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

Abstract

The dibenzo[3n]crown-n were synthesised starting from bis[2-(o-hydroxyphenoxy)ethyl]ether obtained from bis[2-(o-formylphenoxy)ethyl]ether via Baeyer-Villiger oxidation in H2O2/CH3COOH in a good yield. The cyclic condensation ofbis[2-(o-hydroxyphenoxy)ethyl]etherwith tri- and tetraethylene glycol bisdichlorides andthe bisditosylate of pentaethylene glycol in DMF/Me2CO3 afforded the large cyclic ethers of dibenzo[21]crown-7, dibenzo[24]crown-8 and dibenzo[27]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, Ka, in acetonitrile were estimated. Dibenzo[21]crown-7 was the best both for K+ and Rb+ binding but showed too small an effect on Cs+. Dibenzo[24]crown-8 exhibited the binding power in the order of Rb+ > K+ > Na+ > Cs+. However, dibenzo[27]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.