A DFT study of reduction of nitrobenzene to aniline with SnCl2 and hydrochloric acid

A fundamental reduction reaction, nitrobenzene to aniline in SnCl₂ and hydrochloric acid, was investigated by density functional theory (DFT) calculations. First, the change of SnCl₂ → SnCl₄^2? → Cl₄SnH^? was discussed, and the reaction path of SnCl₄^2? + H₃O⁺ → Cl₄SnH^? + H₂O was obtained. Starting from nitrobenzene, six elementary processes were found so as to arrive at the protonated aniline. The hydride ion from Cl₄SnH^? is connected always to the cationic nitrogen, and the proton is always to oxygens. An intermediate Ph?N⁺H₂OH was obtained, which is isomerized to the para O?H adduct protonated imine via the Bamberger rearrangement. This species may undergo the H^? acceptance at the sp² N⁺H₂ center. In the nitrobenzene reduction, the proton enhances the electrophilicity of the nitrogen center, which makes the hydride shift ready. N?H bonds are formed, and N?O bonds are cleaved both by the proton attach and subsequent H₂O elimination and by the formal [1,5] OH shift. Copyright © 2016 John Wiley & Sons, Ltd.     

Quantum chemical studies of the solvation of the hydroxide ion

Abstract

To understand and model the solvation of the hydroxide ion, OH(H₂O)^? _n clusters, n = 1?5, are studied using ab initio quantum chemical techniques, largely at the MP2 level of theory using a double zeta plus polarization functions basis extended by diffuse functions. Energies and vibrational frequencies, together with thermodynamic quantities such as enthalpies, entropies and Gibbs free energies, are computed. This permits comparison with experimental estimates of the successive thermodynamic changes associated with the reaction OH(H₂O)^? _n + H₂O → OH(H₂O)^? _n+1. The theoretical values are in good agreement with experiment. The free energy of hydration of OH^? is modelled by a composite discrete-continuum method where the effects of the first hydration shell (n = 3) are obtained from the gas phase cluster calculation, while the long-range effects are modelled using self consistent reaction field theory, namely by calculating the solvation energy of OH(H₂O)^? _n in a dielectric continuum. The best estimate of the solvation (free) energy at 298 K is ?84·5 kcal mol^?1, compared to the experimental value of ?102·8 kcal mol^?1.     

Spectroscopic evidence for the effect of the ortho H<Subscript>2</Subscript>O spin on the electron transfer in photosynthesis

A spin mechanism for electron transfer control in the reaction center of purple bacteria in photosynthesis is proposed. Rotation and conversion of the ortho/para spin isomers of two H₂O molecules located near the special pair of the reaction center are treated as the sources of the coherent modulations of transient kinetics. Modulation of the collective wave function of the reaction center electrons by the total proton spin of ortho H₂O is a key feature allowing the molecule to play the role of a gate controlling the electron transfer. The iron atom in the reaction center with the gradient magnetic field is treated as a catalyst removing the strict forbiddenness of H₂O ortho/para conversion. It is shown that the modulation of the reaction center stimulated emission kinetics observed in the field of femtosecond pulses coincides with the rotational transitions of ortho/para H₂O. Influence of the effect of the electric field (Stark effect) on the level displacement and ortho/para conversion rate is discussed.     

Adsorption and decomposition of H2O on a K-covered Pt(111) surface

The adsorption of H₂O on clean and K-covered Pt(111) was investigated by utilizing Auger, X-ray and ultra-violet photoemission spectroscopies. The adsorption on Pt(111) at 100–150 K was purely molecular (ice formation) in agreement with previous work. No dissociation of this adsorbed H₂O was noted on heating to higher temperatures. On the other hand, adsorption of H₂O on Pt(111) + K leads to dissociation and to the formation of OH species which were characterized by a work function increase, an O 1s binding energy of 530.9 eV and UPS peaks at 4.7 and 8.7 eV below the Fermi level. The amount of OH formed was proportional to the K coverage for θ_K > 0.06 whereas no OH could be detected for θ? 0.06. Dissociation of H₂O occurred already at T = 100 K, with a sequential appearance of O 1s peaks at 531 and 533 eV representing OH and adsorbed H₂O, respectively. At room temperature and above only the OH species was observed. Annealing of the surface covered with coadsorbed K/OH indicated the high stability of this OH species which could be detected spectroscopically up to 570 K. The adsorption energy of H₂O coadsorbed with K and OH on Pt(111) is increased relative to that of H₂O on Pt. The work function due to this adsorbed H₂O increases whereas it decreases for H₂O on Pt(111). The energy shifts of valence and O1s core levels of H₂O on Pt + K as deduced from a comparison of gas phase and adsorbate spectra are 2.8–4.2 eV compared to ≈ 1.3–2.3 eV for H₂O on Pt (111). This increased relaxation energy shift suggests a charge transfer screening process for H₂O on Pt + K possibly involving the unoccupied 4a₁ orbital of H₂O. The occurrence of this mode of screening would be consistent with the higher adsorption energy of H₂O on Pt + K and with its high propensity to dissociate into OH and H.     

Self-oscillatory heterogeneous recombination of hydrogen atoms and nonequilibrium desorption of molecules from the surface (Teflon)

The channel of the accommodation of the energy of a heterogeneous chemical reaction (recombination of hydrogen atoms) related to vibrational V-V exchange between excited chemical reaction products and adsorption layer molecules (H₂O, HDO, D₂O, and H₂) was studied by the method of modulated molecular beams. The chemical reaction was found to proceed in an oscillatory mode caused by the nonequilibrium character of its elementary steps. The participation of adsorbed molecules in accommodation was studied by analyzing nonequilibrium desorption of these molecules. An isotope effect was observed in nonequilibrium desorption. The kinetic mechanism of the reaction and the micromechanism of elementary reaction events, which determine the “physical” mechanism of catalysis in the system under study, are discussed.     

Interaction of H2O with a clean and oxygen precovered Ni(110) surface studied by XPS

The adsorption and reaction of H₂O on clean and oxygen precovered Ni(110) surfaces was studied by XPS from 100 to 520 K. At low temperature (T<150 K), a multilayer adsorption of H₂O on the clean surface with nearly constant sticking coefficient was observed. The O 1s binding energy shifted with coverage from 533.5 to 534.4 eV. H₂O adsorption on an oxygen precovered Ni(110) surface in the temperature range from 150 to 300 K leads to an O 1s double peak with maxima at 531.0 and 532.6 eV for T=150 K (530.8 and 532.8 eV at 300 K), proposed to be due to hydrogen bonded O_ads… HOH species on the surface. For T>350 K, only one sharp peak at 530.0 eV binding energy was detected, due to a dissociation of H₂O into O_ads and H₂. The s-shaped O 1s intensity-exposure curves are discussed on the basis of an autocatalytic process with a temperature dependent precursor state.     

H2O interaction with clean and oxygen precovered Ni(110)

The interaction of water vapour with clean as well as with oxygen precovered Ni(110) surfaces was studied at 150 and 273 K, using UPS, ΔΦ, TDS, and ELS. The He(I) (He(II)) excited UPS indicate a molecular adsorption of H₂O on Ni(110) at 150 K, showing three water-induced peaks at 6.5, 9.5 and 12.2 eV below E_F (6.8, 9.4 and 12.7 eV below E_F). The dramatic decrease of the Ni d-band intensity at higher exposures, as well as the course of the work function change, demonstrates the formation of H₂O multilayers (ice). The observed energy shift of all water-induced UPS peaks relative to the Fermi level (ΔE_max = 1.5 eVat 200 L) with increasing coverage is related to extra-atomic relaxation effects. The activation energies of desorption were estimated as 14.9 and 17.3 kcal/mole. From the ELS measurements we conclude a great sensitivity of H₂O for electron beam induced dissociation. At 273 K water adsorbs on Ni(110) only in the presence of oxygen, with two peaks at 5.7 and 9.3 eV below E_F (He(II)), being interpreted as due to hydroxyl species (OH)^δ? on the surface. A kinetic model for the H₂O adsorption on oxygen precovered Ni(110) surfaces is proposed, and verified by a simple Monte Carlo calculation leading to the same dependence of the maximum amount of adsorbed H₂O on the oxygen precoverage as revealed by work function measurements. On heating, some of the (OH)^δ? recombines and desorbs as H₂O at ? 320 K, leaving behind an oxygen covered Ni surface.     

The low temperature water formation reaction on Pt(111): A static SIMS and TDS study

The formation of water by the reaction of preadsorbed oxygen with hydrogen on a Pt(111) surface has been characterized, using secondary ion mass spectroscopy, below the desorption temperature of H₂O (180 K). The concentration of chemisorbed water was monitored during the reaction by following the SIMS H₃O⁺ signal. Reaction profiles were measured over a temperature range of 120 to 153 K, and an H₂ pressure range of 10^-9 to 10^-6 Torr. Under all conditions the reaction profiles were characterized by an induction time, a region of rapid reaction, and finally a steady decline in the rate. In the rapid region, an overall activation energy of 2.9 ± 0.3 kcalmol^-1 and a half-order H₂ pressure dependence were observed. At low initial oxygen concentrations the induction time increased and the maximum rate decreased. The reaction was slow in the absence of gas phase hydrogen, even when the surface coverage of hydrogen was relatively high. Water and hydrogen thermal desorption spectra, measured after stopping the reaction by removal of gas phase hydrogen, were complex functions of the H₂ exposure, exhibiting several peaks between 170 and 400 K. However, after an exposure large enough to drive the reaction to completion, only one H₂O peak at 173 K and one H₂ peak at 350 K were observed. The results indicate that only a fraction of the total H(a) on the surface was readily available for reaction during H₂ exposure at T ? 153 K. the remainder either recombined to form H₂ or reacted with O(a) during the thermal desorption ramp. There is good evidence for a surface rearrangement during the induction period. A model is proposed which involves the formation of water clusters that accelerate the rate.     

Adsorption and diffusion of H2O molecule on the Be(0001) surface: A density-functional theory study

Using first-principles calculations, we systematically study the adsorption behavior of a single molecular H₂O on the Be(0001) surface. We find that the favored molecular adsorption site is the top site with an adsorption energy of about 0.3 eV, together with the detailed electronic structure analysis, suggesting a weak binding strength of the H₂O/Be(0001) surface. The adsorption interaction is mainly contributed by the overlapping between the s and pz states of the top-layer Be atom and the molecular orbitals 1b₁ and 3a₁ of H₂O. The activation energy for H₂O diffusion on the surface is about 0.3 eV. Meanwhile, our study indicates that no dissociation state exists for the H₂O/Be(0001) surface.     

Velocity dependence of the chemi-ionization of H2O and D2O on impact of 21S and 23S helium atoms

The velocity dependence for the ionization of H₂O and D₂O to form H₂O⁺ and D₂O⁺ in collisions with both 2³S and 2¹S metastable helium atoms has been measured in a crossed molecular beam apparatus using a mechanical velocity-selector on the metastable beam. The cross-sections are found to be proportional to the —n power of the relative collision energy, with n ? 0.4 for both metastable atoms in both gases. The branching ratios H₂O⁺/OH⁺ and D₂O⁺/OD⁺ were both found to be 4.3 for both metastable helium atoms, and to be independent of the relative collision energy.     

Adsorption of H2O on Al(111)

The adsorption of H₂O on Al(111) has been studied by ESDIAD (electron stimulated desorption ion angular distributions), LEED (low energy electron diffraction), AES (Auger electron spectroscopy) and thermal desorption in the temperature range 80–700 K. At 80 K, H₂O is adsorbed predominantly in molecular form, and the ESDIAD patterns indicate that bonding occurs through the O atom, with the molecular axis tilted away from the surface normal. Some of the H₂O adsorbed at 80 K on clean Al(111) can be desorbed in molecular form, but a considerable fraction dissociates upon heating into OH_ads and hydrogen, which leaves the surface as H₂. Following adsorption of H₂O onto oxygen-precovered Al(111), additional OH_ads is formed upon heating (perhaps via a hydrogen abstraction reaction), and H₂ desorbs at temperatures considerably higher than that seen for H₂O on clean Al(111). The general behavior of H₂O adsorption on clean and oxygen-precovered Al(111) (θ_O ? monolayer) is rather similar at low temperature, but much higher reactivity for dissociative adsorption of H₂O to form OH _adsis noted on the oxygen-dosed surface around room temperature.     

Surface reaction mechanism of Y2O3 atomic layer deposition on the hydroxylated Si(1 0 0)-2 × 1: A density functional theory study

The surface reaction mechanism of Y₂O₃ atomic layer deposition (ALD) on the hydroxylated silicon surface is investigated by using density functional theory. The ALD process is designed into two half-reactions, i.e., Cp₃Y (Cp = cyclopentadienyl) and H₂O half-reactions. For the Cp₃Y half-reaction, the chemisorbed complex is formed along with the change of metal-Cp bonding from Y-C(π) to Y-C₁(σ). For the H₂O half-reactions, the chemisorbed energies are increased with the relief of steric congestion around yttrium metal center. In addition, Gibbs free energy calculations show that it is thermodynamically favorable for the Cp₃Y half-reactions. By comparing with the reaction of H₂O with {Si}-(O₂)YCp, it is thermodynamically more favorable and kinetically less favorable for the reactions of H₂O with {Si}-OYCp₂ as well as with {Si}-OYCp(OH).     

Influence of water on HFO-1234yf oxidation pyrolysis via ReaxFF molecular dynamics simulation

ABSTRACT

The effect of water molecules on HFO-1234yf oxidation pyrolysis was investigated by ReaxFF-molecular dynamics simulation from 1900 to 4200?K. The initial pyrolysis of HFO-1234yf starts around 2500?K and the water molecules participate in chemical reactions at 2800?K when the reactants pyrolysis reached the highest reaction rate. The primary products including HF, COF₂ and CO₂ are observed at 2600, 2700 and 2900?K, respectively. The influence of water molecules on products is mainly reflected in the promotion activity on the conversion from COF₂ to CO₂ and the generation of HF molecules. Four formation pathways are observed and calculated to further elucidate the procedure of pyrolysis. The main conversion process from H₂O to HF is the ?F?+?H₂O?=?HF+?OH reaction, and the paths from H₂O to ?OH radical and COF₂ to ?CFO radical which are promoted by ?F and ?H radical, respectively, have relatively low energy barriers of 10.44 and 40.29?kJ/mol, and both reaction processes released HF molecules.     

X-ray K-absorption studies ofsome ruthenium compounds

X-ray K-absorption studies of ruthenium in ruthenium metal,RuO₂, K₂(RuCl₆) and K₄[Ru(CN)₆]: 3H₂O have been carried out using 400 mm bent crystal (mica) spectrograph. K-absorption edge of ruthenium in these compounds lies on the higher energy side with respect to that in the ruthenium metal; the divalent K₄[Ru(CN)₆]·3H₂O gives the shift in the range of tetravalent compounds RuO₂ and K₂[RuCl₆]. This discrepancy has been explained on the basis of molecular orbital picture.     

A molecular-beam investigation of the reaction H2 + 12O2 → H2O on Pd(111)

Using molecular-beam relaxation techniques and isotopic exchange experiments, the water-formation reaction on Pd(111) has been shown to proceed via a Langmuir-Hinshelwood mechanism. The reaction product H₂O is emitted from the surface with a cosine distribution. The rate-determining step is the formation of OH_ad in the reaction O_ad + H_ad → OH_ad. The activation energy for this step is 7 kcal/mole with a pre-exponential factor, v, of 4 × 10^?8 cm² atom^?1 sec^?1. This value for v lies well below that observed for simple second-order desorption of dissociatively adsorbed diatomic gases, but is roughly of the order of that obtained for the oxidation of CO on Pd(111). The formation of H₂O proceeds differently under conditions of excess O₂ or H₂. In an excess of H₂, the kinetics is dominated by the transport of atomic hydrogen between the bulk and the surface as was found for the H?D exchange reaction on Pd(111). In an excess of O₂, diffusion of hydrogen into the bulk is blocked by adsorbed oxygen and the hydrogen reservoir available for reaction at the surface is decreased by several orders of magnitude. This results in a drastic reduction of the reaction rate which can be reversed by increasing the partial pressure of H₂.     

Optoacoustic detection of multiple photon molecular absorption in a strong IR field

A new method based on the optoacoustic effect has been proposed to measure multiple photon absorption at vibrational molecular transitions in a strong IR laser field. Comparison measurements of the average absorbed energy have been done by this method for molecules with different dissociation limits in a strong CO₂-laser field, the field intensity changed therewith by four orders. For the poly-atomic molecules C₂H₄ and SF₆ having a comparatively low dissociation limit, the absorption increases monotonously as the power density of laser radiation P increases up to the dissociation limit. For three-atom molecules, such as D₂O and OCS, absorption saturation takes place with P ? 10 MW/cm².     

Studies on the Photoacoustic Spectrum of Crystal of an Amino-Acid Copper Complex [Cu(L-Phe)(O-Phen)(H2O)]NO3-H2O

Crystal of an amino-acid copper complex [Cu(L-Phe)(O-Phen) (H₂O)]NO₃ H₂O was synthesized, and its photoacoustic spectrum was recorded under room temperature. A semi-empirical method of coordinate-field theory was utilized to calculate the d-d transition energy. With the results, we explained the spectrum satisfactorily.     

硫酸催化乙二醛气体相水化反应机理和速率常数理论计算研究

采用M06-2X和CCSD(T)高阶量化计算和传统过渡态理论研究硫酸催化乙二醛气体相水化反应.对HCOCHO+H₂O, HCOCHO+H₂O+H₂O, HCOCHO+H₂O+H₂O, HCOCHO+H₂O...H₂SO₄和HCOCHO+H₂O+H₂SO₄五个路径的反应机理和速率常数进行了研究.计算结果表明硫酸具有较强的催化能力,能显著减小乙二醛水化反应的能垒,在CCSD(T)/6-311++G(3df,3pd)//M06-2X/6-311++G(3df,3pd)理论水平,当硫酸分子参与乙二醛水化反应时,反应能垒从37.15 kcal/mol减少至7.08 kcal/mol.在室温条件下,硫酸催化乙二醛水化反应的反应速率1.34×10^-11 cm³/(molecule.s),是等量水分子参与乙二醛水化反应的速率的10¹²倍,大于乙二醛与OH自由基反应的反应速率1.10×10^-11 cm³/(molecule.s).这表明大气条件下,硫酸催化乙二醛水化反应可以发生,同乙二醛与OH自由基反应相竞争.     

Structures of proton solvates in the HCl-H2O-(CH3)2NCHO system as determined by IR spectroscopy and quantum-chemical calculations

The structures of proton solvates in the HCl-H₂O-(CH₃)₂NCHO (DMFA) system at H₂O: DMFA ratios ranging from 1: 1 to 21: 1 are studied by the IR spectroscopy method. It is demonstrated that H₂O?H⁺?OH₂ ions and (CH₃)₂NCHO?H⁺?OH₂ mixed solvates with a strong quasi-symmetrical hydrogen bond are formed in solutions. With an increase in the DMFA concentration, the fraction of H₅O ₂ ⁺ ions decreases. At HCl: H₂O ≥ 1: 3 and arbitrary DMFA concentrations, only mixed proton solvates are formed. The continuous absorption coefficients for the (CH₃)₂NCHO?H⁺?OH₂ ions are determined. The results obtained are compared with the results of quantum-chemical calculations of the structure and relative stability of the (DMFA) _m H⁺(H₂O) _n (m = 0–2, n = 0–3) positively charged complexes which were performed by the B3LYP/6-31++G(d,p) DFT method. We identified 19 stable configurations with chain, cyclic, and branched structures. Most of these configurations contain the (CH₃)₂NCHO?H⁺?OH₂ fragment. The parameters of the O?H⁺?O bridge show that some configurations have a strong quasi-symmetrical hydrogen bond. In some cases, the proton is located between two DMFA molecules. The H₂O?H⁺?OH₂ bridge is observed in none of the stable configurations of the (DMFA) _m H⁺(H₂O) _n (m ≠ 0) complexes.