- A Bioinspired Molybdenum Catalyst for Aqueous Perchlorate Reduction
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Perchlorate (ClO4-) is a pervasive, harmful, and inert anion on both Earth and Mars. Current technologies for ClO4- reduction entail either harsh conditions or multicomponent enzymatic processes. Herein, we report a heterogeneous (L)Mo-Pd/C catalyst directly prepared from Na2MoO4, a bidentate nitrogen ligand (L), and Pd/C to reduce aqueous ClO4- into Cl- with 1 atm of H2 at room temperature. A suite of instrument characterizations and probing reactions suggest that the MoVI precursor and L at the optimal 1:1 ratio are transformed in situ into oligomeric MoIV active sites at the carbon-water interface. For each Mo site, the initial turnover frequency (TOF0) for oxygen atom transfer from ClOx- substrates reached 165 h-1. The turnover number (TON) reached 3840 after a single batch reduction of 100 mM ClO4-. This study provides a water-compatible, efficient, and robust catalyst to degrade and utilize ClO4- for water purification and space exploration.
- Bi, Eric Y.,Gao, Jinyu,Liu, Jinyong,Palmer, Jacob,Ren, Changxu,Sun, Jiaonan,Wu, Yiying,Yang, Peng,Zhu, Mengqiang
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- ELECTROCHEMICAL BEHAVIOR OF SELENIUM AND SELENIUM COMPOUNDS IN SODIUM TETRACHLOROALUMINATE MELTS.
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The electrochemistry of selenium and various selenium compounds in AlCl//3:NaCl melts has been investigated by a variety of techniques including pulse and cyclic voltammetry, coulometry, and the rotating-disk electrode. It was found that selenium can be reduced, in both acid and basic melts, by a single two-electron step to selenide which exists in the melt as either AlSeCl or AlSeCl//2** minus (or their analogous solvated species Al//2SeCl//5** minus and Al//2SeCl//6**2** minus ) depending upon the acidity. The mechanism for the oxidation of selenium to Se(IV) was found to be dependent upon the melt acidity. In basic melts, selenium was first oxidized by a two-electron step to an Se(II) species and then by a further two-electron step to Se(IV). In acid melts the oxidation is a single quasireversible four-electron step. This work is of interest in the areas of high energy density batteries and fuel cells.
- Robinson,Osteryoung
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- Understanding the roles of strictly conserved tryptophan residues in O 2 producing chlorite dismutases
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The chlorite dismutases (Clds) degrade ClO2- to O2 and Cl- in perchlorate respiring bacteria, and they serve still poorly defined cellular roles in other diverse microbes. These proteins share 3 highly conserved Trp residues, W155, W156, and W227, on the proximal side of the heme. The Cld from Dechloromonas aromatica (DaCld) has been shown to form protein-based radicals in its reactions with ClO2 - and peracetic acid. The roles of the conserved Trp residues in radical generation and in enzymatic function were assessed via spectroscopic and kinetic analysis of their Phe mutants. The W155F mutant was the most dramatically affected, appearing to lose the characteristic pentameric oligomerization state, secondary structure, and heme binding properties of the WT protein. The W156F mutant initially retains many features of the WT protein but over time acquires many of the features of W155F. Conversion to an inactive, heme-free form is accelerated by dilution, suggesting loss of the protein's pentameric state. Hence, both W155 and W156 are important for heme binding and maintenance of the protein's reactive pentameric structure. W227F by contrast retains many properties of the WT protein. Important differences are noted in the transient kinetic reactions with peracetic acid (PAA), where W227F appears to form an [Fe(iv)O]-containing intermediate, which subsequently converts to an uncoupled [Fe(iv)O + AA+] system in a [PAA]-dependent manner. This is in contrast to the peroxidase-like formation of [Fe(iv)O] coupled to a porphyrin π-cation radical in the WT protein, which decays in a [PAA]-independent manner. These observations and the lack of redox protection for the heme in any of the Trp mutants suggests a tendency for protein radical formation in DaCld that is independent of any of these conserved active site residues.
- Blanc, Beatrice,Rodgers, Kenton R.,Lukat-Rodgers, Gudrun S.,Dubois, Jennifer L.
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- Copper(II) catalyses the reduction of perchlorate by both formaldehyde and by dihydrogen in aqueous solutions
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During an effort to synthesize the trans-III-copper(II) complex with 1,4,8,11-tetramethyl-pyro-phosphonate-1,4,8,11-tetra-aza-cyclo-tetradecane, using only perchlorate salts, it was noted that the perchlorate is reduced to chloride. Analysis of the reactions leading to this surprising result points out that Cu(H2O)42+ catalyzes the reduction of perchlorate by H2 and by CH2O. These reactions are slow at room temperature and ambient pressures. A plausible mechanism, supported by DFT calculations, is proposed pointing out that the role of CuH+ under mild conditions cannot be ignored.
- Shamir, Dror,Meyerstein, Dan,Zilbermann, Israel,Burg, Ariela,Albo, Yael,Shames, Alexander I.,Vainer, Radion,Borojovich, Eitan J.C.,Yardeni, Guy,Kornweitz, Haya,Maimon, Eric
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- Configuration Control in the Synthesis of Homo- and Heteroleptic Bis(oxazolinylphenolato/thiazolinylphenolato) Chelate Ligand Complexes of Oxorhenium(V): Isomer Effect on Ancillary Ligand Exchange Dynamics and Implications for Perchlorate Reduction Catalysis
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This study develops synthetic strategies for N,N-trans and N,N-cis Re(O)(LO-N)2Cl complexes and investigates the effects of the coordination spheres and ligand structures on ancillary ligand exchange dynamics and catalytic perchlorate reduction activities of the corresponding [Re(O)(LO-N)2]+ cations. The 2-(2′-hydroxyphenyl)-2-oxazoline (Hhoz) and 2-(2′-hydroxyphenyl)-2-thiazoline (Hhtz) ligands are used to prepare homoleptic N,N-trans and N,N-cis isomers of both Re(O)(hoz)2Cl and Re(O)(htz)2Cl and one heteroleptic N,N-trans Re(O)(hoz)(htz)Cl. Selection of hoz/htz ligands determines the preferred isomeric coordination sphere, and the use of substituted pyridine bases with varying degrees of steric hindrance during complex synthesis controls the rate of isomer interconversion. The five corresponding [Re(O)(LO-N)2]+ cations exhibit a wide range of solvent exchange rates (1.4 to 24,000 s-1 at 25°C) and different LO-N movement patterns, as influenced by the coordination sphere of Re (trans/cis), the noncoordinating heteroatom on LO-N ligands (O/S), and the combination of the two LO-N ligands (homoleptic/heteroleptic). Ligand exchange dynamics also correlate with the activity of catalytic reduction of aqueous ClO4- by H2 when the Re(O)(LO-N)2Cl complexes are immobilized onto Pd/C. Findings from this study provide novel synthetic strategies and mechanistic insights for innovations in catalytic, environmental, and biomedical research.
- Liu, Jinyong,Wu, Dimao,Su, Xiaoge,Han, Mengwei,Kimura, Susana Y.,Gray, Danielle L.,Shapley, John R.,Abu-Omar, Mahdi M.,Werth, Charles J.,Strathmann, Timothy J.
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- Production of Sb(IV) chloro complex by flash photolysis of the corresponding Sb(III) and Sb(V) complexes in CH3CN and CHCl3
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[SbCl6]2- was formed in the flash photolysis of [SbCl6]3- or [SbCl6]- in both solutions of CH3CN and CHCl3 in the presence of an excess of chloride. [SbCl6]2- had absorption maxima at 293, 328, and 390 nm in CH3CN. A similar absorption spectrum of [SbCl6]2- was also obtained in CHCl3. The lifetime of [SbCl6]2- was much shorter in CHCl3 than in CH3CN. [SbCl6]- was easily reduced to [SbCl6]3- upon continuous UV- irradiation in CH3CN as well as in CHCl3. On the other hand, [SbCl6]3- was oxidized to [SbCl6]- in CHCl3 in the presence of oxygen, but was not in CH3CN. The spectrum and the decay rate of [SbCl6]2- were not essentially affected by oxygen in both solutions of CH3CN and CHCl3.
- Shinohara, Nobuyoshi,Ohshima, Masaaki
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- Electron-beam decomposition of carbon tetrachloride in air/nitrogen
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Carbon tetrachloride (CCl4, approximately 10, 50, and 100 ppm) in air and nitrogen was irradiated with electron beams in both the presence and absence of water. The absorbed doses ranged from 1.2 to 18.0 kGys. An absorbed dose of 18 kGy led to approximately 90% decomposition of CCl4 at a concentration of 10 ppm in dry air. The presence of water lowered the decomposition rate in air by 20%, but not in nitrogen. Negative oxygen ions (O2/-) formed upon the irradiation of wet air played a role in the oxidation of CCl4. Water molecules became negative cluster ions (O2/-(H2O)n) with negative oxygen ions, which depressed the oxidation.
- Hirota,Arai,Hashimoto
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- Pseudophase Ion-Exchange Model Applied to Kinetics in Aqueous Micelles under Extreme Conditions: A Simple Modification
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The dehydrochlorination of 1,1-diphenyl-2,2,2-trichloroethane (DTE) with hydroxide ion was studied in the presence of hexadecyltrimethylammonium hydroxide (CTAOH) micelles at 25.0 deg C, under conditions where the pseudophase ion-exchange model (PPIE) normally fails (high sodium hydroxide and salt concentrations).A simple modification of the model, which includes the variable degree of dissociation concept and the contribution of the counterion in the aqueous phase to the interfacial counterion concentration, allows the application of the PPIE model to all ranges of counterion concentrations in the presence and absence of added salts.
- Ferreira, Ligia Catarina Mello,Zucco, Cesar,Zanette, Dino,Nome, Faruk
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- Kinetics and Mechanism of the Chlorine Dioxide-Tetrathionate Reaction
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The chlorine-dioxide-tetrathionate reaction was studied spectrophotometrically in the pH range 4.55-5.55 at 25.0 ± 0.2 °C and 0.5 M ionic strength adjusted with sodium acetate as a buffer component. The stoichiometry was found to be S4O6 2- + 4°ClO2 + 5H2O → 4SO42- + ClO3- + 3Cl- + 10H+with small deviations at high excess of chlorine dioxide with no chloride ion initially present. The initial presence of chloride not only affects the stoichiometry but also accelerates the reaction. A 14-step mechanism, including four known and two newly proposed intermediates, is suggested to describe the observed behavior of the system.
- Horvath, Attila K.,Nagypal, Istvan,Epstein, Irving R.
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- First Micelle-Free Photoredox Catalytic Access to Hydrated Electrons for Syntheses and Remediations with a Visible LED or even Sunlight
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Hydrated electrons are super-reductants, yet can be generated with visible light when two photons are pooled, most efficiently through storing the energy of the first photon in a radical pair formed by the reduction of an excited catalyst by a sacrificial donor. All previous such systems for producing synthetically useable amounts of hydrated electrons with an LED in the visible range had to resort to compartmentalization by SDS micelles to curb the performance-limiting recombination of the pair. To overcome micelle-imposed constraints on sustainability and applications, we have instead attached carboxylate groups to a ruthenium (tris)bipyridyl catalyst such that its pentaanionic radical strongly repels the dianionic radical of the bioavailable donor urate. We have explored the influence of the Coulombic interactions on the electron generation by a time-resolved study from microseconds to hours, including for comparison the unsubstituted complex, which forms a monocationic radical, with and without SDS micelles. The new homogeneous electron source is best with regard to stability and total electron output; it has a broader synthetic scope because it does not entail micellar shielding of less hydrophilic compounds, which particularly facilitates cross-couplings; and it tolerates supramolecular containers as carriers of water-insoluble substrates or products. As an application in the field, we demonstrate the solar remediation of a recalcitrant chloro-organic bulk chemical.
- Naumann, Robert,Goez, Martin
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- Matrix Effect on Hydrogen Atom Tunneling from Alkane to Free Deuterium Atoms in Cryogenic Solid
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ESR study on alkyl radicals generated in deuterated organic matrixes at 77 K by hydrogen atom tunneling from alkane molecules to free deuterium atoms has been carried out for elucidating control factors for the tunneling. For small alkane molecules, the tunneling rate is determined by the height of the potential energy barrier for the tunneling. For larger molecules in glassy matrixes, the rate decreases with increasing number and length of alkyl chains bonded to a carbon atom to be hydrogen abstracted. The tunneling rate from antepenultimate tertiary carbon is much slower than that from penultimate secondary carbon, even the potential energy barrier is lower. This abnormal effect is explained as being due to the steric hindrance by matrix molecules to the deformation of alkane molecules during the reaction. The alkyl chains surrounded by matrix molecules prevent the deformation of the chemical bonds of the carbon atom from the initial sp3 to the final sp2 configuration, which may cause the increase of the thickness of the potential energy barrier and thereby decrease of the tunneling rate. Free deuterium atoms in a crystalline adamantane matrix selectively abstract hydrogen atoms from the antepenultimate tertiary carbon, probably due to less steric hindrance to the deformation.
- Ichikawa, Tsuneki,Kagei, Koh-Ichi,Tachikawa, Hiroto,Ishitani, Yoshinobu
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- The trans Effect in Gold(III) complexes. Kinetics os Substitution Reactions of the Trichloro(phenyl)aurate(III) Anion in Methanol
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The - ion undergoes reversible solvolysis of the chloride trans to C6H5- in methanol solution.The kinetics of the approach to equilibrium on adding excess of LiCl have been followed by stopped-flow spectrophotometry at temperatures below 0 de
- Ahmed, Etmina,Clark, Robin J. H.,Tobe, Martin L.,Cattalini, Lucio
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- A High-Temperature Photochemical Kinetics Study of the O + HCl Reaction from 350 to 1480 K
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Rate coefficients for the O + HCl reaction have been measured by using two differently designed high-temperature photochemistry (HTP) reactors.Measurements were made under pseudo-first-order conditions, , at temperatures from 350 to 1480 K and pressures from 100 to 613 Torr.Ground-state O atoms were generated by flash photolysis of O2 or CO2 and monitored by time-resolved atomic resonance fluorescence with pulse counting.The data show non-Arrhenius behavior and are well fitted by the empirical expression k(T) = 7.5 * 1E-22 T3.13 exp(-1550 K/T) cm3 molecule-1 s-1.Combining the present data with published measurements in the 350-720 K range yields k(T) = 5.6 * 1E-21 T2.87 exp(-1766 K/T) cm3 molecule-1 s-1 for the 350-1480 K range with a 2? confidence interval of 23percent, which figure includes a liberal allowance for potential systematic errors.The contribution to the observed reaction rates of vibrationally excited HCl at equilibrium concentrations is inferred to be negligible.The experimental results are consistent with transition-state theory (TST) calculations.
- Mahmud, Khaled,Kim, Jong-Sung,Fontijn, Arthur
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- Reactions of negative ions with ClN3 at 300 K
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The reactivity of ClN3 with 17 negative ions has been investigated at 300 K. The electron affinity (EA) of ClN3 was bracketed to be between that of NO2 and N3, giving EA(ClN3) = 2.48 ± 0.20 eV, in agr
- Eyet, Nicole,Freel, Keith,Heaven, Michael C.,Viggiano
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- Substitution reactions of [Fe4S4Cl4]2- with ButNC or Et2NCS2-: Trapping intermediates and detecting new pathways
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Kinetic studies on the substitution reaction between [Fe4S4Cl4]2- and ButNC or Et2NCS2- are reported. The binding of small molecules and ions to Fe-S clusters is a fundamental step in substitution reactions but can be difficult to follow directly because these reactions are rapid and often associated with small spectroscopic changes. A novel kinetic method is reported which allows the time course of molecule and ion binding to Fe-S clusters to be followed by monitoring the lability of the cluster. Using a stopped-flow, sequential-mix apparatus, [Fe4S4Cl4]2- and L (L = Et2NCS2- or ButNC) are rapidly mixed, and after a known time (δ) the resulting solution is mixed with a solution of PhS-. The thiolate substitutes for the chloro ligands on the cluster, in a reaction which is easy to follow because of the large change in the visible absorption spectrum. The rate of this substitution is extremely sensitive to whether L is bound to the cluster or not. By correlation of δ with the rate of the reaction with PhS-, the time course of the reaction between [Fe4S4Cl4]2- and L can be mapped out. In studies where L = ButNC this technique has allowed the detection of an intermediate {[Fe4S4Cl4(CNBut)]2-} which cannot be detected spectrophotometrically. In further studies, the substitution reactions of [Fe4S4Cl4]2- with PhS-, Et2NCS2-, or ButNC are all perturbed by the addition of Cl-. In all cases a common pathway for substitution is evident, but with Et2NCS2- an additional, slower pathway becomes apparent under conditions where the common pathway is completely inhibited by Cl-.
- Dunford, Adrian J.,Henderson, Richard A.
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- Photocatalytic Degradation of Rhodamine B using Aqueous Free-Base Porphyrin and Metalloporphyrins of Mn, Fe and Sn
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The aqueous-porphyrins used in clinical studies for photodynamic therapy (PDT) are exploited as the photocatalysts for the first time in the photodegradation of rhodamine B in the acetone medium. The porphyrins such as free-base porphyrin TPPS4 and MnTPPS4Cl, FeTPPS4Cl, a dimer (FeTPPS4)2-O and SnTPPS4Cl2 were synthesized and characterized by ultraviolet-visible, infrared, 1H NMR, fluorescence spectroscopies and elemental analysis. The band-gap energies of the respective porphyrins were determined using DRS spectroscopy. They have shown 100% degradation of the dye within 25-40 min, which was confirmed by HPLC and ion-chromatography. This has revealed that semiconductor aqueous-porphyrins may be a good choice as photocatalysts in the photodegradation of rhodamine B dye.
- Gokakakar, S. D.,Salker, A. V.
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p. 834 - 840
(2022/03/16)
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- Degradation of tri(2-chloroisopropyl) phosphate by the UV/H2O2 system: Kinetics, mechanisms and toxicity evaluation
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A photodegradation technology based on the combination of ultraviolet radiation with H2O2 (UV/H2O2) for degrading tri(chloroisopropyl) phosphate (TCPP) was developed. In ultrapure water, a pseudo-first order reaction was observed, and the degradation rate constant reached 0.0035 min?1 (R2 = 0.9871) for 5 mg L?1 TCPP using 250 W UV light irradiation with 50 mg L?1 H2O2. In detail, the yield rates of Cl? and PO43? reached 0.19 mg L?1 and 0.58 mg L?1, respectively. The total organic carbon (TOC) removal rate was 43.02%. The pH value of the TCPP solution after the reaction was 3.46. The mass spectrometric detection data showed a partial transformation of TCPP into a series of hydroxylated and dechlorinated products. Based on the luminescent bacteria experimental data, the toxicity of TCPP products increased obviously as the reaction proceeded. In conclusion, degradation of high concentration TCPP in UV/H2O2 systems may result in more toxic substances, but its potential application for real wastewater is promising in the future after appropriate optimization, domestication and evaluation.
- He, Huan,Ji, Qiuyi,Gao, Zhanqi,Yang, Shaogui,Sun, Cheng,Li, Shiyin,Zhang, Limin
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- Selective C-H halogenation over hydroxylation by non-heme iron(iv)-oxo
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Non-heme iron based halogenase enzymes promote selective halogenation of the sp3-C-H bond through iron(iv)-oxo-halide active species. During halogenation, competitive hydroxylation can be prevented completely in enzymatic systems. However, synthetic iron(iv)-oxo-halide intermediates often result in a mixture of halogenation and hydroxylation products. In this report, we have developed a new synthetic strategy by employing non-heme iron based complexes for selective sp3-C-H halogenation by overriding hydroxylation. A room temperature stable, iron(iv)-oxo complex, [Fe(2PyN2Q)(O)]2+ was directed for hydrogen atom abstraction (HAA) from aliphatic substrates and the iron(ii)-halide [FeII(2PyN2Q)(X)]+ (X, halogen) was exploited in conjunction to deliver the halogen atom to the ensuing carbon centered radical. Despite iron(iv)-oxo being an effective promoter of hydroxylation of aliphatic substrates, the perfect interplay of HAA and halogen atom transfer in this work leads to the halogenation product selectively by diverting the hydroxylation pathway. Experimental studies outline the mechanistic details of the iron(iv)-oxo mediated halogenation reactions. A kinetic isotope study between PhCH3 and C6D5CD3 showed a value of 13.5 that supports the initial HAA step as the RDS during halogenation. Successful implementation of this new strategy led to the establishment of a functional mimic of non-heme halogenase enzymes with an excellent selectivity for halogenation over hydroxylation. Detailed theoretical studies based on density functional methods reveal how the small difference in the ligand design leads to a large difference in the electronic structure of the [Fe(2PyN2Q)(O)]2+ species. Both experimental and computational studies suggest that the halide rebound process of the cage escaped radical with iron(iii)-halide is energetically favorable compared to iron(iii)-hydroxide and it brings in selective formation of halogenation products over hydroxylation.
- Rana, Sujoy,Biswas, Jyoti Prasad,Sen, Asmita,Clémancey, Martin,Blondin, Geneviève,Latour, Jean-Marc,Rajaraman, Gopalan,Maiti, Debabrata
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p. 7843 - 7858
(2018/10/31)
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- Kinetics and mechanism of the chromium(VI) catalyzed decomposition of hypochlorous acid at elevated temperature and high ionic strength
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An important reaction step in the industrial production of NaClO3 (electrochemical chlorate process) is the thermal decomposition of HOCl/OCl- to yield ClO3- and Cl-. It is widely accepted that this reaction is accelerated by aqueous chromium(vi) species. A detailed kinetic study was conducted under industrially relevant conditions, i.e. at high ionic strength (6.0 M) and elevated temperature (80 °C), to investigate this phenomenon. The decomposition of hypochlorous acid was followed in the presence of Cr(vi) or phosphate (PO43-) or without any additive. In addition to the beneficial pH buffering effect of Cr(vi), the CrO42- form of chromium(vi) was found to slightly catalyze the decomposition of hypochlorous acid. The overall rate of HOCl decomposition can be expressed as -dcHOCl/dt = kdec[HOCl]2[OCl-] + kcat[HOCl]2[CrO42-]. The corresponding rate constants were determined, kdec = 9.4 ± 0.1 M-2 s-1 and kcat = 4.6 ± 0.8 M-2 s-1, and mechanistic interpretation of the catalytic rate law is given. The contribution of the catalytic path to the overall rate of decomposition changes from ca. 30% at pH = 8 to ca. 70% at pH = 6.
- Kalmár, József,Szabó, Mária,Simic, Nina,Fábián, István
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p. 3831 - 3840
(2018/03/21)
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- Gas-Phase Reaction of Methyl n-Propyl Ether with OH, NO3, and Cl: Kinetics and Mechanism
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Rate constants at room temperature (293 ± 2 K) and atmospheric pressure for the reaction of methyl n-propyl ether (MnPE), CH3OCH2CH2CH3, with OH and NO3 radicals and the Cl atom have been determined in a 100 L FEP-Teflon reaction chamber in conjunction with gas chromatography-flame ionization detector (GC-FID) as the detection technique. The obtained rate constants k (in units of cm3 molecule-1 s-1) are (9.91 ± 2.30) × 10-12, (1.67 ± 0.32) × 10-15, and (2.52 ± 0.14) × 10-10 for reactions with OH, NO3, and Cl, respectively. The products of these reactions were investigated by gas chromatography-mass spectrometry (GC-MS), and formation mechanisms are proposed for the observed reaction products. Atmospheric lifetimes of the studied ether, calculated from rate constants of the different reactions, reveal that the dominant loss process for MnPE is its reaction with OH, while in coastal areas and in the marine boundary layer, MnPE loss by Cl reaction is also important.
- Zhu, Jianqiang,Wang, Shuyan,Tsona, Narcisse T.,Jiang, Xiaotong,Wang, Yifeng,Ge, Maofa,Du, Lin
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p. 6800 - 6809
(2017/09/23)
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- Semi-hard magnetic properties of nanoparticles of cobalt ferrite synthesized by the co-precipitation process
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The nanoparticles ferromagnetic materials CoFe2O4have been synthesized by the co-precipitation method and annealed at various temperatures from 773 to 1223 K. The influence of the heat treatment on the structural, morphological and magnetic properties of CoFe2O4nanoparticles was investigated. The structure, morphology and magnetic properties of the annealing samples were reached by mean of X-ray diffraction (XRD), scanning electron microscopy (SEM) techniques and measurement of hysteresis loop. The average crystallite size, lattice parameter and X-ray density were calculated from X-ray diffraction data. All samples have the cubic spinel structure with average crystallite sizes increasing from 30 to 178 nm with the temperature. The results show that CoFe2O4nanoparticles prepared by this method have small and more uniform size. The measurements of the hysteresis loop, performed at both 10 K and 300 K, indicate a ferromagnetic behavior of nanoparticles. Also the measurement at 300 K shows that the sample annealed at 1023 K is magnetically harder than the other samples. The coercive fields are 1.58 kOe against the values inferior at 0.61 kOe for the other samples. Indeed, the remanent magnetization is 31.85 emu g?1for the hard magnetic sample against 13.02 and 17.29 emu g?1for the soft magnetic samples annealed at 773 and 1223 K, respectively. The origin of the hard-soft magnetic properties of nanoparticles CoFe2O4is discussed in terms of the co-existence of secondary phases β-Fe2O3, CoO2and the distribution of Fe2+and Co2+ions within the lattice.
- Hosni,Zehani,Bartoli,Bessais,Maghraoui-Meherzi
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p. 1295 - 1301
(2016/10/30)
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- Design and construction of a bifunctional magnetically recyclable 3D CoMn2O4/CF hybrid as an adsorptive photocatalyst for the effective removal of contaminants
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Herein, a magnetic microsphere CoMn2O4 (MS-CoMn2O4) with a 3D architecture was constructed directly on cellulose fiber (CF) substrates from wastepaper by a solvothermal synthesis method with further calcination treatment. The designed hybrid shows excellent dual functions including rapid catalytic oxidation of tetracycline (TC)/methylene blue (MB) and a high adsorption capacity. What's more, the hybrid is easily recycled using an external magnetic field. In comparison with that of pure MS-CoMn2O4, the enhanced adsorption ability and photocatalytic activity of MS-CoMn2O4/CFs can mainly be attributed to the introduced cellulose fiber supporter in the hybrid system. MS-CoMn2O4 incorporated CFs can improve the efficient separation of photogenerated electron-hole pairs and the transport pathway of electrons. More importantly, introduction of CFs can help to enrich and further improve the degradation efficiency of organic contaminants. The possible mechanism for the enhancement of the photocatalytic activity has been elucidated in detail. The reusability analysis revealed that the MS-CoMn2O4/CF hybrid exhibited superb cycling stability after 5 cycles. This study provides novel insights into the design and construction of high capacity sorbents as strongly adsorptive photocatalysts to perform catalytic degradation of organic contaminants.
- Zheng, Jianhua,Hu, Yandong,Zhang, Lei
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p. 25044 - 25051
(2017/09/29)
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- Measuring the rate constant of the reaction between chlorine atoms and CHF2Br by Cl atom resonance fluorescence
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The rate constant of the reaction between Cl atoms and CHF2Br has been measured by chlorine atom resonance fluorescence in a flow reactor at temperatures of 295–368 K and a pressure of ~1.5 Torr. Lining the inner surface of the reactor with F-32L fluoroplastic makes the rate of the heterogeneous loss of chlorine atoms very low (khet ≤ 5 s–1). The rate constant of the reaction is given by the formula k = (4.23 ± 0.13) × 10–12e(–15.56 ± 1.58)/RT cm3 molecule–1 s–1 (with the activation energy in kJ/mol units). The possible role of this reaction in the extinguishing of fires producing high concentrations of chlorine atoms is discussed.
- Larin,Spasskii,Trofimova,Proncheva
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p. 308 - 312
(2016/07/06)
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- Mechanism of thermal decomposition of allyltrichlorosilane with formation of three labile intermediates: dichlorosilylene, allyl radical, and atomic chlorine
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It is experimentally found that allyltrichlorosilane dissociates under vacuum pyrolysis (~10–2 Torr) at temperatures above 1100 K to form three labile intermediates: allyl radical, dichlorosilylene, and monoatomic chlorine. On the basis of experimental and theoretical data obtained, it is shown that the decomposition reaction proceeds in two steps. The first step is a typical reaction of homolytic decomposition to two radicals (C3H5 and SiCl3) at the weakest Si—C bond. Due to weakness of the Si—Cl bond in the SiCl3 radical, the energy of which is even somewhat lower than the dissociation energy of the Si—C bond in starting AllSiCl3, this radical undergoes further dissociation to SiCl2 and Cl, thus resulting in three intermediates of different classes of highly reactive species formed from AllSiCl3.
- Boganov,Promyslov,Krylova,Zaitseva,Egorov
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p. 1216 - 1224
(2017/02/05)
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- Bioinspired complex-nanoparticle hybrid catalyst system for aqueous perchlorate reduction: Rhenium speciation and its influence on catalyst activity
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A highly active catalyst for reduction of the inert water contaminant perchlorate (ClO4-) to Cl- with 1 atm H2 at 25 °C is prepared by noncovalently immobilizing the rhenium complex ReV(O)(hoz)2Cl (hoz = 2-(2′-hydroxyphenyl)-2-oxazoline) together with Pd0 nanoparticles on a porous carbon support. Like the Mo complex centers in biological oxyanion reductases, the immobilized Re complex serves as a single site for oxygen atom transfer from ClO4- and ClOx- intermediates, whereas Pd0 nanoparticles provide atomic hydrogen reducing equivalents to sustain redox cycling of the immobilized Re sites, replacing the more complex chain of electron transfer steps that sustain Mo centers within oxyanion reductases. An in situ aqueous adsorption method of immobilization was used to preserve the active ReV(O)(hoz)2 structure during bimetallic catalyst preparation and enable study of Re redox cycling and reactions with ClO4-. Heterogeneous reaction kinetics, X-ray photoelectron spectroscopy, and experiments with homogeneous model Re complexes are combined to obtain insights into the catalytic reaction mechanisms and the influence of Re speciation on catalyst reactivity with ClO4-. Redox cycling between hoz-coordinated ReV and ReVII species serves as the main catalytic cycle for ClO4- reduction. Under reducing conditions, approximately half of the immobilized hoz-coordinated ReV is further reduced to ReIII, which is not directly reactive with ClO4-. A small fraction of the hoz-coordinated ReVII species can dissociate to ReO4- and free hoz, which are then reductively reimmobilized as a less reactive mixture of ReV, ReIII, and ReI species. This study provides an example wherein highly active metal complexes that were originally developed for homogeneous organic phase catalysis can be incorporated into heterogeneous catalysts for practical environmental applications. Findings suggest a general blueprint for developing hybrid catalysts combining single-site transition metal complexes with hydrogen-activating metal nanoparticles.
- Liu, Jinyong,Choe, Jong Kwon,Wang, Yin,Shapley, John R.,Werth, Charles J.,Strathmann, Timothy J.
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p. 511 - 522
(2015/03/04)
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- Synthesis and characterization of Pt/AgVO3 nanowires for degradation of atrazine using visible light irradiation
-
A hydrothermal method was used to prepare β-AgVO3 nanowire, a photo-assisted deposition (PAD) method was used to prepare Pt/β-AgVO3 nanowires. β-AgVO3 and Pt/β-AgVO3 nanowires were characterized using XRD, BET, UV-Vis spectroscopy, Pl, TEM, and XPS techniques. The results reveal that platinum was present as platinum metal and it is well dispersed on the surface of β-AgVO3 nanowire. The photocatalytic degradation of atrazine under visible light irradiation was used to measure the photocatalytic performance of the β-AgVO3 and Pt/β-AgVO3 nanowires. The photocatalytic activity of Pt/β-AgVO3 nanowires have higher photocatalytic activity than β-AgVO3 nanowire. The reason for the high photocatalytic activity of Pt/β-AgVO3 nanowires may be due to the synergic effect between Pt and β-AgVO3.
- Malkhasian, Aramice Y.S.
-
p. 394 - 399
(2015/08/06)
-
- Enhanced photocatalytic degradation of methylene blue under vacuum ultraviolet irradiation
-
A vacuum ultraviolet (VUV) lamp was used as the irradiation of photocatalysis to enhance the degradation of methylene blue (MB), a model dye compound. In contrast to photocatalysis under 254 nm UV irradiation (UV/TiO 2), photocatalysis under VUV irradiation (VUV/TiO2) exhibited much higher efficiency in MB degradation and mineralization and needed less TiO2 dosage. The rate constant of MB degradation in VUV/TiO2 (0.0793 min-1) is about 4 times of that of UV/TiO2 (0.0205 min-1). The MB mineralization rate is also greatly increased from 12.5% in UV/TiO2 to 47.7% in VUV/TiO 2 after 60 min of irradiation. Multiple advanced oxidation processes including photocatalytic oxidation and VUV photo-oxidation coexist in VUV/TiO2 to substantially produce highly reactive species (such as OH and energetic photons), which is responsible for efficient degradation and mineralization of MB.
- Huang, Haibao,Leung, Dennis Y.C.,Kwong, Philip C.W.,Xiong, Jing,Zhang, Lu
-
p. 189 - 194
(2013/02/25)
-
- Enhancing the anion affinity of urea-based receptors with a Ru(terpy) 22+ chromophore
-
Covalent linking of a Ru(terpy)22+ substituent improves recognition and sensing properties of the urea subunit toward anions. Urea's anion affinity is enhanced by the electrostatic attraction exerted by the RuII cation and by the electron-withdrawing effect exerted by the entire polypyridine-metal complex. Such an enhancement of the anion affinity, which results from the combination of a through-space and a through-bond effect, is greater than that exerted by the classical neutral electron-withdrawing substituent nitrophenyl. Small yet significant modifications of π-π* and MLCT bands of the Ru(terpy)22+ chromophore, detected through UV-vis spectrophotometric titrations, allowed the determination of the constants for the formation of receptor-anion H-bond complexes in diluted MeCN solution. On 1H NMR titration experiments, carried out under more concentrated conditions, the interaction of a second Cl- ion was observed, taking place through an outer-sphere mechanism. The Ru(terpy) 22+ substituent favors the deprotonation of a urea N-H fragment on addition of a second equivalent of fluoride, with formation of HF2-.
- Baggi, Giorgio,Boiocchi, Massimo,Ciarrocchi, Carlo,Fabbrizzi, Luigi
-
p. 5273 - 5283
(2013/06/26)
-
- Atmospheric chemistry of CF3CH2OCH3: Reaction with chlorine atoms and OH radicals, kinetics, degradation mechanism and global warming potential
-
FTIR smog chamber techniques were used to measure k(Cl + CF 3CH2OCH3) = (2.28 ± 0.44) × 10-11 and k(OH + CF3CH2OCH3) = (4.9 ± 1.3) × 10-13 cm3 molecule-1 s-1 in 700 Torr total pressure of air at 296 ± 2 K. The atmospheric lifetime of CF3CH2OCH3 is estimated at 25 days. Reaction of Cl atoms with CF3CH2OCH 3 proceeds 79 ± 4% at the CH3 group and 22 ± 2% at the CH2 group. Reaction with OH radicals proceeds 55 ± 5% at the CH3 group yielding CF3CH2OCHO and 45 ± 5% at the CH2 group yielding COF2 and CH 3OCHO as primary oxidation products. The infrared spectrum of CF 3CH(O)OCH3 was measured and a global warming potential GWP100 = 8 was estimated. The atmospheric chemistry and environmental impact of CF3CH2OCH3 is discussed in context of the use of hydrofluoroethers as CFC substitutes.
- ?sterstr?m, Freja From,Nielsen, Ole John,Sulbaek Andersen, Mads P.,Wallington, Timothy J.
-
-
- Catalytic reactions of chlorite with a polypyridylruthenium(ii) complex: Disproportionation, chlorine dioxide formation and alcohol oxidation
-
cis-[Ru(2,9-Me2phen)2(OH2) 2]2+ reacts readily with chlorite at room temperature at pH 4.9 and 6.8. The ruthenium(ii) complex can catalyze the disproportionation of chlorite to chlorate and chloride, the oxidation of chlorite to chlorine dioxide, as well as the oxidation of alcohols by chlorite. The Royal Society of Chemistry 2012.
- Hu, Zongmin,Du, Hongxia,Man, Wai-Lun,Leung, Chi-Fai,Liang, Haojun,Lau, Tai-Chu
-
p. 1102 - 1104
(2012/02/17)
-
- Temperature (290-400 K) and pressure (5-900 Torr) dependence of the kinetics of the reactions of chlorine atoms with propene and 1-butene
-
Rate constants for reactions of chlorine atoms with propene (k1) and 1-butene (k2) were measured relative to that of chlorine atoms with n-butane (k3) at 295-400 K in 5-900 Torr of N2 using gas chromatographic a
- Kaiser,Wallington
-
p. 187 - 192
(2011/02/28)
-
- Heterogeneous catalytic reduction of perchlorate in water with Re-Pd/C catalysts derived from an oxorhenium(V) molecular precursor
-
The molecular Re(V) complex, chlorobis(2-(2′-hydroxyphenyl)-2- oxazoline)-oxorhenium(V), Re(O)(hoz)2Cl, has been investigated as a suitable precursor, when combined with activated carbon powder containing 5 wt % Pd, to provide a heterogeneous catalyst for the reduction of aqueous perchlorate by hydrogen. Two general methods for catalyst preparation have been adopted: first, by a standard "incipient wetness" impregnation of the carbon powder with handling under largely aerobic conditions for convenience and, second, by a completely anaerobic procedure maintaining a hydrogen atmosphere during adsorption of the complex in water onto the powder. Both types of catalyst were efficient for the complete reduction of perchlorate to chloride within a few hours at room temperature over a range of initial concentrations (2-200 ppm) under 1 atm of H2 and acidic conditions (pH 2.7-3.7). The perchlorate reduction profiles displayed pseudo-first-order kinetics, and the rates were insensitive to excess chloride. Complete reduction of perchlorate was observed even at pH 5.9 in a phosphate buffer over the course of two weeks. Under comparable conditions, chlorate reduction proceeded ca. 10 times more quickly than perchlorate reduction. The impregnated catalyst was examined by STEM/EDS, which revealed a wide distribution in Pd nanoparticle sizes and also suggested that the Re complex did not aggregate preferentially on or near the Pd particles. XPS of this material provided evidence for reduced Pd after the reaction, but only a +7 oxidation state was seen for the Re sites both pre- and postreduction. Elemental analyses of the catalyst materials taken pre- and postreduction showed variable amounts of Re loss (0-50%) but relatively unchanged amounts of nitrogen. These results show the need to maintain a reducing atmosphere during the preparation and operation of the catalyst in order to achieve optimum activity and stability.
- Zhang, Yunxia,Hurley, Keith D.,Shapley, John R.
-
p. 1534 - 1543
(2011/04/17)
-
- Dynamics of Cl (2Pj) atom formation in the photodissociation of fumaryl chloride (ClCO - CH = CH - COCl) at 235 nm: A resonance enhanced multiphoton ionization (REMPI) time-of-flight (TOF) study
-
The photodissociation dynamics of fumaryl chloride (ClCO-CH=CH-COCl) has been studied in a supersonic molecular beam around 235 nm using resonance enhanced multiphoton ionization (REMPI) time-of-flight (TOF) technique by detecting the nascent state of the primary chlorine atom. A single laser has been used for excitation of fumaryl chloride and the REMPI detection of chlorine atoms in their spin-orbit states, Cl (2P3/2) and Cl* (2P1/2). We have determined the translational energy distribution, the recoil anisotropy parameter, β, and the spin-orbit branching ratio for chlorine atom elimination channels. To obtain these, measured polarization-dependent and state-specific TOF profiles are converted into kinetic energy distributions, using a least-squares fitting method, taking into account the fragment recoil anisotropies, βi. The TOF profiles for both Cl and Cl* are found to be independent of laser polarization; i.e., β is well characterized by a value of 0.0, within the experimental uncertainties. Two components, namely, the fast and the slow, are observed in the translational energy distribution, P(ET), of Cl and Cl* atoms, and assigned to be formed from different potential energy surfaces. The average translational energies for the fast components of the Cl and Cl* channels are 14.9 ± 1.6 and 16.8 ± 1.6 kcal/mol, respectively. Similarly, for the slow components, the average translational energies of the Cl and Cl* channels are 3.4 ± 0.8 and 3.1 ± 0.8 kcal/mol, respectively. The energy partitioning into the translational modes is interpreted with the help of various models, such as impulsive and statistical models. Apart from the chlorine atom elimination channel, molecular hydrogen chloride (HCl) elimination is also observed in the photodissociation process. The HCl product has been detected, using a REMPI scheme in the region of 236-237 nm. The observation of the molecular HCl in the dissociation process highlights the importance of the relaxation process, in which the initially excited parent molecule relaxes to the ground state from where the molecular (HCl) elimination takes place.
- Kawade, Monali,Saha, Ankur,Upadhyaya, Hari P.,Kumar, Awadhesh,Naik, Prakash D.,Bajaj
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p. 1538 - 1546
(2011/05/07)
-
- Dissection of the mechanism of manganese porphyrin-catalyzed chlorine dioxide generation
-
Chlorine dioxide, an industrially important biocide and bleach, is produced rapidly and efficiently from chlorite ion in the presence of water-soluble, manganese porphyrins and porphyrazines at neutral pH under mild conditions. The electron-deficient manganese(III) tetra-(N,N-dimethyl)imidazolium porphyrin (MnTDMImP), tetra-(N,N-dimethyl)benzimidazolium (MnTDMBImP) porphyrin, and manganese(III) tetra-N-methyl-2,3-pyridinoporphyrazine (MnTM23PyPz) were found to be the most efficient catalysts for this process. The more typical manganese tetra-4-N-methylpyridiumporphyrin (Mn-4-TMPyP) was much less effective. Rates for the best catalysts were in the range of 0.24-32 TO/s with MnTM23PyPz being the fastest. The kinetics of reactions of the various ClOx species (e.g., chlorite ion, hypochlorous acid, and chlorine dioxide) with authentic oxomanganese(IV) and dioxomanganese(V)MnTDMImP intermediates were studied by stopped-flow spectroscopy. Rate-limiting oxidation of the manganese(III) catalyst by chlorite ion via oxygen atom transfer is proposed to afford a trans-dioxomanganese(V) intermediate. Both trans-dioxomanganese(V)TDMImP and oxoaqua-manganese(IV)TDMImP oxidize chlorite ion by 1-electron, generating the product chlorine dioxide with bimolecular rate constants of 6.30 × 10 3 M-1 s-1 and 3.13 × 103 M-1 s-1, respectively, at pH 6.8. Chlorine dioxide was able to oxidize manganese(III)TDMImP to oxomanganese(IV) at a similar rate, establishing a redox steady-state equilibrium under turnover conditions. Hypochlorous acid (HOCl) produced during turnover was found to rapidly and reversibly react with manganese(III)TDMImP to give dioxoMn(V)TDMImP and chloride ion. The measured equilibrium constant for this reaction (Keq = 2.2 at pH 5.1) afforded a value for the oxoMn(V)/Mn(III) redox couple under catalytic conditions (E′ = 1.35 V vs NHE). In subsequent processes, chlorine dioxide reacts with both oxomanganese(V) and oxomanganese(IV)TDMImP to afford chlorate ion. Kinetic simulations of the proposed mechanism using experimentally measured rate constants were in agreement with observed chlorine dioxide growth and decay curves, measured chlorate yields, and the oxoMn(IV)/Mn(III) redox potential (1.03 V vs NHE). This acid-free catalysis could form the basis for a new process to make ClO2.
- Umile, Thomas P.,Wang, Dong,Groves, John T.
-
p. 10353 - 10362
(2011/11/29)
-
- PLP-LIF study of the reactions of chlorine atoms with C2H 2, C2H4, and C3H6 in 2-100 Torr of N2 diluent at 295 K
-
Pulsed laser photolysis-laser-induced fluorescence (PLP-LIF) techniques were used to study the reactions of Cl(2P3/2) atoms with C2H2 (k1), C2H4 (k 2), and C3/su
- Iwasaki, Erika,Chiba, Hitoshi,Nakayama, Tomoki,Matsumi, Yutaka,Wallington, Timothy J.
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p. 174 - 178
(2010/09/17)
-
- Kinetics of the reaction of Cl atoms with CHCl3 over the temperature range 253-313 K
-
The reaction CHCl3 + Cl → CCl3 + HCl was studied in the atmospherically relevant temperature range from 253 to 313 K and in 930 mbar of N2 diluent using the relative rate method. A temperature dependent reaction rate constant, valid in the temperature range 220-330 K, was determined by a fit to the result of the present study and that of Orlando (1999); k = (3.77 ± 0.32) × 10-12 exp((-1011 ± 24)/T) cm3 molecule-1 s-1.
- Nilsson, Elna J.K.,Hoff, Janus,Nielsen, Ole John,Johnson, Matthew S.
-
p. 160 - 162
(2010/09/17)
-
- Organosulfur oxoacids. Part 2. A novel dimethylthiourea metabolite - Synthesis and characterization of the surprisingly stable and inert dimethylaminoiminomethane sulfonic acid
-
A new metabolite of the biologically active thiocarbamide dimethylthiourea (DMTU) has been synthesized and characterized. DMTU's metabolic activation in the physiological environment is expected to be dominated by S-oxygenation, which produces, successively, the sulfenic, sulfinic, and sulfonic acids before forming sulfate and dimethylurea. Only the sulfinic and sulfonic acids are stable enough to be isolated. This manuscript reports on the first synthesis, isolation, and characterization of the sulfonic acid: dimethylaminoiminomethanesulfonic acid (DMAIMSOA). It crystallizes in the orthorhombic Pbca space group and exists as a zwitterion in its solid crystal form. The negative charge is delocalized over the sulfonic acid oxygens and the positive charge is concentrated over the planar N-C-N framework rather than strictly on the sp2-hybridized cationic carbon center. As opposed to its sulfinic acid analogue, DMAIMSOA is extremely inert in acidic environments and can maintain its titer for weeks at pH 6 and below. It is, however, reasonably reactive at physiological pH conditions and can be oxidized to dimethylurea and sulfate by mild oxidants such as aqueous iodine.
- Petersen, Jeffrey L.,Otoikhian, Adenike A.,Morakinyo, Moshood K.,Simoyi, Reuben H.
-
p. 1247 - 1255
(2011/02/24)
-
- Kinetics of the reactions of chlorine atoms with a series of acetates
-
The kinetics of the reactions of Cl atoms with a series of alkyl acetates were investigated using relative and absolute rate methods in 2-700 Torr of N2 at room temperature. Consistent results were obtained using the two methods. The data from
- Xing, Jia-Hua,Takahashi, Kenshi,Hurley, Michael D.,Wallington, Timothy J.
-
p. 268 - 272
(2009/12/04)
-
- Ion imaging studies of ClONO2 photodissociation: Primary branching ratios and secondary dissociation
-
The photodissociation dynamics of ClONO2 at 235 nm has been reinvestigated using velocity map ion imaging. We report branching ratios for the Cl + NO3 and ClO + NO2 channels to be 0.49:0.51 with anisotropy parameters of β
- Kim, Hahkjoon,Greenwald, Erin E.,North, Simon W.
-
-
- Concerted dismutation of chlorite ion: Water-soluble iron-porphyrins as first generation model complexes for chlorite dismutase
-
Three iron-5,10,15,20-tetraarylporphyrins (Fe(Por-Ar4), Ar = 2,3,5,6-tetrafluro-N, N, N-trimethylanilinium (1), N, N, N-trimethylanilinium (2), and p-sulfonatophenyl (3)) have been investigated as catalysts for the dismutation of chlorite (CIO
- Zdilla, Michael J.,Lee, Amanda Q.,Abu-Omar, Mahdi M.
-
p. 2260 - 2268
(2009/09/08)
-
- Chlorine-catalyzed ozone destruction: Cl atom production from ClOOCl photolysis
-
Recent laboratory measurements of the absorption cross sections of the ClO dimer, ClOOCl, have called into question the validity of the mechanism that describes the catalytic removal of ozone by chlorine. Here we describe direct measurements of the rate-d
- Wilmouth, David M.,Hanisco, Thomas F.,Stimpfle, Richard M.,Anderson, James G.
-
p. 14099 - 14108
(2010/06/12)
-
- Atmospheric chemistry of 3-pentanol: Kinetics, mechanisms, and products of Cl atom and OH radical initiated oxidation in the presence and absence of NOx
-
Smog chamber/FTIR techniques were used to study the atmospheric chemistry of 3-pentanol and determine rate constants of k(Cl+3-pentanol) = (2.03 ± 0.23) × 10-10 and k(OH+3-pentanol) = (1.32 ± 0.15) × 10-11 cm3 moleculesup
- Hurley,Wallington,Bjarrum,Javadi,Nielsen
-
p. 8053 - 8060
(2009/04/13)
-
- Adiabatic and nonadiabatic dynamics in the C H3 (CD3) +HCl reaction
-
The scattering dynamics leading to the formation of Cl (P 32 2) and Cl* (P 12 2) products of the C H3 +HCl reaction (at a mean collision energy ? Ecoll ? =22.3 kcal mol-1) and the Cl (P 32 2) products of the C D3 +HCl reaction (at ? Ecoll ? =19.4 kcal mol-1) have beeninvestigated by using photodissociation of C H3 I and C D3 I as sources of translationally hot methyl radicals and velocity map imaging of the Cl atom products. Image analysis with a Legendre moment fitting procedur e demonstrates that, in all three reactions, the Cl Cl* products are mostly forward scattered with respect to the HCl in the center-of-mass (c.m.) frame but with a backward scattered component. The distributions of the fraction of the available energy released as translation peak at ft =0.31-0.33 for all the reactions, with average values that lie in the range ? ft ? =0.42-0.47. The detailed analysis indicates the importance of collision energy in facilitating the nonadiabatic transitions that lead to Cl* production. The similarities between the c.m.-frame scattering and kinetic energy release distributions for Cl and Cl* channelssuggest that the nonadiabatic transitions to a low-lying excited potent ial energy surface (PES) correlating to Cl* products occur after passagethrough the transition state region on the ground-state PES. Branching fractions for Cl* are determined to be 0.14±0.02 for the C H3 +HC l reaction and 0.20±0.03 for the C D3 +HCl reaction. The difference cannot be accounted for by changes in collision energy, mass effects,or vibrational excitation of the photolytically generated methyl radica l reagents and instead suggests that the low-frequency bending modes of the C D3 H or C H4 coproduct are important mediators of the nonadiabaticcouplings occurring in this reaction system.
- Retail, Bertrand,Pearce, Julie K.,Greaves, Stuart J.,Rose, Rebecca A.,Orr-Ewing, Andrew J.
-
-
- Collision energy dependence of the O(1D) + HCl -OH + Cl( 2P) reaction studied by crossed beam scattering and quasiclassical trajectory calculations on ab initio potential energy surfaces
-
The dynamics of the O(1D) + HCl → OH + Cl(2P) reaction are investigated by a crossed molecular beam ion-imaging method and quasiclassical trajectory calculations on the three ab initio potential energy surfaces, the ground 11A′ and two excited (1 1A″ and 21A′) states. The scattering experiment was carried out at collision energies of 4.2, 4.5, and 6.4 kcal/mol. The observed doubly differential cross sections (DCSs) for the Cl(2P) product exhibit almost no collision energy dependence over this inspected energy range. The nearly forward-backward symmetric DCS indicates that the reaction proceeds predominantly on the ground-state potential energy surface at these energies. Variation of the forward-backward asymmetry with collision energy is interpreted using an osculating complex model. Although the potential energy surfaces obtained by CASSCF-MRCI ab initio calculations exhibit relatively low potential barriers of 1.6 and 6.5 kcal/mol for 1 1A″ and 21A′, respectively, the dynamics calculations indicate that contributions of these excited states are small at the collision energies lower than 15.0 kcal/mol. Theoretical DCSs calculated for the ground-state reaction pathway agree well with the observed ones. These experimental and theoretical results suggest that the titled reaction at collision energies less than 6.5 kcal/mol is predominantly via the ground electronic state.
- Kohguchi, Hiroshi,Suzuki, Toshinori,Nanbu, Shinkoh,Ishida, Toshimasa,Mil'nikov, Gennady V.,Oloyede, Ponmile,Nakamura, Hiroki
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p. 818 - 825
(2008/10/09)
-
- Experimental and theoretical study of the carbon-13 and deuterium kinetic isotope effects in the Cl and OH reactions of CH3F
-
A laser flash photolysis-resonance fluorescence technique has been employed to determine absolute rate coefficients for the CH3F + Cl reaction in N2 bath gas in the temperature range of 200-700 K and pressure range of 33-133 hPa. The data were fitted to a modified Arrhenius expression k(T) = 1.14 × 10-12 x (T/ 298)226 exp{-313/T}. The OH and Cl reaction rates of 13CH3F and CD3F have been measured by long-path FTIR spectroscopy relative to CH3F at 298 ± 2 K and 1013 ± 10 hPa in purified air. The FTIR spectra were fitted using a nonlinear least-squares spectral fitting method including line data from the HITRAN database and measured infrared spectra as references. The relative reaction rates defined by α = klight/k heavy were determined to be kOH+CH3F/kOH+CD3F = 4.067 ± 0.018, kOH+CH3F/kOH+13CH3F = 1-067 ± 0.006, kCl+CH3F/kCl+CD3F = 5.11 ± 0.07, and kCl+CH3F/kCl+13CH3F = 1-016 ± 0.006. The carbon-13 and deuterium kinetic isotope effects in the OH and Cl reactions of CH3F have been further investigated by quantum chemistry methods and variational transition state theory.
- Marinkovic, Marina,Gruber-Stadler, Margret,Nicovich, J. Michael,Soller, Raenell,Muelhaeuser, Max,Wine, Paul H.,Bache-Andreassen, Lihn,Nielsen, Claus J.
-
p. 12416 - 12429
(2009/06/17)
-
- Experimental and theoretical investigation of electron attachment to S F5 Cl
-
Thermal electron attachment to S F5 Cl has been studied with the flowingafterglow Langmuir probe technique. The rate coefficient is moderate, 4 .8 (±1.2) × 10-8 cm3 s-1, and invariant with temperature over the temperature range of 300-550 K. The reaction is dissociative, forming mainly S F5- +Cl. Minor yields of Cl- and F Cl- were also found. The yields of the minor channels increase slightly with temperature. Statistical unimolecular rate modeling is employed to elucidate the characterof the dissociation pathways and to support the assumption that the dis sociations involve the formation of metastable anionic S F5 Cl-.
- Doren, Jane M. Van,Miller, Thomas M.,Viggiano, Albert A.,Spanel, Patrik,Smith, David,et al.
-
-
- Effect of chloride ion on the kinetics and mechanism of the reaction between chlorite ion and hypochlorous acid
-
The effect of chloride ion on the chlorine dioxide formation in the ClO2--HOCl reaction was studied by following ?ClO2 concentration spectrophotometrically at pH 5-6 in 0.5 M sodium acetate. On the basis of the earlier experimental data collected without initially added chloride and on new experiments, the earlier kinetic model was modified and extended to interpret the two series of experiments together. It was found that the chloride ion significantly increases the initial rate of ?ClO2 formation. At the same time, the ?ClO2 yield is increased in HOCl but decreased in ClO2- excess by the increase of the chloride ion concentration. The two-step hydrolysis of dissolved chlorine through Cl2 + H2O ? Cl 2OH- + H+ and Cl2OH- ? HOCl + Cl- and the increased reactivity of Cl 2OH- compared to HOCl are proposed to explain these phenomena. It is reinforced that the hydrolysis of the transient Cl 2O2 takes place through a HOCl-catalyzed step instead of the spontaneous hydrolysis. A seven-step kinetic model with six rate parameters (constants and/or ratio of constants) is proposed on the basis of the rigorous least-squares fitting of the parameters simultaneously to 129 absorbance versus time curves measured up to ~90% conversion. The advantage of this method of evaluation is briefly outlined.
- Kormanyos, Balazs,Nagypal, Istvan,Peintler, Gabor,Horvath, Attila K.
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p. 7914 - 7920
(2009/02/08)
-
- Kinetics and mechanism of oxidation of some thioacids by benzyltrimethylammonium chlorobromate
-
The oxidation of some thioacids, viz., thioplycollic, thiolactic and thiomalic acids by benzyltrimethylammonium chlorobromate (BTMACB) has been studied in acetic acid. The reaction is first order with respect to BTMACB. Michaelis-Menten type of 'kinetics have been observed with respect to the reductants. The reaction has been studied in solvents of different compositions of acetic acid and water. The solvent composition effect has been analysed using Grunwald-Weinstein equation. A mechanism involving the formation of an intermediate complex in the pre-equilibrium and its subsequent decomposition in slow step has been proposed.
- Tiwari, Vandana,Kumbhani,Shastri,Sharma, Vinita
-
p. 1520 - 1523
(2009/05/16)
-
- Mechanism of the gas phase reaction of chlorine atoms with butanone
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Smog chamber/FTIR techniques were used to study the Cl atom initiated oxidation of CH3C(O)CH2CH3 in 700-760 Torr of N2 at 296 K. The reaction of Cl atoms with CH3C(O)CH2CH3 proceeds via hydrogen abstraction with 73 ± 9% of reaction occurring at the -CH2- group. Relative rate techniques were used to measure k(Cl + CH3C(O)CHClCH3) = (5.62 ± 0.81) × 10-12 cm3 molecule-1 s-1. It was deduced that the CH3C(O)CHCH3 radical reacts with Cl2 with a rate constant of the order of 10-14 to 10-13 cm3 molecule-1 s-1.
- Iwasaki,Taketani,Takahashi,Matsumi,Wallington,Hurley
-
p. 274 - 279
(2008/10/09)
-
- Photochemically induced autocatalysis in the chlorate ion-iodine system
-
Light initiates an autocatalytic reaction sequence in the chlorate ion-iodine reaction. A previous report on the same system (Oliveira, A. P.; Faria, R. B. J. Am Chem. Soc. 2005, 127, 18022-18023.) failed to recognize the role of photoinitiation by the diode-array spectrophotometer used in the experiments. A mechanism is proposed to interpret the observations. Copyright
- Galajda, Monika,Lente, Gabor,Fabian, Istvan
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p. 7738 - 7739
(2008/02/04)
-
- Thermochemistry is not a lower bound to the activation energy of endothermic reactions: A kinetic study of the gas-phase reaction of atomi-chlorine with ammonia
-
The rate constant for Cl + NH3 → HCl + NH2 has been measured over 290-570 K by the time-resolved resonance fluorescence technique. Ground-state Cl atoms were generated by 193 nm excimer laser photolysis of CCl4 and reacted under pseudo-first-order conditions with excess NH3. The forward rate constant was fit by the expression k1 = (1.08 ± 0.05) × 10-11 exp(-11.47 ± 0.16 kJ mol-1/RT) cm3 molecule-1 s-1, where the uncertainties in the Arrhenius parameters are ±1 σ and the 95% confidence limits for k1 are ±11%. To rationalize the activation energy, which is 7.4 kJ mol -1 below the endothermicity in the middle of the 1/T range, the potential energy surface was characterized with MPWB1K/6-31++G(2df,2p) theory. The products NH2 + HC1 form a hydrogen-bonded adduct, separated from Cl + NH3 by a transition state lower in energy than the products. The rate constant for the reverse process k-1 was derived via modified transition state theory, and the computed k-1 exhibits a negative activation energy, which in combination with the experimental equilibrium constant yields k1 in fair accord with experiment.
- Gao, Yide,Alecu,Hsieh,Morgan, Brad P.,Marshall, Paul,Krasnoperov, Lev N.
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p. 6844 - 6850
(2008/10/09)
-
- Kinetic study of the ClOO + NO reaction using cavity ring-down spectroscopy
-
Cavity ring-down spectroscopy was used to study the reaction of ClOO with NO in 50-150 Torr total pressure of O2/N2 diluent at 205-243 K. A value of k(ClOO+NO) = (4.5 ± 0.9) × 10-11 cm3 molecule-1 s-1 at 213 K was determined (quoted uncertainties are two standard deviations). The yield of NO2 in the ClOO + NO reaction was 0.18 ± 0.02 at 213 K and 0.15 ± 0.02 at 223 K. An upper limit of k(ClOO+Cl2) -14 cm3 molecule-1 s-1 was established at 213 K. Results are discussed with respect to the atmospheric chemistry of ClOO and other peroxy radicals.
- Enami, Shinichi,Hoshino, Yosuke,Ito, Yuki,Hashimoto, Satoshi,Kawasaki, Masahiro,Wallington, Timothy J.
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p. 3546 - 3551
(2008/10/09)
-
- Kinetics and mechanism of the oxidation of sulfite by chlorine dioxide in a slightly acidic medium
-
The sulfite-chlorine dioxide reaction was studied by stopped-flow method at I = 0.5 M and at 25.0 ± 0.1 °C in a slightly acidic medium. The stoichiometry was found to be 2 SO32- + 2-ClO2 + H2O → 2SO42- + Cl- + ClO 3- + 2H+ in ClO2 excess and 6SO 32- + 2·ClO2 → S2O 62- + 4SO42- + 2Cl- in total sulfite excess ([S(IV)] = [H2SO3] + [HSO 3-] + [SO32-]). A nine-step model with four fitted kinetic parameters is suggested in which the proposed adduct SO3C1O22- plays a significant role. The pH-dependence of the kinetic traces indicates that SO32- reacts much faster with ClO2 than HSO3- does.
- Horvath, Attila K.,Nagypal, Istvan
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p. 4753 - 4758
(2008/10/09)
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- Kinetic study of the collisional quenching of spin-orbitally excited atomic chlorine, Cl(2P1/2), by H2O, D2O, and H2O2
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Rate constants for the collisional quenching of spin-orbitally excited Cl(2P1/2) atoms by H2O, D2O, and H2O2 were determined at ~295 K using laser-flash photolysis and laser-induced fluores
- Kono, Mitsuhiko,Takahashi, Kenshi,Matsumi, Yutaka
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- Kinetics, mechanism, and thermochemistry of the gas phase reaction of atomic chlorine with dimethyl sulfoxide
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A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the reaction of chlorine atoms with dimethyl sulfoxide (CH3S(O)CH3; DMSO) as a function of temperature (270-571 K) and pressure (5-500 Torr) in nitrogen bath gas. At T = 296 K and P ≥ 5 Torr, measured rate coefficients increase with increasing pressure. Combining our data with literature values for low-pressure rate coefficients (0.5-3 Torr He) leads to a rate coefficient for the pressure independent H-transfer channel of k1a = 1.45 × 10-11 cm3 molecule -1 s-1 and the following falloff parameters for the pressure-dependent addition channel in N2 bath gas: k1b,0 = 2.53 × 10-28 cm6 molecule-2 s -1; k1b,∞ = 1.17 × 10-10 cm 3 molecule-1 s-1, Fc = 0.503. At the 95% confidence level, both k1a and k1b(P) have estimated accuracies of ±30%. At T > 430 K, where adduct decomposition is fast enough that only the H-transfer pathway is important, measured rate coefficients are independent of pressure (30-100 Torr N2) and increase with increasing temperature. The following Arrhenius expression adequately describes the temperature dependence of the rate coefficients measured at over the range 438-571 K: k1a, = (4.6 ±0.4) × 10-11 exp[-(472 ± 40)/T) cm3 molecule-1 s-1 (uncertainties are 2σ, precision only). When our data at T > 430 K are combined with values for k1a at temperatures of 273-335 K that are obtained by correcting reported low-pressure rate coefficients from discharge flow studies to remove the contribution from the pressure-dependent channel, the following modified Arrhenius expression best describes the derived temperature dependence: k1a = 1.34 × 10-15T1.40 exp(+383/T) cm3 molecule-1 s-1 (273 K ≤ T ≤ 571 K). At temperatures around 330 K, reversible addition is observed, thus allowing equilibrium constants for Cl-DMSO formation and dissociation to be determined. A third-law analysis of the equilibrium data using structural information obtained from electronic structure calculations leads to the following thermochemical parameters for the association reaction: ΔrH298o = -72.8 ±2.9 kJ mol -1, ΔHo0 = -71.5 ±3.3 kJ mol -1, and ΔrS298o = -110.6 ±4.0 J K-1 mol-1. In conjunction with standard enthalpies of formation of Cl and DMSO taken from the literature, the above values for Δrffo lead to the following values for the standard enthalpy of formation of Cl-DMSO: ΔfH298 o = -102.7 ± 4.9 kJ mol-1 and Δ rHo0 = -84.4 ±5.8 kJ mol-1. Uncertainties in the above thermochemical parameters represent estimated accuracy at the 95% confidence level. In agreement with one published theoretical study, electronic structure calculations using density functional theory and G3B3 theory reproduce the experimental adduct bond strength quite well.
- Nicovich,Parthasarathy,Pope,Pegus,McKee,Wine
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p. 6874 - 6885
(2008/10/09)
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- Kinetics of the gas-phase reaction of OH with HCl
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The reaction of hydroxyl radicals with hydrogen chloride (reaction 1) has been studied experimentally using a pulsed-laser photolysis/pulsed-laser-induced fluorescence technique over a wide range of temperatures, 298-1015 K, and at pressures between 5.33 and 26.48 kPa. The bimolecular rate coefficient data set obtained for reaction 1 demonstrates no dependence on pressure and exhibits positive temperature dependence that can be represented with modified three-parameter Arrhenius expression within the experimental temperature range: k1 = 3.20 × 10-15T0.99 exp(-62 K/T) cm3 molecule-1 s-1. The potential-energy surface has been studied using quantum chemical methods, and a transition-state theory model has been developed for the reaction 1 on the basis of calculations and experimental data. The model results in modified three-parameter Arrhenius expressions: k1 = 8.81 × 10-16T1.6 exp(58 K/T) cm3 molecule-1 s-1 for the temperature range 200-1015 K and k1 = 6.84 × 10-19T 2.12 exp(646 K/T) cm3 molecule-1 s-1 for the temperature dependence of the reaction 1 rate coefficient extrapolation to high temperatures (500-3000 K). A temperature dependence of the rate coefficient of the Cl + H2O → HCl + OH reaction has been derived on the basis of the experimental data, modeling, and thermochemical information.
- Bryukov, Mikhail G.,Dellinger, Barry,Knyazev, Vadim D.
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p. 936 - 943
(2008/10/09)
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- Femtosecond pump-probe studies of nitrosyl chloride photochemistry in solution
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We present a femtosecond pump-probe study of the primary events of nitrosyl chloride (ClNO) photochemistry in solution. Following 266 nm photolysis, the resulting evolution in optical density is measured for ClNO dissolved in acetonitrile, chloroform, and dichloromethane. The results demonstrate that photolysis results in the production of a photoproduct that has an absorption band maximum at 295 nm in acetonitrile and 330 nm in chloroform and dichloromethane. To determine the extent of Cl production, comparative photochemical studies of methyl hypochlorite (MeOCl) and C1NO are performed. Photolysis of MeOCl in solution results in the production of the Cl:solvent charge-transfer complex; therefore, a comparison of the spectral evolution observed following MeOCl and ClNO photolysis under identical photolysis conditions is performed to determine the extent of Cl production following ClNO photolysis. We find that similar to the gas-phase photochemistry, Cl and NO formation is the dominant photochemical channel in acetonitrile. However, the photochemistry in chloroform and dichloromethane is more complex, with a second product formed in addition to Cl and NO. It is proposed that in these solvents photoisomerization also occurs, resulting in the production of ClON. The results presented here represent the first detailed examination of the solution phase photochemistry of ClNO.
- Cooksey, Catherine C.,Johnson, Kevin J.,Reid, Philip J.
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p. 8613 - 8622
(2008/10/09)
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- Three autocatalysts and self-inhibition in a single reaction: A detailed mechanism of the chlorite-tetrathionate reaction
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The chlorite-tetrathionate reaction has been studied spectrophotometrically in the pH range of 4.65-5.35 at T = 25.0 ± 0.2°C with an ionic strength of 0.5 M, adjusted with sodium acetate as a buffer component. The reaction is unique in that it demonstrates autocatalysis with respect to the hydrogen and chloride ion products and the key intermediate, HOCl. The thermodynamically most-favorable stoichiometry, 2S4O6 2- + 7ClO2- + 6H2O → 8SO 42- + 7Cl- + 12H+, is not found. Under our experimental conditions, chlorine dioxide, the chlorate ion, or both are detected in appreciable amounts among the products. Initial rate studies reveal that the formation of chlorine dioxide varies in an unusual way, with the chlorite ion acting as a self-inhibitor. The reaction is supercatalytic (i.e., second order with respect to autocatalyst H+). The autocatalytic behavior with respect to Cl- comes from chloride catalysis of the chlorite-hypochlorous acid and hypochlorous acid-tetrathionate subsystems. A detailed kinetic study and a model that explains this unusual kinetic behavior are presented.
- Horvath, Attila K.,Nagypal, Istvan,Epstein, Irving R.
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p. 9877 - 9883
(2008/10/09)
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- A kinetic and product study of the Cl + HO2 reaction
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The absolute rate data and product branching ratios for the reactions Cl+HCl→HCL+O2 and Cl+HO2→OH+ClO were measured. The measurement of consumption of HO2 in excess Cl yielded K la and the measurement of the consumption of Cl in excess HO 2 yielded a total rate coefficient. For the product measurement, an excess of Cl was added to known concentrations of HO2 and the reaction was allowed to reach completion. Numerical simulations were used to check the interferences from secondary chemistry in both the kinetic and product experiments and also to quantify the losses incurred during the conversion process HO2→OH for detection purposes.
- Hickson, Kevin M.,Keyser, Leon F.
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p. 6887 - 6900
(2008/10/09)
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