Showing papers on "Free-radical reaction published in 2000"

Mechanism and Kinetics of the OH-Radical Intervention during Fenton Oxidation in the Presence of a Significant Amount of Radical Scavenger (Cl-)

Abstract: Orange II, the 4-(2-hydroxy-1-naphthylazo)benzenesulfonic acid Na-salt, was taken as a model for the oxidation of organic compounds in photoassisted Fenton process in the presence of Cl--anion in solution. The HO• radicals seem to originate due to the photolysis of Fe(OH)2+ complexes in solution, whereas the Cl2-• radical was a product of the photolysis of the FeCl2+ complexes. The rate constants for the reaction of HO• and Cl2-• radicals with Or II were determined by laser kinetic spectroscopy: kOH•+OrII = 6.0 × 109(M s)-1 and kCl2•+OrII = 3.7 × 107 (M s)-1. A significant decrease in the rate of decoloration was observed for Orange II upon addition of Cl- (10 mM), but further addition of Cl- only marginally affected the latter reaction rate. Chlorinated hydrocarbons are observed as the products of Orange II oxidation in photoassisted and dark Fenton processes in the presence of Cl- anions. Light irradiation was observed to decrease the amount of chlorinated organic products (AOX) in solution as compared...

Thermal desorption mass spectrometric analysis of organic aerosol formed from reactions of 1-tetradecene and O3 in the presence of alcohols and carboxylic acids

Abstract: The chemistry of secondary organic aerosol formation from reactions of 1-tetradecene and O3 in dry air in the presence of excess alcohols and carboxylic acids was investigated in an environmental chamber using a thermal desorption particle beam mass spectrometer. Temperature-programmed thermal desorption of collected aerosol shows that in each reaction two major aerosol products are formed. The more volatile compounds in each pair of products are α-alkoxytridecyl or α-acyloxytridecyl hydroperoxides, which were identified by comparison of mass spectra with those of standard compounds generated by the corresponding liquid-phase ozonolysis reactions. The formation of organic hydroperoxides in the gas and liquid phases is consistent with a mechanism involving reactions of the alcohols and carboxylic acids with stabilized Criegee biradicals generated in the alkene−O3 reaction. The less volatile compounds are α-alkoxy-α‘-hydroxyditridecyl or α-acyloxy-α‘-hydroxyditridecyl peroxides (peroxyhemiacetals) formed by...

Photocatalytic Degradation of 1,10-Dichlorodecane in Aqueous Suspensions of TiO2: A Reaction of Adsorbed Chlorinated Alkane with Surface Hydroxyl Radicals

Abstract: 1,10-Dichlorodecane (D2C10) is shown to be effectively photodegraded in aqueous suspensions of TiO2 using a photoreactor equipped with 300 nm lamps. Solutions exposed to UV light intensities of 3.6 × 10-5 Ein L-1 min-1, established by ferrioxalate actinometry, showed negligible direct photolysis in the absence of TiO2. The degradation rate was optimal with 150 mg/L of TiO2 and a D2C10 concentration (240 μg/L) approaching its solubility limit. Kinetics of photodegradation followed a Langmuir−Hinshelwood model suggesting that the reaction occurred on the surface of the photocatalyst. The presence of h+vb and OH• radical scavengers, including methanol and iodide, inhibited the degradation supporting a photooxidation reaction. Electron scavengers (Ag+, Cu2+, and Fe3+) had small effects on the degradation rate. The lack of transformation of D2C10 in acetonitrile as solvent indicated that the major oxidants were OH• radicals. The presence of tetranitromethane, effectively eliminating the formation of free OH• r...

Synthesis of maleic anhydride grafted polyethylene and polypropylene, with controlled molecular structures

Abstract: This article discusses a new chemical route to prepare maleic anhydride (MA) grafted polyethylene and polypropylene polymers with controlled molecular structure, that is, MA grafted content and polymer molecular weight and composition distributions. The chemistry involves a free radical graft reaction of maleic anhydride with poly(ethylene-co-p-methylstyrene) and poly(propylene-co-p-methylstyrene) copolymers. Under a suspension reaction condition, the grafting reaction takes place selectively on the p-methylstyrene units in the copolymer, due to high reactivity of p-methyl group and favorable mixing between p-methylstyrene units and chemical reagents in the swollen amorphous phases. The resulting polymer shows no detectable molecular weight change during the reaction, and the MA grafted content increases with the increase of initiator and p-methylstyrene concentrations. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1337–1343, 2000

Electron spin resonance study on chemical crosslinking reaction mechanisms of polyethylene using a chemical agent. V. Comparison with polypropylene and ethylene‐propylene copolymer

Abstract: We studied the chemical reaction process of polypropylene (PP), ethylene-propylene copolymer (EPM), and ethylene-propylene-diene copolymer (EPDM) crosslinking induced by dicumyl peroxide (DCP) using electron spin resonance (ESR). Free radicals appeared at an elevated temperature of around 120 °C and the behavior and kinetics of the reaction process were observed at 180 °C. The radical species detected in PP were alkyl type radicals, formed by the abstraction of hydrogen atoms from the tertiary carbon of polymer chains. For EPDM containing a diene component, the radicals were trapped at double bonds in this diene component to form allyl radicals. The resolutions of these spectra were extremely clear; hence, isotropic spectra of these polymer radicals were obtained. We measured the ESR at high temperatures and confirmed that the process of crosslinking induced by DCP was a free radical reaction. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3383–3389, 2000

ESR study on chemical crosslinking reaction mechanisms of polyethylene using a chemical agent. IV. Effect of sulfur‐ and phosphorous‐type antioxidants

Abstract: The effect of an antioxidant on the reaction mechanisms of chemical crosslinking of polyethylene (PE) with dicumyl peroxide (DCP) at high temperatures was investigated using electron spin resonance (ESR). For sulfur- and phosphorous-type antioxidants, changes of radical species and their contents during the PE crosslinking reaction were observed. It was confirmed that these antioxidants reacted preferentially with radicals yielded by decomposed DCP, restraining the crosslinking of PE by the increased antioxidant content. The compound of DCP and antioxidant decomposed to form 2-phenyl isopropyl radicals. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3092–3099, 2000

Novel fluorinated polymers by radical polyaddition of bis(α‐trifluoromethyl‐β‐difluorovinyl) dicarboxylate with ether

Abstract: o develop the radical polyaddition reaction of bis(a-trifluoromethyl-β-difluorovinyl) terephthalate (BFP) with 1,4-dioxane, bis(a-trifluoromethyl-β-difluorovinyl) cyclohexane-1,4-dicarbocylate (FDFC) and bis(a-trifluoromethyl-β-difluorovinyl) adipate (FDFA) were prepared and polyadditions with 1,4-dioxane, diethyl ether, and 1,2-dimethoxyethane were examined in the presence of benzoyl peroxide (BPO). The molecular weight of the polymer obtained from FDFC with dioxane was 2.9X10 3 . A polymer with a molecular weight of 4.5X10 3 was obtained by the reaction of FDFA with 1,4-dioxane initiated with BPO. Polyaddition reactions of FDFC or FDFA with 1,2-dimethoxyethane or diethyl ether were found to produce linear polymers which are soluble in common organic solvents. These results suggested that 1,4-dioxane, diethyl ether and 1,2-dimethoxyethane work as monomers in this reaction system. Postpolymerization of the polymer obtained from BFP with 1,4-dioxane was also examined to yield a polymer of higher molecular weight compared to that of the starting polymer. A postulated polymeratization mechanism of BFP with 1,4-dioxane is briefly discussed.

Reaction pathways and kinetics in the degradation of forging lubricants

Abstract: The stability of a hot forging lubricant determines its effectiveness during operation. Aqueous lubricants, which are increasingly popular because of environmental issues, contain an organic ingredient, a stabilizer, and other species including biocides and corrosion inhibitors. The stability of a model forging lubricant containing dipotassium o-phthalate and sodium silicate in water has been measured over a wide range of temperatures and initial concentrations. The oxidation of the organic species is correlated using kinetic analysis, which reveals that decomposition occurs through a first-order reaction with an activation energy of ≈58.2 kJ/mol. The kinetic result is consistent with a proposed free radical reaction mechanism that is also shown to be consistent with theoretical calculations and results reported for other types of lubricants.

Preparation of 9-hydrocarbyl-9-phosphabicyclononanes

Abstract: 9-Hydrocarbyl-9-phosphabicyclnonanes are prepared by reacting a primary hydrocarbylphosphine with 1,5-cyclooctadiene in a free radical reaction at a temperature below 100 °C.

Mechanism of cyclohexane oxidation by molecular oxygen in the biomimetic iron porphyrin system with proton and electron donors: I. A radical pathway

Abstract: The formation of cyclohexyl hydroperoxide during cyclohexane oxidation by air oxygen in a biomimetic iron porphyrin system with proton (AcOH) and electron (Zn) donors and with or without an electron carrier (methylviologen (MV)) in an acetonitrile solution is detected by gas-liquid chromatography. The kinetics of C6H11OOH decomposition in this system catalyzed by iron porphyrins with various substituents in the phenyl rings is studied, and the rate constants of this process are determined. A kinetic scheme of cyclohexane oxidation is proposed. The contribution of the radical pathway to the reaction product formation is quantitatively estimated in the pseudo-steady-state approximation. For all iron porphyrins under investigation (FeTPP, FeTDCPP, and FeTpivPP), the fraction of the products formed via the radical pathway is smaller than 20%.

Kinetics of the liquid-phase oxidation of cyclooctene in the presence of MnO2

Abstract: The kinetics of the liquid-phase oxidation of cyclooctene by molecular oxygen in the presence of a MnC2 catalyst is studied. It is found that MnC2 is an initiator of this reaction and has no effect on the steps of chain propagation and termination. The oxidation occurs by a radical chain mechanism with the escape of radicals to the bulk of the reaction mixture. Radicals are formed by the interaction of the olefin with the solid catalyst surface. The kinetic parameters of the reaction are calculated.

A new method for determination of the rate constants of reversible homolysis of alkoxyamines in application to the living radical polymerization regime

Abstract: A new method is proposed for determining the rate constant (k d ) of the homolysis of alkoxyamines (RX) from the accumulation kinetics of the paramagnetic product of the reaction (nitroxyl radical X ) measured by EPR spectroscopy under conditions of the reversibility suppressed by adding strong acceptor (X') of hydrocarbon radicals R . competitive with X. The conditions of effective competition are established and expressed in terms of the relationship between the X' and X concentrations. The efficiency, accuracy, and reliability of the method are demonstrated using data for the previously synthesized and characterized styrene-containing RX decomposing in the temperature range of 333-403 K in a styrene medium. The measured k d are compared with the published data and the results of our independent studies.

Measurements of the apparent rate constant for the reaction of iodine monoxide with chlorine monoxide to form iodine atoms

Abstract: An apparatus for measuring the resonance fluorescence signals of iodine and chlorine atoms is constructed to study iodine monoxide reaction with chlorine monoxide. A technique using the reaction of chlorine atoms with C2H6 is developed to calibrate the sensitivity of the apparatus to chlorine atoms. The apparent rate constants for the reaction between 10• and CIO• radicals producing iodine atoms was measured at 295 K kapp = (2.62 ± 0.57) x 10--11 cm3 molecule-1 s-1.

Radical-chain reactions of CCl4 with hydrocarbons in the presence of silica-immobilized copper-containing catalysts

Abstract: The activities of two catalytic systems toward the exchange reaction of CCl4 with hydrocarbons are compared: a copper chloride complex with DMF and polycopperphenylsiloxane (PCPS). PCPS is a very stable catalyst. It completely preserves its catalytic activity after six catalytic cycles. Competitive reactions with the pairs of hydrocarbons suggested a radical-chain mechanism for the title reaction for both catalysts.

Kinetics and mechanism of cyclohexane oxidation with molecular oxygen in the presence of propionic aldehyde

Abstract: The kinetics and mechanism of the liquid-phase oxidation of cyclohexane with molecular oxygen in the presence of the additives of propionic aldehyde are studied at 303.0, 322.5, and 341.5 K by measuring the rates of oxygen and propionic aldehyde consumption and the yields of the main reaction products (cyclohexanol (COL), cyclohexanone (CON), cyclohexyl hydroperoxide, and propionic acid and peracid). A kinetic scheme is proposed and rate constants of elementary reactions are estimated based on the analysis of their rates and the yields of the main cyclohexane products. The key reactions of the main steps (including chain initiation, propagation, and termination) are determined. An increase in the rate of cyclohexane oxidation and the yield of the target products (cyclohexanol, cyclohexanone, and cyclohexyl hydroperoxide) in the presence of propionic aldehyde suggests that highly active acylperoxy radicals participate in chain propagation. The [CON]/[COL] ratio indicates that these products are mainly formed in chain propagation. The strong effect of the Baeyer-Villiger rearrangement on both the rate of oxygen consumption and the yield of the target products at the initial stages of the process and at high propionic aldehyde concentrations is explained.

Relationship of the selectivity effect of aromatic solvents with their electron-donor ability and organic reactant structure in free radical chlorination

Abstract: The effect of several solvents on the selectivity of the free radical chlorination of 1,1-dichloroethane and 1-chloropropane is studied The selective action of aromatic solvents on free radical chlorination is explained This explanation implies that the process involves solvated chlorine atoms and their donor-acceptor complexes with aromatic molecules (ArH→Cl•) as intermediates Using the findings of this work and previous studies, the ratios of the rate constants for hydrogen-atom abstraction from different positions in chloroethane, 1,1-dichloroethane, 1-chloropropane, and 2-chloropropane by solvated chlorine atoms and ArH→-Cl• complexes are determined The differences in the activation energies of the competitive hydrogenatom abstractions from different positions in substrates by the ArH→Cl• complexes and solvated chlorine radicals correlate with two HOMO energies of solvent and substrate molecules The isokinetic relationship is found for all the systems under study (the isokinetic temperature, 523 K)

Kinetic features of radical dissociation in filled acetyl cellulose

Abstract: The kinetic patterns of the diphthaloyl ethane dissociation in acetyl cellulose at 320-370 K with the formation of stable radicals have been considered as a function of the aerosil content. The profound filler effect was found to be upon the temperature dependence of the radical yield. Kinetic parameters of the radical dissociation are determined by the structural modifications of the polymer under shaping of interfaces.

Manganese(III) Acetate Initiated Oxidative Free Radical Reaction Between 1,4-Naphthoquinones and Ethyl Nitroacetate.

Abstract: The manganese(III) initiated oxidative free radical reaction between 1,4-naphthoquinones and ethyl nitroacetate is described. Nitromethyl radical 1 can be generated effectively from the oxidation of ethyl nitroacetate by manganese(III) acetate. Naphtho[2,3- d ]isoxazole-4,9-diones, benzo[ f ]indole-4,9-diones and benzo[ b ]acridine-6,11-diones were prepared effectively from readily available 1,4-naphthoquinones and ethyl nitroacetate.

Mechanism of .OH formation in the thermal decomposition of (≡Si-O)2Si(C2H5)(O-O.) radicals

Abstract: ESR andIR spectroscopy and quantum chemical calculations are used to obtain the mechanistic data on the reaction . The IR bands are assigned by simulating the vibrational spectra of model low-molecular compounds. Quantum chemical calculations provided the data on the shapes of potential energy surface for the systems under study and transition states. These data are used to interpret the experimental data. The title reaction occurs much more readily in the case of organosilicon peroxy radicals than in the case of their hydrocarbon analogs. Surface silanone groups of silica react with ethylene molecules to form the siloxacyclobutane group.

Monitoring of radical thermocatalyzed breakdown of polychlorinated compounds

Abstract: Disposal of polychlorobiphenyls (PCBs) is a current problem still far from a really satisfactory solution. Because of the wide use and the chemical inactivity, the PCB amount to be treated is considerably large. In this paper, the setting-up of a methodical catalytic pyrolysis of polychlorinated compounds is proposed. The monitoring of the final decomposition products by analytical techniques, such as GC and coupled TG-FTIR, allowed to optimize the reaction temperature: the encouraging results, the lower operative temperatures with respect to previous systems and the favourable prospects regarding the environmental impa ct make this methodology open to practical applications at a relative low cost.

Kinetic analysis of systems containing aromatic amine, phenol, and hydroperoxide

Abstract: Processes and phenomena in three-component systems containing a secondary aromatic amine, a sterically hindered phenol, and a hydroperoxide are analyzed from the standpoint of kinetics. The following three phenomena, which are well known, are related to each other: (1) simultaneous phenol and hydroperoxide consumption during the generation of amyl radicals; (2) consecutive consumption of phenol and amine as antioxidants in the initiated oxidation of hydrocarbons; and (3) catalytic acceleration of phenoxyl radical reaction with hydroperoxide by aromatic amines. These three phenomena reflect the process behavior in the title systems in the generation or addition of the corresponding free radicals. It was shown that the main catalytic feature of the reactions in three-component systems is a trend toward their coupled nature. The requirements to the experimental conditions are formulated under which coupling either takes place in full measure or does not play any role at all.