A Concerted Mechanism for the Transfer of the Thiophosphinoyl Group from Aryl Dimethylphosphinothioate Esters to Oxyanionic Nucleophiles in Aqueous Solution

2005 ◽  
Vol 127 (21) ◽  
pp. 7703-7711 ◽  
Author(s):  
Ikenna Onyido ◽  
Krzysztof Swierczek ◽  
Jamie Purcell ◽  
Alvan C. Hengge
Keyword(s):  
Aqueous Solution ◽  
Concerted Mechanism

scholarly journals Effect of the Supporting Electrolyte on Chloroform Reduction at a Silver Electrode in Aqueous Solutions

Molecules ◽  
2021 ◽  
Vol 26 (3) ◽  
pp. 525
Author(s):  
Anna M. Brudzisz ◽  
Agnieszka Brzózka ◽  
Grzegorz D. Sulka
Keyword(s):  
Aqueous Solution ◽  
Cyclic Voltammetry ◽  
Supporting Electrolyte ◽  
Reduction Peak ◽  
Electrocatalytic Reduction ◽  
Silver Surface ◽  
Concerted Mechanism ◽  
Ag Electrode ◽  
Wide Range ◽  
First Time

Herein, we report, for the first time, a comparative study on the electrocatalytic reduction of chloroform on silver in different aqueous supporting electrolytes. Cyclic voltammetry measurements were performed at a wide range of scan rates and concentrations of CHCl3 using 0.05 M NaClO4, NaH2PO4, and Na2HPO4 as supporting electrolytes. We observed that a type of supporting electrolyte anion strongly influences both the potential as well as the current density of the chloroform reduction peak, mainly due to the presence of OH− in an alkaline Na2HPO4 solution, which is a specifically interacting anion. Moreover, the highest sensitivity of the Ag electrode toward CHCl3 reduction was observed in a neutral NaClO4 aqueous solution. It was found that the electroreduction of chloroform at the silver surface occurs via a concerted mechanism regardless of the type of the studied supporting electrolyte.

Kinetics and mechanism of the aminolysis of thioesters and thiocarbonates in solution

2009 ◽  
Vol 81 (4) ◽  
pp. 685-696 ◽  
Author(s):  
Enrique A. Castro
Keyword(s):  
Experimental Data ◽  
Aqueous Solution ◽  
Rate Constant ◽  
Aqueous Ethanol ◽  
Kinetics And Mechanism ◽  
Kinetic Investigation ◽  
Concerted Mechanism ◽  
Tetrahedral Intermediate ◽  
Leaving Group ◽  
The Stability

The aminolysis reactions of thioesters and thiocarbonates, in either aqueous solution or in 44 wt % aqueous ethanol at 25 °C, are subjected to a kinetic investigation. The Brønsted-type plots (lg kN vs. amine pKa, where kN is the nucleophilic rate constant) obtained for these reactions can be grouped in three categories: linear plots with slopes 0.8-1, biphasic plots (two linear portions and a curve in between), and linear plots with slopes 0.4-0.6. The two former plots are attributed to stepwise reactions through a zwitterionic tetrahedral intermediate. The latter plots are associated with a concerted mechanism. The fact that some reactions are stepwise and others concerted depends on the stability of the zwitterionic tetrahedral intermediate. This work shows how the experimental data allows one to assess the mechanism of these reactions. Also discussed are the factors that affect the stability of this intermediate, which in turn determines the pathway followed by the reaction. The factors analyzed in this work are (i) the leaving group of the substrate, (ii) the nature of the amine, (iii) the non-leaving group of the substrate, (iv) the electrophilic group of the substrate (CS vs. CO), and (v) the solvent.

Structures Formed by Cryoprotective Agents Used in Freezc-Etching

1971 ◽  
Vol 29 ◽  
pp. 448-449
Author(s):  
G. G. Cocks ◽  
C. E. Cluthe
Keyword(s):  
Aqueous Solution ◽  
Polyethylene Oxide ◽  
Liquid Nitrogen Temperature ◽  
Ice Crystals ◽  
Etching Technique ◽  
Structural Constituent ◽  
Cryoprotective Agents ◽  
Quick Freezing ◽  
Freeze Etching ◽  
Fractured Surface

The freeze etching technique is potentially useful for examining dilute solutions or suspensions of macromolecular materials. Quick freezing of aqueous solutions in Freon or propane at or near liquid nitrogen temperature produces relatively large ice crystals and these crystals may damage the structures to be examined. Cryoprotective agents may reduce damage to the specimem, hut their use often results in the formation of a different set of specimem artifacts.In a study of the structure of polyethylene oxide gels glycerol and sucrose were used as cryoprotective agents. The experiments reported here show some of the structures which can appear when these cryoprotective agents are used.Figure 1 shows a fractured surface of a frozen 25% aqueous solution of sucrose. The branches of dendritic ice crystals surrounded hy ice-sucrose eutectic can be seen. When this fractured surface is etched the ice in the dendrites sublimes giving the type of structure shown in Figure 2. The ice-sucrose eutectic etches much more slowly. It is the smooth continuous structural constituent surrounding the branches of the dendrites.

Preparation and characterisation of vanadium pentoxide supported rhodium catalyst

1988 ◽  
Vol 46 ◽  
pp. 946-947
Author(s):  
A. Legrouri
Keyword(s):  
Aqueous Solution ◽  
Thermal Decomposition ◽  
Physicochemical Properties ◽  
Surface Area ◽  
Vanadium Pentoxide ◽  
High Purity ◽  
Gas Adsorption ◽  
Rhodium Catalyst ◽  
Optical Methods ◽  
Reducible Oxides

The industrial importance of metal catalysts supported on reducible oxides has stimulated considerable interest during the last few years. This presentation reports on the study of the physicochemical properties of metallic rhodium supported on vanadium pentoxide (Rh/V2O5). Electron optical methods, in conjunction with other techniques, were used to characterise the catalyst before its use in the hydrogenolysis of butane; a reaction for which Rh metal is known to be among the most active catalysts.V2O5 powder was prepared by thermal decomposition of high purity ammonium metavanadate in air at 400 °C for 2 hours. Previous studies of the microstructure of this compound, by HREM, SEM and gas adsorption, showed it to be non— porous with a very low surface area of 6m2/g3. The metal loading of the catalyst used was lwt%Rh on V2Q5. It was prepared by wet impregnating the support with an aqueous solution of RhCI3.3H2O.

TEM observation of iron oxide pillars in montmorillonite

1990 ◽  
Vol 48 (4) ◽  
pp. 882-883
Author(s):  
H. Mori ◽  
Y. Murata ◽  
H. Yoneyama ◽  
H. Fujita
Keyword(s):  
Aqueous Solution ◽  
Iron Oxide ◽  
Fine Particles ◽  
Aqueous Suspension ◽  
Volume Ratio ◽  
Exchange Capacity ◽  
Nano Composites ◽  
Pillared Montmorillonite ◽  
Topographic Features ◽  
Transmission Electron

Recently, a new sort of nano-composites has been prepared by incorporating such fine particles as metal oxide microcrystallites and organic polymers into the interlayer space of montmorillonite. Owing to their extremely large specific surface area, the nano-composites are finding wide application[1∼3]. However, the topographic features of the microstructures have not been elucidated as yet In the present work, the microstructures of iron oxide-pillared montmorillonite have been investigated by high-resolution transmission electron microscopy.Iron oxide-pillared montmorillonite was prepared through the procedure essentially the same as that reported by Yamanaka et al. Firstly, 0.125 M aqueous solution of trinuclear acetato-hydroxo iron(III) nitrate, [Fe3(OCOCH3)7 OH.2H2O]NO3, was prepared and then the solution was mixed with an aqueous suspension of 1 wt% clay by continuously stirring at 308 K. The final volume ratio of the latter aqueous solution to the former was 0.4. The clay used was sodium montmorillonite (Kunimine Industrial Co.), having a cation exchange capacity of 100 mequiv/100g. The montmorillonite in the mixed suspension was then centrifuged, followed by washing with deionized water. The washed samples were spread on glass plates, air dried, and then annealed at 673 K for 72 ks in air. The resultant film products were approximately 20 μm in thickness and brown in color.

The microstructure of functionalized poLyacrylonitrile beads for bioseparations

1990 ◽  
Vol 48 (4) ◽  
pp. 1094-1095
Author(s):  
Eduardo A. Kamenetzky ◽  
David A. Ley
Keyword(s):  
Aqueous Solution ◽  
Affinity Chromatography ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Surface Coverage ◽  
Vacuum Impregnation ◽  
Thin Sections ◽  
Selective Staining ◽  
Low Viscosity ◽  
Diamond Knife

The microstructure of polyacrylonitrile (PAN) beads for affinity chromatography bioseparations was studied by TEM of stained ultramicrotomed thin-sections. Microstructural aspects such as overall pore size distribution, the distribution of pores within the beads, and surface coverage of functionalized beads affect performance properties. Stereological methods are used to quantify the internal structure of these chromatographic supports. Details of the process for making the PAN beads are given elsewhere. TEM specimens were obtained by vacuum impregnation with a low-viscosity epoxy and sectioning with a diamond knife. The beads can be observed unstained. However, different surface functionalities can be made evident by selective staining. Amide surface coverage was studied by staining in vapor of a 0.5.% RuO4 aqueous solution for 1 h. RuO4 does not stain PAN but stains, amongst many others, polymers containing an amide moiety.

Highly efficient and selective photocatalytic CO2 to CO conversion in aqueous solution

2020 ◽  
Vol 56 (27) ◽  
pp. 3851-3854 ◽  
Author(s):  
Xiaomin Chai ◽  
Hai-Hua Huang ◽  
Huiping Liu ◽  
Zhuofeng Ke ◽  
Wen-Wen Yong ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Photocatalytic Performance ◽  
Aqueous Media ◽  
Highly Efficient ◽  
Co Conversion

A Co-based complex displayed the highest photocatalytic performance for CO2 to CO conversion in aqueous media.

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