Revised mechanism of Boyland-Sims oxidation

New computational insights into the mechanism of the Boyland-Sims oxidation of arylamines with peroxydisulfate (S(2)O(8)(2-)) in an alkaline aqueous solution are presented. The key role of arylnitrenium cations, in the case of primary and secondary arylamines, and arylamine dications and immonium cations, in the case of tertiary arylamines, in the formation of corresponding o-aminoaryl sulfates, as prevalent soluble products, and oligoarylamines, as prevalent insoluble products, is proposed on the basis of the AM1 and RM1 computational study of the Boyland-Sims oxidation of aniline, ring-substituted (2-methylaniline, 3-methylaniline, 4-methylaniline, 2,6-dimethylaniline, anthranilic acid, 4-aminobenzoic acid, sulfanilic acid, sulfanilamide, 4-phenylaniline, 4-bromoaniline, 3-chloroaniline, and 2-nitroaniline) and N-substituted anilines (N-methylaniline, diphenylamine, and N,N-dimethylaniline). Arylnitrenium cations and sulfate anions (SO(4)(2-)) are generated by rate-determining two-electron oxidation of primary and secondary arylamines with S(2)O(8)(2-), while arylamine dications/immonium cations and SO(4)(2-) are initially formed by two-electron oxidation of tertiary arylamines with S(2)O(8)(2-). The subsequent regioselectivity-determining reaction of arylnitrenium cations/arylamine dications/immonium cations and SO(4)(2-), within the solvent cage, is computationally found to lead to the prevalent formation of o-aminoaryl sulfates. The formation of insoluble precipitates during the Boyland-Sims oxidation of arylamines was also computationally studied.     

Comment on "Revised electron affinity of SF6 from kinetic data" [J. Chem. Phys. 136, 121102 (2012)

The adiabatic electron affinity (AEA) of SF(6) has been calculated near the relativistic CCSDT(Q) basis set limit. Our best theoretical value (1.0340 ±?0.03 eV) is in excellent agreement with the recently revised experimental value of 1.03?±?0.05 eV reported by Troe et al. [J. Chem. Phys. 136, 121102 (2012)]. While our best nonrelativistic, clamped-nuclei, valence CCSD(T) basis set limit value of 0.9058 eV is in good accord with the previously reported CCSD(T)/CBS values, to obtain an accurate AEA, several additional contributions need to be taken into account. The most important one is scalar-relativistic effects (0.0839 eV), followed by inner-shell correlation (0.0216 eV) and post-CCSD(T) correlation effects (0.0248 eV), the latter almost entirely due to connected quadruple excitations. The diagonal Born-Oppenheimer correction is an order of magnitude less important at -0.0022 eV.     

Comment on decomposition mechanism and thermochemistry of dimethylnitramine

The previously proposed mechanism for the pyrolysis of dimethylnitramine was reexamined to take into consideration several recent experimentally determined rate constants for key elementary steps. The present formulation brings into better agreement the high and low temperature values for the initial fragmentation reactions. Thermochemical values for the various species involved in the decomposition of dimethylnitramine are presented for the temperature range 300–1500 K. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 33: 70–73, 2001     

Comment on "New insights in the electrocatalytic proton reduction and hydrogen oxidation by bioinspired catalysts: a DFT investigation"

In the title paper, Vetere et al. reported a computational investigation of the mechanism of H(2) oxidation/proton reduction using a model of nickel-based electrocatalysts that incorporates pendant amines in cyclic phosphorus ligands. These catalysts are attracting considerable attention owing to their high turnover rates and relatively low overpotentials. These authors interpreted the results of their calculations as evidence for a symmetric bond cleavage of H(2) leading directly to two protonated amines in concert with a two-electron reduction of the Ni(II) site to form a Ni(0) diproton state. Proton reduction would involve a reverse symmetric bond formation. We report here an analysis that refutes the interpretation by these authors. We give, for the same model system, the structure of a heterolytic cleavage transition state consistent with the presence of the Ni(II) center acting as a Lewis acid and the pendant amines acting as Lewis bases. We present the associated intrinsic reaction coordinate (IRC) pathway connecting the dihydrogen (η(2)-H(2)) adduct and a hydride-proton state. We report also the transition state and associated IRC for the proton rearrangement from a hydride-proton state to a diproton state. Finally, we complete the characterization of the transition state reported by Vetere et al. through a determination of the corresponding IRC. In summary, H(2) oxidation/proton reduction with this class of catalysts involves a heterolytic bond breaking/formation.     

Hydroxyl-radical-initiated oxidation mechanism of bromopropane

Bromopropane has been considered as a replacement for chlorofluorocarbons used as the active component of industrial cleaning solvents, more specifically for HCFC-141b. The proposed mechanism for the atmospheric oxidation of bromopropane is studied via ab initio methodology. Ab initio molecular orbital methods at the CCSD(T)/6-311++G(2df,2p)//MP2/6-31G(d) level of theory have been used to determine the structure and energetics of the 58 species and transition states involved in the atmospheric oxidation of bromopropane. The calculations show that the major oxidation species is bromoacetone. Other brominated species that result from the oxidation are BrCH 2CH 2C(O)H, BrC(O)CH 2CH 3, and BrC(O)H, potential new bromine reservoir species that result from bromopropane in the atmosphere.     

Atmospheric oxidation mechanism of bromoethane

A mechanism for the atmospheric oxidation of bromoethane is proposed from an ab initio study. Using CCSD(T)/6-311++G(2df,2p)//MP2/6-31G(d) level of theory, the structure and energetics of the 35 species and transition states involved in the atmospheric oxidation of bromoethane are examined. From these calculations, reaction enthalpies and activation energies to characterize the potential energy surface of the proposed mechanism for the complete atmospheric degradation of bromoethane are determined. The studies revealed that the hydrogen abstraction from the alpha carbon has the lowest activation energy barrier of all the possible abstractions, making this pathway the most energetically favored pathway for the atmospheric oxidation process. The brominated species that result from the oxidation at the alpha carbon are BrC(O)CH(3) and BrC(O)H. Other species resulting from oxidation initiated at the beta carbon are also identified.     

Comment on a proposed excitation mechanism in argon ICPs

The author points to experimental results, published in the literature, which provide indirect evidence of overpopulations of highly excited levels of both argon and analyte species, with respect to the LTE populations, in the analytically favourable, non-thermal zone of toroidal ICPs. Considering this evidence and a mechanism proposed in the literature to explain results of measurements of spatial emission characteristics in ICPs, the author suggests the likeliness that the collisional-radiative model of Bates, Kingston, and MmcWhirter as elaborated by fujimoto for a so-called predominantly recombining plasma, might provide a key for understanding some basic phenomena in the non-thermal region of argon ICPs. The dominant mechanisms would then involve Penning ionisation by excited argon atoms (not exclusively metastables) and three-body ion-electron recombination.     

Comment on "Selective adsorption of tannins onto hide collagen fibres"

In a recent publication by Liao et al.[1], the section 1.3 Modeling of adsorption kinetics, authors mentioned a pseudo- second-order model from eq. (3) to eq. (5). In fact, the second order kinetic expression for the adsorption systems of divalent metal ions using sphagnum moss peat has been reported by Ho[2]. In order to distinguish the kinetics equation based on adsorption capacity of solid from concentration of solution, Ho's second order rate expression has been named pseudo-second order[2-5]. The most frequently cited papers were published in Chemical Engineering Journal[3], Process Biochemistry[4] and Water Research[5].