Study of quenching of S2 emission by addition of oxygen to a hydrogen flame in molecular emission cavity analysis

Interferences of oxygen on S₂ emission were measured for a hydrogen-oxgen flame in molecular emission cavity analysis and are discussed in terms of the emission intensities and temperatures in different regions of the flame. When a little oxygen is added to a hydrogen flame, S₂ emission is usually quenched. It also brings about a reduction in temperature in the lower region of the flame, where a cavity is introduced. However, in a “lower burnt hydrogen-oxygen flame”, in which hydrogen reacts instantly with added oxygen at the burner top, S₂ emission is not quenched by addition of oxygen, and the intensity and the flame temperature increase linearly with increasing oxygen flow-rate. Therefore, it is apparent that an increase in flame temperature is not responsible for the quenching. It is suggested that the existence of unburnt oxygen in the lower region of the flame can cause the quenching owing to the destruction of S₂ molecules to form sulphur-oxygen compounds.     

TG-MS与Py-GC相结合法研究惰性气氛下含硫模型化合物热解过程中硫的脱除及释放行为研究

采用热重-质谱法(TG-MS)和热解-气相色谱法(Py-MS)相结合的方法对模型化合物(十四硫醇、二丁基硫醚、苯硫醚、二甲基噻吩、苯并噻吩和二苯并噻吩等)在惰性气氛下硫的脱除及释放行为进行研究。惰性气氛下硫的脱除顺序为:十四硫醇>二丁基硫醚>二甲基噻吩>苯并噻吩>苯硫醚>二苯并噻吩,苯硫醚除外,该顺序与含硫官能团的热分解顺序一致。在热解过程中,所有模型化合物在质谱和气相色谱仪上均被检测到SO₂;除苯硫醚和二苯并噻吩外,其他模型化合物中均检测到了COS;而只在十四硫醇、二丁基硫醚和二甲基噻吩中检测到了H₂S。且热解气中SO₂含量要显著高于H₂S和COS。这是由于活性炭作载体时,惰性气氛下内部氢的含量显著小于内部氧的含量,所以大多数的含硫自由基易与内部氧结合以SO₂的形式逸出。对于苯硫醚、苯并噻吩和二苯并噻吩中没有检测到H₂S,是由于内部氢的不足,使得含硫自由基不能与内部氢结合,所以没有检测到H₂S逸出。     

Development of novel and sensitive methods for the determination of sulfide in aqueous samples by hydrogen sulfide generation-inductively coupled plasma-atomic emission spectroscopy

Two new, simple and accurate methods for the determination of sulfide (S²⁻) at low levels (μg L⁻¹) in aqueous samples were developed. The generation of hydrogen sulfide (H₂S) took place in a coil where sulfide reacted with hydrochloric acid. The resulting H₂S was then introduced as a vapor into an inductively coupled plasma-atomic emission spectrometer (ICP-AES) and sulfur emission intensity was measured at 180.669 nm. In comparison to when aqueous sulfide was introduced, the introduction of sulfur as H₂S enhanced the sulfur signal emission. By setting a gas separator at the end of the reaction coil, reduced sulfur species in the form of H₂S were removed from the water matrix, thus, interferences could be avoided. Alternatively, the gas separator was replaced by a nebulizer/spray chamber combination to introduce the sample matrix and reagents into the plasma. This methodology allowed the determination of both sulfide and sulfate in aqueous samples. For both methods the linear response was found to range from 5 μg L⁻¹ to 25 mg L⁻¹ of sulfide. Detection limits of 5 μg L⁻¹ and 6 μg L⁻¹ were obtained with and without the gas separator, respectively. These new methods were evaluated by comparison to the standard potentiometric method and were successfully applied to the analysis of reduced sulfur species in environmental waters.     

Degradation of organic sulfur compounds by a coal-solubilizing Fungus

Paecilomyces sp. TLi, a coal-solubilizing fungus, was shown to degrade organic sulfur-containing coal substructure compounds. Di-benzothiophene was degraded via a sulfur-oxidizing pathway to 2,2′-dihydroxybiphenyl. No further metabolism of that compound was observed. Ethyl phenyl sulfide and diphenyl sulfide were degraded to the corresponding sulfones. A variety of products were formed from dibenzyl sulfide, presumably via free radical intermediates. Diphenyl disulfide and dibenzyl disulfide were cleaved to the corresponding thiols and other single-ring products. It was concluded that degradation of organic sulfur compounds byPaecilomyces involves an oxidative attack localized at the sulfur atom.     

Control of Redox Events by Dye Encapsulation Applied to Light‐Driven Splitting of Hydrogen Sulfide

Solar production of hydrogen by consuming low‐value waste products is an attractive pathway that has both economic and environmental benefits. Inspired by the reactive pocket of enzymes, a synthetic platform to combine photocatalytic hydrogen evolution with sulfide oxidation in a one‐pot process via control over the location of the electron‐transfer steps is developed. The redox‐active coordination vessel Ni‐ TFT , which has an octahedral pocket, encapsulates an organic dye to pre‐organize for photocatalytic proton reduction via an oxidative quenching pathway using the nickel corners as catalysts, generating molecular hydrogen and the oxidized dye. The oxidized dye is displaced by a neutral dye and oxidizes sulfide once outside the pocket to give element sulfur. The overall reaction constitutes hydrogen sulfide splitting, forming molecular hydrogen and elemental sulfur, which is analogous to the water‐splitting reaction.     

The synthesis of bismuth sulfide,antimony sulfide,and their solid solutions from tribenzylbismuth,tribenzylantimony, and elemental sulfur

The condensed phase reactions of tribenzylbismuth or tribenzylantimony and elemental sulfur under mild thermal conditions (≤275°C) produces the respective sesquisulfides in good yields and high purity. A mixture of the perbenzylated metals and elemental sulfur produces solid solutions of the general formula (Bi_xSb_1-x)₂S₃. It has been demonstrated that it is possible to achieve synthetic control over the size and microstructure of the as produced metal sulfide particles by simply changing reaction conditions. In combination with the condensed phase pyrolysis of tris(benzylthiolato)bismuth, five different microstructures for bismuth sulfide are accessible through compounds containing the benzyl ligand.     

Electrosynthesis of biologically active dicycloalkyl di- and trisulfides involving an H<Subscript>2</Subscript>S—S<Subscript>8</Subscript> redox system

Biologically active dicycloalkyl di- and trisulfides were prepared by the reactions of cycloalkanes C₅—C₇ with H₂S and S₈ under the anodic (cathodic) activation of hydrogen sulfide. In dichloromethane, the electrochemical activation of H₂S in the presence of sulfur can generate sulfur-centered radical intermediates that react with cycloalkanes at room temperature. The current yield of di- and trisulfides depends on the method of redox activation of hydrogen sulfide, the concentration of sulfur, and the time of electrosynthesis. The anodic activation of hydrogen sulfide in the synthesis of dicycloalkyl di- and trisulfides in an excess S8 is more efficient than the cathodic activation. In the series of cycloalkanes C₅—C₇, the highest yield of sulfur-containing products is observed for cycloheptane.     

Effects of chromium ion on sulfur removal during pyrolysis and hydropyrolysis of coal

The effects of impregnated Cr³⁺ on sulfur removal during pyrolysis and hydropyrolysis of coal were investigated by loading CrCl₃ into raw, demineralized and pyrite removed coal, respectively. The results indicate that Cr has no effect on the removal of pyrite. Cr affects the removal of total sulfur by forming Cr₇S₈ and affecting the removal of organic sulfur. Cr acts as the sulfur removing agent by promoting the decomposition of the unstable organic sulfur at low temperature. However, it behaves to be sulfur fixing agent between 400 and 700 °C so as to inhibit the evolution of H₂S, even in hydropyrolysis. With the increase of temperature from 700 to 1050 °C, a certain ratio of Cr₇S₈ is converted into organic sulfur during pyrolysis; however, almost all the Cr₇S₈ is reduced into Cr at 1050 °C during hydropyrolysis. And Cr significantly promotes the removal of organic sulfur at high temperature within reducing atmosphere. The XPS results indicate that the sulfur is enriched on coke surface by Cr, which is attributable to the formation of Cr₇S₈ as well as the transfer of organic sulfur from bulk to surface during pyrolysis and hydropyrolysis.     

Indirect determination of cyanide by molecular emission cavity analysis

Nanogram amounts of cyanide were indirectly determined by molecular emission cavity analysis. The method is based on the reaction of cyanide with sulphite-formaldehyde addition compound and the measurement of the S₂ emission produced either from the sulphite released or from the addition compound. The relative standard deviations are 2.13% and 1.66% and the recoveries are 99% and 100% using the released sulphite peak and the addition compound peak, respectively. Potential interfering anions were investigated.     

Low-temperature catalytic decomposition of hydrogen sulfide into hydrogen and diatomic gaseous sulfur

The thermodynamics of three pathways of the hydrogen sulfide decomposition reaction is considered. In the thermal process, the gas-phase dissociation of hydrogen sulfide yields hydrogen and diatomic singlet sulfur. Over sulfide catalysts, the reaction proceeds via the formation of disulfane (H₂S₂) as the key surface intermediate. This intermediate then decomposes to release hydrogen into the gas phase, and adsorbed singlet sulfur recombines into cyclooctasulfur. Over metal catalysts, H₂S decomposes via dissociation into surface atoms followed by the formation of gaseous hydrogen and gaseous triplet disulfur. The last two pathways are thermodynamically forbidden in the gas phase and can take place at room temperature only on the surface of a catalyst. An alternative mechanism is suggested for hydrogen sulfide assimilation in the chemosynthesis process involving sulfur bacteria. To shift the hydrogen sulfide decomposition equilibrium toward the target product (hydrogen), it is suggested that the reaction should be conducted at room temperature as a three-phase process over a solid catalyst under a layer of a solvent that can dissolve hydrogen sulfide and sulfur. In this case, it is possible to attain an H₂S conversion close to 100%. Therefore, hydrogen sulfide can be considered as an inexhaustible source of hydrogen, a valuable chemical and an environmentally friendly energetic product.     

Molecular emission cavity analysis : Part XI. The determination of carbonyl compounds

Formaldehyde (2–750 μg), acetaldehyde (0.05–1.0 μg) and acetone (0.4–3.5 smg) can be determined in aqueous solution (? 17.5 ml) by MECA. Sodium sulphite solution (5 ml, 500 p.p.m. S) and 1.5 ml of l M phosphoric acid are added and the delayed S₂ emission from the sulphite addition compound in 5 ml of the solution is measured in a MECA cavity; a hydrogen-nitrogen flame is used. Mixtures of formaldehyde and acetone can be determined simultaneously on the basis of the resolved MECA peaks of their sulphite addition compounds, after evaporation of the excess of sulphite from the cavity.     

Sulfurization of γ-oxo esters; study of the resulting sulfur compounds

Abstract

Treatment of aliphatic γ-oxo esters with hydrogen chloride/hydrogen sulfide gives three sulfur compounds: an alkyl-5-mercaptothiolan-2-one, an alkyl-4-thiolen-2-one and an alkyl-3-thiolen-2-one. Chemical properties of these products are reported. With aromatic γ-oxo esters we obtain a thiophenic compound.     

HIGH TEMPERATURE REACTIONS OF HYDROGEN SULFIDE AND THIOLS WITH ORGANIC COMPOUNDS

Abstract

The high temperature reaction of hydrogen sulfide with chloro- and bromosubstituted aromatic and heteroaromatic compounds is a convenient method for synthesis of the corresponding thiols and sulfides. The reaction of hydrogen sulfide with ortho-dihalosubstituted aromatic compounds may be directed toward the formation of thianthrene or dibenzo thiophene and their derivatives. The high temperature reaction of thiophenol with chloro- and bromoderivatives of aromatic and heteroaromatic compounds affords the corresponding mixed sulfides. The reaction with ortho-substituted halogen derivatives leads to formation of the sulfur heterocycles of the thianthrene, thioxanthene and dibenzothiophenene series.

The high temperature reaction of hydrogen sulfide with vinyl chloride gives vinylthiol and thiophene. Hydrogen sulfide initiates pyrolytic transformations of thiophene, aniline and benzaldehyde into dithienyls, 5.10-dihydrophenazine and stilbene, respectively. The reaction mechanism has been discussed.     

Molecular emission cavity analysis: Part 20. Indirect determination of amines by their reaction with the formaldehyde—sulphite addition compound

Aromatic and aliphatic amines and hydrazine in the range 1–30 × lO^-5 M are determined by measuring the S₂ emission in a carbon cavity held in a hydrogen—nitrogen flame arising from the formation of an addition compound between the amine, formaldehyde and sulphite. As little as 1.8 ng of aniline in 5 μl (4 × 10^-6 M) can be detected.     

Decomposition of Picolyl Radicals at High Temperature: A Mass Selective Threshold Photoelectron Spectroscopy Study

The reaction products of the picolyl radicals at high temperature were characterized by mass-selective threshold photoelectron spectroscopy in the gas phase. Aminomethylpyridines were pyrolyzed to initially produce picolyl radicals (m/z=92). At higher temperatures further thermal reaction products are generated in the pyrolysis reactor. All compounds were identified by mass-selected threshold photoelectron spectroscopy and several hitherto unexplored reactive molecules were characterized. The mechanism for several dissociation pathways was outlined in computations. The spectrum of m/z=91, resulting from hydrogen loss of picolyl, shows four isomers, two ethynyl pyrroles with adiabatic ionization energies (IE_ad) of 7.99 eV (2-ethynyl-1H-pyrrole) and 8.12 eV (3-ethynyl-1H-pyrrole), and two cyclopentadiene carbonitriles with IE′s of 9.14 eV (cyclopenta-1,3-diene-1-carbonitrile) and 9.25 eV (cyclopenta-1,4-diene-1-carbonitrile). A second consecutive hydrogen loss forms the cyanocyclopentadienyl radical with IE′s of 9.07 eV (T₀) and 9.21 eV (S₁). This compound dissociates further to acetylene and the cyanopropynyl radical (IE=9.35 eV). Furthermore, the cyclopentadienyl radical, penta-1,3-diyne, cyclopentadiene and propargyl were identified in the spectra. Computations indicate that dissociation of picolyl proceeds initially via a resonance-stabilized seven-membered ring.     

Perfluorotetramethylenesulfur difluoride and its derivatives. Perfluoro-1,3-dithietane octafluoride and perfluoro-1,4-dithiane octafluoride

The fluorination of perfluorotetramethylene sulfide with chlorine monofluoride under controlled conditions results in the formation of both sulfur(IV) and sulfur(VI) compounds as main products. While perfluorotetramethylenesulfur tetrafluoride is very stable to thermolysis and to chemical attack, the hydrolysis of the novel perfluorotetramethylenesulfur difluoride affords perfluorotetramethylene sulfoxide, and its pyrolysis gives perfluro(di-n-butyl)disulfide. Chlorine monofluoride converts perfluorotetramethylene sulfoxide to perfluorotetramethyl-enesulfur oxyfluoride, and perfluorotetramethylene sulfone is obtained quantitatively as a decomposition product in contact with Pyrex glass. Perfluoro-1,3-dithietane octafluoride and perfluoro-1,4-dithiane octafluoride are also formed by the reaction of corresponding perfluorocyclic sulfides with CIF at ambient temperature. Infrared, mass and ¹⁹F NMR spectroscopic as well as thermodynamic data are reported.     

Analysis of atmospheric sulfur gases by capillary gas chromatography with atomic emission detection

The atomic emission detector (AED) has been found to be a sensitive and selective instrument for analysis of atmospheric sulfur gases by capillary gas chromatography. It was possible to determine atmospheric dimethyl sulfide at concentrations below 0.3 nmol/m³ typical of the remote marine environment in winter. Sample analyses from the Australian Baseline Air Pollution Station, Cape Grim, are used to illustrate this. In comparison with other sulfur-specific detectors previously used for this work, the AED has been found to exhibit the best combination of specificity and sensitivity. A configuration comprising a series of valves, gas calibration loops, and a cryogenic trap prior to the GC-AED was used for sample analysis. Standard addition of sulfur hexafluoride was found to assist determination of carbonyl sulfide, as it could be used to take into account the magnitude of signal quenching from coeluting gases. The AED was also found to be a selective detector for the direct injection of water-soluble dimethyl sulfide oxidation products.     

The cleavage mechanism of 1,4-dithiaspiro(4.4)nonane by gas-phase pyrolysis

The initial product formed in the pyrolysis of 1,4-dithiaspiro(4.4)nonane (I) is the thioketone (7). During pyrolysis at 600 °C, this material has been isolated in absolute yields as high as 4.85%. The increase in yield of benzene (1), toluene (3), and naphthalene (14) as the temperature is increased from 600 to 800 °C could be anticipated from dehydrogenation under pyrolysis conditions.The other products isolated, with the exception of the rearrangement products and toluene, appear to arise via further pyrolytic reaction of thioketone (7). These saturated products are dehydrogenated by sulfur to generate the aromatic compounds.     

Continuous-flow molecular emission cavity analysis for sulphide

Sulphide (1–10 μg ml^?1) is determined by mixing the sample with an excess of orthophosphoric acid in a segmented continuous-flow system. The hydrogen sulphide evolved is swept into the cavity for generation of S₂ emission. The analysis is completely automated, requires no sample pretreatment and samples can be analyzed at 24 h^?1.     

Determination of chlorpromazine hydrochloride in tablets by molecular emission cavity analysis

Sulphur in chlorpromazine hydrochloride (2–50 mg) is oxidized by dichromate in condensed phosphoric acid (CPA) to sulphate, which in turn is reduced to hydrogen sulphide by heating with tin dissolved in CPA. The gas is carried by nitrogen to a steel cavity situated in a hydrogen/nitrogen flame and the S₂ emission is measured at 384 nm. The method is applied to determine the drug in powdered tablets. No sample pretreatment is needed; the procedure takes 10 min.