Tetraazanaphthalenes compounds

Covalent hydration has been demonstrated in the following families of compounds 1,6-naphthyridines, quinazolines, quinazoline. 3-oxides, four families of l,3,x-triazanapththalenes, both l,4,x-triazanaphthalenes, pteridines and some other tetraazanaphthalenes, and 8-azapurines these compounds are discussed in that order. In general, for any particular compound (e.g. 6-hydroxypteridine) the highest ratio of the hydrated to the anhydrous species follows the order cation > neutral species > anion. In some cases, however, anion formation is possible only when the species are hydrated, e.g. pteridine cf. 21 and N-methyl-hydroxypteridines (Section III, E, 1, d). Table V in ref. 10 should be consulted for the extent of hydration in the substances discussed here. 

Increasing numbers of nitrogen atoms increase not only the kinetic susceptibility toward attack but also the thermodynamic stability of the adducts. Reversible covalent hydration of C = N bonds has been observed in a number of heterocyclic compounds (76AHC(20)117). Pyrimidines with electron-withdrawing groups and most quinazolines show this phenomenon of covalent hydration . Thus, in aqueous solution the cation of 5-nitropyrimidine exists as (164) and quinazoline cation largely as (165). These cations possess amidinium cation resonance. The neutral pteridine molecule is covalently hydrated in aqueous solution. Solvent isotope effects on the equilibria of mono- (166) and dihydration (167) of neutral pteridine as followed by NMR are near unity (83JOC2280). The cation of 1,4,5,8-tetraazanaphthalene exists as a bis-covalent hydrate (168). 

Among condensed heterocyclic compounds formation of radical ions have been proved for the following compounds radical anions of acridine [117], phthalazine [126], phenazine [70, 126], 1,4,5,8-tetraazanaphthalene [131], 9,10-diazaphenanthrene [129], 2,2 -biiso-benzimidazolidine [129], and phenothiazone [108] radical cations for... 

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