Electron transfer reaction in the chromium(VI)-manganese(II) system in the presence of ethylenediaminetetraacetic acid (EDTA)

Abstract

Upon addition of Cr VI to a solution of ethylenediaminetetraacetic acid (EDTA) and Mn II , a transient species appears which has an absorption maximum at 500 nm. Kinetic studies of the outer-sphere oxidation of the Mn II -EDTA complex with the Cr VI -EDTA complex have been investigated by visible spectrophotometry at 25°C. The formation of a transient species has been characterized spectrophotometrically and the encounter complex formation constants have been determined (K OS ¼ 1:75 Â 10 2 and 1.66 Â 10 3 mol À2 dm 6 for [EDTA] and [Mn II ] variations, respectively). The effect of total [EDTA], [Mn II ], [Cr VI ] and [HClO 4] on the rate of the reaction was determined. On addition of HClO 4 , there is a decrease in the rate constants. The reaction product is the Cr III -EDTA complex with k max ¼ 400 and 550 nm. On the basis of the various observations and product characterization a most plausible outer-sphere mechanism has been envisaged.

Fe(III) photocatalytic reduction of Cr(VI) by low-molecular-weight organic acids with α-OH

“…Transition metal ions, such as Mn(II), can greatly catalyze the reduction of Cr(VI) by organic acids [5,7,8]. The enhancement of reduction of Cr(VI) by citric acid in the presence of Mn(II) is attributed to the ring structure formation between Mn(II) and citric acid, which increases the activity of ␣-OH and thus results in the formation of a Cr(VI)-citric acid-Mn(II) complex [5,7].…”

Kinetic studies on the reaction of N-(2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetate chromium(III) with hydrogen peroxide

“…It is documented that aminopolycarboxylic acids are oxidized by Cr(VI) [18][19][20], but under the conditions employed in this study, the reaction between H 3 L and Cr(VI) is negligible.…”

Chromium Speciation by HPLC-DAD/ICP-MS: Simultaneous Hyphenation of Analytical Techniques for Studies of Biomolecules

“…NH 4 NO 3 was used to prepare the mobile phase; the aqueous solution was adjusted to pH 7 with NH 4 OH (28% NH 3 in water, ≥99.99% purity, Sigma Aldrich, USA), Table 1 . The monitored wavelengths for [Cr(III)-EDTA] − and Cr(VI) were 550 nm [ 15 , 16 , 17 , 18 , 19 ] and 371 nm [ 15 , 20 ], respectively. The calibration curve for the total determination of Cr was prepared in aqueous medium from the sequential dilution of the standard solution of Cr(VI) at concentrations 1; 5; 10; 50; 100 e 250 µg L −1 ( Table 2 ).…”