Temperature vs. time sequences to palliate deactivation in parallel and in series-parallel with the main reaction: parametric study

The calculation of temperature vs. time sequences to palliate catalyst deactivation in an integral reactor has been studied either by maintaining constant the conversion at the reactor outlet in a simple reaction or by maintaining constant the concentration of a given component at the outlet in a complex reaction system. The experimental systems studied, which are a simple one (dehydration of 2-ethylhexanol) and a complex one (isomerization of cis-butene), have kinetic models of the Langmuir-Hinshelwood-Hougen-Watson type for the main reaction and deactivation, with deactivation by coke dependent on the concentration of the reaction components. In the reaction of dehydration of 2-ethylhexanol deactivation occurs in parallel with the main reaction and in the isomerization of cis-butene deactivation occurs in series-parallel with the main reaction. A parametric study has been carried out for both reaction systems. The sequences calculated have been experimentally proven in an automated reaction apparatus.     

Recent advances in oxidative C–C coupling reaction of amides with carbon nucleophiles

The C–C coupling reaction of N-electron withdrawing group (EWG) protected amides with coupling partners is one of the most important methods for C–C bond formation at the α-position of amides to directly give α-substituted amides. Of the four reactions, namely, the reaction via the generation of carbanion with an electrophile, that via the generation of carbon radical with a radical donor, that via the generation of iminium ion species with a nucleophile (oxidative coupling reaction), and that using a transition metal carbenoid, the oxidative coupling reaction presents a challenge although the reaction products are very useful for the transformation of a wide range of nitrogen-containing derivatives. In this review, recent developments in the oxidative coupling reaction of N-EWG protected amides with nucleophiles are summarized with focus on the reaction using a transition metal, the transition-metal-free reaction, the enantioselective reaction using a chiral catalysts, and the organocatalyzed oxidative coupling reaction.     

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.     

Highly efficient synthesis of linear pyrrole oligomers by twofold Heck reactions

The twofold Heck reaction of the vinylpyrroles 3a and 3b with the iodobenzenes 4a-c led to the linear pyrrole oligomers 5, 6, and 7. The synthesis of both symmetrical and unsymmetrical oligomers, such as 10a and 10b, was also accomplished by a Heck reaction of 8 and 9 and by a Heck reaction of 3a and 11 followed by a Wittig reaction and a second Heck reaction with 8. The pentacyclic oligomers 14 and 19 were prepared by a twofold Heck reaction of 13 with 4 and by a twofold Heck reaction of 15 with 16 followed by a Wittig reaction and a twofold Heck reaction with 8.     

Implicit versus explicit solvent in free energy calculations of enzyme catalysis: Methyl transfer catalyzed by catechol O-methyltransferase

We compare free energy calculations for the methyl transfer reaction catalyzed by catechol O-methyltransferase using the quantum mechanical/molecular mechanical free energy method with implicit and explicit solvents. An analogous methylation reaction in a solution is also studied. For the explicit solvent model, we use the three-point transferable intermolecular potential model, and for the implicit model, we use the generalized Born molecular volume model as implemented in CHARMM. We find that activation and reaction free energies calculated with the two models are very similar, despite some structural differences that exist. A significant change in the polarization of the environment occurs as the reaction proceeds. This is more pronounced for the reaction in a solution than for the enzymatic reaction. For the enzymatic reaction, most of the changes take place in the protein rather than in the solvent, and, hence, the benefit of having an instantaneous relaxation of the solvent degrees of freedom is less pronounced for the enzymatic reaction than for the reaction in a solution. This is a likely reason why energies of the enzyme reaction are less sensitive to the choice of atomic radii than are energies of the reaction in a solution.     

焦炭溶损反应动力学及其模型研究

利用未反应核收缩模型对高炉焦炭与CO2的反应动力学进行了研究，建立了以可测参数（R）表达的焦炭与CO2的反应动力学关系式。并对反应速率常数和有效扩散系数、表观反应活化能和有效扩散活化能及反应过程中各步骤阻力进行了分析。结果表明，（1）焦炭与CO2的反应符合未反应核收缩模型。（2）反应的表观活化能Ea=124.5kJ/mol，有效扩散活化能ED=642.4 kJ/mol；界面化学反应的阻力随反应温度升高而增加；残余灰层内的内扩散传质阻力相对比例随温度升高而下降。（3）焦炭溶损反应在低温区主要受内扩散控制，随着温度升高，反应由外扩散、化学反应和内扩散三步控制；当进入高温区，反应进行一段时间后主要受内扩散控制。     

Highly efficient one-pot three-component Mannich reaction in water catalyzed by heteropoly acids

[reaction: see text] Heteropoly acids efficiently catalyzed the one-pot, three-component Mannich reaction of ketones with aromatic aldehydes and different amines in water at ambient temperature and afforded the corresponding beta-amino carbonyl compounds in good to excellent yields and with moderate diastereoselectivity. This method provides a novel and improved modification of the three-component Mannich reaction in terms of mild reaction conditions and clean reaction profiles, using very a small quantity of catalyst and a simple workup procedure.     

Copper-catalyzed enantioselective Henry reactions of alpha-keto esters: an easy entry to optically active beta-nitro-alpha-hydroxy esters and beta-amino-alpha-hydroxy esters

The catalytic enantioselective Henry reaction of alpha-keto esters with nitromethane has been developed. The reaction conditions have been optimized by the screening of different chiral Lewis acids, solvents, and bases, and it was found that the copper(II)-tert-butyl bisoxazoline complex in combination with triethylamine catalyzed a highly enantioselective reaction giving optically active beta-nitro-alpha-hydroxy esters in high yields and with excellent enantiomeric excesses. The scope of the reaction is demonstrated by the reaction of a variety of different alpha-keto esters. The catalytic enantioselective Henry reaction of beta,gamma-unsaturated-alpha-keto esters proceeds as a 1,2-addition reaction exclusively, in contrast to the uncatalyzed reaction where both the 1,2- and 1,4-addition products are formed. It is demonstrated that the beta-nitro-alpha-hydroxy esters can be converted into, e.g., Boc-protected beta-amino-alpha-hydroxy esters in high yields and without loss of optical purity. The mechanism for the reaction is discussed, and it is postulated that both the alpha-keto ester and nitromethane/nitronate is coordinated to the metal center during the reaction course.     

Multichannel quench-flow microreactor chip for parallel reaction monitoring

This paper describes a multichannel silicon-glass microreactor which has been utilized to investigate the kinetics of a Knoevenagel condensation reaction under different reaction conditions. The reaction is performed on the chip in four parallel channels under identical conditions but with different residence times. A special topology of the reaction coils overcomes the common problem arising from the difference in pressure drop of parallel channels having different length. The parallelization of reaction coils combined with chemical quenching at specific locations results in a considerable reduction in experimental effort and cost. The system was tested and showed good reproducibility in flow properties and reaction kinetic data generation.     

Adduct of dimedone and 1,2-dibenzoylethene in reactions with nitrogen binucleophiles

Dimedone adduct with 1,2-dibenzoylethene in reaction with p-phenylenediamine formed a bispyrrole derivative, and with benzidine and ethylenediamine afforded the corresponding monopyrroles. The reaction of the initial adduct with tryptamine results in a product containing a pyrrole and an indole fragments. Both versions of N-heterocyclization proceed in the reaction with urea yielding derivatives of tetrahydroindole and pyrrole. In the reaction with hydrazine hydrate a substituted pyridazine was obtained as a result of a dimedone molecule elimination from the intermediate cyclization product.     

维生素K3电化学反应机理的紫外光谱电化学研究

用薄层池循环伏安法和现场薄层池紫外光谱电化学法研究了维生素Ｋ３（ＶＫ３）在铂电极上的电化学反应机理。薄层池循环伏安实验结果表明：ＶＫ３的电化学反应为二步１ｅ准可逆过程，现场薄层池紫外光谱电化学的实验结果和Ｎｅｒｎｓｔ图解分析表明：电解还原反应的最后产物为２－甲基－１，４－萘酚。该反应偶合有前行化学反应；还原产物经电解氧化的产物为２－甲基－１，４－萘酚。该反应偶合有前行化学反应；还原产物经电解氧化的     

Ring cleavage of aziridines by difluoroamine: mechanistic insights from ab initio and DFT study

cis-2,3-Dimethylaziridine reacts with difluoroamine to give the corresponding alkene and nitrogen with retention of configuration. We have carried out a DFT study of this reaction to clarify the reaction mechanism by considering a multistep reaction pathway with possible intermediacy of several three- and four-membered cyclic intermediates and transition states (TSs). The energetics of this reaction shows that the reaction takes place in four steps including a three-membered azamine intermediate. Both the energetics and the stereochemical outcome of this reaction rule out the formation of a four-membered diazetine intermediate during the reaction. Although the first N-N bond formation step is rate determining, the final step, asynchronous concerted cleavage of the azamine intermediate, explains the stereochemistry of this reaction. The asynchronous nature of the final step makes the reaction Woodward-Hoffmann allowed, as reported by Yamabe and Minato (J. Phys. Chem. A 2001, 105, 7281). Computations at HF and MP2 levels confirm the same trends in energetics. Single point energy computations at B3LYP, MP2, and QCISD levels with the 6-311++G(d,p) and cc-pVTZ basis sets show that the larger basis sets predict higher free energies of activation and less negative free energies of reaction. Intrinsic reaction coordinate (IRC) analyses reveal the asynchronous nature of the first and the last steps of the reaction. The deamination of trans-2,3-dimethylaziridine was shown to follow a course of reaction similar to that of the cis isomer.     

Kinetics of phenol oxidation with ozone in a thin layer on a solid surface

Ozone has been reacted with phenol in thin supported layers, and the dynamics of this reaction has been investigated. The stoichiometry of this reaction coincides with the stoichiometry of the same reaction in solution. Specific reaction rate (β) has been determined for various phenol conversions. The effective rate constant of the reaction, estimated by extrapolating β to zero reaction time, is significantly higher than the rate constant of the reaction in solution. The reaction between ozone and phenol is diffusion-controlled. The reaction products form a barrier layer, which protects the deeper phenol layers against ozone. The barrier layer is as thick as 8–15 phenol monolayers.     

Solvent reduced wittig olefination reactions with halo containing conjugated phosphoranes

The Wittig reaction of carbaldehydes with alkoxycarbonylhalomethylidenetriphenylphosphoranes can be performed with ease in solventless systems. The analogous reaction of carbaldehydes with acylhalomethylidenetriphenylphosphoranes requires a small amount of solvent, such as chloroform, in order for the reaction to proceed. The products of the reaction are versatile precursors for further transformations, such as the Suzuki-Miyaura cross-coupling reaction.     

关于反应分子数定义的讨论

There are two different views on the definition of reaction molecularity in physical chemistry textbooks and related literatures so far. We give a deep discussion about this conception herein. Starting with the development of chemical kinetics and the definition of elementary reaction and state-state reaction, we clarify that elementary reaction and state-state reaction are the conceptions belonging to macro-and micro-systems, respectively, and reaction molecularity is also belonging to micro-conception. Based on this conclusion, we think that the more reasonable definition of reaction molecularity should be "the number of chemical particles that take part in a state-state reaction (or an elementary chemi-physical reaction) as a reactant".     

An Mo theoretical study on the reaction of benzocyclobutene with ethylene. Concerted vs stepwise

In an attempt to determine the reaction mechanism of the Diels-Alder type cycloaddition reaction of benzocyclobutene with dienophiles, the stabilities for the assumed intermediate structures were examined by using MINDO/3, STO-3G, and 4-31G methods. The potential energies of the ring-opening reaction of the benzocyclobutene and cycloaddition reaction of quinodimethane with a dienophile were obtained by MINDO/3 and discussed in relation to the controversial reaction mechanism of the cycloaddition, concerted vs stepwise mechanisms. The results lead to a conclusion that the reaction involves a biradical intermediate followed by a stepwise cycloaddition.     

Kinetics of Reaction of Bromo-epoxy Resin with Oleic Acid catalyzed by Dimethyl benzyl amine

The kinetics of reaction of bromo-epoxy resin with oleic acid in the presence of dimethylbenzylamine catalyst was studied. The reaction is a zero order reaction with respect to oleic acid, first order with respect to epoxy group and 0. 74 order with respect to dimethylbenzylamine. The reaction rate constants at various temperatures and activation energy were determined. The mechanism of this reaction was discussed. Keywords Tetrabromobisphenol-A, Bromo-epoxy resin, Oleic acid kinetics, Reaction mechanism     

Influence of low-frequency vibrations on the chemical reaction rate in the liquid phase for reagent association

A bistable state of a reaction system was theoretically shown to be possible for a multistage chemical reaction in the case of reagent association. The conditions for the bistability origin with a possible substantial change in the rate of reaction product formation were determined. The conditions for the appearance of oscillations of intermediate concentrations and the possibility for the origination of the corresponding acoustic frequencies were studied. The action of external vibrations with the frequency coinciding with that of intrinsic intermediate concentration oscillations can increase the reaction rate of reaction product formation.     

The reaction of porphyrins with organolithium reagents

Porphyrins react readily with organolithium reagents, preferentially in the meso positions. The overall reaction is a nucleophilic substitution and proceeds via initial reaction of the organic nucleophile with a meso carbon yielding an anionic species which is hydrolyzed to a porphodimethene (5,15-dihydroporphyrin), formally constituting an addition reaction to two Cm positions. Subsequent oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) yields meso-substituted porphyrins. The reaction is highly versatile as it is accomplished in high, often quantitative yields with various alkyl or aryl lithium reagents. In addition, LiR can be used for reaction with a variety of metal complexes (best with NiII, but also with ZnII, CuII, and CoII) and most useful with free base porphyrins. Similarly beneficial this reaction can be used in sequence for the introduction of 1, 2, 3, or 4 (different) meso substituents giving for the first time an entry into any desired meso-substituted porphyrin. If meso-substituted porphyrins are used, reaction with LiR can be used for either the preparation of phlorins (already known reaction), porphodimethenes (5,15-dihydroporphyrins, including those with exocyclic double bonds, for example, 5(1),5(2)-didehydroporphyrins) or chlorins (2,3-dihydroporphyrins) depending on the substituent type in the reactant porphyrins. Thus, this reaction presents a generally applicable method for the facile and versatile functionalization of porphyrins.     

The photokinetics of phenothiazine dyes with titanium trichloride in different solvents

The kinetic parameters of photoinduced electron transfer reaction of two phenothiazine dyes, methylene blue and methylene green with titanium trichloride, were determined in water and different aqueous-alcoholic solvents at different acidities by using a specially designed optical system. The rate of photoinduced electron transfer reaction was measured by determining the quantum yield of the reaction. The methylene green had a higher reactivity as compared to methylene blue with titanium trichloride. The graphical analysis showed that the reaction of dye with titanium trichloride follows pseudo–first-order kinetics. A reaction mechanism was proposed by considering the different excited states of dye and their possible interaction with the solvent and titanium trichloride. The different steps in the reaction mechanism were taken into consideration for deriving rate equations, which were used to determine the different rate constants in the reaction mechanism in different solvents.