Crown-containing naphtho- and anthraquinones: synthesis and complexation with alkali and alkaline-earth metal cations

Author： Martyanov T. Ushakov E. Savelyev V. Klimenko L.

ISSN： 1066-5285

Source： Russian Chemical Bulletin, Vol.61, Iss.12, 2012-12, pp. : 2282-2294

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Abstract

Novel naphtho- and anthraquinones conjugated with benzo- and dibenzo-18-crown-6 ethers were obtained. Their complexation reactions with Groups Ia and IIa metal perchlorates in acetonitrile were studied by spectrophotometric titration. In most cases, the complexation involves the crown ether moiety; the stability constant of the resulting complex decreases in the following order: Ba²⁺ > Sr²⁺ > Ca²⁺ > Na⁺. For crown-containing anthraquinone imines characterized by prototropic “imine-enamine” tautomerism, the complexation shifts the equilibrium toward the imine species, which allow these compounds to be classified among a rarely occurring type of tautomeric chromoionophores. Unlike other cations, the magnesium ions preferably interact with the heteroatoms of the anthraquinone moiety (the imine N atom, the OH group, and the carbonyl O atom of the benzamido group); the logK value reaches 4.4. The chelation to the Mg²⁺ cations and the effect of the complexation on the tautomeric equilibrium was confirmed by quantum chemical calculations.