Novel Methods of Synthesis of Dibenzo[3n]crown-n and Their Cation Binding Studied by Fluorescence Spectroscopy. Part V

The dibenzo3n]crown-n were synthesised starting from bis2-(o-hydroxyphenoxy)ethyl]ether obtained from bis2-(o-formylphenoxy)ethyl]ether via Baeyer-Villiger oxidation in H₂O₂/CH₃COOH in a good yield. The cyclic condensation ofbis2-(o-hydroxyphenoxy)ethyl]etherwith tri- and tetraethylene glycol bisdichlorides andthe bisditosylate of pentaethylene glycol in DMF/Me₂CO₃ afforded the large cyclic ethers of dibenzo21]crown-7, dibenzo24]crown-8 and dibenzo27]crown-9. The structures were analysed with IR, ¹H NMR, ¹³C NMR and low-resolution mass spectroscopy methods. The Na⁺, K⁺, Rb⁺ and Cs⁺ cations' recognition of the molecules were conducted withsteady-state fluorescence spectroscopy. The 1:1 association constants, K_a, in acetonitrile were estimated. Dibenzo21]crown-7 was the best both for K⁺ and Rb⁺ binding but showed too small an effect on Cs⁺. Dibenzo24]crown-8 exhibited the binding power in the order of Rb⁺ > K⁺ > Na⁺ > Cs⁺. However, dibenzo27]crown-9 displayed marked binding with only K⁺ but not with Rb⁺ or with Cs⁺ cations probably due to the heavy atom effect of fluorescence quenching.