4,4′‐Bis(dimethylamino)benzophenon (Michlers Keton) — ein universeller Indikator zur Bestimmung der Acidität, Dipolarität und Polarisierbarkeit von Reaktionsmedien

Abstract

4,4′‐Bis(dimethylamino)benzophenone (Michler's Ketone) — a Common Indicator of the Acidity and Dipolarity/Polarizability of Reaction Media The solvatochromisms of Michler's Ketone ( 1 ) and the iron (II) complex Fe(phen) 2 (CN) 2 ( 2 ) has been investigated in 73 solvents of different polarity. The solvent‐induced UV/Vis‐absorption shifts of 1 and 2 are mainly attributed to both the hydrogen‐bond donor acidity and dipolarity/polarizability of the solvent as verified by a Kamlet‐Taft correlation analysis and comparison with common solvent‐polarity scales such as Reichardt's E T ( 30 ) values and the acceptor scale of Gutmann. Michler's Ketone exhibits the largest positive solvatochromism known so far. The specific role of phenolic solvents has been discussed with regard to a charge‐transfer complexation between the positively polarized ring of 1 , caused by the hydrogen‐bond formation at the carbonyl oxygen, and the aromatic ring of the phenol.