Theoretical Research on the Multi-channel Reaction Mechanism of CHF Radical with HNCO by Density Functional Theory

The reaction mechanism of CHF radical with HNCO was investigated by the B3LYP method of density functional theory （DFT）, while the geometries and harmonic vibration frequencies of reactants, intermediates, transition states and products were calculated at the B3LYP/6-311＋＋G＊＊ level. In the temperature range of 100-2600 K, the statistical thermody- namics and Eyring transition state theory with Winger correction were used to study the thermodynamic and kinetic characters of the channel with low energy barrier. In addition, the analysis on the combining interaction between CHF radical and HNCO was performed by atom-in-molecules theory （AIM） and natural bond orbitals （NBO） analysis. The calculation results indicated that the reaction of CHF radical with HNCO had ten channels, and the channel of NH direct extraction （CHF ＋ HNCO→IM6→TS7→IM7→CHFNH ＋ CO） in singlet state was the main channel with low potential energy and high equilibrium constant and reaction rate constant. CHFNH and CO were the main products.

ON THE KINETICS AND MECHANISM OF THE COPOLYMERIZATION OF ACRYLONITRILE WITH STYRENE IN THE PRESENCE OF COPPER CHLORIDE

The copolymerization of styrene (St) and acrylonitrile (AN) complexed with CuCl_2 monomer by a free radicalmechanism was performed using benzoyl peroxide as an initiator at 65℃ under N_2 atmosphere for 150 min. The rate ofpolymerization (R_p) was found to increase linearly with the concentration (in mol/L) of CuCl_2, AN and St through scalingrelations. The activation energy of the copolymerization process in the presence and absence of CuCl_2 was found to be46.5 kJ/mol and 102 kJ/mol, respectively. The viscosity average molecular weigh of the copolymer and the k_p^2/k_t ratio weredctermired to further assess the accelerating effect of CuCl_2 on the copolymerization process. The copolymerization processin the presence of CuCl_2 has a radical complex mechanism.

New insights for the catalytic oxidation of cyclohexane to K-A oil

Au-based catalysts have been reported to be active in the cyclohexane oxidation to K-A oil, but they showed some limitiations in terms of productivity, selectivity and required reaction conditions. The possibility to overcome some of these limits has been explored coupling Au with Cu, which can be suitable for undergoing the electron-switch in the initial step of the cyclohexane oxidation. Hence, a bimetallic 2 wt% Au Cu/Al_(2)O_(3) catalyst was tested in the oxidation of cyclohexane, working at mild conditions of 120 ℃ and 4 bar of O_(2). The combination of the catalyst with a very small amount of benzaldehyde used as cheaper and non-toxic radical initiator allowed to obtain a very high productivity of cyclohexanol and cyclohexanone(45 mmol*m L/mgmet*h) with a selectivity of 94%. Moreover, comparing the catalysed reaction with the non-catalysed one, the role of the catalyst has been disclosed.

Balancing the Activity and Selectivity of Propane Oxidative Dehydrogenation on NiOOH(001)and(010)

Propane oxidative dehydrogenation(ODH)is an energy-efficient approach to produce propylene.However,ODH suff ers from low propylene selectivity due to a relatively higher activation barrier for propylene formation compared with that for further oxidation.In this work,calculations based on density functional theory were performed to map out the reaction pathways of propane ODH on the surfaces(001)and(010)of nickel oxide hydroxide(NiOOH).Results show that propane is physisorbed on both surfaces and produces propylene through a two-step radical dehydrogenation process.The relatively low activation barriers of propane dehydrogenation on the NiOOH surfaces make the NiOOH-based catalysts promising for propane ODH.By contrast,the weak interaction between the allylic radical and the surface leads to a high activation barrier for further propylene oxidation.These results suggest that the catalysts based on NiOOH can be active and selective for the ODH of propane toward propylene.

Quantum chemical investigation on photodegradation mechanisms of sulfamethoxypyridazine with dissolved inorganic matter and hydroxyl radical

Sulfamethoxypyridazine（SMP） is one of the commonly used sulfonamide antibiotics（SAs）.SAs are mainly studied to undergo triplet-sensitized photodegradation in water under natural sunlight with other coexisting aquatic environmental organic pollutants.In this work,SMP was selected as a representative of SAs.We studied the mechanisms of triplet-sensitized photodegradation of SMP and the influence of selected dissolved inorganic matter,i.e.,anions（Br^-,Cl^-,and NO^-_3） and cations ions（Ca^（2＋）,Mg^（2＋）,and Zn^（2＋）） on SMP photodegradation mechanism by quantum chemical methods.In addition,the degradation mechanisms of SMP by hydroxyl radical（OH·） were also investigated.The creation of SO_2 extrusion product was accessed with two different energy pathways（pathway-1 and pathway-2） by following two steps（step-I and step-II） in the tripletsensitized photodegradation of SMP.Due to low activation energy,the pathway-1 was considered as the main pathway to obtain SO_2 extrusion product.Step-II of pathway-1 was measured to be the rate-limiting step（RLS） of SMP photodegradation mechanism and the effect of the selected anions and cations was estimated for this step.All selected anions and cations promoted photodegradation of SMP by dropping the activation energy of pathway-1.The estimated low activation energies of different degradation pathways of SMP with OH·radical indicate that OH·radical is a very powerful oxidizing agent for SMP degradation via attack through benzene derivative and pyridazine derivative ring.

Regulation of radicals by hydrogen-donor solvent in direct coal liquefaction

Radicals are important intermediates in direct coal liquefaction.Certain radicals can cause the cleavage of chemical bonds.At high temperatures,radical fragments can be produced by the splitting of large organic molecules,which can break strong chemical bonds through the induction pyrolysis of radicals.The reaction between the formation and annihilation of coal radical fragments and the effect of hydrogen-donor solvents on the radical fragments are discussed in lignite hydrogenolysis.Using the hydroxyl and ether bonds as indicators,the effects of different radicals on the cleavage of chemical bond were investigated employing density functional theory calculations and lignite hydrogenolysis experiments.Results showed that the adjustment of the coal radical fragments could be made by the addition of hydrogendonor solvents.Results showed that the transition from coal radical fragment to H radical leads to the variation of product distribution.The synergistic mechanism of hydrogen supply and hydrogenolysis of hydrogen-donor solvent was proposed.

Theoretical study on the formation mechanism of polychlorinated dibenzothiophenes/thianthrenes from 2-chlorothiophenol molecules

Homogeneous formation of polychlorinated dibenzothiophenes/thianthrenes（PCDT/TAs）,sulfurated compounds analogous to polychlorinated dibenzo-p-dioxin/dibenzofurans（PCDD/Fs）, has been well-documented to occur via radical–radical coupling reactions from chlorinated thiophenol precursors. However, the current understanding of the formation mechanism of PCDT/TAs is exclusively limited to the inherent point of view that chlorothiophenoxy radicals act as the only required intermediates for PCDT/TAs. This study investigates reaction pathways for the formation of PCDT/TAs involving two new types of radical species, i.e., substituted phenyl radicals and substituted thiophenoxyl diradicals. Taking 2-chlorothiophenol（2-CTP） as a model compound for chlorothiophenols,we found that apart from the mostly discussed chlorothiophenoxy radicals, substituted phenyl radicals and substituted thiophenoxyl diradicals could also be readily formed via the reaction of 2-CTP with H radicals. Furthermore, direct self-and cross-coupling of these radicals can result in the formation of PCDT/TAs, including 1-monochlorothianthrene（1-MCTA）, 1,6-dichlorothianthrene（1,6-DCTA）, 4,6-dichlorodibenzothiophene（4,6-DCDT）and 1,6-dichlorodibenzothiophene（1,6-DCDT）. The pathways proposed in this work are proven to be both thermodynamically and kinetically favorable. Particularly, comparisons were made between the formation mechanisms of sulfurated and oxygenated dioxin systems from an energetic point view, showing that replacing oxygen with sulfur atoms greatly reduces the activation barriers of the rate-controlling steps involved in the PCDT/TA formation processes compared with those involved for PCDD/Fs. The calculated results in this work may improve our understanding of the formation mechanism of PCDT/TAs from chlorothiophenol precursors and should be informative to environmental scientists.

Mechanism and rate constants for complete series reactions of 19 fluorophenols with atomic H

Fluorine-containing halogenated fluorophenol may have effect as intermediate species involved in the formation of polyfluorinated dibenzo-p-dioxin/dibenzofurans （PFDDs/Fs）. The mechanism for the atomic H initiated reactions with complete series of nineteen fluorophenol congeners was studies using the density functional theory. At the MPWB1K,/6-31＋G（d,p） level, the geometries and frequencies of reactants, transition states, and products were obtained, and the accurate energetic values were acquired at the MPWB 1K/6-311 ＋G（3df,2p） level. The rate constants were evaluated by the canonical variational transition-state theory with the small curvature tunneling contribution over a wide temperature range of 600-1000 K. The study shows that the intramolecular hydrogen-bond in the ortho-substituted FPs as well as the inductive effect of the electron-withdrawing fluorine and steric repulsion of multiple substitutions may ultimately be responsible for the relative strength of the O-H bonds in FPs. The results can be used for further studies on PFDD/Fs formation mechanism.

Mechanism and kinetic properties of NO_3-initiated atmospheric degradation of DDT

In this article, the NO3 radical-initiated atmospheric oxidation degradation of DDT was theoretically investigated using molecular orbital theory calculations. All the calculations of intermediates, transition states and products were performed at the MPWB1K/6-311＋G（3df,2p）//MPWB1K/6- 31＋G（d,p） level of theory. Several energetically favorable reaction pathways were revealed. The formation mechanisms of secondary pollutants were presented and discussed. The rate constants were deduced over the temperature range of 273-333 K using canonical variational transition-state （CVT） theory with the small curvature tunneling （SCT） method. Our study shows that H abstraction from the alkyl group and NO3 addition to the Ca atom of the benzene ring are the dominant reaction pathways. The rate-temperature formula of the overall rate constants is k（T）（DDT＋NO3） = （7.21 ~ 10-15）exp（-153.81/T） cm3/（mol.sec） over the possible atmospheric temperature range of 273-333 K. The atmospheric lifetime of DDT determined by NO3 radical is about 52.5 days, which indicates that it can be degraded in the gas phase within several months.

High selective epoxidation of 2-methylpropene over a Mo-based oxametallacycle reinforced nano composite

Compared with the gas-solid phase reactions,the epoxidation of light olefins in the liquid phase could realize the highly selective preparation of epoxides at a lower temperature.Nevertheless,the C=C bond of light olefins is more difficult to activate,and it is still a challenge to realize the dual activation of the oxidant and light olefins in one reaction system.In this contribution,an oxametallacycle reinforced nanocomposite(Mo(O_(2))_(2)@RT)is prepared via an oxidative pretreatment strategy,and its epoxidation performance to 2-methylpropene in liquid-phase with tert-butyl hydroperoxide(TBHP)as an oxidant is evaluated.A set of advanced characterizations including field emission scanning electron microscopy,X-ray photoelectron spectroscopy,in-situ Fourier transform infrared spectroscopy(FT-IR),electron spin-resonance spectroscopy,and high-resolution mass spectrometer are implemented to confirm the physicochemical properties and the catalytic behaviors of Mo(O_(2))_(2)@RT.This catalyst has a fast kinetic response and exhibits excellent catalytic activity in 2-methylpropene epoxidation to produce 2-methylpropylene oxide(MPO;select.:99.7%;yield:92%),along with good reusability and scalability.Moreover,the main epoxidation mechanism is deduced that TBHP is activated by Mo(O_(2))_(2)@RT to generate the highly active tert-butyl peroxide radical,which realizes the epoxidation of 2-methylpropene to yield MPO.

Simultaneous Improvements of Thermal Stability and Mechanical Properties of Poly(propylene carbonate) via Incorporation of Environmental-friendly Polydopamine

Inspired by the photoprotection, radical scavenging of melanin together with versatile adhesive ability of mussel proteins, polydopamine（PDA） nanoparticles were successfully prepared and incorporated into environmentally friendly polymer, poly（propylene carbonate）（PPC） via solvent blending. The prepared composites exhibited excellent thermal stability in air and nitrogen atmosphere and extraordinary mechanical properties. The composites displayed eminent increase of temperature at 5% weight loss（T5%） by 30-100 K with 0.3 wt%-2.0 wt% loadings, meanwhile, the tensile strength and Young＇s modulus were significantly improved from 11.5 MPa and 553.7 MPa to 40.5 MPa and 2411.2 MPa, respectively. The kinetic calculation indicated that improvement of T5% is presumably derived from suppressing chain-end unzipping. The glass transition temperature（Tg） of the PPC/PDA composites increased by 8-10 K. This is probably due to hydrogen bonding interaction since the abundant proton donors along PDA chains would interact with proton acceptors like C = O and C―O―C in PPC which would cause restriction of segmental motion of PPC chains.