressure of 200-800 psi (1.38-5.52 MPa). The UF resin-bonded plywood is suitable for indoor applications but is generally unsuitable for outdoor use. For outdoor applications phenol-formaldehyde, resorcinol-formaldehyde, or melamine-formaldehyde resins are more suitable. 

Phenolic resins are also extensively used in the binding of foundry molds. Both resol and novolak resins are used for this application. The sand is coated with the phenolic resin at a rate of 3 to 4%. The PF resin can be used both as an organic solvent solution and in powder form. Coating of the substrate can be done both at ambient or at higher temperature. In higher-temperature coatings novolaks are the preferred resins and in this application, waterborne resins (75% resin) can also be used. Hexamethylenetetramine as well as wax are added. Hexamine is often added separately from the resin to avoid precuring. 

Possible crosslinkers are formaldehyde as aqueous solution [268], paraformaldehyde [263,265,267,269], UFC [270,271], UF resins [272], aqueous formaldehyde solution emulsified in an oil [273], dimethylolurea [274] or urea and phenol methylols with longer chains to overcome steric hindrance. Tannins can also be hardened by addition of hexamethylenetetramine (hexamine) [275], whereby these boards show a very low formaldehyde emission [269,275 281]. The autocatalytic hardening of tannins without any addition of formaldehyde or other aldehyde as crosslinker is possible, if alkaline Si02 is present as a catalyst at high pH or just as a consequence of the catalysis of the reaction induced by a lignocellulosic surface [282]. 

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