Titanium and zirconium ferrocene-substituted enolates and their reaction products with benzaldehyde and acetophenone: structural and kinetic studies of the aldol condensation pathway

1995 ◽  
Vol 14 (9) ◽  
pp. 4101-4108 ◽  
Author(s):  
Patrick Veya ◽  
Pier Giorgio Cozzi ◽  
Carlo Floriani ◽  
Francois P. Rotzinger ◽  
Angiola Chiesi-Villa ◽  
...  
Keyword(s):  
Aldol Condensation ◽  
Kinetic Studies ◽  
Reaction Products

STUDIES ON A LIPOXIDASE SYSTEM FROM SUNFLOWER SEEDS AND SEEDLINGS

1958 ◽  
Vol 36 (11) ◽  
pp. 1149-1157 ◽  
Author(s):  
Oluf L. Gamborg ◽  
Saul Zalik
Keyword(s):  
Kinetic Studies ◽  
Maximum Activity ◽  
Sunflower Seeds ◽  
Reaction Products ◽  
Total Oxidation ◽  
Ph Optimum ◽  
Potassium Oleate ◽  
Enzyme Preparations ◽  
Cytoplasmic Proteins ◽  
Total Fat

Lipoxidase activity was obtained in enzyme preparations from sunflower seeds and seedlings. A partly purified preparation from seedlings was used for enzyme kinetic studies. The pH optimum was 6.8 and 100% oxygen was required for maximum activity. The Michaelis constant, with potassium linoleate as substrate, was 1.64 × 10−3 M. The reaction products were conjugated dienes. Enzyme activity was not affected by various metal and sulphydryl inhibitors nor by α-tocopherol, but catechol, α-naphthol, ethanol, and potassium oleate were inhibitory. Oil from flax, rape, and sunflower seeds reduced total oxidation of linoleate by the enzyme. Copper sulphate increased the rate and total oxidation of the linoleate–lipoxidase system, but iron, manganese, magnesium, and calcium were without effect. Lipoxidase activity was associated with mitochondrial (15,000 × g), intermediate (25,000 × g), and microsomal (100,000 × g) fractions, as well as with the soluble cytoplasmic proteins. Lipoxidase activity in seedlings increased during initial stages of germination, then decreased. The most rapid depletion of total fat in the seedlings coincided with maximum lipoxidase activity.

scholarly journals New Hypothesis for the Molecular Mechanism of Surface-Dependent Activation of Hageman Factor (Factor XII)

1977 ◽  
Author(s):  
John H. Griffin
Keyword(s):  
Ellagic Acid ◽  
Disulfide Bonds ◽  
Kinetic Studies ◽  
Factor Xii ◽  
Reaction Products ◽  
Surface Binding ◽  
Proteolytic Activation ◽  
Hageman Factor ◽  
New Hypothesis ◽  
Dependent Mechanism

The surface-dependent mechanism of activation of highly purified human Hageman factor (HF) was studied using 3H-DFP uptake as a quantitative active site titrant. HF was treated in various ways and the reaction mixture was exposed to 3 mM 3H-DFP for 5 min at 37°. Following addition of SDS and removal of free DFP by dialysis, the reaction products were analyzed on SDS gels. In solution, the HF zymogen at 80,000 MW took up 0.015 mol DFP per mol HF. HF bound to kaolin, celite, or ellagic acid with or without high MW kininogen took up the same 0.015 mol DFP per mol HF. However, HF bound to celite or kaolin with high MW kininogen and kallikrein took up 0.9 mol DFP per mol HF into a 28,000 MW fragment of HF. In approximately half of these activated HF molecules, this 28,000 MW fragment was linked by disulfide bonds to a 52,000 MW fragment in a surface-bound 80,000 MW form of activated HF. In clotting assays, DFP did not inhibit kaolin-bound HF unless the surface-bound HF first had been proteolytically activated by kallikrein.Kinetic studies of the cleavage of 125I-HF by kallikrein or by plasmin in the presence of high MW kininogen showed that kaolin-bound HF was cleaved more than 20 times faster than HF in solution.These results suggest that binding to kaolin or celite or ellagic acid, classically known as “activating surfaces”, does not convert a detectable fraction (< 1%) of the bound HF molecules to active enzymes. Rather, surface-binding makes HF molecules much more susceptible to proteolytic activation in the presence of high MW kininogen, and the reciprocal proteolytic activations of HF and prekallikrein are thus greatly stimulated by “activating surfaces”.

Kinetic Studies of Hydrodeoxygenation of Ethyl Ester of Decane Acid over a Ni-Cu-Mo/Al2O3 Catalyst

2019 ◽  
Vol 19 (1) ◽  
pp. 33-39
Author(s):  
R. G. Kukushkin ◽  
S. I. Reshetnikov ◽  
S. G. Zavarukhin ◽  
P. M. Eletskiy ◽  
V. A. Yakovlev
Keyword(s):  
Contact Time ◽  
Noble Metals ◽  
Flow Reactor ◽  
Experimental Studies ◽  
Kinetic Studies ◽  
Nickel Catalysts ◽  
Effective Rate ◽  
Main Reaction ◽  
Reaction Products ◽  
Fixed Catalyst

Nickel-based catalysts for hydrodeoxygenation of vegetable oils are an alternative to the systems based on noble metals and sulfide catalysts for hydrotreatment. Modification of the nickel catalysts with molybdenum and copper allows the yield of target products to be increased and the corrosion resistance of the catalytic system to be improved. The studies were aimed at establishing relationships between temperature, contact time and activity of the modified nickel-containing catalyst to hydroxygenation of esters of fatty carboxylic acids, as well as at determining effective kinetic parameters of the reactant consumption. A flow reactor with the fixed catalyst bed was used for experimental studies at РН2 = 0.25 MPa, temperatures 270, 285, 300 and 315 °C, contact time varied from 600 to 1800 s. It was shown that the selectivity to the main reaction products – nonane and decane – did not change upon varying the reaction temperature and contact time. The experimental data were used for determining the effective rate constants and activation energy of the reaction.

Photocatalytic Decomposition of Metoprolol and Its Intermediate Organic Reaction Products: Kinetics and Degradation Pathway

2016 ◽  
Vol 14 (3) ◽  
pp. 809-820 ◽  
Author(s):  
Alfonso Pinedo ◽  
Mariana López ◽  
Elisa Leyva ◽  
Brenda Zermeño ◽  
Benito Serrano ◽  
...  
Keyword(s):  
Uv Light ◽  
Reaction Pathway ◽  
Kinetic Studies ◽  
Initial Reaction Rate ◽  
Degradation Pathway ◽  
Photocatalytic Decomposition ◽  
Initial Reaction ◽  
Low Molecular Weight ◽  
Reaction Products ◽  
Constant Flow Rate

Abstract High purity metoprolol prepared by neutralization of an aqueous solution of metoprolol tartrate is efficiently mineralized to CO2 and water by photocatalysis with TiO2, UV light and a constant flow rate of oxygen. Since the tartrate anions were eliminated, all the HO• generated by photocatalysis reacted efficiently with the aromatic part of the medication. The reaction pathway includes two routes of degradation. The first one includes the transformation of metoprolol to hydroquinone via formation of 4-(2-methoxyethyl)phenol, 2-(4-hydroxyphenyl)ethanol and 4-hydroxybenzaldehyde. Metoprolol is also degraded directly to hydroquinone. Then, this aromatic compound is oxidized to 1,2,4-benzenetriol, which is rapidly oxidized to low molecular weight organic acids before being completely mineralized to CO2 and water. Kinetic studies indicated that the initial reaction rate of the degradation of metoprolol, 4-(2-methoxyethyl)phenol, 2-(4-hydroxyphenyl)ethanol and 4-hydroxybenzaldehyde is described by the LH-HW model.

The Mechanism of the Alkali catalysed Phenol-Formaldehyde reaction

1955 ◽  
Vol 8 (2) ◽  
pp. 194 ◽  
Author(s):  
JS Fitzgerald ◽  
RJL Martin
Keyword(s):  
Induction Period ◽  
Aldol Condensation ◽  
Phenol Formaldehyde ◽  
Kinetic Studies ◽  
Bimolecular Reaction ◽  
Hydrogen Ion ◽  
Catalysed Reaction ◽  
Alkaline Reaction ◽  
Cannizzaro Reaction ◽  
Mechanism Of The Reaction

Kinetic studies on the 2,3,4,5-tetramethylphenol(prehnitenol)- and 2,6-xylenol-formaldehyde reactions indicate that the alkali catalysed reaction is not a simple bimolecular reaction. The rate of the 2,6-xylenol-formaldehyde reaction in the presence of excess alkali has been shown to be proportional to [phenoxide]1.4 [formaldehyde]1.4 [free alkali]-0.4. The mechanism of the reaction has been interpreted as a reaction between the phenoxide ion and CH2=O together with other simultaneous reactions. It is unlikely that the +CH2OH plays any part in the alkali catalysed reaction. Attempts have been made to interpret the results on the basis that a hemiformal rearranges to a phenol alcohol and that the ion +CH2OPh reacts with a phenoxide ion. In any case it is not possible to give a complete mechanism with certainty. The degree of formation of hemiformal is too small to be detected by hydrogen ion measurements. When the Cannizzaro reaction of formaldehyde is carried out in the presence of a phenol, the phenoxide Ions catalyse a condensation which 1s presumably an aldol condensation. This reaction having a long induction period and being autocatalytic does not assume importance In the early stages of the reaction. A compound, probably 2,2'-dihydroxy-3,3',4,4',5,5',6,6'-octamethyldiphenylmethane, has been isolated from the alkaline reaction between prehnitenol and formaldehyde.

Structure and Reactivity in Oxidation of Elastomers

1965 ◽  
Vol 38 (5) ◽  
pp. 1198-1213 ◽  
Author(s):  
Parry M. Norling ◽  
T. C. P. Lee ◽  
A. V. Tobolsky
Keyword(s):  
Solid Phase ◽  
Kinetic Studies ◽  
Radical Mechanism ◽  
Reaction Products ◽  
Olefin Oxidation ◽  
Oxidation Of Hydrocarbons ◽  
Free Radical Mechanism ◽  
Hydrocarbon Polymers ◽  
A Chain ◽  
Competing Reactions

Abstract Oxidation of hydrocarbons is a much studied and much reviewed subject, yet much remains to be understood about complexities of competing reactions that take place as hydrocarbons react with oxygen. The generally accepted free radical mechanism for low temperature reaction (below 200° C) stems from kinetic studies by Semenov, Hinshelwood, Farmer, Gee, Bolland, and Bateman of hydrocarbon and olefin oxidation in the gas and liquid phase: Such a chain mechanism appears to be straightforward, but studies of autoxidations are complicated by sensitivity to trace metals, which decompose hydroperoxides, and to the nature of reaction products, which may function as inhibitors or accelerators. The character of the reaction may vary considerably with time as these reaction products accumulate. Hydroperoxides may decompose by unimolecular or bimolecular pathways to produce alkoxy, peroxy, or hydroxyl radicals. These are known to have various selectivities and hence will produce different propagating species with differing rates of termination. Alternately hydroperoxides may react with sulfur, nitrogen, aldehydic, basic, or acidic functions producing no radicals at all. Such reactions vary drastically from one system to another. The study of autoxidations thus becomes the challenging problem of trying to separate one reaction from another. One method of avoiding such difficult problems is to work under simplifying conditions. One approach is to study oxidations with an external initiator such as azobisisobutyronitrile or benzoyl peroxide under conditions such that the hydroperoxides formed during oxidation are relatively stable products. This has been most successfully applied to kinetic studies on liquid hydrocarbons containing benzylic or allylic hydrogens. This review is concerned with some recent work on initiated oxidations of hydrocarbon polymers in the solid phase and attempts to show how the results may be related to the more complicated autoxidation process.

STUDIES ON A LIPOXIDASE SYSTEM FROM SUNFLOWER SEEDS AND SEEDLINGS

1958 ◽  
Vol 36 (1) ◽  
pp. 1149-1157 ◽  
Author(s):  
Oluf L. Gamborg ◽  
Saul Zalik
Keyword(s):  
Kinetic Studies ◽  
Maximum Activity ◽  
Sunflower Seeds ◽  
Reaction Products ◽  
Total Oxidation ◽  
Ph Optimum ◽  
Potassium Oleate ◽  
Enzyme Preparations ◽  
Cytoplasmic Proteins ◽  
Total Fat

Lipoxidase activity was obtained in enzyme preparations from sunflower seeds and seedlings. A partly purified preparation from seedlings was used for enzyme kinetic studies. The pH optimum was 6.8 and 100% oxygen was required for maximum activity. The Michaelis constant, with potassium linoleate as substrate, was 1.64 × 10−3 M. The reaction products were conjugated dienes. Enzyme activity was not affected by various metal and sulphydryl inhibitors nor by α-tocopherol, but catechol, α-naphthol, ethanol, and potassium oleate were inhibitory. Oil from flax, rape, and sunflower seeds reduced total oxidation of linoleate by the enzyme. Copper sulphate increased the rate and total oxidation of the linoleate–lipoxidase system, but iron, manganese, magnesium, and calcium were without effect. Lipoxidase activity was associated with mitochondrial (15,000 × g), intermediate (25,000 × g), and microsomal (100,000 × g) fractions, as well as with the soluble cytoplasmic proteins. Lipoxidase activity in seedlings increased during initial stages of germination, then decreased. The most rapid depletion of total fat in the seedlings coincided with maximum lipoxidase activity.

Phenolic Resins – Characterizations and Kinetic Studies of Different Resols Prepared with Different Catalysts and Formaldehyde/Phenol Ratios (I)

2002 ◽  
Vol 10 (5) ◽  
pp. 341-360 ◽  
Author(s):  
J. Bouajila ◽  
G. Raffin ◽  
H. Waton ◽  
C. Sanglar ◽  
J.O. Païsse ◽  
...  
Keyword(s):  
Kinetic Studies ◽  
Size Exclusion ◽  
Kinetic Properties ◽  
Reaction Products ◽  
Phenolic Resins ◽  
Chemical Assay ◽  
Exclusion Chromatography ◽  
Kinetics Of Formation ◽  
Minor Compounds

The physicochemical and kinetic properties of resols prepared with different catalysts (NaOH, LiOH and Ba(OH)2) and variable formaldehyde/phenol ratios (2.5 £ R £ 3.5) were followed to determine their effects on the mechanisms and reaction products at a fixed pH and temperature. Kinetic monitoring and quantification of residual monomers were carried out by liquid chromatography coupled with mass spectrometry (LC/UV/MS), by 13C nuclear magnetic resonance (NMR) and by chemical assay for formaldehyde. Oligomer formation (n ≥ 2) was determined by LC/UV/MS, size exclusion chromatography (SEC) and 13C NMR. It was found that minor compounds form during syntheses (phenol methanol hemiacetals, hemiacetals of phenol and of oligomers…) and that the ratio R affects primarily the kinetics of formation of monomers and oligomers, in contrast to the catalysts that modify reaction mechanisms. The understanding of the structure of the resols was an important step for the determination of the final properties of the material.

scholarly journals Directed Synthesis of Humic and Fulvic Derivatives with Enhanced Antioxidant Properties

Agronomy ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 2047
Author(s):  
Alexander B. Volikov ◽  
Nikita V. Mareev ◽  
Andrey I. Konstantinov ◽  
Alexandra A. Molodykh ◽  
Sofia V. Melnikova ◽  
...  
Keyword(s):  
Humic Substances ◽  
Humic Acids ◽  
Antioxidant Properties ◽  
Kinetic Studies ◽  
Fulvic Acids ◽  
Mass Spectrometry Analysis ◽  
Reaction Products ◽  
Spectrometry Analysis ◽  
And Control ◽  
Kinetics Of

Redox moieties, which are present in the molecular backbone of humic substances (HS), govern their antioxidant properties. We hypothesized that a directed modification of the humic backbone via incorporation of redox moieties with known redox properties might provide an efficient tool for tuning up antioxidant properties of HS. In this work, hydroquinonoid and hydronaphthoquinonoid centres were used, which possess very different redox characteristics. They were incorporated into the structure of coal (leonardite) humic acids CHA) and peat fulvic acids (PFA). For this goal, an oxidative copolymerization of phenols was used. The latter was induced via oxidation of hydroquinones and hydroxynapjtaquinones with a use of Fenton’s reagent. The structure of the obtained products was characterized using NMR and FTIR spectroscopy. H/D labelling coupled to FT ICR mass spectrometry analysis was applied for identification of the reaction products as a tool for surmising on reaction mechanism. It was shown that covalent -C-C- bond were formed between the incorporated redox centers and aromatic core of HS. The parent humic acids and their naphthoquinonoid derivatives have demonstrated high accepting capacity. At the same time, fulvic acids and their hydroquinonoid derivatives have possessed both high donor and high antioxidant capacities. The kinetic studies have demonstrated that both humic acids and their derivatives showed much slower kinetics of antioxidant reactions as compared to fulvic acids. The obtained results show, firstly, substantial difference in redox and antioxidant properties of the humic and fulvic acids, and, secondly, they can serve as an experimental evidence that directed chemical modification of humic substances can be used to tune and control antioxidant properties of natural HS.

scholarly journals Photocatalytic degradation of Bisphenol A: Kinetic studies and determination of the reaction pathway

2018 ◽  
Vol 16 (5) ◽  
Author(s):  
Luis F. Garay Rodríguez ◽  
Brenda Zermeño ◽  
Karla Alejandra López De la O ◽  
Elisa Leyva ◽  
Edgar Moctezuma
Keyword(s):  
Aqueous Solutions ◽  
Photocatalytic Degradation ◽  
Reaction Rate ◽  
Reaction Pathway ◽  
Batch Reactor ◽  
Analytical Techniques ◽  
Kinetic Studies ◽  
Degradation Process ◽  
Reaction Products ◽  
Uv Lamps

The photocatalytic degradation of BPA aqueous solutions with commercial TiO2 (Evonik P25) was carried out in a home-made batch reactor illuminated with four UV lamps (λmax= 365 nm) in order to determine the kinetic parameters of the reaction rate equation and to identify and quantify some of the most stable aromatic intermediate reaction products. Low concentration (20 ppm) BPA solutions were completely degraded and mineralized in less than three hours of reaction. Whereas, BPA aqueous solutions with concentration above 50 ppm are transformed in other chemical compounds in 6 hours of reaction and fully mineralized in 15 hours of reaction. Kinetic analysis of the experimental results of BPA concentration as a function of time indicated that this photocatalytic degradation process follows a LH-HW reaction rate law where the reaction order shift from zero order to first order as the reactant concentration is decreased. Analysis of the reaction samples by different analytical techniques indicated that BPA is mineralized via formation of hydroquinone, benzoquinone, benzene-triol, catechol, and phenol by two simultaneous reaction pathways.

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