Transformation of organic sulfur and its functional groups in nantong and laigang coal under microwave irradiation

The microwave irradiation experiment of Nantong coal (NTC) and Laigang coal (LGC) has been carried out in a microwave oven and the transformation of organic sulfur and its functional groups was investigated via compact sulfur tester and Fourier transform infrared spectra. The dielectric properties of coal sample are also measured by an Agilent N5244A network analyzer. The result shows that a certain amount of organic sulfur in both NTC and LGC is transformed into iron sulfide, sulfate, and sulfur-containing gas after irradiation of microwave. The retention proportion of the three typical sulfur-containing functional groups in coal is ranking as: disulfide bond (S—S) > sulfinyl (SO) > sulfydryl (—SH), and such phenomenon has been explained by the first principle calculation based on the density functional theory. The calculation results of Fukui indices, electrostatic potential, and frontier orbital analysis indicate the reactivity of the SO and SS is lower than that of the —SH. The calculated bond dissociation enthalpies and bond dissociation times indicate the chemical bonds of —SH and S—S need more time to rupture than SO when microwave power is 1000 W. © 2019 Wiley Periodicals, Inc.     

Conversion of hydrogen sulfide to elemental sulfur byChlorobium thiosulfatophilum in a CSTR with a sulfur-settling separator

Chlorobium thiosulfatophilum may be used for the bioconversion of hydrogen sulfide to elemental sulfur or sulfate. Sulfur is the preferred product because of problems in the disposal of sulfate. A CSTR with a sulfur-settling separator has been used to preferentially produce and recover elemental sulfur. The simple nutritional requirements of the bacterium and differences in densities and average cell and sulfur particle sizes make a CSTR with a sulfur-settling separator attractive. A bench-scale study has been carried out to determine the optimum process conditions to maximize H₂S conversion, cell growth, elemental sulfur production, and to minimize sulfate production. The liquid effluent typically contained about 425–550 mg/L elemental sulfur. The sulfate concentration was maintained at levels below 100 mg/L. It was possible to remove up to 57 Μmol min⁻¹ L⁻¹ of H₂S from the gas stream. An experiment over a period of 392 h showed stable performance. For Presentation at the Fifteenth Symposium on Biotechnology for Fuels and Chemicals, Colorado Springs, CO.     

Thiozonation and thiozonolysis of triatomic sulfur (S<Subscript>3</Subscript>) on the C<Subscript>70</Subscript> fullerene: a DFT study

Density functional theory calculations have been carried out to investigate the [2?+?x] x?=?1, 2, and 3 cycloaddition reactions (paths A, B, and C) of triatomic sulfur (S₃) with the C₇₀ fullerene in terms of geometry, energies, and electronic structures. The thiozonation (S₃) on the hexagon–hexagon and hexagon–pentagon bonds of the C₇₀ fullerene through 1,3-dipolar reaction, i.e., [2?+?3] cycloaddition, is generally exothermic, while through the chelotrope additions, i.e., [2?+?1] cycloaddition, are endothermic. The results indicate that the 1,3-dipolar cycloaddition is the most preferable path. Having more negative values of reaction energies E_r together with the lower barrier heights, thiozonation of the hexagon–hexagon bonds is thermodynamically and kinetically more favorable than hexagon–pentagon ones. Moreover, the addition of thiozone to the hexagon–hexagon bonds near the pole area of the C₇₀ leads to more negative reaction energies. Therefore, it is established that the arrangement and position of C=C bonds play an important role in the thiozonation of C₇₀ fullerene. Thiozonolysis of triatomic sulfur (S₃) indicates that S–S bond cleavage has not occurred, instead a sulfur bridge over a C–C bond or a four-membered ring of 1,2-dithietane-1-sulfide is preferred to be formed.     

Homolytic Decomposition of Sulfonyl Chlorides

The products, kinetic parameters, and activation entropy of thermal decomposition of sulfonyl chloride groups in chlorosulfonated polyethylene (CSPE) have been studied for the first time, and it has been demonstrated that the decomposition mechanism involves simultaneous cleavage of two bonds (carbon–sulfur and sulfur–chlorine) to give an SO₂ molecule and two free radicals, which can be useful in the process of polymer structuring. The radical mechanism has been confirmed by the formation of 2,3-diphenyl-2,3- dimethylbutane on heating CSPE in isopropylbenzene. The simultaneous cleavage of two bonds is supported by the low activation energy and pre-exponential factor in the Arrhenius equation, as well as by negative activation entropy values.     

On the structures and fragmentation of [Me2S∵SMe2]+ and [Et2S∵SEt2]+: Tandem mass spectrometry metastable and collision-induced dissociation results

An experimental study of the metastable and collision-induced dissociation (CID) spectra of [Me₂S∵SMe₂]⁺ and [Et₂S∵SEt₂]⁺ has been carried out. These ions are examples of species that contain two-center-three-electron (2c–3e) sulfur-sulfur bonds. The metastable and CID spectra provide experimental evidence of the atomic connectivity and of the 2c–3e bonds. The metastable cleavage of the S∵S 2c–3e bonds appears to occur with no reverse activation barriers and to result in small average kinetic energy releases. Fragmentation of the same bonds by CID results in the most intense product for both ions. Comparisons with the metastable and CID spectra of [MeSSMe]⁺, an ion with a two-center-two-electron (2c–2e) sulfur-sulfur bond, are made and strongly support the difference in the sulfur-sulfur bonding.     

Microwave sintering of nickel ferrite nanoparticles processed via sol–gel method

Magnetic nickel ferrite (NiFe₂O₄) was prepared by sol–gel process and calcined in the 2.45 GHz singlemode microwave furnace to synthesize nickel nanopowder. The sol–gel method was used for the processing of the NiFe₂O₄ powder because of its potential for making fine, pure and homogeneous powders. Sol–gel is a chemical method that has the possibility of synthesizing a reproducible material. Microwave energy is used for the calcining of this powder and the sintering of the NiFe₂O₄ samples. Its use for calcination has the advantage of reducing the total processing time and the soak temperature. In addition to the above combination of sol–gel and microwave processing yields to nanoscale particles and a more uniform distribution of their sizes. X-ray diffraction, energy dispersive X-ray spectroscopy, transmission electron microscopy and vibrating sample magnetometer were carried out to investigate structural, elemental, morphological and magnetic aspects of NiFe₂O₄. The results showed that the mean size and the saturation magnetization of the NiFe₂O₄ nanoparticles are about 30 nm and 55.27 emu/g, respectively. This method could be used as an alternative to other chemical methods in order to obtain NiFe₂O₄ nanoparticles.     

An ab initio study of the structure and torsional modes of the H2SO4 molecule

Ab initio calculations at the STO—3G and 4—31G levels have been carried out for the H₂SO₄ molecule as a function of the pair of twist angles of the HO bonds about the respective OS bonds. Values for the remaining bond angles and lengths were taken from the recent microwave structural determination by Kuczkowski et al. The results indicate a minimum energy for a structure with a (sc, sc) conformation and C₂ symmetry, where sc denotes synclinal, or gauche. This structure corresponds to that observed. At a higher energy of 11.5 kJ mol^?1 (4—31G) there is a structure with a (+sc, ?sc) conformation and C_s symmetry. The torsional modes corresponding to the a and b irreducible representations of the C₂ point group are estimated to have frequencies of 280 and 265 cm^?1, respectively.     

Bond Energy Scheme for Estimating Heats of Formation of Monomers and Polymers. VI. Sulfur Compounds

The bond energy scheme is extended to sulfur compounds and heats of formation and atomization energy terms derived from thermochemical data reviewed to 1977, for bonds of sulfur with carbon, hydrogen, halogens, and oxygen atoms. A precision of ± 1 kcal/mole was attainable for the covalent bonds of divalent sulfur in the lowest oxidation state S(± II). The higher valency states: S(IV) and S(VI) involve polar contributions depending upon the electrouegativity of the combining atom as well as (d^π -p^π) orbital promotion energies which are specific to the compound and transferable to other molecules only with a limited precision, no better than about ± 3 kcal/mole. The atomization energy terms (E_a ^25°C) of various bonds of sulfur a are found consistent with the experimental bond dissociation energies and bear a relationship with bond lengths and force constants as observed in the previous work. Heats of polymer-forming reactions and heats of formation of sulfur-containing monomers and polymers are estimated from the newly derived bond energy terms.     

Investigations of the hydrogen bond in the crystals of tropolone and thiotropolone via car-parrinello and path integral molecular dynamics

Car-Parrinello and path integrals molecular dynamics (CPMD and PIMD) simulations were carried out for the 10π-electron aromatic systems: 2-hydroxy-2,4,6-cycloheptatrien-1-one, commonly known as Tropolone (I) and 2-hydroxy-2,4,6-cycloheptatriene-1-thione, called Thiotropolone (II) in vacuo and in the solid state. The extremely fast proton transfer (FPT) and “prototropy” tautomerism in the keto-enol (thione-enethiol) systems have been analyzed on the basis of CPMD and PIMD methods level. Comparisons of two-dimensional (2D) free-energy landscapes of reaction coordinate δ-parameter and R_O…O or R_O…S distances shows that the OH… tautomer to be more favorable in the Thiotropolone. The hydrogen between the oxygen and the sulfur atoms adopts a starkly asymmetrical position in the double potential well. The values of the energy barriers for the FPT were calculated and suggested a strong hydrogen bond with low barrier for FPT mechanism. These studies and the 2D average index of π-delocalization 〈λ〉 landscape of time evolutions of R_O1…O2 and R_C7O2 or R_C7S1 distances for the both crystals indicate that hydrogen bonds in the crystals of Tropolone (I) and Thiotropolone (II) have characteristic properties for the type of bonding model resonance-assisted hydrogen bonds and also low-barrier hydrogen bonds. In the crystal of the Thiotropolone (II), we found the hydrogen bond O H…S existing without the equilibrium of the two tautomers whereas in the crystal of the Tropolone (I) has been confirmed the hydrogen bond O H…O existing with the equilibrium of the two tautomers. It was also found the significant differences in frequency, speed, and the image of the FPT in the studied crystals. © 2018 Wiley Periodicals, Inc.     

Microwave assisted preparation of Eu2+-doped Åkermanite Ca2MgSi2O7

A rapid and energy efficient microwave assisted solid state preparative route for europium-doped Åkermanite (Ca₂MgSi₂O₇) has been developed. This method reduces the reaction time and energy needed by more than 90%, compared to the preparation carried out in a conventional furnace. The obtained samples are phase pure as has been determined using synchrotron X-ray powder diffraction data and Rietveld analyses. Scanning electron microscopy was employed to investigate the morphology of the microwave prepared compounds whilst energy dispersive X-ray spectroscopy (EDX) was used to verify the elemental composition of the specimens. A systematic investigation of the influence of the utilized microwave setup is presented. Finally, the microwave prepared materials were subject to temperature dependent photoluminescence measurements in order to investigate the thermal quenching of the luminescence.     

Ab initio studies of H2PXYH molecules (X,Y = O,S)

Ab initio molecular orbital theory is applied to the study of P? O and P? S bonding in the hypervalent phosphinic (H₂POOH), phosphinothioic (H₂POSH), and phosphinodithioic (H₂PSSH) acid molecules. Intramolecular proton exchange reactions are followed using the intrinsic reaction coordinate and Self-Consistent-Field energy localized orbitals. The P? O and PS bonds are characterized via force constants, phosphorus d orbital populations, and localized orbitals and are best described as either normal single bonds or dative bonds augmented by π back donation from the oxygen or sulfur lone pairs. The anions of these acids are also investigated, and they are found to contain only dative bonds to sulfur and oxygen.     

Decomposition of Gaseous Sulfide Compounds in Air by Pulsed Corona Discharge

The effectiveness of applying a pulsed corona discharge to the destruction of olfactory pollution in air was investigated. This paper presents a comparative study of the decomposition of three representative sulfide compounds in diluted concentrations: hydrogen sulfide (H₂S), dimethyl sulfide (DMS), and ethanethiol (C₂H₅SH), which could be completely removed when a sufficient but reasonable energy density was deposited in the gas. DMS showed the lowest energy cost (around 30 eV/molecules); C₂H₅SH and H₂S had an EC of respectively 45 eV and 115 eV. The efficiency of the non-thermal plasma process increased with decreasing the initial concentration of sulfide compounds, while the energy yield remained almost unchanged. SO₂ was the only identified byproduct of H₂S decomposition, but the sulfur balance suggests the formation of undetected SO₃. The byproducts analyzed during the degradation of DMS and C₂H₅SH enabled to propose a reaction mechanism, starting with radical attack and breaking of C–S bonds.     

Cl原子与CH2SH自由基反应机理及电子密度拓扑研究

采用MP2(Full)/6-311G(d,p)和B3LYP/6-311G(d,p)找到了反应Cl＋CH₂SH→HCl＋CH₂S的两个可能的反应通道, 得到了各反应通道的反应物、中间体、过渡态和产物的优化构型、谐振频率. 对反应进程中若干关键点进行了电子密度拓扑分析, 讨论了反应进程中键的断裂、生成和化学键的变化规律, 找到了该反应的结构过渡区(结构过渡态)和能量过渡态, 发现了反应热与结构过渡区之间的关系.     

Mechanisms and energetics of free radical initiated disulfide bond cleavage in model peptides and insulin by mass spectrometry

We investigate the mechanism of disulfide bond cleavage in gaseous peptide and protein ions initiated by a covalently-attached regiospecific acetyl radical using mass spectrometry (MS). Highly selective S–S bond cleavages with some minor C–S bond cleavages are observed by a single step of collisional activation. We show that even multiple disulfide bonds in intact bovine insulin are fragmented in the MS2 stage, releasing the A- and B-chains with a high yield, which has been challenging to achieve by other ion activation methods. Yet, regardless of the previous reaction mechanism studies, it has remained unclear why (1) disulfide bond cleavage is preferred to peptide backbone fragmentation, and why (2) the S–S bond that requires the higher activation energy conjectured in previously suggested mechanisms is more prone to be cleaved than the C–S bond by hydrogen-deficient radicals. To probe the mechanism of these processes, model peptides possessing deuterated β-carbon(s) at the disulfide bond are employed. It is suggested that the favored pathway of S–S bond cleavage is triggered by direct acetyl radical attack at sulfur with concomitant cleavage of the S–S bond (S_H2). The activation energy for this process is substantially lower by ∼9–10 kcal mol^–1 than those of peptide backbone cleavage processes determined by density functional quantum chemical calculations. Minor reaction pathways are initiated by hydrogen abstraction from the α-carbon or the β-carbon of a disulfide, followed by β-cleavages yielding C–S or S–S bond scissions. The current mechanistic findings should be generally applicable to other radical-driven disulfide bond cleavages with different radical species such as the benzyl and methyl pyridyl radicals.     

The role of the sulfur 3d orbitals in bond formation in sulfur-containing compounds

The role of the sulfur 3d orbitals in bond formation is discussed by taking into account the influence of the environment on the orbitals of the sulfur atom in the molecules. The calculation results of a series of prototype molecules containing sulfur such as SF₂ SF₄, NSF₃, SF₀, H₂S are reported. It is convincingly shown that in highly electronegative environment the energy levels of the sulfur 3d orbitals are reduced to the vicinity of those of the ligand valence orbitals and their spatial distributions are contracted to the bonding area, and therefore they can participate in bond formation to a certain extent, which is enhanced by the formation of the d-p π back bonds. It seems that the result reported in this paper is helpful for the solution of the long-standing debate about the sulfur 3d orbital participation in bond formation.     

Sulfur radical cation-peptide bond complex in the one-electron oxidation of S-methylglutathione

Neighboring group participation was investigated in the *OH-induced oxidation of S-methylglutathione in aqueous solutions. Nanosecond pulse radiolysis was used to obtain the spectra of the reaction intermediates and their kinetics. Depending on the pH, and the concentration of S-methylglutathione, pulse irradiation leads to different transients. The transients observed were an intramolecularly bonded [>S thereforeNH2]+ intermediate, intermolecularly S thereforeS-bonded radical cation, alpha-(alkylthio)alkyl radicals, alpha-amino-alkyl-type radical, and an intramolecularly (S thereforeO)+-bonded intermediate. The latter radical is of particular note in that it supports recent observations of sulfur radical cations complexed with the oxygen atoms of peptide bonds and thus has biological and medical implications. This (S thereforeO)+-bonded intermediate had an absorption maximum at 390 nm, and we estimated its formation rate to be >or=6x10(7) s(-1). It is in equilibrium with the intermolecularly S thereforeS-bonded radical cation, and they decay together on the time scale of a few hundred microseconds. The S thereforeS-bonded radical cation is formed from the monomeric sulfur radical cation (>S*+) and an unoxidized S-methylglutathione molecule with the rate constant of 1.0x10(9) M(-1) s(-1). The short-lived [>S thereforeNH2]+ intermediate is a precursor of decarboxylation, absorbs at approximately 390 nm, and decays on the time scale of hundreds of nanoseconds. Additional insight into the details of the association of sulfur radical cations with the oxygen atoms of the peptide bonds was gained by comparing the behavior of the S-methylglutathione (S thereforeO+-bonded five-membered ring) with the peptide gamma-Glu-Met-Gly (S thereforeO+-bonded six-membered ring). Conclusions from experimental observations were supported by molecular modeling calculations.     

Quantum-Chemical Modeling of the Effect of a Continuous Random Network on Stabilization of Charged and Neutral Defects in a-S

Quantum-chemical modeling of the stabilization of neutral and charged defects in amorphous sulfur (a-S) has been carried out. The atoms constituting the three nearest coordination spheres of a defect were modeled using the cluster approximation at the HF/6-31G* level. The interaction of the defect region with distant fragments of a continuous random network was calculated using the polarizable continuum model (PCM), in which the medium surrounding the cluster was considered as a continuum with the experimental permittivity for a-S. The energy of formation of charged defects E _def based on threefold coordinated sulfur atoms (C ₃ ⁺ , ₃ ^? )is close to the homolytic bond cleavage energy E _b. For neutral defects, E _def < E _b. Such defects can be the sites with a negative correlation energy, which are responsible for specific properties of chalcogenide glassy semiconductors.     

Reclaiming of ground rubber tire (GRT) by a novel reclaiming agent

The present paper describes the mechanical reclaiming of ground rubber tire (GRT) by tetra methyl thiuram disulfide (TMTD), a multi-functional reclaiming agent. The versatility of the proposed agent is that it acts as a reclaiming agent during reclaiming and as a curing agent during revulcanization of the reclaimed sample. Reclaiming of GRT was carried out on an open two roll mixing mill at various time intervals and different concentrations of the reclaiming agent (TMTD). The degree of reclaiming was evaluated by measurement of the gel content, inherent viscosity of sol rubber, Mooney viscosity of the reclaimed rubber, crosslink density, swelling ratio and molecular weight between two crosslink bonds as a function of milling time. Also, the influence of the gel content on crosslink density at various time intervals on the open two roll mixing mill was determined. A unique correlation between gel fraction and crosslink density obtained at various time intervals and concentrations of reclaiming agent indicated that an optimization of the concentration of TMTD and milling time has a positive influence on improving the efficiency of reclaiming. The reclaiming conditions have been optimized in view of the mechanical properties of the revulcanized GRT and the aging resistance properties of the revulcanized reclaim. The influence of the concentration of sulfur on the mechanical properties in the revulcanized reclaim was also studied. Scanning electron microscopy (SEM) studies further indicate the coherency and homogeneity in the revulcanized reclaim rubber when reclamation is carried out by optimum concentration of TMTD after maximum time of reclaiming.     

Kinetic Study on the Selective Oxidation of H2S Containing Excess Water and Ammonia

The selective oxidation of hydrogen sulfide containing excess water and ammonia was studied over V₂O₅/SiO₂ catalysts. H₂S was successfully converted to elemental sulfur and ammonium thiosulfate (ATS) without considerable emission of sulfur dioxide. Kinetic studies were carried out to describe the complex reaction paths. This revised version was published online in June 2006 with corrections to the Cover Date.     

Oxidative cleavage of C-Si bonds in polyhydroxylated silacyclopentanes

Oxidative cleavage of C-Si bonds of polyhydroxylated silacyclopentanes under various conditions have led to both the desired polyols and to Peterson elimination products. Further studies on the reactivity of these silacycles, under acidic and basic conditions have been carried out, leading to unexpected results. Treatment of these silacycles under basic conditions thus provided various diols after the cleavage of C_sp³-Si bonds. A mechanistic rationale has been proposed for each case.