Triazoles acid/base properties

More recently, Stepanov et al. (1989) investigated the acid-base properties of the zwitterion 3.22 which is obtained in the diazotization of 5-amino-3-nitro-l,2,4-triazole. Under alkaline conditions the (Z)-diazoate dianion 3.23 is formed. It can be isomerized thermally to give the (E)-diazoate dianion 3.24. If the solution of this compound is acidified, the primary addition of a proton takes place at the anionic ring nitrogen yielding 3.25, and subsequently the hydrogen-bond-stabilized (Z)-iso-mer (3.26). Further acidification gives the nitrosoamine (3.27). 

The acid-base properties of the ground and excited states of [Ru(bpy)2(im)2] and [Ru(bpy)2(l,2,4-triazole)2] have been investigated. Both complexes are stronger acids in the excited than the ground states." Representative triazoles, L or HL, have been incorporated into the complexes [Ru(bpy)2L]"" (n = 1 or 2). Electronic spectroscopic and electrochemical properties have been reported all the ligands are weaker tt acceptors than bpy." " The crystal structures of... 

The direct incorporation of a fluorine atom in the ring essentially affects versatile physicochemical and chemical characteristics of the heterocyclic system, in particular, its tautomerism, dipole moment, and the acid-base properties. For instance, tautomeric equilibria involving NH-unsubstituted fluoro derivatives of 1,2,3-triazoles [22, 23], 1,2,4-triazoles [24], and tetrazoles [25-28] were explored in a series of theoretical studies. The acid-base properties of these heterocycles (in particular, the CH-acidity of some among them) were also studied [28-30]. These investigations showed that the fluorine atom attached to the heterocyclic system changed significantly the character of the electron density distribution and consequently the polarity of the heterocycle, strongly increased its acidity and decreased its basicity. 

Assignment of the l,2,4-triazolo[l,5-c]pyrimidine structures to the products obtained from the previously described cyclizations and not the alternative [4,3-c] structures has been rationalized and corroborated on the basis of (a) preference of cyclization at the more nucleophilic triazole ring N2 rather than at its less nucleophilic N4 (65JOC3601 88JMC1014), (b) inability of the obtained products to undergo acid- or base-catalyzed Dimroth rearrangement, a property characteristic of the thermodynamically less stable [4,3-c] isomers (91JMC281), (c) comparison with unequivocally prepared... 

Cheng L, Wang JQ, Gou SH. A new three-dimensional cobalt(II) coordination polymer based on biphenyl-2,2 6,6 -tetracarboxylic acid and 1,2,4-triazole synthesis, crystal structure and magnetic properties. Inorg Chem Commun 2011 14(1) 261. ... 

Ozden S, Uniigiir ( elik S, Bozkurt A. Polymer electrolyte membranes based on / -toluenesulfonic acid doped poly(l-vinyl-1,2,4-triazole) synthesis, thermal and proton conductivity properties. J Polym Sci Part B Polym Phys 2010 48(10) 1016-21. 

Diamines of type (177) or (178) undergo the expected copolymerization with aromatic acid dichlorides e.g. terephthaloyl dichloride). The resulting thiadiazolyl polymers possess useful mechanical properties, but do not display greater stability to light than their analogues based on triazole or oxadiazole their thermal stability is inferior. 

Cul in 1 1 methanol/water with triethylamine as base. The second set, uses 0.2 equiv. of CUSO4 and 0.3 equiv. of ascorbic acid in 1 1 methanol/water. In these reactions the triazole compounds were, therefore, purified by flash chromatography before characterization for the observation of quantitative changes in photophysical properties after triazole formation. 

The presence of lone pair electrons on the 1,2,3-triazole nitrogen atoms and the acidic C-H can promote intra- and interpolymer chain interactions and enhance gel formation in triazole-based polymers. In Chap. 5, Chow, Lo and Chen survey the chemistry and properties of Triazole-Based Polymer Gels . 

---