Radicals In Liquid Phase Research Articles

Kinetic analysis of aerobic oxidation catalyzed by a hybrid heterogeneous-homogeneous system containing supported Mn and V oxides and N-hydroxyphthalimide

The activities of transition metal oxide (TMO) heterogeneous catalysts based on individual components such as VOX, and MnOX supported on TiO2 and TiO2-SiO2 as cocatalysts in catalytic systems complemented with N-hydroxyphthalimide (NHPI) in the processes of aerobic liquid-phase radical chain oxidation of alkylarenes (RH) was investigated. The mechanisms of catalysis by NHPI in a liquid phase and participation of TMO in the chain initiation stage were discussed. Catalytic activities of Mn- and V-oxide catalysts were compared with the results of molecular hydrogen temperature programmed reduction profiles (H2-TPR) of the catalysts, revealing correlation between them. Reaction enthalpies calculated via a semi-empirical method for model structures of catalytic centers explained the obtained experimental results. Finally, catalytic cumene oxidation was presented using a reactions scheme identifying the concomitant role of heterogeneous initiation and homogeneous propagation and termination steps for the oxidation process proceeding via a free-radical mechanism.

L-Dehydroascorbic acid recycled by thiols efficiently scavenges non-thermal plasma-induced hydroxyl radicals

Recent development in electronics has enabled the use of non-thermal plasma (NTP) to strictly direct oxidative stress in a defined location at near-physiological temperature. In preclinical studies or human clinical trials, NTP promotes blood coagulation, wound healing with disinfection, and selective killing of cancer cells. Although these biological effects of NTP have been widely explored, the stoichiometric quantitation of free radicals in liquid phase has not been performed in the presence of biocompatible reducing agents, which may modify the final biological effects of NTP. Here we quantitated hydroxyl radicals, a major reactive oxygen species generated after NTP exposure, by electron paramagnetic resonance (EPR) spectroscopy using two distinct spin-trapping probes, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and 3,3,5,5-tetramethyl-1-pyrroline-N-oxide (M4PO), in the presence of thiols or antioxidants. l-Ascorbic acid (AsA) at 25–50 μM concentrations (physiological concentration in the serum) significantly scavenged these hydroxyl radicals, whereas dithiothreitol (DTT), reduced glutathione (GSH), and N-acetyl-cysteine (NAC) as thiols were required in millimolar concentrations to perform scavenging activities. l-Dehydroascorbic acid (DHA), an oxidized form of AsA, necessitated the presence of 25–50 μM DTT or sub-millimolar concentrations of GSH and NAC for the scavenging of hydroxyl radicals and failed to scavenge hydroxyl radicals by itself. These results suggest that the redox cycling of AsA/DHA via thiols and cellular AsA metabolism are important processes to be considered while applying NTP to cells and tissues. Further studies are warranted to elucidate the interaction between other reactive species generated by NTP and biomolecules to promote biological and medical applications of NTP.

Significant enhancement of micropollutant photocatalytic degradation using a TiO2 nanotube array photoanode based photocatalytic fuel cell

This study evaluated the application of a membrane-free photocatalytic fuel cell composed of a TiO2 nanotube array photoanode and a Cu cathode, i.e. TNA-Cu PFC system, for micropollutant removal from water. Significantly enhanced removal of a commonly present aqueous micropollutant 4-chloro-2-methylphenoxyacetic acid (MCPA) was obtained in this TNA-Cu PFC system: the TNA-Cu PFC system achieved better MCPA degradation compared to the conventional photocatalytic method using the same catalyst. In the TNA-Cu PFC system, the MCPA degradation was largely promoted under acidic conditions, indicating this as an important operational condition. The enhancement of MCPA degradation in the TNA-Cu PFC system involved better e−/h+ separation and generation of other oxidants: in conventional photocatalytic process, hydroxyl radicals in liquid phase contributed to 93.7% MCPA degradation while only 2.4% MCPA degradation was mediated by other oxidants like O2−, H2O2, HO2; for MCPA degradation in the TNA-Cu PFC system, the contribution of hydroxyl radicals in the liquid phase decreased to 83.6%, while contribution of other oxidants like O2−, H2O2, HO2 increased to 15.3%. This change in MCPA degradation mechanisms was confirmed via degradation intermediates analysis by LC-MS/MS. The study on the effect of electrolyte concentration suggests that when operated under acidic conditions, addition of electrolyte is not required. The TNA-Cu PFC system was shown to work well in the presence of up to 15 mg/L natural organic matter (originating from two large rivers), high amounts of common inorganic ions, and even in WWTP effluent. The TNA-Cu PFC system also exhibited relatively good stability after several cycles of repeated use. The obtained results demonstrated that this is an adequate system for micropollutant removal from water at various places in the water cycle, i.e. as polisher of WWTP effluents before discharge or for cleaning intake water before producing drinking water.

Silver Nanoparticle Catalysis of the Liquid-Phase Radical Chain Oxidation of Cumene by Molecular Oxygen

A study was carried out on the initiated liquid-phase radical chain oxidation of cumene by molecular oxygen at 70 °C in the presence of silver micro- and nanoparticles. The addition of silver micro- and nanoparticles (10 mg/mL) into the reaction mixture enhances the reaction rate. The catalytic effect for silver nanoparticles was found to be greater than for silver microparticles. The radical nature of this reaction was shown using inhibitors and a scheme was proposed for the catalytic action of silver nanoparticles in the oxidation of substrates by molecular oxygen.

Determination of tocopherols as lipid antioxidants in vegetable oils and animal fats

The content of vitamin E (tocopherols) in natural vegetable oils and fats has been determined by microcalorimetry. This technique belongs to kinetic methods for determining vitamin E, which are based on the capacity of tocopherol to inhibit liquid-phase radical oxidation reactions. It has been shown on a model reaction of initiated oxidation of cumene that fatty oils inhibit the radical reaction with an induction period proportional to the content of tocopherols in oil. From experimental curves, the content of tocopherols in oils obtained by different technological methods has been estimated. It has been shown that the amount of tocopherols is an indicator of the oil quality; therefore, the method proposed can be used to control the way of oil manufacture, oil quality, and the presence of synthetic antioxidants.

Enhancement of Photochemical Grafting of Terminal Alkenes at Surfaces via Molecular Mediators: The Role of Surface-Bound Electron Acceptors

The use of ultraviolet light to functionalize the surface of carbon-based materials with terminal alkenes has emerged as a way to overcome the high chemical stability of these surfaces to create functional interfaces. It was previously shown that surface-bound trifluoroacetic acid protected 10-aminodec-1-ene (TFAAD) can be used to promote the grafting of unreactive alkenes using 254 nm light, but the mechanism by which this enhancement occurs was not understood. Here, we present a detailed study of how surface-bound TFAAD enhances the grafting of organic molecules to the surface of hydrogen-terminated amorphous carbon. Infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy experiments show that pregrafting TFAAD onto carbon surfaces greatly enhances the subsequent grafting of 1-dodecene, dodecane and dodecane-d26 by locally facilitating photoemission of electrons. Using a photopatterned TFAAD “seed” layer, we demonstrate that subsequent grafting of these hydrocarbons is enhanced in regions immediately adjacent to the seed and proceeds almost exclusively parallel to the carbon surface. The roles of liquid-phase radical species, valence band holes, and the photochemical fragmentation of surface species in controlling the overall reaction mechanism are discussed.

Autoacceleration of the free-radical chain luminescent oxidation of U(IV) with xenon trioxide in aqueous HClO4

Autoacceleration is observed in the chemiluminescent radical chain oxidation of U(IV) with xenon trioxide in aqueous perchloric acid in a Teflon (not conventional glass) reactor. The decay of chemiluminescence accompanying the reaction between U(IV) and XeO3 in the case of excess oxidizer obeys a first-order kinetic equation only at low U(IV) concentrations of 10−5–10−6 mol/l. Autoacceleration takes place at comparatively high reactant concentrations, when the contribution from the heterogeneous loss of radicals on the reactor walls into chain termination is comparatively small and the role of degenerate chain branching reactions is significant. It is inferred that a critical phenomenon rare for liquid-phase radical chain processes takes place in U(IV) oxidation with xenon trioxide: a comparative small increase in the reactant concentrations causes this chemiluminescent redox process to pass from the quasi-steady-state regime to autoacceleration.

Strong effect of a solid surface on a liquid-phase radical chain chemiluminescence reaction. Oxidation of UIV by dioxygen

The reaction of uranium(IV) with O2 in aqueous solutions of HClO4 is accompanied by chemiluminescence (CL). The CL intensity and the reaction kinetics are appreciably affected by introduction of the glass beads with a radius of 1 mm. In the presence of 1600 beads (the surface area of the glass is 200 cm2), the yield of CL dereases 32-fold. The effect of the solid surface on the kinetic and chemiluminescence parameters of the liquid-phase radical chain reaction is due to the increased role of chain termination upon heterogeneous decay of the HO 2 . and.OH radicals.

Synthesis and reactivity of metal-containing monomers 49. Synthesis and structure of low-valence transition metal acrylates and their polymers

The methods for synthesis of Cu1+, Fe2+, Cr2+, and V3+ acrylates were elaborated. The compounds obtained were characterized by elemental analyses, data of IR, X-ray photoelectron, and Mossbauer spectroscopy, magnetochemistry, and mass spectrometry. Polymeric products were obtained by liquid-phase radical polymerization of metal acrylates. Changes in the electronic state of the ions and their nearest ligand environment during polymerization were observed.

Conformation, environment and reactivity of radicals in copolymerization of methyl methacrylate/ethylene glycol dimethacrylate

The electron spin resonance (e.s.r.) spectra of radicals observed during the copolymerization of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA) consist of 13 lines in the initial liquid phase, but change to 9 lines as the copolymerization proceeds. The experimental spectra have been simulated by use of a model based upon a Gaussian distribution of dihedral angles about a most stable conformation. The simulations suggest that the e.s.r. spectra are superpositions of spectra arising from three types of radicals: a liquid-phase radical giving rise to a 13-line spectrum and two solid-phase radicals giving rise to two slightly different 9-line spectra. The two types of 9-line spectra correspond to terminal radicals on EGDMA and MMA residues. The ratio of the two types of solid-phase radicals is correlated with the degree of disorder of the reacting system, which accounts for the observed dependence of both initiator efficiency and final radical concentration upon the weight fraction of EGDMA. When copolymerization proceeded to medium conversion, ultra-violet irradiation of the samples reinitiated the reaction and caused a temporary reappearance of the 13-line spectrum, indicating that some propagating radicals are trapped in the polymer matrix.

ChemInform Abstract: Reaction Between C6H5(CH3)CHOO· and HO2· Radicals in Liquid Phase. Part 1. Product Study at 371 K

ChemInformVolume 20, Issue 36 Preparative Organic Chemistry ChemInform Abstract: Reaction Between C6H5(CH3)CHOO· and HO2· Radicals in Liquid Phase. Part 1. Product Study at 371 K G. MOGER, Cent. Res. Inst. Chem., Hung. Acad. Sci., H-1525 Budapest, Hung.Search for more papers by this authorD. GAL, Cent. Res. Inst. Chem., Hung. Acad. Sci., H-1525 Budapest, Hung.Search for more papers by this author G. MOGER, Cent. Res. Inst. Chem., Hung. Acad. Sci., H-1525 Budapest, Hung.Search for more papers by this authorD. GAL, Cent. Res. Inst. Chem., Hung. Acad. Sci., H-1525 Budapest, Hung.Search for more papers by this author First published: September 5, 1989 https://doi.org/10.1002/chin.198936112Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume20, Issue36September 5, 1989 RelatedInformation

Reaction between C6H5(CH3)CHOO• and HO•2 radicals in liquid phase. I. Product study at 371 K

AbstractBoth 1‐phenylethyl peroxy (HRO•2) and HO•2 radicals were generated simultaneously by the photochemical interaction of triplet anthraquinone (TQ) with ethylbenzene (RH2) at 371 K and the quantum yields of product formations have been measured. Evidences have been presented that the interaction of HO•2 and HRO•2 radicals yields alkoxy radicals (HRO•) and comparison has been carried out between the reaction of hydrogen abstraction by HRO•2 leading to alcohol and the reaction of β‐scission of HRO•, producing benzaldehyde.—According to the measurements k/kβ = 0.3 ± 0.1 M−1.

Liquid-phase radical reactions of octanal and tert-butyl hydroperoxide

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLiquid-phase radical reactions of octanal and tert-butyl hydroperoxideGeorge W. Mushrush and Robert N. HazlettCite this: J. Org. Chem. 1985, 50, 13, 2387–2390Publication Date (Print):June 1, 1985Publication History Published online1 May 2002Published inissue 1 June 1985https://doi.org/10.1021/jo00213a041RIGHTS & PERMISSIONSArticle Views116Altmetric-Citations12LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (576 KB) Get e-Alerts Get e-Alerts

ChemInform Abstract: ISOMERIZATION OF UNSTABLE ORGANOMETALLIC RADICALS IN LIQUID‐PHASE REACTIONS

Chemischer InformationsdienstVolume 11, Issue 3 Reviews ChemInform Abstract: ISOMERIZATION OF UNSTABLE ORGANOMETALLIC RADICALS IN LIQUID-PHASE REACTIONS R. KH. FREIDLINA, R. KH. FREIDLINASearch for more papers by this authorA. B. TERENT'EV, A. B. TERENT'EVSearch for more papers by this author R. KH. FREIDLINA, R. KH. FREIDLINASearch for more papers by this authorA. B. TERENT'EV, A. B. TERENT'EVSearch for more papers by this author First published: January 22, 1980 https://doi.org/10.1002/chin.198003387AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume11, Issue3January 22, 1980 RelatedInformation

Kinetics of radical polymerization. XX. Energy transfer processes in liquid-phase radical reactions

In order to account for the significant stoichiometric anomalies observed in the course of investigations on inhibited radical polymerization, the author propounded the hot-radical hypothesis, according to which the reaction heat released during the formation of the active centers can serve as a source of activation energy in the subsequent reactions. This hypothesis is based on the assumption that the relaxation (the vibrational deactivation of the hot radicals) is essentially a slow process. To control this assumption in a direct way, the author conducted experiments in which vibrationally excited radicals were produced by UV irradiation of the initiators. The primary hot radicals formed were added onto various unsaturated compounds and thus transformed into more stable radicals, the concentrations of which could be measured with the aid of the ESR method. A comparison of the steady concentrations of the intermediate radicals formed under the effects of thermal and hot radicals, respectively, permits the rate and the probability of the relaxation of the hot radicals to be determined.

The reactivity of some stable radicals

1. We have studied the reactivity of a series of stable radicals in reaction with ethyl benzene, determining the preexponents and activation energies. 2. Dianisylazotoxy forms a π-complex with ethyl benzene which has a lowered reactivity. 3. We have made several suggestions as to the possibility of occurrence of a compensation effect in liquid phase radical reactions.