Reaction Of Hydroperoxides Research Articles

Kinetics of acid-catalyzed cleavage of cumene hydroperoxide

The cleavage of cumene hydroperoxide, in the presence of sulfuric acid, to form phenol and acetone has been examined by adiabatic calorimetry. As expected, acid can catalyze cumene hydroperoxide reaction at temperatures below that of thermally-induced decomposition. At elevated acid concentrations, reactivity is also observed at or below room temperature. The exhibited reactivity behavior is complex and is significantly affected by the presence of other species (including the products). Several reaction models have been explored to explain the behavior and these are discussed.

Inhibition of the Fenton reaction by nitrogen monoxide

The toxicity of iron is believed to originate from the Fenton reaction which produces the hydroxyl radical and/or oxoiron2+. The effect of nitrogen monoxide on the kinetics of the reaction of iron(II) bound to citrate, ethylenediamine-N,N'-diacetate (edda), ethylenediamine-N,N,N',N'-tetraacetate (edta), (N-hydroxyethyl)amine-N,N',N'-triacetate (hedta), and nitrilotriacetate (nta) with hydrogen peroxide was studied by stopped-flow spectrophotometry. Nitrogen monoxide inhibits the Fenton reaction to a large extent. For instance, hydrogen peroxide oxidizes iron(II) citrate with a rate constant of 5.8x10(3) M(-1) s(-1), but in the presence of nitrogen monoxide, the rate constant is 2.9x10(2) M(-1) s(-1) . Similar to hydrogen peroxide, the reaction of tert-butyl hydroperoxide with iron(II) complexes is also efficiently inhibited by nitrogen monoxide. Generally, nitrogen monoxide binds rapidly to a coordination site of iron(II) occupied by water. The rate of oxidation is influenced by the rate of dissociation of the nitrogen monoxide from iron(II).

Enantioselective Formation Pathway of a Trihydroxy Fatty Acid during Mashing

The lipoxygenases from barley (LOX-1) and malt (LOX-1 and LOX-2) catalyze the peroxidation of linoleic acid into 9-hydroperoxy-10E,12Z-octadecadienoic acid and 13-hydroperoxy-9Z,11E-octadecadienoic acid (HPODE). LOX-1 and LOX-2 accept free linoleic acid and nonpolar and polar glycerol esterified linoleic acid as substrates. The reactive hydroperoxides (HPODE) are e.g., reduced to the corresponding hydroxides (HODE). In finished malt, 9 ppm free HODE, 100 ppm triacylglycerol esterified HODE, and 66 ppm polar esterified HODE were analyzed by isotope dilution assay (18O1-13-HODE). Rearrangement products of HPODEs, the epoxyols, are hydrolyzed to trihydroxyoctadecenoic acids (THOE). These THOE isomers were investigated in detail. The positional isomers of THOE, 9,10,13- and 9,12,13-THOE, represent eight diastereomers and eight enantiomers, respectively. During mashing, a hitherto unknown enzyme cascade is activated, which only leads to the formation of (9S,12S,13S)-THOE that can be analyzed as free acid in wort and finally in beer. This reaction sequence is highly regio- and stereo-selective and may serve as a plant signaling pathway. The 9S,12S,13S-THOE isomer was formerly described as fungicide in rice blast disease and recently as an antiviral compound. Compared with mono- and dihydroxy fatty acids, the trihydroxy fatty acids are poorly degraded by yeast, and thus, accumulate in beer.

CpMo(CO)3Cl as a precatalyst for the epoxidation of olefins

The tricarbonyl complex CpMo(CO) 3 Cl was found to act as a precatalyst for the reaction of tert-butyl hydroperoxide and olefins to yield the corresponding epoxides and diols. Under the reaction conditions, oxidative decarbonylation leads to the formation of the dioxo complex CpMOO 2 Cl. The catalytic recyclability and the effect of temperature on the catalytic results have been examined, and a reaction mechanism proposed, supported by kinetic modelling.

THE INFLUENCE OF LIGHT ON THE SHELF LIFE OF PACKAGED OLIVE OIL

A mathematical model was introduced to describe the oxidative alterations taking place in packaged olive oil stored in various packaging materials and conditions. The consequent set of mass transport equations for the diffusion of oxygen through the packaging wall and the reaction of hydroperoxides inside the oil mass for various combinations of the aforementioned parameters, introduced a non-linear system, which was numerically solved. Special interest was given to the influence of light on the parameters used and on the reaction constants. In addition, the probability of the packaged olive oil not to reach the end of its shelf life during a certain time period, was estimated and proposed as a quality reduction indicator. The presence of light could by itself stimulate the oxidative degradations inside olive oil resulting in a sharp reduction of its shelf life. A clear synergistic effect between oxygen and light was also observed, while the increase of temperature had a contradictory effect on the preservation of the product. Finally, it was predicted that storage of olive oil at low temperatures under dark conditions offers a significantly high possibility for a prolonged shelf life of even beyond 24 months.

Contributions of Organic Peroxides to Secondary Aerosol Formed from Reactions of Monoterpenes with O3

The role of organic peroxides in secondary organic aerosol (SOA) formation from reactions of monoterpenes with O3 was investigated in a series of environmental chamber experiments. Reactions were performed with endocyclic (alpha-pinene and delta3-carene) and exocyclic (beta-pinene and sabinene) alkenes in dry and humid air and in the presence of the OH radical scavengers: cyclohexane, 1-propanol, and formaldehyde. A thermal desorption particle beam mass spectrometer was used to probe the identity and volatility of SOA components, and an iodometric-spectrophotometric method was used to quantify organic peroxides. Thermal desorption profiles and mass spectra showed that the most volatile SOA components had vapor pressures similar to pinic acid and that much of the SOA consisted of less volatile species that were probably oligomeric compounds. Peroxide analyses indicated that the SOA was predominantly organic peroxides, providing evidence that the oligomers were mostly peroxyhemiacetals formed by heterogeneous reactions of hydroperoxides and aldehydes. For example, it was estimated that organic peroxides contributed approximately 47 and approximately 85% of the SOA mass formed in the alpha- and beta-pinene reactions, respectively. Reactions performed with different OH radical scavengers indicated that most of the hydroperoxides were formed through the hydroperoxide channel rather than by reactions of stabilized Criegee intermediates. The effect of the OH radical scavenger on the SOA yield was also investigated, and the results were consistent with results of recent experiments and model simulations that support a mechanism based on changes in the [HO2]/[RO2] ratios. These are the first measurements of organic peroxides in monoterpene SOA, and the results have important implications for understanding the mechanisms of SOA formation and the potential effects of atmospheric aerosol particles on the environment and human health.

Physico-chemical aspects of polyethylene processing in an open mixer. Part 16: Mechanisms and kinetics of ketone formation at low temperature

Ketones are formed essentially on various reactions of polyethylene hydroperoxide. In the low temperature range (150–160 °C), some reactions are the same as in the high temperature range (170–200 °C) of the experiments. However, there is much more complexity at low temperature than at high temperature. The experimental kinetics reveals three significantly different processes compared to only two at high temperature. Ketone formation according to a constant rate results from the cage reaction between a peroxy radical and a hydroperoxide group during the chain propagation reaction. One of the reactions envisaged for the ketones formed according to the rate increasing with processing time in the initial stages is similar from the chemical point of view to the reaction yielding ketones according to the constant rate. The reaction proceeds between the hydroperoxides accumulated in an elementary volume and the peroxy radicals responsible for an additional oxidation of this volume. It cannot be accounted for by formal homogeneous kinetics that accounts well for the constant rate but by the heterogeneous kinetics taking into account repeated oxidation of elementary volumes. The second possibility of ketone formation according to the rate increasing with time is based on bimolecular hydroperoxide decomposition involving mainly associated hydroperoxides. The kinetic treatment for this process combines the heterogeneous kinetics of oxidation volume overlapping with monomolecular decomposition of associated hydroperoxides. The rate constant deduced from the data is in agreement with literature values as well as with the values deduced previously from the experiments with PE melts.

Physico-chemical aspects of polyethylene processing in an open mixer. Part 14: Product yield on reaction of hydroperoxide with alcohol groups

The views from solution-type chemistry cannot be transposed to polymer melts. The bimolecular reaction between hydroperoxide and alcohol groups is a typical example in this respect. It is the dominant hydroperoxide decomposition reaction in the advanced stages of polyethylene processing in the high temperature range (170–200 °C). In part, the alkoxy/alkoxy radical pair resulting from the decomposition reacts directly in the cage by disproportionation and combination. In part, it is transformed into a caged alkoxy/alkyl radical pair following hydrogen abstraction by one of the alkoxy radicals. The alkoxy/alkyl radical pair reacts by combination or disproportionation in the cage or is transformed into an alkyl/alkyl radical pair on hydrogen abstraction by the remaining alkoxy radical. Combination or disproportionation of the alkyl/alkyl radical pair is considerably faster than oxygen addition and/or cage disruption. The bimolecular reactions of the three caged radical pairs remove the free radicals from the polymer melt. There is no chain reaction initiated by those radicals. This explains previous findings concerning the absence of initiation by the hydroperoxides formed and decomposed in polyethylene melts. The relative quantities of oxidation products calculated from the model are compatible with the experimental results. The comparison yields quantitative values for the probabilities of the different cage reactions. The rate constants for the reactions between the alkoxy/alkoxy and alkoxy/alkyl radical pairs can be deduced from the probabilities, taking intramolecular hydrogen abstraction by the alkoxy radical as a reference. They are comparable to the corresponding rate constants for low molecular mass compounds in solution. The knowledge of these values allows calculation of the oxidation product yields at any temperature.

Quantitative determination of total lipid hydroperoxides by a flow injection analysis system

A flow injection analysis (FIA) system coupled with a fluorescence detection system using diphenyl-1-pyrenylphosphine (DPPP) was developed as a highly sensitive and reproducible quantitative method of total lipid hydroperoxide analysis. Fluorescence analysis of DPPP oxide generated by the reaction of lipid hydroperoxides with DPPP enabled a quantitative determination of the total amount of lipid hydroperoxides. Use of 1-myristoyl-2-(12-((7-nitro-2-1,3-benzoxadiazol-4-yl)amino) dodecanoyl)-sn-glycero-3-phosphocholine as the internal standard improved the sensitivity and reproducibility of the analysis. Several commercially available edible oils, including soybean oil, rape-seed oil, olive oil, corn oil, canola oil, safflower oil, mixed vegetable oils, cod liver oil, and sardine oil were analyzed by the FIA system for the quantitative determination of total lipid hydroperoxides. The minimal amounts of sample oils required were 50 microg of soybean oil (PV = 2.71 meq/kg) and 3 mg of sardine oil (PV = 0.38 meq/kg) for a single injection. Thus, sensitivity was sufficient for the detection of a small amount and/or low concentration of hydroperoxides in common edible oils. The recovery of sample oils for the FIA system ranged between 87.2+/-2.6% and 102+/-5.1% when PV ranged between 0.38 and 58.8 meq/kg. The CV in the analyses of soybean oil (PV = 3.25 meq/kg), cod liver oil (PV = 6.71 meq/kg), rapeseed oil (PV = 12.3 meq/kg), and sardine oil (PV = 63.8 meq/kg) were 4.31, 5.66, 8.27, and 11.2%, respectively, demonstrating sufficient reproducibility of the FIA system for the determination of lipid hydroperoxides. The squared correlation (r2) between the FIA system and the official AOCS iodometric titration method in a linear regression analysis was estimated at 0.9976 within the range of 0.35-77.8 meq/kg of PV (n = 42). Thus, the FIA system provided satisfactory detection limits, recovery, and reproducibility. The FIA system was further applied to evaluate changes in the total amounts of lipid hydroperoxides in fish muscle stored on ice.

Fundamental Aspects of Gas Phase Ion Chemistry Studied Using the Selected Ion Flow Tube Technique

Gas phase ion chemistry using the selected ion flow tube (SIFT) technique is discussed with the focus on fundamental studies on ion structure, energetics, reactivity, and dynamics: Laser-induced fluorescence (LIF) kinetics/dynamics of N2+(v) ions (vibrationally state-selected ion-molecule reactions; energy transfer processes), mechanisms of prototypical organic ion reactions (SN2 nucleophilic substitution and kinetic isotope effects; hydrogen/deuterium exchange; isotope effects in termolecular association), and ion-molecule reactions with biological implications (SN2 reactions at a nitrogen center; ECO2 elimination reactions of alkyl hydroperoxides). Anion chemistry of small nitroalkanes is also presented. A powerful combination of SIFT and negative ion photoelectron spectroscopy is used to study thermochemistry and structure of energetic and exotic ions (alkyl peroxides; anionic derivatives of diazo and azole compounds, cyclooctatetraene, and cyclopentanone). Finally, some of the new directions in SIFT research are discussed, i.e., reactions of ions with polyatomic organic radicals, and chemical ionization mass spectrometry with new detection schemes.

Browning reactions between oxidised vegetable oils and amino acids

Browning reactions of oxidised lipids with amino acids were studied in mixtures of refined soybean or rapeseed oil with alanine, valine, lysine, serine, cystine, cysteine, methionine, proline, and tryptophan. Oils were deposited in thin layers on cellulose fibres impregnated with the individual amino acids. The reaction proceeded in the dark, in dry air, at 50°C and at free access of oxygen. The browning determined at 430 nm followed a nearly zeroth order reaction without any induction period. The browning was very weak in the absence of amino acids, and all amino acids increased the browning rate, especially cysteine, methionine, and even more proline and tryptophan. The reaction rates were nearly the same in mixtures with rapeseed and soybean oils. Small amounts of hydroperoxides did not appreciably affect the browning rate. In the presence of copper ions, which belong to the most active catalysts of oxidation, the reaction rate was substantially higher. On the contrary, in the presence of antioxidants, the reaction rate was reduced to a marked degree but no induction period was observed. The probable main reaction mechanism was the reaction of lipid hydroperoxides, free radicals produced by their decomposition and/or unsaturated aldehydes under the formation of unsaturated imines which further polymerised into brown macromolecular substances.  

Simulating the Formation of Secondary Organic Aerosol from the Photooxidation of Toluene

Environmental Context. Atmospheric particulate material can affect climate by absorbing and scattering solar radiation and by altering the properties of clouds. They are also implicated as a health risk. Secondary organic aerosol (SOA) material makes an important contribution to this particulate burden. SOA material results from the transfer of gas-phase species into a particle state after the formation of products from the reaction of atmospheric volatile organic compounds (VOCs) with oxygen. SOA from the oxidation of aromatic hydrocarbons, such as toluene, a gasoline fuel component, is important in the polluted urban environment and yet formation mechanisms are not well understood. Abstract. The formation and composition of secondary organic aerosol (SOA) from the gas-phase photooxidation of toluene has been simulated using the Master Chemical Mechanism version 3.1 (MCM v3.1) coupled to a representation of the transfer of organic material from the gas phase to a particle phase. The mechanism was tested against data from a series of toluene photooxidation experiments performed at the European Photoreactor (EUPHORE) outdoor smog chamber in Valencia, Spain. Simulated aerosol mass concentrations compared reasonably well with the measured SOA data after absorptive partitioning coefficients were increased by a factor of between 20 and 80, although the simulated onset of SOA growth was delayed with respect to the experiments. A simplified representation of peroxyhemiacetal adduct formation, from the reaction of organic hydroperoxides with aldehydes in the condensed organic phase, was included in the mechanism and this reduced the required scaling of partitioning coefficients and reduced the time-lag in simulated SOA growth. These observations, and the dependence of SOA formation efficiency upon the initial NO concentration, strongly imply the significant occurrence of association reactions in the condensed organic phase and the important role of organic hydroperoxides in SOA formation. Aerosol data from photooxidation experiments of intermediate degradation products (butenedial, 4-oxo-pentenal, and ortho-cresol) were also simulated using the developed mechanism.

In vivo transformations of dihydroartemisinic acid in Artemisia annua plants

[15- 13C 2H 3]-dihydroartemisinic acid ( 2a ) and [15-C 2H 3]-dihydroartemisinic acid ( 2b ) have been fed via the root to intact Artemisia annua plants and their transformations studied in vivo by one-dimensional 2H NMR spectroscopy and two-dimensional 13C– 2H correlation NMR spectroscopy ( 13C– 2H COSY). Labelled dihydroartemisinic acid was transformed into 16 12-carboxy-amorphane and cadinane sesquiterpenes within a few days in the aerial parts of A. annua, although transformations in the root were much slower and more limited. Fifteen of these 16 metabolites have been reported previously as natural products from A. annua. Evidence is presented that the first step in the transformation of dihydroartemisinic acid in vivo is the formation of allylic hydroperoxides by the reaction of molecular oxygen with the Δ 4,5-double bond in this compound. The origin of all 16 secondary metabolites might then be explained by the known further reactions of such hydroperoxides. The qualitative pattern for the transformations of dihydroartemisinic acid in vivo was essentially unaltered when a comparison was made between plants, which had been kept alive and plants which were allowed to die after feeding of the labelled precursor. This, coupled with the observation that the pattern of transformations of 2 in vivo demonstrated very close parallels with the spontaneous autoxidation chemistry for 2 , which we have recently demonstrated in vitro, has lead us to conclude that the main ‘metabolic route’ for dihydroartemisinic acid in A. annua involves its spontaneous autoxidation and the subsequent spontaneous reactions of allylic hydroperoxides which are derived from 2 . There may be no need to invoke the participation of enzymes in any of the later biogenetic steps leading to all 16 of the labelled 11,13-dihydro-amorphane sesquiterpenes which are found in A. annua as natural products.

Handbook of free radical initiators

Preface. Symbols and Abbreviations. PART I: INITIATORS. Chapter 1. Mechanism of Decomposition of Initiators. 1.1 Introduction. 1.2 Nonconcerted Unimolecular Decomposition. 1.3 Concerted Fragmentation of Initiators. 1.4 Anchimerically Assisted Decomposition of Peroxides. 1.5 Decay of Initiators to Free Radicals and Molecular Products. 1.6 Chain Decomposition of Initiators. References. Chapter 2. Cage Effect. 2.1 Introduction. 2.2 Experimental Evidence for the Cage Effect. 2.3 Mechanistic Schemes of Cage Effect. 2.4 Cage Effect in Solid Polymers. References. Chapter 3. Methods of Study of Initiator Decomposition and Free Radical Generation. 3.1 Kinetic Decay of Initiator (KDI). 3.2 Kinetic Product Formation (KPF). 3.3 Acceptors of Free Radicals (AFR). 3.4 Kinetic Chain Initiated Reaction (KIR). 3.5 Chemiluminescence (CL) Method. References. Chapter 4. Dialkyl Peroxides and Hydroperoxides. 4.1 Dialkyl Peroxides. 4.2 Hydroperoxides and Peracids. References. Chapter 5. Diacyl Peroxides, Peroxy Esters, Polyatomic, and Organometallic Peroxides. 5.1 Diacyl Peroxides. 5.2 Peroxy Esters. 5.3 Decomposition of Polyatomic Peroxides. 5.4 Organometallic Peroxides. References. Chapter 6. Organic Polyoxides. 6.1 Dialkyl Trioxides. 6.2 Hydrotrioxides. 6.3 Tetroxides. References. Chapter 7. Azo Compounds. 7.1 Synthesis and Structure of Azo Compounds. 7.2 Thermochemistry of Azo Compounds. 7.3 Decomposition of Azo Compounds. References. Chapter 8. Compounds with Weak C-C, N-N, C-N and N-O Bonds. 8.1 Polyphenylhydrocarbons. 8.2 Substituted Hydrazines. 8.3 Alkoxyamines. 8.4 Nitro Compounds. 8.5 Nitrates and Nitrites. 8.6 Disulfides and Polysulfides. 8.7 Organometallic Compounds. References. PART II: BIMOLECULAR REACTIONS OF FREE RADICAL GENERATION. Chapter 9. Parabolic Model of Bimolecular Homolytic Reaction. 9.1 Introduction. 9.2 Principles for the Parabolic Model of Bimolecular Homolytic Reaction. 9.3 Parameters of Bimolecular Homolytic Reaction in the Parabolic Model. References. Chapter 10. Bimolecular and Trimolecular Reactions of Free Radical Generation by Dioxygen. 10.1 Reaction of Dioxygen with C-H Bonds of Organic Compounds. 10.2 Reaction of Dioxygen with the Double Bond of Olefins. 10.3 Trimolecular Reaction of Radical Initiation by Dioxygen. References. Chapter 11. Bimolecular Reactions of Free Radical Generation by Ozone. 11.1 Initiation of Radicals by Ozone Reactions. 11.2 Chain Reactions of Ozone Decomposition. References. Chapter 12. Bimolecular Reactions of Hydroperoxides with Free Radical Generation. 12.1 Bimolecular Decomposition of Hydroperoxides. 12.2 Bimolecular Reactions of Hydroperoxides with a pi-Bond to Olefins. 12.3 Bimolecular Reactions of Hydroperoxides with C-H, N-H, and O-H Bonds of Organic Compounds. 12.4 Acid Catalysis for Homolytic Reactions of Hydroperoxides. 12.5 Reaction of Peroxides with Amines. References. Chapter 13. Free Radical Generation by Olefins. 13.1 Reactions of Retrodisproportionation. 13.2 Chain Initiation in Thermal Radical Polymerization. References. Chapter 14. Free Radicals Generation by Haloid Molecules and Nitrogen Dioxide. 14.1 Reactions of Fluorine Compounds. 14.2 Reactions of Dichlorine and Other Chlorine Compounds. 14.3 Initiation by Nitrogen Dioxide. References. Chapter 15. Free Radical Generation by Reactions of Ions with Molecules. 15.1 Decomposition of Hydrogen Peroxide Catalyzed by Transition Metal Ions. 15.2 Catalysis by Ions and Complexes of Transition Metals in Liquid-Phase Oxidation of Organic Compounds. 15.3 Reactions of Free Radicals with Transition Metal Ions. 15.4 Oxidation of Transition Metal Ions by Dioxygen. 15.5 Oxidation of Organic Compounds by Transition Metal Ions. 15.6 Reduction of Peroxides by Radical Anions. References. PART III: REACTIONS OF FREE RADICALS. Chapter 16. Isomerization and Decomposition of Free Radicals. 16.1 Intramolecular Abstraction of Hydrogen Atom. 16.2 Cyclization of Free Radicals. 16.3 Decyclization of Cyclic Radicals. 16.4 Fragmentation of Free Radicals. References. Chapter 17. Free Radical Abstraction Reactions. 17.1 Classification of Radical Abstraction Reactions. 17.2 Enthalpy of Reaction. 17.3 Force Constants of Reacting Bonds. 17.4 Triplet Repulsion. 17.5 Electron Affinity of Atoms in Reaction Center. 17.6 Repulsion of Atoms Forming the Reaction Center. 17.7 Influence of pi-Bonds in the Vicinity of the Reaction Center. 17.8 Steric Effect. 17.9 Polar Effect in Radical Reactions. 17.10 Effect of Multidipole Interaction. 17.11 Solvating Effect. References. Chapter 18. Free Radical Reactions of Hydrogen Transfer and Substitution. 18.1 Reactions of Hydrogen Atom Transfer from a Free Radical to a Molecule. 18.2 Free Radical Substitution Reactions. 18.3 Reaction of Peroxides with Ketyl Radicals. References. Chapter 19. Free Radical Addition. 19.1 Enthalpy and Entropy of Free Radical Addition. 19.2 Empirical Correlation Equations. 19.3 Quantum Chemical Calculations for the Activation Energy. 19.4 Parabolic Model of Radical Addition. 19.5 Contribution of Enthalpy for an Addition Reaction to Its Activation Energy. 19.6 Force Constants of Reacting Bonds. 19.7 Triplet Repulsion in the Transition State of Addition Reactions. 19.8 Influence of Neighboring pi-Bonds on the Activation Energy of Radical Addition. 19.9 Role of the Radius of the Atom Bearing the Free Valence. 19.10 Interaction of Two Polar Groups. 19.11 Multidipole Interaction in Addition Reactions. 19.12 Steric Hindrance. 19.13 Addition of Alkyl Radicals to Dioxygen. References. Chapter 20. Recombination and Disproportionation of Free Radicals. 20.1 Alkyl Radicals. 20.2 Macroradicals. 20.3 Peroxyl Radicals. References. Index.

Separation and identification of DMPO adducts of oxygen-centered radicals formed from organic hydroperoxides by HPLC-ESR, ESI-MS and MS/MS

Many electron spin resonance (ESR) spectra of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) radical adducts from the reaction of organic hydroperoxides with heme proteins or Fe 2+ were assigned to the adducts of DMPO with peroxyl, alkoxyl, and alkyl radicals. In particular, the controversial assignment of DMPO/peroxyl radical adducts was based on the close similarity of their ESR spectra to that of the DMPO/superoxide radical adduct in conjunction with their insensitivity to superoxide dismutase, which distinguishes the peroxyl adducts from the DMPO/superoxide adduct. Although recent reports assigned the spectra suggested to be DMPO/peroxyl radical adducts to the DMPO/methoxyl adduct based on independent synthesis of the adduct and/or 17O-labeling, 17O-labeling is extremely expensive, and both of these assignments were still based on hyperfine coupling constants, which have not been confirmed by independent techniques. In this study, we have used online high performance liquid chromatography (HPLC or LC)/ESR, electrospray ionization-mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS) to separate and directly characterize DMPO oxygen-centered radical adducts formed from the reaction of Fe 2+ with t-butyl or cumene hydroperoxide. In each reaction system, two DMPO oxygen-centered radical adducts were separated and detected by online LC/ESR. The first DMPO radical adduct from both systems showed identical chromatographic retention times (t R = 9.6 min) and hyperfine coupling constants ( a N = 14.51 G, a H β = 10.71 G, and a H γ = 1.32 G). The ESI-MS and MS/MS spectra demonstrated that this radical was the DMPO/methoxyl radical adduct, not the peroxyl radical adduct as was thought at one time, although its ESR spectrum is nearly identical to that of the DMPO/superoxide radical adduct. Similarly, based on their MS/MS spectra, we verified that the second adducts ( a N = 14.86 G and a H β = 16.06 G in the reaction system containing t-butyl hydroperoxide and a N = 14.60 G and a H β = 15.61 G in the reaction mixture containing cumene hydroperoxide), previously assigned as DMPO adducts of t-butyloxyl and cumyloxyl radical, were indeed from trapping t-butyloxyl and cumyloxyl radicals, respectively.

Regioselective Radical Cyclization Initiated by the Reaction of Allylic Hydroperoxides with Iron(II) Sulfate.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Regioselective radical cyclization initiated by the reaction of allylic hydroperoxides with iron(II) sulfate

Treatment of 1-methyl-2-methylene-1-cyclohexyl hydroperoxide with a mixture of FeSO 4/CuCl 2 yielded 1-(1-chlorocyclohexyl)ethanone as the major product consistent with 6- endo- trig cyclization of the intermediate 5-acetylhex-5-enyl radical. This strategy was extended to the ring enlargement of a series of 1-isopropenylcycloalkyl hydroperoxides. Regioselective 7- or 8- endo- trig cyclization reactions could be achieved by treatment of the corresponding cyclopentyl or cyclohexyl hydroperoxides with either a mixture of FeSO 4/CuCl 2 or with FeSO 4 only. The influence of substituents on the efficiency of the 8- endo- trig cyclization process was also explored.

Fullerenes as a tert-butylperoxy radical trap, metal catalyzed reaction of tert-butyl hydroperoxide with fullerenes, and formation of the first fullerene mixed peroxides C(60)(O)(OO(t)Bu)(4) and C(70)(OO(Bu)(10).

tert-Butylperoxy radicals generated by TBHP and Ru(PPh3)3Cl2 or other catalysts adds to C60 and C70 to form stable multiadducts, C60(O)(OOtBu)4 and C70(OOtBu)10. The four tert-butylperoxy groups in the C60 mixed peroxide are located around a pentagon, and the epoxy O occupies the remaining 6,6-bond connected to the same pentagon. The C70 decaadduct shows an unprecedented C2 symmetry with the 10 tert-butylperoxy groups added around the central part of C70 by consecutive 1,4-addition. The compounds are fully characterized by spectroscopic data.

Interaction of tert -butyl Hydroperoxide with Hypochlorous Acid. A Spin Trapping and Chemiluminescence Study

The formation of radical species during the reaction of tert-butyl hydroperoxide and hypochlorous acid has been investigated by spin trapping and chemiluminescence. A superposition of two signals appeared incubating tert-butyl hydroperoxide with hypochlorous acid in the presence of the spin trap f -(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN). The first signal (aN = 1.537mT, agH = 0.148mT) was an oxidation product of POBN caused by the action of hypochlorous acid. The second spin adduct (aN = 1.484mT, agH = 0.233mT) was derived from a radical species that was formed in the result of reaction of tert-butyl hydroperoxide with hypochlorous acid. Similarly, a superposition of two signals was also obtained using the spin trap N-tert-butyl- f -phenylnitrone (PBN). tert-Butyl hydroperoxide was also treated with Fe2+ or Ce4+ in the presence of POBN. Using Fe2+ a spin adduct with a N= 1.633mT and agH = 0.276mT was observed. The major spin adduct formed with Ce4+ was characterised by αN = 1.480mT and agH = 0.233mT. The reaction of tert-butyl hydroperoxide with hypochlorous acid was accompanied by a light emission, that time profile and intensity were identical to those emission using Ce4+. The addition of Fe2+ to tert-butyl hydroperoxide yielded a much smaller chemiluminescence. Thus, tert-butyl hydroperoxide yielded in its reaction with hypochlorous acid or Ce4+ the same spin adduct and the same luminescence profile. Because Ce4+ is known to oxidise organic hydroperoxides to peroxyl radical species, it can be concluded that a similar reaction takes place in the case of hypochlorous acid.

Physico-chemical aspects of polyethylene processing in an open mixer: 8. Various reactions of polyethylene hydroperoxide in the melt

Hydroperoxides generated on polyethylene processing in air show complex behavior. The maximum hydroperoxide concentration reached in the experiments decreases significantly with increasing processing temperature. In the temperature range 150–160 °C, the maximum of the hydroperoxide concentration is determined by preferential reaction of the peroxy radicals with the hydroperoxides accumulating in the melt. Abstraction of the tertiary hydrogen atom of the secondary hydroperoxide by a peroxy radical yields a new hydroperoxide group. Simultaneously the original hydroperoxide is transformed into an α-alkyl-hydroperoxy radical. Monomolecular decomposition of the last yields a ketone and a hydroxyl radical continuing the chain reaction. Thus, the hydroperoxide group destroyed is replaced by another one so that the concentration remains practically constant for some time, especially at 150 °C. In the temperature range 170–200 °C, the maximum of the hydroperoxide concentration is determined by bimolecular decomposition of hydroperoxide groups sufficiently close. This is a consequence of initial non-homogeneous distribution of the hydroperoxides in the melt. It is caused by “clusters” of hydroperoxide groups resulting from the reactions initiated by a pair of primary radicals before geminate termination. A concerted reaction involving two hydroperoxide groups as well as the tertiary hydrogen atom of one of the hydroperoxide groups accounts for the data. The mechanisms and kinetics of the reactions are discussed.