Reactions of N-heteroaromatic bases with nitrous acid. Part I. Diazotisation and nitrosation of α- and γ-amino-derivatives in dilute acid solutions

Reductive electrografting of in situ produced diazopyridinium cations: Tailoring the interface between carbon electrodes and electroactive bacterial films

“…2-amino-, 3-amino-and 4-aminopyridine have been shown to diazotize in diluted aqueous mineral acids. [18,[32][33][34] After diazotization, the generated diazonium salt leads to the corresponding hydroxypridine as the main decomposition product. [18] The diazotization of the three amino derivatives was studied by UV-Visible absorption spectroscopy under the experimental conditions used for electrografting, i.e.…”

“…This latter band corresponds to the absorption of 2-hydroxypyridinium molecules ( max = 278 nm, dotted line in Figure 1A). The broad band at 283 nm can be assigned to the mixed absorptions of the produced diazopyridinium cations [32,34] and of 2-hydroxypyridinium molecules which are formed from diazopyridinium hydrolysis.…”

“…Similarly, after addition of NaNO 2 , the intensity of the absorption band of 4-aminopyridine at 262 nm is also observed to decrease monotonically with the growth of a new band at 233 nm after 5h, corresponding to the absorption of 4-hydroxypyridinium ( Figure 1C). We can infer that the absorption band of the produced diazopyridinium cations, at 285 nm, [32] is fully overlapped by the absorption band of residual (protonated) 4-aminopyridine by taking into account that the molar extinction coefficient for the diazopyridinium is much lower ( = 2720 L.mol -1 .cm -1 ) than that of the 4-amino-derivative ( = 18850 L.mol -1 .cm -1 ). [36] The UV-Vis spectroscopic study cannot allow the identification of all the decomposition products of the diazopyridinium cations but the results indicate that diazopyridinium cations are formed with the three aminopyridine derivatives upon in situ diazotization in aqueous acidic medium, and that they are eventually transformed into their hydrolyzed adducts.…”

A study of some pyridylazo dyestuffs as chromogenic reagents and the elucidation of the nature of their metal complex spectra

“…3 shows the bulky diethylamino group on the right , lying out of the plane of the ring system . Chelation leads to the transfer of a strongly electropositive charge to the chromophore, so that in the extreme mesomeric structures II and III an effect approaching protonation of the diethylamino nitrogen is observed.…”

Μελετη Αντιδρασεων Ετεροκυκλικων Αρωματικων Νιτρωδαμινων

“…Προκειμένου λοιπόν να περιορισθεί ο αριθμός των νιτρωδωτικών μέσων, η αντίδραση μελετάται σε διαλύματα HCIO4, όπου δε σχηματίζεται HOCIO^ σε μοριακή μορς>ή και δε συμμετέχει στην αντίδραση 3 , σε αντίθεση με ό,τι συμβαίνει σε διαλύματα άλλων ισχυρών οξέων. Έτσι σε διαλύματα HCl χα ιόντα Cl~ καταλύουν τη νιτρώδωση γιατί, εκτός από τα άλλα νιτρωδωτικά μέσα που σχηματίζονται στο υπερχλωρικό οξύ, σχηματίζεται και HOC!…”