The influence of activated carbon on the thermal decomposition of sodium ethyl xanthate

The thermal decomposition of SEX in a nitrogen atmosphere was studied by coupled thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR), and by pyrolysis-gas chromatography-mass spectrometry (py-GC-MS). The TG curve exhibited two discrete mass losses of 45.8% and 17.8% respectively, at 200 and 257–364°C. The evolved gases identified as a result of the first mass loss were carbonyl sulfide (COS), ethanol (C₂H₅OH), ethanethiol (C₂H₅SH), carbon disulfide (CS₂), diethyl sulfide ((C₂H₅)₂S), diethyl carbonate ((C₂H₅O)₂CO), diethyl disulfide ((C₂H₅)₂S₂), and carbonothioic acid, O, S, diethyl ester ((C₂H₅S)(C₂H₅O)CO). The gases identified as a result of the second mass loss were carbonyl sulfide, ethanethiol, and carbon disulfide. Hydrogen sulfide was detected in both mass losses by py-GC-MS, but not detected by FTIR. The solid residue was sodium hydrogen sulfide (NaSH).SEX was adsorbed onto activated carbon, and heated in nitrogen. Two discrete mass losses were still observed, but in the temperature ranges 100–186°C (7.8%) and 186–279°C (11.8%). Carbonyl sulfide and carbon disulfide were now the dominant gases evolved in each of the mass losses, and the other gaseous products were relatively minor. It was demonstrated that water adsorbed on the carbon hydrolysed the xanthate to cause the first mass loss, and any unhydrolysed material decomposed to give the second mass loss.Mr. N. G. Fisher would like to thank the A. J. Parker CRC for Hydrometallurgy for the provision of a PhD scholarship.     

Difference in Conversions Between Dimethyl Sulfide and Methanethiol in a Cold Plasma Environment

This study compared the conversion of two malodorous substances, dimethyl sulfide (CH₃SCH₃, DMS) and methanethiol (CH₃SH) in a cold plasma reactor. The DMS and CH₃SH were successfully destroyed at room temperature. DMS decomposed less than CH₃SH at the same conditions. In oxygen-free condition, CS₂ and hydrocarbons were the major products, while SO₂ and CO_x were main compounds in oxygen-rich environments. The DMS/Ar plasma yielded more hydrocarbons and less CS₂ than that of CH₃SH/Ar plasma. In the CH₃SH/O₂/Ar plasma, rapid formation of SO and CO resulted in the yields much more amounts of SO₂ and CO₂ than those in the DMS/O₂/Ar plasma; and remained only a trace of total hydrocarbons, CH₂O, CH₃OH, CS₂, and OCS. The major differences between the reaction mechanisms of DMS and CH₃SH were also proposed and discussed.     

H2S splitting on Cu(110): Insight from combined periodic density functional theory calculations and microkinetic simulation

Practical copper (Cu)‐based catalysts for the water–gas shift (WGS) reaction was long believed to expose a large proportion of Cu(110) planes. In this work, as an important first step toward addressing sulfur poisoning of these catalysts, the detailed mechanism for the splitting of hydrogen sulfide (H₂S) on the open Cu(110) facet has been investigated in the framework of periodic, self‐consistent density functional theory (DFT‐GGA). The microkinetic model based on the first‐principles calculations has also been developed to quantitatively evaluate the two considered decomposition routes for yielding surface atomic sulfur (S*): (1) H₂S → H₂S* → SH* → S* and (2) 2H₂S → 2H₂S* → 2SH* → S* + H₂S* → S* + H₂S. The first pathway proceeding through unimolecular SH* dissociation was identified to be feasible, whereas the second pathway involving bimolecular SH* disproportionation made no contribution to S* formation. The molecular adsorption of H₂S is the slowest elementary step of its full decomposition, being related with the large entropy term of the gas‐phase reactant under realistic reaction conditions. A comparison of thermodynamic and kinetic reactivity between the substrate and the close‐packed Cu(111) surface further shows that a loosely packed facet can promote the S* formation from H₂S on Cu, thus revealing that the reaction process is structure sensitive. The present DFT and microkinetic modeling results provide a reasonably complete picture for the chemistry of H₂S on the Cu(110) surface, which is a necessary basis for the design of new sulfur‐tolerant WGS catalysts. © 2013 Wiley Periodicals, Inc.     

Colorimetric Carbonyl Sulfide (COS)/Hydrogen Sulfide (H2S) Donation from γ‐Ketothiocarbamate Donor Motifs

Hydrogen sulfide (H₂S) is a biologically active molecule that exhibits protective effects in a variety of physiological and pathological processes. Although several H₂S‐related biological effects have been discovered by using H₂S donors, knowing how much H₂S has been released from donors under different conditions remains challenging. Now, a series of γ‐ketothiocarbamate (γ‐KetoTCM) compounds that provide the first examples of colorimetric H₂S donors and enable direct quantification of H₂S release, were reported. These compounds are activated through a pH‐dependent deprotonation/β‐elimination sequence to release carbonyl sulfide (COS), which is quickly converted into H₂S by carbonic anhydrase. The p‐nitroaniline released upon donor activation provides an optical readout that correlates directly to COS/H₂S release, thus enabling colorimetric measurement of H₂S donation.     

Corona[5]arenes Accessed by a Macrocycle‐to‐Macrocycle Transformation Route and a One‐Pot Three‐Component Reaction

Corona[5]arenes, a novel type of macrocyclic compound that is composed of alternating heteroatoms and para ‐arylenes, were synthesized efficiently by two distinct methods. In a macrocycle‐to‐macrocycle transformation approach, S₆‐corona[3]arene[3]tetrazine underwent sequential S_NAr reactions with HS‐C₆H₄‐X‐C₆H₄‐SH (X=S, CH₂, CMe₂, SO₂, and O) to produce the corresponding corona[3]arene[2]tetrazines. Different corona[3]arene[2]tetrazine compounds were also constructed in a straightforward manner by a one‐pot three‐component reaction of HS‐C₆H₄‐X‐C₆H₄‐SH (X=S, CH₂, CMe₂, SO₂, and O) with diethyl 2,5‐dimercaptoterephthalate and 2 equiv of 3,6‐dichlorotetrazine under very mild conditions. All corona[5]arenes adopted 1,2,4‐alternate conformational structures in the crystalline state yielding similar nearly regular pentagonal cavities. Both the cavity size and the electronic property of the acquired macrocycles were fine‐tuned by the nature of the bridging element X.     

Thermal studies on thorium(IV) complexes of 1-butyl-1-methylpiperazinium iodide

Thorium(IV) complexes of the type Th(NO₃)₄·3L·2C₂H₅OH, Th(SCN)₄·L·C₂H₅OH and Th(SO₄)₂·2L·2C₂H₅OH (L=1-butyl-1-methylpiperazinium iodide(I) have been synthesised. From thermogravimetric (TG) curves, the decomposition pattern of the compounds has been analysed. The order, activation energy and apparent activation entropy of the thermal decomposition reaction have been elucidated. The heat of reaction has been calculated from differential thermal analysis (DTA) studies.     

SnS and SnS2 thin films deposited using a spin‐coating technique from intramolecularly coordinated organotin sulfides

Synthesis and applications of organotin(II) sulfide ({2,6‐(Me₂NCH₂)₂C₆H₃}Sn)₂(μ‐S) ( 1 ), organotin(II) thiophenolate {2,6‐(Me₂NCH₂)₂C₆H₃}Sn(SPh) ( 2 ) and organotin(IV) heptasulfide {2,6‐(Me₂NCH₂)₂C₆H₃}₂Sn₂S₇ ( 3 ) as potential single‐source precursors (SSPs) for the deposition of SnS or SnS₂ thin films using a spin‐coating method are reported. Compounds 1 , 2 and 3 differ either by tin oxidation state or by Sn:S ratio (Sn:S = 2:1 in 1 , 1:1 in 2 and 2:7 in 3 ). It is shown that compound 1 is not a suitable SSP for thin‐film fabrication using the spin‐coating process because of its incomplete decomposition at annealing temperature. However, compounds 2 and 3 seem to be promising SSPs for spin‐coating of amorphous semiconducting thin films of SnS and SnS₂, respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

密度泛函理论研究十二烷硫醇在Au(111)面上的吸附

采用第一性原理方法研究了十二烷硫醇(C₁₂H₂₅SH)分子在Au(111)面上未解离和解离吸附的结构、能量和吸附性质,在此基础上分析判断长链硫醇分子在Au(111)面吸附时S―H键的解离, 以及分子链长度对吸附结构和能量的影响. 计算了S原子在不同位置以不同方式吸附的系列构型, 结果表明在S―H键解离前和解离后,均存在两种可能的表面结构, 直立吸附构型和平铺吸附构型; 未解离的C₁₂H₂₅SH分子倾向于吸附在top位, 吸附能为0.35-0.38 eV; H原子解离后C₁₂H₂₅S基团倾向于吸附在bri-fcc位, 吸附能量为2.01-2.09 eV. 比较分析未解离吸附和解离吸附, 发现C₁₂H₂₅SH分子未解离吸附相较于解离吸附要稳定, 未解离吸附属于弱化学吸附.局域电子态密度和差分电荷密度分析进一步验证了S―H解离后S原子与表面之间成键的数目增加, 而且键合更强. 同时我们发现长链硫醇的吸附能量较短链硫醇的吸附能量略大, S原子与表面Au原子之间的距离略小.     

The properties of calibration errors in the analysis of reduced sulfur compounds by the combination of a loop injection system and gas chromatography with pulsed flame photometric detection

In order to evaluate the extent of analytical biases involved in the GC calibration, we conducted a series of experiments to examine the calibration methods of trace gas components. For the purpose of this comparative study, gaseous standards of reduced sulfur compounds (RSC) including hydrogen sulfide (H₂S), methanethiol (CH₃SH), dimethyl sulfide (DMS), carbon disulfide (CS₂), and dimethyl disulfide (DMDS) were calibrated by the combination of a GC/PFPD technique and a loop-injection method. In the course of this study, two different types of calibration methods were tested and compared: incremental-injection of a given standard with the fixed standard concentration (FSC) versus injection of multiple standards (with different concentrations) at the fixed standard volume (FSV). In the case of the FSV calibration, a notable increase in the GC sensitivity is apparent with decreasing loop size (or injection volume). For instance, the calibration slope for RSC obtained using a 10 μl loop system was approximately three times higher than that for a 250 μl one. However, the results obtained by the FSC method exhibit much poorer sensitivity than its counterpart with slight differences in their sensitivities across different standard concentrations (due to such factors as the matrix effect from varying injection volumes). Thus, the overall results of this study confirm that the detailed characterization of the selected calibration method (e.g., the use of FSV approach relative to FSC) is of primary significance to perform an accurate quantification of trace gases.     

A tandem mass spectrometry study of the gas phase RSC6H5Cr+L (R = H,C6H5; L = arene) and C6H5SSC6H5Cr+ ions

Ion-molecule reactions of chromium containing ions with arylsulfides have been studied in the gas phase and their products have been characterized by tandem mass spectrometry. C₆H₅SH and (C₆H₅)₂S react as typical aromatic compounds and give rise to Cr⁺C₆H₅SR] and RC₆H₅Cr⁺QH₅SR′ [R = H, CH₃, CH(CH₃)₂; R′ = H, C₆H₅] ions. Metastable ion mass spectra of the latter species show that the metal is more strongly bound to diphenylsulfide than to alkylbenzenes. C₆H₅SSC₆H₅ reacts with chromium-containing ions to form only Cr⁺(C₆H₅SSC₆H₅). The decomposition characteristics of this ion and, in particular, the presence of a recovery signal in the neutralization-reionization mass spectrum are in keeping with the formation of a 1,2-dithia[2]cyclophane complex ion, which rearranges into a structurel(s) that contains Cr?S bond(s). No evidence was found for metal atom insertion into S?S, C?S, or S?H bonds.     

Solid-phase microextraction—Gas chromatography to determine volatile organic sulfur compounds in the air at sewage treatment plants

Solid-phase microextraction (SPME) was applied to the determination of 7 volatile organic sulfur compounds (VOSCs), which were analysed by gas chromatography-mass spectrometry. The compounds studied were ethyl mercaptan (CH₃CH₂SH), dimethyl sulfide ((CH₃)₂S), carbon disulfide (CS₂), propyl mercaptan (C₃H₈S), butyl mercaptan (C₄H₁₀S), dimethyl disulfide ((CH₃)₂S₂) and 1-pentanethiol (C₅H₁₂S). Temperature and time conditions of SPME extraction were optimised and the method was validated, with good linearity in a calibration range between 0.1 and 1000 μg m⁻³. Method detection limits ranged between 0.01 and 0.08 μg m⁻³ and method quantification limits were between 0.10 and 0.25 μg m⁻³, allowing real samples taken from several different areas of a sewage treatment plant to be analysed. Repeatability of the method between samples went from 5.6% for pentanethiol up to 14.2% for carbon disulfide, and concentrations of total target compounds were found between 18 and 529 μg m⁻³, depending on the sampling site.     

Reactions of Group V Metal Atoms with Hydrogen Sulfide:Argon Matrix Infrared Spectra and Theoretical Calculations

The reaction of laser-ablated vanadium, niobium and tantalum atoms with hydrogen sulfide has been investigated using matrix isolation FTIR and theoretical calculations. The metal atoms inserted into the H-S bond of H₂S to form the HMSH molecules (M=V, Nb, Ta), which rearranged to H₂MS molecules on annealing for Nb and Ta. The HMSH molecule can also further react with another H₂S to form the H₂M(SH)₂ molecules. These new molecules were identified on the basis of the D₂S and H₂³⁴S isotopic substitutions. DFT (B3LYP and BPW91) theoretical calculations are used to predict energies, geometries, and vibrational frequencies for these novel metal dihydrido complexes and molecules. Reaction mechanism for formation of group V dihydrido complex was investigated by DFT internal reaction coordinate calculations. The dissociation of HVSH gave VS+H₂ on broad band irradiation and reverse reaction happened on annealing. Based on B3LYP calculation releasing hydrogen from HVSH is endothermic only by 13.5 kcal/mol with lower energy barrier of 16.9 kcal/mol.     

Chemisorption of thiol‐functionalized metallocene molecules on Si(111)‐ Ag√3×√3 surface: A density functional theory study

Herein, chemical adsorption properties of the thiol‐functionalized metallocene molecules [M(C₅H₄SH)₂] on Si(111)‐Ag√3×√3 surface were investigated using density functional theory calculation. For this purpose, thiol‐modified ferrocene [Fe(C₅H₄SH)₂], osmocene [Os(C₅H₄SH)₂], and ruthenocene [Ru(C₅H₄SH)₂] molecules were attached on the surface via two different binding models. The more favorable chemical binding energies of [Fe(C₅H₄SH)₂], [Os(C₅H₄SH)₂], and [Ru(C₅H₄SH)₂] molecules were calculated as ?3.42, ?2.15, and ?2.00 eV, respectively. The results showed that the adsorption energies of metallocene molecules change independently by increasing the radius of metal ions where on going down the group of the periodic table. The calculated adsorption energies showed that [Fe(C₅H₄SH)₂] molecule was more stable on the Si(111)‐Ag√3×√3 surface. By calculating the electronic band structure for metallocene/Si(111)‐Ag√3×√3 surfaces, we identified a flat dispersion band in a part of the surface Brillouin zone. © 2015 Wiley Periodicals, Inc.     

Identifying Optimal Zeolitic Sorbents for Sweetening of Highly Sour Natural Gas

Raw natural gas is a complex mixture comprising methane, ethane, other hydrocarbons, hydrogen sulfide, carbon dioxide, nitrogen, and water. For sour gas fields, selective and energy‐efficient removal of H₂S is one of the crucial challenges facing the natural‐gas industry. Separation using nanoporous materials, such as zeolites, can be an alternative to energy‐intensive amine‐based absorption processes. Herein, the adsorption of binary H₂S/CH₄ and H₂S/C₂H₆ mixtures in the all‐silica forms of 386 zeolitic frameworks is investigated using Monte Carlo simulations. Adsorption of a five‐component mixture is utilized to evaluate the performance of the 16 most promising materials under close‐to‐real conditions. It is found that depending on the fractions of CH₄, C₂H₆, and CO₂, different sorbents allow for optimal H₂S removal and hydrocarbon recovery.     

Analysis of sulfur-containing compounds in ambient air using solid-phase microextraction and gas chromatography with pulsed flame photometric detection

A new analysis method for sulfur-containing compounds in air using solid-phase microextraction (SPME), gas chromatography and pulsed flame photometric detection (PFPD), SPME-GC-PFPD method, has been developed. The analysis method is simple, fast and easily performed. To demonstrate the usefulness and versatility of the method air samples collected in geothermal areas in Rotorua, at a muddy beach in Auckland (cities in New Zealand), and in a wastewater treatment plant were analysed. COS, H₂S, CS₂, SO₂, CH₃SH, (CH₃)₂S and CH₃(CH₂)₂CH₂SH were identified in the samples from Rotorua. It was noted that air quality in residential areas with respect to sulfur compounds was better than that around geothermal sources. Samples from the wastewater treatment plant contained COS, H₂S, CS₂, SO₂, CH₃SH, (CH₃)₂S and (CH₃)₂S₂. It was found that the emission of sulfur compounds was reduced in the course of the wastewater treatment process. The potential impact of the detected sulfur compounds on human health is briefly discussed.     

FTIR spectra of matrix isolated complexes between sulfur compounds

The matrix isolation technique has been coupled with Fourier transform infrared spectroscopy to isolate and to characterize the complex between methanethiol and dimethyl sulfide as well as the complexes between sulfur dioxide and a series of dialkyl sulfides including (CH₃)₂S, (C₂H₅)₂S and CH₃SC₂H₅. The 1:1 CH₃SH-S(CH₃)₂ complex was isolated and characterized by the i.r. frequency shifts of the sub-molecule methanethiol. In each of the SO₂/sulfide systems, evidence was obtained for the formation of a 1:1 complex through the disulfide interaction. Vibrational assignments were also suggested for the 1:2, sulfide-(SO₂)₂, complexes.     

The performance of a Ru?Mo sulfide catalyst for H2S decomposition

A γ-alumina-supported bimetallic Ru-Mo sulfide catalyst preparedvia precipitation from homogeneous solution (PFHS) has been used to effect the abstraction of H₂ from H₂S. The decomposition reaction was also carried out over Al₂O₃-supported RuS₂ and MoS₂ catalysts synthesizedvia PFHS. The performance of bimetallic system exceeded (ca. 40%) the simple additive activities of the constituent monometallic sulfide catalysts and about 2–3 times the individual activities of the monometallic sulfide samples, suggesting chemical synergism between Ru and Mo in the Ru-Mo catalyst. In particular, comparison with other catalysts in the literature showed that specimens preparedvia PFHS exhibited better activities than those from direct sulfidation of the metal oxide. Kinetic study over the Ru-Mo bimetallic sulfide catalyst in a quartz micro-reactor at 110 kPa and between 783–973 K revealed a 1st order dependency on H₂S partial pressure and an activation energy of about 92 kJ mol⁻¹. The irreversible adsorption of H₂S on a coordinatively unsaturated site is thought to be the rate-limiting step.     

The effect of ionization and CH3 ligand for hydrogen storage in Co‐ and Ni‐based organometallic compounds

Maximum capacities of the hydrogen storage in organometallic compounds consisting of Co and Ni atoms bound to C_mH_m ring (m = 4, 5; capped type) were, respectively, found as 3.48 and 3.49 wt % (Guo et al., Struct Chem, 2009, 20, 1107). Here, we extend this study to structures having a transition metal (TM) inserted in C_mH_m ring (inserted type), having TM located on either a C₄H or a C₅H molecule, and the CH₃ ligand bound to the organometallic compounds. We find that for the CoC₄H₄ and NiC₄H₄ complexes, the capped types are 1.39 eV and 1.41 eV higher in energy than the inserted types, respectively, while the ground states for CoC₅H₅ and NiC₅H₅ complexes are found to be the capped type, which are lower than the inserted types, respectively, by 1.27 eV and 1.31 eV. The maximum capacity of hydrogen storage reached 5.13 wt % for both of CoC₄H(H₂)₃ complex and the inserted‐type CoC₄H₄(H₂)₃ complex with a reasonable binding energy (0.3–1.0 eV per H₂). The positively charged C₄H₄ and C₅H₅ molecules do not only improve the capacity of hydrogen storage but also make all H₂ adsorbing in molecular form and keep the adsorption energy in an ideal range. After adding the CH₃ ligand to the compounds, the average adsorption energy of H₂ decreased to an ideal range 0.61–0.94 eV per H₂ and the stability of the compounds is also improved. Finally, we analyze the HOMO–LUMO gaps and display the kinetic stability when H₂ was added to organometallic compounds. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

The reactions of hydrogen atoms with bis(trifluoromethyl)disulfide

The reactions of hydrogen atoms produced by the mercury-photosensitized decomposition of H₂ with bis(trifluoromethyl)disulfide has been studied. The rate coefficient for the primary reaction, H + CF₃SSCF₃ → CF₃SH + CF₃S, was determined in competition with the reaction H + C₂H₄S → SH + C₂H₄ to have the value k = (3.0 ± 0.18) × 10¹⁴ exp[-(4560 ± 140)/RT] cm³ mol^?1 S^?1. The high A factor can be partially accounted for by assuming free rotation for the two CF₃ groups and the SCF₃ groups about the S—S bond in the transition state. The relatively high activation energy is attributed to inductive and orbital overlap effects. CH₃SH, H₂S, and CF₃SH all react with CF₃SSCF₃ to yield solid complexes which were not explored further.     

An Exploratory Flow Reactor Study of H2S Oxidation at 30–100 Bar

Hydrogen sulfide oxidation experiments were conducted in O₂/N₂ at high pressure (30 and 100 bar) under oxidizing and stoichiometric conditions. Temperatures ranged from 450 to 925 K, with residence times of 3–20 s. Under stoichiometric conditions, the oxidation of H₂S was initiated at 600 K and almost completed at 900 K. Under oxidizing conditions, the onset temperature for reaction was 500–550 K, depending on pressure and residence time, with full oxidization to SO₂ at 550–600 K. Similar results were obtained in quartz and alumina tubes, indicating little influence of surface chemistry. The data were interpreted in terms of a detailed chemical kinetic model. The rate constants for selected reactions, including SH + O₂ ⇄ SO₂ + H, were determined from ab initio calculations. Modeling predictions generally overpredicted the temperature for onset of reaction. Calculations were sensitive to reactions of the comparatively unreactive SH radical. Under stoichiometric conditions, the oxidation rate was mostly controlled by the SH + SH branching ratio to form H₂S + S (promoting reaction) and HSSH (terminating). Further work is desirable on the SH + SH recombination and on subsequent reactions in the S₂ subset of the mechanism. Under oxidizing conditions, a high O₂ concentration (augmented by the high pressure) causes the termolecular reaction SH + O₂ + O₂ → HSO + O₃ to become the major consumption step for SH, according to the model. Consequently, calculations become very sensitive to the rate constant and product channels for the H₂S + O₃ reaction, which are currently not well established.