Three-electron oxidations. 18. Carbon-13 and deuterium isotope effects in the cooxidation of 2-hydroxy-2-methylbutyric acid and 2-propanol. Evidence for a two-step mechanism

Ramesh, Swaminathan; Mahapatra, Surendra N.; Liu, Juei H.; Rocek, Jan

doi:10.1021/ja00407a036

Cited by 18 publications

(5 citation statements)

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“…Scheme 2 outlines a mechanism that is consistent with the previous studies (12-17) and the EPR results presented above. It is proposed that the reduction of Cr(VI) by ascorbate is a two electron process (eq 10) because the amount of Cr (IV) was much higher than the amount of Cr (V) detected in these studies, and a two-electron transfer would be expected for a cis-coordinating diol (74,75). If the reduction does occur by a one electron pathway (eqn 17- Cr(IV) + ascH" -* Cr(III) + ase*" (19) then the reaction of Cr(V) with ascorbate must be faster than the reaction of Cr(IV) with ascorbate to account for the predominance of Cr(IV) trapped by Mn(II) and absence of a Cr(V) signal at high ascorbate to Cr(VI) ratios.…”

Section: Discussionmentioning

confidence: 88%

Reaction of Chromium(VI) with Ascorbate Produces Chromium(V), Chromium(IV), and Carbon-Based Radicals

Stearns

Wetterhahn

1994

Chem. Res. Toxicol.

179

150

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Reaction of potassium dichromate with sodium ascorbate was studied by EPR spectroscopy at room temperature, in 0.10 M N-[2-hydroxyethyl]piperazine-N'-[2-ethanesulfonic acid] (HEPES), phosphate, cacodylate, and tris(hydroxymethyl)aminomethane hydrochloride (Tris.HCl) buffers at pH 7.0, in the presence of 0.10 M spin trap [5,5-dimethyl-1-pyrroline 1-oxide or 2-methyl-N-(4-pyridinylmethylene)-2-propanamine N,N'-dioxide]. Chromium(V), ascorbate radical, CO2-, and other carbon-based spin trap-radical adducts were observed. Chromium(V), CO2-, and the carbon-based radicals were observed at low ratios of ascorbate to chromium, and ascorbate radical was observed at high ratios of ascorbate to chromium. The presence of Cr(IV) was detected indirectly by reaction with Mn(II) and a subsequent decrease in the Mn(II) EPR signal. More Cr(IV) was found for the higher reaction ratios of ascorbate to Cr(VI). The only buffer effect observed was a relative decrease of the Cr(V) signal in Tris.HCl vs HEPES, phosphate, and cacodylate buffers, no change in the radical adducts was observed. There was no evidence for reactive oxygen species an intermediates in this reaction. Addition of the singlet oxygen trap 2,2,6,6-tetramethyl-4-piperidone hydrochloride showed no 2,2,6,6-tetramethyl-1-piperidinyloxy radical formation. The Cr(V) species did not react with dioxygen, and dioxygen did not affect the formation of carbon-based radicals. A mechanism consistent with these observations is discussed.

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Section: Discussionmentioning

confidence: 88%

Reaction of Chromium(VI) with Ascorbate Produces Chromium(V), Chromium(IV), and Carbon-Based Radicals

Stearns

Wetterhahn

1994

Chem. Res. Toxicol.

179

150

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“…The additional advantage comes from sensitivity of the Cr(VI) photoreduction to the surface catalytic effects [129,[171][172][173][174] or to the presence of an additional electron donors and/or acceptors: then a synergistic effect is observed in two-or multi-component systems [172][173][174][175][176][177]. The role of the environmental photoactivators can be played as well by semiconductors such as TiO 2 (both rutile and anatase), WO 3 , Fe 2 O 3 , SrTiO 3 , etc., which were found to drive the Cr(VI) to Cr(V) photoreduction, and finally to Cr(III) stable product [178][179][180][181][182][183].…”

Section: Photoreduction Of Chromate(vi)mentioning

confidence: 99%

Homogeneous photocatalysis by transition metal complexes in the environment

Cieśla

Kocot

Mytych

et al. 2004

Journal of Molecular Catalysis A: Chemical

219

116

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“…Initial one- (5), two-( 6), or three- (7) electron reductions of Cr" have been proposed for chromic oxidations of organic substrates. However, it is generally acknowledged that an initial two-electron reduction occurs for carboxylic…”

Section: Methodsmentioning

confidence: 99%

Easy experiments for detection of chromium intermediates

Signorella¹,

Rizzotto²,

Mulero³

et al. 1992

J. Chem. Educ.

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Detection of reaction intermediates is an important matter when a kinetic experiment is carried out, to reinforce the mechanism derived from the rate law. However, this task may be difficult when the transient species are very short-lived, and under kinetic conditions they may not be observed. If this is so, conditions under which detection would be feasible will have to be found out, and students should be taught to do it.Herein oxidations of organic substrates by potassium dichromate in aqueous solution have been chosen as model systems, since both Crv and Crvl complexes involved in these reactions (1) may be detected easily. When CrVI is mixed with biologically related molecules in aqueous solution, growth and decay of CrVI and Crv intermediates are observed, with "stability" ascribed to complex formation with substrate (2). Besides, stable Crv compounds with ahydroxy-acids having a tertiary alcohol group have been isolated and characterized (3). Identification of Crv intermediates has led to the consideration that such species may be involved in the molecular processes leading to the onset of cancer formation, and they are likely candidates

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Three-electron oxidations. 18. Carbon-13 and deuterium isotope effects in the cooxidation of 2-hydroxy-2-methylbutyric acid and 2-propanol. Evidence for a two-step mechanism

Cited by 18 publications

References 0 publications

Reaction of Chromium(VI) with Ascorbate Produces Chromium(V), Chromium(IV), and Carbon-Based Radicals

Reaction of Chromium(VI) with Ascorbate Produces Chromium(V), Chromium(IV), and Carbon-Based Radicals

Homogeneous photocatalysis by transition metal complexes in the environment

Easy experiments for detection of chromium intermediates

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