Radical Conversions Research Articles

Mechanistic and kinetic investigation of electro-activated (Bi)sulfite system for pollutants reduction and oxidation: Role of oxysulfur radicals

Electro-activated sulfite or bisulfite [E-S (IV)] system is a green technology in environmental remediation. This study developed a comprehensive kinetic model to simulate S (IV) oxidation and contaminants degradation. The results revealed that the mechanism and kinetics of S (IV) oxidation varied across different regions, leading to the dominance of different radicals. In kinetics-controlled and mix-controlled regions at low current density, the rate-determining step (RDS) for S (IV) electro-oxidation was the first electron transfer with the generation of SO3•-/HSO3• contributing to BrO3- reduction. In diffusion-controlled region at high current density, oxygen evolution accelerated the rate of quenching SO3•-/HSO3•, being the RDS for S (IV) oxidation. Consequently, SO4•- dominated benzoic acid (BA) oxidation. However, due to the SO3•-/HSO3• oxidation by oxygen and SO4•- reduction by S (IV), the utilization of specific radicals was limited. To maximize the reduction and oxidation efficiency, the influence of current density and S (IV) concentration on the electrode reaction rates (i.e., electro-generation rates of SO3•-/HSO3• (r1) and oxygen (rO2)) and radical conversion efficiencies were simulated. Enhancing r1 but inhibiting rO2 in mix-controlled region improved the reduction rate. Meanwhile, balancing r1 and rO2 in diffusion-controlled region maximized the oxidation rate. Specifically, the E-HSO3- system was more effective for reduction due to the lower electro-oxidation rate and oxygen oxidation rate of HSO3• compared to SO3•-. Conversely, the E-SO32- system was more suitable for oxidation with higher rates of oxysulfur radical conversions. Based on the kinetic model, the most cost-effective current density and S (IV) concentration for reduction, oxidation and simultaneous reduction and oxidation were determined. This study significantly guided the utilization of the E-S (IV) system for various contaminants degradation.

Radical chemistry of nitrosoarenes: concepts, synthetic applications and directions.

Nitrosoarenes are readily available and highly reactive, making them promising building blocks in organic chemistry. The recent development of radical conversions of nitrosoarenes provides an alternative and powerful platform for the facile construction of a wide range of sterically hindered secondary amines and high-value N-heterocycles that are difficult to obtain through other means. Accordingly, a great variety of radical transformations such as additions, cascade reactions by radical relay, and multi-component reactions of nitrosoarenes have been extensively developed. In this review, we aim to summarize the recent progress on the radical reactions of nitrosoarenes with special emphasis on the scope, limitations, and underlying working mechanism. Hopefully, this review will provide a useful guideline for researchers for further exploration of valuable radical transformations and applications of nitrosoarenes.

Major Barriers and Challenges to Integrating ICT in Education

From the start of the information age, ICT has upheld an essential role in improving the quality of education. Thus, lots of countries desire to perk up the effectiveness and quality of the learning process, and consider ICT as one tool to attain that target. This role in education involves assisting students to learn and teachers to execute their teaching vocation more efficiently. As a result of quick developments in a short period, ICT has turned out to be the focus of interest for pedagogical settings. Swift developments in ICT have also led to radical conversions in education. This brings about the significance for training teachers and students for these changes in the information society. Integration of ICT is essential to upgrade the quality of education and how ICT might permit teachers to construct different pathways. In these backgrounds, educator’s shifting role in the 21st century entails a vital role, which is to be the leader for connecting technological novelties to teaching/learning process. At this point, essential competencies and the degree of willingness are key factors in the implementation process of new ICT. The major objective of this study is to get experiential data on the current use of ICT by teachers and students to come up with strategies and action plans for integrating educational technologies in the Algerian higher educational system. More purposely, the study endeavours to investigate teachers' perceptions of barriers and challenges that may influence integrating ICTs in the teaching process, . The findings will be discussed in relation to learning theories in addition to the pedagogical outcomes for the use of ICT in EFL context.

Negative Parental Influences on Religious Conversion: Implications for Pastoral Care

This essay discusses the contribution that psychoanalytic psychology has made to research on religious conversion and asks what implications it might have for pastoral practice. Some of conversion’s most dramatic manifestations occur amid familial instability, or negative parental influences, that stand to be misinterpreted by religious leaders if their full psycho-spiritual context is not understood. The Freudian tradition has provided some context as to why people with rocky upbringings might undergo dramatic change. The data supports the conclusion that these radical conversions are much less a sign of direct supernatural influence than they are of a need for the converts to receive pastoral care in working through a “crisis stage” of faith development.

Reactivity of Polymers on Exposure to Nitrogen Dioxide

The mechanism of reactions of nitrogen dioxide with polymers of different classes is considered. In reactions with carbon-chain polymers at 298 K, nitrogen dioxide can only add to extrinsic double bonds that are formed in the synthesis of the polymers. The mechanism of reactions of nitrogen dioxide with polymers of different classes is considered. In reactions with carbon-chain polymers at 298 K, nitrogen dioxide can only add to extrinsic double bonds that are formed in the synthesis of the polymers. These reactions resulted in dinitro compounds and nitro nitrites. At elevated temperatures, carbonyl and hydroxyl groups are formed in these polymers along with nitration products. Active participants of NO2 reactions with rubbers are double bonds converting into nitroalkyl and alkyl radicals initiating then free radical conversions of these polymers. Polymers containing amide, urethane and imide groups are rather sensitive to NO2. These materials undergo essential changes in the chemical structure with formation of stable nitrogen-containing radicals. The reactions of nitrogen dioxide provide a simple method of the spin-labeled polymer preparation.

Radical-driven carbonyl-to-acid conversion and acid degradation in tropospheric aqueous systems studied by CAPRAM

Abstract Model studies on the aqueous phase radical-driven processing of carbonyl compounds and acids in clouds and deliquescent particles were performed. The model exposed that aqueous radical conversions of carbonyl compounds and its oxidation products can contribute potentially to the formation of functionalised organic acids. The main identified C 2 –C 4 organic gas phase precursors are ethylene glycol, glycolaldehyde, glyoxal, methylglyoxal and 1,4-butenedial. The aqueous phase is shown to contribute significantly with about 93%/63%, 47%/8%, 31%/4%, 7%/4%, 36%/8% to the multiphase oxidative fate of these compounds under remote/urban conditions. Interestingly, the studies revealed that aqueous chemical processing is not only limited to in-cloud conditions but also proceeds in deliquescent particle phase with significant fluxes. Oxalic acid is shown to be formed preferably in deliquescent particles subsequent to the in-cloud oxidations. Mean aqueous phase oxalate formation fluxes of about 12, 42 and 0.4 ng m −3 h −1 in the remote, urban and maritime scenario, respectively. Additionally, the turnovers of the oxidation of organics such as methylglyoxal by NO 3 radical reactions are identified to be competitive to their OH pendants. At the current state of CAPRAM, mean C 2 –C 4 in-cloud oxidation fluxes of about 0.12 and 0.5 μg m −3 h −1 are modelled under the idealised remote and urban cloud conditions. Finally, turnovers from radical oxidations were compared with those of thermal reactions. It is demonstrated that, based on the sparse kinetic data available organic accretion reaction might be of interest in just a few cases for cloud droplets and aqueous particles but generally do not reach the oxidative conversion rates of the main radical oxidants OH and NO 3 . Interestingly, oxidation reactions of H 2 O 2 are shown to be competitive to the OH radical conversions in cases when H 2 O 2 is not readily used up by the S(IV) oxidation.

Conversion and Attachment Insecurity Among Orthodox Jews

Radical conversion, which entails a sweeping transformation of existing meaning systems, is often precipitated by emotional distress. Nevertheless, although many individuals turn toward religion when distressed, few undertake total and radical conversions. Previous research suggests that insecurely attached individuals—who resemble James's disillusioned, doubting, and divided sick souls—may be particularly prone to radical conversions. Thus, the present research examined insecure parental attachment history and convert status among 122 Orthodox and 31 non-Orthodox Jews, hypothesizing that converts to and from Orthodox Judaism, who undertake an all-encompassing transformation of beliefs, behaviors, values, and life's purpose, would report greater insecurity in parental attachment history than nonconverts. Results indicate that converts report greater maternal and paternal insecurity, as compared to both nonconverts and those with intra-Orthodox religious change. Thus, further research examining insecure attachment, and associated religious stressors and doubts, may uncover some of the individual differences underlying radical conversions.

EPR and1H and13C NMR study of nitroxyl radical conversions in strong and superstrong acids

1. Nitroxyl radicals of derivatives of 3-imidazoline-3-oxide and 3-imidazoline in solutions of strong or superstrong acids undergo reversible disproportionation to form dications: oxoammonium salts protonated at the nitronium or imino group, and diprotonated hydroxylamino derivatives. The stability of the oxoammonium salts and the hydroxylamino derivatives depends both on the structure of the initial radical and on the acid used. 2. The radical cations that are present in the equilibrium mixture in concentrations from fractions to several percent are protonated only on the nitronium or imino group.

Thermolysis of aromatic hydrocarbons in coking of petroleum residua

This article presents the results from a radiochemical study of the thermolysis of the aromatic hydrocarbons present in straight-run resids from West Siberian and Kotur-Tepe crudes. Alkylphenanthrenes containing /sup 14/C radiocarbon in the ring (AP-1) or in the side chain (AP-2) were used as the radioactive indicators. It is determined that the distribution of radioactivity in the products from coking the West Siberian vacuum resid is almost identical for the resids containing AP-1 and AP-2. The results indicate that the thermolysis of aromatic hydrocarbons of the medium-sulfur vacuum resid from West Siberian crudes proceeds at a rate approximately one-half that for the low-sulfur vacuum resid from Kotur-Tepe crude. The difference in reaction rates is attributed to the presence, in the medium-sulfur starting material, of compounds that inhibit radical conversions of the aromatic hydrocarbons present in the resid.

Free radicals in dicarboxylic acids: an e.s.r. study of radical conversions in gamma-irradiated single crystals of glutaric acid and glutaric-2,2,4,4-d4 acid.

The gamma-radiation-induced free radicals in single crystals of glutaric acid and glutaric-2,2,4,4-d4 acid were studied in the temperature range 77-300 K by e.s.r. techniques. At 77 K the decarboxylation radical and the anion are stabilized. At higher temperatures the decarboxylation radical is found to be converted into a hydrogen abstraction radical with an activation energy of 6.3 +/- 0.5 kcal/mole for the non-deuterated crystal. This radical is stable at room temperature. The anion seems be be converted to an unidentified intermediate radical which in turn is converted to the gamma-acyl radical. An analysis of the g-value anisotropy and of the 13C hyperfine splitting variation for this radical in the deuterated crystal is consistent with the assigned radical structure. By heat treatment the alpha-acyl radical is converted to another form of the hydrogen abstraction radical with an activation energy of 9.6 +/- 0.6 kcal/mole in the deuterated crystal. U.V.-light (gamma = 254 nm) transforms one of the room temperature radicals into the other.

Free radical conversions of two component polyurethanes by the action of light

Various physico-chemical methods were used to investigate photo-oxidation and photolysis (initiated by ferric chloride additives) of crosslinked polyurethanes based on hydroxyl containing branched oligoesters of different chemical structures. The type of macroradical was established and a kinetic study made of dark and photochemical degradation.

The kinetics of radical decay in crystalline amino acids. 7. Monohydrates

The kinetics of radical decay in x-irradiated single crystals of L-arginine hydrochloride monohydrate, L-asparagine monohydrate, and L-histidine hydrochloride monohydrate have been studied. At temperatures sufficiently low that no measurable dehydration occurs, radical decay fits a model which includes distinct activation energies for the combination of nearby radicals and for diffusion of distant radicals to within a critical reaction distance. At temperatures sufficiently high that significant dehydration occurs on the time scale of radical decay, two types of behavior were observed. In L-asparagine monohydrate and L-histidine hydrochloride monohydrate, radical decay became rapid only upon completion of dehydration, whereas in L-arginine hydrochloride monohydrate radical decay became rapid at the start of dehydration and was completed well before dehydration was complete. At intermediate temperatures the radical decay kinetics appear to be a combination of the diffusion-controlled process and the dehydration-assisted one. No radical conversions were observed during decay.

An ESR Study of Light- and Temperature-Induced Free Radical Conversions in Single Crystals of Dihydrouracil

In dihydrouracil a reversible free radical conversion between the two hydrogen-abstraction radicals 5-yl and 6-yl has been found. Thus, the 6-yl to 5-yl transformation takes place if an irradiated sample is cooled below 220 K and exposed to light with wavelengths below 450 nm. The reverse process is initiated by a subsequent heating of the sample. The kinetics for both the light- and temperature-induced processes have been studied. The results indicate that an intramolecular hydrogen transfer process is more probable than a corresponding intermolecular one. Comparison is made with other unsaturated and saturated pyrimidine derivatives.

Copolymerizations initiated by mechano‐radicals on particle surfaces of poly(tetrafluoroethylene)

AbstractMechanical fracture of solid poly(tetrafluoroethylene) (PTFE) produces main‐chain scissions of the polymer, and free radicals, called mechano‐radicals, are trapped on fresh surfaces generated by the fracture. These radical conversions were verified by ESR observation when several monomers—methylmethacrylate, vinylacetate, and ethylene—were brought into contact with these mechano‐radical, and the copolymerizations of PTFE with these monomers were demonstrated. It was found that a new surface property, wettability of water, was added to the solid PTFE by the copolymerization with vinyl acetate, although the bulk nature of PTFE was not changed.

ChemInform Abstract: ELECTRON SPIN RESONANCE STUDY OF X‐IRRADIATED SINGLE CRYSTALS OF DIMETHYL SULFONE

The ESR spectra of x‐irradiated single crystals of dimethyl sulfone, O2S(CH3)2 have been examined at temperatures from 77 to 353 K. Between 77–153 K the spectra are dominated by an isotropic quartet of lines of intensity ratio 1:3:3:1, centered at g=2.0026±0.0001, with a hyperfine interval of 20.9±0.2 G. This spectrum originates from a methyl radical formed by the breaking of an S–C bond. On warming, the intensity of the methyl quartet decreased markedly at 163 K, being replaced by a singlet signal after several irreversible radical conversions had taken place. This singlet, which was stable from 173 to 333 K, is characterized by g values 2.0022, 2.0061, and 2.0067±0.0001. No hyperfine structure was observed. This spectrum is attributed to the O2ṠCH3 radical. The g=2.0022 is oriented perpendicular to the –SO2 plane, as expected for an unpaired electron principally located in a 3p (π) orbital on the S atom. The other g values are symmetrically located with respect to the two S–O bonds and lie on the SO2 pl...

Electron spin resonance study of x-irradiated single crystals of dimethyl sulfone

The ESR spectra of x-irradiated single crystals of dimethyl sulfone, O2S(CH3)2 have been examined at temperatures from 77 to 353 K. Between 77–153 K the spectra are dominated by an isotropic quartet of lines of intensity ratio 1:3:3:1, centered at g=2.0026±0.0001, with a hyperfine interval of 20.9±0.2 G. This spectrum originates from a methyl radical formed by the breaking of an S–C bond. On warming, the intensity of the methyl quartet decreased markedly at 163 K, being replaced by a singlet signal after several irreversible radical conversions had taken place. This singlet, which was stable from 173 to 333 K, is characterized by g values 2.0022, 2.0061, and 2.0067±0.0001. No hyperfine structure was observed. This spectrum is attributed to the O2ṠCH3 radical. The g=2.0022 is oriented perpendicular to the –SO2 plane, as expected for an unpaired electron principally located in a 3p (π) orbital on the S atom. The other g values are symmetrically located with respect to the two S–O bonds and lie on the SO2 plane. This indicates that the remaining S–C bond, on warming, reorients itself into the SO2 plane. Observation of the 33S spectrum confirms this interpretation. Spin densities of the unpaired electron on the S atom are ρ3s=0.074 and ρ3p=0.33.

Initiated oxidation of solid polystyrene and the effect of antioxidants on this process

AbstractThe paper is concerned with the kinetics of radical conversions in solid polystyrene (PS) induced by decomposition of free‐radical initiators over the temperature range of 60–90°C. A complex quantitative study of PS oxidation was carried out. The kinetics of initiator decomposition and of hydroperoxide accumulation, the variations in chemiluminescence (CL) intensity accompanying polymer oxidation were studied. The CL spectrum and the changes in molecular weight in the course of oxidation were measured. A method for determination of the relative antiradical activity of antioxidants, based on the competition between the antioxidant and the stable radical for the active radical was proposed. The activity of valence‐saturated antioxidants in the solid phase was found to become more uniform compared to the liquid phase, whereas that of stable nitroxide radicals was abnormally high. Initiated solid PS oxidation occurred by a chain mechanism with formally linear termination of the chain. The chain length of 3.0 ± 0.5 was independent of temperature. A model of initiated PS oxidation is proposed. It implies structural inhomogeneity of the sample, resulting in different probabilities of radical formation in the polymer bulk in the course of initiator decomposition in various sample zones. The model permits quantitative description of the kinetics of hydroperoxide accumulation, stable radical consumption, and of variations in CL intensity during initiated and inhibited PS oxidation.

Study of free radical conversions of a polycarbonate based on 1,1-di-(4-hydroxyphenyl)cyclohexane (ilon) by the esr method

1. The interaction of ilon and chlorine atoms produced by the photoreduction of additions of ferric chloride, was investigated by the ESR method at 77°K. 2. Under the action of light, an impurity of ferric chloride may lead to destruction of the polymer with breakdown of the macromolecules at the carbonate groups and C-Ar bonds. 3. Chlorine atoms also strip H atoms from the cyclohexane ring of the macromolecule with the formation of substituted cyclohexyl radicals.

ESR study on radical conversions in irradiated low‐density polyethylene

AbstractESR studies were carried out on radical conversions by thermal and photochemical mechanisms in low‐density polyethylene irradiated mainly with electron beams at −196°C both in vacuum and in the presence of CO. According to the spectral change, the following radical conversions were elucidated for the samples irradiated in vacuo [eqs. (1) and (1′)] and in the presence of CO [eqs. (2) and (2′)]. magnified image From the resemblance of the ESR spectrum observed after direct photolysis of polyethylene to that observed after photo‐induced radical conversions of the allylic radicals, it is concluded that an eight‐line ESR spectrum observed immediately after photolysis of polyethylene at −196°C could be attributed more reasonably to the alkyl radicals CH2CHCH3 than to CH2CH2 and CH2CHCH2.

ESR Studies on Radical Conversions in Irradiated Single Crystals of Succinic Acid

The ESR studies on the radical conversions from primary to room temperature stable radicals in irradiated single crystals of succinic acid have been carried out with aid of fumaric acid-doped crystals. Since in the doped crystals the spectrum of succinic acid anion was replaced by that of furmaric acid anion, it was possible to identify the spectrum arising from ĊH2CH2COOH, which has been postulated for a long time as a precursor of the room temperature stable radical CH3ĊHCOOH. It has been further found that a part of ĊH2CH2COOH converts into HOOCĊHCH2COOH at − 100°C and then the radical isomerization from ĊH2CH2COOH to CH3CHCOOH takes place at − 100 − ∼ − 75° C following the conformational change which is favorable to the intramolecular hydrogen transfer. The freshly formed CH3CHCOOH radical has a different conformation from that of the room temperature stable species. The stable conformation is achieved by the 180° rotation around the C–C bond between the CH and carboxyl carbon atoms in the unstable species. Besides these, the conversion process from the succinic acid anion to HOOCĊHCH2COOH and HOOCCH2CH2C=O has been also studied. These results are based on the hyperfine and g tensors determined in the present work for CH2CH2COOH and unstable and stable CH3ĊHCOOH as well as the stable anion.