Acetone cation chemistry under varying electron density conditions: from unimolecular decomposition to dissociative recombination processes

The chemistry of ionized acetone:Ar mixtures under varied ionizing electron density conditions has been studied using matrix‐isolation techniques. Gaseous acetone diluted in excess argon gas was subjected to electron bombardment with 300 eV electrons at currents between 20 and 200 μA. Linear wire ‘pin’ and metal ‘plate’ electron collector geometries were employed, allowing a wide range of electron density conditions to be explored. The products of subsequent reaction processes were matrix isolated and analyzed by Fourier transform infrared absorption spectroscopy. Products included methane, ketene, 1‐propen‐2‐ol (the enol isomer of acetone), CO, HCO, ethane, ethane, acetylene and CCCO. Product absolute and relative yields varied with acetone number density, the choice of anode geometry and the rate of electron bombardment. The overall chemistry observed is rationalized in terms of mechanistic steps involving unimolecular cation decomposition, ion–molecule reactions, radical–radical reactions and dissociative recombination processes. Copyright © 2013 John Wiley & Sons, Ltd.     

Electron-bombardment matrix isolation and PEPICO studies as complementary techniques in ion chemistry: an FTIR study of the decomposition of the vinyl fluoride cation

FTIR spectra have been obtained for matrices formed following electron bombardment of gas mixtures containing varying amounts of vinyl fluoride (VF) in Ar (1:400 to 1:25 600; VF/Ar). The major matrix‐isolated products are a π‐complex of HF/C₂H₂, fluoroacetylene (HC≡CF) and two isomers of C₂H₂F^?. These products correspond well with the products of photoionization of VF near 15.8 eV. These observations support the dominant mechanism of ionization in the EB‐MI environment as charge transfer of the substrate molecule to Ar^?+. Some differences are noted between the observed EB‐MI products and the results from PEPICO studies, primarily in that the EB‐MI products are observed as neutralized forms. The close correlation in EB‐MI and photoionization results allows the EB‐MI technique to be utilized as an ion structural analysis tool in complement to PEPICO studies, and allows the use of PEPICO studies to help predict and elucidate high‐pressure chemistry mechanisms through EB‐MI studies. The differences in the EB‐MI results and ions observed using the PEPICO technique are rationalized in terms of the differences in the experimental techniques. Using VF as the test system, reagent partial pressure conditions that best complement PEPICO studies are determined. Although the major results are observed for all VF partial pressures, dilute samples give rise to further ionization of the primary products, and more concentrated samples give rise to radical—radical reaction chemistry. As a result, a nominal range of 1:3200 (VF/Ar) is demonstrated to provide the best correlation with the gas‐phase PEPICO measurements. Copyright © 2011 John Wiley & Sons, Ltd.     

Plasma chemistry of NO in complex gas mixtures excited with a surfatron launcher

The plasma chemistry of NO has been investigated in gas mixtures with oxygen and/or hydrocarbon and Ar as carrier gas. Surface wave discharges operating at microwave frequencies have been used for this study. The different plasma reactions have been analyzed for a pressure range between 30 and 75 Torr. Differences in product concentration and/or reaction yields smaller than 10% were found as a function of this parameter. The following gas mixtures have been considered for investigation: Ar/NO, Ar/NO/O2, Ar/NO/CH4, Ar/CH4/O2, Ar/NO/CH4/O2. It is found that NO decomposes into N2 and O2, whereas other products such as CO, H2, and H2O are also formed when CH4 and O2 are present in the reaction mixture. Depending on the working conditions, other minority products such as HCN, CO2, and C2 or higher hydrocarbons have been also detected. The reaction of an Ar/NO plasma with deposits of solid carbon has also been studied. The experiments have provided useful information with respect to the possible removal of soot particles by this type of plasma. It has been shown that carbon deposits are progressively burned off by interaction with the plasma, and practically 100% decomposition of NO was found. Plasma intermediate species have been studied by optical emission spectroscopy (OES). Bands and/or peaks due to N2*, NO*, OH*, C2*, CN*, CH*, or H* were detected with different relative intensities depending on the gas mixture. From the analysis of both the reaction products and efficiency and the type of intermediate species detected by OES, different plasma reactions and processes are proposed to describe the plasma chemistry of NO in each particular mixture of gases. The results obtained provide interesting insights about the plasma removal of NO in real gas exhausts.     

Chlorodifluoroacetyl cyanide, ClF2CC(O)CN: synthesis, structure, and spectroscopic characterization

The novel molecule difluorochloroacetyl cyanide, ClF(2)CC(O)CN, has been characterized by IR (gas phase, Ar matrix), Raman (liquid), (19)F and (13)C NMR, and photoelectron (PES) spectroscopies; photoionization mass spectrometry (PIMS); and gas electron diffraction (GED). The conformational properties of ClF(2)CC(O)CN have been studied by joint application of vibrational spectroscopy, GED, and quantum chemical calculations. The existence of two conformers is detected in the gas and liquid phases, in which the C-Cl bond adopts gauche and syn orientations with respect to the C═O group. The computed enthalpy difference is in harmony with the experimental results of the gauche being more stable than the syn conformer by ΔH° = 1.3 kcal mol(-1) (MP2/cc-pVTZ). The valence electronic properties and the possible ionization and dissociation processes of the title compound are studied using the PES and PIMS. The experimental first vertical ionization energy of 12.0 eV corresponds to the ejection of an electron of the oxygen lone pairs. Taking into account the properties and broad applications of acyl cyanides, ClF(2)CC(O)CN is a promising new precursor in preparative chemistry.     

Fourier transform infrared matrix-isolation analysis of acetaldehyde fragmentation products after charge exchange with Ar•+ under varied ionization density conditions

The products of the Ar^?+ charge exchange ionization of acetaldehyde have been isolated and compared with related photoionization results and computational work. Acetaldehyde has been used to assess the effect of varied ion density in the ionization region of the electron bombardment matrix isolation apparatus. The amount of acetaldehyde destruction has been measured for constant gas‐sample composition and constant ionization current for two anode geometries: a pin anode and a plate anode. For the same ionization current, a pin‐shaped anode demonstrates higher precursor molecule destruction efficiency (85%) than the plate‐shaped anode (30%), resulting in substantial effect on the yield and quantity of isolated products. When the plate anode is used, the observed infrared products correspond to matrix‐isolated carbon monoxide (CO), methane (CH₄), ketene (CH₂CO), ethynyloxy radical (HCCO), formyl radical (HCO^?), acetyl radical (CH₃CO^?), vinyl alcohol (H₂C = CH‐OH), and cationic proton‐bound dimer, Ar₂H⁺. When the pin anode is used, the same products are observed with different relative proportions and new absorption features corresponding to dicarbon monoxide (CCO) and methyl radical (CH₃^?) are observed. The surprising observation of infrared absorptions corresponding to vinyl alcohol along with low yield of products anticipated through the analysis of photoelectron–photoionization coincidence measurements suggests that the initially formed fragmentation products are able to further react within the matrix‐isolation environment to influence observed product yields. Related experiments, using the isotopomer CD₃CHO, suggest that the observed products are formed via radical–radical reactions that occur under the high pressure conditions of the matrix isolation environment. Copyright © 2011 John Wiley & Sons, Ltd.     

FTIR研究HCO自由基与NO2反应的动力学

为了减少和控制油品在燃烧时 NOx的排放 ,对 NOx再燃烧进程的动力学研究一直受到人们的关注 [1,2].迄今为止 ,对于该进程中的一些可能参与的基元化学反应知道甚少 .从实验测得的总速率常数看 ,在室温下 ,主反应 HCO自由基与 NO2的反应是一个相当快速的反应 [3],其总速率常数约为 3.3× 1013 cm3· mol－ 1· s－ 1.但是 ,有关该反应体系的产物分布情况及其反应机理目前还未见报导 .该反应体系在热力学上存在着下列 放热反应 [4]:　　反应 [1a－ 1e]可在低压条件下发生 ,而反应 [1f－ 1g]只能在高压范围内产生 [5,6].本文是以高纯度的甲…     

Low Temperature Photochemistry of the Acetone/2-Propanol System

During UV.-irradiation of acetone/2-propanol mixtures at ?70° products of photo-addition of acetone to intermediate enols are formed. The yields of these products exceed the yield of pinacol, the major room temperature product. At ?70° the photoadditions are favoured by the long lifetime of acetone enol (≥ 5000 s).     

Electrochemical Initiated C‐N Coupling of 3‐Methylcatechol and n‐Hexylamine in a Flow Cell Monitored with ESI‐MS

The electrochemical initiated heterocoupling of 3‐methylcatechol and n‐hexylamine was investigated. The oxidation of 3‐methylcatechol was performed in an electrochemical flow cell with glassy carbon as the working electrode. As a result, the two‐electron, two‐proton oxidised chinone intermediate undergoes a C‐N coupling reaction in the presence of an amine (Michael addition). This mono coupling product can undergo a second two‐electron, two‐proton oxidation depending on acidic or basic conditions and substrate ratios. This flow cell was coupled on‐line with electrospray ionisation mass spectrometry to identify the possible coupling products. Higher substrate concentrations were performed off‐line as first scale‐up experiments in a two‐step procedure.     

Analysis of reaction products in the oxidation reactions of hydrocarbons by means of matrix-isolation FTIR spectroscopy

Summary The application of matrix isolation-FTIR spectroscopy for the product analysis of reaction systems in atmospheric chemistry is described. A mixture of Ar and O₂ with a molar composition of 80% and 20%, respectively, is used as carrier gas. The Ar/O₂ matrix deposited at 7±1 K exhibits an O₂-doublet absorption band centred at 1550 cm^–1 and 1551.5 cm^–1 which can be used as an internal reference for calibration purposes. The reaction products isolated in the Ar/O₂ matrix give sharp and well-defined absorption bands which are suitable for quantitative analysis. Various procedures and associated problems in the calibration are discussed in detail. The matrix isolation-FTIR technique was applied to the ozonolysis of simple alkenes and the photooxidation of biacetyl.     

Theoretical study on ionization process in aqueous solution

Ionization potential (ionization energy) is a fundamental quantity characterizing electronic structure of a molecule. It is known that the energy in solution phase is significantly different from that in the gas phase. In this report, vertical and adiabatic ionization processes in aqueous solution are studied based on a hybrid method of quantum chemistry and statistical mechanics called reference interaction site model-SCF-spacial electron density distribution method. A role of solvation effect is elucidated through molecular level information, i.e., solvent distribution function around solute molecule. By utilizing the linear response regime, a simple expression to evaluate the spectral width from the distribution function is proposed and compared with experimental data.     

Accelerating Spirocyclic Polyketide Synthesis using Flow Chemistry

Over the past decade, the integration of synthetic chemistry with flow processing has resulted in a powerful platform for molecular assembly that is making an impact throughout the chemical community. Herein, we demonstrate the extension of these tools to encompass complex natural product synthesis. We have developed a number of novel flow‐through processes for reactions commonly encountered in natural product synthesis programs to achieve the first total synthesis of spirodienal A and the preparation of spirangien A methyl ester. Highlights of the synthetic route include an iridium‐catalyzed hydrogenation, iterative Roush crotylations, gold‐catalyzed spiroketalization and a late‐stage cis‐selective reduction.     

FTIR analysis of dimethyl ether decomposition products following charge transfer ionization with Ar+ under matrix isolation conditions

Fourier transform infrared spectroscopic analysis has been performed on argon matrices formed following electron bombardment of argon/dimethyl ether mixtures. Products consistent with the ionization and subsequent fragmentation of dimethyl ether cation have been observed. Following ionization of dimethyl ether, fragmentation occurs that is consistent with ionization energy greater than 15 eV due to efficient charge transfer from dimethyl ether to Ar(+) as the major ionization process. Major products observed in the infrared spectra are methane, formaldehyde, HCO(*), CO, and Ar(2)H(+). These products are consistent with the known fragmentation of photoionized dimethyl ether in a 15-16 eV ionization energy range. However, the observation of dehydrogenated products is consistent with additional abstraction of hydrogen from proximally located species isolated within the matrix. Analogous experiments employing CD(3)OCH(3) give similar results, and the observed isotopically substituted products are consistent with the proposed fragmentation pathways.     

Dimerization of ionized 4‐(methyl mercapto)‐phenol during ESI,APCI and APPI mass spectrometry

A novel ion/molecule reaction was observed to occur under electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and atmospheric pressure photo ionization (APPI) conditions, leading to dimerization of ionized 4‐(methyl mercapto)‐phenol followed by fast H^· loss. The reaction is particularly favored during ESI, which suggests that this ion/molecule reaction can occur both in the solution inside the ESI‐charged droplets and in the gas‐phase environment of most other atmospheric pressure ionization techniques. The dimerization reaction is inherent to the electrolytic process during ESI, whereas it is more by ion/molecule chemistry in nature during APCI and APPI. From the tandem mass spectrometry (MS/MS) data, accurate mass measurements, hydrogen/deuterium (H/D) exchange experiments and density functional theory (DFT) calculations, two methyl sulfonium ions appear to be the most likely products of this electrophilic aromatic substitution reaction. The possible occurrence of this unexpected reaction complicates mass spectral data interpretation and can be misleading in terms of structural assignment as reported herein for 4‐(methyl mercapto)‐phenol. Copyright © 2009 John Wiley & Sons, Ltd.     

Determinations of Intermediate Neutral Species in Hydrocarbon Discharge Plasma

This work reports laser ionization combined with Time-Of-Flight (TOF) mass spectrometry investigation on intermediate species in the hydrocarbon plasma of atmospheric-pressure fast-flow pulsed dc-discharge. All neutral intermediate species including transient radicals from benzene/Ar discharge have been characterized by a molecular beam sampling combined with TOF mass spectrometry. This shows that with a hydrocarbon gas mixture of 0.3% C₆H₆ in Ar discharge the intermediate species consist of simple radicals (such as C₂, C₅H₅, C₇H₇) and polycyclic organic molecules (C₁₀H₈, C₁₃H₁₀, C₁₄H₁₀). Theoretical studies on total energies and ionization potentials of the intermediate species have been carried out using the hybrid density functional theory. Effect of the ionization potential on mass spectral intensity has been discussed. Based on the observed data, the possible major neutral reaction channels of the plasma chemistry have been discussed. The developed experimental method has implications in volatile organic compounds removing and impurities diagnosis in Tokamak edge-plasma.     

Ethane cation decomposition characterization by EBMI spectroscopy: gas‐phase dissociative recombination as a source of secondary products

The decomposition products of the d₆‐ethane cation following charge‐transfer ionization with Ar⁺, under conditions of varying ionization electron current, have been isolated in solid argon matrices at 18 K and examined using Fourier transform infrared spectroscopy. Gas samples containing 1 : 1600 d₆‐ethane : Ar were subjected to electron bombardment by using either a high (pin) or a low (plate) ionization density anode configuration with ionization currents between 20 and 150 μA. Under high ionization density conditions, the observed major products were d₄‐ethene (C₂D₄) and d₂‐acetylene (C₂D₂), with smaller yields of C₂D₅, C₂D₃, and C₂D. The yield of each dehydrogenation product was enhanced with increased current. Analogous experiments employing the low ionization density plate anode resulted in reduced C₂D₆ destruction and the formation of only C₂D₄ and C₂D₂. The results suggest the onset of dissociative recombination processes under high ion density conditions. In this context, the results can be interpreted as a dissociative recombination of primary ion products, which gives rise to further dehydrogenation, and appearance of additional neutral radical products. Copyright © 2012 John Wiley & Sons, Ltd.     

Direct kinetics study of the product‐forming channels of the reaction of isoprene‐derived hydroxyperoxy radicals with NO

A direct kinetics study of the product‐forming channels of the reaction of isoprene‐derived hydroxyalkylperoxy radicals with NO has been performed at 100 Torr pressure and 298 K using the turbulent flow technique with high‐pressure chemical ionization mass spectrometry for the detection of reactants and products. For comparative purposes, a similar study was also performed for the reaction of 1‐ and 2‐butene‐derived hydroxyalkylperoxy radicals with NO. The measured hydroxyalkylnitrate product channel branching ratios were determined to be 0.061, 0.068, and 0.070 for the 1‐butene, 2‐butene, and isoprene systems, respectively. The results are compared to previous measurements of the hydroxyalkylnitrate‐branching ratios for these systems, and the atmospheric significance of the results is discussed. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 353–361, 2007     

Experimental and theoretical investigations of IR spectra and electronic structures of the U(OH)2, UO2(OH), and UO2(OH)2 molecules

Reactions of laser-ablated U atoms and H2O2 molecules produce UO2, H2UO2, and UO2(OH)2 as major products and U(OH)2 and HU(O)OH as minor products. Complementary information is obtained from similar reactions of U atoms with D2O2, with H2 + O2 mixtures, and with H2O in excess Ar. Through extensive relativistic density functional theory calculations, we have determined the geometry structures and ground states of these U species with a variety of oxidation states U(II), U(IV), U(V), and U(VI). The calculated vibrational frequencies, IR intensities, and isotopic frequency ratios are in good agreement with the experimental values, thus supporting assignments of the observed matrix IR spectra. We propose that the reactions proceed by forming an energized [U(OH)4] intermediate from reactions of the excited U atom with two H2O2 molecules. Because of the special stability of the U(VI) oxidation state, this intermediate decomposes to the UO2(OH)2 molecule, which reveals a distinctive difference between the chemistries of U and Th, where the major product in analogous Th reactions is the tetrahedral Th(OH)4 molecule owing to the stable Th(IV) oxidation state.     

Characterization of the photodegradation products of metolachlor: structural elucidation,potential toxicity and persistence

Aqueous solutions of metolachlor and metolachlor‐d₆ were photolyzed with UV‐visible radiations. The structures of 15 by‐products of metolachlor were determined through gas chromatography‐mass spectrometry analyses using electron and chemical ionization combined with multistage mass spectrometry. The photolysis by‐products of metolachlor resulted mainly from dehalogenation and hydroxylation, in some cases accompanied by cyclization. In silico tests for toxicity prediction showed that the toxicity of some photolysis products is expected to be greater than that of metolachlor. Persistence studies showed that the by‐product relative abundances vary in large amounts with the irradiation time. The post‐photolysis evolution of the solution was also studied, in order to determine the persistence of the main by‐products. It allowed to establish that most of the by‐products can be found more than 12 h after the end of the photolysis, which is of a great concern as treated water is generally available for consumption only a few hours after treatment in most of industrial processes. Copyright © 2012 John Wiley & Sons, Ltd.     

用NH4Cl氯化Li2CO3的研究

近年来利用熔盐电解法制备Al-Li合金已开始受到重视。但由于LiCl具有强烈的吸水性给工艺及其电解质溶液物化性质的研究带来很大的困难。因此本文利用热分析手段研究了NH_4Cl氯化Li_2CO_3的反应,为今后在电解工艺及其基础研究中用NH_4Cl定量氯化Li_2CO_3取代直接使用LiCl提供依据。     

Chemical effects of low energy electron impact on hydrocarbons in the gas phase: III. Cyclopropane

The simulated radiolysis of cyclopropane with low energy electrons (3.5 to 15.0 eV) was investigated. The setup used for the irradiations has been described previously. Appearance curves of the various products formed under electron impact were determined. The features observed on these curves yield various indications.(1) Some products arise from the dissociation of excited molecules. Contributing states are the following ones: a triplet state at 7.4 eV, singlet states at 6.7 and/or 7.7 eV, at 8.55 eV, at 9.4 and/or 9.95 eV and superexcited states lying around 10.2 eV. As in other hydrocarbons studied, the electron impact excitation cross section shows a steep increase at the ionization potential. (2) Other products result from ion fragmentation and ion—molecule reactions.A reaction scheme was proposed to account for the chemical effects associated with excited states and the yields of excited molecules in dissociating states were derived from experimental data. The observations relative to excited molecule fragmentation are in conformity with photolysis data. Additional information on the decomposition processes of molecules excited in the triplet state at 7.4 eV, in the singlet states at 6.7 and/or 7.7 eV and in the superexcited states were obtained.Owing to the complexity of ionic mechanisms it was not possible to distinguish between the contributions of ionization and excitation. Only the radiation chemical yield of products, G(products), was evaluated. The values found for G(products) just above the ionization potential are close to the data obtained in conventional radiolysis which could indicate that secondary electrons having such energies play an important role in radiation chemistry.