Structure of azo coupling products of 5-nitro-2,1-benzisothiazole-3-diazonium hydrogensulphate with aromatic amines

Synthesis and characterization of triazenes derived from sulfonamides

“…In addition, triazene compounds were also characterised by their UV absorption. Maximum absorption bands of triazenes were detected at 352-389 nm (20,(37)(38)(39)(40). The APCI-MS spectra of 1-3 and 1a-3a showed molecular ion [M + +1] which confirmed its molecular weight.…”

Stable Triazenes Derived from 2‐Alkylaminonaphthalenes and 5‐Nitrobenzo[c]‐1,2‐thiazole‐3‐diazonium Hydrogensulfate

“…The stability of triazenes 1 in acid media has been ascribed to a different site of protonation of these substances1–3 in comparison to common 1,3‐diphenyltriazenes. Protonation at the heterocyclic nitrogen atom (Scheme ) has been proposed.…”

“…In our previous papers we described the formation of extraordinarily stable triazenes by the reaction of 5‐nitrobenzo[ c ]‐1,2‐thiazole‐3‐diazonium hydrogensulfate with primary and secondary anilines and their 3‐chloro and 3‐methyl derivatives 1–3. We found that the azo coupling reaction of the said anilines with this diazonium salt gives a mixture of triazenes 1 in addition to azo compounds 2 (i.e.…”

“…Triazenes 1 are extraordinarily stable in acid media. Half lives of their decomposition to the diazonium salt and amine in 0.5 mol L –1 H 2 SO 4 in aqueous acetic acid (1:1 v/v) are in the order of magnitude of hours 1,3. 1,3‐Diaryltriazenes in the benzene series decomposed at a measurable rate in aqueous ethanol (20 % v/v) in buffers at room temperature already at pH <7.…”

“…The decomposition of triazenes 1 obtained by azo coupling with N ‐alkylanilines gives the original 5‐nitrobenzo[ c ]‐1,2‐thiazole‐3‐diazonium, whereas the decomposition of triazenes derived from primary anilines produces substituted benzenediazonium salts and 3‐amino‐5‐nitrobenzo[ c ]‐1,2‐thiazole 1,3. The reason for the extraordinary stability of triazenes 1 probably lies in the fact that they are protonated at a different site in comparison to the protonation of common 1,3‐diaryltriazenes: whereas 1,3‐diaryltriazenes are protonated at the nitrogen atom adjacent to the azo group,4–6 triazenes 1 are presumably protonated mostly at the heterocyclic nitrogen atom,1–3 which leads to the formation of a structure stabilized by a classic benzene ring (Scheme ). However, this presumption cannot be confirmed experimentally.…”