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

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 + (CH₃)₃COH → H₂ + ^•CH₂C­(CH₃)₂OH reaction in aqueous solution is definitively determined to be (1.0 ± 0.15) × 10⁵ M^–1 s^–1, 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 + (CH₃)₃COH 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

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