- Isomers of HSCO: IR absorption spectra of t-HSCO in solid Ar.
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Irradiation of an Ar matrix sample containing H2S and CO (or OCS) with an ArF excimer laser at 193 nm yields trans-HSCO (denoted t-HSCO). New lines at 1823.3, 931.6, and 553.3 cm(-1) appear after photolysis and their intensity enhances after annealing; secondary photolysis at 248 nm diminishes these lines and produces OCS and CO. These lines are assigned to C-O stretching, HSC-bending, and C-S stretching modes of t-HSCO, respectively, based on results of 13C-isotopic experiments and theoretical calculations. Theoretical calculations using density-functional theories (B3LYP and PW91PW91) predict four stable isomers of HSCO: t-HSCO, c-HSCO, HC(O)S, and c-HOCS, listed in increasing order of energy. According to calculations with B3LYP/aug-cc-pVTZ, t-HSCO is planar, with bond lengths of 1.34 A (H-S), 1.81 A (S-C), and 1.17 A (C-O), and angles angle HSC congruent with 93.4 degrees and angle SCO congruent with 128.3 degrees; it is more stable than c-HSCO and HC(O)S by approximately 9 kJ mol(-1) and more stable than c-HOCS by approximately 65 kJ mol(-1). Calculated vibrational wave numbers, IR intensities, and 13C-isotopic shifts for t-HSCO fit satisfactorily with experimental results. This new spectral identification of t-HSCO provides information for future investigations of its roles in atmospheric chemistry. (c) 2004 American Institute of Physics
- Lo, Wen-Jui,Chen, Hui-Fen,Wu, Yu-Jong,Lee, Yuan-Pern
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- Carbonyl sulfide hydrolase from thiobacillus thioparus strain thi115 is one of the β-carbonic anhydrase family enzymes
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Carbonyl sulfide (COS) is an atmospheric trace gas leading to sulfate aerosol formation, thereby participating in the global radiation balance and ozone chemistry, but its biological sinks are not well understood. Thiobacillus thioparus strain THI115 can grow on thiocyanate (SCN-) as its sole energy source. Previously, we showed that SCN- is first converted to COS by thiocyanate hydrolase in T. thioparus strain THI115. In the present work, we purified, characterized, and determined the crystal structure of carbonyl sulfide hydrolase (COSase), which is responsible for the degradation of COS to H2S and CO2, the second step of SCN- assimilation. COSase is a homotetramer composed of a 23.4 kDa subunit containing a zinc ion in its catalytic site. The amino acid sequence of COSase is homologous to the β-class carbonic anhydrases (β-CAs). Although the crystal structure including the catalytic site resembles those of the β-CAs, CO2 hydration activity of COSase is negligible compared to those of the β-CAs. The α5 helix and the extra loop (Gly150-Pro158) near the N-terminus of the α6 helix narrow the substrate pathway, which could be responsible for the substrate specificity. The k cat/Km value, 9.6 × 105 s-1 M-1, is comparable to those of the β-CAs. COSase hydrolyzes COS over a wide concentration range, including the ambient level, in vitro and in vivo. COSase and its structurally related enzymes are distributed in the clade D in the phylogenetic tree of β-CAs, suggesting that COSase and its related enzymes are one of the catalysts responsible for the global sink of COS.
- Ogawa, Takahiro,Noguchi, Keiichi,Saito, Masahiko,Nagahata, Yoshiko,Kato, Hiromi,Ohtaki, Akashi,Nakayama, Hiroshi,Dohmae, Naoshi,Matsushita, Yasuhiko,Odaka, Masafumi,Yohda, Masafumi,Nyunoya, Hiroshi,Katayama, Yoko
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- Rate Constant for the Reaction between OH and CS2 at 298 and 520 K
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In an attempt to resolve discrepancies between published values of the rate constant for the reaction between hydroxyl radical and carbon disulfide, the reaction has been studied in a discharge flow system by using resonance fluorescence for kinetic measurements and mass spectrometry for product analysis.On the basis of the measured rate constant for disappearance of OH and measurements of the amount of carbonyl sulfide formed, it was estimated that for the reaction HO + CS2 -> HS + OCS, k 3s-1 at 520 K and 3s-1 at 298 K, upper limits being specified because of the inability to isolate exclusively this reaction channel, and because of possible involvement of wall reactions.These results confirm the low values found for this rate constant in two very recent studies.
- Leu, Ming-Taun,Smith, Roland H.
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- Selection of the type of methane conversion for catalytic reduction of sulfur dioxide
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Catalytic reduction of sulfur dioxide with converted gas obtained by various methods of conversion of natural gas was studied to select the most active reducing agent for SO2. Pleiades Publishing, Ltd., 2012.
- Kasumova
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- Direct formation of Ge-C bonds from GeO2
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Germanium dioxide in the presence of 5% KOH reacted with dimethyl carbonate (DMC) at 250 °C to give (MeO)4Ge. The reaction of GeO2 and DMC is similar to that reported for SiO2; however, the rate of reaction for germanium is much higher than that of the corresponding silicon reaction. In a side-by-side experiment using SiO2 and GeO2 where the surface area of the silicon dioxide was 2 orders of magnitude higher than that of the GeO2, the base-catalyzed reaction with DMC was about an order of magnitude higher for the germanium dioxide. When GeO2 and 5% KOH were reacted with DMC at 350 °C, two products formed: (MeO)4Ge (70%) and MeGe(OMe)3 (30%). Confirmation of the identity of MeGe(OMe)3 was by GCMS, 1H and 13C NMR, and comparison to an authentic sample made by reaction of MeGeCl3 with NaOMe. Experiments to determine the mechanism of the direct formation of Ge-C from GeO2 ruled out participation from CO, H2, or carbon. The KOH-catalyzed reaction of other metal oxides was explored including B2O3, Ga2O3, TiO2, Sb2O3, SnO2, and SnO. Boron reacted to give unknown volatile products. Antimony reacted to give a solid which analyzed as Sb(OMe)3. SnO reacted with DMC to give a mixture that included (MeO)4Sn and possibly Me3Sn(OMe).
- Lewis, Larry N.,Litz, Kyle E.,Anostario, Joseph M.
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- Synthesis and reactivity of a nickel(ii) thioperoxide complex: Demonstration of sulfide-mediated N2O reduction
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The thiohyponitrite ([SNNO]2-) complex, [K(18-crown-6)][LtBuNiII(κ2-SNNO)] (LtBu = {(2,6-iPr2C6H3)NC(tBu)}2CH), extrudes N2 under mild heating to yield [K(18-crown-6)][LtBuNiII(η2-SO)] (1), along with minor products [K(18-crown-6)][LtBuNiII(η2-OSSO)] (2) and [K(18-crown-6)][LtBuNiII(η2-S2)] (3). Subsequent reaction of 1 with carbon monoxide (CO) results in the formation of [K(18-crown-6)][LtBuNiII(η2-SCO)] (4), [K(18-crown-6)][LtBuNiII(S,O:κ2-SCO2)] (5), [K(18-crown-6)][LtBuNiII(κ2-CO3)] (6), carbonyl sulfide (COS) (7), and [K(18-crown-6)][LtBuNiII(S2CO)] (8). To rationalize the formation of these products we propose that 1 first reacts with CO to form [K(18-crown-6)][LtBuNiII(S)] (I) and CO2, via O-atom abstraction. Subsequently, complex I reacts with CO or CO2 to form 4 and 5, respectively. Similarly, the formation of complex 6 and COS can be rationalized by the reaction of 1 with CO2 to form a putative Ni(ii) monothiopercarbonate, [K(18-crown-6)][LtBuNiII(κ2-SOCO2)] (11). The Ni(ii) monothiopercarbonate subsequently transfers a S-atom to CO to form COS and [K(18-crown-6)][LtBuNiII(κ2-CO3)] (6). Finally, the formation of 8 can be rationalized by the reaction of COS with I. Critically, the observation of complexes 4 and 5 in the reaction mixture reveals the stepwise conversion of [K(18-crown-6)][LtBuNiII(κ2-SNNO)] to 1 and then I, which represents the formal reduction of N2O by CO.
- Hartmann, Nathaniel J.,Wu, Guang,Hayton, Trevor W.
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- Hydrogen Sulfide Induced Carbon Dioxide Activation by Metal-Free Dual Catalysis
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The role of metal free dual catalysis in the hydrogen sulfide (H2S)-induced activation of carbon dioxide (CO2) and subsequent decomposition of resulting monothiolcarbonic acid in the gas phase has been explored. The results suggest that substituted amines and monocarboxylic type organic or inorganic acids via dual activation mechanisms promote both activation and decomposition reactions, implying that the judicious selection of a dual catalyst is crucial to the efficient C-S bond formation via CO2 activation. Considering that our results also suggest a new mechanism for the formation of carbonyl sulfide from CO2 and H2S, these new insights may help in better understanding the coupling between the carbon and sulfur cycles in the atmospheres of Earth and Venus. It's a gas, gas, gas: The role of metal-free dual catalysis in the hydrogen sulfide-induced activation of carbon dioxide has been explored by means of quantum chemical calculations. These results suggest a new mechanism for the formation of carbonyl sulphide in the atmospheres of Earth and Venus.
- Kumar, Manoj,Francisco, Joseph S.
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- Mechanistic aspects of ketene formation deduced from femtosecond photolysis of diazocyclohexadienone, o-phenylene thioxocarbonate, and 2-chlorophenol
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The photochemistry of diazocyclohexadienone (1), o-phenylene thioxocarbonate (2), and 2-chlorophenol (3) in solution was studied using time-resolved UV-vis and IR transient absorption spectroscopies. In these three cases, the same product cyclopentadienyl ketene (5) is formed, and two different mechanistic pathways leading to this product are discussed: (a) rearrangement in the excited state (RIES) and (b) a stepwise route involving the intermediacy of vibrationally excited or relaxed carbene. Femtosecond UV-vis detection allows observation of an absorption band assigned to singlet 2-oxocyclohexa-3,5- dienylidene (4), and this absorption feature decays with an ～30 ps time constant in hexane and acetonitrile. The excess vibrational energy present in nascent carbenes results in the ultrafast Wolff rearrangement of the hot species. IR detection shows that photoexcited o-phenylene thioxocarbonate (2) and 2-chlorophenol (3) efficiently form the carbene species while diazocyclohexadienone (1) photochemistry proceeds mainly by a concerted process.
- Burdzinski, Gotard,Kubicki, Jacek,Sliwa, Michel,Réhault, Julien,Zhang, Yunlong,Vyas, Shubham,Luk, Hoi Ling,Hadad, Christopher M.,Platz, Matthew S.
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- Degradation of an acetylene terminated sulfone (ATS) resin I. In an oxygen free environment
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A study of the rates and mechanisms of degradation of an acetylene terminated sulfone resin, more precisely, bis[4-(3-ethynyl phenoxy) phenyl] sulfone and its higher oligomers, under high vacuum conditions, and under a flowing atmosphere of nitrogen, was
- Stevenson,Goldfarb
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- Progress toward colorimetric and fluorescent detection of carbonyl sulfide
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We report here that a fluorescent benzobisimidazolium salt (TBBI) can be used for the fluorescent and colorimetric detection of carbonyl sulfide (COS) over related heterocumulenes including CO2 and CS2 in wet MeCN. The reaction between TBBI and COS in the presence of fluoride yields a highly fluorescent (λem = 354 nm) and colored product (λmax = 321, 621 nm), that is readily observed by the naked eye. We view these results as a first step toward developing activity-based probes for COS detection.
- Cerda, Matthew M.,Fehr, Julia M.,Sherbow, Tobias J.,Pluth, Michael D.
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- Monothiocarbamates Strongly Inhibit Carbonic Anhydrases in Vitro and Possess Intraocular Pressure Lowering Activity in an Animal Model of Glaucoma
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A series of monothiocarbamates (MTCs) were prepared from primary/secondary amines and COS as potential carbonic anhydrase (CA, EC 4.2.1.1) inhibitors, using the dithiocarbamates, the xanthates, and the trithiocarbonates as lead compounds. The MTCs effectively inhibited the pharmacologically relevant human (h) hCAs isoforms I, II, IX, and XII in vitro and showed KIs spanning between the low and medium nanomolar range. By means of a computational study, the MTC moiety binding mode on the CAs was explained. Furthermore, a selection of MTCs were evaluated in a normotensive glaucoma rabbit model for their intraocular pressure (IOP) lowering effects and showed interesting activity.
- Vullo, Daniela,Durante, Mariaconcetta,Di Leva, Francesco Saverio,Cosconati, Sandro,Masini, Emanuela,Scozzafava, Andrea,Novellino, Ettore,Supuran, Claudiu T.,Carta, Fabrizio
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- Infrared chemiluminescence studies of the H+(CH3)3COCl and H+RC(O)SCl (R = Cl, F, OCH3) reactions: Observation of OCS infrared chemiluminescence
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Infrared chemiluminescence from a room-temperature flow reactor was used to study the reactions of H atoms with (CH3)3COCl, ClC(O)SCl, FC(O)SCl, and CH3OC(O)SCl. Infrared emission spectra were recorded from the HCl, HF, and OCS products. The anharmonic shifts from bands involving ν1, ν2, and ν3 excitation are too small to obtain information about bending vs stretch excitation of OCS from the Δν3 = -1 spectra; however, a computer simulation method was developed to analyze the Δν3 = -1 transition to assign the average total vibrational energy of OCS, 〈Ev(OCS)〉. The enthalpy changes for the carbonylsulfenyl chloride reactions were estimated from ab initio calculations. The proposed mechanism for the carbonylsulfenyl chlorides includes two reaction pathways: one involves interaction with the S-Cl bond to give HCl; the second involves an RC(O)SCl·H adduct that subsequently gives RH and OCS (+Cl). The 〈Ev(OCS)〉 values were 17.2, 14.6, and 8.4 kcal mol-1 from FC(O)SCl, CH3OC(O)SCl, and ClC(O)SCl, respectively. The fraction of the available energy released as HCl vibrational energy, {fv(HCl)〉, from reaction with the S-Cl bond was approximately 0.3 for all three reactions. The reaction mechanism for H+(CH3)3COCl, which was employed as a reference reaction, is thought to be direct abstraction and 〈fv(HCl)〉 is 0.23.
- Manke II,Setser
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- Experimental and theoretical studies on bis(chlorocarbonyl)trisulfane, ClC(O)SSSC(O)Cl
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Bis(chlorocarbonyl)trisulfane, ClC(O)SSSC(O)Cl, was prepared by the reaction of (CH3)2CHOC(S)SC(S)OCH(CH3)2 and SO2Cl2 at 65 °C. The compound was characterized and identified by vibrational
- Tobón, Yeny A.,Cozzarín, Melina V.,Della Védova, Carlos O.,Romano, Rosana M.
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- 96: A Giant Self-Assembled Copper(I) Supramolecular Wheel Exhibiting Photoluminescence Tuning and Correlations with Dynamic Solvation and Solventless Synthesis
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The hierarchical self-organization of structurally complex high-nuclearity metal clusters with metallosupramolecular wheel architectures that are obtained from the self-Assembly of smaller solvated cluster units is rare and unique. Here, we use the potentially heteroditopic monothiocarbonate ligand and demonstrate for the first time the synthesis and structure of a solvated non-cyclic hexadecanuclear cluster [Cu{SC(O)OiPr}]16·2THF (1) that can simultaneously desolvate and self-Assemble in solution and subsequently form a giant metallaring, [Cu{SC(O)OiPr}]96 (2). We also demonstrate a luminescent precursor to cluster (2) can be achieved through a solventless and rapid mechanochemical synthesis. Cluster (2) is the highest nuclearity copper(I) wheel and the largest metal cluster containing a heterodichalcogen (O, S) ligand reported to date. Cluster (2) also exhibits solid-state luminescence with relatively long emission lifetimes at 4.1, 13.9 (μs). The synthetic strategy described here opens new research avenues by replacing solvent molecules in stable {Cu16} clusters with designed building units that can form new hybrid and multifunctional finite supramolecular materials. This finding may lead to the development of novel high-nuclearity materials self-Assembled in a facile manner with tunable optical properties.
- Gupta, Arvind K.,Kishore, Pilli V. V. N.,Cyue, Jhih-Yu,Liao, Jian-Hong,Duminy, Welni,Van Zyl, Werner E.,Liu
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- C-Nitrosothioformamide: A Donor Template for Dual Release of HNO and H2S
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C-Nitrosothioformamide was demonstrated to be a donor template for dual release of HNO and COS triggered by a retro-Diels-Alder reaction. COS is an H2S precursor in the presence of carbonic anhydrase. This process produces HNO and H2S in a slow but steady manner. As such, the direct reaction between HNO and H2S under this situation appears to be minor. This may provide a useful tool for studying the synergistic effects of HNO and H2S.
- Kelly, Shane S.,Ni, Xiang,Radford, Miles N.,Xian, Ming,Yuen, Vivian
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- Alkylsulfenyl thiocarbonates: precursors to hydropersulfides potently attenuate oxidative stress
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The recent discovery of the prevalence of hydropersulfides (RSSH) species in biological systems suggests their potential roles in cell regulatory processes. However, the reactive and transient nature of RSSH makes their study difficult, and dependent on the use of donor molecules. Herein, we report alkylsulfenyl thiocarbonates as a new class of RSSH precursors that efficiently release RSSH under physiologically relevant conditions. RSSH release kinetics from these precursors are tunable through electronic modification of the thiocarbonate carbonyl group's electrophilicity. In addition, these precursors also react with thiols to release RSSH with a minor amount of carbonyl sulfide (COS). Importantly, RSSH generation by these precursors protects against oxidative stress in H9c2 cardiac myoblasts. Furthermore, we demonstrate the ability of these precursors to increase intracellular RSSH levels.
- Aggarwal, Sahil C.,Khodade, Vinayak S.,Paolocci, Nazareno,Pharoah, Blaze M.,Toscano, John P.
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p. 8252 - 8259
(2021/06/22)
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- Insights into the Mechanism of Thiol-Triggered COS/H2S Release from N-Dithiasuccinoyl Amines
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The hydrolysis of carbonyl sulfide (COS) to form H2S by carbonic anhydrase has been demonstrated to be a viable strategy to deliver H2S in a biological system. Herein, we describe N-dithiasuccinoyl amines as thiol-triggered COS/H2S donors. Notably, thiol species especially GSH and homocysteine can trigger the release of both COS and H2S directly from several specific analogues via an unexpected mechanism. Importantly, two representative analogues Dts-1 and Dts-5 show intracellular H2S release, and Dts-1 imparts potent anti-inflammatory effects in LPS-challenged microglia cells. In conclusion, N-dithiasuccinoyl amine could serve as promising COS/H2S donors for either H2S biological studies or H2S-based therapeutics development.
- Zhou, Shengchao,Mou, Yujie,Liu, Miao,Du, Qian,Ali, Basharat,Ramprasad, Jurupula,Qiao, Chunhua,Hu, Li-Fang,Ji, Xingyue
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p. 8352 - 8359
(2020/09/07)
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- Alkylamine-Substituted Perthiocarbamates: Dual Precursors to Hydropersulfide and Carbonyl Sulfide with Cardioprotective Actions
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The recent discovery of hydropersulfides (RSSH) in mammalian systems suggests their potential roles in cell signaling. However, the exploration of RSSH biological significance is challenging due to their instability under physiological conditions. Herein, we report the preparation, RSSH-releasing properties, and cytoprotective nature of alkylamine-substituted perthiocarbamates. Triggered by a base-sensitive, self-immolative moiety, these precursors show efficient RSSH release and also demonstrate the ability to generate carbonyl sulfide (COS) in the presence of thiols. Using this dually reactive alkylamine-substituted perthiocarbamate platform, the generation of both RSSH and COS is tunable with respect to half-life, pH, and availability of thiols. Importantly, these precursors exhibit cytoprotective effects against hydrogen peroxide-mediated toxicity in H9c2 cells and cardioprotective effects against myocardial ischemic/reperfusion injury, indicating their potential application as new RSSH- and/or COS-releasing therapeutics.
- Khodade, Vinayak S.,Pharoah, Blaze M.,Paolocci, Nazareno,Toscano, John P.
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supporting information
p. 4309 - 4316
(2020/03/05)
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- Investigation of the reaction pathway for synthesizing methyl mercaptan (CH3SH) from H2S-containing syngas over K-Mo-type materials
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The reaction pathway for synthesizing methyl mercaptan (CH3SH) using H2S-containing syngas (CO/H2S/H2) as the reactant gas over SBA-15 supported K-Mo-based catalysts prepared by different impregnation sequences
- Lu, Jichang,Liu, Pan,Xu, Zhizhi,He, Sufang,Luo, Yongming
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p. 21340 - 21353
(2018/06/26)
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- Inhibition of Mitochondrial Bioenergetics by Esterase-Triggered COS/H2S Donors
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Hydrogen sulfide (H2S) is an important biological mediator, and synthetic H2S donating molecules provide an important class of investigative tools for H2S research. Here, we report esterase-activated H2S donors that function by first releasing carbonyl sulfide (COS), which is rapidly converted to H2S by the ubiquitous enzyme carbonic anhydrase (CA). We report the synthesis, self-immolative decomposition, and H2S release profiles of the developed scaffolds. In addition, the developed esterase-triggered COS/H2S donors exhibit higher levels of cytotoxicity than equivalent levels of Na2S or the common H2S donors GYY4137 and AP39. Using cellular bioenergetics measurements, we establish that the developed donors reduce cellular respiration and ATP synthesis in BEAS 2B human lung epithelial cells, which is consistent with COS/H2S inhibition of cytochrome c oxidase in the mitochondrial respiratory chain although not observed with common H2S donors at the same concentrations. Taken together, these results may suggest that COS functions differently than H2S in certain biological contexts or that the developed donors are more efficient at delivering H2S than other common H2S-releasing motifs.
- Steiger, Andrea K.,Marcatti, Michela,Szabo, Csaba,Szczesny, Bartosz,Pluth, Michael D.
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p. 2117 - 2123
(2017/08/23)
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- Visible-Light-Triggered Uncaging of Carbonyl Sulfide for Hydrogen Sulfide (H2S) Release
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Generation of hydrogen sulfide (H2S) is challenging and few methods are capable of localized delivery of this gas. Here, a boron dipyrromethene-based carbamothioate (BDP-H2S) that is uncaged by visible light of 470 nm to generate carbonyl sulfide (COS), which is rapidly hydrolyzed to H2S in the presence of carbonic anhydrase, a widely prevalent enzyme, is reported.
- Sharma, Ajay Kumar,Nair, Mrutyunjay,Chauhan, Preeti,Gupta, Kavya,Saini, Deepak K.,Chakrapani, Harinath
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supporting information
p. 4822 - 4825
(2017/09/22)
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- Unexpectedly Stable (Chlorocarbonyl)(N-ethoxycarbonylcarbamoyl)disulfane, and Related Compounds That Model the Zumach-Weiss-Kühle (ZWK) Reaction for Synthesis of 1,2,4-Dithiazolidine-3,5-diones
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The Zumach-Weiss-Kühle (ZWK) reaction provides 1,2,4-dithiazolidine-3,5-diones [dithiasuccinoyl (Dts)-amines] by the rapid reaction of O-ethyl thiocarbamates plus (chlorocarbonyl)sulfenyl chloride, with ethyl chloride and hydrogen chloride being formed as coproducts, and carbamoyl chlorides or isocyanates generated as yield-diminishing byproducts. However, when the ZWK reaction is applied with (N-ethoxythiocarbonyl)urethane as the starting material, heterocyclization to the putative "Dts-urethane"? does not occur. Instead, the reaction directly provides (chlorocarbonyl)(N-ethoxycarbonylcarbamoyl)disulfane, a reasonably stable crystalline compound; modified conditions stop at the (chlorocarbonyl)[1-ethoxy-(N-ethoxycarbonyl)formimidoyl]disulfane intermediate. The title (chlorocarbonyl)(carbamoyl)disulfane cannot be converted to the elusive Dts derivative, but rather gives (N-ethoxycarbonyl)carbamoyl chloride upon thermolysis, or (N-ethoxycarbonyl)isocyanate upon treatment with tertiary amines. Additional transformations of these compounds have been discovered, providing entries to both known and novel species. X-ray crystallographic structures are reported for the title (chlorocarbonyl)(carbamoyl)disulfane; for (methoxycarbonyl)(N-ethoxycarbonylcarbamoyl)disulfane, which is the corresponding adduct after quenching in methanol; for [1-ethoxy-(N-ethoxycarbonyl)formimidoyl](N′-methyl-N′-phenylcarbamoyl)disulfane, which is obtained by trapping the title intermediate with N-methylaniline; and for (N-ethoxycarbonylcarbamoyl)(N′-methyl-N′-phenylcarbamoyl)disulfane, which is a short-lived intermediate in the reaction of the title (chlorocarbonyl)(carbamoyl)disulfane with excess N-methylaniline. The new chemistry and structural information reported herein is expected to contribute to accurate modeling of the ZWK reaction trajectory.
- Barany, George,Britton, Doyle,Chen, Lin,Hammer, Robert P.,Henley, Matthew J.,Schrader, Alex M.,Young, Victor G.
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p. 11313 - 11321
(2015/12/01)
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- Matrix isolation and spectroscopic properties of the methylsulfinyl radical CH3(O)S
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The atmospherically highly relevant methylsulfinyl radical CH 3(O)S was generated thermally under flash pyrolysis conditions and isolated in Ar matrices at 10 K; the allyl radical is a byproduct. CH 3(O)S and its D3- and 13C-isotopologues were characterized through the excellent agreement between experimental and computed IR and UV/Vis spectra.
- Reisenauer, Hans Peter,Romanski, Jaroslaw,Mloston, Grzegorz,Schreiner, Peter R.
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supporting information
p. 9467 - 9469
(2013/10/01)
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- SUPPORTED MO-O-K-MExOy CATALYST FOR THE SYNTHESIS OF METHANETHIOL FROM HIGH H2S-CONTAINING SYNGAS
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This invention is related to a preparation method of a supported catalyst Mo—O—K-MexOy for the synthesis of methanethiol from H2S-containing syngas. The catalyst comprises of an active component of Mo—O—K-based species, an active promoter and a support denoted as metal (or metals)-carrier. The support is prepared by electroless plating method in such a way that the metal or metals chosen are plated onto the surface of the carrier. Transition metal, especially Fe, Co or Ni are selected to be the plating metal, while SiO2, Al2O3 or TiO2 are selected to be carrier. The catalyst thus prepared is found to be efficient for the synthesis of methanethiol from H2S-containing syngasor carbon oxides/hydrogen mixtures, especially regarding a minor formation of the by-product CO2.
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Page/Page column 3; 4
(2010/12/29)
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- FTIR studies of O(3P) atom reactions with CSe2, SCSe, and OCSe
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The overall rate coefficients of the reactions of CSe2, SCSe, and OCSe with O(3P) atom have been determined to be kCSe2 = (1.4 ± 0.2) × 10-10 cm3 molecule-1 s-1, kSCSe = (2.8 ± 0.3) × 10-11 cm3 molecule-1 s-1, and kOCSe = (2-4 ± 0.3) × 10-11 cm3 molecule -1 s-1 at 301-303 K using Fourier transform infrared (FTIR) absorption spectroscopy. The measurements have been accomplished by calibrating against the literature value of the rate coefficient for O( 3P) with CS2 (4 × 10-12 cm3 molecule-1s-1). A product channel giving OCSe in 32.0 ± 4.2% yield has been found for the O + CSe2 reaction. Although CO was also detected, its generation could be attributed to subsequent reactions of OCSe with O atoms. The corresponding reaction for O + SCSe gives OCS and OCSe as observable products, with their yields given as 32.2 ± 4.5 and 30.2 ± 3.3%, respectively. Computational studies using UB3LYP/aug-cc-PVTZ methods have been used particularly to determine the reaction pathways for the channels in which OCS or OCSe is produced.
- Li, Shuping,Chwee, Tsz Sian,Fan, Wai Yip
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p. 11815 - 11822
(2008/10/09)
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- The mechanisms of hydrolysis of alkyl N-alkylthioncarbamate esters at 100°C
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The hydrolysis of ethyl N-ethylthioncarbamate (ETE) at 100°C was studied in the range of 7 mol/L HCl to 4 mol/L NaOH. The pH-rate profile showed that the hydrolysis occurred through specific acid catalysis at pH 6.5. The Hammett acidity plot and the excess acidity plot against X were linear. The Bunnett-Olsen plot gave a negative slope indicating that the conjugate acid was less hydrated than the neutral substrate. It was concluded that the acid hydrolysis occurred by an Al mechanism. The neutral species hydrolyzed with general base catalysis shown by the Bronsted plot with β = 0.48 ± 0.04. Water acted as a general base catalyst with (pseudo-)first-order rate constant, kN = 3.06 × 10-7 s-1. At pH > 6.5 the rate constants increased, reaching a plateau at high basicity. The basic hydrolysis rate constant of ethyl N,N-diethylthioncarbamate, which must react by a BAc2 mechanism, increased linearly at 1-3 mol/L NaOH with a second-order rate constant, k2 = 2.3 × 10-4 (mol/L)-1 s-1, which was 10 times slower than that expected for ETE. Experiments of ETE in 0.6 mol/L NaOH with an excess of ethylamine led to the formation of diethyl thiourea, presenting strong evidence that the basic hydrolysis occurred by the E1cb mechanism. In the rate-determining step, the E1cb mechanism involved the elimination of ethoxide ion from the thioncarbamate anion, producing an isothiocyanate intermediate that decomposed rapidly to form ethylamine, ethanol, and COS.
- Humeres, Eduardo,Sanchez, Maria De Nazare,Lobato, Conceicao M. L.,Debacher, Nito A.,De Souza, Eduardo P.
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p. 1483 - 1491
(2007/10/03)
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- Production of formaldehyde from CH4 and H2S
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A method wherein a sour natural gas stream can be treated to produce primarily carbon monoxide from methane, and the carbon monoxide and hydrogensulfide are reacted to produce methyl mercaptans, (primarily methanethiol (CH3SH) and a small amount of dimethyl sulfide (CH3SCH3)). The methyl mercaptans preferably are passed in contact with a catalyst comprising a supported metal oxide or a bulk metal oxide in the presence of an oxidizing agent and for a time sufficient to convert at least a portion of the methyl mercaptan to formaldehyde (CH2O), and sulfur dioxide (SO2).
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-
Page column 18
(2010/02/05)
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- Kinetics and mechanisms of the pyridinolysis of phenyl and 4-nitrophenyl chlorothionoformates formation and hydrolysis of 1-(aryloxythiocarbonyl) pyridinium cations
-
The title reactions are subjected to a kinetic study in water, at 25.0 °C, and an ionic strength of 0.2 M (KCl). By following the reactions spectrophotometrically two consecutive reactions are observed: the first is formation of the corresponding thionocarbamates (1-(aryloxythiocarbonyl)- pyridinium cations) and the second is their decomposition to the corresponding phenol and pyridine, and COS. Pseudo-first-order rate coefficients (k obsd1 and kobsd2, respectively) are found under excess amine. Plots of kobsd1 vs free pyridine concentration at constant pH are linear, with the slope (kN) independent of pH. The Bronsted-type plots (log kN vs pKa of the conjugate acids of the pyridines) are linear with slopes β = 0.07 and 0.11 for the reactions of phenyl and 4-nitrophenyl chlorothionoformates, respectively. These Bronsted slopes are in agreement with those found in other stepwise reactions of the same pyridines in water, where the formation of a tetrahedral intermediate is the rate-determining step. In contrast to the stepwise mechanism of the title reactions that for the reactions of the same substrates with phenols is concerted, which means that substitution of a pyridino moiety in a tetrahedral intermediate by a phenoxy group destabilizes the intermediate. The second reaction corresponds to the pyridine-catalyzed hydrolysis of the corresponding 1-(aryloxythiocarbonyl)pyridinium cation. Plots of k obsd2 VS free pyridine concentration at constant pH are linear, with the slope (kH) independent of pH. The Bronsted plots for kH are linear with slopes β = 0.19 and 0.26 for the reactions of the phenyl and 4-nitrophenyl derivatives, respectively. These low values are explained by the fact that as pKa increases the effect of a better pyridine catalyst is compensated by a worse leaving pyridine from the corresponding thionocarbamate.
- Castro, Enrique A.,Cubillos, Maria,Santos, Jose G.
-
p. 4802 - 4807
(2007/10/03)
-
- Isomers of OCS2: IR absorption spectra of OSCS and O(CS 2) in solid Ar
-
Irradiation of an Ar matrix sample containing O3 and CS 2 with a KrF excimer laser at 248 nm yielded new lines at 1402.1 (1404.7), 1056.2 (1052.7), and 622.3 (620.5) cm-1; numbers in parentheses correspond to species in a minor matrix site. Secondary photolysis at 308 nm diminished these lines and produced mainly OCS and SO2. Annealing of this matrix to 30 K yielded a second set of new lines at 1824.7 and 617.8 cm-1. The first set of lines are assigned to CS stretching, O-S stretching, and S-C stretching modes of carbon disulfide S-oxide, OSCS; and the second set of lines are assigned to CO stretching and OCS bending modes of dithiiranone, O(CS2), respectively, based on results of 34S- and 18O-isotopic experiments and quantum-chemical calculations. These calculations using density-functional theory (B3LYP/aug-cc-pVTZ) predict four stable isomers of OCS2: O(CS 2), SSCO, OSCS, and SOCS, listed in order of increasing energy. According to calculations, O(CS2) has a cyclic CS2 moiety and is the most stable isomer of OCS2. OSCS is planar, with bond angles OSC?111.9° and SCS?177.3°; it is less stable than SSCO and O(CS2) by ～102 and 154 kJ mol-1, respectively, and more stable than SOCS by ～26 kJ mol-1. Calculated vibrational wave numbers, IR intensities, 34S- and 18O-isotopic shifts for OSCS and O(CS2) fit satisfactorily with experimental results.
- Lo, Wen-Jui,Chen, Hui-Fen,Chou, Po-Han,Lee, Yuan-Pern
-
p. 12371 - 12378
(2008/01/27)
-
- Thermal analysis of black powder
-
While there is abundant literature describing the factors affecting the performance and the mechanical sensitivity of black powder, only a few papers are devoted to its thermal properties. Previous work indicated that no exothermic reactions were observed below 300°C in an inert gas environment. In the present work a variety of thermal techniques (DSC, TG, simultaneous TG-DTA-FTIR-MS, ARC, HFC) has been used to study the thermal decomposition of black powder. Exothermic reactions were observed at temperatures as low as 230 and 140°C in inert and oxidizing atmospheres, respectively. The latter exothermic reaction is due to sulfur oxidation.
- Turcotte,Fouchard,Turcotte,Jones
-
p. 105 - 118
(2008/10/08)
-
- Cationic ring-opening polymerization of five-membered cyclic thiocarbonate bearing an adamantane moiety via selective ring-opening direction
-
A novel five-membered cyclic thiocarbonate bearing adamantane moiety, 4,6-dioxatetracyclo-[6.3.1.1.3,10O3,7]tridecane-5-thio (1), was synthesized from 1,2-adamantanediol and thiophosgene in the presence of pyridine. Monomer 1 underwent cationic ring-opening polymerization initiated by triethyl-oxonium tetrafluoroborate (Et3OBF4), methyl trifluoromethanesulfonate (TfOMe), trifluoromethanesulfonic acid (TfOH), and H2O with 2 mol% of boron trifluoride etherate (BF3OEt2) in CH2Cl2 at 30° to afford the polythiocarbonate by isomerization of the thiocarbonyl group into a carbonyl group with selective ring-opening direction. The number-average molecular weight and polydispersity of the polymer obtained by polymerization with H2O/BF3OEt2 were 10 600 and 1.44, respectively. The temperature with 5% weight loss of the obtained polymer was 338°C. Monomer 1 expanded as large as 14% during the polymerization.
- Kameshima, Hisamitsu,Nemoto, Nobukatsu,Sanda, Fumio,Endo, Takeshi
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p. 5769 - 5773
(2007/10/03)
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- Kinetics and mechanism of the reaction of xenon tetroxide with carbon disulfide
-
The dependence of the rate of the reaction of XeO4 with CS2 on the concentrations of reactants and diluent gases He, O2, and CO2 was studied at room temperature. A reaction mechanism was proposed.
- Aleinikov,Vasil'ev,Kashtanov,Makarov,Chernyshev
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p. 452 - 456
(2008/10/08)
-
- Reactions of 2-unsubstituted 1H-imidazole 3-oxides with heterocumulenes and dimethyl acetylenedicarboxylate
-
Reaction of 2-unsubstituted 1H-imidazole 3-oxides with isocyanates, isothiocyanates, and dimethyl acetylenedicarboxylate led to the formation of 2-functionalized imidazole derivatives. Stepwise reaction mechanisms via zwitterionic intermediates are propos
- Mlostoń, Grzegorz,Gendek, Tomasz,Heimgartner, Heinz
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p. 5405 - 5412
(2007/10/03)
-
- Correlation of the rates of solvolysis of phenyl chlorothionoformate and phenyl chlorodithioformate
-
The specific rates of solvolysis of phenyl chlorothionoformate (PhOCSCl) are remarkably similar to those previously reported for phenyl chlorothioformate (PhSCOCl). When analyzed using the extended Grunwald-Winstein equation over the usual range of solvent types, these solvolyses show essentially identical divisions into the solvents favoring the addition-elimination channel and those favoring the ionization channel. The introduction of one sulfur caused a partial shift away from the addition-elimination pathway, which was dominant over the full range of solvents for phenyl chloroformate (PhOCOCl). Consistent with these results, introduction of the second sulfur within phenyl chlorodithioformate (PhSCSCl) leads to a completion of this shift, such that an extended Grunwald-Winstein treatment of the specific rates of solvolysis now shows the ionization pathway to be dominant over the full range of solvents.
- Kevill, Dennis N.,D'Souza, Malcolm J.
-
p. 1118 - 1122
(2007/10/03)
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- Kinetic effects induced by cellulose on water-catalyzed reactions. Hydrolysis of 2,4-dinitrophenyl cellulose xanthate and some sugar xanthate ester analogues
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The hydrolysis of 2,4-dinitrophenyl cellulose xanthate (CelXDNP) was studied in 10% v/v aqueous ethanol at 25°C and μ = 0.1 (KCl). The water- catalyzed hydrolysis showed that, as for p-nitrobenzyl cellulose xanthate, it occurs through two parallel reactions with rate constants k'(H2O) = 4.40 x 10-3 s-1 for the fast hydrolysis, and k''(H2O) = 6.90 x 10-5 s-1 for the slow hydrolysis. The entropy of activation of the fast hydrolysis was 0.7 ± 1.8 cal K-1 mol-1. External nucleophiles such as hydroxide and simple amines show simple first-order kinetics. The spontaneous hydrolysis of CelXDNP in acetone-water mixtures indicates that the fast reaction does not occur through water polymers and that for water molarity higher than 30 M there are no acetone molecules (or very few) in the highly ordered cybotactic region of cellulose. The spontaneous hydrolysis of methyl 4,6-O-benzylidene- α-D-glucopyranoside 3-(S-p-nitrobenzyl-xanthate) although is faster than the 6-isomer, it is slower than the fast hydrolysis of p-nitrobenzyl cellulose xanthate (CelXNB). Also ΔS(+) is highly negative (-41.0 cal K-1 mol-1), as it is for alkyl and sugar analogues. Only for the fast hydrolyses of CelXDNP and CelXNB is the entropy of activation almost zero. It is concluded that there is no neighbouring OH effect on the fast hydrolysis of cellulose xanthate esters. The hydrolysis of 2,4-dinitrophenyl cellulose xanthate (CelXDNP) was studied in 10% v/v aqueous ethanol at 25°C and μ = 0.1 (KCl). The water-catalyzed hydrolysis showed that, as for p-nitrobenzyl cellulose xanthate, it occurs through two parallel reactions with rate constants k′H2O = 4.40 × 10-3 s-1 for the fast hydrolysis, and k″H2O = 6.90 × 10-5 s-1 for the slow hydrolysis. The entropy of activation of the fast hydrolysis was 0.7 ± 1.8 cal K-1 mol-1. External nucleophiles such as hydroxide and simple amines show simple first-order kinetics. The spontaneous hydrolysis of CelXDNP in acetone-water mixtures indicates that the fast reaction does not occur through water polymers and that for water molarity higher than 30 M there are no acetone molecules (or very few) in the highly ordered cybotactic region of cellulose. The spontaneous hydrolysis of methyl 4,6-O-benzylidene-α-D-glucopyranoside 3-(S-p-nitrobenzyl-xanthate) although is faster than the 6-isomer, it is slower than the fast hydrolysis of p-nitrobenzyl cellulose xanthate (CelXNB). Also ΔS≠ is highly negative (-41.0 cal K-1 mol-1), as it is for alkyl and sugar analogues. Only for the fast hydrolyses of CelXDNP and CelXNB is the entropy of activation almost zero. It is concluded that there is no neighbouring OH effect on the fast hydrolysis of cellulose xanthate esters.
- Humeres, Eduardo,Sequinel, Luiz Fernando,Nunes, Mauricea,Oliveira, Celia M.S.,Barrie, Patrick J.
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p. 960 - 965
(2007/10/03)
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- One-electron redox potential of thiobenzoic acid. Kinetic characteristics of benzoylthiyl radical β-fragmentation
-
By means of pulse radiolysis, one-electron oxidation of benzoylthiolate (PhCOS- was achieved by the azide radical (N3*) in aqueous solution. The spectrum of the resulting benzoylthiyl radical (PhCOS*) shows a broad absorption in the wavelength region from 350 to 500 nm. With N3*/N3- as reference couple, the reduction potential E°(PhCOS*/PhCOS-) was measured to be 1.21 V vs NHE. Using the pK(a) of 2.48 for thiobenzoic acid (PhCOSH), we derive the standard reduction potential E°(PhCOS*, H+/PhCOSH) to be 1.36 V vs NHE. This reduction potential implies an S-H bond energy of PhCOSH of 87 kcal/mol, which is very close to the bond energy of an alkylthiol S-H bond (87.4 kcal/mol). At 22 °C, the PhCOS* radicals decay with a rate constant of 8.5 x 103 s-1 to form colorless species. This process is presumed to be the β-fragmentation of the PhCOS* radical, PhCOS* → Ph* + COS. The kinetics of the β-fragmentation of the PhCOS* radical was found to follow the Arrhenius equation, log(k2/s-1) = (12.3 ± 0.1) - (11.4 ± 0.2)/θ, where θ = 2.3RT kcal/mol. Strong evidence for this process was provided byproduct identification by GCMS, where the main products of the γ- irradiation-induced N3* radical oxidation of PhCOS- in 0.1 M NaN3 solution were found to be phenyl azide (PhN3) and aniline (PhNH2). These products were formed via addition of the Ph* radical to N3- to form the PhN3(-*) radical anion, which subsequently disproportionated. In the Discussion, we summarize the reduction potentials and the bond dissociation energies of related thiols and their oxygen couterparts. The β-fragmentation of PhCOS* radicals resembles that of the oxygen counterpart, benzoyloxyl radical (PhCOO*), and their thermochemical properties are also compared.
- Zhao, Rong,Lind, Johan,Merényi, Gábor,Eriksen, Trygve E.
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p. 2811 - 2816
(2007/10/03)
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- Kinetics and Mechanism of the Pyridinolysis of Alkyl Aryl Thionocarbonates
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The reactions of methyl 4-nitrophenyl, ethyl 4-nitrophenyl, and ethyl 2,4-dinitrophenyl thionocarbonates (MNPTOC, ENPTOC, and EDNPTOC, respectively) with a series of 3- and 4-substituted pyridines are subjected to a kinetic investigation in water, 25.0°C, ionic strength 0.2 M (maintained with KCl). Under amine excess, pseudo-first-order rate coefficients (kobsd) are obtained, which are linearly proportional to the free-pyridine concentration. The second-order rate coefficients (kN) are obtained as the slopes of these plots. The Broensted-type plots found for the two mononitro derivatives coincide in one straight line (same slope and intercept) of slope β=1.0. The EDNPTOC pyridinolysis shows a curved Broensted-type plot with slopes β1= 0.1 (high pKa], β2 = 1.0 (low pKa), and pKao = 6.8 (pKa value at the center of curvature). These plots are consistent with the existence of a zwitterionic tetrahedral intermediate (T±) on the reaction pathway whereby expulsion of aryloxide anion from T± is rate determining (k2 step) at low pKa for EDNPTOC (and in the whole pKa range for MNPTOC and ENPTOC), and there is a change to rate-limiting formation of T± (k1 step) at high pKa for EDNPTOC. Comparison of these Broensted plots among them and with similar ones permits the following conclusions: (i) There is no variation of kN by substitution of methoxy by ethoxy as the nonleaving group of the substrate. (ii) The pKao value is smaller for the less basic aryloxide nucleofuge due to a larger k25 value. (iii) The change of C=S by C=O as the electrophilic center of the substrate results in larger values for both k1 (amine expulsion rate) and k2, and also a larger k-1/k2 ratio for the carbonyl derivative. There is also an increase of k1 by the same change. The K1k2 (= k1k2/k-1) values are larger for the pyridinolysis of methyl 2,4-dinitrophenyl and methyl 4-nitrophenyl carbonates compared to the corresponding thionocarbonates (EDNPTOC and MNPTOC, respectively). (iv) Pyridines are more reactive than isobasic secondary alicyclic amines toward ENPTOC when either the k1 step or the k2 step is rate limiting. This is explained by the softer nature of pyridines than alicyclic amines (k1 step) and the greater nucleofugality (k-1) of the latter amines than isobasic pyridines, leading to a larger k2/k-1 ratio for pyridines (k2 is little affected by the amine nature), and therefore a larger K1k2 value when the k2 step is rate determining.
- Castro, Enrique A.,Cubillos, Maria,Santos, Jose G.,Tellez, Jimena
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p. 2512 - 2517
(2007/10/03)
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- Photolysis of matrix-isolated CF3C(O)SH and CF3C(O)SCl
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Perfluoroacetylthiol, CF3C(O)SH, and perfluoroacetylsulphenyl chloride, CF3C(O)SCl, were irradiated in an inert gas matrix to produce CF3SH and CO, and CF3SCl, CF3Cl, CO and SCO, respectively. The compounds are identified by evaluating the apparition of new bands in the FTIR spectrum of the matrix-isolated substance. The results are compared with related studies of similar compounds taking into account both the irradiation and the stability of the formed products.
- Ulic,Gobbato,Della Vedova
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p. 171 - 175
(2007/10/03)
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- The kinetics and mechanism of pyrite thermal decomposition
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Pyrite (FeS2) decomposition in He, N2, CO2-CO-SO2,O2-CO2 and H2S-H2gas mixtures was studied from 400-590 °C using optical microscopy, X-ray diffraction, electron microprobe analyses, and gas chromatography. The rate constants were determined from the weight loss and the thickness change of pyrite in reacted samples. The temperature dependent composition of the product, pyrrhotite (Fe1-xS), was measured by electron microprobe analysis and X-ray diffraction. Pyrite decomposition to pyrrhotite and sulfur vapor (dominantly S2) was observed in all gases and follows linear kinetics. The apparent activation energy of pyrite thermal decomposition is 297± 34 kJ mol-1 in inert gases (e.g. He, N2), and 275±20 kJ mol-1 in purified CO2 and in low concentration CO-SO2 gas mixtures with CO2. The rate constants are the same regardless of gas composition at a given temperature. In oxidizing (O2-CO2) or reducing (H2S-H2) gas mixtures, the rate constants are larger than that in inert gases because additional reactions between pyrite and oxidizing/reducing gases accelerate the overall process while reducing the apparent activation energies. A mechanism of pyrite decomposition, which explains our experimental results, as well as the discordant activation energy data in the literature, is proposed. WILEY-VCH Verlag GmbH, 1997.
- Hong,Fegley Jr.
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p. 1870 - 1881
(2007/10/03)
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- Retro-ene type fragmentation of allylic dithiolcarbonates
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The formation of 2-alkenyl alkyl sulfides from S-(2-alkenyl) S-alkyl dithiocarbonates with extrusion of COS was found to be effectively catalyzed by Lewis acids. The ab initio calculations strongly suggested that the reaction falls into category of 'retro-alkylthio-ene' reaction.
- Eto, Masashi,Nishimoto, Mitsuhiro,Kubota, Shoji,Matsuoka, Toshikazu,Harano, Kazunobu
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p. 2445 - 2448
(2007/10/03)
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- On the synergism between La2O2S and CoS2 in the reduction of SO2 to elemental sulfur by CO
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In our study of the catalytic reduction of SO2 to elemental sulfur by CO in the presence of La2O2S and CoS2, a synergistic effect between the two sulfides was observed which not only increased the catalytic activity but also suppressed the formation of the side-product COS. It was also found that the crystal phase of CoS2, which can be easily reduced by CO, could be retained when La2O2S coexisted even in small quantities. A mechanism was proposed based on the COS intermediate mechanism and the remote control concept.
- Ma, Jianxin,Fang, Ming,Lau, Ngai Ting
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p. 251 - 259
(2008/10/08)
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- Sulfuration of yttrium oxide in a flux of sodium carbonate and sulfur: Reinvestigation
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Reactions of yttrium oxide with sodium carbonate-sulfur flux are reinvestigated by IR spectroscopy, gas evolution analysis, XRD, and elemental analysis. Initially, the terminal bond of the polymeric sulfur is attacked by sodium carbonate to form sodium polysulfide with the evolution of CO2 and COS. Yttrium oxide reacts with CO2 forming yttrium oxycarbonate, which consecutively reacts with sulfur supplied by sodium polysulfide at high temperatures to give yttrium oxysulfide. The reaction of yttrium oxide with CO2 is a solid-gas reaction producing a porous layer. Thus the reaction rate is independent of the original particle size of yttrium oxide. Gauthier-Villars.
- Chang, So-Young,Choi, Q. Won,Choi, Han,Mho, Sun-Il,Pyun, Chong-Hong,Kim, Chang-Hong
-
p. 1123 - 1134
(2008/10/08)
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- A Potential Surface Map of the H-/N2O System. The Gas Phase Ion Chemistry of HN2O-
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Dunkin, Fehsenfeld and Ferguson have reported that the gas phase reaction between H- and N2O in a flowing afterglow instrument forms HO- and N2 with medium efficiency.The potential surface (UMP2-FC/6-311++G**//RHF/6-311++G**) for the H-/N2O system confirms this to be the predominant reaction following initial approach of H- towards the central nitrogen of N2O to form unstable intermediate -(N2O)>.The intermediate then decomposes to HO- and N2 via a deep channel.The potential surface also shows the direct formation of adducts -O-+N(H)=N- and cis HN=NO-.However these are formed with excess energy: the former converts principally into reactants, while the latter decomposes to HO- and N2. Ions having the formula 'HN2O-' may be formed in the gas phase by the reactions (i) HNO- + N2O --> HN2O- + NO, and (ii) NH2- + Me3CCH2ONO --> HN2O- + Me3CCH2OH.The product anion is stabilized by removal of some of its excess energy by the eliminated neutral.Evidence is presented which indicates that the product is either cis or trans HN=NO-, or a mixture of both .The characteristic ion molecule reaction of HN=NO- involves oxidative oxygen transfer to suitable neutral substrates.For example: HN2O- + CS2 --> HS- + N2 + COS.
- Sheldon, John C.,O'Hair, Richard A. J.,Downard, Kevin M.,Gronert, Scott,Krempp, Michele,et al.
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p. 155 - 166
(2007/10/02)
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- Novel synthesis of S-alkyl thiocarbamates from amines, carbon monoxide, elemental sulfur, and alkyl halides in the presence of a selenium catalyst
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Carbonyl selenide easily reacted with elemental sulfur at low temperature to form carbonyl sulfide in a good yield, and reaction of ammonium salts of selenocarbamates with elemental sulfur brought about ready transformation to those of thiocarbamates. On the basis of the high catalytic activity of selenium for carbonylation of amines with carbon monoxide in addition to these important findings, a convenient new method for synthesis of S-alkyl thiocarbamates was developed through the carbonylation of amines with carbon monoxide and elemental sulfur in the presence of a selenium catalyst under mild conditions followed by alkylation of ammonium salts of the thiocarbamates with alkyl halides.
- Mizuno, Takumi,Nishiguchi, Ikuzo,Sonoda, Noboru
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p. 5669 - 5680
(2007/10/02)
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- UNTERSCHIEDLICHES VERHALTEN VON AROMATISCHEN PHOSPHITEN GEGENUEBER ACYLSULFENYLCHLORIDEN
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The acylsulfenyl chlorides 1 or 2 react with acyclic and cyclic aromatic phosphites.The acyclic derivative 3 gives the corresponding thiophosphate 4 and the cyclic derivatives 5 give the corresponding phosphates 6.The different behaviour is discussed. Key words: Acylsulfenyl chlorides; aromatic phosphites; oxidation of P(III) compounds.
- Gloede, J.,Lutze, G.
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p. 265 - 270
(2007/10/02)
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- Mechanistic Studies of the OH-Initiated Oxidation of CS2 in the Presence of O2
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We have investigated production of carbon- and sulfur-conatining end products of the OH-initiated oxidation of CS2 in the presence of O2, an important atmospheric chemical reaction which is known to proceed via the following three elementary steps: OH + CS2 + M CS2OH + M; CS2OH + O2 -> products.Two different experimental approaches were employed.In one set of experiments (CP-FTIR studies) continuous photolysis of CH3ONO/NO/CS2/Air mixtures at 298 K and 700-Torr total pressure was combined with product detection by Fourier transform infrared spectroscopy; these studies measured moles of products formed per mole of CS2 consumed.In a second set of experiments (LFP-TDLAS studies) 248-nm laser flash photolysis of H2O2/CS2/N2O/He/O2 mixtures at 298 K and 25-100-Torr total pressure was combined with product detection by time-resolved tunable diode laser absorption spectroscopy; in this case, the quantity measured was moles of product formed per mole of OH consumed.In both studies OCS and CO are observed as carbon-containing products with yields of 0.83 +/- 0.08 and 0.16 +/- 0.03, respectively; uncertainties represent estimates of absolute accuracy at the 95percent confidence level.The LFP-TDLAS experiments demonstrate that the above yields represent prompt product formation; i.e., OCS and CO are formed either as primary products of the CS2OH + O2 reaction or as products of a fast (k > 10-15 cm3 molecule-1 s-1) secondary reaction of a primary product with O2.The CP-FTIR experiments show that, under atmospheric conditions, SO2 is produced with a yield of 1.15 +/- 0.10; in this case, the LFP-TDLAS results strongly suggest that only about three-fourths of the SO2 is formed as a prompt product, with the remainder generated via slow reaction of SO (generated as a prompt product of the CS2OH + O2 reaction) with O2.The implications of our results for understanding the detailed mechanism of the very complex CS2OH + O2 reaction are discussed, as are their implications for understanding the atmospheric cycles of CS2 and OCS.
- Stickel, R. E.,Chin, M.,Daykin, E. P.,Hynes, A. J.,Wine, P. H.,Wallington, T. J.
-
p. 13653 - 13661
(2007/10/02)
-
- Dynamics of Metastable Dissociation and Photodissiciation of the Gas-Phase Cluster Ion (OCS:C2H2)+
-
The dynamics of dissociation of (OCS:C2H2)+ have been examined by using mass-analyzed ion kinetic energy spectrometry (MIKES).Kinetic energy release distributions for the dissociations were determined by analysis of the MIKES peak shapes.Metastable dissociation yields OCS+ and C2H2S+ as the ionic products of the cluster ion bond cleavage and a sulfur ion transfer reaction, respectively.The latter channel is exothermic by more than 25 kcal/ mol, and the kinetic energy release distribution is highly nonstatistical.Ab initio calculations on the ground-state reactants of the S+ - transfer reaction indicate that although the thioketene structure is the lowest energy isomer of C2H2S+, the alternative isomeric species, thiirene molecular ion, is also permitted by the thermochemistry of the reaction.Photodissociation experiments were performed in the photon energy range 2.1-4.5 eV, using a crossed laser beam-ion beam geometry.The photodissociation cross section increases apparently smoothly from about 8 x 10-20 cm2 at 2.1-eV photon energy to 4 x 10-18 cm2 at 3.5 eV.The ionic products formed in this energy range are OCS+ and C2H2+, which appear in an essentially constant ratio of 6:1.Analysis of the angular distributions of the OCS+ and C2H2+ photoproducts indicates that both dissociation channels arise from excitation to a repulsive excited state.Analysis of the kinetic energy release distributions provides an upper limit to the cluster bond dissociation energy of about 1.15 eV and suggests a sulfur-carbon bonding interaction in the cluster ion.These results are supported by ab initio calculations, which indicate a bond dissociation energy of 0.875 eV, and that the most stable form of (OCS:C2H2)+ is with near ?-bonding between The S atom of OCS and one of the carbons of C2H2.
- Graul, Susan T.,Bowers Michael T.
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p. 8328 - 8337
(2007/10/02)
-
- Effect of Oxidants on the Oxidative Coupling of Methane over a Lead Oxide Catalyst
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Oxidative coupling of methane was studied over a PbO/MgO catalyst using a variety of oxidants such as N2O, NO, CO2, and SO2.While N2O showed both high activity and selectivity for the title reaction, NO produced CO2, exclusively.The coupling reaction was assumed to proceed via the redox cycle of Pb and PbO on each oxidant mentioned above.Carbon dioxide produced small amounts of C2 hydrocarbons and CO, while SO2, was inactive for the reaction.Oxygen, N2O, CO2 could oxidize the Pb/MgO which has been formed by the reaction of PbO/MgO with methane at 1023 K.Thus-prepared PbO/MgO produced C2 hydrocarbons from methane.Even NO, which gave no C2 hydrocarbons in the CH4-NO cofeed reaction, converted the Pb/MgO to PbO/MgO and the PbO/MgO gave C2 hydrocarbons exclusively upon reacting with CH4.NO seems to oxidize the methyl radical, which is an intermediate of the coupling reaction to CO2.The ineffectiveness of SO2 as an oxidant was attributed to the formation of PbS, which is inactive in the methane activation.
- Asami, Kenji,Shikada, Tsutomu,Fujimoto, Kaoru
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p. 266 - 271
(2007/10/02)
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- Gas-Phase Chemistry of the Dimethyaluminum Oxide Ion and Related Aluminum Oxide Ions: Comparison of Reactivity with Siloxide Ions
-
The anion [CH3)2Alo]- (1) has prepared In a flowing afterglow selected ion flow tube (FA-SIFT) by ion selection from the reaction mixture of trimethylaluminum dimer and hydroxide. This unusual ion is quite reactife and has extensively studied. It with halogen-containing compounds of several types, including fluorobenzene, chlorobenzene, bromofluorobenzene, acetyl chloride, and HF, to give {(CHj^AKOHJX] , where X = F, Cl, and Br. Its chemistry with hexafteorabenzene and silicon tetrafluoride has also detailed as have a number of reactions with carboxylic adds, esters, anhydrides, sulfur-containing neutrals, alcohols, water, and ammonia. The dominant reaction pattern of 1 involves six-centered processes which require a relatively acidic hydrogen and a lone pair donor atom in the neutral reactant. In these reactions, ion 1 abstracts a proton as the lone pair atom to aluminum, often with concomitant extrusion of a small, neutral molecule. We have compared the reactifity of 1 with that of [(CH3)3SiO]- and briefly examined other aluminum oiide ions. The kinetics of several reactions as well the thermochemical relationships among some of these ions have studied, Acidity studies coupled with thermochemical analysis establish that the conjugate acid of [A1O]~ is A1OH, not HA1O. Computational studies out to the reaction of trimethylaluminum and hydroxide, and the acidities and of A1OH and HA1O.
- Damrauer, Robert,Krempp, Mich?ele,Micheal,Gordon
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p. 2393 - 2400
(2007/10/02)
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- Oxidation of CS2 by Reaction with OH. 2. Yields of HO2 and SO2 in Oxygen
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The products of the OH-initiated oxidation of CS2 have been investigated.Analysis of the OH loss and the HS production using a laser magnetic resonance (LMR) discharge-flow apparatus yielded k1 3 molecule-1 s-1 for the reaction OH + CS2 -> HS + OCS (1) (340 K and 5 Torr (He)).The oxidation of CS2 is enhanced by O2 due to the following mechanism: OH + CS2 = CS2OH (2), and CS2OH + O2 -> products (3).HO2 was identified by LMR detection as a major product from this chemistry.The HO2 yield was measured in a pulsed photolysis experiment by modeling OHtemporal profiles with NO added to convert HO2 to OH.The HO2 yield was 95 +/- 15percent of the OH consumed by reactions 2 and 3 ( 50 Torr (He), 249 and 299 K).Discharge-flow experiments employing chemical ionization mass spectrometric (CIMS) detection of OH and SO2 showed that 90 +/- 20 percent of the OH consumed by reactions 2 and 3 leads to SO2 production.
- Lovejoy, Edward R.,Murrells, Timothy P.,Ravishankara, A. R.,Howard, Carleton J.
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p. 2386 - 2393
(2007/10/02)
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- Gas- Phase Ion Chemistry of Siloxide and Silamide Ions by Using the Flowing Afterglow. Unusual Rearrangements Involving SiO and SiS Bond Formation
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Siloxide ions undergo O/S exchange reactions with suitable sulfur-containing neutrals, e.g.H3SiO- + CS2 -> H3SiS- + COS.Silamide ions similarly undergo NR/O and NR/S exchange reactions together with nucleophilic displacement reactions, e.g.: .No simple correlation between rate and mechanism is observed for all the studied reactions.
- O'Hair, Richard A.J.,Sheldon, John C.,Bowie, John H.,Damrauer, Robert,DePuy, Charles H.
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p. 489 - 496
(2007/10/02)
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