<b>Kinetics and Mechanisms of Reactions of Chromium(IV) and Iron(II) Species in Acidic Solution</b>

Espenson, James H.; King, Edward L.

doi:10.1021/ja00904a002

Cited by 53 publications

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“…These facts seem to reflect that the interaction takes place between the hexacyanomanganate(II1) and the chromate ions. A similar interaction has been reported between Fe(II1) and Cr(VI), which form a cationic complex of formula FeCrOi (6). Of course, the conditions in which these two reactions take place are quite different, and the product of the Mn(CN)i--CrOz-interaction will surely have a different structure from that of the FeCrOi ion, probably a CN--bridged Mn-Cr binuclear compound.…”

Section: The M~( C N )~--C~o $ -Reaction Kinetics Of Reactionsupporting

confidence: 63%

Formation of hexacyanomanganate(II) in cyanide medium and kinetics and mechanism of its oxidation by chromate

López-Cueto¹,

Duarte²

1989

Can. J. Chem.

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GUILLERMO L~PEZ-CUETO and MIGUEL DUARTE. Can. J. Chem. 67,279 (1989). The rate of formation of hexacyanomanganate(I1) is first-order in Mn(I1) and depends on both the cyanide and hydroxide concentrations. The experimental results agree with a reaction mechanism which involves manganese(I1) cyano-and hydroxocomplexes. Chromate slowly oxidizes hexacyanomanganate(I1). The kinetics of this reaction is first-order on hexacyanomanganate(II), and the experimental rate constant depends on the chromate concentration according to the equation kc,, = 3kK[Cr(VI)]/(l + K[Cr(VI)]). The effect of both the CN-and the OH-ions is slighter. A tentative mechanism is proposed which involves a pre-equilibrium with the formation of a hexacyanomanganate(I1)-chromate complex, followed by a monomolecular decomposition. By comparing this reaction mechanism with that of other one-electron chromate reductions, it appears that hexacyanomanganate(I1) behaves like octacyanomolybdate(IV) rather than like hexacyanoferrate(I1) and other substitution-inert reductants. Both the equilibrium constants for the complex formation and the rate constant for its decomposition are evaluated, and voltammetric evidence of the formation of hexacyanomanganate(II1)-chromate complexes is also presented.Key words: hexacyanomanganate(II), formation rate, oxidation with chromate, kinetics, mechanism.

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Section: The M~( C N )~--C~o $ -Reaction Kinetics Of Reactionsupporting

confidence: 63%

Formation of hexacyanomanganate(II) in cyanide medium and kinetics and mechanism of its oxidation by chromate

López-Cueto¹,

Duarte²

1989

Can. J. Chem.

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“…The k3 term in the rate law is also subject to an ambiguity in that an alternate mechanism could also be written V2+ + V z + e VzOH3+ + H + (18) (19) H2Cr04 f V20H3+ + products (20) where k3 would be identified as KdK,k,. Support for this mechanism comes from the fact that a vanadium- a comparison can be made with the dimerization cons t a n P for vanadium(II1) which is given by the equation [(VOH)24f][H+]2/[V3+]2 = 1.26 X It should be expected that Kd would be less than 1.26 X because of the lower charge on vanadium(I1) and because of stabilization of the dimer due to the extra hydrogen ion.…”

Section: Discussionmentioning

confidence: 99%

Kinetics and mechanism of the reaction between vanadium(II) and chromium(VI)

Bridges¹,

Mukherjee²,

Gordon³

1972

Inorg. Chem.

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would activation parameters for the other reactions with an apparent substitution-controlled mechanism.It is possible that the rapid manganese(II1) oxidation of thiocyanate is also substitution controlled, as found in the analogous reaction with ~o b a l t ( I I I ) .~ If the trends observed in complexation reactions of Fe3taq 14,15,24 and substitution-controlled redox reactions of C O~+~~~,~~ are maintained in the rnanganese(II1) series (24) D. Seewald and E. Sutin, Inorg. Chem., 2, 643 (1963).then the rate of the Mn3+,,-SCN-reaction might be expected to be somewhat higher than those for complexation by Br-and C1-, the rate constants of which are presumably a t least lo6 M-l sec-I a t 25°.The rate of oxidation of V(I1) with Cr(V1) to form V(II1) in perchloric acid solution was studied a t lo", primarily under second-order conditions and with V(I1) in excess. The observed rate law for the reaction in 1.00 M NaC104 is -d[Cr(VI)]/ dt = (k1 + kz[H+] + k3[V(II)])[HCr04-] [V(II)] where kl = (1.02 i 0.01) X 1oj iM-' sec-l, k2 = (7.9 i 0.26) x 104 M-2 sec-', and ka = (1.27 + 0.09) X lo7 M -2 sec-l. The first step in the reaction results in the direct formation of V(II1)by means of a one-electron redox process. Evidence is presented for the absence of the direct formation of vanadium(1S') under the conditions of these experiments. A mechanism is proposed based on the observed rate law, IntroductionThe net reaction between chromium(V1) and vanadium(I1) in acid solution when V(I1) is in excess can be represented by the equation

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“…The nature of these species depends upon the pH and the concentration of potassium dichromate [36]. These species are designated as Cr 2 Taking into account the nature of the chromium(III) species, interestingly, it is to be noted that chro-…”

Section: Reaction In the Absence Of Hclomentioning

confidence: 99%

“…The reduction of chromium(VI) by various metal ions [iron(II), vanadium(IV), vanadium(III), neptunium(V), iridium(III) and molybdenum(IV)] has been the subject of investigations by a large number of researchers [1][2][3][4][5][6][7][8][9][10]. In the redox reactions of chromium with organic reductants, manganese(II) also plays an important role [11][12][13][14][15].…”

Section: Introductionmentioning

confidence: 99%

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

Babu

Khan

Kabir-ud-Din

2004

Transition Met Chem

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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.

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Kinetics and Mechanisms of Reactions of Chromium(IV) and Iron(II) Species in Acidic Solution

Cited by 53 publications

References 0 publications

Formation of hexacyanomanganate(II) in cyanide medium and kinetics and mechanism of its oxidation by chromate

Formation of hexacyanomanganate(II) in cyanide medium and kinetics and mechanism of its oxidation by chromate

Kinetics and mechanism of the reaction between vanadium(II) and chromium(VI)

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

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