Kinetics and modeling of the H2?O2?NOx system

The addition of NO (0 to 400ppm) to mixtures of H₂ (ca. 1%) and O₂ (0.7 to 22%) has been studied over the temperature range 700 to 825 K, in a flow reactor at atmospheric pressure. The overall effect of NO is to promote the oxidation of H₂ but high concentrations of O₂ actually inhibit the NO-promoted oxidation of H₂. A detailed kinetic mechanism has been constructed and found to describe the experimental observations. The promotion of the oxidation of H₂ arises through the catalytic cycle The ability of R.34 to reactivate chains normally terminated by the formation of HO₂ is a key feature of this system. The predictions are highly sensitive to the rate of the reaction R.5 and the rate constants for this reaction is the only adjustable parameter required in the model. The value of k_5,N2 found to describe all the results has an absolute uncertainty <35%. The uncertainty relative to other important rate constants in the H₂? O₂ system is less than 10%. © 1995 John Wiley & Sons, Inc.     

Hydrothermal Synthesis, Characterization and Catalytic Properties of Nanoporous MoO3/ZrO2 Mixed Oxide

Introduction Theisobutane/butenealkylationintherefiningin dustryforobtainingacleangasolinewithahigh octane valueisveryimportant[1,2].Sulfuricandhydrofluoric acidsareusedascatalystsinthecurrentindustrial processesfortheisobutane/butenealkylation,inwhich ca…     

Synthesis,Structure and Characterization of Three Metal Molybdate Hydrates: Fe(H2O)2(MoO4)2·H3O,NaCo2(MoO4)2(H3O2)and Mn2(MoO4)3·2H3O

Three metal molybdate hydrates,Fe(H2O)2(MoO4)2·H3O(FeMo),NaCo2(MoO4)2(H3O2)(CoMo)and Mn2(MoO4)3·2H3O(MnMo),were synthesized by the mixed-solvent-thermal methods and characterized by singlecrystal X-ray...     

Density functional study of Fe2 ?N2

The interaction of two iron atoms with molecular nitrogen was studied by means of density functional techniques. Calculations were of the all-electron type, and both conventional local and gradient-dependent approximate (GDA) models were used. A ground state (GS) of linear structure was found for Fe₂-N₂ with 2S + 1 = 7; whereas a distorted tetrahedral structure, being also a septuplet, was located at 4.0 and 14.3 kcal/mol above the GS, at the local and GDA levels of theory, respectively. The N-N bond is moderately perturbed in the GS, but it is strongly activated in the tetrahedral mode: It has bond orders of 2.6 and 1.5, vibrational frequencies of 2148 and 1496 cm^-1, and equilibrium bond lengths of 1.14 and 1.24 Å, for the linear and tetrahedral geometries, respectively. These values are 3.0, 2359 cm^-1, and 1.095 Å, for free N₂. At GDA level of theory, the Fe₂-N₂ binding energy is 15 kcal/mol, which is bigger than that of Fe-N₂ (9 kcal/mol). The π-back donation, in the linear GS, is of 0.31 electrons, but the total charge transfer, from Fe₂ to N₂, is only 0.05 units. This is relevant in comparison with the tetrahedral mode, where the Fe₂ to N₂ total charge transfer is of 0.45 electrons, yielding a stronger activated N₂ moiety. © 1996 John Wiley & Sons, Inc.     

Modeling the H bond donor strength of ?OH, ?NH,and ?CH sites by local molecular parameters

A quantum chemical model is introduced to predict the H‐bond donor strength of monofunctional organic compounds from their ground‐state electronic properties. The model covers ? OH, ? NH, and ? CH as H‐bond donor sites and was calibrated with experimental values for the Abraham H‐bond donor strength parameter A using the ab initio and density functional theory levels HF/6‐31G** and B3LYP/6‐31G**. Starting with the Morokuma analysis of hydrogen bonding, the electrostatic (ES), polarizability (PL), and charge transfer (CT) components were quantified employing local molecular parameters. With hydrogen net atomic charges calculated from both natural population analysis and the ES potential scheme, the ES term turned out to provide only marginal contributions to the Abraham parameter A, except for weak hydrogen bonds associated with acidic ? CH sites. Accordingly, A is governed by PL and CT contributions. The PL component was characterized through a new measure of the local molecular hardness at hydrogen, η(H), which in turn was quantified through empirically defined site‐specific effective donor and acceptor energies, EE_occ and EE_vac. The latter parameter was also used to address the CT contribution to A. With an initial training set of 77 compounds, HF/6‐31G** yielded a squared correlation coefficient, r², of 0.91. Essentially identical statistics were achieved for a separate test set of 429 compounds and for the recalibrated model when using all 506 compounds. B3LYP/6‐31G** yielded slightly inferior statistics. The discussion includes subset statistics for compounds containing ? OH, ? NH, and active ? CH sites and a nonlinear model extension with slightly improved statistics (r² = 0.92). © 2008 Wiley Periodicals, Inc. J Comput Chem 2009     

Preparation and Characterization of Reduced Graphene Oxide–Fe3O4 Nanocomposites in Polyacrylamide

Russian Journal of Physical Chemistry A - A hydrogel nanocomposite composed of reduced graphene oxide (RGO), iron oxide (Fe3O4) nanoparticles, and polyacrylamide (PAM) was prepared using radical...     

Studies on the Synthesis and Characterization of Pd?TiO2?SiO2 Nanocomposite for Electroanalytical Applications

A nanocomposite of Pd? TiO₂? SiO₂ is developed through a sol‐gel process from the reaction products of titanium isopropoxide followed by mixing the same with palladium linked 3‐glycidoxypropyltrimethoxysilane. The reaction product is sonicated and calcinated to obtain the nanocomposite of Pd? TiO₂? SiO₂. The calcination at 600 °C yielded an amorphous structure whereas at 900 °C it resulted into a nanocrystalline structure. The nanocomposite of palladium was further characterized by TEM, XRD, IR and EDS. The material acts as an efficient electrocatalyst. Electrocatalysis of ascorbic acid is observed at 0.1 V vs. Ag/AgCl, shows linearity between 1 µM and 1 mM in 0.1 M phosphate buffer (pH 7.0).     

C?H Hydroxylation Using a Heterocyclic Catalyst and Aqueous H2O2

Substituted benzoxathiazines function as catalysts for the selective hydroxylation of tertiary C? H bonds. Mechanistic studies have revealed an unanticipated disparity between oxaziridine reactivity and catalyst performance and have given way to a new catalyst and an aqueous H₂O₂ reaction protocol that greatly facilitate such transformations (see scheme).

     

Catalytic Functionalization of C(sp2)?H and C(sp3)?H Bonds by Using Bidentate Directing Groups

C? H bonds are ubiquitous in organic compounds. It would, therefore, appear that direct functionalization of substrates by activation of C? H bonds would eliminate the multiple steps and limitations associated with the preparation of functionalized starting materials. Regioselectivity is an important issue because organic molecules can contain a wide variety of C? H bonds. The use of a directing group can largely overcome the issue of regiocontrol by allowing the catalyst to come into proximity with the targeted C? H bonds. A wide variety of functional groups have been evaluated for use as directing groups in the transformation of C? H bonds. In 2005, Daugulis reported the arylation of unactivated C(sp³)? H bonds by using 8‐aminoquinoline and picolinamide as bidentate directing groups, with Pd(OAc)₂ as the catalyst. Encouraged by these promising results, a number of transformations of C? H bonds have since been developed by using systems based on bidentate directing groups. In this Review, recent advances in this area are discussed.     

An ab initio interpretation in gas phase and aqueous solution of the generalized anomeric effect in R?O?CR2?NR2 (R = H,CH3)

The conformational stability of aminomethanol and its methylated derivatives has been investigated by means of ab initio methods in the gas phase and aqueous solution. Among the computational levels employed, HF/6‐31G**//HF/6‐31G** calculations correctly describe the conformational features of this series of compounds, and agree well with the results obtained using larger basis sets and including ZPE or electron correlation corrections. Calculated energies and geometries follow the known trends associated to the generalized anomeric effect. Thus, the most stable conformers exhibit preferences for the trans orientations of the Lp N C O and Lp O C N moieties. However, reverse anomeric effects are observed when a methyl group is bonded to the oxygen, because the Lp O C N unit prefers a gauche orientation (that is, trans Me O C N). The natural bond orbital (NBO) method was employed to explain the cited conformational preferences. According to the NBO results, trans arrangements are preferred because the stabilization due to charge delocalization is more important than electrostatic and steric contributions. This explanation agrees with the conclusions obtained by other independent procedures based on energy decomposition schemes. The NBO method was also used to explain the origin of the rotational barriers around the C O and C N bonds in terms of the balance between unfavorable hyperconjugation and electrostatic and steric effects. Changes in conformational stability caused by methylations in different molecular positions were also explained by the influence of the methyl groups on lone‐pair delocalization and on steric effects. Finally, the effect of solvation was studied by means of the ab initio PCM method, and the significant changes on relative energies found were analyzed. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 462–477, 2000     

Copper‐Catalyzed Intramolecular C(sp3)?H and C(sp2)?H Amidation by Oxidative Cyclization

The first copper‐catalyzed intramolecular C(sp³) H and C(sp²) H oxidative amidation has been developed. Using a Cu(OAc)₂ catalyst and an Ag₂CO₃ oxidant in dichloroethane solvent, C(sp³) H amidation proceeded at a terminal methyl group, as well as at the internal benzylic position of an alkyl chain. This reaction has a broad substrate scope, and various β‐lactams were obtained in excellent yield, even on gram scale. Use of CuCl₂ and Ag₂CO₃ under an O₂ atmosphere in dimethyl sulfoxide, however, leads to 2‐indolinone selectively by C(sp²) H amidation. Kinetic isotope effect (KIE) studies indicated that C H bond activation is the rate‐determining step. The 5‐methoxyquinolyl directing group could be removed by oxidation.     

Synthesis and Characterization of a One- dimensional Molybdenum Oxide （H2enMe）[Mo3O10]

A hybrid organic-inorganic material (H2enMe)[Mo3O10] (C3H12Mo3N2O10, Mr = 523.97) has been synthesized under hydrothermal conditions and its crystal structure was determined by X-ray diffraction. It crystallizes in the orthorhombic system, space group Pnma with a = 12.430(2), b = 7.6089(12), c = 11.9553(19) , V = 1130.7(3) 3, Dc = 3.078 g/cm3, Z = 4, μ(MoKa) = 3.328 mm1, F(000) = 1000, the final R = 0.0256 and wR = 0.0716 for 1314 observed reflections with I > 2σ(I). A total of 11780 reflections were measured and 1325 were unique (Rint = 0.0244). It consists of infinite one-dimensional edge-sharing MoO6 octahedral chains with [Mo3O10]2 moieties. The protonated diaminopropane cations are located between the chains and linked to the oxygen atoms of the inorganic skeletal backbones by hydrogen bonds. It is indicated that the as-synthesized compound displays photochromic property in the solid state.     

Mild ArI‐Catalyzed C(sp2)?H or C(sp3)?H Functionalization/C?O Formation: An Intriguing Catalyst‐Controlled Selectivity Switch

A tandem C(sp²) H and C(sp³) H functionalization/C O bond formation catalyzed by iodine(III) reagents generated in situ has been developed. The method shows wide scope under mild conditions and exhibits an unprecedented selectivity profile that can be switched depending on the catalyst employed.     

Manganese‐Catalyzed Dehydrogenative [4+2] Annulation of N?H Imines and Alkynes by C?H/N?H Activation

Described herein is a manganese‐catalyzed dehydrogenative [4+2] annulation of N H imines and alkynes, a reaction providing highly atom‐economical access to diverse isoquinolines. This transformation represents the first example of manganese‐catalyzed C H activation of imines; the stoichiometric variant of the cyclomanganation was reported in 1971. The redox neutral reaction produces H₂ as the major byproduct and eliminates the need for any oxidants, external ligands, or additives, thus standing out from known isoquinoline synthesis by transition‐metal‐catalyzed C H activation. Mechanistic studies revealed the five‐membered manganacycle and manganese hydride species as key reaction intermediates in the catalytic cycle.