Catalytic effect of copper on the hexacyanoferrate(III)-cyanide redox reaction-I The uncatalysed and catalysed reactions

A kinetic study of the hexacyanoferrate(III)-cyanide redox reaction has been made in connection with development of a new catalytic method for copper. The reaction kinetics change with time from first- to second-order dependence with respect to hexacyanoferrate(III). The reaction is nearly inverse first-order with respect to hexacyanoferrate(II) and first-order with respect to cyanide. The reaction shows a strong positive primary salt effect, but a very small increase in the reaction rate with temperature is found. A parallel reaction proceeds with a first-order dependence with respect to hydroxide. A tentative mechanism is proposed for the first reaction, involving the formation of cyanogen radicals. The second reaction corresponds to the well-known decomposition of hexacyanoferrate(III) in alkaline medium. The catalysed reaction exhibits similar kinetics with respect to hexacyanoferrate(II) and (III) but is zero-order with respect to cyanide and hydroxide and first-order with respect to catalyst. The proposed mechanism involves two consecutive interactions of the hexacyanoferrate(III) with copper(I) and with copper(II) cyanide complexes respectively, followed by a 2-electron oxidation of a co-ordinatively bridging cyanide group.     

Impact of water on the OH + HOCl reaction

The effect of a single water molecule on the OH + HOCl reaction has been investigated. The naked reaction, the reaction without water, has two elementary reaction paths, depending on how the hydroxyl radical approaches the HOCl molecule. In both cases, the reaction begins with the formation of prereactive hydrogen bond complexes before the abstraction of the hydrogen by the hydroxyl radical. When water is added, the products of the reaction do not change, and the reaction becomes quite complex yielding six different reaction paths. Interestingly, a geometrical rearrangement occurs in the prereactive hydrogen bonded region, which prepares the HOCl moiety to react with the hydroxyl radical. The rate constant for the reaction without water is computed to be 2.2 × 10(-13) cm(3) molecule(-1) s(-1) at room temperature, which is in good agreement with experimental values. The reaction between ClOH···H(2)O and OH is estimated to be slower than the naked reaction by 4-5 orders of magnitude. Although, the reaction between ClOH and the H(2)O···HO complex is also predicted to be slower, it is up to 2.2 times faster than the naked reaction at altitudes below 6 km. Another intriguing finding of this work is an interesting three-body interchange reaction that can occur, that is HOCl + HO···H(2)O → HOCl···H(2)O + OH.     

The electrochemical reaction mechanism of selenocystine on selenium-gold film modified glassy carbon electrode

A simple and selective voltammetric method based on selenium-gold film modified glassy carbon electrode has been developed for investigating electrochemical reaction mechanism of selenocystine. With N₂ saturated, redox reactions between selenocystine (SeC) and selenocysteine (SeCys) were judged to be two simple electron-transfer processes. With air saturated, the reduction reaction was diagnosed to be EC catalytic reaction (the chemical oxidation reaction of the SeCys by O₂ (C) following the electron-transfer reaction (E)) and oxidation reaction is a simple electron-transfer process. With pure O₂ saturated, only reduction peak was observed and the reaction was judged to be EC catalytic reaction. The electron-transfer numbers of redox reaction were calculated to be 2 by chronocoulometry and rotating disk electrode.     

Reaction mechanisms and structural characterization of the reactive intermediates observed after the photolysis of 3-(hydroxymethyl)benzophenone in acetonitrile, 2-propanol, and neutral and acidic aqueous solutions

Nanosecond time-resolved resonance Raman (ns-TR(3)) spectroscopy was employed to investigate the photoinduced reactions of 3-(hydroxymethyl)benzophenone (1) in acetonitrile, 2-propanol, and neutral and acidic aqueous solutions. Density functional theory calculations were utilized to help the interpretation of the experimental spectra. In acetonitrile, the neutral triplet state 1 [denoted here as (m-BPOH)(3)] was observed on the nanosecond to microsecond time scale. In 2-propanol this triplet state appeared to abstract a hydrogen atom from the solvent molecules to produce the aryphenyl ketyl radical of 1 (denoted here as ArPK of 1), and then this species underwent a cross-coupling reaction with the dimethylketyl radical (also formed from the hydrogen abstraction reaction) to form a long-lived light absorbing transient species that was tentatively identified to be mainly 2-(4-(hydroxy(3-(hydroxymethyl)phenyl)methylene)cyclohexa-2,5-dienyl)propan-2-ol. In 1:1 H(2)O:CH(3)CN aqueous solution at neutral pH, (m-BPOH)(3) reacted with water to produce the ArPK of 1 and then underwent further reaction to produce a long-lived light absorbing transient species. Three photochemical reactions appeared to take place after 266 nm photolysis of 1 in acidic aqueous solutions, a photoreduction reaction, an overall photohydration reaction, and a novel photoredox reaction. TR(3) experiments in 1:1 H(2)O:CH(3)CN aqueous solution at pH 2 detected a new triplet biradical species, which is associated with an unusual photoredox reaction. This reaction is observed to be the predominant reaction at pH 2 and seems to face competition from the overall photohydration reaction at pH 0.     

三苯基环戊二烯扩环反应研究

研究在高氯酸银作用下,三苯基环戊二烯扩环氧化生成三苯基取代吡喃盐的反应,并初步探讨了反应机理     

手性双噁唑啉配体在不对称合成中的应用

双噁唑啉手性配体已广泛用于不对称Henry反应、环丙烷化反应、Aldol反应、烷基化反应、环加成反应中,并表现出很高的对映选择性和催化活性,成为最有用的手性配体之一。文章综述了近10年来双噁唑啉手性配体及高分子受载手性双噁唑啉在不对称合成中的研究进展。     

Rapid solid-state metathesis routes to aluminum nitride

Metathesis (exchange) reactions offer the possibility of controlling temperature through a judicious choice of precursors. Here, a reaction between AlCl(3) and Ca(3)N(2) is found to produce phase-pure aluminum nitride (AlN) in seconds. The CaCl(2) byproduct salt, whose formation drives this highly exothermic reaction, is simply washed away after reaction completion. SEM images demonstrate that the AlN product is a micron-sized powder, while TEM shows well-formed crystallites. Thermodynamic calculations indicate that a reaction temperature of 2208 K could be reached under adiabatic conditions. Using an in situ thermocouple and a stainless steel reactor vessel to hold the precursors, a reaction temperature of 1673 K is measured 0.8 s after initiation. Switching to a thermally insulating ceramic vessel produces a maximum reaction temperature of 2010 K because of the more nearly adiabatic conditions. The high reaction temperature appears to be critical to forming phase-pure AlN. Experiments with Li(3)N, instead of Ca(3)N(2), produce lower temperatures (1513 K), resulting in both Al and Al(2)O(3) impurities.     

Water formation reaction on Pt(111): role of the proton transfer

The catalytic water formation reaction on Pt(111) was investigated by kinetic Monte Carlo simulations, where the interaction energy between reaction species and the high mobility of H(2)O molecule was considered. Results obtained clearly reproduce the scanning tunneling microscopy images which show that the reaction proceeds via traveling the reaction fronts on the O-covered Pt(111) surface by creating H(2)O islands backwards. The reaction front is a mixed layer of OH and H(2)O with a (square root 3 x square root 3)R30(o) structure. Coverage change during the reaction is also reproduced in which the reaction consists of three characteristic processes, as observed by the previous experiments. The simulation also revealed that the proton transfer from H(2)O to OH plays an important role to propagate the water formation.     

On the effect of copper (II) and chloride ions on the iodate-hydrogen peroxide reaction in the presence and absence of manganese (II)

The effect of copper (II) and chloride ions on the manganese (II) catalyzed iodate-peroxide reaction has been examined with reference to the hydrogen peroxide-iodic acid-manganese (II)-organic species oscillatory reaction. The observations are considered to provide evidence for iodine dioxide as the key intermediate in the manganese (II) catalyzed reaction. Kinetic data for the copper (II) catalyzed reaction are reported.     

Reaction of stabilized Criegee intermediates from ozonolysis of limonene with sulfur dioxide: ab initio and DFT study

The mechanism of the reaction of the sulfur dioxide (SO(2)) with four stabilized Criegee intermediates (stabCI-CH(3)-OO, stabCI-OO, stabCIx-OO, and stabCH(2)OO) produced via the ozonolysis of limonene have been investigated using ab initio and DFT (density functional theory) methods. It has been shown that the intermediate adduct formed by the initiation of these reactions may be followed by two different reaction pathways such as H migration reaction to form carboxylic acids and rearrangement of oxygen to produce the sulfur trioxide (SO(3)) from the terminal oxygen of the COO group and SO(2). We found that the reaction of stabCI-OO and stabCH(2)OO with SO(2) can occur via both the aforementioned scenarios, whereas that of stabCI-CH(3)-OO and stabCIx-OO with SO(2) is limited to the second pathway only due to the absence of migrating H atoms. It has been shown that at the CCSD(T)/6-31G(d) + CF level of theory the activation energies of six reaction pathways are in the range of 14.18-22.59 kcal mol(-1), with the reaction between stabCIx-OO and SO(2) as the most favorable pathway of 14.18 kcal mol(-1) activation energy and that the reaction of stabCI-OO and stabCH(2)OO with SO(2) occurs mainly via the second reaction path. The thermochemical analysis of the reaction between SO(2) and stabilized Criegee intermediates indicates that the reaction of SO(2) and stabilized Criegee intermediates formed from the exocyclic primary ozonide decomposition is the main pathway of the SO(3) formation. This is likely to explain the large (~100%) difference in the production rate in the favor of the exocyclic compounds observed in recent experiments on the formation of H(2)SO(4) from exocyclic and endocyclic compounds.     

Kinetic study of Berthelot reaction steps in the absence and presence of coupling reagents

Several reaction steps in the Berthelot reaction for the determination of ammonia have been separately studied. A reaction order of two has been confirmed for the reaction between HOCl and NH(3). The rate constant for this reaction has been determined to be 3.2 x 10(6)l.mole(-1).sec(-1). The first evidence for the formation of benzoquinonechlorimine is presented. Pentacyanoferrate coupling reagents which accelerate the production of indophenol have been found to operate on the reaction between NH(2)Cl and phenol. The rate constant for the final step of the reaction sequence has been determined to be 5.3 x 10(-3)l.mole(-1).sec(-1). A reaction between chlorimine and pentacyanoferrate compounds has been found to be responsible for the formation of a green product in the presence of excess of coupling reagent.     

Tandem Blaise-Nenitzescu reaction: one-pot synthesis of 5-hydroxy-α-(aminomethylene)benzofuran-2(3H)-ones from nitriles

In contrast to the reaction of benzoquinones with β-enaminoesters providing indoles (Nenitzescu reaction), the tandem one-pot reaction of the Blaise reaction intermediate, zinc bromide complex of β-enaminoesters, with benzoquinone affords 5-hydroxy-α-(aminomethylene)benzofuran-2(3H)-ones in good to excellent yields (tandem Blaise-Nenitzescu reaction).     

Heterogeneous interactions of calcite aerosol with sulfur dioxide and sulfur dioxide-nitric acid mixtures

The heterogeneous chemistry of sulfur dioxide with CaCO(3) (calcite) aerosol as a function of relative humidity (RH) has been studied under isolated particle conditions in an atmospheric reaction chamber using infrared absorption spectroscopy. The reaction of SO(2) with calcite produced gas phase CO(2) as a product in addition to the conversion of the particulate carbonate to sulfite. The reaction extent was found to increase with elevated RH, as has been observed for the similar reaction with HNO(3), but much higher relative humidities were needed to significantly enhance the reaction. Mixed experiments in which calcite aerosol was exposed to both HNO(3) and SO(2) were also performed. The overall reaction extent at a given relative humidity did not appear to be increased by having both reactant gases present. The role of carbonate aerosol as an atmospheric sink for sulfur dioxide and particulate nitrogen and sulfur correlations are discussed.     

Kinetics of the O + ICN reaction

The kinetics of the O + ICN reaction was studied using a relative rate method, with O + C(2)H(2) as the competing reaction. Carbon monoxide products formed in the competing reaction and subsequent secondary chemistry were detected as a function of reagent ICN pressure to obtain total rate constants for the O + ICN reaction. Analysis of the experimental data yields rate constants of k(1) = (3.7 ± 1.0 to 26.2 ± 4.0) × 10(-14) cm(3) molecule(-1) s(-1) over the total pressure range 1.5-9.5 Torr. Product channel NCO + I, the only bimolecular exothermic channel of the reaction, was investigated by detection of N(2)O in the presence of NO and found to be insignificant. An ab initio calculation of the potential energy surface (PES) of the reaction at the CCSD(T)/CEP-31G//DFT-B3LYP/CEP-31G level of theory was also performed. The pathways leading to bimolecular product channels are kinetically unfavorable. Formation and subsequent stabilization of an ICNO adduct species appears to dominate the reaction, in agreement with the experimentally observed pressure dependent rate constants.     

Thermal decomposition of CF3 and the reaction of CF2 + OH --> CF2O + H

The reflected shock tube technique with multipass absorption spectrometric detection (at a total path length of approximately 1.75 m) of OH-radicals at 308 nm has been used to study the dissociation of CF3-radicals [CF3 + Kr --> CF2 + F + Kr (a)] between 1,803 and 2,204 K at three pressures between approximately 230 and 680 Torr. The OH-radical concentration buildup resulted from the fast reaction F + H2O --> OH + HF (b). Hence, OH is a marker for F-atoms. To extract rate constants for reaction (a), the [OH] profiles were modeled with a chemical mechanism. The initial rise in [OH] was mostly sensitive to reactions (a) and (b), but the long time values were additionally affected by CF2 + OH --> CF2O + H (c). Over the experimental temperature range, rate constants for (a) and (c) were determined from the mechanistic fits to be kCF3+Kr = 4.61 x 10-9 exp(-30,020 K/T) and kCF2+OH = (1.6 +/- 0.6) x 10-10, both in units of cm3 molecule-1 s-1. Reaction (a), its reverse recombination reaction reaction (-a), and reaction (c) are also studied theoretically. Reactions (c) and (-a) are studied with direct CASPT2 variable reaction coordinate transition state theory. A master equation analysis for reaction (a) incorporating the ab initio determined reactive flux for reaction (-a) suggests that this reaction is close to but not quite in the low-pressure limit for the pressures studied experimentally. In contrast, reaction (c) is predicted to be in the high-pressure limit due to the high exothermicity of the products. A comparison with past and present experimental results demonstrates good agreement between the theoretical predictions and the present data for both (a) and (c).     

氯甲交联基聚苯乙烯微球的氨甲基化改性及其席夫碱型螯合树脂微球的制备

以氯甲基化交联聚苯乙烯(CMCPS)微球为出发物质,首先在催化剂KI存在下,与六次甲基四胺(HMTA)进行Delepine反应,制得氨基化改性的聚苯乙烯微球AMCPS;然后再使微球AMCPS与水杨醛(SA)发生Schiff碱反应,制备了Schiff碱型螯合树脂SACPS微球,采用红外光谱法表征了其化学结构。 重点研究了CMCPS微球氨基化改性Delepine反应的影响因素,探讨了反应机理。 研究结果表明,催化剂KI对CMCPS微球表面的苄氯基团与HMTA之间的Delepine反应,具有很强的催化作用;使用极性较强的溶剂DMSO及在较高的温度(80 ℃)下反应,氯甲基转变为氨甲基的效率高;Schiff碱型螯合树脂SACPS对Cu2+离子具有良好的螯合能力。     

Effect of Polyethyleneimine Assisting the Growth of Eu-doped ZnO Nanowire Arrays in Mannich Reaction

In study on the growth reaction mechanism of Eu-doped ZnO nanowire(NW), the intermedium of reaction is characterized by measures such as FTIR. Besides, the influences of polyethyleneimine(PEI) on morphology, structure and photoelectric property of NW are observed by SEM, TEM, XRD, UV-vis and PL spectrum. According to the result, it manifests that Eu-doped ZnO NW array growth response experiences six mutually associated reaction processes in PEI-HMTA system:(a) chelation reaction of PEI and Zn~(2+) Eu~(3+);(b) protonation reaction of PEI and NH_3;(c) decomposition reaction of hexamethylenetetramine(HMTA);(d) Mannich reaction of HCHO and PEI;(e) formation of precursor of Eu-doped ZnO;(f) dehydration condensation of Eu-doped ZnO precursors, further forming a doped ZnO NW array. Among them, PEI is the key factor of the whole doping growth reaction process. It both plays a role in modifying the growth of ZnO NW and makes it become longer and thinner. In the meantime, it also facilitates doping of Eu and enables ZnO NW to capture more photoelectrons and higher transmission rate, which is critical to improve photovoltaic performance of optoelectronic devices.     

氢原子共线交换反应的动力学计算I.Cl与HCl反应几率的振荡现象研究

我们利用超球坐标对共线Cl+HCl(V-3)→ClH(V'≤3)+Cl作了一维精确量子计算,计算所用势能面是LEPS型,Et=-3.23KJ/mol, 得到了态态反应几率等动力学信息, 通过分析结果发现, 反应是振动绝热的, 即以对角(V'-V')反应几率为主,非对角(V' V')反应几率小于0.1, 反应几率随总能量表现出强裂地振荡, 在有阱的势能面上动力学共振增强。     

Dynamics of the gas-phase reactions of chloride ion with fluoromethane: high excess translational activation energy for an endothermic S(N)2 reaction.

Guided ion beam tandem mass spectrometry techniques are used to examine the competing product channels in the reaction of Cl(-) with CH(3)F in the center-of-mass collision energy range 0.05-27 eV. Four anionic reaction products are detected: F(-), CH(2)Cl(-), FCl(-), and CHCl(-). The endothermic S(N)2 reaction Cl(-) + CH(3)F --> CH(3)Cl + F(-) has an energy threshold of E(0) = 181 +/- 14 kJ/mol, exhibiting a 52 +/- 16 kJ/mol effective barrier in excess of the reaction endothermicity. The potential energy of the S(N)2 transition state is well below the energy of the products. Dynamical impedances to the activation of the S(N)2 reaction are discussed, including angular momentum constraints, orientational effects, and the inefficiency of translational energy in promoting the reaction. The fluorine abstraction reaction to form CH(3) + FCl(-) exhibits a 146 +/- 33 kJ/mol effective barrier above the reaction endothermicity. Direct proton transfer to form HCl is highly inefficient, but HF elimination is observed above 268 +/- 95 kJ/mol. Potential energy surfaces for the reactions are calculated using the CCSD(T)/aug-cc-pVDZ and HF/6-31+G(d) methods and used to interpret the dynamics.     

A highly enantioselective hetero-Diels-Alder reaction of aldehydes with Danishefsky's diene catalyzed by chiral titanium(IV) 5,5',6,6',7,7',8,8'-octahydro-1,1'-bi-2-naphthol complexes

The catalytic effect of chiral Lewis acids on the hetero-Diels-Alder reaction between aldehydes and Danishefsky's diene (1) has been investigated. A variety of combinations of different ligands and Lewis acids have been examined as catalysts for the hetero-Diels-Alder reaction between benzaldehyde and 1, and it has been found that the readily accessible Ti(IV)-H(8)-BINOL (TiHBOL) complex is a very effective catalyst for the reaction, leading to products with very high enantioselectivity (up to 99% ee) and yield (92%). The hetero-Diels-Alder reaction of other aldehydes with 1 under the catalysis of TiHBOL is a general reaction which proceeds well with very high enantioselectivity and isolated yield for various aldehydes at 0 degrees C to room temperature. Based on the experimental results, the proposed mechanism of the hetero-Diels-Alder reaction and the dihedral angle effects of ligands are discussed.