Kinetics of the Reaction of Chromium(VI) with Tris(1,10-phenanthroline)iron(II) Ions in Acidic Solutions. Anion and Medium Effects:  Perchlorate versus Triflate

Abstract

Reinvestigation of the reaction between title reagents in aqueous acidic triflate and perchlorate media revealed an unusual difference: the reaction is strictly first-order with respect to the concentration of Fe(phen)3(2+) (phen = 1,10-phenanthroline) in the triflate medium but shows an additional, but we believe artifactual, higher-order term in the perchlorate medium. We postulate that the apparent orders with respect to [Fe(phen)3(2+)] in (H/Li)ClO4 do not indicate the actual chemical mechanism but, in whole or in part, the orders, particularly the higher-order component, reflect an interaction specific to Fe(phen)3(2+) or Fe(phen)3(3+) and ClO4(-) in solution. Data in (H/Li)O3SCF3 solutions indicate that, in the absence of added Fe(phen)3(3+), the first of the three sequential electron-transfer steps is rate controlling. Reactions started in the presence of the product Fe(phen)3(3+) occur somewhat more slowly, suggesting the first electron transfer is reversible. This finding allows the relative rate constants for Cr(V) oxidation and reduction to be evaluated, with limited precision, by two methods of analysis. The dependences on [Cr(VI)] can be resolved into contributions from the species HCrO4(-) and Cr2O7(2-), each of which in turn depends on [H+]. The reaction mechanism is discussed in light of the data obtained in the triflate medium. Further, the rate constants for certain steps can be considered in light of E0 for the Cr(VI)/(V) couple.

Measurements and Simulations of the Acidity Dependence of the Kinetics of the Iron-Catalyzed Belousov–Zhabotinsky Reaction: Proton-Catalysis in the Electron Transfer Reaction Involving the [Fe(phen)3]3+ Species

“…Hence, the focus has to be on the [Fe­(phen) 3 ] 3+ species and its solvation and aggregation. It has been pointed out that, in order for an outer sphere electron transfer to occur, the electron donor must first come in close contact with the electron acceptor and that bulky ligands and coordinated anions may block the approach of the electron donor. , Investigations into the effects of anions on the rate of electron transfer between substitution-inert transition metal complexes showed both increases − and decreases , in the rates of electron transfer reactions as a result of anion addition. These different anion effects can be rationalized by noting that all the increased reaction rates are between two transition metal cations and the decreased reaction rates are between two neutral transition metal complexes or a neutral transition metal complex and a cation.…”

Pulsed Electrochemical Deposited Nano-Iron for Water Treatment

“…The former is highly toxic and carcinogenic to human and animals, while the latter is generally non-toxic [4] [5] [6]. Conse-gents including hydrogen sulfide [7], divalent iron [8] [9], Fe(II)-bearing minerals [5] [10], thios and thiols [11] [12], etc. Recently, zero-valent iron (Fe 0 ) has been tested for the remediation of polluted waters, and it is established that halogenated hydrocarbons such as nitro- [13] [14], and chloro-compounds [15], toxic metals nitrate and arsenate [16] [17] [18] [19] [20] are effectively transformed by the Fe 0 to relatively more benign products.…”

Aqueous Cr(VI) reduction by electrodeposited zero-valent iron at neutral pH: Acceleration by organic matters

“…Consequently, the reduction of the Cr(VI) to the Cr(III) is of environmental interest. Much work has been focused on the cleanup of Cr(VI)-contaminated waters by various reducing reagents including hydrogen sulfide [7], divalent iron [8,9], Fe(II)-bearing minerals [5,10], thios and thiols [11,12], etc. Recently, zero-valent iron (Fe 0 ) [13][14][15][16] has been tested for the remediation of polluted waters, and it is established that halogenated hydrocarbons such as nitro- [14,15] and chloro-compounds [13,16], toxic metals [2,17], nitrate and arsenate [18][19][20] are effectively transformed by the Fe 0 to relatively more benign products.…”