Complexing Abilities of N-[ω-(Long-chain alkyl)oligo(oxyethylene)]Monoaza Crown Ethers with Metal Cations in Water and in Methanol

Abstract

N-[co-(Long-chain alkyl)oligo(oxyethylene)] monoaza crown ethers (Cx⋅E(m+1)-N(15, 18), x: 8 and 12, m: 0-2) were prepared from alkyl oligo(oxyethylene) chlorides and N-unsubstituted monoaza crown ethers (Scheme 1). From the measurements of cloud points, it was found that the introduction of oxyethylene units between monoaza crown ring and alkyl moiety increased the hydrophilicities compared with those in the N-alkyl monoaza crown ethers (Cs-N(15, 18), x: 8 and 12) (Table 2). Most of the changes in the cloud points (ΔTcp) of Cx⋅E(m+1)-N(15, 18) and Cs-N(15, 18) between the absence and the presence of metal chlorides showed "positive" values (Fig.1, 2 and Table 3), and it was found that z1T0p of these compounds as well as alkyl crown ethers depended on such factors as the size of the crown ring, the number of oxygen atoms in the side chain and the kind of metal cations. On the other hand, complexing stability constants log 1(11) for these monoaza crown compounds with Na + and K+ in methanol and in water/methanol (10: 90 v/v) mixture at 25°C were measured by Frensdorff's method. It was observed that the stability constants for CsE(m+1)-N(15, 18) having oxygen atoms in the side chain were much higher than those for Cs-N(15, 18) with both cations (Table 4). These results show that the oxygen atoms in the side chain make a remarkable contribution to the complexation with metal cations. Besides, a good correlation between 4 TO and log K, ' was observed (Fig.3) and it was indicated that 4Tcp was able to be an index of complexing abilities for these monoaza crown compounds with metal cations in water.