27 research outputs found
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Mechanistic Insight into Peroxydisulfate Reactivity: Oxidation of the cis,cis-[Ru(bpy)₂(OH₂)]₂O⁴⁺ "Blue Dimer"
One-electron oxidation of the μ-oxo dimer
(cis,cis-[Ruᴵᴵᴵ(bpy)₂(OH₂)]₂O⁴⁺, {3,3}) to {3,4} by S₂O₈²⁻ can
be described by three concurrent reaction pathways corresponding
to the three protic forms of {3,3}. Free energy
correlations of the rate constants, transient species dynamics
determined by pulse radiolysis, and medium and temperature
dependencies of the alkaline pathway all suggest that the ratedetermining
step in these reactions is a strongly nonadiabatic
dissociative electron transfer within a precursor ion pair
leading to the {3,4}|SO₄²⁻|SO₄•− ion triple. As deduced from the SO₄•− scavenging experiments with 2-propanol, the SO₄•−
radical then either oxidizes {3,4} to {4,4} within the ion triple, effecting a net two-electron oxidation of {3,3}, or escapes in
solution with ∼25% probability to react with additional {3,3} and {3,4}, that is, effecting sequential one-electron oxidations. The
reaction model presented also invokes rapid {3,3} + {4,4} → 2{3,4} comproportionation, for which kcₒₘ ∼5 × 10⁷ M⁻¹ s⁻¹ was
independently measured. The model provides an explanation for the observation that, despite favorable energetics, no oxidation
beyond the {3,4} state was detected. The indiscriminate nature of oxidation by SO₄•− indicates that its fate must be
quantitatively determined when using S₂O₈²⁻ as an oxidant
Beyond fossil fuel–driven nitrogen transformations
How much carbon does it take to make nitric acid? The counterintuitive answer nowadays is quite a lot. Nitric acid is manufactured by ammonia oxidation, and all the hydrogen to make ammonia via the Haber-Bosch process comes from methane. That's without even accounting for the fossil fuels burned to power the process. Chen et al. review research prospects for more sustainable routes to nitrogen commodity chemicals, considering developments in enzymatic, homogeneous, and heterogeneous catalysis, as well as electrochemical, photochemical, and plasma-based approaches
Carbon Dioxide: Physiological Catalyst for Peroxynitrite-Mediated Cellular Damage or Cellular Protectant?
Hydrogen Atom Reactivity toward Aqueous <i>tert</i>-Butyl Alcohol
Through a combination of pulse radiolysis, purification,
and analysis
techniques, the rate constant for the H + (CH<sub>3</sub>)<sub>3</sub>COH → H<sub>2</sub> + <sup>•</sup>CH<sub>2</sub>C(CH<sub>3</sub>)<sub>2</sub>OH reaction in aqueous solution is definitively
determined to be (1.0 ± 0.15) × 10<sup>5</sup> M<sup>–1</sup> s<sup>–1</sup>, which is about half of the tabulated number
and 10 times lower than the more recently suggested revision. Our
value fits on the Polanyi-type, rate–enthalpy linear correlation
ln(<i>k</i>/<i>n</i>) = (0.80 ± 0.05)Δ<i>H</i> + (3.2 ± 0.8) that is found for the analogous reactions
of other aqueous aliphatic alcohols with <i>n</i> equivalent
abstractable H atoms. The existence of such a correlation and its
large slope are interpreted as an indication of the mechanistic similarity
of the H atom abstraction from α- and β-carbon atoms in
alcohols occurring through the late, product-like transition state. <i>tert</i>-Butyl alcohol is commonly contaminated by much more
reactive secondary and primary alcohols (2-propanol, 2-butanol, ethanol,
and methanol), whose content can be sufficient for nearly quantitative
scavenging of the H atoms, skewing the H atom reactivity pattern,
and explaining the disparity of the literature data on the H + (CH<sub>3</sub>)<sub>3</sub>COH rate constant. The ubiquitous use of <i>tert</i>-butyl alcohol in pulse radiolysis for investigating
H atom reactivity and the results of this work suggest that many other
previously reported rate constants for the H atom, particularly the
smaller ones, may be in jeopardy
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RoemelingMargoBiochemBiophysicsMechanisticInsightPeroxydisulfate.pdf
One-electron oxidation of the μ-oxo dimer
(cis,cis-[Ruᴵᴵᴵ(bpy)₂(OH₂)]₂O⁴⁺, {3,3}) to {3,4} by S₂O₈²⁻ can
be described by three concurrent reaction pathways corresponding
to the three protic forms of {3,3}. Free energy
correlations of the rate constants, transient species dynamics
determined by pulse radiolysis, and medium and temperature
dependencies of the alkaline pathway all suggest that the ratedetermining
step in these reactions is a strongly nonadiabatic
dissociative electron transfer within a precursor ion pair
leading to the {3,4}|SO₄²⁻|SO₄•− ion triple. As deduced from the SO₄•− scavenging experiments with 2-propanol, the SO₄•−
radical then either oxidizes {3,4} to {4,4} within the ion triple, effecting a net two-electron oxidation of {3,3}, or escapes in
solution with ∼25% probability to react with additional {3,3} and {3,4}, that is, effecting sequential one-electron oxidations. The
reaction model presented also invokes rapid {3,3} + {4,4} → 2{3,4} comproportionation, for which kcₒₘ ∼5 × 10⁷ M⁻¹ s⁻¹ was
independently measured. The model provides an explanation for the observation that, despite favorable energetics, no oxidation
beyond the {3,4} state was detected. The indiscriminate nature of oxidation by SO₄•− indicates that its fate must be
quantitatively determined when using S₂O₈²⁻ as an oxidant