Mechanism of the Electrochemical Carboxylation of Aromatic Ketones in Dimethylformamide

2003 ◽  
Vol 68 (8) ◽  
pp. 1379-1394 ◽  
Author(s):  
Abdirisak A. Isse ◽  
Armando Gennaro
Keyword(s):  
Radical Anion ◽  
Reduction Process ◽  
Kinetic Control ◽  
Peak Potential ◽  
Ketyl Radical ◽  
Aromatic Ketones ◽  
Experimental Parameters ◽  
Scan Rate ◽  
Kinetics Of ◽  
Electrochemical Carboxylation

The mechanism of the electrochemical carboxylation of several benzophenones (X-C6H4COC6H5; X = 4-OCH3, 4-CH3, H, 3-Cl, 3-CF3, 4-CF3 and 4-CN) and several ring-substituted acetophenones (Y-C6H4COCH3; Y = 4-OCH3, H, 3-OCH3, 3-Cl, 3-CF3, 4-CF3, 3-CN and 4-CN) has been investigated by cyclic voltammetry in dimethylformamide. In the presence of CO2, all compounds exhibit a single irreversible peak representing a 2 e reduction process. The reaction mechanism has been analysed using the dependence of the peak potential Ep on various experimental parameters such as the concentrations of the reactant, the scan rate and the temperature. Also the kinetics of the electrocarboxylation reaction has been examined. The whole set of results has been carefully analysed in the framework of an ECE-DISP mechanism. It has been found that, under the conditions employed, the electrocarboxylation reaction is always under a mixed ECE-DISP1 kinetic control. The first step of the reaction is an attack, via the oxygen atom, of the electrogenerated ketyl radical anion RR'CO•- at CO2. Further reduction of the carbonate-like adduct arising by such an attack followed by a second carboxylation reaction gives an arene-2-carboxylic acid.

Trypsin entrapped within liposomes. Partition of a low-molecular-mass substrate as the main factor in kinetic control of hydrolysis

1991 ◽  
Vol 56 (3) ◽  
pp. 712-717 ◽  
Author(s):  
Jana Formelová ◽  
Albert Breier ◽  
Peter Gemeiner ◽  
Lubica Kurillová
Keyword(s):  
Molecular Mass ◽  
Egg Yolk ◽  
Kinetic Control ◽  
Hydrolysis Kinetics ◽  
Liposomal Membrane ◽  
Kinetics Of ◽  
Main Factor

Trypsin has been entrapped within liposomes prepared from egg yolk phospholipides by the method of controlled dialysis, and the hydrolysis kinetics of Nα-benzoyl-DL-arginine p-nitroaniline catalyzed by the liposome-entrapped trypsin has been studied by monitoring the flux of substrate and product across the liposomal membrane. The partitioning of the substrate and product between liposomal and extraliposomal environment has been found to represent the main factor in the kinetic control of the hydrolysis.

scholarly journals Reduction Mechanism of Fine Hematite Ore Particles in Suspension

2021 ◽  
Author(s):  
Zhiyuan Chen ◽  
Christiaan Zeilstra ◽  
Jan van der Stel ◽  
Jilt Sietsma ◽  
Yongxiang Yang
Keyword(s):  
Particle Size ◽  
Temperature Drop ◽  
Reduction Rate ◽  
Reduction Process ◽  
Reciprocal Relationship ◽  
Drop Tube ◽  
Surface Nucleation ◽  
Order Of Magnitude ◽  
Relationship Of ◽  
Kinetics Of

AbstractIn order to understand the pre-reduction behaviour of fine hematite particles in the HIsarna process, change of morphology, phase and crystallography during the reduction were investigated in the high temperature drop tube furnace. Polycrystalline magnetite shell formed within 200 ms during the reduction. The grain size of the magnetite is in the order of magnitude of 10 µm. Lath magnetite was observed in the partly reduced samples. The grain boundary of magnetite was reduced to molten FeO firstly, and then the particle turned to be a droplet. The Johnson-Mehl-Avrami-Kolmogorov model is proposed to describe the kinetics of the reduction process. Both bulk and surface nucleation occurred during the reduction, which leads to the effect of size on the reduction rate in the nucleation and growth process. As a result, the reduction rate constant of hematite particles increases with the increasing particle size until 85 µm. It then decreases with a reciprocal relationship of the particle size above 85 µm.

Kinetics of synthesizing process for obtaining iron nanopowder by chemical-metallurgical method under isothermal conditions

2021 ◽  
pp. 72-77
Author(s):  
Tien Hiep Nguyen ◽  
◽  
Van Minh Nguyen ◽  
Keyword(s):  
Hydrogen Reduction ◽  
Average Particle Size ◽  
Chemical Deposition ◽  
Reduction Process ◽  
Nitrogen Adsorption ◽  
Specific Rate ◽  
Average Particle ◽  
Isothermal Conditions ◽  
Electron Microscopes ◽  
Kinetics Of

In this work the kinetics of synthesizing process of metallic iron nanopowder by hydrogen reduction from α-FeOOH hydroxide under isothermal conditions were studied. α-FeOOH nanopowder was prepared in advance by chemical deposition from aqueous solutions of iron nitrate Fe(NO3)3 (10 wt. %) and alkali NaOH (10 wt. %) at room temperature, pH = 11, under the condition of continuous stirring. The hydrogen reduction process of α-FeOOH nanopowder under isothermal conditions was carried out in a tube furnace in the temperature range from 390 to 470 °C. The study of the crystal structure and composition of the powders was performed by X-ray phase analysis. The specific surface area S of the samples was measured using BET method by low-temperature nitrogen adsorption. The average particle size D of powders was determined via the measured S value. The size characteristics and morphology of the particles were investigated by transmission and scanning electron microscopes. The calculation of the kinetic parameters of the hydrogen reduction process of α-FeOOH under isothermal conditions was carried out by the Gray-Weddington model and Arrhenius equation. It is shown that the rate constant of reduction at 470 °C is approximately 2.2 times higher than in the case at 390 °C. The effective activation energy of synthesizing process of iron nanopowder by hydrogen reduction from α-FeOOH was ~38 kJ/mol, which indicates a mixed reaction mode. In this case, the kinetics overall process is limited by both the kinetics of the chemical reaction and the kinetics of diffusion, respectively, an expedient way to accelerate the process by increasing the temperature or eliminate the diffusion layer of the reduction product by intensive mixing. It is show that Fe nanoparticles obtained by hydrogen reduction of its hydroxide at 410 °C, corresponding to the maximum specific rate of the reduction process, are mainly irregular in shape, evenly distributed, the size of which ranges from several dozens to 100 nm with an average value of 75 nm.

Reduction Kinetics of Mill Scale Briquettes by Using A3 Fine Coal as a Reductant

2021 ◽  
Vol 21 (4) ◽  
pp. 2563-2567
Author(s):  
Nguyen Hoang Viet ◽  
Pham Ngoc Dieu Quynh ◽  
Nguyen Thi Hoang Oanh
Keyword(s):  
Reaction Rate ◽  
Reduction Process ◽  
Reduction Reaction ◽  
Reaction Rate Constant ◽  
Reduction Degree ◽  
Furnace Temperature ◽  
Time Duration ◽  
Mill Scale ◽  
Fine Coal ◽  
Kinetics Of

In this work, a mixture of mill scale with 5 wt% molasses as binder was pressed under pressure of 200 MPa to prepare briquettes. The reduction process was performed at the temperature of 1000, 1050, 1100, 1150 and 1200 °C in the bed of A3 fine coal as the reductant. The degree of reduction was evaluated at time duration of 15, 30, 45, 60, 90 and 150 minutes, after the furnace temperature reached the predetermined reduction temperature. The highest reduction degree is 94.7% at the reduction process temperature of 1200 °C. Reaction rate constant (k) increased from 4.63×10-4 to 5.03×10-3 min-1 when the temperature increased from 1000 to 1200 °C. The apparent activation energy of the reduction reaction (Ea) is about 95.6 kJ/mole.

The enhancement of nitrification by indirect aeration and kinetic control in a submerged biofilm reactor

1994 ◽  
Vol 30 (11) ◽  
pp. 79-90 ◽  
Author(s):  
Sheng-Kun Chen ◽  
Sheng-Shung Cheng
Keyword(s):  
Suspended Solid ◽  
Biofilm Reactor ◽  
Nitrifying Bacteria ◽  
Flow Mode ◽  
Kinetic Control ◽  
Surface Loading ◽  
Low Concentrations ◽  
Film Reactor ◽  
Corrugated Plates ◽  
Kinetics Of

A submerged biological fixed-film reactor packed with plastic corrugated plates was employed to treat a wastewater of 100-400 mg NH4+-N/l and 80-130 mg COD/l. Nitrification and COD removal occurred in the reactor simultaneously. The kinetics of ammonium inhibition was studied, and used to control the bioreactor with the optimum condition. This operation strategy of kinetic control was able to reduce the duration of the acclimation of nitrifying bacteria in the reactor, and to enhance the removal of ammonium up to 95-98 %. The flow mode of indirect aeration in the reactor was able to maintain the suspended solid in the effluent below 4 mg/l without biofilm sloughing-off throughout the 300 operation days. In addition, the kinetic control and indirect aeration strategy of operation were able to obtain stable and low concentrations of COD, ammonium and nitrite in the effluent, and a high biomass of 14 g VSS/l in the reactor, when the influent loading of ammonium was up to 0.74 kg NH4+-N/m3-day associated with the medium surface loading of 10.4 g NH4+-N/m2-day.

Preparation of nanostructured titanium carbonitride particles by Mg-thermal reduction

2005 ◽  
Vol 20 (4) ◽  
pp. 844-849 ◽  
Author(s):  
D.W. Lee ◽  
J.H. Ahn ◽  
B.K. Kim
Keyword(s):  
Process Optimization ◽  
Reduction Process ◽  
Liquid Solution ◽  
Thermal Reduction ◽  
Titanium Carbonitride ◽  
Feeding Rates ◽  
Nitrogen Gas ◽  
Nanostructured Titanium ◽  
Experimental Parameters ◽  
Excess Mg

Nanostructured titanium carbonitride (TiC0.5N0.5) powders were synthesized by a Mg-thermal reduction process. The evaporated liquid solution made from TiCl4 + ¼C2Cl4 reacted with liquid magnesium protected with nitrogen gas. The extremely fine titanium carbonitride particles of about 50 nm were successfully produced by the reaction of Ti and C atoms released from chloride reduction with liquid magnesium and nitrogen gas. After the reduction process, the residual phases of MgCl2 and the excess Mg were removed by mechanical vacuum conditions. To obtain the maximized stoichiometry of product, the process optimization with thermodynamic study was performed with various experimental parameters such as reaction temperatures and solution feeding rates.

Sorption Kinetics of Uranium-238, Neptunium-237, Caesium-134, and Strontium-85 on a Glacial Deposit

1997 ◽  
Vol 506 ◽  
Author(s):  
L.N. Moyes ◽  
D.J. Bunker ◽  
J.T. Smith ◽  
F.R. Livens ◽  
C.R. Hughes ◽  
...  
Keyword(s):  
Waste Disposal ◽  
Kinetic Models ◽  
Sorption Kinetics ◽  
Kinetic Control ◽  
Glacial Deposit ◽  
Sorption Behaviour ◽  
Low Level ◽  
The Individual ◽  
Kinetics Of ◽  
Uptake Mechanisms

ABSTRACTBatch sorption experiments have been used to assess the sorption behaviour of four radionuclides, important in the context of low-level waste disposal, on a glacial substrate. Data for sorption of 238U, 237Np, 134Cs and 85Sr are compared and agree well with independent studies. A series of well-established kinetic models have been used to describe the individual uptake mechanisms and rate parameters reported. Sorption occurs via both equilibrium and kinetically controlled pathways, with neptunium sorption being under kinetic control to the greatest extent.

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