Metal Cation Transport Studies Comparing Dibenzo-18-crown-6 (DB18C6) with N, N, N‘, N‘;-Tetrakis (n-propyl)-2, 3- naphthalenedioxydiacetamide (NPr)

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The previously synthesized 3,6-dioxa-4,5-disubstitutedoctanedicarboxamides including NPr bind cations in methanol in the order: Ca2+ > Sr2+ > Ba2+ > Mg2+ ≫ Na+, K+. These compounds also extract Group II cations better than Group I cations from water to dichloromethane. In contrast, these diacetamides were found by W. Simon et al., to sense Na+ ≫ Ca2+ when they were incorporated into ion-selective electrodes using a low dielectric constant solvent. It was of interest to determine the order of Group I and Group II cation transport rates of these compounds using a three-phase system with a liquid organic phase of low dielectric constant. We now report that NPr transports thiocyanates in such a system using dichloromethane in the order K+ (7.2) > Ca2+ (6.6) > Ba2+ (5.8) > Na+ (1). The transport rate for KSCN with DB18C6 is 20.5 times faster than with NPr.

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