硫酸溶液中胶束催化Ce(IV)氧化D-甘露糖

Kinetics of D-mannose oxidation by cerium (IV) was studied in a sulfuric acid medium at 40℃ both in absence and presence of ionic micelles. In both cases, the rate of the reaction was first-order in D-mannose and in cerium(Ⅳ), which decreased with increasing [H2SO4]. This suggested that the redox reaction followed the same mechanism. The reaction proceeded through formation of an intermediate complex, which was proved by kinetic method. The complex underwent slow unimolecular decomposition to a free radical that reacted with cerium (Ⅳ) to afford the product. The catalytic role of cationic cetyltrimethylammonium bromide (CTAB) micelles was best explained by the Menger-Portnoy model. The study of the effect of CTAB also indicated that a negatively charged species was reactive form of cerium (Ⅳ). From the kinetic data, micelle-cerium (Ⅳ) binding and rate constants in micellar medium were evaluated.The anionic micelle of sodium dodecyl sulfate plays no catalytic role. The oxidation has the rate expression --d[Ce(Ⅳ)]= k1Kcl[D-mannose] [Ce(Ⅳ)]dt Different activation parameters for micelle catalyzed and uncatalyzed paths were also calculated and discussed.     

硫酸存在时N-溴代苯二甲酰亚胺对甘露糖的胶束催化氧化

The kinetics of micellar-catalyzed oxidation of mannose by N-bromophthalimide was studied in the presence of sulfuric acid at 313 K. The orders of reaction with respect to [mannose], [oxidant], and [H+] were found to be fractional, first, and negative fractional order, respectively. Anionic micelles of sodiumdodecyl sulfate showed a partial inhibitory effect, while cationic micelles of cetyltrimethylammonium bromide increased the reaction rate with the same kinetic behavior. The reaction was catalyzed by cationic micelles, because of favorable electrostatic/thermodynamic/hydrophobic/hydrogen bonding between reactants and cationic micelles. Their catalytic roles are best explained by Berezin’s model. A variation of [phthalimide] showed that the rate of reaction decreased with increasing [phthalimide]. It was observed that, an increase of [mercuric acetate] had no effect on reaction velocity. The influence of salts on the reaction rate was also studied. The rate constant (kW ), binding constants (KS+KO), and corresponding activation parameters (Ea, ⊿H#, ⊿S#, and ⊿G#) were determined. A detailed mechanism with associated reaction kinetics is presented and discussed.     

Kinetics and Mechanism of Iridium（Ⅲ）-Catalyzed Oxidation of Ethanol Amine by Cerium（ Ⅳ ） in Sulfuric Acid Media

In this study, the kinetics and mechanism of the iridium(Ⅲ)-catalyzed oxidation of ethanol amine(EAN) by cerium(Ⅳ) in a sulfuric acid medium was investigated using titrimetric technique of redox in a temperature range of 298—313 K. It was found that the reaction is of first order with respect to Ce(Ⅳ) and Ir(Ⅲ), and a positive fractional order with respect to EAN. It was also found that the pseudo-first-order([EAN][Ce(Ⅳ)]) rate constant kobs decreases with the increase of [H ] and [HSO-4]. Under the protection of nitrogen gas, the reaction system can initiate the polymerization of acrylonitrile, indicating the generation of free radicals. On the basis of the experimental results, a suitable mechanism was proposed. From the dependence of kobs on the concentration of hydrogen sulfate, Ce(SO4)2 was found to be the kinetically active species. The rate constants of the rate-determining step together with the activation parameters were evaluated.     

Kinetics and Mechanism of Iridium(Ⅲ)-Catalyzed Oxidation of Ethanol Amine by Cerium(Ⅳ) in Sulfuric Acid Media

In this study, the kinetics and mechanism of the iridium(Ⅲ)-catalyzed oxidation of ethanol amine(EAN) by cerium(Ⅳ) in a sulfuric acid medium was investigated using titrimetric technique of redox in a temperature range of 298-313 K. It was found that the reaction is of first order with respect to Ce(Ⅳ) and Ir(Ⅲ), and a positive fractional order with respect to EAN. It was also found that the pseudo-first-order([EAN](》)[Ce(Ⅳ)]) rate constant kobs decreases with the increase of [H ] and [HSO-4]. Under the protection of nitrogen gas, the reaction system can initiate the polymerization of acrylonitrile, indicating the generation of free radicals. On the basis of the experimental results, a suitable mechanism was proposed. From the dependence of kobs on the concentration of hydrogen sulfate, Ce(SO4)2 was found to be the kinetically active species. The rate constants of the rate-determining step together with the activation parameters were evaluated.     

Effect of Cationic Micelles on the Kinetics of Interaction of [Cr（Ⅲ）-Gly-Gly]^2＋ with Ninhydrin

The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) on the interaction of chromium dipeptide complex ([Cr(Ⅲ)-Gly-Gly]2 ) with ninhydrin under varying conditions has been investigated. The rates of the reaction were determined in both water and surfactant micelles in the absence and presence of various organic and inorganic salts at 70 ℃ and pH 5.0. The reaction followed first- and fractional-order kinetics with respect to [Cr(Ⅲ)- Gly-Gly2 ] and [ninhydrin]. Increase in the total concentration of CTAB from 0 to 40×10-3 mol·dm-3 resulted in an increase in the pseudo-first-order rate constant (kψ) by a factor of ca 3. Quantitative kinetic analysis of kψ-[CTAB] data was performed on the basis of the pseudo-phase model of the micelles. As added salts induce structural changes in micellar systems that may modify the substrate-surfactant interactions, the effect of some inorganic (NaBr, NaCl, Na2SO4) and organic (NaBenz, NaSal, NaTos) salts on the rate was also explored. It was found that the tightly bound counterions (derived from organic salts) were the most effective.     

阳离子胶束对[Gr(III)-(Gly-Gly)]2+与茚三酮反应动力学的影响

The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) on the interaction of chromium dipeptide complex ([Cr(III)-Gly-Gly]2+) with ninhydrin under varying conditions has been investigated. The rates of the reaction were determined in both water and surfactant micelles in the absence and presence of various organic and inorganic salts at 70 ℃ and pH 5.0. The reaction followed first-and fractional-order kinetics with respect to [Cr(III)-Gly-Gly2+] and [ninhydrin]. Increase in the total concentration of CTAB from0 to 40×10-3mol·dm-3 resulted in an increase in the pseudo-first-order rate constant (kψ) by a factor of ca 3. Quantitative kinetic analysis of kψ-[CTAB] data was performed on the basis of the pseudo-phase model of the micelles. As added salts induce structural changes in micellar systems that may modify the substrate-surfactant interactions, the effect of some inorganic (NaBr, NaCl, Na2SO4) and organic (NaBenz, NaSal, NaTos) salts on the rate was also explored. It was found that the tightly bound counterions (derived fromorganic salts) were the most effective.     

Kinetics and Mechanism of Oxidation of Glycol by Dihydroxydiperiodatonickelate ( Ⅳ )Complex in Aqueous Alkaline Medium

The kinetics of oxidation of glycol by dihydroxydiperiodato nickelate ( Ⅳ) complex (DDN) was studied by spectrophotometry in aqueous alkaline medium in a temperature range of 25-40℃. The reaction was found to be first order with respect to Ni( Ⅳ ) and also to be first order with respect to glycol. The rate increases with the increase in [OH ] and decreases with the increase in [IO-4], showing that dihydroxymonoperiodatonickelate ( Ⅳ )(DMN) is the reactive species of oxidant. Salt effect indicated that the reaction is of ion-dipole type. No free radical was detected. A mechanism of an inner-sphere two-electron transfer reaction involving a preequilibrium between DDN and DMN is proposed, and the rate equation derived from the mechanism can explain all experimental observations. Activation parameters of the rate-determing step and the equilibrium constants were calculated.     

Kinetic Studies on of Veratryl the Lignin Peroxidase Catalyzed Oxidation Alcohol by H2O2 in AOT/Isooctane/ Toluene/Water Reverse Micelles

The steady state kinetics of the lignin peroxidase （LIP） catalyzed oxidation of veratryl alcohol （VA） by H2O2 in a sodium bis（2-ethylhexyl） sulfosuccinate （AOT）/isooctane/toluene/water reverse micellar medium was studied and a comparison with the corresponding aqueous medium was made to understand the effect of the reverse micellar medium on the catalytic mechanism and kinetic parameters. Results indicated that the model reaction in the AOT reverse micelle followed the ping-pong mechanism with true kcat, Km,VA and KmH2O2 being 59.6min^-1, 13.9 mmol· L^-1 and 94.8 μmol·L^-1, respectively; inhibition of high level of H2O2 on LiP followed the reversible competitive pattern with Ki being 0.140 mmol·L^-1. The reaction mechanism and inhibition pattern in the AOT reverse micellar medium were the same as those in bulk aqueous medium, but the kinetic parameters except KmH2O2 were greatly different in the two media. The kcat and Ki values in the reverse micelle were approximately 2 and 20 times smaller than the corresponding values in the aqueous solution, but the Michaelis constant of VA was approximately 100 times greater than that in the aqueous solution. The above mentioned differences in the kinetic parameters were caused by the microheterogeneity and the interface of the AOT reverse micelle, which resulted in the partitioning of VA and H2O2, and by the changes of the conformation of LiP and the reactivity of the substrates.     

STUDIES OF UNUSUAL OXIDATION STATES OF TRANSITION METALS (Ⅰ)——KINETICS AND MECHANISM OF OXIDATION OF POTASSIUM THIOCYANATE BY DIPERIODATOARGENTATE(Ⅲ) ION IN ALKALINE MEDIUM

The kinetics of oxidation of potassium thiocyanate by diperiodatoargentate (Ⅲ) (DPA) ions was studied in aqueous alkaline medium ([OH~-]=7.00×10~(-3)—0.200 mol. dm~(-3)) at a constant ionic strength (μ=0.30 mol. dm~(-3)). It is found that the reaction order in DPA is unity. The dependence of the rate on [OH~-] implies that there are two pathways through which the reaction proceeds. In each pathway, the order in NCS-is fractional and the kinetic data fit well in with Michaelis-Menten process. The influence of ligand on the reaction is examined and the reactive species are inferred. Two pathways of inner-sphere two-electrons transfer are believed to be involved in the oxidation. The rate equations are derived and all the equilibrium constants and rate constants are evaluated. Activation parameters of one pathway are determined.     

STUDIES ON BIO-ANTIOXIDANTS——MICELLAR EFFECTS ON THE REDUCTION OF NITROXIDES BY VITAMIN C

The kinetics of reduction of nitroxides including 4-hydroxy-TEMPO, 4-methoxy-TEMPOand 4-hexanoyloxy-TEMPO, which are of different lipophilicities, by vitamin C in cationic,non-ionic and anionic micelles, i. e. CTAB, Triton X-100 and SDS, respectively, have beenstudied by ESR spectroscopy by a stopped-flow technique. A mechanism for the reactionconducted in micelles is proposed and the rate constants for the elementary reactions areevaluated. It is found that the rates of single electron transfer reactions involving the ni-troxides are dependent on the nature of the micelle and the lipophilicity of the nitroxide.The rates are increased in CTAB, decreased in SDS, whereas unaffected in Triton X-100.And the greater the lipophilicity of the nitroxide, the more pronounced the rate variation.As high as a 3600-fold increase in the rate was observed for 4-hexanoyloxy-TEMPO in CTABover that in SDS. The micellar effects are rationalized on the basis of analysis of parame-ters and line shape of the ESR spectra for     

Simultaneous kinetic spectrophotometric determination of cephalexin and trimethoprim in pharmaceutical preparation and human urine with the aid of chemometrics

A procedure for the simultaneous kinetic spectrophotometric determination of cephalexin and trimethoprim was described. It was based on the different reaction rate of oxidation of these compounds with yellow ammonium cerous （Ⅳ） sulfate in acidic medium and colorless cerous （Ⅲ） sulfate was produced. The overlapped kinetic data was quantitatively resolved by the use of chemometric methods, partial least squares （PLS）, principal component regression （PCR） and radial basis function-artificial neural network （RBF-ANN）. The proposed method was also applied to the simultaneous determination of cephalexin and trimethoprim in pharmaceutical preparation and human urine with satisfied results, which compared well with those obtained by HPLC.     

KINETIC AND APPLICATION: STUDIES ON THE REACTION SYSTEM OF OSMIUM(Ⅳ)-ARSENIC(Ⅲ)-CHLORATE

The experiments have proved that Os(Ⅳ) has very strong catalytic effect on the chlorate oxidation of As(Ⅲ) in perchloric acid media, and As(Ⅲ) exhibits a sensitive single-sweep oscillopolarographic wave at-0.75 V vs. SCE. The kinetics of this catalytic reaction has been investigated by the initial rate procedure. The mechanism has been proposed. A new and highly sensitive catalytic reaction-oscillopolarographic method for the determination of ultratrace amounts of osmium has been described, based on the Os(Ⅳ) catalytic effect on the reaction. The linear range of 5.0×10~(-11)-4.4×10~(-9) mol/L and 6.0×10~(-9)-1.3×10~(-7) mol/L Os was obtained using the fixed-time procedure and the initial rate procedure, respectively. Osmium in refined ore was analysed by this method.     

PHOTOPOLYMERIZATION IN THE MICELLAR SYSTEMSⅡ THE CATALYSIS OF PKT FUNCTIONAL MICELLE*

A kind of cationic compounds, having benzophenone end group and various length chain (PKT) (BP-CH_2N+R_2R'·X~-, R&R' different chain iength alkyl group) were used as photosensitizers. Various BP/TEA systems have been used for study, The efficiency of MMA photopolymerization initiated by them shows PKT>BP in homogeneous water solution and PKT> BP/CTAB in micellar water solution. The results obtained indicate that catalytic effects of PKT type functional micelles are far greater than that of common micelle with the enhancement of polymerization rate over 10 times compared with BP in water solution. The catalytic role, reaction character of PKT, effect of counter ions and retarding effect of oxygen have also been discussed.     

Studies of Unusual Oxidation States of Transition Metals Ⅱ——Kinetics and Mechanism of Oxidation of Pyruvate by Diperiodatoargentate (Ⅲ)Ion

The kinetics of oxidation of pyruvate by diperiodatoargentate( III) ion (DPA) has been studied spec-trophotometrically in alkaline medium. It was found that the reaction order with respect to both DPA and pyruvate is unity and the rate equation can be expressed asThe rate increases with the increase in [OH ] and decreases with the increase in [periodate]. There is a positive ionic strength effect in this reaction system. A mechanism has been proposed to explain the experimental results. The observed activation parameters are presented.     

以方沸石负载Ni(Ⅱ)催化剂修饰的电极电氧化甲醇(英文)

There is a high overvoltage in the oxidation of methanol in fuel cells,and so modified electrodes are used to decrease it.A modified electrode that used Ni(II) loaded analcime zeolite to catalyze the electrooxidation of methanol in alkaline solution was proposed.Analcime zeolite was synthesized by hydrothermal synthesis,and Ni(II) ions were incorporated into the analcime structure,which was then mixed with carbon paste to prepare modified electrode.The electrocatalytic oxidation of methanol on the surface of the modified electrode in alkaline solution was investigated by cyclic voltammetry and chronoamperometry.The effects of the scan rate of the potential,concentration of methanol,and amount of zeolite were investigated.The rate constant for the catalytic reaction of methanol was 6 × 103 cm3 mol-1 s-1 from measurements using chronoamperometry.The proposed electrode significantly improved the electron transfer rate and decreased the overpotential for methanol oxidation.     

Effect of Mn（Ⅱ） and Ce（Ⅳ） Ions on the Oxidation of Lactic Acid by Chromic Acid

The kinetics and mechanism of lactic acid oxidation in the presence of Mn（Ⅱ） and Ce（Ⅳ） ions by chromic acid were studied spectrophotometrically. The oxidation of lactic acid by Cr（Ⅵ） was found to proceed in two measurable steps, both of which gave pyruvic acid as the primary product in the absence of Mn（Ⅱ）.2Cr（Ⅵ）＋2CH3CHOHCOOH→2CH3COCOOH＋Cr（Ⅴ）＋C（Ⅲ） Cr（V）＋CH3CHOHCOOH→Cr（Ⅲ）＋CH3COCOOHThe observed kinetics was explained due to the catalytic and inhibitory effects of Mn（Ⅱ） and Ce（Ⅳ） on the lactic acid oxidation by Cr（Ⅵ）. The reactivity of lactic acid depends upon the experimental conditions. It acts as a two- or three- equivalent reducing agent in the absence or presence of Mn（Ⅱ）. It was examined that Cr（Ⅲ） products resulting from the direct reduction of Cr（Ⅵ） by three-equivalent reducing agents. The oxidation of lactic acid follows the complex order kinetics with respect to [lactic acid]. The activation parameters Eo, △H^#, and AS^# were calculated and discussed.     

新的聚苯乙烯负载锌化合物:高效苯酚氧化催化剂(英文)

The novel recyclable free –ONNO– tetradentate Schiff base ligand N,N′‐bis(2‐hydroxy‐3‐ methox‐ybenzaldehyde)4‐methylbenzene‐1,2‐diamine (3‐MOBdMBn) was synthesized. Complexation of this ligand with zinc(3‐MOBdMBn‐Zn) was performed, and the catalytic activity of the complex was evaluated. The polymer‐supported analog of this complex(P‐3‐MOBdMBn‐Zn) was synthesized, and its catalytic activity was studied. These free and polymer‐anchored zinc complexes were prepared by the reactions of metal solutions with one molar equivalent of unsupported 3‐MOBdMBn or P‐3‐MOBdMBn in methanol under nitrogen. The catalytic activity of 3‐MOBdMBn‐Zn and P‐3‐MOBdMBn‐Zn was evaluated in phenol oxidation. The activity of P‐3‐MOBdMBn‐Zn was signif‐icantly affected by the polymer support, and the rate of phenol conversion was around 50% for polystyrene‐supported 3‐MOBdMBn. The experimental results indicated that the reaction rate was affected by the polymer support, and the rate of phenol conversion was 1.64 μmol/(L·s) in the presence of polystyrene‐supported 3‐MOBdMBn.     

新的聚苯乙烯负载锌化合物:高效苯酚氧化催化剂(英文)

The novel recyclable free –ONNO– tetradentate Schiff base ligand N,N′‐bis(2‐hydroxy‐3‐ methox‐ybenzaldehyde)4‐methylbenzene‐1,2‐diamine (3‐MOBdMBn) was synthesized. Complexation of this ligand with zinc(3‐MOBdMBn‐Zn) was performed, and the catalytic activity of the complex was evaluated. The polymer‐supported analog of this complex(P‐3‐MOBdMBn‐Zn) was synthesized, and its catalytic activity was studied. These free and polymer‐anchored zinc complexes were prepared by the reactions of metal solutions with one molar equivalent of unsupported 3‐MOBdMBn or P‐3‐MOBdMBn in methanol under nitrogen. The catalytic activity of 3‐MOBdMBn‐Zn and P‐3‐MOBdMBn‐Zn was evaluated in phenol oxidation. The activity of P‐3‐MOBdMBn‐Zn was signif‐icantly affected by the polymer support, and the rate of phenol conversion was around 50% for polystyrene‐supported 3‐MOBdMBn. The experimental results indicated that the reaction rate was affected by the polymer support, and the rate of phenol conversion was 1.64 μmol/(L·s) in the presence of polystyrene‐supported 3‐MOBdMBn.     

Electrocatalytic Behavior of Metalloporphyrins(Ⅶ)——Kinetic Study of Cysteine Oxidation on Heat-Treated Cobalt Tetramethoxyphenyl Porphyrin Adsorbed on Graphite

The metnoas or rotating ring-disc electrode(RRDE) ana cyclic voltammetry were used to study the oxidation of cgsteine on heat-treated cobalt tetramethoxyphenyl porphyrin adsorbed on graphite(Co-TMPP/graphite) in solutions of various pH.Experimental results showed that Co-TMPP/graphite exhibits significant catalytic activity for cysteine oxidation in solutions with various pH.The current efficiency of cysteine oxidation on Co-TMPP/graphite in basic media is more than 90%.It was found that the kinetics of cysteine oxidation on Co-TMPP/graphite is a simple irreversible reaction controlled by rate of charge transfer.The standard rate,constants(k) of cysteine oxidation were calculated and the reaction mechanism of this reaction in solutions of various pH wes discussed.     

纳米贵金属插入的粘土用于催化选择性加氢反应

 The use of clay minerals in the synthesis of nanosized noble metal particles to give increased catalytic activity was investigated. Nanosized platinum and ruthenium catalysts intercalated in clay (montmorillonite/hectorite) were synthesised and their catalytic activity was evaluated for the selective hydrogenation of three different α,β-unsaturated aldehydes, namely, crotonaldehyde, cinnamaldehyde, and citral, in a gas phase microreactor. The metal nano-sol was prepared by the chemical reduction of its precursor by the micellar technique in the presence of cetyl trimethyl ammonium bromide (CTAB), and the micelle stabilized metal particles were intercalated in the clay mineral by ion exchange. TEM micrographs of the catalyst particles showed that the metal particles were in the nanometre range. The average diameters of the particles were 1–25 nm. The effects of temperature, metal loading, and hydrogen flow rate on the catalytic activity and selectivity for α,β- unsaturated alcohol were studied. The results were correlated with the structural properties of the catalysts. The products formed in each reaction over the different catalysts showed that the catalysts were very active for hydrogenation, and the selectivity for the desired product, namely, α,β-unsaturated alcohol, was good. The metal catalysts intercalated in montmorillonite showed better selectivity than that in hectorite because of its higher acidity. Increased selectivity for α,β-unsaturated alcohol was observed with increased flow rate of hydrogen.