Rate constants and vibrational distributions for water-forming reactions of OH and OD radicals with thioacetic acid, 1,2-ethanedithiol and tert-butanethiol

Reactions of OH and OD radicals with CH₃C(O)SH, HSCH₂CH₂SH, and (CH₃)₃CSH were studied at 298 K in a fast-flow reactor by infrared emission spectroscopy of the water product molecules. The rate constants (1.3 ± 0.2) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for the OD + CH₃C(O)SH reaction and (3.8 ± 0.7) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for the OD + HSCH₂CH₂SH reaction were determined by comparing the HOD emission intensity to that from the OD reaction with H₂S, and this is the first measurement of these rate constants. In the same manner, using the OD + (C₂H₅)₂S reference reaction, the rate constant for the OD + (CH₃)₃CSH reaction was estimated to be (3.6 ± 0.7) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. Vibrational distributions of the H₂O and HOD molecules from the title reactions are typical for H-atom abstraction reactions by OH radicals with release of about 50% of the available energy as vibrational energy to the water molecule in a 2:1 ratio of stretch and bend modes.     

First application of the depth profile of silica species as a tracer by fast‐atom bombardment mass spectrometry: investigation of the circulation of seawater and silica uptake by diatoms

Silica, represented by SiO₂, is the general name for the compounds composed of Si, O and H with their derivative complexes. Silica forms various chemical species in aquatic solutions, such as a monomer (Si(OH)₃O⁻), dimer (Si₂(OH)₅O), and others. These species are known to vary in their relative abundances in solution depending on the chemical and physical conditions. Silica species dissolved in seawater have been examined by fast-atom bombardment mass spectrometry (FAB-MS) to elucidate the behavior of silica and its circulation as a novel tracer reflecting the chemical and physical conditions of seawater and the bioactivity of diatoms, which take up silica. In the seawater of Tokyo Bay, silica species such as [Si(OH)₂O₂Na]⁻ ([monomer–Na]⁻), [Si₂(OH)₅O₂]⁻ ([dimer]⁻), [Si₂(OH)₄O₃Na]⁻ ([dimer–Na]⁻), [Si₄(OH)₇O₅]⁻ ([cyclic tetramer]⁻), [Si₄(OH)₆O₆Na]⁻ ([cyclic tetramer–Na]⁻), [Si₄(OH)₉O₄]⁻ ([linear tetramer]⁻) and [Si₄(OH)₈O₅Na]⁻ ([linear tetramer–Na]⁻) were observed and assigned by FAB-MS. To investigate the suitability of silica species as a tracer, the relative peak intensity ratios of silica species observed in the mass spectra, i.e. the profiles of the ratio of the linear tetramer to the cyclic tetramer (m/z 329/311) and the ratio of the dimer to the cyclic tetramer (m/z 173/311) against depth, were examined to determine the annual changes and reproducibility of the depth profiles. In particular, the depth profile of the relative ratio of the linear tetramer to the cyclic tetramer, 329/311, exhibits critical changes depending on the seawater budget. These changes in the relative ratios were identified by an experiment involving a simple sodium chloride solution system. Our measurement is expected to elucidate the dynamics of silica and its role as ‘food’ for diatoms, and we showed that speciation using mass spectrometry is a powerful tool for examining elemental behavior in nature and environmental changes. Our results suggest that a silica tracer is useful for investigating the behavior of seawater in small coastal regions and the uptake of silica by diatoms. Copyright © 2009 John Wiley & Sons, Ltd.     

1,1,1,3,3,-pentafluorobutane (HFC-365mfc): atmospheric degradation and contribution to radiative forcing

The rate constant for the reaction of the hydroxyl radical with 1,1,1,3,3-pentafluorobutane (HFC-365mfc) has been determined over the temperature range 278–323K using a relative rate technique. The results provide a value of k(OH+CF₃CH₂CF₂CH₃)=2.0×10⁻¹²exp(−1750±400/T) cm³ molecule⁻¹ s⁻¹ based on k(OH+CH₃CCl₃)=1.8×10⁻¹² exp (−1550±150/T) cm³ molecule⁻¹ s⁻¹ for the rate constant of the reference reaction. Assuming the major atmospheric removal process is via reaction with OH in the troposphere, the rate constant data from this work gives an estimate of 10.8 years for the tropospheric lifetime of HFC-365mfc. The overall atmospheric lifetime obtained by taking into account a minor contribution from degradation in the stratosphere, is estimated to be 10.2 years. The rate constant for the reaction of Cl atoms with 1,1,1,3,3-pentafluorobutane was also determined at 298±2 K using the relative rate method, k(Cl+CF₃CH₂CF₂CH₃)=(1.1±0.3)×10⁻¹⁵ cm³ molecule⁻¹ s⁻¹. The chlorine initiated photooxidation of CF₃CH₂CF₂CH₃ was investigated from 273–330 K and as a function of O₂ pressure at 1 atmosphere total pressure using Fourier transform infrared spectroscopy. Under all conditions the major carbon-containing products were CF₂O and CO₂, with smaller amounts of CF₃O₃CF₃. In order to ascertain the relative importance of hydrogen abstraction from the (SINGLE BOND)CH₂(SINGLE BOND) and (SINGLE BOND)CH₃ groups in CF₃CH₂CF₂CH₃, rate constants for the reaction of OH radicals and Cl atoms with the structurally similar compounds CF₃CH₂CCl₂F and CF₃CH₂CF₃ were also determined at 298 K k(OH+CF₃CH₂CCl₂F)=(8±3)×10⁻¹⁶ cm³ molecule⁻¹ s⁻¹; k(OH+CF₃CH₂CF₃)=(3.5±1.5)×10⁻¹⁶ cm³ molecule⁻¹ s⁻¹; k(Cl+CF₃CH₂CCl₂F)=(3.5±1.5)×10⁻¹⁷ cm³ molecule⁻¹ s⁻¹]; k(Cl+CF₃CH₂CF₃)<1×10⁻¹⁷ cm³ molecule⁻¹ s⁻¹. The results indicate that the most probable site for H-atom abstraction from CF₃CH₂CF₂CH₃ is the methyl group and that the formation of carbonyl compounds containing more than a single carbon atom will be negligible under atmospheric conditions, carbonyl difluoride and carbon dioxide being the main degradation products. Finally, accurate infrared absorption cross-sections have been measured for CF₃CH₂CF₂CH₃, and jointly used with the calculated overall atmospheric lifetime of 10.2 years, in the NCAR chemical-radiative model, to determine the radiative forcing of climate by this CFC alternative. The steady-state Halocarbon Global Warming Potential, relative to CFC-11, is 0.17. The Global Warming Potentials relative to CO₂ are found to be 2210, 790, and 250, for integration time-horizons of 20, 100, and 500 years, respectively. © 1997 John Wiley & Sons, Inc.     

Kinetic study of the reaction OH + HI by laser photolysis-resonance fluorescence

The gas phase reaction of OH radicals with hydrogen iodide (HI) has been studied using a Laser Photolysis-Resonance Fluorescence (LP-RF) apparatus, recently developed in our group. The measured rate constant at 298 K was (2.7 ± 0.2) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. This rate constant is compared with the ones of the reactions OH + HCl and OH + HBr. The role of the reaction OH + HI in marine tropospheric chemistry is discussed. In addition, the LP-RF apparatus was tested and validated by measuring the following rate constants (in cm³ molecule⁻¹ s⁻¹ units): 𝓀(OH + HNO₃) = (1.31 ± 0.06) × 10⁻¹³ at p = 27 and 50 Torr of argon and 𝓀(OH + C₃H₈) = (1.22 ± 0.08) × 10⁻¹². These rate constants are in very good agreement with the literature data.     

Kinetics of the gas-phase reactions of the oh radical with selected glycol ethers,glycols, and alcohols

Using a relative rate method, rate constants have been measured for the gas-phase reactions of the OH radical with 1-hexanol, 1-methoxy-2-propanol, 2-butoxyethanol, 1,2-ethanediol, and 1,2-propanediol at 296±2 K, of (in units of 10⁻¹² cm³ molecule⁻¹ s⁻¹): 15.8±3.5; 20.9±3.1; 29.4±4.3; 14.7±2.6; and 21.5±4.0, respectively, where the error limits include the estimated overall uncertainties in the rate constants for the reference compounds. These OH radical reaction rate constants are higher than certain of the literature values, by up to a factor of 2. Rate constants were also measured for the reactions of 1-methoxy-2-propanol and 2-butoxyethanol with NO₃ radicals and O₃, with respective NO₃ radical and O₃ reaction rate constants (in cm³ molecule⁻¹ s⁻¹ units) of: 1-methoxy-2-propanol, (1.7±0.7)×10⁻¹⁵, and <1.1×10⁻¹⁹; and 2-butoxyethanol, (3.0±1.2)×10⁻¹⁵, and <1.1×10⁻¹⁹. The dominant tropospheric loss process for the alcohols, glycols, and glycol ethers studied here is calculated to be by reaction with the OH radical, with lifetimes of 0.4–0.8 day for a 24 h average OH radical concentration of 1.0×10⁶ molecule cm⁻³. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 533–540, 1998     

The hydroxyl radical reaction rate constants and atmospheric reaction products of three siloxanes

The relative rate technique has been used to measure the hydroxyl radical (OH) reaction rate constant of hexamethyldisiloxane (MM, (CH₃)₃Si-O-Si(CH₃)₃), octamethyltrisiloxane (MDM, (CH₃)₃Si-O-Si(CH₃)₂-O-Si(CH₃)₃), and decamethyltetrasiloxane (MD₂M, (CH₃)₃Si-O-Si(CH₃)₂-O-Si(CH₃)₂-O-Si(Ch₃)₃). Hexamethyldisiloxane, octamethyltrisiloxane, and decamethyltetrasiloxane react with OH with bimolecular rate constants of 1.32 ± 0.05 × 10⁻¹² cm³molecule⁻¹s⁻¹, 1.83 ± 0.09 × 10⁻¹² cm³ molecule⁻¹s⁻¹, and 2.66 ± 0.13 × 10⁻¹² cm³molecule⁻¹s⁻¹, respectively. Investigation of the OH + siloxane reaction products yielded trimethylsilanol, pentamethyldisiloxanol, heptamethyltetrasiloxanol, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and other compounds. Several of these products have not been reported before because these siloxanes and the proposed reaction mechanisms yielding these products are complicated. Some unusual cyclic siloxane products were observed and their formation pathways are discussed in light of current understanding of siloxane atmospheric chemistry. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 445–451, 1997.     

Low-Temperature Oxidation of Carbon Monoxide: The Synthesis and Properties of a Catalyst Based on Titanium Dioxide,Nanodiamond, and Palladium for CO Oxidation

A catalyst based on TiO₂ and nanodiamond with a 10 wt % palladium content of the catalyst was synthesized. The effect of the nanodiamond content on the catalytic properties in a reaction of CO oxidation at room temperature and low concentrations of CO (<100 mg/m³) was studied. It was established that, at a nanodiamond content of the catalyst from 7 to 9 wt % and a palladium content of 10 wt %, the rate of CO oxidation reached a maximum, and it was higher by a factor of 2.5 than the rate of CO oxidation on a catalyst based on pure TiO₂, which included palladium clusters. With the use of transmission electron microscopy, XRD X-ray diffractometry, and X-ray photoelectron spectroscopy, it was found that the clusters of palladium covered with palladium oxide with an average cluster size of 4 nm were formed on the surface of the TiO₂ carrier. It was assumed that the catalyst synthesized is promising for applications in catalytic and photocatalytic air-cleaning systems.     

Utilization of Solid Acid SO42−/TiO2 as Catalyst to the Three‐Component Mannich Reaction at Ambient Temperature

The three‐component Mannich reaction of among dimethyl malonate, aromatic primary amine, and aromatic aldehyde was made successfully in the presence of solid acidic catalyst SO₄²⁻/TiO₂, with excellent catalytic activity, as compared to SO₄²⁻/γ‐Al₂O₃ and SO₄²⁻/ZnO. To the best of our knowledge, SO₄²⁻/TiO₂ prepared at varied calcination temperatures can perform different intensities of Lewis and Brønsted acidities. Because of this point, under the optimum conditions, the effect of SO₄²⁻/TiO₂ (prepared at 200°C) was much more than that of SO₄²⁻/TiO₂ (prepared at 300°C or 400°C) in the three‐component Mannich reaction. In observing ionization activation mode of the three‐component Mannich reaction, it disclosed that the plausible mechanism possibly undergoes formation of aldimines and transformation of aldimines into β‐amino esters by applying solid acidic catalyst SO₄²⁻/M_xO_y.     

Rate constants for the reactions of methylvinyl ketone,methacrolein, methacrylic acid,and acrylic acid with ozone

Rate constants for the reaction of ozone with methylvinyl ketone (H₂C(DOUBLEBOND)CHC(O)CH₃), methacrolein (H₂C(DOUBLEBOND)C(CH₃)CHO), methacrylic acid (H₂C(DOUBLEBOND)C(CH₃)C(O)OH), and acrylic acid (H₂C(DOUBLEBOND)CHC(O)OH) were measured at room temperature (296±2 K) in the presence of a sufficient amount of cyclohexane to scavenge OH-radicals. Results from pseudo-first-order experiments in the presence of excess ozone were found not to be consistent with relative rate measurements. It appeared that the formation of the so-called Criegee-intermediates leads to an enhanced decrease in the concentration of the two organic acids investigated. It is shown that the presence of formic acid, which is known to react efficiently with Criegee-intermediates, diminishes the observed removal rate of the organic acids. The rate constant for the reaction of ozone with the unsaturated carbonyl compounds methylvinyl ketone and methacrolein was found not to be influenced by the addition of formic acid. Rate constants for the reaction of ozone determined in the presence of excess formic acid are (in cm³ molecule⁻¹ s⁻¹): methylvinyl ketone (5.4±0.6)×10⁻¹⁸; methacrolein (1.3±0.14)×10⁻¹⁸; methacrylic acid (4.1±0.4)×10⁻¹⁸; and acrylic acid (0.65±0.13)×10⁻¹⁸. Results are found to be consistent with the Criegee mechanism of the gas-phase ozonolysis. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 769–776, 1998     

Microwave Synthesis of Pt Clusters on Black TiO2 with Abundant Oxygen Vacancies for Efficient Acidic Electrocatalytic Hydrogen Evolution

Oxygen vacancies-enriched black TiO₂ is one promising support for enhancing hydrogen evolution reaction (HER). Herein, oxygen vacancies enriched black TiO₂ supported sub-nanometer Pt clusters (Pt/TiO₂-O_V) with metal support interactions is designed through solvent-free microwave and following low-temperature electroless approach for the first time. High-temperature and strong reductants are not required and then can avoid the aggregation of decorated Pt species. Experimental and theoretical calculation verify that the created oxygen vacancies and Pt clusters exhibit synergistic effects for optimizing the reaction kinetics. Based on it, Pt/TiO₂-O_V presents remarkable electrocatalytic performance with 18 mV to achieve 10 mA cm⁻² coupled with small Tafel slope of 12 mV dec⁻¹. This work provides quick synthetic strategy for preparing black titanium dioxide based nanomaterials.     

Effects of multidimensional tunneling in the kinetics of hydrogen abstraction reactions of O (3P) with CH3OCHO

Quantum tunneling paths are important in reactions when there is a significant component of hydrogenic motion along the potential energy surface. In this study, variational transition state with multidimensional tunneling corrections are employed in the calculations of the thermal rate constants for hydrogen abstraction from the cis‐CH₃OCHO by O (³P) giving CH₃OCO + OH (R1) and CH₂OCHO + OH (R2). The structures and electronic energies are computed with the M06‐2X method. Benchmark calculations with the CBS_D–T approach give an enthalpy of reaction at 0 K for R1 (−2.8 kcal/mol) and R2 (−2.5 kcal/mol) which are in good agreement with the experiment, i.e. −2.61 and −1.81 kcal/mol. At the low and intermediate values of temperatures, small‐ and large‐curvature tunneling dominate the kinetics of R1, which is the dominant path over the range of temperature from 250 to 1200 K. This study shows the importance of multidimensional tunneling corrections for both R1 and R2, for which the total rate constant at 298 K calculated with the CVT/μOMT method is 8.2 × 10⁻¹⁵ cm³ molecule⁻¹ s⁻¹ which agrees well with experiment value of 9.3 × 10⁻¹⁵ cm³ molecule⁻¹ s⁻¹ (Mori, Bull. Inst. Chem. Res. 1981, 59, 116). © 2018 Wiley Periodicals, Inc.     

Atmospheric Chemistry of Camphor

Rate constants have been measured at 296 ± 2 K for the gas‐phase reactions of camphor with OH radicals, NO₃ radicals, and O₃. Using relative rate methods, the rate constants for the OH radical and NO₃ radical reactions were (4.6 ± 1.2) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ and <3 × 10⁻¹⁶ cm³ molecule⁻¹ s⁻¹, respectively, where the indicated error in the OH radical reaction rate constant includes the estimated overall uncertainty in the rate constant for the reference compound. An upper limit to the rate constant for the O₃ reaction of <7 × 10⁻²⁰ cm³ molecule⁻¹ s⁻¹ was also determined. The dominant tropospheric loss process for camphor is calculated to be by reaction with the OH radical. Acetone was identified and quantified as a product of the OH radical reaction by gas chromatography, with a formation yield of 0.29 ± 0.04. In situ atmospheric pressure ionization tandem mass spectrometry (API‐MS) analyses indicated the formation of additional products of molecular weight 166 (dicarbonyl), 182 (hydroxydicarbonyl), 186, 187, 213 (carbonyl‐nitrate), 229 (hydroxycarbonyl‐nitrate), and 243. A reaction mechanism leading to the formation of acetone is presented, as are pathways for the formation of several of the additional products observed by API‐MS. © 2000 John Wiley and Sons, Inc. Int J Chem Kinet 33: 56–63, 2001     

The hydroxyl radical reaction rate constant and atmospheric transformation products of 2-butanol and 2-pentanol

The relative rate technique has been used to measure the hydroxyl radical (OH) reaction rate constant of +2-butanol (2BU, CH₃CH₂CH(OH)CH₃) and 2-pentanol (2PE, CH₃CH₂CH₂CH(OH)CH₃). 2BU and 2PE react with OH yielding bimolecular rate constants of (8.1±2.0)×10⁻¹² cm³molecule⁻¹s⁻¹ and (11.9±3.0)×10⁻¹² cm³molecule⁻¹s⁻¹, respectively, at 297±3 K and 1 atmosphere total pressure. Both 2BU and 2PE OH rate constants reported here are in agreement with previously reported values [1–4]. In order to more clearly define these alcohols' atmospheric reaction mechanisms, an investigation into the OH+alcohol reaction products was also conducted. The OH+2BU reaction products and yields observed were: methyl ethyl ketone (MEK, (60±2)%, CH₃CH₂C((DOUBLEBOND)O)CH₃) and acetaldehyde ((29±4)% HC((DOUBLEBOND)O)CH₃). The OH+2PE reaction products and yields observed were: 2-pentanone (2PO, (41±4)%, CH₃C((DOUBLEBOND)O)CH₂CH₂CH₃), propionaldehyde ((14±2)% HC((DOUBLEBOND)O)CH₂CH₃), and acetaldehyde ((40±4)%, HC((DOUBLEBOND)O)CH₃). The alcohols' reaction mechanisms are discussed in light of current understanding of oxygenated hydrocarbon atmospheric chemistry. Labeled (¹⁸O) 2BU/OH reactions were conducted to investigate 2BU's atmospheric transformation mechanism details. The findings reported here can be related to other structurally similar alcohols and may impact regulatory tools such as ground level ozone-forming potential calculations (incremental reactivity) [5]. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 745–752, 1998     

CO Oxidation Promoted by the Gold Dimer in Au2VO3− and Au2VO4− Clusters

Investigations on the reactivity of atomic clusters have led to the identification of the elementary steps involved in catalytic CO oxidation, a prototypical reaction in heterogeneous catalysis. The atomic oxygen species O^.? and O^2? bonded to early‐transition‐metal oxide clusters have been shown to oxidize CO. This study reports that when an Au₂ dimer is incorporated within the cluster, the molecular oxygen species O₂^2? bonded to vanadium can be activated to oxidize CO under thermal collision conditions. The gold dimer was doped into Au₂VO₄^? cluster ions which then reacted with CO in an ion‐trap reactor to produce Au₂VO₃^? and then Au₂VO₂^?. The dynamic nature of gold in terms of electron storage and release promotes CO oxidation and O? O bond reduction. The oxidation of CO by atomic clusters in this study parallels similar behavior reported for the oxidation of CO by supported gold catalysts.     

Dramatically Enhanced Li-Ion Storage of ZnO@C Anodes through TiO2 Homogeneous Hybridization

Amorphous nanoparticles of ZnO and TiO₂ embedded in carbon nanocages (AZT⊂CNCs) were successfully synthesized through a simple annealing process of TiO₂-coated zeolitic imidazolate framework-8 (ZIF-8). In the current anode of AZT⊂CNCs, tiny ZnO and TiO₂ nanoparticles were uniformly distributed in the carbon matrix (carbon nanocages), which could effectively buffer the volume expansion of electroactive ZnO and provide excellent electric conductivity. After fully investigating the electrochemical performance of the AZT⊂CNCs samples obtained with different additive amounts of tetrabutyl orthotitanate (TBOT) for TiO₂ coating, it has been found that AZT-30 (0.1 g ZIF-8 with 30 mL TBOT) shows the best cycle stability (510 mA h g⁻¹ after 350 cycles at 200 mA g⁻¹) and a superior rate capability (610 mA h g⁻¹ after 3500 cycles at 2 A g⁻¹). The greatly enhanced Li-ion storage performance could be ascribed to the fact that the introduction of amorphous TiO₂ could activate the reversible lithiation/delithiation reaction of ZnO during the charge/discharge process.     

Rate coefficients for the reactions of OH radicals with Methylglyoxal and Acetaldehyde

Rate coefficients have been measured for the reaction of OH radicals with methylglyoxal from 260 to 333 K using the discharge flow technique and laser-induced fluorescence detection of OH. The rate coefficient was found to be (1.32±0.30) × 10^?11 cm³ molecule^?1 s^?1 at room temperature, with a distinct negative temperature dependence (E/R of ?830 ± 300 K). These are the first measurements of the temperature dependence of this reaction. The reaction of OH with acetaldehyde was also investigated, and a rate coefficient of (1.45 ± 0.25) × 10^?11 cm³ molecule^?1 s^?1 was found at room temperature, in accord with recent studies. Experiments in which O₂ was added to the flow showed regeneration of OH following the reaction of CH₃CO radicals with O₂. However, chamber experiments at atmospheric pressure using FTIR detection showed no evidence for OH production. FTIR experiments have also been used to investigate the chemistry of the CH₃COCO radical formed by hydrogen abstraction from methylglyoxal. © 1995 John Wiley & Sons, Inc.     

Mechanism and Kinetics of the Reaction of Nitrosamines with OH Radical: A Theoretical Study

The reaction of nitrosodimethylamine, nitrosoazetidine, nitrosopyrrolidine, and nitrosopiperidine with the hydroxyl radical has been studied using electronic structure calculations in gas and aqueous phases. The rate constant was calculated using variational transition state theory. The reactions are initiated by H‐atom abstraction from the αC─H group of nitrosamines and leads to the formation of alkyl radical intermediate. In the subsequent reactions, the initially formed alkyl radical intermediate reacts with O₂ forming a peroxy radical. The reaction of peroxy radical with other atmospheric oxidants, such as HO₂ and NO radicals, is studied. The structures of the reactive species were optimized by using the density functional theory methods, such as M06‐2X, MPW1K, and BHandHLYP, and hybrid methods G3B3. The single‐point energy calculations were also performed at CCSD(T)/6‐311+G(d,p)// M062X/6‐311+G(d,p) level. The calculated thermodynamical parameters show that the reactions corresponding to the formation of intermediates and products are highly exothermic. We have calculated the rate constant for the initial H‐atom abstraction and subsequent favorable secondary reactions using canonical variational transition state theory over the temperature range of 150–400 K. The calculated rate constant for initial H‐atom abstraction reaction is ∼3 × 10⁻¹² cm³ molecule⁻¹ s⁻¹ and is in agreement with the previous experimental results. The calculated thermochemical data and rate constants show that the reaction profile and kinetics of the reactions are less dependent on the number of methyl groups present in the nitrosoamines. Furthermore, it has been found that the atmospheric lifetime of nitrosamines is around 5 days in the normal atmospheric OH concentration.     

Hydrogen‐Atom Abstraction from Methane by Stoichiometric Vanadium–Silicon Heteronuclear Oxide Cluster Cations

Vanadium–silicon heteronuclear oxide cluster cations were prepared by laser ablation of a V/Si mixed sample in an O₂ background. Reactions of the heteronuclear oxide cations with methane in a fast‐flow reactor were studied with a time‐of‐flight (TOF) mass spectrometer to detect the cluster distribution before and after the reactions. Hydrogen abstraction reactions were identified over stoichiometric cluster cations [(V₂O₅)_n(SiO₂)_m]⁺ (n=1, m=1–4; n=2, m=1), and the estimated first‐order rate constants for the reactions were close to that of the homonuclear oxide cluster V₄O₁₀⁺ with methane. Density functional calculations were performed to study the structural, bonding, electronic, and reactivity properties of these stoichiometric oxide clusters. Terminal‐oxygen‐centered radicals (O_t ^. ) were found in all of the stable isomers. These O_t ^. radicals are active sites of the clusters in reaction with CH₄. The O_t ^. radicals in [V₂O₅(SiO₂)_1–4]⁺ clusters are bonded with Si rather than V atoms. All the hydrogen abstraction reactions are favorable both thermodynamically and kinetically. This work reveals the unique properties of metal/nonmetal heteronuclear oxide clusters, and may provide new insights into CH₄ activation on silica‐supported vanadium oxide catalysts.     

Determination of the rate constants for the gas-phase reactions of methyl butenol with OH radicals,ozone, NO3 radicals,and Cl atoms

Using a relative rate method, rate constants for the gas-phase reactions of 2-methyl-3-buten-2-ol (MBO) with OH radicals, ozone, NO₃ radicals, and Cl atoms have been investigated using FTIR. The measured values for MBO at 298±2 K and 740±5 torr total pressure are: k_OH=(3.9±1.2)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹, k_O3=(8.6±2.9)×10⁻¹⁸ cm³ molecule⁻¹ s⁻¹, k=(8.6±2.9)×10⁻¹⁵ cm³ molecule⁻¹ s⁻¹, and k_Cl=(4.7±1.0)×10⁻¹⁰ cm³ molecule⁻¹ s⁻¹. Atmospheric lifetimes have been estimated with respect to the reactions with OH, O₃, NO₃, and Cl. The atmospheric relevance of this compound as a precursor for acetone is, also, briefly discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 589–594, 1998     

Efficient aerial oxidation of different types of alcohols using ZnO nanoparticle–MnCO3-graphene oxide composites

Graphene–metal nanocomposites have been found to remarkably enhance the catalytic performance of metal nanoparticle-based catalysts. In continuation of our previous report, in which highly reduced graphene oxide (HRG)-based nanocomposites were synthesized and evaluated, we present nanocomposites of graphene oxide (GRO) and ZnO nanoparticle-doped MnCO₃ ([ZnO–MnCO₃/(1%)GRO]) synthesized via a facile, straightforward co-precipitation technique. Interestingly, it was noticed that the incorporation of GRO in the catalytic system could noticeably improve the catalytic efficiency compared to a catalyst (ZnO–MnCO₃) without GRO, for aerial oxidation of benzyl alcohol (BzOH) employing O₂ as a nature-friendly oxidant under base-free conditions. The impacts of various reaction factors were thoroughly explored to optimize reaction conditions using oxidation of BzOH to benzaldehyde (BzH) as a model substrate. The catalysts were characterized using X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, Energy dispersive X-ray spectroscopy (EDX), Brunauer-Emmett-Teller (BET), and Raman spectroscopy. The (1%)ZnO–MnCO₃/(1%)GRO exhibited significant specific activity (67 mmol.g⁻¹.hr⁻¹) with full convversion of BzOH and >99% BzH selectivity within just 6 min. The catalytic efficiency of the (1%)ZnO–MnCO₃/(1%)GRO nanocomposite was significantly better than the (1%)ZnO–MnCO₃/(1%)HRG and (1%)ZnO–MnCO₃ catalysts, presumably due to the existence of oxygen-possessing groups on the GRO surface and as well as a very high surface area that could have been instrumental in uniformly dispersing the active sites of the catalyst, i.e., ZnO–MnCO₃. Under optimum circumstances, various kinds of alcohols were selectively transformed to respective carbonyls with full convertibility over the (1%)ZnO–MnCO₃/(1%)GRO catalyst. Furthermore, the highly effective (1%)ZnO–MnCO₃/(1%)GRO catalyst could be successfully reused and recycled over five consecutive runs with a marginal reduction in its performance and selectivity.