Triazine stability

Melamine - formaldehyde polymers. Melamine (2 4 6-triamino-1 3 5-triazine), obtained by heating dicyandiamide under pressure, condenses with formalin to give melamine - formaldehyde polymers (Beetle - Melamine), which have similar uses, but better stability to heat... 

A large number of hindered phenoHc antioxidants are based on the Michael addition of 2,6-di-/ f2 -butylphenol and methyl acrylate under basic catalysis to yield the hydrocinnamate which is a basic building block used in the production of octadecyl 3-(3,5-di-/ f2 butyl-4-hydroxyphenyl)propionate, [2082-79-3], tetrakis(methylene-3(3,5-di-/ f2 butyl-4-hydroxylphenyl)propionate)methane [6683-19-8], and many others (63,64). These hindered phenolic antioxidants are the most widely used primary stabilizers in the world and are used in polyolefins, synthetic and natural mbber, styrenics, vinyl polymers, and engineering resins. 2,6-Di-/ f2 -butylphenol is converted to a methylene isocyanate which is trimerized to a triazine derivative... 

Oligomeric hindered amine light stabilizers are effective thermal antioxidants for polypropylene. Thus 0.1% of A[,Af-bis(2,2,6,6-tetramethyl-4-piperadinyl)-l,6-hexanediamine polymer, with 2,4,6-trichloro-l,3,5-triazine and 2,4,4-trimethyl-2-pentaneainine [70624-18-9] (35) (Fig. 5), protects polypropylene multifilaments against oxidation when exposed at 120°C in a forced-air oven (22) for 47 days. 3,5-Di-/ l -butyl-4-hydroxytoluene [128-37-0] (0.1%) affords protection for only 14 days. 

Although all the rings in Figure 1 contain six tt-electrons, the accumulation of electronegative nitrogen atoms in the polyaza structures leads to hydrolytic as well as thermal instability. This is noticeable in pyrimidine, and marked in the triazines and tetrazine. Some stability can be conferred by appropriate substitution, as we shall outline later. 

Perhaps the most firmly based report for the formation of an azete involves flash pyrolysis of tris(dimethylamino)triazine (303). This gave a red pyrolysate believed to contain the highly stabilized azete (304) on the basis of spectroscopic data. The putative azete decomposed only slowly at room temperature, but all attempts to trap it failed (73AG(E)847). Flash pyrolysis of other 1,2,3-triazines gives only acetylenes and nitriles and it is not possible to tell whether these are formed by direct <,2-l-<,2-l-<,2 fragmentation of the triazine or by prior extrusion of nitrogen and collapse to an azete (81JCR(S)162). 

The increase in thermodynamic stability of 85 is achieved by easy ring opening (01H127). This knowledge allows one to control the regioselectivity of the oxidative amination of the 6-aryl-l,2,4-tiiazine 4-oxides 53, obtaining either (i) the 5-amino-1,2,4-triazine 4-oxides 56 in the reaction of 53 with amines at low temperature in the presence of the oxidant or (ii) the 3-amino-1,2,4-triazine 4-oxides 88, provided the reaction is carried out in two steps (addition and oxidation) at room temperature or higher. 

The first systematic theoretical study on dihydro-1,2,4-triazines was recently carried out (98JOC5824) the stabilities of all the possible unsubstituted dihydro-1,2,4-triazines were calculated using various theoretical methods, all reliable calculation methods consistently show that the 2,5-dihydro isomer 98 is the most stable. This is in perfect agreement with the experimental observations all the synthetic methods used for the preparation of dihydro-1,2,4-triazines result in 2,5-dihydro isomer 98, provided the structures of the reactants and the reaction mechanism allow its formation. Thus, although Metze and Scherowsky (59CB2481) claimed the formation of 1,2-dihydro-1,2,4-triazine 92 (R = = Ph) in the reduction... 

If the formation of a 2,5-dihydro isomer 98 is not allowed, other dihydro-1,2,4-triazines are formed aeeording to their order of stability ealeulated by various theoretieal methods (see Table III) (98JOC5824). 

UV absorbers have been found to be quite effective for stabilization of polymers and are very much in demand. They function by the absorption and harmless dissipation of the sunlight or UV-rich artificial radiation, which would have otherwise initiated degradation of a polymer material. Meyer and Geurhart reported, for the first time in 1945 [10], the use of UV absorber in a polymer. They found that the outdoor life of cellulose acetate film was greatly prolonged by adding phenyl salicylate (salol) [10]. After that, resorcinol monobenzoate, a much more effective absorber, was introduced in 1951 [11] for stabilization of PP, but salol continued to be the only important commercial stabilizer for several years. The 2,4-dihydroxybenzophenone was marketed in 1953, followed shortly by 2-hydroxy-4-methoxybenzophenone and other derivatives. Of the more commonly known UV absorbers, the 2-hydroxybenzophenones, 2-hy-droxy-phenyl-triazines, derivatives of phenol salicylates, its metal chelates, and hindered amine light stabilizers (HALS) are widely used in the polymer industry. 

The efficacy of RF in stabilizing small rings is well illustrated by the fact that the azete from trifluoro-l,2,3-triazine is considerably more reactive. Trapping experiments were unsuccessful and a polymer was isolated at room temperature. The dimer (41) forms an observable anion with CsF, which confirmed the endo structure [87CC1699 90JCS(P1)975, 90JCS(P1)983], In contrast, trifluoro-l,2,4,-triazine is resistant to vapor phase photoysis and flow pyrolysis [87JCS(P1) 1251]. 

Previous methods involved the construction of the triazine onto a pyra-zole ring with suitable functionality. On the other hand, the reverse construction is also possible. Thus, 356 was prepared (87MI8) from 355 with hydrazine. The stability of 356 to dilute acids and bases was studied (87MI8) (Scheme 76). 

It does have a number of draw backs. It has poor thermal stability (a property common to most formaldehyde release biocides) and, in some instances, may cause blackening of metalworking fluid concentrates if heated above 50°C for a period of time. Recently, this active ingredient was placed on Annex 1 of the Dangerous Substances Directive having been identified as a potential skin sensitiser. This means that formulations containing efficacious levels of this class of triazine in them would have to be labelled with R43 - may cause sensitisation by skin contact. This is unacceptable to many UK customers. As this material is only bactericidal, it needs to be co-formulated with a fungicide to provide complete protection for a product. 

This material shares many of the advantages of the triazine biocides. They are relatively cheap, compatible with most formulations and provide a source of reserve alkalinity. In addition, at the time of writing, there are no requirements for labelling R43 with this class of material. It shares similar disadvantages to the triazines, possessing poor thermal stability. Oxizolidines also need to be co-formulated with a fungicide to provide complete protection for a product. 

Stability Very stable over several years of shelf life, under normal illumination and extreme temperatures. Stable in neutral, slightly acid, or basic media. Sublimes at high temperatures and when heated, especially at high temperatures in acid or basic media, hydrolyzes to hydroxyatrazine (2-hydroxy-4-ethylamino-6-isopropylamino-S-triazine), which has no herbicidal activity... 

Triazines are well-known compounds with high thermal stability and higher EA than 1,3,4-oxadiazoles (PBD) and 1,2,4-triazoles (TAZ, 92). Schmidt et al. studied a series of dimeric 1,3,5-triazine ethers for application as ETMs for OLEDs [150], However, despite their high EA, the efficiency of the OLEDs improved only modestly. One possible explanation is due to their rather poor electron mobilities. 

In the case of quaternary derivatives made from the non-planar aliphatic amines 7.64, 7.65 and 7.66, steric strains further destabilise the C-N+ bond so that reaction with cellulose occurs under alkaline conditions at 30 °C, whereas temperatures of about 40-50 °C are required for the pyridinium derivatives 7.67. The quaternisation approach appeared to offer the opportunity to prepare dyes yielding reactivity levels intermediate between those of aminochloro- and dichlorotriazine dyes without loss of the desirable stability of the dye-fibre bond to acidic conditions that is characteristic of aminohalotriazine dyes. Unfortunately, this ideal was not attainable because of the objectionable odours of the tertiary amines liberated by the fixation reaction and the sensitivity of the reactivity behaviour of the quaternised derivatives to the nature of the chromogen attached to the triazine ring, making it difficult to select compatible combinations of dyes. 

The H+ and NH forms of homoionic montmorillonite promote the hydrolysis of chloro-s-triazines to the hydroxy analogs (hydroxy-s-triazines) (73). Apparently, the surface acidity of these clays was extremely high, since no degradation was observed in control experiments conducted at pH 3.5 in homogeneous aqueous solution. Russell et al. (73) suggested that the hydroxy-s-triazine products were stabilized in the protonated form at the silicate surface. The IR spectra of these surface complexes agreed with the spectra obtained in 6N HC1, and it was inferred that the pH at the clay surface was 3 to 4 units lower than that measured in suspension. 

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