Ionic Reaction Mechanism Research Articles

An experimental study of organic-inorganic interactions during vitrinite maturation

Vitrinite reflectance is a parameter widely used to determine the extent of thermal maturation in sedimentary basins. Laboratory heating experiments were conducted to examine the role of aqueous fluid and sediment composition, temperature, and time on the development of vitrinite reflectance at elevated temperatures and pressures. Samples of organic-lean Middle Valley sediment containing dispersed vitrinite and Wyodak Coal composed almost entirely of vitrinite were heated in the presence of compositionally variable aqueous fluids at 225° to 375°C and 350 bars. Inorganic fluid composition was monitored as a function of time, and vitrinite reflectance was measured at the termination of each experiment. The rate of vitrinite maturation was influenced by inorganic fluid and vitrinite composition, in addition to time and temperature during the experiments. In particular, the rate at which vitrinite reflectance increased for a given temperature correlated positively with in situ H + activity. This observation suggests that acid catalyzed ionic reaction mechanisms and/or catalytically active transition metals and sulfur species play an important role in organic transformations responsible for increased vitrinite reflectance. The activity of other inorganic ionic species such as Mg ++, Ca ++, Na +, K +, and SO 4 =, and the redox state of the fluid did not influence the rate of vitrinite maturation during these experiments. Results of this study demonstrate that the geochemical environment surrounding vitrinite influences the rate of maturation. The presence of water may facilitate reaction pathways that are not readily available in dry systems. Vitrinite maturation profiles that deviate from what are considered to be “normal” trends may reflect subsurface variations in the composition of pore fluids or the presence or absence of an aqueous phase in contact with vitrinite particles. Accordingly, kinetic models that consider organic reactions responsible for increased vitrinite reflectance in terms of time and temperature alone may not accurately account for geochemical processes occurring in natural systems.

Lewis Acid Catalyzed Reactions of Thioketones with 1,2-Epoxycyclohexane and 1,2-Epoxycyclopentane

Non-enolizable thioketones and 1,2-epoxycycloalkanes undergo a Lewis acid catalyzed addition reaction to give 1,3-oxathiolanes. Appropriate reaction conditions are CH2Cl2 as the solvent, BF 3.Et2O as the Lewis acid, and a temperature between -78° and r.t. Under the reaction conditions, the 1,3-oxathiolanes are only moderately stable. They decompose to yield the corresponding epithiocycloalkane and ketone. In general, 1,3- dithiolanes are isolated as minor products or, after prolonged reaction, as the main product. These secondary products are formed via the Lewis acid catalyzed reaction of the intermediate epithiocycloalkane and a second molecule of the thioketone. In the reaction of thiobenzophenone and 1,2-epoxycyclohexane, trans-8,8-diphenyl-7,9-dioxabicyclo[4.3.0]nonane is formed in small amounts as an additional side product (Scheme 12). In all cases, the newly formed heterocycle and the carbocycle are trans-fused. This result is consistent with a nucleophilic ring-opening of the complexed oxirane by the thioketone via inversion of the configuration and subsequent formation of the O(1)-C(2) bond of the 1,3-oxathiolane (Scheme 13). The surprising formation of the fused 1,4-oxathiepan derivative 23 (Scheme 9) is in accordance with an ionic reaction mechanism (cf. Scheme 15).

The HCl+ClONO 2 reaction rate on various water ice surfaces

The reaction ClONO 2+HCl → Cl 2+HNO 3 on ice surfaces was investigated using a fast flow reactor coupled to a chemical ionization mass spectrometer. Rough and relatively smooth ice surfaces and single-crystal ice particles were employed to investigate the effect of the different surface morphologies on the reaction mechanism. Large reaction probabilities ( γ>0.1), independent of HCl partial pressure in the range from 2×10 −7 to 8×10 −6 Torr, were measured on these three ice surfaces. These results are consistent with an ionic reaction mechanism involving HCl solvation on a liquid-like surface layer.

Investigation of transient species in pulse-irradiated poly(ethylene terephthalate) film

A pulse radiolysis study of poly(ethylene terephthalate), PET, film has been carried out with the main aims of investigating charge trapping. In PET, pulse radiolysis gives electron-positive hole pairs. Both charges can be stabilized by the reaction with polymeric matrix. In the first step, the PET radical anions and cations are formed (transient absorption maxima at ∼ 370 and 530 nm). During the second step, the electron is transferred from a PET radical anion to an ester group, followed by formation of an ester radical anion (transient absorption maximum at 430 nm). The recombination of these ionic species leads to an excited state formation observed during and after the 1-μs pulse. Spectral distribution of luminescence observed for pulse-irradiated PET (emission bands at ∼ 340, ∼ 370, and 400–410 nm) was similar to the one obtained for photoexcited PET. The detailed mechanism of ionic reactions in PET is proposed and discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2853–2862, 1999

Solvent–catalyst interactions in the decomposition process of 2-isopropylnaphthalenehydroperoxide into 2-naphthol and acetone

Decomposition of 2-isopropylnaphthalenehydroperoxide (2-IPNHP) proceeds through either ionic or radical reaction mechanism. 2-Naphthol and acetone are produced by ionic reactions, however, dimethyl-2-naphthylcarbinol and 2-acetonaphthone productions through radical reactions cannot be avoided because of induced decomposition effects. In this work, we performed the acid-catalysed decomposition of 2-IPNHP for 2-naphthol and acetone production in the presence of eight different solvents and three different acid catalysts. The results were discussed in combination with the ionic reaction mechanism to evaluate the solvent–catalyst interactions. Dodecane, isopropylnaphthalene, propyl acetate, acetone (aprotic solvents of low dielectric constant); acetonitrile, nitrobenzene (NB) (aprotic solvents of high dielectric constant), acetic acid (AcOH) (protogenic solvent) and methyl alcohol (MeOH) (amphiprotic solvent) were used separately with oxyacids HClO 4 and H 2SO 4, and hydroacid HCl. 2-IPNHP decomposition and 2-naphthol production rates increased with increasing dipole moment of aprotic solvents. The highest reaction rates were obtained in the protogenic solvent AcOH and in the aprotic solvent NB where the reactions in the amphiprotic solvent MeOH resulted in the lowest reaction rates. In addition to characters of the solvent and catalyst of the decomposition medium, the composition of the reactant mixture also affected the reaction mechanism and decomposition yield. According to the experimental results, AcOH and HClO 4 are the favourable solvent and catalyst for 2-naphthol production, respectively. 61% yield of 2-naphthol was achieved in the presence of AcOH by 0.114 mol dm −3 HClO 4 with the medium concentrations of 1.078 mol dm −3 2-IPNHP, 0.222 mol dm −3 DMNC, 8.680×10 −3 mol dm −3 AN and 0.255 mol dm −3 H 2O 2.

The Formation of the Sulfur Halides SX4 from SX2 and X2: Reaction Enthalpies, Transition States, and Activation Energies for X=F and Cl

Polar reaction mechanisms in sulfur chemistry may be more common than expected. Quite asymmetric, high-energy transition states TS1 and TS2 separate the sulfur halides SF4 and SCl4 from their dissociation products SF2+F2 and SCl2+Cl2, respectively, indicating almost ionic reaction mechanisms.

Thermodynamic behaviour of carbon in CaO-SiO2slag system

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Nitrate effect in the heterogeneous hydrolysis of dinitrogen pentoxide on aqueous aerosols

The heterogeneous hydrolysis of N2O5 was investigated on NaHSO4, Na2SO4, and NaNO3 aerosols. The experiments were performed in the large Aerosol Chamber at FZ Julich at room temperature and ambient pressure for several relative humidities. These salts are components of aerosols in the marine and coastal boundary layer. For the sodium sulfate aerosols at relative humidities of 50–70% the reaction probabilities γN2O5 were in the range of 0.02–0.04. For NaNO3 aerosol at similar relative humidities we observed γN2O5 of 0.0018–0.0032. With increasing relative humidity, i.e. with increasing dilution of the nitrate concentration in the aerosol droplets, γN2O5 increases to 0.023 at 90% relative humidity. Our observation of decreasing γN2O5 with increasing nitrate concentration can be explained within the framework of an ionic mechanism for the hydrolysis of N2O5, if the recombination reaction of NO2+ with NO3- to N2O5 is considered. By a steady state analysis we derived analytical expressions of γN2O5 as a function of the nitrate concentration for a reaction either throughout the aerosol volume or in a thin surface shell. Accordingly, increasing nitrate concentration should enhance the lifetime of physically dissolved N2O5(aq) and as a consequence the heterogeneous hydrolysis of N2O5 should change from a near-surface to a volume reaction. The observation of such a specific nitrate effect can be regarded as further experimental evidence for the ionic reaction mechanism in the uptake of N2O5 on aqueous aerosols. A nitrate effect may gain (local) importance in the atmosphere if increasing NOX emissions translate in an increasing nitrate fraction in the secondary aerosol of anthropogenic origin.

Recent advances in the energetics and mechanisms of gas-phase ionic reactions

Abstract

Decomposition of Formic Acid under Hydrothermal Conditions

The thermal decomposition of formic acid was studied in dilute aqueous solutions and in the absence of added oxygen at temperatures between 320 and 500 °C and pressures between 178 and 303 atm for residence times between 1.4 and 80 s. Under these conditions, the formic acid conversion ranged from 38% to 100%, and the major products were always CO2 and H2, which indicates that decarboxylation is the preferred reaction path for formic acid decomposition under hydrothermal conditions. CO also appeared as a product, which shows that a dehydration path is available, but the CO yield was always at least an order of magnitude lower than the yields of CO2 and H2. The kinetics of formic acid disappearance and product formation at temperatures above 320 °C are consistent with a reaction rate law that is first order in formic acid. The implications of the present results to the generally accepted molecular decomposition mechanism are discussed, as are the alternative free-radical, ionic, and surface-catalyzed reaction mechanisms proposed in the literature.

Ammonium Dinitramide: Kinetics and Mechanism of Thermal Decomposition

Thermal decomposition of ammonium dinitramide (ADN) has been studied by differential scanning calorimetry (DSC) and thermal gravimetry combined with mass spectrometry (TG−MS). ADN decomposes in the range 130−230 °C with an overall heat release of 240 ± 40 kJ mol-1. The product gases have been identified by MS as NH3, H2O, NO, N2O, NO2, HONO, and HNO3. The global activation energy determined from TG experiments decreases from 175 ± 20 kJ mol-1 at the beginning of the reaction to 125 ± 20 kJ mol-1 when the reaction is near completion. Experiments conducted at different carrier gas flow rates indicate that the reaction is catalyzed by product gases released during the reaction. A condensed phase ionic reaction mechanism is proposed, in which ammonium nitrate and ammonium mononitramide (NH4NNO2) are formed as intermediates in two competing channels.

Reactions of Organic Compounds in Explosive-Driven Shock Waves

Shock waves of 1 μs duration and peak temperatures from 900 to 1400 K and pressures from 6 to 16 GPa have been applied to measurement of the rates of a broad spectrum of organic compounds including decomposition of explosives. All reaction rates are consistent with known activation parameters and reaction conditions, and there is no indication of unique chemical processes connected with the subnanosecond rise time of the shock front. Reactions having both positive and negative activation volumes have been studied. Extreme pressure favors ionic reaction mechanisms, whereas extreme temperature favors homolytic mechanisms. Either influence may dominate; thus, cyclohexyl nitrate in benzene gives cyclohexylbenzene by a reaction of Friedel−Crafts type, whereas neopentyl nitrate undergoes homolysis, β-scission, and recombination to give 2-nitro-2-methylpropane. When methanol is used as a solvent, it ionizes extensively and promotes a variety of reactions which ordinarily require acid or base catalysis such as es...

Ionisation and solvation of stratospherically relevant molecules on ice films

Heterogeneous reactions of stratospheric reservoir species such as HCl, N2O5 and ClONO2 on type I (nitric acid hydrates) and type II (water-ice) polar stratospheric cloud (PSC) particles are believed to play an important role in the extremely large losses of stratospheric ozone observed during the Antarctic spring. Laboratory studies of such processes, using thin ice films as PSC particle surface mimics, can provide mechanistic information about individual elementary steps and overall reaction schemes. IR and mass spectrometry have been used to identify reaction products and intermediates and it has been shown that the primary step in all the studied reaction schemes involves the formation of ionic surface species. Furthermore, the nature and stability of the ions are found to be inextricably linked with the amount of ‘free’ water available to solvate them. The following questions are also addressed: Are adsorbed ions (e.g. nitrate, chloride and oxonium) reactive on ice surfaces? If so, are the products formed the same as those suggested when their corresponding molecular parents are involved? The answers, which have important implications for understanding stratospheric heterogeneous chemistry, are discussed in terms of ionic reaction mechanisms and novel surface intermediates.

Ionic reaction mechanisms in pre-mixed flames disclosed by stable-isotope labelling

The methane–oxygen fuel system was investigated using deuterium labelling methods. The pre-mixed flames were burnt on a simple quartz burner and sampled directly by a VG PlasmaQuad instrument, which consists of a quadrupole mass spectrometer equipped with a high-temperature molecular beam inlet. The genesis of the predominant ions C3H3+ and C2H3O+ and their eventual routes of decomposition are discussed. The proposed mechanisms are supported by thermochemical considerations and appropriate tandem mass spectrometric experiments on alternatively generated ions.

Intra‐ and intermolecular reactions of aromatic radical cations: An account of mechanistic concepts and methods in mass spectrometry

AbstractInvestigations in the authors's laboratory in Bielefeld and elsewhere on the mechanism of the intramolecular and intermolecular aromatic substitution via radical cations are reviewed with the aim of presenting an example for the development of mass spectrometric methods and concepts for the study of the mechanisms of gaseous ionic reactions. An intramolecular aromatic substitution resulting in the loss of a hydrogen or a substituent from an aromatic ring of the molecule ions by the attack of a nucleophilic heteroatom in the side‐chain was first observed in the normal electron impact (EI) mass spectra and was studied by substituent effects on ion abundance, ionization energy and appearance energy. This led to the construction of a two‐step mechanism of the intramolecular aromatic substitution with a rate‐determining first addition step. Subsequently, this fragmentation reaction was studied for a series of systems by tandem mass spectrometry, confirming the two‐step mechanism and yielding an excellent insight into the dynamics of the substitution process. The bimolecular variety of the nucleophilic aromatic substitution via radical cations was investigated recently by Fourier transform ion cyclotron resonance spectrometry. The results for a series of halogenated benzenes and NH3, CH3NH2 and (CH3)2NH as the nucleophile corroborate the conclusions drawn from the study of unimolecular reaction mechanisms. It is shown that in all cases the formation and further reaction of the addition intermediate play a crucial role. This can be perceived by the application of the configuration mixing reactivity model to the addition reaction, and by the concept of classical and distonic radical cations. This review on a specific reaction mechanism shows clearly the excellent techniques and methods which the developments in mass spectrometry have provided for a detailed study of the mechanisms of ionic reactions in the gas phase.

Simulation of electric field effects in premixed methane flames

The objective of this study is to predict the effect of electric fields on the ionic structure of one-dimensional methane flames. The chemical kinetic mechanism devised for this study combines existing methane oxidation mechanisms with a series of chemiionization, ion-molecule, and dissociative-recombination reactions thought to be important to the ionic structure of methane flames. The governing equations include Poisson's equation to describe the electric field intensity in the flames. The model correctly predicted several features in the ionic structure of methane flames. The model was used to predict saturation currents as a function of peak flame temperature from which the apparent activation energy for the saturation process was determined. The predicted apparent activation energy compared well with the experimental range of values. This analysis determined that the rate-limiting reaction in the overall ionic reaction mechanism is: C 2H 3O + + H 2 → H 3O + + C 2H 2.

Detection of neutral and ionic reaction mechanisms in molecular clusters

Techniques based on picosecond resonance-enhanced multiphoton ionization and mass-selective ion photodissociation are described as a means for studying complex reaction mechanisms in molecular clusters. A set of experiments is described that can identify the cluster-size specific reactions that occur by the overlapping processes of neutral dissociation/fragment ionization, parent ionization/dissociation, and parent ion photoexcitation/dissociation. These molecular beam techniques are demonstrated for the case of neutral and ionic photon transfer and evaporation in clusters of phenol in (NH(3))(n), as well for radical chemistry and van der Waals dissociation in (CH(3)I) (n) clusters.

Mass spectrometry of alkylbenzenes and related compounds. Part I. Gas‐phase ion chemistry of alkylbenzene radical cations

From the vantage point of an organic chemist, many previously obscure fragmentation and isomerization processes of gaseous organic ions have become chemically reasonable reaction pathways. The term scrambling, used formerly as a synonym for mechanistic dilemmas concerning crazy atoms, has almost vanished from mass spectrometry literature in recent years, mostly because of the recognition of well-defined ionic intermediates and reaction mechanisms occurring before, during, or even after the actual cleavage of a molecular bond. The conceptual links between organic mass spectrometry and general organic chemistry have grown in many ways. In this respect, positively charged aromatic species have played a key role, owing to their inherent stability. The investigation of alkylbenzenes, in particular, has been a central focus of mass spectrometry since its application to the analysis of petroleum and gasoline in the mid-twentieth century, and has provided much insight into the intrinsic stability and reactivity of organic ions. Besides, and in connection with, the evergreens of organic mass spectrometry (e.g., the C7H7+/C7H8+' ion problem and the McLafferty rearrangement), new information has emerged during three decades of investigating the mass spectrometry of alkylbenzenes. This two-part review summarizes the mass spectrometry of alkylbenzenes and related compounds. Part one collects the gas-phase chemistry of ionized alkylbenzenes and part two describes that of protonated alkylbenzenes. This is in part due to the different relations to organic chemistry of the open-shell, radical ions (M+') on the one hand, and closed-shell ions such as [M+H]+, on the other. These two classes of ions also have different relevance to analytic applications of mass spectrometry. The radical ions of alkylbenzenes are discussed in Part I, owing to their historical priority and their broad occurrence in standard electron ionization (EI) mass spectrometry. Protonated benzene and alkylbenzenes (al

Aflatoxin B1S: Revised Structure for the Sodium Sulfonate Formed by Destruction of Aflatoxin B1 with Sodium Bisulfite ,

A promising method for the destruction of aflatoxin B1 in commodities is treatment with sodium bisulfite to yield a single major product, aflatoxin B1S. On the basis of nuclear magnetic resonance, ultraviolet and infrared spectra, elemental analysis, mass spectroscopy, deuterium labeling and stability to highly acidic conditions, the structure of aflatoxin B1S was established as the 15 α-sodium sulfonate of aflatoxin B1 The formation of aflatoxin B1 products substituted at the 15 position only is unprecedented and implies an unusual mechanism. The formation of a single trans addition product under conditions that seemingly rule out a previously proposed free radical mechanism suggested a newly proposed ionic reaction mechanism. The completeness of the reaction and the water solubility of aflatoxin B1S support the promising use of bisulfite to destroy aflatoxin.

On the Dark Stability of the Magenta Azomethine Dye Image Obtained from Two-Equivalent Pyrazolone Couplers

Dark stability of the magenta dye image obtained from 2-equivalent 3-acylamino-5-pyrazolone couplers was investigated from the viewpoint of the reaction of the magenta dye with the residual coupler.A correlation was found between the reaction rate and the pKa values of the starting 3acylamino-5-pyrazolone couplers, i.e., the couplers with the lowest pKa values showed the least reactivity. This observation suggests that the reaction proceeds via an ionic reaction mechanism rather than by a radical reaction mechanism.The use of couplers with low pKas for colour negative film makes it possible to remove formaldehyde from the stabilizing bath in colour negative processing.