17693-79-7Relevant articles and documents
Mechanism of dihydrogen cleavage by high-valent metal oxo compounds: Experimental and computational studies
Collman,Slaughter,Eberspacher,Strassner,Brauman
, p. 6272 - 6280 (2001)
The oxidation of dihydrogen by metal tetraoxo compounds was investigated. Kinetic measurements of the oxidations of H2 by MnO4- and RuO4, performed by UV-vis spectroscopy, showed these reactions to be quite rapid at 25 °C (k1 ≈ (3-6) x 10-2 M-1 s-1). Rates measured for H2 oxidation by MnO4- in aqueous solution (using KMnO4) and in chlorobenzene (using nBu4NMnO4) revealed only a minor solvent effect on the reaction rate. Substantial kinetic isotope effects [(kH2/kD2 = 3.8(2) (MnO4- aq), 4.5(5) (MnO4-, C6H5C1 soln) and 1.8(6) (RuO4, CCl4 soln)] indicated that H-H bond cleavage is rate determining and that the mechanism of dihydrogen cleavage is likely similar in aqueous and organic solutions. Third-row transition-metal oxo compounds, such as OsO4, ReO4-, and MeReO3, were found to be completely unreactive toward H2. Experiments were performed to probe for a catalytic hydrogen/deuterium exchange between D2 and H20 as possible evidence of dihydrogen σ-complex intermediates, but no H/D exchange was observed in the presence of various metal oxo compounds at various pH values. In addition, no inhibition of RuO4-catalyzed hydrocarbon oxidation by H2 was observed. On the basis of the available evidence, a concerted mechanism for the cleavage of H2 by metal tetraoxo compounds is proposed. Theoretical models were developed for pertinent MnO4- + H2 transition states using density functional theory in order to differentiate between concerted [2 + 2] and [3 + 2] scissions of H2. The density functional theory calculations strongly favor the [3 + 2] mechanism and show that the H2 cleavage shares some mechanistic features with related hydrocarbon oxidation reactions. The calculated activation energy for the [3 + 2] pathway (ΔH? = 15.4 kcal mol-1) is within 2 kcal mol-1 of the experimental value.
The formation and destruction of H3O-
Miller, Thomas M.,Viggiano, A. A.,Miller, Amy E. Stevens,Morris, Robert A.,Henchman, Michael,et al.
, p. 5706 - 5714 (2007/10/02)
We report the first measurements of rate constants for formation and reaction of the Ion Phys. 49, 311 (1983)>, namely, dehydrogenation of formaldehyde by hydroxide to form hydrated-hydride ion and carbon monoxide.The OD- + H2CO reaction is about 35percent efficient at 298 K, with OD-/OH- exchange occurring in about half the reactions.H3O- was observed to undergo thermal dissociation in a helium carrier gas at room temperature with a rate constant of 1.6 * 10-12 cm3 s-1.We also studied a new reaction in which H3O- is formed: The association of OH- with H2 in a He carrier gas at low temperatures.The rate coefficient for this ternary reaction is 1*10-30 cm6 s-1 at 88 K.Rate coefficients and product branching fractions were determined for H3O- reactions with 19 neutral species at low temperatures (88-194 K) in an H2 carrier.The results of ion-beam studies, negative-ion photoelectron spectroscopy, and ion-molecule reaction data allow us to specify the hydride-water bond energy D0298(H- - H2O) = 14.4+/-1.0 kcal mol-1 (0.62+/-0.04 eV).The heat of formation of H3O-, -37.5+/-1.0 kcal mol-1, and the proton affinity of H3O-, 386.0+/-1.0 kcal mol-1, are derived from these results.Dissociation of H3O- into OH- and H2 requires 4.5+/-1.0 kcal mol-1 energy.
