Physikalisch‐chemische Eigenschaften und Elektronenstruktur der Azo‐Verbindungen. Teil XI: Bemerkung zur Struktur des Azonium‐Kations des p,p′‐Bis‐dimethylamino‐azobenzols

The absorption spectrum of p,p′‐bis‐dimethylamino‐azobenzene has been measured in solvents of different acidities. The bathochromic shift of the long‐wave transition associated with protonation of the azo link falls in line with the corresponding shifts, observed for a series of p′‐substituted p‐dimethylamino‐azobenzenes. The same is true – inside wider limits of error – for the pK′ values of the equilibrium: base + H⊕ ⇆ azonium‐cation of these compounds. These results support the view that protonation of p,p′‐bis‐dimethylamino‐azobenzene does not differ in principle from that of the unsymmetric p′‐substituted p‐dimethylaminoazobenzenes.