On the Mechanism and Substituent Effects of the Tl(III) Oxidation of Phenylethylenes in Methanol

1973 ◽  
Vol 51 (14) ◽  
pp. 2366-2374 ◽  
Author(s):  
L. Nadon ◽  
M. Tardat ◽  
M. Zador ◽  
S. Fliszar
Keyword(s):  
Substituent Effects ◽  
Oxidation Products ◽  
Rate Determining Step ◽  
Mechanism Of Reaction

The oxidation of phenylethylenes by Tl(NO3)3 in methanol proceeds rapidly and selectively to give the products resulting from the migration of aryl groups, i.e., (i) the 1,1-dimethoxy-2-phenylethanes from the corresponding styrenes, (ii) the phenylacetones from the α-methylstyrenes, and (iii) the two possible deoxybenzoines from the 1,1,-diphenylethylenes. The kinetic results, which indicate the formation of the thallic–organic intermediate to be the rate determining step, are discussed in terms of the mechanism of reaction and show the role of the coordination of Tl(III). Hammett's relationship, with ρ = −4.2, describes the substituent effects for the competitive oxidation of ring-substituted styrenes and α-methylstyrenes. The relative migratory aptitudes of aryl groups, as determined from the oxidation products of ring-substituted 1,1-diphenylethylenes, is correlated to Brown's σ+ constants, with ρ+ = −2.27.

Mechanistic Insights into Fe Catalyzed α-C-H Oxidations of Tertiary Amines

2019 ◽  
Author(s):  
Christopher J. Legacy ◽  
Frederick T. Greenaway ◽  
Marion Emmert
Keyword(s):  
Free Radical ◽  
Catalytic Mechanism ◽  
Catalyst System ◽  
Oxidation Products ◽  
Tertiary Amines ◽  
Catalyst Activation ◽  
Rate Determining Step ◽  
Fe Catalyst ◽  
Ligand Coordination ◽  
Rate Kinetics

We report detailed mechanistic investigations of an iron-based catalyst system, which allows the α-C-H oxidation of a wide variety of amines, including acyclic tertiary aliphatic amines, to afford dealkylated or amide products. In contrast to other catalysts that affect α-C-H oxidations of tertiary amines, the system under investigation employs exclusively peroxy esters as oxidants. More common oxidants (e.g. tBuOOH) previously reported to affect amine oxidations via free radical pathways do not provide amine α-C-H oxidation products in combination with the herein described catalyst system. Motivated by this difference in reactivity to more common free radical systems, the investigations described herein employ initial rate kinetics, kinetic profiling, Eyring studies, kinetic isotope effect studies, Hammett studies, ligand coordination studies, and EPR studies to shed light on the Fe catalyst system. The obtained data suggest that the catalytic mechanism proceeds through C-H abstraction at a coordinated substrate molecule. This rate-determining step occurs either at an Fe(IV) oxo pathway or a 2-electron pathway at a Fe(II) intermediate with bound oxidant. We further show via kinetic profiling and EPR studies that catalyst activation follows a radical pathway, which is initiated by hydrolysis of PhCO3 tBu to tBuOOH in the reaction mixture. Overall, the obtained mechanistic data support a non-classical, Fe catalyzed pathway that requires substrate binding, thus inducing selectivity for α-C-H functionalization.<br>

scholarly journals The Effectiveness of Glutathione Redox Status as a Possible Tumor Marker in Colorectal Cancer

2021 ◽  
Vol 22 (12) ◽  
pp. 6183
Author(s):  
Delia Acevedo-León ◽  
Lidia Monzó-Beltrán ◽  
Segundo Ángel Gómez-Abril ◽  
Nuria Estañ-Capell ◽  
Natalia Camarasa-Lillo ◽  
...  
Keyword(s):  
Colorectal Cancer ◽  
Redox State ◽  
Reduced Glutathione ◽  
Redox Status ◽  
Oxidation Products ◽  
Interventional Study ◽  
Thiol Redox State ◽  
Thiol Redox ◽  
Glutathione Redox

The role of oxidative stress (OS) in cancer is a matter of great interest due to the implication of reactive oxygen species (ROS) and their oxidation products in the initiation of tumorigenesis, its progression, and metastatic dissemination. Great efforts have been made to identify the mechanisms of ROS-induced carcinogenesis; however, the validation of OS byproducts as potential tumor markers (TMs) remains to be established. This interventional study included a total of 80 colorectal cancer (CRC) patients and 60 controls. By measuring reduced glutathione (GSH), its oxidized form (GSSG), and the glutathione redox state in terms of the GSSG/GSH ratio in the serum of CRC patients, we identified significant changes as compared to healthy subjects. These findings are compatible with the effectiveness of glutathione as a TM. The thiol redox state showed a significant increase towards oxidation in the CRC group and correlated significantly with both the tumor state and the clinical evolution. The sensitivity and specificity of serum glutathione levels are far above those of the classical TMs CEA and CA19.9. We conclude that the GSSG/GSH ratio is a simple assay which could be validated as a novel clinical TM for the diagnosis and monitoring of CRC.

Electrophilic additions to allenes. VI. The role of steric versus electronic effects in the reactions of arenesulphenyl halides with allenes

1980 ◽  
Vol 58 (24) ◽  
pp. 2737-2744 ◽  
Author(s):  
Dennis G. Garrattz ◽  
Pierre L. Beaulieu
Keyword(s):  
Positive Charge ◽  
Steric Effects ◽  
Rate Data ◽  
Electronic Effects ◽  
Rate Determining Step ◽  
Minimal Importance ◽  
Electrophilic Additions

The role of steric and electronic effects during the rate and product determining steps for the addition of arenesulphenyl chlorides to 1,3-disubstituted allenes has been briefly examined. Both effects appear to be generally of minimal importance during the rate determining step. The available rate data indicate the presence of little, if any, build up of positive charge on sulphur. These results are interpreted in terms of an SN2 attack on bivalent sulphur leading to an alkylidenethiiranium ion intermediate. Steric effects are of greater importance in the product determining step, particularly when the sulphenyl chlorides possess two bulky ortho substituents, as in the case of 2,4,6-triisopropylbenzenesulphenyl chloride.

From the Understanding of the Reaction Mechanism Towards Optimizing the Deposition Rate and Optoelectronic Properties of a-Si:H

1989 ◽  
Vol 149 ◽  
Author(s):  
S. Veprek ◽  
M. Heintze ◽  
R. Bayer ◽  
N. Jurčik-Rajman
Keyword(s):  
Reaction Mechanism ◽  
Surface Coverage ◽  
Kinetic Studies ◽  
Reactive Intermediates ◽  
Sticking Coefficient ◽  
High Quality ◽  
Rate Determining Step ◽  
Homogeneous Good ◽  
Good Agreement

ABSTRACTWe present new results of kinetic studies of the deposition of high quality a-Si:H which strongly support the reaction mechanism suggested in our earlier papers: 1. SiH4 → SiH2; 2. SiH2 + SiS4 → Si2H6 (SiH2 + Si2H6 → Si3H6); 3. Si2H6 → 2a-Si:H (Si3H8 → 3a-Si:H). The “SiH3 mechanism”, as promoted by several workers, is in contradiction with these experimental facts.The di- and trisilane, which have a much higher reactive sticking coefficient than monosilane, play the role of reactive intermediates which facilitate the heterogeneous decomposition of silicon carrying species at the surface of the growing film. The values of the reactive sticking coefficient of Si2H6 and Si3H8 depend on the surface coverage by chemisorbed hydrogen; they increase with decreasing surface coverage. Under the conditions of the growth of high quality a-Si:H films the reactive sticking coefficient of disilane amounts to 10−4 to 10−2 which is in a good agreement with recent data of other authors.The rate determining step of the growth of high quality a-Si:H films is the desorption of hydrogen from the surface of the growing film. This can be strongly enhanced by ion bombardment at impact energy of <100 eV. In this way, homogeneous, good quality films were deposited at rates up to 1800 Angströms/min, and there is a well justified hope that this rate can be further increased.

A Density Functional Theory Study of the Isomerization of Substituted 2and#39;-hydroxychalcones to the Corresponding Flavanones

2021 ◽  
Vol 43 (1) ◽  
pp. 25-25
Author(s):  
Said Abdelqadar Said Said Abdelqadar Said ◽  
Omar A Shareef and Abdulkhalik S Alkazzaz Omar A Shareef and Abdulkhalik S Alkazzaz
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Ring Closure ◽  
Basis Set ◽  
Functional Theory ◽  
Rate Determining Step ◽  
The Density Functional Theory ◽  
Electronic And Structural Properties ◽  
Maximum Hardness Principle

The transformation of 2and#39;-hydroxychalcones to their corresponding flavanones was studied theoretically by the use of the density functional theory (DFT) with B3-LYP/ 6-311G basis set to get important information about the role of both of electronic and structural properties in this process. The obtained energies were found to be in agreement with our previous results that obtained from HPLC studies. The estimated hardness, polarizability, and electrophilicity profiles were found to obey the maximum hardness principle (MHP), minimum polarizability principle (MPP), and the minimum electrophilicity principle (MEP) respectively. Flavanone ring closure was found to be the rate-determining step.

scholarly journals Oxidation of human haemoglobin by copper. Mechanism and suggested role of the thiol group of residue β-93

1977 ◽  
Vol 165 (1) ◽  
pp. 141-148 ◽  
Author(s):  
C C Winterbourn ◽  
R W Carrell
Keyword(s):  
Electron Transfer ◽  
Binding Sites ◽  
Equilibrium Dialysis ◽  
Thiol Group ◽  
Thiol Groups ◽  
Human Haemoglobin ◽  
High Affinity ◽  
Rate Determining Step ◽  
Haemoglobin Molecule

Addition of Cu(II) ions to human oxyhaemoglobin caused the rapid oxidation of the haem groups of the beta-chain. Oxidation required binding of Cu(II) to sites involving the thiol group of beta-93 residues and was prevented when these groups were blocked with iodoacetamide or N-ethylmaleimide. Equilibrium-dialysis studies showed three pairs of binding sites, two pairs with high affinity for Cu(II) and one pair with lower affinity. It was the second pair of high-affinity sites that were blocked with iodoacetamide and were involved in haem oxidation. Cu(II) oxidized deoxyhaemoglobin at least ten times as fast as oxyhaemoglobin, and analysis of rates suggested that binding rather than electron transfer was the rate-determining step. No thiol-group oxidation to disulphides occurred during the period of haem oxidation, although it did occur subsequently in the presence of oxygen, or when Cu(II) was added to methaemoglobin. It is proposed that thiol oxidation did not occur because there exists a pathway of electron transfer between the haem group and copper bound to the beta-93 thiol groups. The route for this electron transfer is discussed, as well as the implications as to the function of the beta-93 cysteine in the haemoglobin molecule.

Sign in / Sign up

Export Citation Format

Share Document