The synthesis and complexation study of some coumestan and coumestan analog derivatives of crown ethers using conductometry

Abstract

8,9-Dihydroxycoumestans, the 8,9-dihydroxy-6 H-benzofuro[3,2- c][1]-benzopyran-6-one, derivatives were prepared from corresponding 4-hydroxy-2 H-[1]benzopyran-2-one and catechol in oxidizing mixture KIO 3/CH 3COONa/H 2O/acetone while for the oxidative coupling of cyclohexane-1,3-dione and catechol, K 3[Fe(CN) 6]/CH 3COONa/H 2O/acetone was used. The derivatives of 8,9-dihydroxycoumestan and 8,9-dihydroxy-1,4-dimethy-6 H-benzofuro[3,2- c][1]-benzopyran-6-one and two coumestan analog compounds reacted with the bis-dihalides of polyglycols in CH 3CN/Me 2CO 3 to furnish coumestano-12-Crown-4, 15-Crown-5 and 18-Crown-6. The crude products were purified using silica gel chromatography with chloroform. The obtained novel pure crown ethers were identified with IR, 1H NMR, 13C NMR, mass spectroscopy and elemental analysis. Formation constants for complexation between NaClO 4 and the various coumestano-crown ethers in the solvent acetonitrile at 25 °C were determined from conductance measurements. The method also permits accurate evaluation of association equilibrium constants between the complex species (M–Coumestano-crown ether) + and the anion. The magnitudes of these ion association constants are related to the nature of the solvation of the cation and of the complexed cation. Structures of crown compound–cation complexes in acetonitrile are estimated from the conductance parameters ( κ, Λ and α) as well as complex formation constant { K e = ( Λ MA m − Λ)/(( Λ − Λ MLA m )[L])}. The complexation study indicates 1:1 complex formation between the metal ion and the crown ether. All the experimental studies have been conducted using the ratio 1:1 of the metal ion and the crown ether.