Chemical Reactions of Antioxidants Used in Vulcanized Rubber

1957 ◽  
Vol 30 (2) ◽  
pp. 681-688
Author(s):  
P. Schneider
Keyword(s):  
Natural Rubber ◽  
Chemical Reactions ◽  
Aromatic Amines ◽  
Unsaturated Compound ◽  
Partition Chromatography ◽  
Atmospheric Conditions ◽  
Reaction Products ◽  
Kinetics Of Oxidation ◽  
Vulcanized Rubber ◽  
Kinetics Of

Abstract The work of Farmer and other authors has shown that the oxidation of unsaturated polymers proceeds via primary formed hydroperoxides. The addition of antioxidants, including chiefly compounds of the class of the phenols and secondary aromatic amines, makes it possible to delay to a great extent the chemical changes taking place in unsaturated compounds. The mechanism of the action of phenols in the oxidation has been explained by Bolland. It is difficult to separate from the polymer the reaction products which are formed from the antioxidant by the dehydrogenating action of the polymeric hydroperoxide radical. In view of the fact, however, that the kinetics of oxidation in the presence of added peroxide corresponds to the autoxidation of the unsaturated compound, the reaction between phenols or secondary aromatic amines and organic or inorganic oxidation agents has been studied in detail by several workers. Depending on type, position, and number of the substituents, different reaction products are formed from phenols. Diphenylamine reacts with manganese dioxide to form a mixture of N,N′-diphenylbenzidine and the corresponding quinonedianil. N,N,N′-tri-2-naphthyl-1,2-naphthylenediamine is formed from di-2-naphthylamine with potassium permanganate, whereas under similar conditions phenyl-2-naphthylamine forms N,N′-diphenyl-N-2-naphthyl-1,2-naphthylenediamine. Starting from the deduction that the chemical reaction products of the antioxidants accumulate on the surface of the vulcanized rubber due to decreasing solubility, pure gum stocks of cured natural rubber containing diphenylamine, N-phenyl-1- and 2-naphthylamine have been exposed to atmospheric conditions for 8 months. The dark colored reaction products could be removed mechanically from the surface of the cured goods after wetting with methanol. After evaporation, the residue was taken up in ethylidene chloride and the resulting solution evaporated to dryness. Amorphous mixtures of brown colored compounds were isolated from the vulcanizate containing diphenylamine and N-phenyl-2-naphthylamine, the reaction products of the N-phenyl-2-napthylamine being obtained as a dark colored tar. In addition to other compounds, the presence of the N,N′-diphenyl-N-2-naphthyl-1,2-naphthylenediamine was proved by paper partition chromatography of the resulting azodyestuff obtained from the mixture of the reaction products from phenyl-2-naphthylamine by coupling with diazotized 1-aminonaphthalene trisulfonic acid. The presence of this compound had also been shown by the ultraviolet spectra. In the same manner, small quantities of the N,N′-diphenylbenzidine could be recognized from the corresponding azodyestuff formed from the reaction product of diphenylamine. Due to extensive oxidation, the presence of reaction products could not be proved in any appreciable quantity from the reaction mixture of the phenyl-1-naphthylamine.

Heats of Vulcanization of Synthetic Rubbers

1944 ◽  
Vol 17 (2) ◽  
pp. 404-411 ◽  
Author(s):  
P. L. Bruce ◽  
R. Lyle ◽  
J. T. Blake
Keyword(s):  
Carbon Black ◽  
Natural Rubber ◽  
Chemical Reactions ◽  
Side Reaction ◽  
Heat Evolution ◽  
Butyl Rubber ◽  
Vulcanized Rubber ◽  
Principal Reaction ◽  
Low Sulfur ◽  
Quantity Of Heat

Abstract 1. The heats of vulcanization for natural rubber and Buna-S are nearly equal. The data for both materials indicate two different chemical reactions during vulcanization. At low sulfur percentages, the principal reaction forms soft vulcanized rubber and is accompanied by little or no heat evolution. Above the 2 per cent sulfur region, a second reaction predominates, forming hard rubber and producing a relatively large quantity of heat. 2. The presence of an accelerator (Santocure) in Buna-S has little, if any, effect on heat of vulcanization. 3. The addition of carbon black to Buna-S lowers the heat of vulcanization in the region above 4 per cent sulfur. The calories evolved in a 10 per cent sulfur compound decrease linearly with percentage of carbon black. 4. The heats of vulcanization of Buna-N (Hycar OR-15) indicate the presence of two chemical reactions. Unlike natural rubber and Buna-S, the ebonite reaction does not predominate until the sulfur concentration is raised above 10 per cent. 5. The heat of vulcanization of Butyl rubber with sulfur is equal to the heat evolved with natural rubber containing 0.6 per cent sulfur. If one sulfur atom reacts per double bond, the maximum amount combining would be 0.72 per cent sulfur. During the vulcanization of Butyl rubber with p-quinone dioxime and lead peroxide, a large amount of heat is evolved by a side reaction between the vulcanizing agents. The reaction involving the Butyl rubber produces about 6 calories per gram, a considerably higher value than the 1 calorie produced by sulfur vulcanization. 6. The heat of vulcanization of Neoprene-GN without added agents corresponds to a value for smoked sheet rubber containing 4.5 per cent sulfur. The addition of zinc oxide and magnesia decreases the heat of vulcanization.

Kinetics of oxidation of cis-bis(ethylenediamine)isothiocyanatonitrocobalt(III) ion with peroxodisulphate

1979 ◽  
Vol 44 (12) ◽  
pp. 3588-3594 ◽  
Author(s):  
Vladislav Holba ◽  
Olga Volárová
Keyword(s):  
Ionic Strength ◽  
Rate Constants ◽  
Oxidation Kinetics ◽  
Reaction Rate ◽  
Salt Effect ◽  
Activation Parameters ◽  
Reaction Products ◽  
Kinetics Of Oxidation ◽  
Thermodynamic Activation Parameters ◽  
Kinetics Of

The oxidation kinetics of cis-bis(ethylenediamine)isothiocyanonitrocobalt(III) ion with peroxodisulphate was investigated in the medium of 0.01 M-HClO4 in dependence on the ionic strength and temperature and the reaction products were identified. Extrapolated values of thermodynamic activation parameters were determined from the temperature dependence of the rate constants extrapolated to zero ionic strength. The distance of the closest approach was estimated for the reacting ions by evaluating the primary salt effect. To elucidate the mechanism, the influence of the cyclic polyether 18-crown-6 on the reaction rate was followed.

Mechanisms for ozone-initiated removal of biomass burning products from the atmosphere

2018 ◽  
Vol 15 (2) ◽  
pp. 83 ◽  
Author(s):  
Jianfei Sun ◽  
Qiong Mei ◽  
Bo Wei ◽  
Long Huan ◽  
Ju Xie ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Rate Constants ◽  
Computational Method ◽  
Atmospheric Conditions ◽  
Reaction Products ◽  
Positive Dependence ◽  
Elementary Reactions ◽  
Criegee Intermediates ◽  
Ozone Addition ◽  
Kinetics Of

Environmental contextAn important product of biomass burning is catechol: its presence in the atmosphere can have adverse effects on health, and can lead to the formation of secondary organic aerosols. We report a theoretical study on the mechanisms and kinetics of removal of catechol from the atmosphere by reaction with ozone. These data will provide insight into the ozonolysis of other lignin compounds produced by biomass burning. AbstractWe examined the ozone-initiated oxidation of catechol, an intermediate of lignin pyrolysis in the atmosphere, by using the theoretical computational method at the M06-2X/aug-cc-pVDZ//M06-2X/6-31+G(d,p) level. Six ozone-addition channels of the initial reactions and the further reactions of the Criegee intermediates are proposed. The complete degradation processes of the Criegee intermediates in the presence of NO and H2O were elucidated. The predicted reaction products for the ozonolysis of catechol, such as malealdehyde (P10), oxalic acid (P11) and CO2, were detected experimentally in the gas-phase. Moreover, the microcanonical rate constants of the crucial elementary reactions were determined by the Rice–Ramsperger–Kassel–Marcus theory. The total rate constant for the ozonolysis of catechol under atmospheric conditions is 1.37 × 10−18 cm3 molecule−1 s−1, which compares favourably to the experimentally determined values. The bimolecular rate constants showed positive dependence on temperature and negative dependence on pressure. The atmospheric lifetime of catechol with respect to ozone was estimated to be 12.07 days. We also found that the ozonolysis of catechol is more likely to occur in aqueous solution. The present work has provided a comprehensive investigation of the ozonolysis of catechol. The methods we used can serve as a model for analysing the ozonolysis of other lignin compounds.

Kinetics and mechanism of the oxidation of 1-propane thiol by 2,6-dichlorophenolindophenol in acidic medium

1982 ◽  
Vol 60 (15) ◽  
pp. 1928-1932 ◽  
Author(s):  
M. Kashyap ◽  
K. K. Mishra ◽  
N. K. Pandey
Keyword(s):  
Kinetic Data ◽  
Acidic Medium ◽  
Reaction System ◽  
Activation Parameters ◽  
Molar Ratio ◽  
Water Medium ◽  
Reaction Products ◽  
Kinetics Of Oxidation ◽  
Acetone Water ◽  
Kinetics Of

The kinetics of oxidation of 1-propanethiol by 2,6-dichlorophenolindophenol have been studied in acetone–water medium and in the presence of phosphate buffer. The principal reactants interact in a molar ratio of 2:1 forming disulphide and dihydroindophenol. The reaction follows second order kinetics in indophenol while the order is unity in thiol. The rate increases linearly on increasing [H+]. The rate of oxidation increases on increasing the ionic strength as well as the dielectric constant of the reaction system. The addition of reaction products has no effect on the rate. Activation parameters have been evaluated and a suitable mechanism consistent with kinetic data is suggested.

Vulcanization. Part VII. Kinetics of Sulfur Vulcanization of Natural Rubber in Presence of Delayed-Action Accelerators

1965 ◽  
Vol 38 (1) ◽  
pp. 1-14 ◽  
Author(s):  
A. Y. Coran
Keyword(s):  
Positive Integer ◽  
Stearic Acid ◽  
Natural Rubber ◽  
Zinc Ion ◽  
Square Root ◽  
Reaction Products ◽  
Sulfur Concentration ◽  
Sulfur Vulcanization ◽  
Delayed Action ◽  
Kinetics Of

Abstract The scheme and treatment of the kinetics of scorch-delay vulcanization proposed in a previous paper were applied to natural rubber sulfur vulcanization accelerated by 2,2′-thiobisbenzothiazole (MBTS), 2-(N-cyclohexyl)benzothizaolesulfenamide (CBS), 2-(N-morpholinothio)benzothiazole (MOR), or 2-(N,N-diisopropyl)benzothiazolesulfenamide (DPBS). According to the scheme (see PDF for diagram) where the subscript x = a positive integer. The specific rates k1 and k2 and the ratiok4/k3′ were related to starting concentrations of accelerator, sulfur, and stearic acid. In general, an increase in stearic acid concentration or a decrease in accelerator concentration induces an increase in k1 or k4/k3′ but a decrease in k2. An exception to this is that, when the highly hindered sulfenamide DPBS is used as the accelerator, k1 does not change with changes in starting concentrations. It is interesting that k2 does not respond appreciably to changes in sulfur concentration when sulfenamides are used, unless the sulfur concentrations are extremely low. In contrast to this, k2 increases linearly with the square root of the sulfur concentration when MBTS is used. The changes in rates which occur with changes in the starting concentrations were attributed to the formation of chelates between zinc ion (brought into solution by stearic acid) and accelerator, intermediate reaction products, or crosslink precursors. The differences noted between the rates obtained with the three sulfenamides were attributed to differences in steric hindrance and stability.

Kinetics and Mechanism of Oxidation of L-Proline by Heptavalent Manganese: A Free Radical Intervention and Decarboxylation

2005 ◽  
Vol 2005 (1) ◽  
pp. 13-17 ◽  
Author(s):  
R.T. Mahesh ◽  
M.B. Bellakki ◽  
S.T. Nandibewoor
Keyword(s):  
Reaction Rate ◽  
Activation Parameters ◽  
Solvent Polarity ◽  
Reaction Scheme ◽  
Slow Step ◽  
Reaction Products ◽  
Experimental Conditions ◽  
Kinetics Of Oxidation ◽  
Reaction Constants ◽  
Kinetics Of

The kinetics of oxidation of L-proline by permanganate in alkaline medium was studied spectrophotometrically. The reaction is first order with respect to[MnO4-] and is an apparent less than unit order, each in [L-proline] and [alkali] under the experimental conditions. The reaction rate increases with increase in ionic strength and decrease in solvent polarity of the medium. Addition of reaction products has no effect on the reaction rate. A mechanism involving the formation of a complex between the oxidant and substrate has been proposed. The reaction constants involved in the mechanism were evaluated. There is a good agreement between the observed and calculated rate constants under varying experimental conditions. The activation parameters with respect to the slow step of the proposed reaction scheme were evaluated and discussed.

Some Features of the Aging of Vulcanized Rubber in Light

1956 ◽  
Vol 29 (2) ◽  
pp. 593-597
Author(s):  
Yu S. Zuev ◽  
A. S. Kuzminskiĭ
Keyword(s):  
Natural Rubber ◽  
Intimate Relationship ◽  
Photochemical Reactions ◽  
Butyl Rubber ◽  
Reaction Products ◽  
Intermediate Reaction ◽  
Vulcanized Rubber ◽  
Rubber Vulcanizate

Abstract The action of light on rubber articles is almost always accompanied by a rise of their temperature. We may assume also, on the basis of a number of literature data, that there is a still more intimate relationship between the processes of light and the heat aging of vulcanizates. It is known that the rate of purely photochemical reactions depends but little on temperature. Such a dependence is noticeable, however, in such cases as the following: (1) when photoreactions and thermoreactions develop parallel to, and independently of, one another, their rates being found to be additive; (2) when they have a common level of reaction and common intermediate reaction products, and also when there exists a reciprocal activation of photo- and thermoreactions by one another. In this case, a change of temperature (within known limits) should bring about a change of the rate of photochemical reactions which is greater than the additive change. This has been confirmed by experiments on a number of vulcanizates. Thus, for example, there are data to the effect that the light aging of a natural-rubber vulcanizate is sharply accelerated by an increase of temperature from 25° to 75–100° C, and the same is true of Butyl rubber.

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.

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