Amines, 371 imidazoles

The introduction of monomers containing polar groups such as tertiary amines, imidazoles, pyrrolidones, pyridines, etc., gives the polymer dispersant properties that will be discussed in the article on dispersant additives for lubricants. 

Imidazole and its derivatives form an interesting and important class of hetero cyclic aromatic amines Imidazole is approximately 100 times more basic than pyndme... 

The unusual structure 125 displays an acylborane group the latter was formed from carboxyborane as a complex with secondary or tertiary amines, imidazole, or pyridine derivatives. The synthetic pathway (Scheme 31) consisted in an oxidation with NBS, substitution with cyanide, then treatment with 2-aminopyridine <2004JOM3567>. 

Ylide formation, and hence X-H bond insertion, generally proceeds faster than C-H bond insertion or cyclopropanation [1176], 1,2-C-H insertion can, however, compete efficiently with X-H bond insertion [1177]. One problem occasionally encountered in transition metal-catalyzed X-H bond insertion is the deactivation of the (electrophilic) catalyst L M by the substrate RXH. The formation of the intermediate carbene complex requires nucleophilic addition of a carbene precursor (e.g. a diazocarbonyl compound) to the complex Lj,M. Other nucleophiles present in the reaction mixture can compete efficiently with the carbene precursor, or even lead to stable, catalytically inactive adducts L M-XR. For this reason carbene X-H bond insertion with substrates which might form a stable complex with the catalyst (e.g. amines, imidazole derivatives, thiols) often require larger amounts of catalyst and high reaction temperatures. 

Occurrence of Acyclic Amines, Imidazoles, Catecholamines, and Indoles"... 

The differential reactivity of the sterically hindered and unhindered isocyanate groups of tolylene-2,4-diisocyanate facilitates the stepwise conjugation of hapten (R) and protein (P) amino groups (Fig. 3, Rn 7). jd.jj -Difluoro-m,m -dinitrobenzene (DFDNB) reacts with numerous functionalities including primary and secondary amines, imidazoles, and phenols to yield mixtures of conjugated materials (Fig. 3, Rn 8). This reaction is apparently harder to control than the diisocyanate reactions, but it is much more versatile. 

Fig. 15. Structure of the prosthetic group in (a) rhodopsin, where the retinal Schiff base is in an 1 l-co,6-j-cir-l2-s-ew conformation (b) delocalized excited singlet state (c) bathorhodopsin. where the chromophore is a hexaene amine-imidazole complex. From van der Meer et al. [127],...

Epoxy resins may be cured in the manner of polyadditions, i. e., homogeneously catalyzed by multifunctional amines and isocyanates, or cyclic anhydride, dicyan-diamide, or biguanide derivatives. On the other hand epoxy resins are also subject to homopolymerization. The catalysts represent Lewis bases, preferably tertiary amines, imidazoles, or ureas (the latter exclusively for the dicyandiamide curing)... 

Polymer blends leading to high-end polymers, e.g. from sulfonated polymers (sPEEK - sulfonated polyether-etherketone, sPPSU - sulfonated polyphenyl-sulfone) combined with alkaline components (amine, imidazole, polybenzimidazole) The combination results in ionic cross-linked phases. Commercially available polymers can be modified by different sulfonation reagents. Another possibility is to combine different monomers based on block co-polymers. The conductivity can be controlled by the number of S03H groups due to the dependence of the water uptake from the number of groups ([23] and references cited therein). 

Polyphenols. Polyphenols react with epoxy resins on heating, but require an accelerator (e.g., tertiary amines, imidazoles). On account of their low color stability, powder coatings based on this combination are not used for decorative purposes, but exclusively for functional purposes where high thermal, mechanical, and chemical resistance is required (e.g., pipe coatings). 

Other materials such as tertiary amines, imidazoles, BF3 complexes, antimony fluoride complexes and iodonium and sulphoninm salts can act as anionic or cationic initiators of the epoxy resin cure. 

Tsotra and co-workers [33] showed that when blends of epoxy resin and PANI are doped with dodecylbenzene snlfonic acid and cnred with various acidic and alkaline hardeners such as amine, imidazole, anhydride and boron trifluoride a relationship is developed between the shonlder at the 1,585 cm band in the spectral region 1,575-1,560 cm with the degree of volume resistivity developed. 

Typically, dicyandiamide is used at levels of 5-7 parts per 100 parts liquid epoxy, and at 3-4 parts per 100 solid epoxy resin. It can be used for one-component formulations with long shelf life. The moderately high curing temperature can be reduced by adding accelerators such as amines, imidazoles, or urea derivatives. Applications include prepregs and composites, printed circuit boards, structural adhesives, powder coatings, and lacquers and varnishes. 

Cure accelerators <1 Catalyze cure Amines, imidazoles, organophosphines, Lewis acids... 

Unlike other amines, imidazole catalyses the isomerisation of benzylpenicillin to benzylpenicillenic acid [38] (Bundgaard, 1971a,b, 1972, 1976a). The rate law shows that the nucleophilic reaction with imidazole to give the intermediate penicilloylimidazole [65] is general base catalysed by another molecule of imidazole and general acid catalysed by the conjugate acid of imidazole. 

Accelerators usually used are amines, imidazoles, organophosphines, urea derivatives, or Lewis bases and their organic salts Usual accelerators, however, tend to... 

Ionic bonding Acid Pyridine, amine, imidazole Ionic bonding... 

Several types of hardeners are used in the curing Aliphatic amines Amidoamines Aromatic amines Cycloaliphatic amines Imidazoles Polyamides Anhydrides Polysulfides Mercaptans Dicyandiamide (DiCy)... 

Bao et al. reported a cascade addition/cyclization process for preparing 2-heteroatom substituted benzimidazoles from o-haloarylcarbodiimides 72. Upon nucleophilic addition with amines, imidazoles and phenols, intermediates 75 might form, which in turn underwent intramolecular C-N bond formation to provide 2-amino benzimidazoles 73 and 2-aryloxy benzimidazoles 74 (Scheme 26) [58]. 

Similarly, this laboratory has recently described the synthesis of constrained peptidomimetics (118, Scheme 11.14) via intramolecular palladium-catalysed cinnamylation of a variety of amino acid side chains containing heteroatom nucleophiles (117, XH = amine, imidazole, phenol, carbo y). This procedure is remarkable for its scope and efficiency, proceeding rapidly and in high yield independent of the nature of the residues and chain length of the peptide. Further, protection of guanidine, alcohol and amide side chains was not required. These and similar templates would appear to be quite suitable for library investigations. 

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