Theoretical Study of the Reaction Mechanism and Kinetics of HO2 with XCHO (X = F,Cl)

The reactions of HO₂ with FCHO and ClCHO have been theoretically investigated by combining beyond‐CCSD(T) electronic structure benchmarks, validated density functional theory, and canonical variational transition state theory with small‐curvature tunneling, coupled‐torsions anharmonicity, and high‐frequency anharmonicity. This investigation explores three different reaction mechanisms: radical addition plus a hydrogen transfer, radical addition, and hydrogen abstraction. The calculated results show that the dominant reaction pathway is the terminal oxygen atom of HO₂ added to the carbon atom of XCHO (X = F, Cl) and simultaneously the hydrogen atom of HO₂ transferred to the oxygen atom of the C=O group in XCHO. The reaction barriers of the other reaction pathways are so high that these processes are negligible in the atmosphere. Although the barrier height of the dominant reaction pathway in the HO₂ + FCHO reaction is 0.61 kcal/mol higher than that of the corresponding HO₂ + ClCHO reaction, the HO₂ + FCHO reaction is faster than the HO₂ + ClCHO reaction because the variational effects of HO₂ + ClCHO is more obvious than that of the HO₂ + FCHO. The present results show that the HO₂ + FCHO reaction may be important in the atmosphere. The present results should be useful in evaluating the atmospheric fate of XCHO (X = F, Cl).     

Pulse radiolysis study on the mechanisms of reactions of CCl3OO. radical with quercetin, rutin and epigallocatechin gallate

The mechanisms of reactions between CC1₃OO^? radical and quercetin, rutin and epigallocatechin gallate (EGCG) have been studied using pulse radiolytic technique. It is suggested that the electron transfer reaction is the main reaction between CC1₃OO^? radical and rutin, EGCG, but there are two main pathways for the reaction of CC1₃OO^? radical with quercetin, one is the electron transfer reaction, the other is addition reaction. The reaction rate constants were determined. It is proved that quercetin and rutin are better CC1₃OO^? radical scavengers than EGCG.     

单分子水对H_2O_2+Cl气相反应影响的理论研究

在aug-cc-pVTZ基组下采用CCSD(T)和B3LYP方法,研究了H2O2+Cl反应,并考虑在大气中单个水分子对该反应的影响.结果表明,H2O2+Cl反应只存在一条生成产物为HO2+HCl的通道,其表观活化能为10.21kJ·mol-1.加入一分子水后,H2O2+Cl反应的产物并没有发生改变,但是所得势能面却比裸反应复杂得多,经历了RW1、RW2和RW3三条通道.水分子在通道RW1和RW2中对产物生成能垒的降低起显著的负催化作用,而在通道RW3中则起明显的正催化作用.利用经典过渡态理论(TST)并结合Wigner矫正模型计算了216.7-298.2 K温度范围内标题反应的速率常数.结果显示,298.2 K时通道R1的速率常数为1.60×10-13cm3·molecule-1·s-1,与所测实验值非常接近.此外,尽管通道RW3的速率常数kRW3比对应裸反应的速率常数kR1大了46.6-131倍,但该通道的有效速率常数k'RW3却比kR1小了10-14个数量级,表明在实际大气环境中水分子对H2O2+Cl反应几乎没有影响.     

Pyrolysis of trifluoroacetaldehyde. The formation of trifluoromethane and hexafluoroethane

The thermal decomposition of trifluoroacetaldehyde at temperatures f 471 to 519°C has been studied by measuring the rates of formation of CF₃H and C₂F₆. It is concluded that the high-pressure reaction mechanism involves a Rice-Herzfeld reaction scheme with first-order initiation and second-order termination via CF₃ combination. However, a falloff in reaction rates is observed at pressures below 100 mmHg. The Arrhenius parameters of the three rate constants corresponding to the overall reaction, the initiation reaction, and an abstraction reaction have been evaluated.     

Stopped-flow study of the gas-phase reaction of ozone with organic sulfides: Dimethyl sulfide

The autoinhibiting reaction of ozone with dimethyl sulfide (DMS), has been studied at 296°K and 1.1 kPa (8 torr) as a function of the concentrations of both reactants. The major products of the reaction are H₂CO, H₂O, CO, and SO₂. The specific rate of primary attack of O₃ on DMS is immeasurably slow. It is suggested that the rapid overall rate observed for this reaction is due to a chain reaction initiated by the very slow primary reaction. It is concluded that reaction (1) cannot be important under atmospheric conditions and that the major loss process for DMS in the atmosphere is probably reaction with photochemically generated free radicals.     

Pulse radiolysis study on the mechanisms of reactions of CCl3OO. radical with quercetin, rutin and epigallocatechin gallate

The mechanisms of reactions between CC1₃OO^• radical and quercetin, rutin and epigallocatechin gallate (EGCG) have been studied using pulse radiolytic technique. It is suggested that the electron transfer reaction is the main reaction between CC1₃OO^• radical and rutin, EGCG, but there are two main pathways for the reaction of CC1₃OO^• radical with quercetin, one is the electron transfer reaction, the other is addition reaction. The reaction rate constants were determined. It is proved that quercetin and rutin are better CC1₃OO^• radical scavengers than EGCG.     

Multiple‐pathways of carbon dioxide binding by a Lewis acid [B(C6F5)3] and a lewis base [P(tBu)3]: The energy landscape perspective

Using the reaction‐relevant two‐dimensional potential energy surface, an accurate reaction‐pathway mapping and ab inito molecular dynamics, it is shown that CO₂ capture by P(tBu)₃ and B(C₆F₅)₃ species has many nearly degenerate reaction‐routes to take. The explanation of that is in the topography of the transition state (saddle) area. An ensemble of asynchronous reaction‐routes of CO₂ binding is described in fine detail. © 2013 Wiley Periodicals, Inc.     

The reaction between solid lead and chlorine gas

When lead reacts with a chlorine atmosphere the reaction rate shows a logarithmic rate law followed by a parabolic one. Both reaction rates can be explained by assuming that electron holes in the reaction product are rate-determining. In the beginning, the reaction of holes with lead (I) ions on lead ion lattice sites in PbCl₂ is the rate-determining step; later, the transport of holes by diffusion through the growing PbCl₂ layer becomes rate-determining.An oxide layer on the lead before chlorination retards the reaction, while, on the contrary, traces of oxygen in the chlorine gas accelerate the reaction. Both phenomena can be explained by assuming that a mixed compound PbO_1?xCl_2x is formed. It is concluded that the presence of impurities in the system may influence the reaction rate drastically.     

A new reforming process based on CH4 decomposition using a hydrogen-permeating membrane reactor

A new reforming process was studied using Ni/SiO₂ with a hydrogen-permeating membrane reactor. Nickel catalyst supported on SiO₂ is highly active for CH₄-H₂O-O₂ reaction in membrane reactor and the reaction close to CH₄ + 0.35O₂ + 1.3H₂O → CO₂ + 3.3H₂ proceeds at 873 K. Since the selectivity to carbon and CO₂ increased and decreased with decreasing contact time respectively, it is considered that the reaction was started by decomposition of CH₄ followed by oxidation of C and water shift reaction. Therefore, the reaction mechanism was different from so-called autothermal reforming (ATR) reaction.     

A new reforming process based on CH4 decomposition using a hydrogen-permeating membrane reactor

A new reforming process was studied using Ni/SiO₂ with a hydrogen-permeating membrane reactor. Nickel catalyst supported on SiO₂ is highly active for CH₄?H₂O?O₂ reaction in membrane reactor and the reaction close to CH₄+0.35O₂+1.3H₂O→CO₂+3.3H₂ proceeds at 873 K. Since the selectivity to carbon and CO₂ increased and decreased with decreasing contact time respectively, it is considered that the reaction was started by decomposition of CH₄ followed by oxidation of C and water shift reaction. Therefore, the reaction mechanism was different from so-called autothermal reforming (ATR) reaction.     

Theoretical study on the reaction mechanism of CN radical with ketene

The bimolecular single collision reaction potential energy surface of CN radical with ketene (CH2CO) was investigated by means of B3LYP and QCISD(T) methods. The calculated results indicate that there are three possible channels in the reaction. The first is an attack reaction by the carbon atom of CN at the carbon atom of the methylene of CH2CO to form the intermediate NCCH2CO followed by a rupture reaction of the C-C bond combined with -CO group to the products CH2CN CO. The second is a direct addition reaction between CN and CH2CO to form the intermediate CH2C(O)CN followed by its isomerization into NCCH2CO via a CN-shift reaction, and subsequently, NCCH2CO dissociates into CH2CN CO through a CO-loss reaction. The last is a direct hydrogen abstraction reaction of CH2CO by CN radical. Because of the existence of a 15.44 kJ/mol reaction barrier and higher energy of reaction products, the path can be ruled out as an important channel in the reaction kinetics. The present theoretical computation results, which give an available suggestion on the reaction mechanism, are in good agreement with previous experimental studies.     

Heterogeneous aspects of acid hydrolysis of α-cellulose

Hydrolysis of α-cellulose by H₂SO₄ is a heterogeneous reaction. As such the reaction is influenced by physical factors. The hydrolysis reaction is therefore controlled not only by the reaction conditions (acid concentration and temperature) but also by the physical state of the cellulose. As evidence of this, the reaction rates measured at the high-temperature region (above 200°C) exhibited a sudden change in apparent activation energy at a certain temperature, deviating from Arrhenius law. Furthermore, α-cellulose, once it was dissolved into concentrated H₂SO₄ and reprecipitated, showed a reaction rate two orders of magnitude higher than that of untreated cellulose, about the same magnitude as cornstarch. The α-cellulose when treated with a varying level of H₂SO₄ underwent an abrupt change in physical structure (fibrous form to gelatinous form) at about 65% H₂SO₄. The sudden shift of physical structure and reaction pattern in response to acid concentration and temperature indicates that the main factor causing the change in cellulose structure is disruption of hydrogen bonding. Finding effective means of disrupting hydrogen bonding before or during the hydrolysis reaction may lead to a novel biomass saccharification process.     

High-temperature thermodynamics of chemical transport-reactions in the tungsten halophosphonitrile systems

The composition of the gas-phase in the heterogeneous reaction systems W-(PNCl₂)_n and W-(PNBr₂)_n are calculated on a digital computer, based on the concept that thermodynamic equilibrium is achieved at the gas—solid interface and that the rate of reaction is not controlled by reaction kinetics. Allowance is made for the presence of oxygen and the gettering properties of the phosphorus are considered.     

A DFT study on a mutipathways,one product reaction: Initially divergent radical reactions reconverge to form a single product

The mechanism for initially divergent radical reactions reconverging to form a single product is studied using density functional theory calculations. The calculation results suggest that there are six possible pathways from reactants to products. The free energy barriers of the rate‐determining steps of each pathway are almost equal. Thus, different from usual reaction, the selectivity of this reaction is determined by the relative value of free energy barriers of the two competitive reactions, that is, cyclization and bimolecular trapping, rather than that of rate‐determining steps. In all reaction pathways, cyclization reaction is more competitive than bimolecular trapping reaction due to its low free energy barrier. In addition, the free energy barriers of bimolecular trapping reaction between Bu₃SnH and reactants are all lower than that of NC? C₆H₁₁. However, Bu₃SnH is not always suitable due to its large steric repulsion. © 2014 Wiley Periodicals, Inc.     

钴基催化剂催化环己烯氢甲酰化研究

以氯化钴和锰铁合金粉为钴基催化体系的前驱体,研究了该催化剂体系对环己烯氢甲酰化反应制备环己烷基甲醛的催化性能;并考察了溶剂、温度、压力等反应条件的影响.实验结果表明,选用四氢呋喃作为溶剂,反应的活性较高,选择性较好.在反应温度为145℃,合成气压力为8.0MPa,钴与烯烃的物质的量的比为0.01,反应时间为0.5h条件下,能得到环己烯的转化率为89%,环己烷基甲醛的选择性达到96%的结果.     

Theoretical study on the reaction mechanism of (CH<Subscript>3</Subscript>)<Subscript>3</Subscript>CO<Superscript>.</Superscript> radical with NO

The reaction mechanism of (CH₃)₃CO^. radical with NO is theoretically investigated at the B3LYP/6-31G* level. The results show that the reaction is multi-channel in the single state and triplet state. The potential energy surfaces of reaction paths in the single state are lower than that in the triple state. The balance reaction: (CH₃)₃CONO⇔(CH₃)₃CO^.+NO, whose potential energy surface is the lowest in all the reaction paths, makes the probability of measuring (CH₃)₃CO^. radical increase. So NO may be considered as a stabilizing reagent for the (CH₃)₃CO^. radical.     

Two-stage mechanism of the dicarbollyliron redox-reaction at electrode coated with a monolayer of behenic acid and hemin

The dicarbollyliron (Cb₂Fe^-) redox reaction is studied at an amalgamated platinum electrode coated with a monolayer of behenic acid on top of which hemin is adsorbed. The redox reaction of Cb₂Fe^- involves two stages. First, an electrochemical reaction of adsorbed hemin proceeds, which involves the electron transfer through the dielectric monolayer; it is followed by the hemin’s chemical redox reaction with dissolved Cb₂Fe^-. It is shown that the adsorbed hemin transformation, no matter how small, is sufficient for the stimulation of the Cb₂Fe^- redox reaction.     

Is charge development a measure of SN2 transition state structure?

Application of the configuration mixing model to the S_N2 reaction illustrates that charge development in an S_N2 reaction is not linearly related to the position of the transition state along the reaction coordinate.     

八甲基环四硅氧烷阴离子乳液聚合反应的研究

研究了八甲基环四硅氧烷(D_4)在十二烷基本磺酸(DBSA)及其钠盐(Na-DBSA)作用下的阴离子乳液聚合反应,讨论了温度、乳化剂和催化剂用量对反应速度及聚合物分子量的影响。认为该聚合反应包括D_4的水解开环、D_4和羟基硅氧烷的加成及羟基硅氧烷之间的缩合三类基本反应,乳液颗粒表面是主要反应区。     

Fluctuating Storage of the Active Phase in a Mn-Na2WO4/SiO2 Catalyst for the Oxidative Coupling of Methane

Structural dynamics of a Mn-Na₂WO₄/SiO₂ catalyst were detected directly under reaction conditions during the oxidative coupling of methane via in situ XRD and operando Raman spectroscopy. A new concept of fluctuating storage and release of an active phase in heterogeneous catalysis is proposed that involves the transient generation of active sodium oxide species via a reversible reaction of Na₂WO₄ with Mn₇SiO₁₂. The process is enabled by phase transitions and melting at the high reaction temperatures that are typically applied.