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The aquation of the cis-bis(iminodiacetato)chronlate(III) ion and the ti.cLns(Sac)-bis(meth3.liminodiacetato)chr~~nate(IlI) ion in acidic aqueous medium has been studied spectrophotometrically. The products of the aquation are the iminodiacetatotriaquochromium(II1) cation and the methyliminodiacetatotriaquochromium( 111) cation, respectively. In the reaction involving the cis-bis(imiiiodiacetato)chromate(III) ion, two distinct aquation steps were observed. The first observable step showed the rate lawThe second step gave the rate lawl'alues of k ' , k". and k"' a t 25.0" and ionic strength 0.9 are 7.08 X 10-3 JI-1 sec-1, 1.71 X 10-' sec-1, and 1.28 X M-' sec-1, respectively. The activation parameters for k', k", and k'" are AH+' = 15.3 f 0.4 kcal mol-', ASF = -17.0 f 1.5 cal deg-1 mol-'; AH& = 17.0 i : 0.6 kcal mol-', AS* = -18.7 ik 2.1 cal deg-1 mol-'; and AH* = 24.3 i : 0.4 kcal mol-', AS* = 5.1 i 1.4 cal deg-' mol-', respectively. In the aquation of the tuans(fac)-bis(metliyliminodiacetato)chromate(III) ion, an aquation step was observed with the rate law = (k'[H10+] + k"[H30]2)[complex] d [complex] dt ~ I-alues of k' and k" at 25.0" and ionic strength 0.9 are 1.88 X 10-4 36-1 sec-1 and 5.74 X J k -2 sec-l, respectively. The activation parameters for k' and k" are AH* = 17.0 i 0.3 kcal mol-1, AS* = -18.6 i 1.1 cal deg-l mol-'; and AH+' = 15.6 It 0.2 kcal mol-', AS'? = -21.2 i . 0.7 cal deg-l mol-', respectively. Reaction mechanisms for both systems, which are in agreement with the experimental data, are proposed.

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In solutions containing both oxygen and one of the metal ions Zn+1 2 3, Sr+2, TI+, Y+3, Cd+2, a new polarographic reduction wave was observed at potentials less cathodic than that required to reduce the most easily reducible species (either the metal ion or the oxygen) in the sample. The variation of the height of this new wave was investigated as a function of the concentration of oxygen and the various metal ions. The results of this study made possible a determination of the stoichiometry of the process responsible for the new wave.Controlled potential coulometry and controlled potential electrolysis were used to obtain information about the reduction process. The reduction products, prepared by electrochemical methods, were found to be the superoxides of zinc, strontium, and thallium; and the peroxides of cadmium and yttrium.The effect of alkali and alkaline earth metal ions on the polarographic reduction of oxygen in dimethylsulfoxide (DMSO) solutions was reported (7). The reduction waves were markedly dependent upon the cation composition of the test solution. Peover (2) has reported similar type findings for the polarographic reduction of several quiñones in dimethylformamide. Our earlier work had indicated that this shifting of the waves was quite complex and suggested that the metal ion was possibly participating in some type of catalytic reduction of the oxygen. Preliminary investigations with added zinc salts showed a somewhat similar shifting of the waves along with changes in the height of the shifted wave as a function of the zinc ion concentration. The purpose of this investigation was to examine the effect of added metal ions in more detail and, if possible, electrochemically produce and identify the reduction products. EXPERIMENTAL Materials. The DMSO was obtained from the Matheson Company. This and the other chemicals were used as described previously (7). The nitrates of zinc, cadmium, strontium, thallium, and yttrium were of reagent grade and used without further purification.Stock solutions of the metal salts were prepared in DMSO. The zinc, cadmium, strontium, and yttrium solutions were standardized by complexometric titrations with ethylenediaminetetraacetic acid disodium salt. The thallous solution was standardized by amperometric titration with potassium iodide.Apparatus. A three-electrode polarograph of the ORNL type described by Kelley, Jones, and Fisher (3) was used to record all polarograms. The use of three-electrode polarography resulted in improved polarograms when compared to conventional two-electrode polarograms. The slope of the E vs. logOdi)/i plots for the first reduction wave of oxygen was found to be 61 mV.

The slow decomposition of manganese(III) ethylenediaminetetraacetate complex was studied by spectrophotometric methods. The observed kinetics were explained by assuming three parallel reactions all of which were first order in the complex concentration when above 2 mmoles/l. The rate law was found to be: decomposition rate), with rate constants h = 0.60 sec."1 M~\ h2 = 1.70 X 10-6 sec.-1, h2 = 2.62 X 10_8sec. ~l M~l, Kz -0.51 X 10-3 M. The products of all the steps were found to be carbon dioxide, formaldehyde, and manganese(II) complex. The previously reported inhibition due to manganese(II) was shown to be due to its effect in complexing free EDTA. The difference in the rates due to terms one and three of the rate law was explained by the protonation of the free EDTA. It was necessary to invoke a steady-state mechanism to explain the variation of the rate with the concentration of the manganese(III) complex.

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