Azidinium‐Salze. 25. Mitteilung . Symmetrische Azopyridinon‐Farbsalze: Synthese, spektrophotometrische und acidobasische Eigenschaften, Metallkomplex‐Bildung und kinetische Untersuchung der Azo‐Kupplung

Symmetrical Azopyridinone Dyes: Synthesis, Spectrophotometrical and Acidobasic Properties, Metal‐Complex Formation and Kinetical Investigation of the Azo‐Dye Formation The 13 substituted symmetrical azopyridinone dyes 2a–n were synthesized and their VIS spectra measured. The p K * a values of some dyes and of pyridinone coupling components were determined in MeOH/H 2 O 64:36. The metal‐complex formation of the dyes with Cd 2+ , Zn 2+ , Co 2+ , Ni 2+ , and Cu 2+ was investigated, and complex‐formation constants of the 1:1 complexes were determined in H 2 O for 2k ( Table 2 ) and in dimethylformamide/H 2 O 1:1 for some other azopyridinone dyes ( Table 3 ). The mechanism of the azo‐dye formation was investigated and found to be much more complicated than expected. A mechanism of the coupling reaction was developed ( see Scheme 4 ) and fitted by least‐squares calculations.