Heterocyclic compounds, aromatic triazoles

Many chemical compounds have been described in the Hterature as fluorescent, and since the 1950s intensive research has yielded many fluorescent compounds that provide a suitable whitening effect however, only a small number of these compounds have found practical uses. Collectively these materials are aromatic or heterocycHc compounds many of them contain condensed ring systems. An important feature of these compounds is the presence of an unintermpted chain of conjugated double bonds, the number of which is dependent on substituents as well as the planarity of the fluorescent part of the molecule. Almost all of these compounds ate derivatives of stilbene [588-59-0] or 4,4 -diaminostilbene biphenyl 5-membeted heterocycles such as triazoles, oxazoles, imidazoles, etc or 6-membeted heterocycles, eg, coumarins, naphthaUmide, t-triazine, etc. 

Examples of aromatic amines that can be dia-zotized are shown in Fig. 13.83. This extremely abbreviated list is designed to show that a wide variety of amines can be used, including hydrophobic, weakly basic, hydrophilic, and heterocyclic compounds. orf/zo-Diamines are not typically used because of their propensity to undergo triazole formation (Fig. 13.84). 

A rich coordination chemistry of aromatic diazine (N-N), especially pyridazine and phthalazine related ligands has emerged over the last three decades,1-72 and recently open-chain diazine (N-N) coordination chemistry has been well developed, especially by Thompson and others.62-113 Many types of aromatic heterocyclic compounds contain a 1,2-diazine (N-N) moiety, e.g., pyridazine and its 3,6-disubstituted derivatives (Scheme 1, Type 1), phthalazine, condensed phthalazines and their substituted derivatives (Scheme 1, Type 2), and other compounds such as pyrazole, triazole, thiadiazole, tetrazole, indazole, 1,2,4-triazine, 1,2,4,5-tetrazine, and thiadiazepines. Alternatively, the 1,2-diazine (N-N) moiety also exists as an open-chain entity in some related compounds, e.g., A-substituted-amide hydrazonimidates (Scheme 1, Type 3), A-substituted-amide hydrazonidates (Scheme 1, Type 4), A-substituted hydrazides (Scheme 1, Type 5), A-substituted amidrazones (Scheme 1, Type 6), and A-sub-stituted hydrazidates (Scheme 1, Type 7). 

The mesomeric effect of the C=S linkage is very pronounced and is responsible for the facile quaternization of heterocyclic N-alkylated thiones (159) this effect is operative even when such a shift does not increase the aromaticity of the ring. Thione derivatives of pyridazine, benzothiazole, quinazoline, 1,3-thiazine, triazole,and isoindole are examples of compounds which readily form quaternary salts. 

A study of ketene A, O-acetals has shown that such compounds derived from lactam acetals may be used in the preparation of larger heterocyclic systems via reaction with a 1,3-dipolar species, the initial cycloadducts stabilizing their structures by aromatization. Pyrrolo[2,3-i/]-l,2,3-triazole derivatives, however, do not undergo such elimination reactions and stable cycloadducts may be obtained. Thus, the lactam acetals (133) give the ketene A,0-acetals (134), which on reaction with p-nitrophenyl azide yield substituted pyrrolo[2,3-d]-l,2,3-triazole derivatives (135) <86CB359l>. 

Abstract Synthesis methods of various C- and /V-nitroderivativcs of five-membered azoles - pyrazoles, imidazoles, 1,2,3-triazoles, 1,2,4-triazoles, oxazoles, oxadiazoles, isoxazoles, thiazoles, thiadiazoles, isothiazoles, selenazoles and tetrazoles - are summarized and critically discussed. The special attention focuses on the nitration reaction of azoles with nitric acid or sulfuric-nitric acid mixture, one of the main synthetic routes to nitroazoles. The nitration reactions with such nitrating agents as acetylnitrate, nitric acid/trifluoroacetic anhydride, nitrogen dioxide, nitrogen tetrox-ide, nitronium tetrafluoroborate, V-nitropicolinium tetrafluoroborate are reported. General information on the theory of electrophilic nitration of aromatic compounds is included in the chapter covering synthetic methods. The kinetics and mechanisms of nitration of five-membered azoles are considered. The nitroazole preparation from different cyclic systems or from aminoazoles or based on heterocyclization is the subject of wide speculation. The particular section is devoted to the chemistry of extraordinary class of nitroazoles - polynitroazoles. Vicarious nucleophilic substitution (VNS) reaction in nitroazoles is reviewed in detail. 

Most diazotized heterocyclic amines undergo normal coupling reactions with common aromatic coupling components, as well as with some C—H acidic compounds . This pertains for five-membered ring systems such as pyrrols 46 pyrazoles imidazoles 45 , l,2,4-(49) and 1,2,3-triazoles 50... 

Most common electron transporters are derived from heterocyclic aromatic compounds, either as pure organic materials or as metal coordination complexes. Pure organic molecules such as phenanthrolines, oxidiazoles, and triazoles can have high electron mobilities (Figure 25). Some of the highest carrier mobilities for amorphous molecular materials have been reported for oligofluorenes (lO -lO cm V j-i) 305,313 inefficient carrier... 

Heterocyclic aromatic compounds contain C and H atoms other than carbon and hydrogen (Fig. 6). For the monocyclic molecules Hiickel s rule is applicable. For example both pyridine and pyrrole contain six ti electrons. Unlike the former the lone pair of the latter is delocalized. Armit and Robinson have shown a connection between the electronic sextet and the heteroaromaticity. Due to the electronegativity difference between carbon and nitrogen the bonds in pyridine are not of equal length and the delocalization is not perfect. Five membered heteroaromatics with oxygen and sulfur are furan and thiophene respectively. Pyrazole/imidazole, triazoles and tetrazoles are five membered heteroaromatics with two, three and four nitrogen atoms respectively. Three important aromatic six membered heterocyclic molecules are pyrimidine, pyrazine and pyridazine. Benzofused... 

Triazoles are five-membered aromatic heterocycles that contain three nitrogen atoms located at the 1,2,3 or 1,2,4 positions in the ring. A large munber of ionic compounds that contain a triazole derivative are described as energetic materials. 

Triazole is an aromatic five-membered heterocyclic system consisting of two carbon atoms and three nitrogen atoms including one pair of isomeric chemical compounds 1,2,3-triazole and 1,2,4-triazole. The triazole system is generally chemically stable because all ring atoms have sp -hybridation, and six electrons are delocalized in 7i-molecular orbitals. 

A second synthetic route to poly(aryl ethers) containing heterocyclic units involved the reaction of an aromatic dihydroxy heterocycle with conventional activated difluoro compounds. Bisphenols containing quinoxaline, phenylimidazole, oxadizaole, pyrazole, triazole, phenolphthalein, phenolphthalimidine, and phenolphthalein anilide heterocycles were prepared and polymerized to high molecular weight (84-95), However, the most noteworthy examples are the poly(aryl ether benzimidazoles), prepared from bis(4-hydroxyphenyl) bibenzimidazole, due to their unique combination of adhesive, thermal and mechanical properties (Scheme VIII) (93-95),... 

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