The oxidation of ferrous ions by dissolved oxygen in aqueous solutions in the presence of such chelating agents as EDTA, DTPA, EDTAOH, EDTP, CyDTA and NTA was studied spectrophotometrically. The rate equation for the oxidation reaction is: d[Fe^III]/dt=4k_p[Fe^IIHZ][O_2]+4k_n[Fe^IIZ][O_2] where kp is the rate constant for the (1) reaction; kn, the rate constant for the (2) reaction; FeIIHZ, protonated chelate, and FeIIZ, the normal chelate. &Fe^IIHZ+O_2\xrightarrowk_pFe^IIIZ+HO_2 \labeleq1 &Fe^IIZ+O_2\xrightarrowk_nFe^IIIZ+O_2^-\labeleq2 The linear relationship between log k and log Rf shown by Eq. (3), was obtained from all the experimental results except for those on the EDTPA and CyDTA systems: logk=0.92+0.13logR_f\labeleq3 In Eq. (3), k is 4kp and Rf is KFeIIIL⁄KFeIIHL, for the protonated chelate, while k is 4kn and Rf is KFeIIIL⁄KFeIIL for the normal chelate. In the cases of the DTPA and CyDTA systems, a deviation from the straight line was observed. This can be explained by steric hindrance of the oxygen attack by these chelates.

The relative standard potentials of alkali metals, silver, and thallium metal/ion couples in N,N′-dimethylforrnamide(DMF), dimethyl sulfoxide(DMSO), and propylene carbonate (PC) were measured against an aqueous saturated calomel electrode(SGE). These standard potentials of lithium, sodium, potassium, rubidium, caesium, thallium, and silver are −3.237, −2.898, −3.116, −3.079, −3.079, −0.643, and +0.372 V vs. SGE respectively in DMSO, and −3.163, −2.830, −3.067, −3.040, −3.048, −0.559, and +0.538 V vs. SGE respectively in DMF, and −2.9064, −2.691, −3.002, −2.980, −2.986, −0.402, and +0.813 V vs. SGE respectively in PC. The thallium electrode was found to be stable enough to be used as a reference electrode in these solvents. For the purpose of examining the Debye-Hückel equation for estimating the activity coefficient, the formal potentials of the thallium electrode were measured at various ionic strengths. The Debye-Hückel equation was confirmed to be applicable in these solvents, provided a proper value was chosen for the ionic radius parameter, a, for each solvent–3.6 for DMSO, 5.0 for DMF and 0.0 for PC.

Conductance of univalent ions in DMSO (dimethyl sulfoxide), DMF (dimethylformamide) and PC (propylene carbonate) was determined by use of tetrabutylammonium-tetrabutylborate as standard electrolyte of equal cationic and anionic conductance. Empirical formulation of Stokes’ radius was attempted on the assumption of a structure-cavity affecting the ionic transport in a medium of aprotic and polar solvent as well as water. By application of classical fluid dynamics Stokes’ radius rs is given in terms of −(2⁄3)rc+(1⁄σs) (rc–ro)2, where rc is crystal ionic radius, ro and σs are parameters characteristic of the cavity and molecular sizes, respectively, with respect the solvent.

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The formation constants (Kf) for the 1 : 1 complexes of dibenzo-18-crown-6 (DBG) with alkali metal ions in DMSO (dimethyl sulfoxide), DMF (N,N-dimethyl formamide), and PC (propylene carbonate) have been determined conductometrically. The formation constant sequences of the alkali metal ions with DBG in DMSO, DMF, and PC are K+>Rb+>Cs+≅Na+>>Li+, K+>Rb+>Cs+>Na+>Li+, and K+>>Na+>Rb+>Cs+>Li+ respectively. The Kf value series about the same alkali metal ion among these nonaqueous solvents are given in the order of DMSO<DMF<PC. These results show that the selectivity of DBC toward the alkali metal ions is dependent on the ionic diameter and the ring-hole size of DBC, and that the donor number of the organic solvent as a component factor is important in determining the process of the formation of the DBC complexes constant.