Triazine accelerator

Logothetis [62] describes the use of triazine accelerators in the vulcanization of nitrile and fluoro elastomers. The triazine is more effective than the thiazole accelerators and produces highly reversion-resistant vulcanizates. 

Hie first effect has been exploited in numerous ligand-accelerated [30], enantioselective 1,2-additions of RyZn reagents to aldeliydes [26]. Dimetliylzinc, for example, has a linear structure and is not reactive towards aldehydes or ketones. Upon coordination of triazine, however, a tetraliedral configuration is produced at tlie zinc... 

The one-pot, three-component synthesis of a 20-membered dihydrotri-azine hbrary was also dramatically accelerated through the use of microwave irradiation [79]. Heating a subset of substituted anilines, cyanoguanidine and acetone in the presence of concentrated hydrochloric acid for 35 min at 90 °C in a single-mode microwave reactor gave the corresponding 2,2-dimethyl-1,2-dihydro-s-triazine hydrochloride 51 in comparable yield to conventional conductive heating methods but in a much shorter reaction time and increased purity (Scheme 21). 

Modern life and civilization opened the way to other important practical applications of heterocycles, for example dyestuffs, copolymers, solvents, photographic sensitizers and developers, and in the rubber industry antioxidants and vulcanization accelerators. Some of the sturdiest polymers, such as Kevlar, have aromatic rings. Melamines (2,4,6-triamino-substituted s-triazines) are monomers with numerous applications as both homopolymers and copolymers. Scheme 9 shows a few examples of compounds with various applications in our daily life, having in common the same building block, the aromatic s-triazine. 

Diamino-6-thio-l,3,5-triazines are potentially valuable as crosslinking agents in polymers and as accelerators in vulcanization processes (70MI22000). 

Finklea, H.C. and M.F.J. Fontenot (1996). Accelerated bioremediation of triazine contaminated soils A practical case study. In H.D. 

Steroidal, alicyclic or aromatic annulated pyridines were prepared via a microwave-assisted, base-catalyzed Henry reaction of /1-formyl enamides and nitromethane on an alumina support [97]. Highly substituted tri- and tetrasubstituted pyridines were synthesized in a Bohlmann-Rahtz reaction from ethyl /3-amino crotonate and various alkynones. The reaction involved a Michael addition-cyclodehydration sequence and was effected in a single synthetic step under microwave heating conditions [98]. An alternative approach towards polysubstituted pyridines was based on a reaction sequence involving an inverse electron-demand Diels-Alder reaction between various enamines 45 and 1,2,4-triazines 44 (Sect. 3.6), followed by loss of nitrogen and subsequent elimination-aromatization. Enamines 45 were formed in situ from various ketones and piperidine under one-pot microwave dielectric heating conditions [99]. Furthermore, a remarkable acceleration of the reaction speed (from hours and days to minutes) was observed in a microwave-assisted cycloaddition. Unsymmetrically substituted enamines 45 afforded mixtures of regioisomers (Scheme 35). 

The specific microwave effects were presumably responsible for the observed 40-fold acceleration in microwave-assisted synthesis of 1,3,5-triazines 107 compared to conventional thermal conditions. Thus, microwave heating of benzonitrile and dicyandiamide 106 in an ionic liquid ([bmim]PF6) in the presence of powdered KOH at 130 °C for just 12 min afforded 2,4-diaminotriazine 107 in 87% yield. Under otherwise identical conditions the reaction in a pre-heated oil-bath (130 °C temperature) took 8 hours to afford the target heterocycle 107 in 79% yield [140] (Scheme 57). 

Scheme 57 Microwave-accelerated synthesis of 1,3,5-triazines in ionic liquid...

Yadav and Kapoor [31] investigated the potential of microwaves to accelerate the 3cc reaction between thiazole schifFs base, ammonium acetate and an aldose to diastereoselectively yield the new acyclic C-nucleosides incorporating the thiazolo-5-triazine (xix) structure as the nucleobase. 

We have found that a certain number of polyhalogenated aromatic derivatives such as compounds 1-3 greatly accelerate the rate of bleaching of a number of poly silane derivatives in the solid state (33). This effect is dramatically demonstrated in Figure 5 for a PM PS film doped with —20% by weight of l,4-bis(trichloromethyl)benzene, 1. Similar results were obtained with substituted triazine sensitizers such as 2. In these cases, the polysilane is the primary absorber of the incident radiation. Interestingly, when compound 3, which absorbs at —400 nm, was incorporated into a PM PS film and the sample was irradiated at 404 nm, where only the sen-... 

Most of the catalysts are active only at elevated temperatures, but some are active at room temperature. Co-catalysts or accelerators have also been proposed. A carbodiimide-forming catalyst, 2,4,6-tris(dialkanolamino)-s-triazine was used for fs oducing carbodiimide foams. 

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