Decomposition Of Hydroperoxides Research Articles

Impact of Nonthermal Plasma Treatment on the Oxidation of Lipids with Different Unsaturation Degrees.

Nonthermal plasma (NTP) treatment of food presents a new technology for the industry but raises concerns about lipid oxidation due to the presence of reactive species. Considering the critical role of the degree of unsaturation in lipid oxidation, this study investigates NTP-induced oxidation across various unsaturated lipids. These lipids are six oil samples primarily containing one of the following methylesters: oleate, linoleate, linolenate, arachidonate, eicosapentaenoate, and docosahexaenoate. Samples were treated with a nonthermal surface dielectric barrier discharge. Plasma-induced effects were first examined by classical lipid oxidation indicators, such as the peroxide value and p-anisidine value. The specific volatile oxidation products, including hexanal, nonanal, trans-2-hexenal, and methyl 9-oxononanoate, were determined to further elucidate the impact of ozone-related oxidation. Monitoring the production of selected nonvolatile oxidation products, such as epoxy-, oxo-, and hydroxy fatty acid methylesters, confirmed that plasma treatment facilitated the decomposition of lipid hydroperoxide. Generally, the level of plasma-induced oxidation increased in parallel with the unsaturation degree of the studied samples, except for the quantity of individual volatile carbonyls. The long-term effect of NTP treatment was investigated by a stability test, revealing that the oxidative stability depended on the input gas of plasma treatment, the sensitivity of the treated sample, and the presence of antioxidants. Except for the focus on the NTP impact, this study offered a case study of a comprehensive investigation into lipid oxidation.

Heme-catalyzed degradation of linoleate 9-hydroperoxide (9-HPODE) forms two allylic epoxy-ketones via a proposed pseudo-symmetrical diepoxy radical intermediate

Heme-initiated decomposition of unsaturated fatty acid hydroperoxides creates alkoxyl radicals that propagate a complex series of reactions to hydroxy, keto, epoxy and aldehydic products. Herein, among the products from the hematin-catalyzed degradation of 9-hydroperoxy-linoleic acid (9-HPODE), we observed a double peak on normal-phase HPLC that resolved on RP-HPLC into equal proportions of two epoxy-allylic ketones with identical UV spectra. Their proton NMR spectra were also indistinguishable and consistent with 9,10-trans-epoxy-11E-13-keto- and 9-keto-10E-12,13-trans-epoxy-octadecenoic acids. Acid hydrolysis to the corresponding dihydroxy-ketones and GC-MS analysis identified the earlier eluting product on RP-HPLC as the 9,10-epoxy regio-isomer. Starting from the C9-hydroperoxide, recovery of the two epoxy-ketones in equal proportions suggests their formation from a common intermediate. Earlier work has proposed formation of a pseudo-symmetrical diepoxy radical (9,10-epoxy-11(•)-12,13-epoxy, derived from an epoxy allylic hydroperoxide precursor) in the carbon chain fragmentation leading to aldehydic products. This intermediate in pathways of alkoxyl radical reactions forms equal pairs of aldehydes, and now also a pair of epoxy-ketones, and based on mechanism the same products arise from either 9-HPODE or 13-HPODE. Our results point to the intermediacy of this diepoxy-carbinyl radical in the origin of at least two classes of linoleate peroxidation products, and it should be considered as a viable intermediate for homo-conjugated diene peroxidation in general. The reactions could contribute to the aldehydes and epoxy-ketones in tissues undergoing oxidative transformations of polyunsaturated fatty acids.

Tert-butyl hydroperoxide decomposition as a descriptor for liquid-phase hydrocarbon oxidation over transition metal oxide-based catalysts: a screening study

Tert-butyl hydroperoxide decomposition as a descriptor for liquid-phase hydrocarbon oxidation over transition metal oxide-based catalysts: a screening study

Bioinspired Divergent Synthesis of Aspersteroids A and B.

Aspersteroids A and B are novel ergostane-type 18,22-cyclosterols with immunosuppressive and antimicrobial activities. Herein, we report the first synthesis of these two natural products, which was accomplished in 15 and 14 steps, respectively, from commercially available ergosterol by means of a bioinspired divergent approach. Key features of this synthesis include an unprecedented radical relay cyclization that was initiated by iron(II)-mediated decomposition of an alkyl hydroperoxide to construct the E ring cyclopentane motif; a titanium(III)-mediated diastereoselective radical reduction of an epoxide to install the challenging C22 stereocenter; and highly regioselective, divergent late-stage oxidations to access the highly oxidized core framework.

Activation of alkyl hydroperoxides by manganese complexes of tmtacn for initiation of radical polymerisation of alkenes.

The activation of alkyl hydroperoxides to generate radicals is a key step in the initiation of radical polymerisations in many industrial applications, not least protective coatings. Cobalt soaps (Co(ii) alkyl carboxylates) are highly effective catalysts under ambient conditions but viable alternatives based on less scarce catalysts are desirable, with especially iron and manganese catalysts showing potential. Manganese complexes of the ligand N,N',N″-trimethyl-1,4,7-triazacyclononane (tmtacn) are long established as catalysts for organic oxidations with H2O2, however their reactivity with alkyl hydroperoxides is less studied especially in apolar solvents. Here we show that this family of complexes can be employed as catalysts for the decomposition of alkyl hydroperoxides in apolar solvents such as styrene/methyl methacrylate mixtures and resins based on styrene/bisphenol-A based diglycidyl ether bismethacrylate (BADGE-MA). The progress of alkene polymerisation in crosslinking resins is followed by Raman spectroscopy to establish its dependence on the oxidation state of the manganese catalyst used, as gelation time and onset of autoacceleration are of particular interest for many applications. We show, through reaction progress monitoring with UV/vis absorption and Raman spectroscopy, that the stability of the manganese complexes in the resin mixtures has a substantial effect on curing progress and that the oxidation state of the resting state of the catalyst is most likely Mn(ii), in contrast to reactions with H2O2 as oxidant in which the oxidation state of the resting state of catalyst is Mn(iii). Manganese complexes of tmtacn are shown to be capable initiators of alkene radical polymerisations, and their rich coordination and redox chemistry means that resin curing kinetics can potentially be tuned more readily than with cobalt alkyl carboxylates.

Effect of the cationic surfactant cetyltrimethylammonium bromide on the decomposition of ethylbenzene hydroperoxide

Effect of the cationic surfactant cetyltrimethylammonium bromide on the decomposition of ethylbenzene hydroperoxide

Relationship between PAH4 formation and thermal reaction products in model lipids and possible pathways of PAHs formation

Lipids are closely related to the generation of PAHs during food thermal processing. During heating, lipids mainly triglycerides undergo hydrolysis, oxidation and decomposition. The relationship between the various products and the formation of PAHs is still unclear. This paper investigated the effect of different lipid standards on PAH4 production, and explored their thermal stability and reaction products to delve into nature of the differences in PAH4 production. Fatty acids were more prone to generate PAH4 than glycerides. The higher the degree of esterification of glycerides, the higher its thermal stability and the lower the content of PAH4 generated, implying that hydrolysis of glycerides promoted the generation of PAH4. In addition, there was a positive correlation between unsaturation in lipids and the PAH4 production. After heat treatment, hydroperoxides, unsaturated fatty alcohols and aldehydes, alkenes and aromatic substances were abundant in oleic acid and linoleic acid which produced the most PAH4. Thermal decomposition of lipid hydroperoxides was the pathway for the generation of conjugated hydrocarbon radicals, alcohols, aldehydes, and alkenes. The intramolecular cyclization and Diels-Alder reaction acted as ring-forming reactions, with consequent dehydrogenation, decarboxylation, side-chain breaks and radical reorganization, ultimately facilitating the amplification of the aromatic rings and the formation of PAHs.

Thermal oxidation of blends of polypropylene and polyamide 6/66. Effect of inhibition

The thermal oxidation of the blends of isotactic polypropylene (PP) and mixed copolyamide PA6/66 has been studied in a wide range of compositions: 0, 5, 10, 20, 30, 40, 50 and 100 wt % PA6/66. Data obtained by differential scanning calorimetry (DSC) and FTIR indicate the immiscibility of two polymer phases in the blends. The melting enthalpy of mixtures is increased during oxidation that is explained by chemi-crystallization of PP under PP oxidation. PA6/66 component is found to retard the growth of PP enthalpy during PP oxidation. According to DSC data on the PP/PA6/66 blends in air, PA6/66 phase greatly enhances the oxidation onset temperature of the PP/PA6/66 blends thus indicating the improved thermal stability of new material. The oxygen consumption of the PP/PA6/66 blends at 130°C proceeds with a large oxidation induction time (OIT) which is increased with increase in PA6/66 content. After OIT is ended, a constant oxidation rate is established, which is characteristic of the autoxidation mechanism. Kinetic analysis of the thermal oxidation of the PP/PA6/66 blends was carried out on the base of two models of polyolefin autooxidation with hydroperoxide decomposition via the 1st or the 2nd order reaction. The both models were found to describe the experimental kinetic curves of the oxygen consumption. Two possible explanations of the inhibition of PP oxidation by PA6/66 phase are discussed. The migration of active radicals from the PP phase to the PA6/66 phase with their transformation into low-active PA6/66 radicals may be responsible for inhibition and an increase in OIT of PP. Another mechanism of OIT increase may be related with a change in the structure of the PP/PA6/66 blends depending on PA6/66 content.

Insights into ethylbenzene oxidation catalyzed by transition-metal oxides: Crucial role of hydroperoxide transformation

Selective oxidation of aromatics via a free-radical process is a crucial ingredient in the chemical industry, in which the transformation of hydroperoxide was considered the key step to facilitate the reaction. In this study, the aerobic oxidation of ethylbenzene (EB) to acetophenone (AcPO) catalyzed by carbon nitrides (CNx) supported the transition-metal oxides was performed. Among these catalysts, Co3O4/CNx displayed the highest activity with 48.09 % EB conversion and 77.8 % AcPO selectivity, due to the efficient decomposition of 1-phenylethyl hydroperoxide (PEHP). Notably, in the case of CuO/CNx, the relatively low EB conversion (19.8 %) and high selectivity of AcPO (70.2 %) were observed, while almost no PEHP was detected. Further mechanism investigations revealed that the decomposition of hydroperoxide over CuO/CNx was too fast to generate the reactive free-radicals, which could not efficiently facilitate the propagation steps. Moreover, the addition of tert-butyl hydroperoxide (TBHP) participated in the α-H abstraction of EB and facilitated of radical propagation, showing the distinguished activities over Co3O4/CNx and CuO/CNx.

The Effects of Multistage Fuel-Oxidation Chemistry, Soot Radiation, and Real Gas Properties on the Operation Process of Compression Ignition Engines

The objectives of the study are to reveal the influence of multistage fuel-oxidation chemistry, thermal radiation of soot during the combustion of a small (submillimeter size) fuel droplet, and real gas effects on the operation process of compression ignition engines. The use of the multistage oxidation chemistry of iso-octane in the zero-dimensional approximation reveals the appearance of different combinations of cool, blue, and hot flames at different compression ratios and provides a kinetic interpretation of these phenomena that affect the heat release function. Cool flames are caused by the decomposition of alkyl hydroperoxide, during which a very reactive radical, OH, is formed. Blue flames are caused by the decomposition of H2O2 with the formation of OH. Hot flames are caused by the chain branching reaction between atomic hydrogen and molecular oxygen with the formation of OH and O. So-called “double” cool flames correspond to the sequential appearance of a separated cool flame and a low-intensity blue flame rather than two successive cool flames. The use of a one-dimensional model of fuel droplet heating, evaporation, autoignition, and combustion at temperatures and pressures relevant to compression ignition engines shows that the thermal radiation of soot during the combustion of small (submillimeter size) droplets is insignificant and can be neglected. The use of real gas caloric and thermal equations of state of the matter in a three-dimensional simulation of the operation process in a diesel engine demonstrates the significant effect of real gas properties on the engine pressure diagram and on the NO and soot emissions: real gas effects reduce the maximum pressure and mass-averaged temperature in the combustion chamber by about 6 and 9%, respectively, increases the autoignition delay time by a 1.6 crank angle degree, increase the maximum heat release rate by 20%, and reduce the yields of NO and soot by a factor of 2 and 4, respectively.

Roaming Dynamics in Hydroxymethyl Hydroperoxide Decomposition Revealed by the Full-Dimensional Potential Energy Surface of the CH2OO + H2O Reaction.

The CH2OO + H2O reaction is an important atmospheric process that leads to the formation of formic acid (HCOOH) and water via the intermediate hydroxymethyl hydroperoxide (HOCH2OOH, HMHP). We investigated the intricacies of this process by employing quasiclassical trajectory calculations on an accurate, full-dimensional ab initio potential energy surface (PES). In addition to the direct mechanism via the transition state (TS), an interesting roaming mechanism was found to play the predominant role in producing H2O and HCOOH. This roaming pathway is featured as the near direct dissociation of HMHP into OH and hydroxymethoxy radical, followed by the retraction of OH and abstraction of the H atom, culminating in the formation of H2O. Due to the longer interaction time of the roaming mechanism, less product translational energy was released, but more internal energies of HCOOH were obtained, as compared with the direct TS mechanism. The enhanced yield of H2O and formic acid achieved through roaming dynamics underscores the significance of dynamics simulations based on an accurate full-dimensional PES. This work provides new insights into the dynamics of the CH2OO + H2O reaction and its implications for atmospheric chemistry.

Catalytic activity of iron-containing carbon nanotubes in the oxidation reaction of the diesel fuel fraction

Liquid-phase aerobic oxidation of petroleum hydrocarbons catalyzed by carbon nanoparticles is focused on the real practical implementation over the rational processing of multicomponent petroleum feedstock. The use of metal-containing carbon nanostructures as catalysts allows known oxidation processes to be considered in the most modern strapping and simultaneously raises related questions about kinetics and mechanism of the process. This paper describes the formal kinetic regularities of the liquid-phase aerobic oxidation of the diesel fuel paraffin-naphthenic fraction in the presence of iron-containing multiwalled carbon nanotubes Fe@MWCNT. The purpose of the work is to determine the activity of the catalyst and the mechanism of its action. The reaction was carried out at 80°C, at which thermal decomposition of hydroperoxides is known to be almost non-existent and the reaction does not initiate. The induction period, the profile of the kinetic curves, and the oxygen uptake rate were taken as criteria for catalyst activity. As a result, it was shown that Fe@MWCNT additives have a significant ability to increase the rate of aerobic oxidation of diesel fractions. A general scheme of catalytic oxidation of hydrocarbons of the petroleum fraction in which the catalyst on a nanocarbon carrier reduces the dissociation energy of the C-H bond and activates the decomposition of hydroperoxides into active reactive particles has been proposed. Keywords: metal-containing carbon nanotubes; petroleum hydrocarbons; diesel fuel; paraffin-naphthenic fraction; oxidation induction period; catalytic hydroperoxide decomposition; oxygen uptake rate.

Interaction of acetylcholine with biodegradable biopolyesters and catalysis of the radical decomposition of hydroperoxides in solutions

Interaction of acetylcholine with biodegradable biopolyesters and catalysis of the radical decomposition of hydroperoxides in solutions

A comprehensive two-scale model for predicting the oxidizability of fatty acid methyl ester mixtures

The intricate mechanisms of oil thermooxidation and their accurate prediction have long been hampered by the combinatory nature of propagation and termination reactions involving randomly generated radicals. To unravel this complexity, we suggest a two-scale mechanistic description that connects the chemical functions (scale 1) with the molecular carriers of these functions (scale 2). Our method underscores the importance of accounting for cross-reactions between radicals in order to fully comprehend the reactivities in blends. We rigorously tested and validated the proposed two-scale scheme on binary and ternary mixtures of fatty acid methyl esters (FAMEs), yielding three key insights: (1) The abstraction of labile protons hinges on the carrier, defying the conventional focus on hydroperoxyl radical types. (2) Termination reactions between radicals adhere to the geometric mean law, exhibiting symmetric collision ratios. (3) The decomposition of hydroperoxides emerges as a monomolecular process above 80 °C, challenging the established combinatorial paradigm. Applicable across a wide temperature range (80 °C to 200 °C), our findings unlock the production of blends with controlled thermooxidation stability, optimizing the use of vegetable oils across applications: food science, biofuels, and lubricants.

Crown Ether Complexes with Alkaline Earth Metal Chlorides ‒ Catalysts for the Decomposition of Isopropylbenzene Hydroperoxide

Kinetic and thermodynamic parameters of the decomposition of isopropylbenzene hydroperoxide in chlorobenzene in the presence of dibenzo-18-crown-6 ether (DBK) complexes with CaCl2, SrCl2, BaCl2 have been experimentally obtained. The catalytic activity of alkaline earth metal compounds decreases in the series SrCl2·DBK CaCl2·DBK BaCl2·DBK. The formation of intermediate intermediates in the metal‒complex-hydroperoxide system has been kinetically established. SrCl2·DBK forms the strongest and most ordered structures with isopropylbenzene hydroperoxide, which decay at the highest rates. The formation of intermediate intermediates has been confirmed using quantum chemical modeling.

Advantages of hydroxyl radical water treatment for the fruits and vegetables preservation

In this study, the effects of hydroxyl radical water (HRW) treatment on the functional components, volatile compounds, and preservation properties of cherry tomatoes, grapes, coriander, and celery were investigated. The results demonstrated that HRW treatment could be significantly effective in delaying the color change and decay of fruits and vegetables. The loss of total sugars in the HRW-treated samples was relatively low, ranging from 0.02% to 0.84%. However, other functional components will be more severely affected. Specifically, celery exhibited a 17.95% decrease in total phenols and a 13.01% decrease in ascorbic acid, which may be caused by excessive surface area, indicating that the applicability of HRW to celery remains to be studied. The loss of functional components of both fruits could be controlled under 4%. Throughout the treatment, the phenolic profiles and volatile compounds remained stable. Notably, an increase in partial ester compounds, such as ethyl caproate, was observed in HRW-treated cherry tomatoes, which might improve the sensory function. Moreover, the reduction of some compounds obtained from the decomposition of fatty acid hydroperoxides may enhance the fresh odor of fruits and vegetables. Consequently, HRW treatment emerges as a safe and environmentally friendly technology for postharvest processing of fruits and vegetables.

Experimental and kinetic modeling study of low-temperature oxidation of n-pentane

Attractiveness in advanced low-temperature combustion engines drives a constantly updated understanding of low-temperature oxidation chemistry. In this work, the low-temperature oxidation chemistry of n-pentane in two jet-stirred reactors at atmospheric pressure and in the temperature range of 500–825 K was investigated using combined analysis methods of synchrotron vacuum ultraviolet photoionization mass spectrometry, gas chromatography, and Fourier transform infrared spectroscopy. Furthermore, the gaseous mixture from JSR was collected in acetonitrile for subsequent product characterization using flow injection analysis, high-pressure and ultra-high-pressure liquid chromatography coupled to a Thermo Scientific™ Orbitrap® Q-Exactive high-resolution mass spectrometry. Numerous intermediate species were identified by these analytical methods, which contributed to unraveling the low-temperature oxidation reaction network of n-pentane. A detailed n-pentane model was tentatively developed to reduce deviations between experimental measurements and model predictions by updating the rate constants of C5 keto-hydroperoxide decomposition, C5 hydroperoxy cyclic ether decomposition, and Korcek reactions of C5 keto-hydroperoxide, and by introducing pressure-dependent rate constants for the reaction classes of Q˙OOH + O2, Q˙OOH decompositions, concerted HȮ2-elimination of RȮ2, C5 keto-hydroperoxide decomposition, C5 hydroperoxy cyclic ether decomposition, and Korcek reactions of C5 keto-hydroperoxide, and by adding more detailed sub-mechanisms for C5 cyclic ethers and C5 keto-hydroperoxides. This updated model was validated against a set of available experimental data, including jet-stirred reactor species data and ignition delay times. These exploratory updates of the kinetic model reveal the considerable influence of the rate constants of hydroperoxide decomposition and the pressure-dependent rate constants of key reaction classes on the kinetic model predictions, highlighting the future demands for high-precision quantum chemistry calculations of the pressure-dependent rate constants of the aforementioned reaction classes to reduce mechanism uncertainties and to develop accurate and robust chemical kinetic models.

One-step highly selective catalytic oxidation of cyclohexane to KA-oil over functional CeMn0.5Co0.5Ox composite oxide: Synergistic effects between Mn and Co species with different valences and metal ion ratios

Presently, one-step highly selective oxidation of cyclohexane to KA-oil, which is a crucial organic chemical intermediate for the production of ε-caprolactam and adipic acid, is still a tremendous challenge. In this work, the functional CeMn0.5Co0.5Ox composite oxide catalysts were successfully prepared by glycine-nitrate combustion method. The results showed that 93.0% of selectivity to KA-oil with 4.6% of cyclohexane conversion was achieved over CeMn0.5Co0.5Ox under the optimal reaction conditions. The experimental and characterization results showed that the excellent catalytic performance of CeMn0.5Co0.5Ox is attributed to the synergistic effects between Mn and Co species with different valences and metal ion ratios, which efficiently promote the directional decomposition or reduction of cyclohexyl hydroperoxide (CHHP) intermediate to KA-oil. The density functional theory (DFT) calculations further confirmed the synergistic catalysis of CeMn0.5Co0.5Ox in the selective oxidation. This work affords the new insights into the design of efficient catalyst for the selective oxidation of alkanes.

Understanding of Cumene Oxidation Catalyzed by Metal–Nitrogen–Carbon through Theoretical Simulations and Kinetic Validation

M–N–C materials as catalysts are widely used in hydrocarbon oxidation, the intrinsic role of which has not been well illustrated. In this study, M–N–C (M = Fe, Co, Cu, Zn) as model catalysts for cumene oxidation through theoretical calculations and experiment validation are studied. The changes of Gibbs free energy (ΔG) for the elementary steps demonstrate that the activation of cumene/O2 molecules and the decomposition of cumene hydroperoxide (CHP) play a significant role in cumene oxidation. The interactions between M–N–C and cumene, O2, and CHP are fully investigated. There are strong interactions between FeNC/CoNC and O2, cumene, and CHP, in which the activation of cumene and O2 and the decomposition of CHP occurred more easily, thereby promoting the catalytic activity. Although the adsorption energy over CuNC (ΔECuNC) for cumene is comparable to ΔECoNC, the O2 molecule is physically adsorbed on CuNC, which leads to a lower activity than those of FeNC and CoNC. Metal tetraphenyl-porphyrins (MTPPs) with the corresponding structure of M–N–C as the catalysts are used to catalyze the oxidation of cumene. A volcanic curve correlation between the average adsorption energy (ΔEav.) and the conversion rate of cumene catalyzed by MTPPs is observed. The kinetic experiments confirmed that CoTPP displays the best catalytic activity, due to the high k80 and low activation energy for the crucial steps of cumene oxidation, which is consistent with the theoretical results.

Experimental and theoretical study on ionic liquid [Bmim]Br-catalyzed decomposition of cumene hydroperoxide into dimethylbenzyl alcohol

The Ionic Liquid 1-butyl-3methyl-imidazolium bromide ([Bmim]Br) was found to be a good catalyst for the decomposition of Cumene Hydroperoxide(CHP) to ɑ,ɑ-Dimethylbenzyl alcohol(CA). The mechanism of [Bmim]Br-catalyzed conversion of CHP to CA has been studied using density functional theory(DFT) calculations. The DFT results showed that the Br anion of [Bmim]Br played a crucial role in the decomposition of CHP to CA. The energy barrier of [Bmim]Br-catalyzed decomposition of CHP is 21.4 kcal/mol. This research provides the feasibility of ionic liquid as catalysts for CHP decomposition to CA.