Metal complexes as antioxidants. 7. Kinetics of inhibition of styrene autoxidation by zinc di-isopropyldithiophosphate

1980 ◽  
Vol 58 (1) ◽  
pp. 92-95 ◽  
Author(s):  
J. A. Howard ◽  
S-B. Tong
Keyword(s):  
Chain Transfer ◽  
Peroxy Radical ◽  
Chain Termination ◽  
Oxygen Absorption ◽  
Reaction Products ◽  
Radical Chain ◽  
Chain Initiation ◽  
Styrene Concentration ◽  
Kinetics Of ◽  
Kinetics Of Inhibition

Rates of oxygen absorption by styrene (RH) containing 2,2,3,3-tetraphenylbutane and zinc di-isopropyldithiophosphate at 30 °C obey the rate law [Formula: see text] where Ri is the rate of free-radical chain initiation. This order with respect to the styrene concentration implies extensive chain transfer from the poly(peroxystyryl)peroxy radical to a radical derived from the inhibitor. Reaction products confirm the displacement of a di-isopropyldithiophosphoryl radical in the chain termination reaction.Diethyldithiophosphoric acid also inhibits styrene autoxidation by a mechanism which involves extensive chain transfer.

The Kinetics of Inhibition of the Action of Thrombin by the Fibrinopeptides Formed during the Clotting of Fibrinogen

1966 ◽  
Vol 16 (01/02) ◽  
pp. 277-295 ◽  
Author(s):  
A Silver ◽  
M Murray
Keyword(s):  
Amino Acids ◽  
Competitive Inhibition ◽  
Amorphous Material ◽  
Peptide Bond ◽  
Initial Reaction ◽  
Reaction Products ◽  
Coagulation Mechanism ◽  
Kinetics Of ◽  
Kinetics Of Inhibition ◽  
Burk Plot

SummaryVarious investigators have separated the coagulation products formed when fibrinogen is clotted with thrombin and identified fibrinopeptides A and B. Two other peaks are observed in the chromatogram of the products of coagulation, but these have mostly been dismissed by other workers. They have been identified by us as amino acids, smaller peptides and amorphous material (37). We have re-chromatographed these peaks and identified several amino acids. In a closed system of fibrinogen and thrombin, the only reaction products should be fibrin and peptide A and peptide B. This reasoning has come about because thrombin has been reported to be specific for the glycyl-arginyl peptide bond. It is suggested that thrombin also breaks other peptide linkages and the Peptide A and Peptide B are attacked by thrombin to yield proteolytic products. Thrombin is therefore probably not specific for the glycyl-arginyl bond but will react on other linkages as well.If the aforementioned is correct then the fibrinopeptides A and B would cause an inhibition with the coagulation mechanism itself. We have shown that an inhibition does occur. We suggest that there is an autoinhibition to the clotting mechanism that might be a control mechanism in the human body.The experiment was designed for coagulation to occur under controlled conditions of temperature and time. Purified reactants were used. We assembled an apparatus to record visually the speed of the initial reaction, the rate of the reaction, and the density of the final clot formed after a specific time.The figures we derived made available to us data whereby we could calculate and plot the information to show the mechanism and suggest that such an inhibition does exist and also further suggest that it might be competitive.In order to prove true competitive inhibition it is necessary to fulfill the criteria of the Lineweaver-Burk plot. This has been done. We have also satisfied other criteria of Dixon (29) and Bergman (31) that suggest true competitive inhibition.

Metal complexes as antioxidants. V. Inhibition of hydrocarbon autoxidation by cupric complexes of dialkyldithiophosphoric and dialkyldithiocarbamic acids

1978 ◽  
Vol 56 (2) ◽  
pp. 157-163 ◽  
Author(s):  
J. H. B. Chenier ◽  
J. A. Howard ◽  
J. C. Tait
Keyword(s):  
Liquid Phase ◽  
Initial Rate ◽  
Copper Ions ◽  
Radical Scavenging ◽  
Peroxy Radical ◽  
Oxygen Absorption ◽  
Inhibition Rate ◽  
Chain Initiation ◽  
Considerable Length ◽  
Alkylperoxy Radicals

Liquid-phase reactions of alkylperoxy radicals with cupric complexes of dialkyldithiophosphoric and dialkyldithiocarbamic acids have been examined. These complexes have been shown to be extremely efficient peroxy radical scavenging antioxidants for hydrocarbon autoxidation. Initial rates of oxygen absorption by typical hydrocarbons were extremely slow implying inhibition rate constants > 106 M−1 s−1. The initial rate of disappearance of the dithiocarbamate was equal to the rate of chain initiation (Ri) whereas the rate of disappearance of the dithiophosphate was twice as fast as Ri. In both cases the rate of complex disappearance slowed down as the complex was consumed. Autoxidation of styrene commenced as soon as the complex disappeared while cumene did not absorb oxygen for a considerable length of time after complex destruction. Cumylperoxy radicals were converted to α-cumyl alcohol, α-methylstyrene, and acetophenone by reaction with these complexes and the copper ions were eventually precipitated as copper sulphate. In the case of the dithiocarbamate three intermediate cupric complexes were detectee by epr spectroscopy.

scholarly journals Kinetic studies in the chemistry of rubber and related materials. I. The thermal oxidation of ethyl linoleate

1946 ◽  
Vol 186 (1005) ◽  
pp. 218-236 ◽  
Keyword(s):  
Thermal Decomposition ◽  
Reaction Mechanism ◽  
Thermal Oxidation ◽  
Molecular Oxygen ◽  
Kinetic Studies ◽  
Ethyl Linoleate ◽  
Chain Termination ◽  
Radical Chain ◽  
Kinetics Of ◽  
Sole Product

The kinetics of the initial stages of the thermal oxidation of ethyl linoleate (by molecular oxygen) have been investigated in the temperature range 35—75° C. From consideration of chemical and kinetic evidence the reaction mechanism has been established: oxidation chains are initiated by thermal decomposition of ethyl linoleate hydroperoxide (which in the early stages of oxidation is substantially the sole product). The chain propagation reactions are identified as R — + O 2 → R O 2 — and R O 2 — + R H → R OOH + R — (where R H represents ethyl linoleate). Chain termination occurs by mutual destruction of the radical chain carriers, R — and R O 2 — .

Kinetic Studies in the Chemistry of Rubber and Related Materials. II. The Kinetics of Oxidation of Unconjugated Olefins

1947 ◽  
Vol 20 (3) ◽  
pp. 609-617 ◽  
Author(s):  
J. L. Holland ◽  
Geoffrey Gee
Keyword(s):  
Thermal Decomposition ◽  
Kinetic Studies ◽  
Chain Termination ◽  
Low Oxygen ◽  
Chain Reaction ◽  
Kinetics Of Oxidation ◽  
Chain Initiation ◽  
A Chain ◽  
Kinetics Of ◽  
Direct Attack

Abstract A brief review is given of kinetic work on the oxidation of representative mono, 1,4 and 1,5 olefins. The essential process in each case is identified as a chain reaction in which hydrocarbon radicals are formed, absorb oxygen, and then react with another molecule of olefin to give a hydroperoxide and a new free radical. Three methods of chain initiation are considered: (1) direct attack of oxygen on the olefin, (2) thermal decomposition of the hydroperoxide, (3) thermal decomposition of added benzoyl peroxide. Chain termination results from interaction of two free radicals; except at low oxygen pressures, these are both peroxidic.

Kinetics of the thermal decomposition of propylene, and of propylene-inhibited hydrocarbon decompositions

1960 ◽  
Vol 259 (1297) ◽  
pp. 257-266 ◽  
Keyword(s):  
Activation Energy ◽  
Main Chain ◽  
Chain Termination ◽  
Reaction Products ◽  
Kcal Mole ◽  
Allyl Radical ◽  
Individual Reaction ◽  
Benzene Toluene ◽  
The Individual ◽  
Kinetics Of

The main products of the propylene decomposition, studied between 580 and 640°C, were found to be ethylene, methane and hydrogen, in the approximate ratio 2:2:1. Smaller amounts of ethane, propane, butenes, benzene, toluene and diallyl were found, but no allene was detected. The order of the reaction was 3/2, and the activation energy 56⋅7 kcal/mole. A mechanism is proposed, involving an initial split into C 3 H 5 + H and including abstractions by both CH 3 and H; the main chain-terminating step is H + C 3 H 5 . The mechanism is shown to predict the rates of formation of the individual reaction products, and to account satisfactorily for the observed activation energy. Hydrogen atom abstractions by the allyl radical were demonstrated. It is shown that the facts are consistent with the suggestion that in the propylene-inhibited paraffin decompositions there is H abstraction by C 3 H 5 and chain termination by reaction between C 3 H 6 and an alkyl radical. This proposal explains why NO and propylene give rise to the same rates for the fully inhibited reactions, and why smaller amounts of NO are required to produce a given degree of inhibition.

Kinetics of the catalytic hydrodesulphurization reaction system; hydrogenolysis of thiophene

1980 ◽  
Vol 45 (10) ◽  
pp. 2728-2741 ◽  
Author(s):  
Pavel Fott ◽  
Petr Schneider
Keyword(s):  
Atmospheric Pressure ◽  
Active Sites ◽  
Flow Reactor ◽  
Kinetic Equations ◽  
Reaction System ◽  
Reaction Products ◽  
Molybdenum Catalyst ◽  
Cobalt Molybdenum Catalyst ◽  
Kinetics Of ◽  
Reaction Schemes

Kinetics have been studied of the reaction system taking place during the reaction of thiophene on the cobalt-molybdenum catalyst in a gradientless circulation flow reactor at 360 °C and atmospheric pressure. Butane has been found present in a small amount in the reaction products even at very low conversion. In view of this, consecutive and parallel-consecutive (triangular) reaction schemes have been proposed. In the former scheme the appearance of butane is accounted for by rate of desorption of butene being comparable with the rate of its hydrogenation. According to the latter scheme part of the butane originates from thiophene via a different route than through hydrogenation of butene. Analysis of the kinetic data has revealed that the reaction of thiophene should be considered to take place on other active sites than that of butene. Kinetic equations derived on this assumption for the consecutive and the triangular reaction schemes correlate experimental data with acceptable accuracy.

Kinetics of carbon monoxide methanation on a Ni/SiO2 catalyst

1990 ◽  
Vol 55 (7) ◽  
pp. 1678-1685
Author(s):  
Vladimír Stuchlý ◽  
Karel Klusáček
Keyword(s):  
Carbon Monoxide ◽  
Reaction Rate ◽  
Catalyst Activity ◽  
Adsorbed Hydrogen ◽  
Reaction Products ◽  
Co Methanation ◽  
Molar Ratios ◽  
Rate Determining Step ◽  
Higher Temperature ◽  
Kinetics Of

Kinetics of CO methanation on a commercial Ni/SiO2 catalyst was evaluated at atmospheric pressure, between 528 and 550 K and for hydrogen to carbon monoxide molar ratios ranging from 3 : 1 to 200 : 1. The effect of reaction products on the reaction rate was also examined. Below 550 K, only methane was selectively formed. Above this temperature, the formation of carbon dioxide was also observed. The experimental data could be described by two modified Langmuir-Hinshelwood kinetic models, based on hydrogenation of surface CO by molecularly or by dissociatively adsorbed hydrogen in the rate-determining step. Water reversibly lowered catalyst activity and its effect was more pronounced at higher temperature.

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