Reaction 1a Research Articles

HO2 + NO2: Kinetics, Thermochemistry, and Evidence for a Bimolecular Product Channel.

A master equation (ME) analysis of available experimental data has been carried out on the reaction HO2 + NO2 + M ⇋ HO2NO2 + M (1a)/(−1a). The analysis, based on the ME code MESMER, uses both the association and dissociation kinetic data from the literature, and provides improved thermochemistry on reaction 1a. Our preferred model assigns two low-frequency vibrations of HO2NO2 as hindered rotors and couples these to the external rotations. This model gives ΔrH°0(1a) = −93.9 ± 1.0 kJ mol–1, which implies that ΔfH°0 HO2NO2 = −42.0 ± 1.0 kJ mol–1 (uncertainties are 2σ). A significant contributor to the uncertainty derives from modeling the interaction between the internal and external rotors. Using this improved kinetics for reaction 1a/–1a, data at elevated temperatures, 353–423 K, which show no evidence of the expected equilibration, have been reanalyzed, indicating that an additional reaction is occurring that masks the equilibration. Based on a published ab initio study, this additional channel is assigned to the bimolecular reaction HO2 + NO2 → H–NO2 + O2 (1b); H–NO2 is nitryl hydride and has not previously been directly observed in experiments. The output of the master equation analysis has been parametrized and Troe expressions are provided for an improved description of k1a(p,T) and k–1a(p,T).

The helium bubble: Prospects for 3He-fuelled nuclear fusion

The helium bubble: Prospects for 3He-fuelled nuclear fusion

Finite size scaling in the heterogeneous reaction 2A + B2 → 2AB

In the present paper we extend the exact solution previously obtained for the heterogeneous catalytic reaction 2A + B2 → 2AB on small domains, to arbitrary lattice sizes () and calculate the average number of reactive steps necessary to poison the lattice first, . We determine as a function of through Monte Carlo simulations previously contrasted with the exact solution in lattices. We show that follows a power law with , without appreciable transient behaviors, and a scale factor () dependent on the two parameters of the model, the sticking coefficient probability and the desorption probability . The dependence of on both and is determined.

Towards Electrochemical Synthesis of Cement — an Electrolyzer-Based Process for Decarbonating CaCO3 while Producing Useful Gas Streams

Cement production is currently the largest single industrial emitter of CO2, accounting for 8% (2.8 Gtons/year) of global CO2 emissions in 2015. Deep decarbonization of cement manufacturing will require remediation of both the CO2 emissions due to the decomposition of CaCO3 to CaO, and that due to combustion of fossil fuels (primarily coal) in the calcining (~900°C) and sintering (~1,450°C) processes. Here, we demonstrate an electrochemical process that uses neutral water electrolysis to produce a pH gradient in which CaCO3 is decarbonated at low pH and Ca(OH)2 is precipitated at neutral to high pH, concurrently producing a high purity O2/CO2 gas mixture (1:2 molar ratio at demonstrated stoichiometric operation) at the anode and H2 at the cathode, as shown in Figure 1. We show that the solid Ca(OH)2 product readily decomposes and reacts with SiO2 to form alite, the majority cementitious phase in Portland cement. Our electrochemical calcination approach produces concentrated gas streams from which the CO2 may be readily separated and sequestered, the H2 and/or O2 may be used to generate electric power via fuel cells or combustors, the O2 may be used as a component of oxyfuel in the cement kiln to further lower CO2 and NOx emissions, or the output gases may be used for other value-added processes including liquid fuel production. Analysis shows that in a scenario where the hydrogen produced by the reactor is combusted to heat the high temperature kiln, the electrochemical cement process can be powered solely by renewable electricity. Figure 1. Schematic of the electrolyzer-based decarbonation cell. Reactions 1a and 1b are the O2 evolution and H2 evolution half-cell reactions respectively, under near-neutral pH. Reactions 2a and 2b represent the decomposition of CaCO3 and release of CO2. Reaction 3 is the normal formation of water from its component ions. In Reaction 4, the hydroxide ions in Reaction 3 instead go towards the formation of Ca(OH)2, and the protons protonate carbonate ions (Reaction 2b). The overall reaction in which CaCO3 is converted to Ca(OH)2 with the attendant release of H2, O2 and CO2 is shown at the bottom. Figure 1

An investigation on the anti-water properties of phosphorus building gypsum (PBG)-based mortar

This study aimed to manufacture phosphorus building gypsum (PBG)-based mortar with a high water resistance coefficient and to explore the anti-water mechanism of PBG-based mortar containing ground granulated blast furnace slag (GGBS) and calcium hydroxide (CH). The main hydration products of PBG-based mortar were CS(A)H and ettringite (AFt), along with CsH2; the chemical reaction 2A + 6CH + 6CsH0.5 + 55H → 2(C3A·3Cs·32H) occurred in PBG-based mortar; and AFt was produced gradually after the majority of the CsH0.5 was hydrated into CsH2. Gelatinous CS(A)H densely coated the CsH2 crystals to inhibit the connection between CsH2 and water. AFt crystals prevented the CsH2 crystals from water corrosion through the complex actions of the AFt crystals coating the surface of the CsH2 crystals and transforming the direct contact among the CsH2 crystals into the indirect contact among the CsH2 crystals. The contents and morphologies of AFt were the key factors for increasing the water resistance coefficient of PBG-based mortar. As mPG:mGGBS:mCH = 240:160:15, the water-saturated strength and water resistance coefficient of PBG-based mortar reached 20.8 MPa and 0.89, which meant that as long as the mix proportion was appropriate, PBG-based mortar with a high water resistance coefficient can be successfully produced.

Thermal decomposition of propene: A shock-tube/H-ARAS and modeling study

The thermal decomposition of propene (C3H6) was studied in a shock tube behind reflected shock waves in the temperature range 1340–1910K at pressures around 4.6, 2.1, and 0.4bar with argon as bath gas. The initial concentrations of C3H6 were in the range 3.5×10−11–1.8×10−10mol/cm3. Hydrogen atoms were detected time-resolved with atom resonance absorption spectroscopy (ARAS), and rate coefficients, k1a, of the decomposition reaction C3H6+M→C3H5+H+M (1a) were determined. A medium-sized reaction mechanism (29 reactions, 15 species) with kinetic data from the literature was set up, and the [H](t) profiles were simulated and fitted to the experimental profiles with k1a being the only adjustable parameter. The simulations have shown that despite the low initial concentrations of C3H6, a direct determination of k1a from the initial slopes of the [H](t) profiles would result in an overestimation of about 30% mainly because of H-atom production in the fast consecutive decomposition reaction C3H5+M→aC3H4+H+M (aC3H4: allene). The observed temperature and pressure dependence of k1a was modeled with a master equation. At the conditions of our experiments, the rate coefficient of reaction (1a) was found to be close to its low-pressure limit, and the observed temperature and pressure dependence could be characterized by the following bimolecular rate coefficient: k1abim(T)=(8.8±3.8)×1018 exp[–(39970±680) K T–1] cm3/mol s. We recommend the use of this expression for the calculation of k1a in the temperature range 1300–2000K for pressures between 0.3bar and 5bar with Ar or similar colliders as bath gas.

Features of the Diels-Alder reaction between 9,10-diphenylanthracene and 4-phenyl-1,2,4-triazoline-3,5-dione

The Diels-Alder reaction between substituted anthracenes 1a−1j and 4-phenyl-1,2,4-triazoline-3,5 (2) is studied. In all cases except one, the reaction proceeds on the most active 9,10-atoms of substituted anthracenes. The orthogonality of the two phenyl groups at the 9,10-position of diene 1a is found to shield 9,10-reactive centers. No dienophiles with C=C bonds are shown to participate in the Diels-Alder reaction with 1a; however, the reaction 1a + 2 proceeds with the very active dienophile 2,4-phenyl-1,2,4-triazoline-3,5-dione. It is shown that attachment occurs on the less active but sterically accessible 1,4-reactive center of diene 1a. The structure of adduct 3a is proved by 1H and 13C NMR spectroscopy and X-ray diffraction analysis. The following parameters are obtained for reaction 1a + 2 ⇆ 3a in toluene at 25°C: K eq = 2120 M−1, ΔH f ≠ = 58.6 kJ/mol, ΔS f ≠ = −97 J/(mol K), ΔV f ≠ = −17.2 cm3/mol, ΔH b ≠ = 108.8 kJ/mol, ΔS b ≠ = 7.3 J/(mol K), ΔV b ≠ = −0.8 cm3/mol, ΔH r-n = −50.2 kJ/mol, ΔS r-n = −104.3 J/(mol K), ΔV r-n = −15.6 cm3/mol. It is concluded that the values of equilibrium constants of the reactions 1a−1j + 2 ⇆ 3a−3j vary within 4 × 101−1011 M−1.

Experimental study of the reactions of limonene with OH and OD radicals: kinetics and products.

The kinetics of the reactions of limonene with OH and OD radicals has been studied using a low-pressure flow tube reactor coupled with a quadrupole mass spectrometer: OH + C10H16 → products (1), OD + C10H16 → products (2). The rate constants of the title reactions were determined using four different approaches: either monitoring the kinetics of OH (OD) radicals or limonene consumption in excess of limonene or of the radicals, respectively (absolute method), and by the relative rate method using either the reaction OH (OD) + Br2 or OH (OD) + DMDS (dimethyl disulfide) as the reference one and following HOBr (DOBr) formation or DMDS and limonene consumption, respectively. As a result of the absolute and relative measurements, the overall rate coefficients, k1 = (3.0 ± 0.5) × 10(-11) exp((515 ± 50)/T) and k2 = (2.5 ± 0.6) × 10(-11) exp((575 ± 60)/T) cm(3) molecule(-1) s(-1), were determined at a pressure of 1 Torr of helium over the temperature ranges 220-360 and 233-353 K, respectively. k1 was found to be pressure independent over the range 0.5-5 Torr. There are two possible pathways for the reaction between OH (OD) and limonene: addition of the radical to one of the limonene double bonds (reactions 1a and 2a ) and abstraction of a hydrogen atom (reactions 1b and 2b ), resulting in the formation of H2O (HOD). Measurements of the HOD yield as a function of temperature led to the following branching ratio of the H atom abstraction channel: k2b/k2 = (0.07 ± 0.03) × exp((460 ± 140)/T) for T = (253-355) K.

Identification of amino acid derivatives as condensation products between glyceraldehyde and guanine nucleoside

Two degradants observed in a drug formulation of the hepatitis B drug entecavir (Baraclude®), 1 were shown to be identical to the products resulting from the condensation between glyceraldehyde and the guanine nucleoside. The reaction products, 2a and 2b were identified by the analysis of comprehensive NMR data to be two diastereomeric derivatives of alanine implying a novel rearrangement in the reaction between glyceraldehyde and 1.

Reaction OH + OH Studied over the 298–834 K Temperature and 1 - 100 bar Pressure Ranges

Self-reaction of hydroxyl radicals, OH + OH → H(2)O + O (1a) and OH + OH → H(2)O(2) (1b), was studied using pulsed laser photolysis coupled to transient UV-vis absorption spectroscopy over the 298-834 K temperature and 1-100 bar pressure ranges (bath gas He). A heatable high-pressure flow reactor was employed. Hydroxyl radicals were prepared using reaction of electronically excited oxygen atoms, O((1)D), produced in photolysis of N(2)O at 193 nm, with H(2)O. The temporal behavior of OH radicals was monitored via transient absorption of light from a dc discharge in H(2)O/Ar low-pressure resonance lamp at ca. 308 nm. The absolute intensity of the photolysis light was determined by accurate in situ actinometry based on the ozone formation in the presence of molecular oxygen. The results of this study combined with the literature data indicate that the rate constant of reaction 1a, associated with the pressure independent component, decreases with temperature within the temperature range 298-414 K and increases above 555 K. The pressure dependent rate constant for (1b) was parametrized using the Troe expression as k(1b,inf) = (2.4 ± 0.6) × 10(-11)(T/300)(-0.5) cm(3) molecule(-1) s(-1), k(1b,0) = [He] (9.0 ± 2.2) × 10(-31)(T/300)(-3.5±0.5) cm(3) molecule(-1) s(-1), F(c) = 0.37.

A new approximate method for the stochastic simulation of chemical systems: The representative reaction approach

We have developed two new approximate methods for stochastically simulating chemical systems. The methods are based on the idea of representing all the reactions in the chemical system by a single reaction, i.e., by the "representative reaction approach" (RRA). Discussed in the article are the concepts underlying the new methods along with flowchart with all the steps required for their implementation. It is shown that the two RRA methods {with the reaction 2A −> B as the representative reaction (RR)} perform creditably with regard to accuracy and computational efficiency, in comparison to the exact stochastic simulation algorithm (SSA) developed by Gillespie and are able to successfully reproduce at least the first two moments of the probability distribution of each species in the systems studied. As such, the RRA methods represent a promising new approach for stochastically simulating chemical systems.

Branching Ratios in the Hydroxyl Reaction with Propene

The branching ratios for the reactions of attachment of hydroxyl radical to propene and hydrogen-atom abstraction were measured at 298 K over the buffer gas pressure range 60-400 Torr (N(2)) using a subatmospheric pressure turbulent flow reactor coupled with a chemical ionization quadrupole mass spectrometer. Isotopically enriched water H(2)(18)O was used to produce (18)O-labeled hydroxyl radicals in reaction with fluorine atoms. The β-hydroxypropyl radicals formed in the attachment reactions 1a and 1b , OH + C(3)H(6) → CH(2)(OH)C(•)HCH(3) (eq 1a ) and OH + C(3)H(6) → C(•)H(2)CH(OH)CH(3) (eq 1b ), were converted to formaldehyde and acetaldehyde in a sequence of secondary reactions in O(2)- and NO-containing environment. The (18)O-labeling propagates to the final products, allowing determination of the branching ratio for the attachment channels of reaction 1. The measured branching ratio for attachment is β(1b) = k(1b)/(k(1a) + k(1b)) = 0.51 ± 0.03, independent of pressure over the 60-400 Torr pressure range. An upper limit on the hydrogen-abstraction channel, OH + C(3)H(6) → H(2)O + C(3)H(5) (eq 1c ), was determined by measuring the water yield in reactions of OH and OD radicals (produced via H(D) + NO(2) → OH(OD) + NO reactions) with C(3)H(6) as k(1c)/(k(1a) + k(1b) + k(1c)) < 0.05 (at 298 K, 200 Torr N(2)).

The elimination of molecular chlorine catalyzed by BCl3: an aspect of chloroboron subphthalocyanine formation

This study is focused on the final stage of the formation mechanism of chloroboron subphthalocyanine from boron trichloride and phthalonitrile, in the context of recent work on the earlier stages of this reaction. The results of extensive quantum-chemical energetic, structural, and charge-distribution computations show that a catalytic effect of boron trichloride is most probably essential to explain the fact that molecular chlorine is liberated in the formation of chloroboron subphthalocyanine (reaction 2). This process turns out to be closely concerted (reactions 2a and 2b).

Thermochemistry of the [formula omitted] association reaction and enthalpy of formation of [formula omitted]: A quantum chemical study

The thermochemistry of the HOSO 4 radical is of crucial importance for the modeling of the atmospheric sulfur-oxidation cycle, in which HOSO 4 is formed in the reaction HOSO 2 + O 2 + M → HOSO 4 + M (2a). We performed high-level quantum chemical calculations to characterize the energetics of reaction (2a) and obtained the following values for the enthalpy of reaction: Δ R H 0 K (2a) = −71.4 ± 2.0 and Δ R H 298 K (2a) = −72.9 ± 3.0 kJ/mol. For the enthalpy of formation of HOSO 4 , it follows: Δ f H 0 K ( HOSO 4 ) = - 438.0 ± 5.0 kJ / mol and Δ f H 298 K ( HOSO 4 ) = - 447.0 ± 6.0 kJ / mol . These new thermochemical data can serve as a basis for kinetic studies of HOSO 4 reactions in the atmosphere.

Rate Constants and Hydrogen Isotope Substitution Effects in the CH3 + HCl and CH3 + Cl2 Reactions

The kinetics of the CH3 + Cl2 (k2a) and CD3 + Cl2 (k2b) reactions were studied over the temperature range 188-500 K using laser photolysis-photoionization mass spectrometry. The rate constants of these reactions are independent of the bath gas pressure within the experimental range, 0.6-5.1 Torr (He). The rate constants were fitted by the modified Arrhenius expression, k2a = 1.7 x 10(-13)(T/300 K)(2.52)exp(5520 J mol(-1)/RT) and k2b = 2.9 x 10(-13)(T/300 K)(1.84)exp(4770 J mol(-1)/RT) cm(3) molecule(-1) s(-1). The results for reaction 2a are in good agreement with the previous determinations performed at and above ambient temperature. Rate constants of the CH3 + Cl2 and CD3 + Cl2 reactions obtained in this work exhibit minima at about 270-300 K. The rate constants have positive temperature dependences above the minima, and negative below. Deuterium substitution increases the rate constant, in particular at low temperatures, where the effect reaches ca. 45% at 188 K. These observations are quantitatively rationalized in terms of stationary points on a potential energy surface based on QCISD/6-311G(d,p) geometries and frequencies, combined with CCSD(T) energies extrapolated to the complete basis set limit. 1D tunneling as well as the possibility of the negative energies of the transition state are incorporated into a transition state theory analysis, an approach which also accounts for prior experiments on the CH3 + HCl system and its various deuterated isotopic substitutions [Eskola, A. J.; Seetula, J. A.; Timonen, R. S. Chem. Phys. 2006, 331, 26].

The heterogeneous catalytic reaction 2A + B 2 → 2AB exactly solved on a small lattice

We studied a kinetic model of a generic heterogeneous catalytic reaction 2 A ∗ + B 2 ∗ → 2 AB g . This reaction includes the steps of adsorption and desorption of reactants A and B 2, where B 2 requires two neighboring adsorption sites to be adsorbed. We solved the model exactly and without any restriction on a 2 × 2 lattice. Despite the reduced number of sites employed, the solution shows the main general features observed by simulating the mechanism on a large N × N lattice. This result should encourage the search for an analytical solution as a reliable form to unravel details of a chemical reaction prior to performing numerical simulations.

Experimental and Theoretical Studies of Rate Coefficients for the Reaction O(3P) + C2H5OH at High Temperatures

Rate coefficients of the reaction O(3P)+C2H5OH in the temperature range 782-1410 K were determined using a diaphragmless shock tube. O atoms were generated by photolysis of SO2 at 193 nm with an ArF excimer laser; their concentrations were monitored via atomic resonance absorption. Our data in the range 886-1410 K are new. Combined with previous measurements at low temperature, rate coefficients determined for the temperature range 297-1410 K are represented by the following equation: k(T)=(2.89+/-0.09)x10(-16)T1.62 exp[-(1210+/-90)/T] cm3 molecule(-1) s(-1); listed errors represent one standard deviation in fitting. Theoretical calculations at the CCSD(T)/6-311+G(3df, 2p)//B3LYP/6-311+G(3df) level predict potential energies of various reaction paths. Rate coefficients are predicted with the canonical variational transition state (CVT) theory with the small curvature tunneling correction (SCT) method. Reaction paths associated with trans and gauche conformations are both identified. Predicted total rate coefficients, 1.60 x 10(-22)T3.50 exp(16/T) cm3 molecule(-1) s(-1) for the range 300-3000 K, agree satisfactorily with experimental observations. The branching ratios of three accessible reaction channels forming CH3CHOH+OH (1a), CH2CH2OH+OH (1b), and CH3CH2O+OH (1c) are predicted to vary distinctively with temperature. Below 500 K, reaction 1a is the predominant path; the branching ratios of reactions 1b,c become approximately 40% and approximately 11%, respectively, at 2000 K.

High-Temperature Shock Tube Measurements of Methyl Radical Decomposition

We have studied the two-channel thermal decomposition of methyl radicals in argon, involving the reactions CH3 + Ar --> CH + H2 + Ar (1a) and CH3 + Ar --> CH2 + H + Ar (1b), in shock tube experiments over the 2253-3527 K temperature range, at pressures between 0.7 and 4.2 atm. CH was monitored by continuous-wave, narrow-line-width laser absorption at 431.1311 nm. The collision-broadening coefficient for CH in argon, 2gamma(CH-Ar), was measured via repeated single-frequency experiments in the ethane pyrolysis system behind reflected shock waves. The measured 2gamma(CH-Ar) value and updated spectroscopic and molecular parameters were used to calculate the CH absorption coefficient at 431.1311 nm (23194.80 cm(-1)), which was then used to convert raw traces of fractional transmission to quantitative CH concentration time histories in the methyl decomposition experiments. The rate coefficient of reaction 1a was measured by monitoring CH radicals generated upon shock-heating highly dilute mixtures of ethane, C2H6, or methyl iodide, CH3I, in an argon bath. A detailed chemical kinetic mechanism was used to model the measured CH time histories. Within experimental uncertainty and scatter, no pressure dependence could be discerned in the rate coefficient of reaction 1a in the 0.7-4.2 atm pressure range. A least-squares, two-parameter fit of the current measurements, applicable between 2706 and 3527 K, gives k(1a) (cm(3) mol(-1) s(-1)) = 3.09 x 1015 exp[-40700/T (K)]. The rate coefficient of reaction 1b was determined by shock-heating dilute mixtures of C2H6 or CH3I and excess O2 in argon. During the course of reaction, OH radicals were monitored using the well-characterized R(1)(5) line of the OH A-X (0,0) band at 306.6871 nm (32606.52 cm(-1)). H atoms generated via reaction 1b rapidly react with O2, which is present in excess, forming OH. The OH traces are primarily sensitive to reaction 1b, reaction 9 (H + O2 --> OH + O) and reaction 10 (CH3 + O2 --> products), where the rate coefficients of reactions 9 and 10 are relatively well-established. No pressure dependence could be discerned for reaction 1b between 1.1 and 3.9 atm. A two-parameter, least-squares fit of the current data, valid over the 2253-2975 K temperature range, yields the rate expression k(1b) (cm(3) mol(-1) s(-1)) = 2.24 x 10(15) exp[-41600/T (K)]. Theoretical calculations carried out using a master equation/RRKM analysis fit the measurements reasonably well.

An Efficient Synthesis of an Apoptosis Inducer, F-3-2-5 by Using Octanol-Accelerated Baylis-Hillman Reaction

F-3-2-5 (Fig. 1) is a novel apoptosis inducer which was recently isolated from Streptomyces sp., of which potent anticancer activity warrants further preclinical investigation as well as extensive structure-activity relationship study. 1 Thus, there has been an urgent need to devise an efficient synthetic method of F-3-2-5 which has a synthetically challenging trisubstituted α,β-unsaturated ketone moiety as an integral part. Herein, we report an efficient synthesis of the title compound by using Baylis-Hillman reaction as the key step. A synthetic plan for the title compound is shown in Figure 2. The Baylis-Hillman reaction 2a,2b of methyl vinyl ketone

Enantioselectivity and Diastereoselectivity in Reductive Radical Cyclization Reactions of 3-(ω-Iodoalkylidene)-piperidin-2-ones

The E-configurated 3-(ω-iodoalkylidene)-piperidin-2-ones 1a-e were prepared from the corresponding ω-tert-butyldi­methylsilyloxyalkanals 5a-e by aldol condensation with N-tert-butyloxycarbonylpiperidone, subsequent silyl deprotection and iodo-dehydroxylation. In the presence of tributylstannane as the reducing agent and of triethylborane as the initiator the iodides underwent a reductive radical cyclization to the corresponding products rac-9a-e (72-90% yield). The hydrogen abstraction occurred enantioselectively in the presence of the chiral complexing agent 2 in toluene as solvent (up to 88% ee). For substrates 1b and 1c, for which both the radical cyclization and the hydrogen abstraction step were stereogenic, the insignificant change in diastereoselectivity indicated that the cyclization step was not enantioselective. A 1:1 stoichiometry for the complex was proven by Job plot experiments. The enantioselectivity of the reaction 1a → 9a was concentration dependent.