Free Radical Addition Reactions Research Articles

Ameliorated DC Insulation Performance of EPDM through Chemical Grafting with a Voltage Stabilizer

Ethylene-Propylene-Diene Rubber (EPDM) is widely utilized as a high-performance insulation material in high-voltage direct current (HVDC) cable accessories, owing to its exceptional electrical and thermal properties. In this study, we have successfully synthesized and employed 4-vinyl oxyacetophenone (VPE) as a modification agent to develop the chemically grafted EPDM materials (EPDM-g-VPE) just through thermal crosslinking reaction and melt blending approach. Infrared spectroscopy results reveal that during thermal cross-linking process, VPE efficiently grafted onto EPDM molecular-chains through free radical addition reaction. Following VPE grafting, the DC dielectric breakdown strength and electrical conductivity of EPDM are significantly increased and noticeably decreased respectively. Theoretical electronic structure calculations corroborate that VPE’s electron-affinity and energy-gap enable it to efficiently absorb thermal electron energy without undergoing collision ionization, thereby enhancing EPDM’s breakdown resistance. Simultaneously, VPE molecules exhibit a high affinity for capturing electron charge carriers within EPDM polymer-molecules. Space charge and thermally stimulated current tests demonstrate that the stable and uniformly distributed charge traps can be effectively introduced into EPDM matrix by grafting VPE modification, thereby suppressing transport and injection of charge carriers. Consequently, this approach substantially improves DC electrical insulation performance of EPDM. This research not only successfully enhances the electrical insulation performance of EPDM but also showcases the wide-ranging potential of chemical modification technology in cable accessory materials.

Cocamidopropyl betaine - a potential source of nitrogen-containing disinfection by-products in pool water.

Water treatment for most public pools involves disinfection with active chlorine leading to the formation of disinfection by-products (DBPs). Among them, nitrogen-containing compounds (N-DBPs) having increased toxicity and adverse effects on human health are of the greatest concern. Being the major component of various body washers for swimmers, cocamidopropyl betaine (CAPB) represents a potential and still underestimated anthropogenic precursor of N-DBPs in pool water. The purpose of this study was to investigate CAPB transformation pathways and mechanisms under the aqueous chlorination conditions. High-performance liquid and two-dimensional gas chromatography hyphenated with high-resolution mass spectrometry were used for the search and tentative identification of the primary and final CAPB transformation products. A wide range of DBPs containing up to five chlorine atoms including these in combination with hydroxyl and additional carbonyl groups has been revealed in model chlorination experiments for the first time. The proposed mechanism of their formation involves nucleophilic substitution of the secondary amide hydrogen atom at the first stage with subsequent free radical and electrophilic addition reactions resulting in non-selective introduction of halogen atoms and hydroxyl groups in the alkyl chain. The deep transformation products include short-chain chlorinated hydrocarbons and their oxidation products as well as dimethylcarbamoyl chloride possessing high toxicity and carcinogenic properties. Targeted analysis of real swimming pool water samples confirmed the results of model experiments enabling semi-quantitative determination of CAPB (0.8µg L-1) and 18 primary DBPs, including 10 chlorine-containing compounds with the total concentration of 0.1µg L-1. Among them, monochloro (50%) and hydroxydichloro (25%) derivatives predominate. The toxicity and health of the main DBPs has been estimated using QSAR/QSTR approach. Thus, the possibility of formation of new classes of potentially toxic chlorine-containing DBPs associated with the widespread use of detergents and cosmetics was shown.

Copper-Catalyzed Radical Addition of Alkynols to Synthesize Difluoroheterocyclic Compounds

A convenient method for the synthesis of fluorine-containing heterocyclic compounds was developed by a copper-catalyzed free radical addition reaction of alkynol and ethyl bromodifluoroacetate. This strategy involves copper-catalyzed free radical addition and molecular lactone exchange of ethynyl alcohol and ethyl bromodifluoroacetate. The method is characterized by easy availability of raw materials, good stereochemical selectivity, and simple operation. More importantly, valuable tetrasubstituted E-configurated alkenes and various vinyl C-Br bonds and difluoromethylene-containing functionalized heterocycles can be obtained by this method.

Dielectric Characteristics of Crosslinked Polyethylene Modified by Grafting Polar-Group Molecules.

Polar group-modified crosslinked polyethylene (XLPE) materials are developed with a peroxide thermochemical method of individually grafting chloroacetic acid allyl ester (CAAE) and maleic anhydride (MAH) to polyethylene molecular-chains, which are dedicated to ameliorating dielectric characteristics through charge-trapping mechanism. By free radical addition reactions, the CAAE and MAH molecules are successfully grafted to polyethylene molecular chains of XLPE in crosslinking process, as verified by infrared spectroscopy molecular characterizations. Dielectric spectra, electric conductance, and dielectric breakdown strength are tested to evaluate the improved dielectric performances. Charge trap characteristics are investigated by analyzing thermal stimulation depolarization currents in combination with first-principles electronic-structure calculations to reveal the polar-group introduced mechanisms of contributing dipole dielectric polarization, impeding electric conduction, and promoting electrical breakdown field. The grafted polar-group molecules, especially for MAH, can introduce deep-level charge traps in XLPE materials to effectively restrict charge injections and hinder charge carrier transports, which accounts for the significant improvements in electric resistance and dielectric breakdown strength.

Coke formation of heavy oil during thermal cracking: New insights into the effect of olefinic-bond-containing aromatics

The distributions of olefinic-bond-containing aromatic hydrocarbon (OAH) and the effect of OAH on coke formation during heavy oil thermal cracking have been rarely studied in the past. Here, the information of olefins in thermally cracked products derived from vacuum residue (VR) was investigated first, and then the effect of OAH on coke formation was elaborated by revealing the evolution characteristics of self/co-addition systems participated by representative OAH model compounds. The results found that OAHs were generated during VR thermal cracking, and they could participate in further reactions to promote coke formation. During thermal reaction, OAHs were more reactive for addition reactions than alkenes, and the reactivity of OAH increased roughly with the number of aromatic rings. Meanwhile, the higher concentration of OAH or the longer thermal reaction time or the higher thermal reaction temperature, the higher conversion of addition products, and the greater condensation degree of reaction products. OAHs participating in the larger structure molecule formation involves free radical addition reactions, which could occur between different OAHs as well as between OAHs and conventional aromatic molecules. More importantly, OAHs could form larger structure molecules by direct addition reaction of unsaturated double bond via non-free radical addition reaction, thus promoting fast coke formation.

Investigating the reaction mechanism of light tar for Shenfu bituminous coal pyrolysis

The generation mechanism of light tar during Shenfu bituminous coal pyrolysis was investigated in this work. TGA, Py-GC/MS, TGA-FTIR and reactive force field simulations (ReaxFF) were implemented to reveal the light tar reaction mechanism. The proposed coal structure model was C3198H3261N51O513S33, whose pyrolysis was simulated using the ReaxFF method. Simulation results showed that the pyrolysis process was divided into activation, pyrolysis, and condensation, which agreed well with TGA results. Based on evolutions of gases in the activation stage, it was discovered that coal pyrolysis was initiated by the cleavage of oxygen-containing groups. Simulated results with the coal unimolecular structure showed that the reaction mechanism of light tar was free radical addition reaction, where free radicals were mainly obtained from the cleavage of C–O chemical bond. Also, it was found that the temperature of 2400 K was the transition point, indicating the transition of dominating bond cleavage from C–O bond to C–C bond. The variation of chemical bond agreed well with TGA-FTIR and Py-GC/MS results, indicating that the simulated results are valid and convincing. Therefore, it was concluded that the free radical addition reaction that was mainly controlled by the rupture of C–O bond was the reaction mechanism of light tar.

Cyclotriphophazene-Centered Six-Arm Eugenol-Linked Low-Dielectric Materials with High Thermostability and Transparency

Two silicon-containing eugenol-based benzocyclobutene monomers were prepared by a simple solvent-free hydrosilylation reaction. After heat treatment, a series of materials were obtained by a free radical addition reaction, [4 + 4] cycloaddition, or [4 + 2] Diels–Alder cycloaddition. All polymers displayed high thermostability with a 5% weight loss temperature (T5d) of over 410 °C and a glass transition temperature (Tg) of up to 216 °C as well as a good transmittance of 90% varying from 500 to 800 nm. In particular, all polymers also exhibited good hydrophobicity with contact angles exceeding 100° and water absorption as low as 8‰ after immersing in boiling water for 72 h. It should be noted that P3 showed excellent dielectric properties with a dielectric constant (Dk) of 2.48 and a dielectric loss (Df) of 6.38 × 10–3 at a high frequency of 2 GHz as well as good flame retardancy due to the high content of cyclotriphophazene compared with those of P1, P2, and previously reported biobased materials. The above advantages indicate that eugenol-based low-dielectric materials have great potential for application in encapsulation resins in the field of microelectronics.

Study on the photopolymerization mechanism of allyl monomers: A photo-driven radical-mediated [3+2] cyclopolymerization mechanism to reduce degradation chain transfer

A novel mechanism for the photopolymerization of multi-functional allyl monomers, namely, photodriven radical-mediated [3 + 2] cyclopolymerization (PRMC), was proposed based on the results of theoretical calculations and experimental measurements. The Ea of the transition state (TS) is calculated using density functional theory to be under 25 kcal/mol. The driving forces of the product are close to −6 kcal/mol, indicating that PRMC can proceed spontaneously. NMR chemical shifts indicate that the cyclization reaction and traditional free radical addition reaction occur at the same time. The photopolymerization kinetics of allyl monomers and the initial radical structure of PRMC were obtained using real-time infrared spectroscopy and electron spin resonance spectroscopy respectively. The results of thermogravimetry and gel permeation chromatography show that high molecular weight polymers are obtained by photopolymerization, in contrast to the miniscule yield obtained by thermal polymerization. These observations show that PRMC can activate the polymerization of inert monomers and reduce the hindrance from degradation chain transfer at a low temperature.

Nonlinear optical modification of single-walled carbon nanotube by decorating with metal and metal-free porphyrins

Two porphyrins functionalized single-walled carbon nanotube nanohybrids (SWCNT-TPP and SWCNT-TPPZn) have been prepared following the free radical addition reaction and subsequent nucleophilic substitution. The results of microscopic structure and morphology analysis, including Fourier transform infrared spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis, confirmed the successful fabrication of SWCNT-TPP and SWCNT-TPPZn nanohybrids. UV–vis absorption, Raman and fluorescence emission studies indicate considerable π-π interactions and effective charge transfer from the porphyrin moieties to the SWCNT. Z-scan investigations show that both nanohybrids exhibit improved nonlinear optical performances in the ns and fs regimes compared to those of individual SWCNT and porphyrins; this is proposed to result from a positive synergistic effect between SWCNT and porphyrins. Due to more effective charge transfer effect, SWCNT-TPP nanohybrid exhibit the best NLO performance at 532 and 800 nm.

How does a weak interaction change from a reactive complex to a saddle point in a reaction?

An activation strain model was used to reveal the behavior of interaction, which was divided into four types as it proceeded from the reaction complex to the saddle point. For the 1,3-dipolar cycloaddition reaction, the interaction remained nearly zero at the first stage, but then decreased dramatically to become negative in the final stage. For the hydrogen atom transfer reaction, it started with a large positive value, which then fell to zero in the end. For Sn2 reaction, it decreased asymptotically from the beginning to the end. For the free radical addition reaction, meanwhile, it began on a zero point and climbed steadily up to a high positive value, but then decreased slightly at the saddle point. The use of an independent gradient model reveals a weak interaction containing both attractive and repulsive forces. These four types of behavior are the result of a compromise/balance between attraction and repulsion forces.

Asphaltenes formation during thermal conversion of deasphalted oil

New asphaltenes are formed during the thermal conversion of heavy oil. When new asphaltenes are formed from deasphalted oil, it erodes the conversion advantage provided by solvent deasphalting prior to visbreaking. The postulate that asphaltenes formation is caused by free radical addition reactions was evaluated. Indene was employed to exacerbate asphaltenes formation during thermal conversion of deasphalted oil at 400 °C. Evidence was provided that indene was involved in addition reactions with itself and with deasphalted oil to produce new n-pentane insoluble material. Whether indene induced increase asphaltenes formation, or whether it formed addition products with the deasphalted oil was not resolved. Self-reaction of indene at 400 °C resulted in extensive formation of n-pentane insoluble material. Formation of n-pentane insoluble material was reduced in mixtures with indane and naphthalene. Using these model systems the presence and nature of addition products was determined. The reported thermal conversion of indene was consistent with reaction chemistry based on molecule-induced homolysis, free radical addition, and propagation / termination by hydrogen transfer. The prevalence of addition reactions and the importance of hydrogen transfer reactions were highlighted, which have implications for modelling reaction chemistry describing thermal conversion of heavy oil.

Photocatalytic and photo-fenton activity of iron oxide-doped carbon nitride in 3D printed and LED driven photon concentrator.

We have synthesized iron oxide doped carbon nitride with 0.5 to 2 wt.% iron oxide and characterized by XPS, TGA, FTIR, SEM, photoluminescence spectroscopy and photoelectrochemical measurements. A herbicide, dicamba was employed as model organic pollutant for degradation in presence with the catalyst and hydrogen peroxide. A 3D printed photon concentrator with two chips on board (COB) LEDs with visible light spectra and two complex parabolic mirror surfaces was used as photo-reactor. The findings revealed that both photocurrent and degradation of dicamba were functions of light intensity and concentrator geometry. The rapid degradation of dicamba can be attributed to the holistic and individual actions of structural components of the photocatalyst. Four distinct phenomena, including photocatalytic activity of carbon nitride, quenching of electron/hole pairs and generation of additional reactive hydroxyl radicals by hydrogen peroxide, Fenton and photo-Fenton activity of iron oxide component of carbon nitride in presence of hydrogen peroxide and photocatalytic activity of iron oxide alone in conjuncture with carbon nitride can contribute to the overall photocatalytic activity of the system. Liquid Chromatography-Mass spectrometry (LCMS) analysis of the degradation products showed loss of chlorine from the aromatic ring and evidence of free radical addition reactions in the course of photocatalysis.

Editorial

Editorial

Robert Neville Haszeldine. 3 May 1925—13 October 2016

Robert Neville Haszeldine was particularly associated with fluorine chemistry. He did outstanding synthetic work on inorganic and organic fluorocarbon derivatives, including fluoroalkyl Grignard and lithium reagents; fluoroalkyl derivatives of mercury, phosphorus, nitrogen and sulphur; fluoroalkyl silicones; fluoro-olefins; and hexafluorobenzene, pentafluoropyridine and their derivatives. He also made major contributions to the study of free-radical addition reactions and developed new routes to carbenes. He discovered a new class of polymers by copolymerizing a nitroso-compound with an olefin or fluoro-olefin to give the –N–O–C–C– repeating unit. His research revealed a mastery of modern ideas on the mechanism of organic and inorganic reactions coupled with outstanding experimental skill and originality. His work yielded over 500 publications, plus more than 150 patents concerning industrial applications of fluorocarbons, and he was awarded several medals. As head of chemistry at the University of Manchester Institute of Science and Technology (UMIST) he developed a world-class fluorine research group and oversaw a new building for the department, which became one of the largest in the UK. Later, as principal of UMIST, he instigated academic developments just before the government severely cut university funding and imposed full-cost fees for overseas students, drastically reducing UMIST's income. His crisis plan for budget cuts proved divisive, and he took early retirement, citing intolerable financial pressures on UMIST. Initially, he continued with consultancy; later, he became deeply involved with his local community, and created a garden that received local and national recognition, including a plant variety named after him.

Additive-free photosynthesis of acrylamide hydrogels initiated with CdS and TiO2 as light visible nano-photocatalysts

Hydrogels are three-dimensional polymer networks which can be synthesized by different techniques, such as free-radical addition reaction which is the most well-known technique in functional vinyl monomer polymerization. Photopolymerization, as an attractive technique, has been used in radical polymerization of monomers and has revitalized interest in the idea that it congregates a wide range of economic and ecological expectations. Due to the spatial–temporal control and a mild curing process of polymerization, photoinitiator semiconductor nano-particles offer great advantages, such as effective and quantitative reaction. Cadmium sulfide nanowire, titanium dioxide (TiO2) nanotube, and TiO2 nanowire were used as visible photocatalysts for photopolymerization of acrylamide hydrogel without using any additive under the sunlight and purple LED irradiations. The effects of different synthetic parameters, including initiator type and concentration and type of light sources, were investigated to achieve hydrogels with maximum swelling capacity. The results showed that the swelling of hydrogel reached 80 g water/g hydrogel when the TiO2 nanowire was used as the photoinitiator. The synthesized semiconductors and hydrogels were characterized by X-ray diffractometry, adsorption isotherm, infrared spectroscopy, thermogravimetric analysis, and transmission electron microscopy. According to the results, the new initiators led to semiconductor-based hydrogels, achieved with high swelling property through a high-speed high-efficient photopolymerization reaction in a safe manner.

Synthesis of Anionic Hydrogels for Uranyl Ion Adsorption

In this study, the anionic hydrogels were prepared in existence of crosslinker (N, N’-methylenebisacrylamide) by free radical addition reaction in aqueous solutions of neutral acrylamide and 2-hydoxyethyl methacrylate monomers and anionic comonomers such as mesaconic acid with 2 carboxyl groups or aconitic acid with 3 carboxyl groups. Hydrogels were characterized by FT-IR and DSC analysis. The effects of temperature, pH, adsorbent mass and concentration on uranyl ion adsorption onto the anionic hydrogels were investigated. It was determined that adsorption of UO 2 2+ ions to prepared hydrogels did not change with temperature and increased with increasing pH. The adsorption of u ranyl ion from aqueous solutions onto the anionic hydrogels was evaluated by applying Giles, Langmuir and Temkin isotherms to experimental results. According to the Giles adsorption isotherms classification of hydrogels UO 2 2+ ions adsorption prepared from adsorption isotherms formed, L type was determined and Langmuir parameters were calculated. It was determined that adsorption of UO 2 2+ ions to hydrogels prepared from R L values calculated for 1000 mg L -1 UO 2 2+ ion concentration is favorable.

Minimally Invasive Hemostatic Materials: Tackling a Dilemma of Fluidity and Adhesion by Photopolymerization in situ

Hemostasis in vivo is a key to success in minimally invasive surgery (MIS). However, solid hemostatic materials cannot pass through the sheath tube of the MIS apparatus, while liquid ones are restricted by their low adhesion, which leads to them peeling off of tissue. To tackle the dilemma of fluidity and adhesion, a formulation containing a multifunctional sucrose allyl ether (SAE) monomer and an alpha-hydroxyketone liquid photoinitiator (HMPP) was applied as a lead hemostatic material for MIS. Real-time infrared results showed that SAE initiated by HMPP can rapidly polymerize into a transparent crosslinking membrane. Quantum chemistry showed that this occurs via a free radical addition reaction mechanism. Thermodynamic properties, such as reaction driving force and enthalpy change, were similar to those for a corresponding small molecular analogue, allyl methyl ether (AME), but the addition rate was lower than that for AME. The CC50 values of SAE and HMPP were also obtained by cell experiments. A hemostasis experiment in vivo was performed by comparing the formulation with chitosan and a traditional Chinese medicine (Yunnan Baiyao powder). The result showed that the formulation had a competitive advantage for use in MIS.

Removal of some cationic dyes from aqueous solution by acrylamide- or 2-hydroxyethyl methacrylate-based copolymeric hydrogels

In this study, anionic hydrogels were prepared using a crosslinker (N,N′-methylenebisacrylamide) through a free radical addition reaction in aqueous solutions of neutral acrylamide or 2-hydroxyethyl methacrylate monomer and anionic monomers, mesaconic acid or aconitic acid. Cationic dyes along with safranine (azine-), nile blue (oxazine-) and methylene blue (thiazine-) were selected as models of pollutants, and adsorption of these dyes onto the hydrogels was investigated. To examine the effect of concentration on adsorption, dye solutions prepared with a concentration range of 5–50 mg l−1 and 0.1 g hydrogel at 25 °C were exposed to the hydrogels until equilibrium was established. Dye adsorption onto the hydrogels was found to be an L type Giles adsorption isotherm. Monolayer sorption capacity and adsorption constant values were calculated from the Langmuir plots. To calculate RL values, a non-dimensional analysis was used and they were always found to be 0 azine > thiazine. Furthermore, the higher the number of carboxyl groups in the hydrogel composition, the higher the adsorbed amount of substance.

Ultrahigh Electrocatalytic Conversion of Methane at Room Temperature.

Due to the greenhouse effect, enormous efforts are done for carbon dioxide reduction. By contrast, more attention should be paid for the methane oxidation and conversion, which can help the effective utilization of methane without emission. However, methane conversion and utilization under ambient conditions remains a challenge. Here, this study designs a Co3O4/ZrO2 nanocomposite for the electrochemical oxidation of methane gas using a carbonate electrolyte at room temperature. Co3O4 activated the highly efficient oxidation of methane under mild electric energy with the help of carbonate as an oxidant, which is delivered by ZrO2. Based on the experimental results, acetaldehyde is the key intermediate product. Subsequent nucleophilic addition and free radical addition reactions accounted for the generation of 2‐propanol and 1‐propanol, respectively. Surprisingly, this work achieves a production efficiency of over 60% in the conversion of methane to produce these long‐term stable products. The as‐proposed regional electrochemical methane oxidation provides a new pathway for the synthesis of higher alcohols with high production efficiencies under ambient conditions.

Graphene oxide : A No‐Acid Low‐Temperature Synthesis from Graphite

AbstractGraphite responds to nitro addition by NO2 radical and the nitro derivative isomerizes to energetically favorable nirito form under ambient condition. This derivative readily hydrolyzed in forming poly‐hydroxylated graphene, “graphenol”. The (graph)‐enol responds to irreversible transformation in its keto form with 1,4 hydrogen shift yielding the graphene oxide (GO) as the end product that also possesses C−H bonds. The conventional methodology used in synthesizing GO under strong acid medium inherently follow this NO2 and similar sigma centric free radical addition reactions. These energy released reactions are supported by density functional theoretical (DFT) calculation.