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1.
固体聚合物电解质在肉桂醇电解氧化中的应用(II)——后续化学反应在电催化反应中的地位及其影响因素 总被引:4,自引:0,他引:4
对影响肉桂醇电极氧化的各种因素作了进一步的讨论. 实验结果表明固体聚合物电解质内水的含量、pH 以及浸入离子交换膜中的二价锰离子的浓度均对该电极反应的电位以及后续化学反应的速度有很大的影响, 在较高的温度下反应时, 有利手提高生成肉桂醛的电流效率. 相似文献
2.
Dr. Anna Żądło‐Dobrowolska Dr. Szymon Kłossowski Dr. Dominik Koszelewski Daniel Paprocki Prof. Ryszard Ostaszewski 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(46):16684-16689
The application of the Ugi reaction to the construction of new peptide scaffolds is an important goal of organic chemistry. To date, there are no examples of the Ugi reaction being performed with a cyclic imine and amine simultaneously. The application of 2‐substituted cyclic imines in an enzymatic three‐component Ugi‐type reaction provides an elegant and attractive synthesis of substituted pyrrolidine and piperidine derivatives in up to 60 % yield. Results on studies of the selection of an enzyme, amount of water, and solvent used in a novel three‐component Ugi reaction and the limitations thereof are reported herein. The presented methodology exploiting enzyme promiscuity in the multicomponent reaction fulfills the requirements associated with green chemistry. Several methods, such as isotope labeling and enzyme inhibition, were used to probe the possible mechanism of this complex synthesis. This research is the first example of an enzyme‐catalyzed Ugi‐type reaction with an imine, amine, and isocyanide. 相似文献
3.
PG McGarraugh RC Johnston A Martínez-Muñoz PH Cheong SE Brenner-Moyer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(34):10742-10752
A new cascade reaction involving an iminium-catalyzed intramolecular oxa-Michael addition followed by an enamine-catalyzed intermolecular Michael addition is reported herein. This cascade reaction generates enantiopure, highly functionalized tetrahydropyrans and tetrahydrofurans in a one-pot reaction and in up to 89?% combined yield and up to 99?% ee. This cascade reaction is catalyzed by diaryl prolinol silyl ethers, which are a privileged class of catalysts. The stereochemical outcome of these cascade reactions is unprecedented. Computational studies indicate that this stereochemical outcome arises from nonclassical hydrogen-bonding interactions between the electrophile and the substrate, and from entropic considerations of preorganization. The unprecedented configurations of the cascade products, combined with the computational models, reveal for the first time that asymmetric induction by diaryl prolinol silyl ether catalysts is not always exclusively reagent controlled. The stereochemical outcome also arises from a kinetic resolution or dynamic kinetic resolution of the β-stereocenter through an enamine-catalyzed intermolecular reaction. This unprecedented organocascade reaction mechanism may be adaptable to diaryl prolinol silyl ether-catalyzed cascade reactions, in which both the iminium- and enamine-catalyzed steps are intermolecular, an underdeveloped type of cascade reaction. 相似文献
4.
The spontaneous reaction between microrods of an organic semiconductor molecule, copper 7,7,8,8-tetracyanoquinodimethane (CuTCNQ) with [AuBr(4)](-) ions in an aqueous environment is reported. The reaction is found to be redox in nature which proceeds via a complex galvanic replacement mechanism, wherein the surface of the CuTCNQ microrods is replaced with metallic gold nanoparticles. Unlike previous reactions reported in acetonitrile, the galvanic replacement reaction in aqueous solution proceeds via an entirely different reaction mechanism, wherein a cyclical reaction mechanism involving continuous regeneration of CuTCNQ consumed during the galvanic replacement reaction occurs in parallel with the galvanic replacement reaction. This results in the driving force of the galvanic replacement reaction in aqueous medium being largely dependent on the availability of [AuBr(4)](-) ions during the reaction. Therefore, this study highlights the importance of the choice of an appropriate solvent during galvanic replacement reactions, which can significantly impact upon the reaction mechanism. The reaction progress with respect to different gold salt concentration was monitored using Fourier transform infrared (FT-IR), Raman, and X-ray photoelectron spectroscopy (XPS), as well as XRD and EDX analysis, and SEM imaging. The CuTCNQ/Au nanocomposites were also investigated for their potential photocatalytic properties, wherein the destruction of the organic dye, Congo red, in a simulated solar light environment was found to be largely dependent on the degree of gold nanoparticle surface coverage. The approach reported here opens up new possibilities of decorating metal-organic charge transfer complexes with a host of metals, leading to potentially novel applications in catalysis and sensing. 相似文献
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A new cascade reaction involving an intramolecular Michael addition followed by an alkyne carbocyclization is presented. The reaction is promoted by a substoichiometric amount of KHMDS and represents one of the rare examples where the carbocyclization of an unactivated alkyne is mediated by an alkali metal base, under mild conditions. The reaction allows the generation of functionally dense, stereochemically defined, tricyclic structures possessing three adjacent stereocenters in good yields and with high stereoselectivity. 相似文献
8.
Angela Kinnell Thomas Harman Matilda Bingham Alan Berry Adam Nelson 《Tetrahedron》2012,68(37):7719-7722
A one-pot, three-component process is described which involves both organo- and enzyme-catalysed carbon–carbon bond-forming steps. In the first step, an organocatalyst catalyses the aldol reaction between acetaldehyde and a glyoxylamide. After dilution with additional aqueous buffer, and addition of pyruvate and an aldolase enzyme variant, a second aldol reaction occurs to yield a final product. Crucially, it was possible to develop a reaction in which both the organo- and enzyme-catalysed reactions could be performed in the same aqueous buffer system. The reaction described is the first example of a one-pot, three-component reaction in which the two carbon–carbon bond-forming processes are catalysed using the combination of an organocatalyst and an enzyme. 相似文献
9.
Richardson RD Desaize M Wirth T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(23):6745-6754
By detailed study of the possible side reactions in the previously reported aziridination of alkenes with N-aminoheterocycles mediated by hypervalent iodine reagents, the requirements to make this reaction catalytic in iodoarene have been determined. The reaction requires an oxidant that will oxidise iodoarenes but that does not oxidise alkenes, but it is possible that no such oxidant actually exists! A method in which the hypervalent iodine reagent can be recycled without the need for reisolation is possible. Further study into the mechanism of this reaction gives tentative evidence that the reaction proceeds through formation of an aminoiodane that reacts directly with the alkene, contrary to previous literature reports in which an acetoxyamine intermediate is suggested. The temperature effect of this reaction is remarkable. 相似文献
10.
Changing the dienophile moiety of an intramolecular Diels-Alder (IMDA) cycloaddition from an allyl ether to an allenyl ether can dramatically change the regioselectivity. We hereby show by density functional theory computations that such unprecedented divergence is produced by an underlying change in the mechanism of the reaction. The allyl ether yields a fused tetrahydrofuran through a classical Diels-Alder reaction, whereas the allenyl ether yields a (methylidene)tetrahydropyran through a stepwise process. The latter reaction involves an extreme asynchronism in the bond-forming events with a diradicaloid intermediate that is stabilized by conjugation and synergistic (captodative) effects. Comparison with intermolecular model D-A reactions, which are concerted processes with various degrees of asynchrony, helps explain the change in regioselectivity for the IMDA reaction of allyl systems and the shift in mechanism for the IMDA reaction of the allenyl derivatives studied. 相似文献
11.
An excellent utility of Schmidt reaction of aldehydes to access corresponding nitriles in an instantaneous reaction is demonstrated. The reaction of aldehydes with NaN(3) and TfOH furnishes the corresponding nitriles in near quantitative yields and tolerates a variety of electron-withdrawing and electron-donating substituents on the substrates. Formanilides, a common side product in Schmidt reaction, is not observed in this reaction. Besides these advantages, the salient feature of this reaction is that it exhibits a remarkable chemoselectivity, as acid and ketone functionalities are well tolerated under the reaction conditions. The reaction is easily scalable, high yielding, and nearly instantaneous. 相似文献
12.
湿法脱硫中亚硫酸盐非催化氧化本征动力学 总被引:1,自引:0,他引:1
亚硫酸盐的氧化是湿法烟气脱硫工艺中的重要过程. 利用间歇式反应装置, 研究了亚硫酸盐非催化氧化的本征反应动力学. 结果表明, 该反应分为两个阶段进行, 即富氧区的快速反应和贫氧区的慢速反应. 在富氧区, 亚硫酸盐和溶解氧的分级数分别为1.0和1.0, 反应的表观活化能为49.3 kJ•mol-1; 在贫氧区, 亚硫酸盐和溶解氧的分级数分别为2.0和0, 反应的表观活化能为122.6 kJ•mol-1. 对反应的机理进行了预测, 结果与实验现象有较好的吻合. 相似文献
13.
Mohammad Salmani Eskandar Keshavarz Alamdari Sadegh Firoozi 《Journal of Thermal Analysis and Calorimetry》2017,128(3):1385-1390
Dissociation of hematite is an undesirable reaction for iron ore pelletizing process leading to severe deterioration in compressive cold strength and reducibility factors. It was shown that raising temperature in an induration machine would cause hematite’s dissociation, which is either present in the primary ore or formed by oxidation of magnetite in the feed. The oxidation reaction of magnetite is exothermic, which complicates temperature control within the non-isothermal area of preheating. Kinetics of the dissociation reaction is the temperature’s primary function, which controls the extent of the reaction. Pure hematite samples were subjected to several runs of thermal analysis carried out under both air and inert atmosphere, in order to achieve a comprehensive knowledge about the temperature dependencies of dissociation kinetics. Due to the observed uniformity, isoconversional methods were chosen in the present work over isothermal and non-isothermal for calculation of kinetic parameters of the reaction. Respectively, activation energy values of hematite dissociation were found to be 324 and 382 kJ mol?1 in inert and air atmosphere. The high value of activation energy implies strong dependency of the single-step reaction rate on the temperature. It was also observed that the forward reaction had higher activation energy than the backward reaction; hence, an increase in temperature results in an overall acceleration of the dissociation reaction. 相似文献
14.
Salinas-Olvera JP Gómez RM Cortés-Guzman F 《The journal of physical chemistry. A》2008,112(13):2906-2912
Hydroformylation is the transformation of an alkene to an aldehyde via the addition of both hydrogen and carbon monoxide. The final aldehyde has one more carbon atom than the precursor alkene. Two isomeric products can result. The regiochemistry of the hydroformylation reaction is believed to be controlled by the olefin insertion step. A reaction mechanism is usually studied by finding the reactants, products, intermediates, and transition states. Alternatively, a chemical reaction can be studied from the redistribution of the electron density along the reaction path connecting the stationary points. The aim of this work is to describe the reaction mechanism of the insertion process by the structural evolution defined by the changes in the electron density during the reaction. 相似文献
15.
对影响肉桂醇电极氧化的各种因素作了进一步的讨论.实验结果表明固体聚合物电解质内水的含量、pH 以及浸入离子交换膜中的二价锰离子的浓度均对该电极反应的电位以及后续化学反应的速度有很大的影响,在较高的温度下反应时,有利手提高生成肉桂醛的电流效率. 相似文献
16.
A reaction of hydrocarbons oxidation in the liquid phase is treated theoretically. The reaction system under discussion is a flow reactor, to the inlet of which the hydrocarbon is constantly delivered in the mixture with an inhibitor under oxygen saturation conditions; the reaction mixture constantly flows from the chamber at the same rate. The reaction gives rise to radicals that can subsequently recombine. It is shown that under certain conditions in this reaction system, three steady states may arise, two of which are stable and the third state is unstable. By varying rate constants of radical reactions by means of an external magnetic field, one can disturb the steady state stability and transfer the system to another steady state, which will be accompanied by an abrupt change in the concentration of reacting substances. 相似文献
17.
Sahasrabudhe K Gracias V Furness K Smith BT Katz CE Reddy DS Aubé J 《Journal of the American Chemical Society》2003,125(26):7914-7922
An asymmetric equivalent of the Schmidt reaction permits stereocontrol in ring expansions of symmetrical cyclohexanones. The procedure involves the reaction of chiral 1,2- and 1,3-hydroxyalkyl azides with ketones under acid catalysis; the initial reaction affords an iminium ether that can be subsequently opened with base. A systematic study of this reaction is reported, in which ketone substrates, chiral hydroxyalkyl azides, and reaction conditions are varied. Selectivities as high as ca. 98:2 are possible for the synthesis of substituted caprolactams, with up to 1,7-stereoselection involved in the overall process. The fact that either possible migrating carbon is electronically identical provides an unusual opportunity to study a ring-expansion reaction controlled entirely by stereoelectronic factors. The mechanism of the reaction and the source of its stereoselectivity are also discussed. 相似文献
18.
The Gomberg-Bachmann reaction is an intermolecular aryl-aryl cross-coupling reaction using an arenediazonium salt and an arene. This digest review surveys recent advances in the Gomberg-Bachmann reaction. More specifically, it focuses on reaction systems that include 1) transition-metal-induced systems, 2) organic promoter-induced systems, 3) electrolytic systems, 4) photoreaction systems, and 5) hybrid systems consisted of a photoredox and a transition-metal catalyst. 相似文献
19.
We study the effects of an external electric field on both the motion of the reaction zone and the spatial distribution of the reaction product, C, in an irreversible A- + B+ -->C reaction-diffusion process. The electrolytes A identical with (A+,A-) and B identical with (B+,B-) are initially separated in space and the ion-dynamics is described by reaction-diffusion equations obeying local electroneutrality. Without an electric field, the reaction zone moves diffusively leaving behind a constant concentration of C's. In the presence of an electric field which drives the reagents towards the reaction zone, we find that the reaction zone still moves diffusively but with a diffusion coefficient which slightly decreases with increasing field. The important electric field effect is that the concentration of C's is no longer constant but increases linearly in the direction of the motion of the front. The case of an electric field of reversed polarity is also discussed and it is found that the motion of the front has a diffusive as well as a drift component. The concentration of C's decreases in the direction of the motion of the front, up to the complete extinction of the reaction. Possible application of the above results to the understanding of the formation of Liesegang patterns in an electric field is briefly outlined. 相似文献