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In this work, a molecular-level kinetic model was built to simulate the vacuum residue (VR) coking process in a semi-batch laboratory-scale reaction kettle. A series of reaction rules for heavy oil coking were summarized and formulated based on the free radical reaction mechanism. Then, a large-scale molecular-level reaction network was automatically generated by applying the reaction rules on the vacuum residue molecules. In order to accurately describe the physical change of each molecule in the reactor, we coupled the molecular-level kinetic model with a vapor-liquid phase separation model. The vapor-liquid phase separation model adopted the Peng-Robinson equation of state to calculate vapor-liquid equilibrium. A separation efficiency coefficient was introduced to represent the mass transfer during the phase separation. We used six sets of experimental data under various reaction conditions to regress the model parameters. The tuned model showed that there was an excellent agreement between the calculated values and experimental data. Moreover, we investigated the effect of reaction temperature and reaction time on the product yields. After a comprehensive evaluation of the reaction temperature and reaction time, the optimal reaction condition for the vacuum residue coking was also obtained.

With the free radical reaction during the pyrolysis process of heavy organics as the background, the research approach based on density functional theory was adopted to exploring the induction of free radicals on covalent bond and its effect on covalent bond dissociation energy. The energies of seven kinds of covalent bond reactions induced respectively by ·CH3, ·OH and ·H were calculated theoretically on the Gaussian 09 program at the level of ωB97XD/6-31G**. The results indicate that the steric hindrance effect plays a significant role in the energy barrier of free radical induced reaction, while the influence of the covalent bond type plays a minor role. When the isogroup induced exchange reaction of ·OH and ·H does not proceed, the induced energy barrier of ·OH is about 40 kJ/mol higher than that of ·H and the induced energy barrier of ·CH3 is about 50 and 90 kJ/mol higher than that of ·OH and ·H respectively. When the isogroup induced exchange reaction of ·OH and ·H works, it will result in the increasing of 70 kJ/mol of the energy barrier. During the process of calculation, the specific situation of induced reaction should be judged and revised. The above values can be used to estimate the energy barriers of different covalent bond induced reactions.

The oxidation of iodine ions (I–) by hydrogen peroxide (H2O2) under acidic conditions was simulated using ab initio calculations. I2 was formed in three radical-free reactions, where the initial HOI-generating step was identified as the rate limiting step with an energy barrier of 24.49 kcal/mol. The subsequent O2-yielding decomposition of H2O2 with HOI was thermodynamically spontaneous, but kinetically slow due to a substantial energy barrier of 41.34 kcal/mol. In addition to small molecules, five common free radicals were also identified: HO•, H4O2I•, HOO•, I•, and $${\text{I}}_{2}^{ - \bullet} $$ . HO• and H4O2I• were produced by homolytic decomposition of the transient H5O3I with an energy barrier of 3.20 kcal/mol firstly. HO• and HOO• were also observed to participate in several reactions which yielded O2. Overall, radical-mediated reaction had significantly lower energy barrier for O2 generation than the non-free radical reaction pathways. In addition to the generation of O2, other species such as H2O2, I2, $${\text{I}}_{3}^{ - }$$ , and HOOI were also formed through the reactions between free radicals and small molecules.

Polycyclic aromatic hydrocarbons (PAHs) are of increasing importance in the advanced material field. Cyclic diaryliodonium salts are non-toxic and environmentally benign arylating reagents. Here, we describe an alkylamine-mediated free radical intramolecular annulation to access PAHs under environmentally friendly conditions. On modulating substituents and their positions in the iodoniums, the free radical reaction controllably underwent three types of cyclization including ring contraction and ring switch to form tricyclic and tetracyclic frameworks of PAHs. Preliminary mechanistic studies implied that alkylamines initiated a radical pathway to complete the cyclization efficiently. Moreover, these acquired products were further converted into diverse complex graphene segments.

Direct thiocyanations of benzylic compounds have been implemented. Here, a new strategy, involving a free radical reaction pathway initiated by AIBN, was used to construct the benzylic sp3 C-SCN bond. In this way, the disadvantage of other strategies involving introducing leaving groups in advance to synthesize benzyl thiocyanate compounds was overcome. The currently developed protocol also involved the use of readily available raw materials and resulted in high product yields (up to 100%), both being great advantages for synthesizing benzyl thiocyanates.

A home-made vacuum ultraviolet (VUV) photoionization linear time-of-flight mass spectrometer (VUVPI-LTOFMS) was utilized to study atmospheric radical reactions. A commercial krypton discharge lamp with photon energy at 10.6 eV was installed as VUV light source and combined with a cage-shape photoionization source to efficiently extract and focus ions. A limit of detection (LOD) of 0.03 μg/L (S/N = 3) for benzene was achieved. A microwave discharge fast flow tube was employed as chemical reactor to produce free radicals and initiate their atmospheric reactions. The concentration of methyl radical was measured with its self-reaction kinetics and the available rate constant. As a representative example, the reaction of the methyl radical with nitric oxide was studied. Both the stable species and radicals involved in the reaction were probed, and the reaction rate constant at room temperature and pressure of 300 Pa was measured to be k(CH3 + NO) = 1.2 × 10−12 cm3/(molecule·s).

Photocatalytic degradation has been considered as an eco-friendly method for the removal of harmful antibiotics. Considering that the fundamental aspect of antibiotic photodegradation is a free radical reaction on the catalyst surface, boosting the generation of surface active free radicals is a direct and effective approach to promote the surface antibiotic oxidation reaction. However, rational regulation of the surface free radicals of photocatalysts is still a big challenge, and has also been rarely investigated. Herein, surface defect engineering was employed to introduce two different surface defect structures (i.e., two-coordinated nitrogen vacancies (N2C) on g-C3N4 and oxygen vacancies on TiO2) on the surface of a g-C3N4/TiO2 Z-scheme photocatalyst by one-step hydrogenation treatment, aiming to effectively modulate the surface active free radicals that directly dominate the surface redox reaction. The resulting defect-rich hydrogenated g-C3N4/TiO2 (H-CN/TiO2) Z-scheme heterojunction produced much more ˙OH and ˙O2− free radicals on the surfaces of TiO2 and g-C3N4, respectively, which would greatly facilitate the surface redox reactions in photocatalytic processes. As expected, the H-CN/TiO2 Z-scheme heterojunction exhibited obviously improved activity in photodegradation of tetracycline hydrochloride compared with those of defect-free photocatalysts. Meanwhile, the effect of defect structures on the surface free radicals of the H-CN/TiO2 photocatalyst was well explored and the photocatalytic mechanism was also discussed. This work paves the way for the regulation of free radical formation via surface defect engineering to further improve the photocatalytic activities of Z-scheme heterostructures.

Polyselenides were conveniently synthesized via the polymerization reaction of dihalohydrocarbons with NaHSe in just one step. The materials were highly active and could catalyze the oxidative cracking reaction of alkenes using O2 as a partial oxidant under mild conditions instead of the traditional energy consuming method. Parallel experimental results demonstrated that the substituents and chemical structures of the dihalohydrocarbon monomers prominently affected the catalytic activities of the as-prepared materials and 1,4-bis(chloromethyl)benzene was found to be the most preferable monomer. The polyselenide-catalyzed reactions proceeded via a unique free radical reaction mechanism due to the distinctive catalyst structures, in which the Se sites of the selenide moieties could not establish contact with the reaction substrate sufficiently enough to meet the requirements for an ionic reaction. These new features of the materials may draw widespread interest from chemists and broaden the horizon for the investigation of related green and energy-saving reactions.

Anthraquinones are recognized as high efficiency photocatalysts which can perform various redox reactions in aqueous or organic phases. We have experimentally proven that 2-BrAQ can undergo hydrogen transfer with an alpha-aromatic alcohol under light conditions, thereby efficiently oxidizing the aromatic alcohol to the corresponding product. The yield of 1-phenethanol to acetophenone can reach more than 96%. In subsequent catalyst screening experiments, it was found that the electronegativity of the substituent at the 2 position of the anthraquinone ring and the acidity of the solvent affect the photocatalytic activity of anthraquinones. After using various aromatic alcohol substrates, 2-BrAQ showed good conversion and selectivity for most aromatic alcohols, but showed C–C bond cleavage and low selectivity with non-α-position aromatic alcohols. In order to explore the mechanism of the redox reaction of 2-BrAQ in acetonitrile solution, the corresponding free radical reaction pathway was proposed and verified by density functional theory (DFT). Focusing on calculations for 2-BrAQ during the reaction and the first-step hydrogen transfer reaction between the 2-BrAQ triplet molecule and the 1-phenylethanol molecule, we recognized the changes that occurred during the reaction and thus have a deeper understanding of the redox reaction of anthraquinone compounds in organic systems.

A photolytically generated ruthenium hydride species catalyzing a free radical cyclization reaction was developed. As the new methodology ensures reproducibility of the free radical reaction of trialkyltin hydrides and a fast hydrogen transfer to the radical intermediates, the methodology provides fast quenching of radical intermediates and thus suppresses rearrangement of radical intermediates before the hydride quench. By offering new reactivity and selectivity to the trialkyltin hydride mediated free radical cyclization reactions, the methodology will find wide range of applications in organic synthesis.

A new type of metal-free catalyst was successfully prepared by doping boron (B) in the carbon nanotube. The catalyst had 99.4% removal of phenol in 60 min at pH 7 by activating peroxymonosulfate (PMS). In order to explore the origin of the high catalytic activity, the samples were characterized by Raman and electron paramagnetic resonance (EPR), and the reactive oxygen species (ROS) in the process of catalytic degradation were investigated. The Raman results showed that the defect sites increased after doping, which indicated that the B doping increases the active sites on the surface of the carbon nanotubes. Identification experiments of ROS found that not only hydroxyl radicals (·OH) and sulfate radical (SO4−∙), but also singlet oxygen (1O2) exist in the system. The presence of multiple free radicals indicated the existence of free radical reaction pathway, and the presence of 1O2 confirmed the existence of non-radical reaction pathway. These results indicated that there were dual reaction pathways for the activation of persulfate by B-doped carbon nanotubes, which was the intrinsic nature for the high catalytic activity of the system.

Newly developed sulfonyl chloride-based regioselective chlorothiolation of alkenes has been disclosed; the reaction is compatible with a variety of functional groups and can be scaled up to the gram scale with no loss in yield. The employment of readily available reactants, mild reaction conditions, and high regioselectivity makes this process very practical. Mechanistic studies revealed a possible free radical reaction pathway.

Although the pyrolysis of coal has been studied for centuries, only few methods, which can evaluate the amount of volatile matter in the case of a change in the reaction mechanism with pyrolysis time, have been developed. In this study, a method for accurately predicting the volatile amount of brown coal depending on temperature and time of pyrolysis has been studied in isothermal condition. This method is based on the kinetic parameters obtained from the pyrolysis process. The kinetic parameters were determined using the first-order series reaction model, which consists of two steps: the first step is rapid weight loss with free radical reaction, and the second step consists of slow weight loss with condensation reaction (char formation). Both steps follow a first-order reaction with different reaction rate constants, which are obtained from the graph of ln(1 – XA) versus the pyrolysis time at each given pyrolysis temperature. The validity of this new method for estimation of the final amount of volatile...

Endohedral metallofullerenes (EMFs) are fullerene cages enclosing various metallic species. The functionalization of EMFs has remarkably blossomed in recent years, in contrast to early efforts that were mainly devoted to their geometric and electronic structures as well as optical and magnetic properties. This review presents an exhaustive survey of the important functionalization approaches of EMFs, mainly focusing on the progress since 2014. The involved reactions include silylation and germylation, Diels–Alder reaction, Bingel–Hirsch reaction, 1,3-dipolar cycloaddition, carbene addition, benzyne addition, free radical reaction, hydroxylation, dimerization, coordination reaction, noncovalent complexation, as well as numerous miscellaneous reactions. We summarize the main factors that affect the reactivity and regioselectivity, focusing particularly on the intriguing interplay between the exohedral groups and internal species. This work highlights the established role of current theoretical studies in further understanding the reactivity and regioselectivity of functionalization reactions. Finally, we discuss potential applications of exohedrally modified EMFs.

To elucidate the mechanism of brominated natural rubber (BNR), eight BNR samples with different bromine content were prepared from latex in different bromination time, and the microstructures were characterized by Fourier transform infrared spectroscopy (FTIR) and 1H-NMR spectroscopy, respectively. The hardness of BNR increased and its nature transformed from elastomer to resin with the increase of bromine content. Unlike chlorinated natural rubber (CNR), FTIR showed that there were no carbonyl groups on the molecular chains of BNR. 1H-NMR spectroscopy revealed that the reaction activity of bromine and the secondary hydrogen atom of BNR were much higher than those of the primary one. The brominated substitution took place in the hydrogen atom of CH3 and CH2 groups firstly, then in the late period of bromination the bond of C=C was transferred to the saturated bond of C-C due to the Markovnikov addition of hydrogen bromide. Based on these findings, the mechanism of BNR from latex could be deduced as a free radical reaction and the detailed bromination process was presented.

This work presents a cost-effective abundant kaolin-based cracking catalyst that has high deoxygenation, mild cracking, and low dehydrogenation performances for waste cooking oil (WCO) upgraded into organic liquid products (OLPs). Acid treated kaolin (ATK) exhibited high yield of 74.4% and high quality liquid products with high oxygen removal of 93.8% and low aromatic contents of 22.5%. The reference catalyst, a commercial petroleum catalyst (CC) could eliminate the most of oxygen (90.8%) but produced too many unexpected aromatics (55.8%). The density of weak Lewis acids was related to the deoxygenation capability. The density of Bronsted acids contributed to hydrogen transfer reactions. The total amount of Bronsted acids was correlated to cracking capability. The cracking by CC primarily followed carbonium ion reaction mechanism, whereas those by the kaolin-based catalysts complied more with free radical reaction mechanism. The deoxygenation active sites were characterized by CH3COOH-TPD for the first time.

This study analyzed the impact of adhesive primer and light-curing on the polymerization kinetics of urethane dimethacrylate-based self-adhesive resin cement combined with free radical reaction. Specimens were prepared by mixing the cement paste with or without adhesive primer. Subsequently, specimens were light-cured or set without light-curing. The degree of conversion (DC), Vickers hardness (Hv), and free radical concentrations were repeatedly measured up to 168 h after the curing initiation. Irrespective of the curing procedures, DC, Hv, and free radical concentration rapidly increased during the initial 30 min of curing. The specimens cured with adhesive primer and/or light-curing generally showed higher values of DC, Hv, and radical concentration than those set by chemical curing alone, especially during the initial polymerization phase. Kinetic analysis using a linear mixed model revealed that the adhesive primer had a higher coefficient estimate than light-curing, indicating that the former had a higher impact on the polymerization. Additionally, the adhesive primer alleviated the Hv reduction caused by water and air during the initial polymerization phase, although light-curing hardly prevented the polymerization inhibition. Therefore, we suggest that application of adhesive primer is beneficial to achieve higher degree of conversion and better mechanical properties of self-adhesive resin cements by enhancing free radical reactions.

A density functional theory-assisted synthesis of self-curing epoxy–acrylic resin (EMPA) is described. The calculated quantum chemistry reaction index of the reacting monomer in the basic state, i.e., the radical reaction index (Fk0), is used as a guide to optimize the synthesis conditions. The reliability of the Fk0-assisted synthesis method is confirmed after evaluating the physical appearance, mechanical properties after curing, and thermal stability of the obtained EMPA. The special functional groups of the resin are characterized by Fourier transform infrared spectroscopy to prove the rationality of the reaction mechanism. The cross-sectional morphology characteristics of the cured resin are observed by field-emission scanning electron microscopy. The results show that the closer the molar ratio of monomers in the reaction to the ratio of Fk0 of the reacting monomers, the better the polymerization performance.

In a water ozonation process, dissolved organics undergo two reactions at least: direct ozone attack and oxidation with hydroxyl radicals generated from the ozone decomposition. In the particular case of urban wastewater contaminated with pharmaceuticals, competition between these two reactions can be studied through application of gas&ndash, liquid reaction kinetics. However, there is a lack in literature about kinetic modeling of ozone processes in water specially in photocatalytic ozonation. In this work, lumped reactions of ozone and hydroxyl radicals with total organic carbon have been proposed. Urban wastewater containing a mixture of eight pharmaceutical compounds has been used to establish the kinetic model that simulates the mineralization process. The kinetic model is based on a mechanism of free radical and molecular reactions and the knowledge of mass transfer, chemical reaction rate constants, and radiation transfer data. According to the model, both single ozonation and photocatalytic ozonation present two distinct reaction periods characterized by the absence and presence of dissolved ozone. In the first period (less than 10 min), pharmaceuticals mainly disappear by direct ozone reactions and TOC variation due to these compounds has been modeled according to gas&ndash, liquid reaction kinetics through a lumped ozone-pharmaceutical TOC fast second order reaction. The corresponding rate constant of this reaction was found to change with time from 3 &times, 105 to 200 M&minus, 1 s&minus, 1 with Hatta values higher than 0.3. In the second period (nearly 5 h), competition between direct and hydroxyl radical reactions takes place and a kinetic model based on a direct and free radical reaction mechanism is proposed. Main influencing parameters to be known were: Direct ozone reaction rate constant, catalyst quantum yield, and hydroxyl radical scavengers. The first two take values of 0.5 M&minus, 1 and 5 &times, 10&minus, 4 mol&middot, photon&minus, 1, respectively, while a fraction of TOC between 10% and 90% that changes with time was found to possess hydroxyl radical scavenger nature.

This study aimed to use a persulfate together with transition metal ions as the reagent to effectively depolymerize lignin into monophenolic compounds under mild conditions (ambient pressure, temperature

In order to understand the reaction mechanism of lignin pyrolysis, the pyrolysis process of guaiacol (o-methoxyphenol) as a lignin model compound was studied by free radical detection technology (electron paramagnetic resonance, EPR) in this paper. It was proven that the pyrolysis reaction of guaiacol is a free radical reaction, and the free radicals which can be detected mainly by EPR are methyl radicals. This paper proposes a process in which four free radicals (radicals 1- C6H4(OH)O*, radicals 5- C6H4(OCH3)O*, methyl radicals, and hydrogen radicals) are continuously rearranged during the pyrolysis of guaiacol.

The mechanism of [2 + 2 + 1] cyclization reactions to access polycyclic sulfonyl indolines via Fe(II)-catalyzed or UV-driven has been investigated by density functional theory (DFT) methods. Mechanistic studies aided by the DFT calculations suggest that the reaction might proceed via a free radical pathway with HSO3· serving as the initiator and terminator of the free radical reaction, which has never been reported to our knowledge. The reactions involve the formation of two five-membered rings. The calculated results show that the first five-membered ring formation is the rate-determining step, with an energy barrier of 3.2 kcal/mol. And the second five-membered ring formation is an exergonic process. It is worth noting that HSO3· radicals are involved in the reaction preceding the formation of the second ring, and they facilitate formation of the second ring. Meanwhile, the most active site was predicted by the condensed Fukui function (CFF) and verified by DFT calculations.

Oxidation-responsive emulsions were obtained by stabilizing mineral oil droplets using amphiphilic poly(vinyl pyrrolidone-co-allyl phenyl sulfide) (P(VP-APS)). 1H nuclear magnetic resonance (NMR) spectroscopy revealed that P(VP-APS) whose APS content was 0%, 3.28%, 3.43% and 4.58% were successfully prepared by free radical reaction and the sulfide of APS was oxidized by H2O2 treatment. X-ray Photoelectron Spectroscopy (XPS) also disclosed that the sulfide of APS was oxidized to sulfone by the oxidizing agent. The optical density of copolymer solutions and the interfacial activity of the copolymers markedly decreased by H2O2 treatment possibly because the sulfide of APS was oxidized and the amphiphilicity of the copolymers were weakened. The increase rate of the oil droplet diameter of the emulsions was outstandingly promoted when H2O2 solution (10%, v/v) was used as an aqueous phase. The phase separation of the emulsions was also expedited by the oxidizing agent. The oxidation of APS and the weakened interfacial activity were thought to be a main reason for the demulsification of P(VP-APS)-stabilized emulsions.

Nowadays, many pre-treatment strategies including pre-chlorination as well as pre-addition of powdered activated carbon (PAC) have been attempted to enhance the removal of algae cells as well as algae by-products by traditional coagulation. This study investigated the effects of these two agents (PAC + Cl) as pre-treatment on the coagulation of two common cyanobacteria (M. aeruginosa (MA) and Pseudoanabaena sp. (PI)) laden water. The results indicated that when PAC and chlorine were combined, the PAC could effectively catalyze chlorine to generate Cl and HO2 /O2 − and thus significantly enhance the organic matter removal in both MA and PI water treatment. Furthermore, the effluent organics of MA water by PAC + Cl contained less tryptophan-like proteins with aromatic structure and more tyrosine-like proteins with chain structure than those by chlorine alone, which might be due to the free radical reaction catalyzed by PAC. However, though the PAC could catalyze chlorine, the algae cells attached to or embedded in PAC particles demonstrated to be more resistant to inactivation by chlorine than non-attached free algae cells. Moreover, when treating algae released micropollutants such as 2-methylisocentaitol (2-MIB), its removal efficiency was more relied on the chlorine dosage. When chlorine dosage was too low, the generated free radical preferred to reacted with background organics rather than 2-MIB, resulting a reduction in 2-MIB removal. This study could provide guidance in proper pre-treatment strategies selection and combination for algae-bloom water treatment.

Pyrolysis of waste tire is attracting widespread interest recently because of the great potential in waste valorization treatment. In this study, the thermal decomposition behavior, pyrolysis mechanism and products distribution of waste bicycle tire were investigated by means of TG-FTIR and Py-GC/MS. According to the TG results, two main pyrolysis stages of waste bicycle tire were observed, which were considered as the decomposition of rubber (285–531 °C) and further pyrolysis of pyrolytic products (663–847 °C), respectively. The volatiles release characteristics and FTIR spectrum at different temperatures exhibited good consistency with pyrolysis behavior. A detail information of pyrolysis products was analyzed by Py-GC/MS, which mainly include gaseous, alkenes and aromatics. The pyrolysis mechanism of waste bicycle tire was belong to free radical reaction, and the possible further pyrolysis pathway of D-limonene and styrene was also presented. Moreover, the products distribution under different pyrolysis final temperatures and heating rates conditions were summarized. Thus, this study could enhance our understanding on more specific details for the pyrolysis process of waste tire to some extent.

A strategy of enhancing the reactivity of lignin molecule towards thermally initiated free radical polymerization was examined. Technical lignin samples were reacted with selected esterification agents (butyric and crotonic anhydrides) leading to extensive conversion of the available hydroxyl groups. The esterified lignins were then subjected to thermal processing in the presence or absence of dicumyl peroxide (DCP). The rheological and viscoelasticity behavior during this process were examined by in-situ rheology and dynamic mechanical analysis (DMA). The functionality and glass transition temperature (Tg) of samples before and after modification were assessed for evaluating the validity of modification. After crotonylation, the lignin derivatives were susceptible to thermally initiated free radical polymerization, especially in the presence of DCP. Upon heating, the lignin crotonate showed a significant increase in storage modulus (E′) from around 200 °C to 260 °C. The Tg of lignin crotonate increased by about 20 °C after thermal treatment in the presence of DCP. Fourier transform infrared spectroscopy (FTIR) analysis of samples that were collected from rheological test confirmed the reaction of C C took place. Vanillyl alcohol as a lignin model compound was subjected to the same modification procedure with lignin to uncover the mechanism by FTIR and nuclear magnetic resonance (NMR) analysis, indicating there are three potential reaction sites: C C, C O and CH2-, among which C C is likely to form a cross-linked network. The conclusions from this study may provide the foundations for a rational design of technical lignin-based polymeric materials, by providing the double bonds to anchor the lignin molecules in the resin or copolymers.

Photostability of all-trans retinyl palmitate (RP) (100% bioactivity) was studied in policosanol oleogels (PCOs) (7–12% w/w policosanol in soybean oil) after UVA irradiation. RP was incorporated into PCOs at levels of 0.04%, 0.1% and 1% (w/w). PCOs efficiently protected RP from UVA-mediated degradation. Over 75% RP-activity remained in PCOs after 4 days of UVA irradiation, while 12% RP-activity remained in soybean oil. HPLC analysis showed that cis-RP was formed in liquid soybean oil after 2 days of UVA irradiation while it was absent in PCOs matrices. PCOs blocked the energy absorption from UVA and further dampened the UVA-mediated ionic photodissociation and free radical reaction due to matrix immobilization. For all samples, RP photodegradation followed a 2nd order reaction. From the reaction kinetics, it would be possible to predict the RP photodegradation rate in PCO matrices. PCOs were shown to be a promising matrix to protect RP from photodegradation.

Mechanochemical degradation (MCD) is a promising eco-friendly method to dispose persistent organic pollutants (POPs). Mechanically induced free-radical attack was thought to be one of the key elements in initiating and accelerating the dechlorination and degradation of POPs. In this study, mechanochemical formation of free-radicals and their roles in the remediation of hexachlorobenzene (HCB) contaminated soil were explored using both of experimental analysis and quantum chemical calculations. It was found that chlorinated phenoxy radicals(CB-O ) can be produced in the milling process and they played a vital role in the dechlorination of HCB, based on the results of electron spin-resonance (ESR) and X-ray photoelectron spectra (XPS). Two transition states of mechanochemical reaction along the formation of pentachlorinated phenoxy radical (PeCB-O ) were located, with the energy barriers of 39.4 and 3.4 kJ/mol. The localized orbital locator (LOL), Mayer bond order and topological analysis were also implemented to depict the process in detail. Free-radical attack dominated dechlorination pathway of HCB in the MCD process was also verified by the Fukui function analysis. The study on the mechanically-induced generation of free-radicals and their associated modes of action on the degradation of HCB will provide a deep insight into mechanochemical remediation mechanism of POPs contaminated soil.

An efficient and practical synthesis of benzothiazine by visible-light-mediated free radical reaction has been developed. This protocol provides a new, facile, eco-friendly strategy to construct benzothiazine and quinoxaline derivatives via formation of C–S and C–N bonds under metal-free condition. This synthesis has been performed under visible light illumination in aqueous ethanol at room temperature using aromatic aldehyde, o-aminothiophenol and isocyanide as reactants.

The atomistic mechanism of nickel (Ni) oxidation in supercritical water (SCW) is investigated using molecular dynamics simulations with a reactive force field. The oxidation kinetics of Ni surfaces in SCW at 300−800 °C and 26−164 kg/m3 are simulated. The adsorption, dissociation, and deprotonation processes of water, and the hydroxylation and oxidation processes of Ni are tracked. The oxidation potential of SCW is found to be higher than that of water at normal state. Charge analysis of deprotonation reveals that the dissociation of water is more likely to be a homolytic reaction instead of a heterolitic one under the supercritical state of relatively high temperatures and low densities. Oxidation in SCW prefers the free radical reaction pathway to the ionic pathway, which appears a gas/steam oxidation scope instead of aqueous oxidation. Reaction rate increases with increased temperature and density of SCW.

In this paper, the inhibition of free radical reaction in the coal oxidation process was taken as the starting point, and free radical scavenger 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) which combines with free radicals very easily to generate inactive substances was regarded as the inhibitor. The occurrence of coal spontaneous combustion was suppressed by inhibiting the chain reaction of free radicals. TEMPO was compared with common halide salt inhibitors through thermogravimetry and differential scanning calorimeter (TG-DSC) thermal analysis, crossing point temperature (CPT), CO production and other data obtained from experiments. The results show that the inhibitory effect of TEMPO is stronger than that of common halide salt inhibitors and the inhibitory effect increases with the rise of TEMPO concentration. The influence of TEMPO on active functional groups in coal at different temperatures was obtained through Fourier transform infrared spectroscopy (FTIR) analysis, suggesting that the inhibitory effect of TEMPO on active functional groups (C O, C H, C O and O H) in coal gets more significant with the rise of temperature and the increase of active free radicals in coal. On this basis, five common active free radical models were constructed, and their active sites and thermodynamic parameters were calculated according to density functional theory (DFT). The calculation reveals that compared with oxygen-containing free radicals, alkyl free radicals are more active in the thermodynamic reactivity with TEMPO. The experiments prove that TEMPO has a very strong inhibitory effect on coal spontaneous combustion, because the combination between TEMPO and alkyl free radicals during coal spontaneous combustion decreases the activity of free radicals and reduces the concentration of active free radicals, thus inhibiting the chain reaction of free radicals.

A mathematical mechanism of the n -pentane pyrolysis process based on free radical reaction model was presented. The kinetic parameters of n -pentane pyrolysis are obtained by quantum chemistry and the reaction network is established. The solution of the stiff ordinary differential equations in the n -pentane pyrolysis model is completed by semi implicit Eular algorithm. Then the pyrolysis mechanism based on free radical reaction model is built, and the computational efficiency increases 10 times by algorithm optimization. The validity of this model and its solution method is confirmed by the experimental results of n -pentane pyrolysis.

A modification method that combines thermal and oxidation treatments was used to improve catalytic activity of activated carbon (AC) which catalyzed ozonation of the aquatic contaminant humic acid (HA). As a consequence of modifying virgin AC, modified AC (ACN2O2N2) had good catalytic performance for ozonation of HA. Apparent first-order rate constants (kapp) were ACN2O2N2 (7.88 × 10−3 s−1) > virgin AC (3.28 × 10−3 s−1). This change was discussed in terms of three factors: textural property, graphitization degree, and surface chemical property. From analysis results, it was deduced that the surface chemical property (the concentration of surface groups) was the main factor that influenced catalytic activity. An increase in the concentration of hydroxyl groups on AC enhanced catalytic activity of AC in ozonation of HA. Effects of phosphate (both a ligand and a strong Lewis base) further confirmed that Lewis acid sites (hydroxyl groups) were the active centers for free radical reaction in catalytic ozonation of AC.

Free radicals play an important role in the oxidizing power of polluted air, the development of aging-related diseases, the formation of ozone, and the production of secondary particulate matter. The high variability of peroxyl radical concentration has prevented the detection of possible trends or distributions in the concentration of free radicals. We present a new method, free radical reaction combined with liquid chromatography photodiode array detection, for identifying and quantifying peroxyl radicals in polluted air. Functionalized graphene was used for loading peroxyl radicals and reactive molecules in air sampling system, which can facilitate reaction kinetics (charge transfers) between peroxyl radicals and reaction molecules. Separation was performed with and without a preliminary exposure of the polluted air sample to reactive molecule(s) system. The integral chromatographic peak areas before and after air sampling are used to quantify the atmospheric peroxyl radicals in polluted air. The utility of the new technique was tested with measurements carried out in the field.

Murrayaquinones A-D is a group of four bioactive carbazole-1,4-dione natural products isolated from the root bark of the plant Murraya eucrestifolia hayata. Murrayaquinone is synthesized in five steps starting from the commercially available 2,4,5-trimethoxybenzaldehyde with an overall yield of 45%. The novelty of this murrayaquinone synthesis is in the use of a Mn(OAc)3 mediated oxidative radical reaction of a N-benzylaminoquinone derivative with 2-cyclohexen-1-one for the late-stage indole ring construction.

Carbonaceous materials are widely used materials in energy storage, biomedicine and electronics. Although many improvements had been achieved, the synthesis of carbon without using any metal catalyst or reducing agent is still a challenge, especially under low temperature conditions. In this paper, we illuminate a free radical mechanism for the synthesis of amorphous carbon hollow spheres in a large scale through the reaction between CCl4 and N,N-dimethylformamide (DMF) at 200 °C. The investigation of the reaction mechanism reveals the reaction possibility of CCl4 with other nitrogenous organic molecules, including dimethylacetamide (DMAC), hexamethylenetetramine (HMTA), diethylenetriamine (DETA), diethylamine (DEA), ethylenediamine (EN), and 1-methyl-2-pyrrolidinone (NMP). The present synthetic methodology provides a non-metal ion participating route to synthesize carbonaceous materials with organic molecules at low temperature.