14873-01-9Relevant academic research and scientific papers
Electron transfer. 50. Reduction of carboxylato-bound chromium(V) with hydrazine
Srinivasan, Vangalur S.,Gould, Edwin S.
, p. 3176 - 3179 (1981)
Solutions of the chromium(V) complex sodium bis(2-ethyl-2-hydroxybutyrato)oxochromate(V) (I) oxidize hydrazinium ion smoothly. Each mole of N2H5+ consumes 2 mol of Cr(V), yielding N2 and a Cr(III) product exhibiting ion-exchange behavior and an electronic spectrum consistent with a chelated monocarboxylato derivative of (H2O)4CrIII. Kinetic results, obtained at pH 3.3-4.6 in the presence of added carboxylato ligand, point to a pair of two-electron transactions. The first of these, an oxidation to N2H2, is rate determining, whereas the second, the conversion to N2, is rapid. Reactions, carried out in trimethylacetate buffers, are inverse first order in added 2-ethyl-2-hydroxybutyrate and are also inhibited by H+. The algebraic form of the rate law (eq 3 in text) is consistent with a two-path mechanism (eq 5-9), both components of which involve preliminary rapid and reversible loss of a carboxylato ion from the Cr(V) oxidant. The resulting monocarboxylato intermediate then may undergo reduction either directly through (outer-sphere) reaction with N2H5+ or, alternatively, via formation of a precursor complex, assembled with loss of H+. The appearance of only one Cr(III) reaction product suggests that the Cr(V) species attacking N2H2 in the final rapid step(s) has the same ligand environment as that attacking N2H5+ in the rate-determining steps.
REACTIONS OF CHROMIUM(II) WITH CHLORO- AND IODOACETONITRILE AND THEIR PENTAAMMINECOBALT(II) COMPLEXES.
Kupferschmidt,Jordan
, p. 991 - 995 (1984)
The products and kinetics of the reaction of chromium(II) with XCH//2CN, and (NH**3)//5CoNCCH//2X**3** plus , where X equals I or Cl, have been studied. For X equals I, the free nitrile yields 25% (H//2O)//5CrCH//2CN**2** plus while the cobalt(III) comple
Preparation, characterization, and aquation kinetics of pyridine N-oxide complexes of chromium(III)
Kotowski, Mirjana,Marcec, Radovan,Butkovic, Vjera,Bakac, Andreja,Orhanovic, Matko
, p. 2894 - 2899 (2007/10/03)
A series of (H2O)5Cr(X-pyO)3+ ions (pyO = pyridine N-oxide, X = H, 3-CH3, 4-CH3, 4-OCH3, 4-NO2) were prepared by the reduction of the corresponding pyridine N-oxide adducts of diperoxochromium(VI) species with acidic ferrous perchlorate. The (H2O)5Cr(X-pyO)3+ complexes undergo aquation to yield Cr(H2O)63+ and X-pyO according to the rate law kobs = ko + k -1[H+]-1. The values of the rate constants extrapolated to 298 K at 1.0 M ionic strength are: k0 = 2.80 × 10-6 s-1, k-1 = 1.86 × 10-8 M s-1 (X = 4-NO2); 7.80 × 10-8, 6.27 × 10-10 (H); 4.80 × 10-8, 3.20 × 10 -10 (3-CH3); 3.05 × 10-8, 1.60 × 10-10 (4-CH3); and 2.37 × 10-9, 4.76 × 10-11 (4-OCH3). The reaction of the 4-OCH 3 complex exhibits two additional terms in the rate law, k 1[H+] + k-2[H+]-2. The binding of 4-OCH3-pyO to chromium is suggested to take place through the methoxy group. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.
Electron transfer. 91. Reactions of carboxylato-bound chromium(V) with arenediols
Ghosh,Bose, Rathindra N.,Gould
, p. 1620 - 1625 (2008/10/08)
The chromium(V) chelate bis(2-ethyl-2-hydroxybutanoato)oxochromate(V) (I) oxidizes the arenediols hydroquinone and 2,3-dihydroxybenzoic acid in solutions buffered with the ligand acid, 2-ethyl-2-hydroxybutanoic acid, and its anion. The observed 1:1 stoichiometry of these reactions corresponds to the formation of the related quinone and Cr(III). The Cr(III) product from the reaction of excess hydroquinone is a bis chelate derived from the ligand anion, having, in addition, a ligand derived from the diol. With 2,3-dihydroxybenzoic acid, the diol appears to have coordinated to Cr(III) as a bidentate ligand. Both reactions are catalyzed by Cr(IV) and pass through semiquinone radicals, ArO2H., for which Cr(IV) and Cr(V) compete. Suggested reaction sequences for the two reductants feature bimolecular steps involving Cr(V) + Ar(OH)2, Cr(V) + ArO2H., and Cr(IV) + ArO2H. (reactions 3, 4, and 6 in the text) but differ in the reaction of Cr(IV) with Ar(OH)2, which is bimolecular with hydroquinone but exhibits kinetic saturation with 2,3-dihydroxybenzoic acid, indicating the formation of a strongly associated complex of the latter with Cr(IV). The suggested reaction sequences, in conjunction with rate constants for the individual steps derived from least-squares refinements of the data, reproduce the experimental kinetic curves. Dependencies of the component specific rates on the concentration of the ligand anion, [Lig-], indicate that partition of Cr(V) and Cr(IV) between ligation levels affects the reactions with hydroquinone but not those with dihydroxybenzoic acid. Acid catalysis of the Cr(IV)-Ar(OH)2 step (k5) for the latter diol points to partial protonation of the Cr(IV)-diol complex (pK = 3.5). Comparisons of calculated electron-transfer rates with those for known outer-sphere reactions indicate that at least three of the four steps involving each diol proceed through bridged activated complexes. In contrast to earlier systems utilizing the proposed mechanism, the prominence of autocatalysis in the oxidation of hydroquinone is limited by the poor selectivity (CrIV vs CrV) of the semiquinone radical rather than by the selectivity of the diol itself. Autocatalysis is not observed in the oxidation of 2,6-dihydroxynaphthalene.
Kinetics and mechanism of the reactions of alkylchromium complexes with aqueous sulfur dioxide
Simmons, Carol A.,Espenson, James H.,Bakac, Andreja
, p. 4093 - 4096 (2008/10/08)
The organopentaaquochromium(III) complexes, (H2O)5CrR2+ (R = alkyl, substituted alkyl, benzyl, and substituted benzyl), react with SO2 in aqueous perchloric acid solutions to yield (H2O)6Cr
σ-Bonded organochromiuin(III) complexes. 3. Decomposition in acid solution of chromium(III) complexes containing pyridylmethyl and polydentate amine ligands
Crouse, Karen,Goh, Lai-Yoong
, p. 478 - 484 (2008/10/08)
The decomposition of σ-bonded (pyridylmethyl)chromium complexes, 2- and 3-NC5H4CH2CrLn (L = dap (1,3-diaminopropane), dien (diethylenetriamine), trien (triethylenetetramine), and [15]aneN4 (tetraazacyclopentadecane)), was investigated in aqueous perchloric acid under aerobic conditions. Except for L = 15[ane]N4, Cr-C bond scission was preceded by complete aquation in the case of the 2-isomers and partial aquation for the 3-isomers. The aquation rates were compared with those of inorganic chromium complexes containing similar amine ligands. Kinetic data for the Cr-C bond cleavage were correlated with those for the analogous ethylenediamine (en) and aquo (H2O) systems. The activation parameters and product studies are in support of a homolytic pathway for the Cr-C bond cleavage.
Kinetics and mechanism of the reaction of CrO22+ with hydrazinium ions in aqueous acidic solutions
Bruhn, Suzanne L.,Bakac, Andreja,Espenson, James H.
, p. 535 - 538 (2008/10/08)
Hydrazinium ion is oxidized by CrO22+ in aqueous perchloric acid at a rate given by -d[CrO22+]/dt = (k0 + k[N2H5+][H+])-[CrO2 2+], with k0 = 7 × 10-4 s-1 and k = 58.1 (μ = 0.10) and 50.4 (μ = 1.0) M-2 s-1 at 25.0°C. The rate-limiting step is believed to be formation of the protonated hydrazyl radical cation, which reacts further when HCrO4- is added but otherwise disproportionates.
The cyclopentylpentaaquochromium(III) ion: Synthesis, characterization, and kinetics of acidolysis, homolysis, and electrophilic cleavage reactions
Espenson, James H.,Connolly, Philip,Meyerstein, Dan,Cohen, Haim
, p. 1009 - 1013 (2008/10/08)
The complex [(H2O)5Cr-c-C5H9]2+ is formed in the reaction of Cr2+ with H2O2 in aqueous solution saturated with cyclopentane. Reaction of Cr2+ with cyclopentyl radical, a step observed directly by pulse radiolysis (k = (8.0 ± 1.0) × 107 M-1 s-1), yields (H2O)5Cr-c-C5H92+, the radical being formed by abstraction from the hydrocarbon with HO?. The complex was isolated chromatographically and characterized by its absorption spectrum and the products of reactions (C5H9Br from Br2, C5H9OH from homolysis in the presence of Fe3+ and Cu2+). It decomposes by parallel unimolecular pathways of acidolysis (→OOH2+ + c-C5H10, k298 = (4.86 ± 0.12) × 10-4 s-1, ΔH≠ = 73.5 ± 2.4 kJ mol-1, ΔS≠ = -61.5 ± 7.9 J mol-1 K-1 and homolysis (→Cr2+ + ?C5H9, k298 = (1.07 ± 0.16) × 10-4 s-1, ΔH≠ = 126 ± 2.9 kJ mol-1, ΔS≠ = 102.5 ± 9.3 J mol-1 K-1), although the latter is a reversible and thermodynamically unfavorable process, which occurs only in the presence of oxidizing agents. The complex also reacts in bimolecular displacement reactions (SE2 mechanism) with Hg2+ (k298 = 1.08 ± 0.20 M-1 s-1), Br2 (k298 = 1.30 ± 0.19 × 104 M-1 s-1), and I2 (k298 = 8.2 M-1 s-1).
Kinetics of chromium(II) reduction of nitrile-bonded cyanoacetate complexes of pentaamminecobalt(III)
Kupferschmidt,Jordan
, p. 3469 - 3473 (2008/10/08)
The chromium(II) reduction of cobalt(III) complexes of the type (NH3)5CoNCCH2R, where R ≡ H, CH2CN, CO2CH3, CONH2, and CO2H, have been studied. The rate law for the cyanoacetic acid complex has the form (k1[H+] + k2Ka)/(Ka + [H+])[cobalt(III)][chromium(II)]. The value of k1[H+] was too small relative to k2Ka to allow it to be accurately determined, but k2 = 2.1 ± 0.1 M-1 s-1 with ΔH2? = 12.5 ± 1.1 kcal mol-1 and ΔS2? = -15.2 ± 3.6 cal mol-1 deg-1, and Ka = 2.7 × 10-2 M, all at 25°C in 0.5 M LiClO4-HClO4. The k2 path has been shown to produce a carboxylate-bound chromium(III) product and is assigned to have a bridged-outer-sphere mechanism. The other complexes are reduced without ligand transfer and have simple second-order rate constants independent of [H+]. Results for the ester are typical with k = 2.34 ± 0.06 × 10-2 M-1 s-1 (25°C, 0.5 M LiClO4-HClO4), ΔH? = 9.5 ± 0.5 kcal mol-1, and ΔS? = -34.2 ± 1.3 cal mol-1 deg-1.
