超临界CO_2在化学反应中的应用进展

本文详细地综述了最近几年来有关超临界CO2流体中的化学反应的研究成果，展望了超临界CO2化学反应的开发应用前景，试图让这一崭新的研究领域受到更加广泛的关注。     

Entropy production in TMDSC

The non-equilibrium process due to irreversible heat exchanges occurring during a temperature modulated differential scanning calorimetry (TMDSC) experiment is investigated in detail. This enables us to define an experimental frequency dependent complex heat capacity from this calorimetric method. The physical meaning of this dynamic heat capacity is discussed. A relationship is clearly established between the imaginary part of this complex quantity and the net entropy created during the experimental time-scale.     

Central limit theorem for chemical kinetics in complex systems

The prevalence of apparently first-order kinetics of reactant disappearance in complex systems with many possible reaction pathways is usually attributed to the dominance of a single rate limiting step. Here, we investigate another possible explanation: that apparently first-order kinetics might arise because the aggregate behavior of many processes, with varying order of reaction and rate constant, approaches a central limit that is indistinguishable from first-order behavior. This hypothesis was investigated by simulating systems of increasing complexity and deriving relationships between the apparent reaction order of such systems and various measures of their complexity. Transformation of a chemical species by parallel irreversible reactions that are zero-, first-, or second-order is found to converge to a central limit as the number of parallel reactions becomes large. When all three reaction orders are represented, on average, in equal proportions, this central limit is experimentally indistinguishable from first-order. A measure of apparent reaction order was used to investigate the nature of the convergence both stochastically and by deriving theoretical limits. The range of systems that exhibit a central limit that is approximately first-order is found to be broad. First-order like behavior is also found to be favored when the distribution of material among the parallel processes (due to differences in rate constants for the individual reactions) is more complex. Our results show that a first-order central limit exists for the kinetics of chemical systems and that the variable controlling the convergence is the physical complexity of reaction systems.     

Determination of furfural in an oscillating chemical reaction using an analyte pulse perturbation technique

A rapid and convenient method for the determination of furfural is presented that is based upon sequential perturbation of the Mn(II)-catalyzed B-Z oscillating system with different amounts of furfural using a continuous-flow stirred tank reactor (CSTR). When the sample was injected, the change in the amplitude and/or period was linearly proportional to the logarithm of the concentration of furfural over the range 3×10⁻⁸∼1×10⁻⁵ mol L⁻¹. This method gave a detection limit of 3×10⁻⁹ mol L⁻¹ under optimum conditions. Finally, the possible mechanism of furfural perturbation in the oscillating reaction is discussed. When the furfural was injected into the Mn(II)-catalyzed B-Z oscillating system, the change in the amplitude and/or period was linearly proportional to the logarithm of the concentration of furfural over the range 3×10⁻⁸~1×10⁻⁵ mol L⁻¹, with a detection limit of 3×10⁻⁹ mol L⁻¹ under optimum conditions.      

Thermodynamic possibilities and constraints of pure hydrogen production by a chromium,nickel, and manganese-based chemical looping process at lower temperatures

The reduction of chromium, nickel, and manganese oxides by hydrogen, CO, CH₄, and model syngas (mixtures of CO + H₂ or H₂ + CO + CO₂) and oxidation by water vapor has been studied from the thermodynamic and chemical equilibrium point of view. Attention was concentrated not only on the convenient conditions for reduction of the relevant oxides to metals or lower oxides at temperatures in the range 400–1000 K, but also on the possible formation of soot, carbides, and carbonates as precursors for the carbon monoxide and carbon dioxide formation in the steam oxidation step. Reduction of very stable Cr₂O₃ to metallic Cr by hydrogen or CO at temperatures of 400–1000 K is thermodynamically excluded. Reduction of nickel oxide (NiO) and manganese oxide (Mn₃O₄) by hydrogen or CO at such temperatures is feasible. The oxidation of MnO and Ni by steam and simultaneous production of hydrogen at temperatures between 400 and 1000 K is a difficult step from the thermodynamics viewpoint. Assuming the Ni—NiO system, the formation of nickel aluminum spinel could be used to increase the equilibrium hydrogen yield, thus, enabling the hydrogen production via looping redox process. The equilibrium hydrogen yield under the conditions of steam oxidation of the Ni—NiO system is, however, substantially lower than that for the Fe—Fe₃O₄ system. The system comprising nickel ferrite seems to be unsuitable for cyclic redox processes. Under strongly reducing conditions, at high CO concentrations/partial pressures, formation of nickel carbide (Ni₃C) is thermodynamically favored. Pressurized conditions during the reduction step with CO/CO₂ containing gases enhance the formation of soot and carbon-containing compounds such as carbides and/or carbonates.     

化学反应热动力学研究的新进展

综述了用热导式热量计研究化学反应热动力学的最新状况,重点评述了动态法和热流法及其在化学与生物领域中的应用     

On the quantum chemical origin for the nonvalidity of Koopmans' theorem in transitionmetal compounds

The quantum chemical origin for the nonvalidity of Koopmans' theorem in transitionmetal compounds of the 3d series is analyzed by means of the Green's function formalism applied in the framework of a semiempirical INDO Hamiltonian. In the case of ferrocene (1), cyclobutadiene iron tricarbonyl (2) and irontetracarbonyl dihydride (3) the self-energy part of a geometric approximation has been partitioned into relaxation and correlation (pair removal, pair relaxation) increments. The breakdown of Koopmans' theorem for strongly localized MOs with large Fe 3d amplitudes is predominantly the result of electronic relaxation lowering the calculated ionization potentials. On the other hand the variation of the pair correlation energy in the cationic hole-state is by no means negligible and acts into the opposite direction as the relaxation increment. These significant pair relaxation contributions explain the wellknown failtures of the ΔSCF approach in combination with large scaleab initio bases. The loss of ground state pair correlation in the outer valence region is small in comparison to relaxation and pair relaxation. The magnitude of the aforementioned reorganization increments has been studied as a function of the localization properties of the MOs and as a function of the one-electron energies of the available particle- and hole-states. The computational findings derived with the INDO model are compared with recentab initio studies.     

Quantitative studies on the preparation of colloidal particles of cobalt hydroxide by the moving chemical reaction boundary method in agarose gel

Quantitative investigations were performed for the synthesis of colloidal particles of cobalt hydroxide in agarose gel by the moving chemical reaction boundary method . The experimental results show that: (1) the sizes of the colloidal particles can be controlled by changing the concentration of agarose gel, (2) the concentration of the colloidal particles is also controlled by changing the concentrations of CoCl₂ and/or NaOH, and (3) most importantly, the concentration of colloidal particles can be predicted with the theory of moving chemical reaction boundary (MCRB). The colloidal particles prepared by the MCRB are amorphous and are more easily oxidized than particles prepared by other methods.     

A possible construction of a complex chemical reaction network

A procedure is suggested for the construction of chemical reaction networks. We define the kinetic communication as a transfer of atoms or atomic groups between two species and determine all the kinetic communications occurring in the possible mechanism of a complex chemical process. The set of kinetic communications is the basis of the communication matrices resulting in the complete network of the overall reaction.Limiting the consideration for certain types of kinetic communications we obtain the reaction subnetworks and selecting arbitrarily species among those participating in the possible mechanism we introduced the concept of the partial subnetworks which correspond to subsets of the complete network.By the simple analysis of the subnetworks it is easy to obtain the sequence network indicating the pathways via which the selected species are formed in the course of the overall process, by the transfer of chosen atoms or atomic groups.     

Studies on the preparation of active oxygen-deficient copper ferrite and its application for hydrogen production through thermal chemical water splitting

Hydrogen generation through thermal chemical water splitting technology has recently received in- creasingly international interest in the nuclear hydrogen production field. Besides the main known sulfur-iodine (S-I) cycle developed by the General Atomics Company and the UT3 cycle (iron, calcium, and bromine) developed at the University of Tokyo, the thermal cycle based on metal oxide two-step water splitting methods is also receiving research and development attention worldwide. In this work, copper ferrite was prepared by the co-precipitation method and oxygen-deficient copper ferrite was synthesized through first and second calcination steps for the application of hydrogen production by a two-step water splitting process. The crystal structure, properties, chemical composition and δ were investigated in detail by utilizing X-ray diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA), atomic absorption spectrometer (AAS), ultraviolet spectrophotometry (UV), gas chro- matography (GC), and so on. The experimental two-step thermal chemical cycle reactor for hydrogen generation was designed and developed in this lab. The hydrogen generation process of water splitting through CuFe2O4-δ and the cycle performance of copper ferrite regeneration were firstly studied and discussed.     

Stacking and quantitative analysis of lovastatin in urine samples by the transient moving chemical reaction boundary method in capillary electrophoresis

A simple, sensitive, and useful concentration method for lovastatin (Lvt) in urine has been developed based on the transient moving chemical reaction boundary method (tMCRBM) in capillary electrophoresis. The MCRB is formed with acidic sample buffer (Gly-HCl) and alkaline running buffer (Gly-NaOH). The following optimal conditions were determined for stacking and separation: electrophoretic buffer of 100 mM Gly- NaOH (pH 11.52), sample buffer of 20 mM Gly-HCl (pH 4.93), fused-silica capillary of 76 cm × 75-μm i.d (67 cm from detector), sample injection at 14 mbar for 3 min. A 21- to 26-fold increase in peak height was achieved for detection of Lvt in urine under the optimal conditions compared with normal capillary zone electrophoresis. By combining the sample pretreatment procedure with the stacking method, the sensitivity of Lvt in urine was increased by 105- to 130-fold. The limits of detection (LOD) and quantification (LOQ) for Lvt in urine were decreased to 8.8 ng/mL and 29.2 ng/mL, respectively. The intra-day and inter-day precision values (expressed as RSD) were 2.23–3.61% and 4.03–5.05%, respectively. The recoveries of the analyte at three concentration levels changed from 82.65 to 100.49%.     

Determination of fumaric and maleic acids with stacking analytes by transient moving chemical reaction boundary method in capillary electrophoresis

The paper presents an on-line transient moving chemical reaction boundary (MCRB) method for simply but efficiently stacking analytes in capillary electrophoresis (CE). The CE technique was developed for a rapid determination of fumaric and maleic acid. Based on the theory of MCRB, Effects of several important factors such as the pH and concentration of running buffer and the conditions of stacking analytes were investigated to acquire the optimum conditions. The optimized separations were carried out in a 20 mmol/L sulphate neutralized with ethylenediamine to pH 6.0 electrolytes using a capillary coated with poly (diallyldimethylammonium chloride) and direct UV detection at 214 nm. The optimized preconcentrations were carried out in 50 mmol/L borax (pH 9.0). The calibration curves were linear in the concentration range of 1.0 × 10⁻⁷–1.0 × 10⁻⁴ mol/L and 5.0 × 10⁻⁷–1.0 × 10⁻⁴ mol/L for fumaric and maleic acid with correlation coefficients higher than 0.9991. The detection limits were 5.34 × 10⁻⁸ mol/L for fumaric acid and 1.92 × 10⁻⁷ mol/L for maleic acid. This method was applied for determination of fumaric acid in apple juice and of fumaric and maleic acid in dl-malic, the recovery tests established for real samples were within the range 95–105%. This work provided a valid and simple approach to detect fumaric and maleic acid.     

Quantum chemical study of the reaction mechanism of the methylmercury cation with 2-mercapto-2-methyltetrahydro-1,4-thiazino[2,3,3,4-i,j]quinolinium chloride in aqueous media

The detoxication properties of 2-mercapto-2-methyltetrahydro-1,4-thiazino[2,3,3,4-i,j]quinolinium chloride (II) with respect to the methylmercury cation (I) in the presence of six water molecules have been studied using the density functional theory (DFT) method. Interaction between I and II leads to generation of the hydroxonium cation, which catalyzes the demethylation process. The elementary stages of two reaction routes have been localized, and their thermodynamic and kinetic characteristics have been determined.     

Method for the calculation of the species balance in the reaction zone

A class of processes for which the problem of species balance can be solved without using any assumptions concerning the mechanism of the chemical event of the reaction was found in the problem of species balance in the reaction zone. The mathematical statement of the problem in this case was discussed; it was shown that the solution is mainly determined by the system geometry. The method for reducing the problem to determination of the probability of species entering the chemical event zone is substantiated; this can be done by the Green function method.     

Domino Knoevenagel/Diels-Alder sequence coupled to Suzuki reaction: a valuable synthetic platform for chemical biology

A small library of peculiar biphenyl and terphenyl-containing spirocyclic triones has been synthesized in parallel by combining the organocatalytic three-component domino Knoevenagel/Diels-Alder sequence to Suzuki coupling. This methodology is fast, general and serves as a platform to gain access to novel chemical tools to probe protein-protein interactions.     

High throughput evaluation of the production of substituted acetylenes by the Sonogashira reaction followed by the Mizoroki-Heck reaction in ionic liquids, in situ, using a novel array reactor

The parallel Sonogashira coupling reaction was carried out under copper-free condition by integrating the advantages of ionic liquids as the reaction media followed by the simultaneous-multiple Mizoroki-Heck reaction in situ by the use of a novel array reactor (SynArray-24). The device provides rapid evaluation of reactions in a short period.     

Some model inhomogeneous electron liquid in D dimensions: relation between energy and chemical potential and a spatial generalisation of Kato's nuclear cusp theorem

After a brief survey on the application of the Thomas–Fermi statistical method to bare Coulomb potential satisfying Laplace equation in D dimensions, which then relates energy and chemical potential, we next focus attention on model atomic ions with merely one and two electrons in D dimensions. In particular, for a bare Coulomb field we use the nodeless radial eigenfunctions given by Herschbach in D dimensions to derive the spatial generalization of Kato's nuclear cusp theorem in D dimensions for D?>?1. The unbinding of H ^? as a function of dimensionality D is also briefly referred.     

Illustration of chemical reaction on the flow of viscous fluid in a deformable permeable layer: A numerical approach

In this article, analysis is carried out for the flow of viscous liquid in a deformable permeable layer. Influence of chemical reaction is considered that will affect the flow behavior. The governing equation describes the coupling between the solid deformation, fluid movement and concentration in the porous layer. However, these complex transformed designed problems are numerically examined retaining “Runge-Kutta fourth-order” in coordination with shooting method. Computational results for the numerous parameters on the flow phenomena such as solid displacement profiles are presented graphically. Moreover, the significant finding of the results is; increasing viscous drag retards the momentum within the permeable stratum whereas increasing particle concentration has opposite impact on the solid displacement within the domain.     

Simple model for the instabilities in the aggregation of silica sols in a sol-gel process

A simple kinetic model based on the Prigogine's Brusselator model was used to explain some unstable non-linear oscillations found in the particle size profile of sols in a sol-gel process. These oscillations were explained, in some previous papers, by using the stability criterion from the non-linear irreversible thermodynamics; it is the excess entropy production that characterizes the stability of a system and the occurrence of new structures. In the solgel reaction considered here, one of the steps is auto-catalytic; this fact produces local gradients in the concentration of one of the chemical components, forming a wide variety of new unstable structures. With this model we obtained a relationship for the reaction constants that determines the unstable character of the reaction, and the dependence of the frequency of oscillations on the reactant concentrations. The dependence of the oscillation frequency on water and ethanol concentrations obtained from the experimental data, were well explained by using this model.