The Kinetics and Mechanism of the Reaction between Barbituric Acid and Glycidol,Part II: Glycidol Reacts with Imide and Methylene Groups

Two derivatives of barbituric acid, 5,5‐diethylbarbituric acid and 1,3‐dimethyl‐barbituric acid, were used to react with glycidol. The kinetics of reactions was studied by continuous determination of epoxide number and acidic number in the reaction mixture aliquots. Based upon the kinetic experiments, the rate equation was formulated, which was consistent with product spectral identification of the derivatives as well as with previously studied reaction of barbituric acid with glycidol. Reaction mechanisms of glycidol with methylene and imide groups of barbituric acid have been proposed.     

Rate Coefficients for the Gas‐Phase Reaction of Ozone with C5 and C6 Unsaturated Aldehydes

Emissions of biogenic volatile organic compounds are higher than those from anthropogenic sources. In this work, we studied the kinetics of the reaction of three unsaturated aldehydes (trans‐2‐pentenal, trans‐2‐hexenal, and 2‐methyl‐2‐pentenal) with ozone in a rigid atmospheric simulation chamber coupled to an FTIR spectrometer at four different temperatures (273, 298, 333, and 353 K). Reaction rate constants (× 10⁻¹⁸ cm³ molecule⁻¹ s⁻¹) at 298 K are 1.24 ± 0.06 for trans‐2‐pentenal (t‐2P), 1.37 ± 0.03 for trans‐2‐hexenal (t‐2H), and 1.58 ± 0.20) for 2‐methyl‐2‐pentenal (2M2P). The following Arrhenius expressions were deduced (cm³ molecule⁻¹ s⁻¹): The obtained data are presented and compared to those reported in the literature at room temperature, as well as to homologous alkenes. The atmospheric lifetimes with respect to ozone, derived from this study, are estimated to vary between 7 and 10 days.     

Cyclic and Acyclic N═N Bonds in Reactions with Some Alkenes and Dienes

The kinetics of the Diels–Alder (DA) reactions of 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione 1 , trans‐diethyl azodicarboxylate 2 , and tetracyanoethene 3 with 1,3‐cyclohexadiene 4 , cycloheptatriene 5 , 1,3‐cycloheptadiene 6 , cyclooctatetraene 7 , and 1,3‐cyclooctadiene 8 in a range of temperatures and pressures has been studied. Values of the enthalpy, entropy, and volume of activation, as well as the enthalpy and volume of reaction have been obtained. Observed reaction rates of 5+1 and 7+1 have been compared with the known rate of norcaradiene 17 formation in the equilibrium , and that of bicyclo[4,2,0]‐octa‐2,4,7‐triene 20 in the equilibrium . The kinetic data show that the rate of formation of 17 from 5 is much greater than the loss rate of dienophile 1 in reaction of 5+1 . In contrast, the formation rate of tautomer 20 is less than the loss rate of dienophile 1 in reaction of 7+1 . This reflects that the consecutive reaction of 5 → 17 (+ 1 ) → 15 is possible whereas the consecutive reaction of 7 → 20 (+ 1 ) → 22 does not occur as the only way.     

The Role of Solvation in the Kinetics and the Mechanism of Hydroperoxide Radicals Addition to π‐Bonds of 1,2‐Diphenylethylene and 1,4‐Diphenylbutadiene‐1,3

A combination of microcalorimetry, the rotating sector method, and ESR at 323 K in the environment of 10 solvents of different polarities was used to measure rate constants of addition of hydroperoxide radicals () to π bonds of trans‐1,2‐diphenylethylene and trans,trans‐1,4‐diphenylbutadiene‐1,3 (k₂) and disproportionation rate constants of these radicals (k₃). With increasing dielectric constant of the medium, k₂ values increase from 69 to 410 M⁻¹ · s⁻¹, and k₃ values almost do not change and are in the range of (1.0 ± 0.2) × 10⁸ M⁻¹ · s⁻¹. A linear dependence of logarithm values of rate constants from the dielectric constant of the medium in the coordinates of the Kirkwood–Onsager equation was found that allows to make a conclusion about the effect of nonspecific solvation in the studied systems. The quantum‐chemical analysis (NWChem, DFT B3LYP/6‐311G**) of the detailed mechanism for addition shows that the influence of the medium polarity reflects the superposition of the effects of nonspecific and specific solvation. The scale of the polar effect will depend on how different solvation energies of the transition and the initial reaction complexes. If a value of the solvation energy of the transition complex is larger than the solvation energy of the initial reaction complex, then the reaction rate should increase with an increase of the solvent's polarity and decrease otherwise.     

Kinetics Investigation of Reaction of Naphthalene with OH Radicals at 1–3 Torr and 240–340 K

The combination of relative rate method with discharge flow and mass spectrometry (RR/DF/MS) technique was employed to determine the rate constant for the gas‐phase reaction of hydroxyl radicals (OH) with naphthalene at 240?340 K and a total pressure of 1–3 Torr. At 298 K, the rate constant was measured to be cm³ molecule^?1 s^?1, which is in good agreement with reported literature values determined using different techniques. The reaction of OH with naphthalene was found to be essentially independent of pressure in a range of 1?3 Torr at both 298 and 340 K. At 240–340 K, the rate constant of this reaction was found to be negatively dependent on temperature, with an Arrhenius expression of k₁(T) cm³ molecule^?1 s^?1 and k₁(T) cm³ molecule^?1 s^?1 using 1,4‐dioxane and styrene as the reference compounds, respectively. The atmospheric lifetime of naphthalene was estimated to be 9.6 h using the rate constant of naphthalene + OH determined at 277 K in the present work.     

Kinetics of the Gas‐Phase Elimination Reaction of Benzyl Chloroformate and Neopentyl Chloroformate

The gas‐phase eliminations of benzyl chloroformate (475–523 K, 31–103 Torr) and neopentyl chloroformate (563–622 K, 37–70 Torr), in a deactivated static reaction vessel, and in the presence of a free radical suppressor, are homogeneous, unimolecular, and follow a first‐order rate law. The rate coefficients are expressed by the following Arrhenius equations: Benzyl chloroformate Neopentyl chloroformate Formation of neopentyl chloride: Formation of 2‐methylbutenes: The derived kinetic and thermodynamic parameters for benzyl chloroformate decomposition indicate the reaction proceeds through a concerted four‐membered cyclic transition state to give benzyl chloride and CO₂ gas. Neopentyl chloroformate undergoes a parallel reaction, where neopentyl chloride formation may arise from a polar‐concerted four‐membered cyclic transition state, whereas the mixture of olefins, 2‐methyl‐2‐butene, and 2‐methyl‐1‐butene appears to be produced from a carbene intermediate. This intermediate seems to be originated from a concerted five‐membered cyclic transition state of the neopentyl substrate.     

Infrared Spectroscopic Evidence for a Heterogeneous Reaction between Ozone and Sodium Oleate at the Gas–Aerosol Interface: Effect of Relative Humidity

The heterogeneous ozonolysis of sodium oleate aerosols in an aerosol flow tube is reported under different relative humidity (RH%) conditions. Submicron sodium oleate particles were exposed to a known ozone concentration and the consumption of sodium oleate was monitored by infrared spectroscopy. When the experimental results are treated as a surface‐mediated reaction (i.e., following a Langmuir–Hinshelwood type mechanism), the following parameters are obtained: at low RH%, = (3 ± 1) × 10^?16 cm³ molecule^?1 and = (0.046 ± 0.006) s^?1; at high RH%, = (6 ± 2) × 10^?16 cm³ molecule^?1 and = (0.21 ± 0.05) s^?1. From these pseudo–first‐order coefficients, the reactive uptake coefficients for dry and aqueous sodium oleate aerosols are calculated as (1.5 ? 0.5) × 10^?7 and (1.7 ? 0.7) × 10^?6, respectively. Hydrated oleate aerosols display both an increase in the ozone trapping ability and an increase in the effective rate reaction at the droplet surface compared to dry aerosol surfaces. These observations may provide an explanation for some of the variability observed between lab studies of dry ozonolysis and real‐world, atmospheric lifetimes of oleic acid–related species.     

Some General Features in the Autocatalytic Reaction between Sulfite Ion and Different Oxidants

The autocatalytic oxidation of a weak acid is a common building block of the pH oscillators. These reactions can be described by a simple general scheme that includes a protonation equilibrium and the oxidation of the protonated form of the weak acid. Here we show that independently from the chemical nature of the oxidizing agent, these reactions bear some general features, namely (1) the change in pH (ΔpH) observed during the reaction is determined by the acidity constant (K_HA) and by the initial concentration of the unprotonated form of the weak acid (A^?): , (2) the inflection time of the autocatalytic reaction (t_i) depends reciprocally on K_HA and on the initial hydrogen ion concentration, and (3) in the presence of a competitive reversible proton‐binding component (D^?), that is not involved in the oxidation process, ΔpH follows a titration‐like curve as the concentration of D^? is increased, t_i is only slightly affected but the maximum rate of the autocatalytic process is significantly reduced. The slowing of the overall reaction is proportional to the acidity constant of the proton‐binding component.     

Experimental and Kinetic Modeling Study of Methanol Ignition and Oxidation at High Pressure

A detailed chemical kinetic model for oxidation of CH₃OH at high pressure and intermediate temperatures has been developed and validated experimentally. Ab initio calculations and Rice–Ramsperger–Kassel–Marcus/transition state theory (RRKM/TST) analysis were used to obtain rate coefficients for , , , and . The experiments, involving CH₃OH/O₂ mixtures diluted in N₂, were carried out in a high‐pressure flow reactor at 600–900 K and 20–100 bar, varying the reaction stoichiometry from very lean to fuel‐rich conditions. Under the conditions studied, the onset temperature for methanol oxidation was not dependent on the stoichiometry, whereas increasing pressure shifted the ignition temperature toward lower values. Model predictions of the present experimental results, as well as rapid compression machine data from the literature, were generally satisfactory. The governing reaction pathways have been outlined based on calculations with the kinetic model. Unlike what has been observed for unsaturated hydrocarbons, the oxidation pathways for CH₃OH under the investigated conditions were very similar to those prevailing at higher temperatures and lower pressures. At the high pressures, the modeling predictions for onset of reaction were particularly sensitive to the reaction.     

Reaction Kinetics of Carbon Dioxide (CO2) Absorption in Sodium Salts of Taurine and Proline Using a Stopped‐Flow Technique

The pseudo–first‐order reaction rate constants (k₀, s^?1) for the reaction of carbon dioxide in aqueous solutions of sodium taurate (NaTau) and sodium prolinate (NaPr) were measured using a stopped‐flow technique at a temperature range of 298–313 K. The solutions concentration varied from 5 to 50 mol m^?3 and from 4 to 12 mol m^?3 for NaTau and NaPr, respectively. Comparing the k₀ values, aqueous NaPr was found to react very fast with CO₂ as compared with the industrial standard aqueous monoethanolamine (MEA) and aqueous sodium taurate (NaTau) was found to react slower than aqueous MEA at the concentration range considered in this work. For the studied amino acid salts, the order of the reactions was found to be unity with respect to the amino acid salt concentration. Proposed reaction mechanisms such as termolecular and zwitterion reaction mechanisms for the reaction of CO₂ with aqueous solutions were used for calculating the second‐order reaction rate constants (k₂, m³ mol^?1 s^?1). The formation of zwitterion during the reaction with CO₂ was found to be the rate‐determining step, and the deprotonation of zwitterion was instantaneous compared to the reverse reaction of zwitterion to form an amino acid salt. The contribution of water was established to be significant for the deprotonation of zwitterion. Comparing the pseudo–first‐order reaction rate constants (k₀, s^?1) of various amino acid salts with CO₂, NaPr was found to be the faster reacting amino acid salt. The activation energy for NaTau was found to be 48.1 kJ mol^?1 and that of the NaPr was found to be 12 kJ mol^?1. The Arrhenius expressions for the reaction between CO₂ and the studied amino acid salts are      

Shock Tube Measurements of the Rate Constant of the Reaction NCN + O2

The rate constant of the comparably slow bimolecular NCN radical reaction NCN + O₂ has been measured for the first time under combustion relevant conditions using the shock tube method. The thermal decomposition of cyanogen azide (NCN₃) served as a clean high‐temperature source of NCN radicals. NCN concentration–time profiles have been detected by narrow‐bandwidth laser absorption at cm^?1. The experiments behind incident shock waves have been performed with up to 17% O₂ in the reaction gas mixture. At such high O₂ mole fractions, it was necessary to take O₂ relaxation into account that caused a gradual decrease of the temperature during the experiment. Moreover, following fast decomposition of NCN₃ and collision‐induced intersystem crossing of the initially formed singlet NCN to its triplet ground state, an unexpected and slow additional formation of triplet NCN has been observed on a 100‐μs timescale. This delayed NCN formation was attributed to a fast recombination of ¹NCN with O₂ forming a ³NCNOO adduct acting as a reservoir species for NCN. Rate constant data for the reaction NCN + O₂ have been measured at temperatures between 1674 and 2308 K. They are best represented by the Arrhenius expression . No pressure dependence has been observed at pressures between 216 and 706 mbar.     

А kinеtiс аnаlysis fоr prоduсtiоn of саlсium bоrоgluсоnаtе frоm colemanite

In this paper, the kinetic model of colemanite dissolution in gluconic acid solutions was carried out in a batch reactor. The effects of the particle size, reaction temperature, stirring speed, gluconic acid concentration, and solid/liquid ratio on colemanite dissolution were experimentally studied. The empirical parameters were the gluconic acid concentration (0.05-0.2 M), the temperature (20-50°C), the solid/liquid ratio (0.05/500-1.5/500 g⋅L⁻¹), particle size (193.5-1000 μm), and stirring speed (400-700 rpm). The kinetic models for heterogeneous solid-liquid reactions were used with the dissolution data in evaluating the kinetic. The dissolution of colemanite in gluconic acid solutions was controlled by diffusion through the product layer. The activation energy was found to be 8.39 kJ⋅mol⁻¹. The rate expression associated with the dissolution rate of colemanite depending on the parameters chosen may be summarized as follows:      

Inhibition of Aquated Sulfur Dioxide Autoxidation by Aliphatic,Acyclic, Aromatic,and Heterocyclic Volatile Organic Compounds

The oxidation of dissolved sulfur dioxide, sulfur(IV), by oxygen proceeds through the involvement of sulfoxy radicals among which sulfate radical anion is the main chain carrier. When organics are present, they inhibit the oxidation of sulfur(IV) via scavenging of SO₄⁻ radicals. In contrast to previous studies, which were limited mostly to aliphatic compounds, this paper presents the results of the effect of 13 new volatile organic compounds (VOCs) including aromatic and heterocyclic on uncatalyzed sulfur(IV) autoxidation at pH 8.2 and 25°C. In all cases, the kinetics was first order in the presence and absence of VOCs and experimental rate law was Eq. (1). (1) where −d[S(IV)]/dt is the rate of sulfur(IV) disappearance, k _obs is the first‐order rate constant in the presence of inhibitor, k _o is the first‐order rate constant in the absence of inhibitor, [S(IV)] is concentration of sulfur(IV) at time, t , and B is an inhibition parameter. VOCs cause inhibition by scavenging sulfate radical anions, which propagate the autoxidation chain. An analysis of B (Eq. (1)) and k _inh (Eq. (2)) values for 21 aliphatic, aromatic, acyclic, and heterocyclic organic compounds showed that these to be related by Eq. (3) for a subgroup and Eq. (4) for b subgroup. (2) a subgroup (benzamide, 2,2‐dimethyl‐1‐propanol, 1‐hexanol, methanol, ethanol, 1‐propanol, 2‐ propanol, 1‐butanol, 2‐butanol, ethylene glycol, rebaudioside A) (3) b  subgroup (o‐toluic acid, m‐toluic acid, p‐toluic acid, 4‐hydroxybenzoic acid, 1‐heptanol, glycerol, sucralose, acesuifame K, glycine, 3‐pentanol) (4)     

Thermal rate constant for the C(3P) + OH(X2Π) → CO(X1Σ) + H(2S) reaction using stochastic energy grained master equation method

In the present work, the kinetic mechanism of the reaction is studied. The rate constants were determined using the Master Equation Solver for Multi-Energy Well Reactions (MESMER). The master equation modeling was also employed to examine the pressure dependence for each pathway involved. The theoretical analysis shows that the overall rate coefficient is practically independent of pressure up to 100 Torr for the temperature range 125-500 K. The unusual dependence of the overall rate constant with temperature was fit with the d-Arrhenius expression , where cm³molecule⁻¹s⁻¹, , and  kJ·mol⁻¹, for 125⩽ T ⩽ 500 K. The thermal rate constant results are in relatively good agreement with other theoretical studies.     

An Experimental Study of the Kinetics of the Reactions of Isopropyl,sec‐Butyl,and tert‐Butyl Radicals with Molecular Chlorine at Low Pressures (0.5–7.0 Torr) in the Temperature Range 190–480 K

In this work, we have measured the rate coefficients of the reactions of isopropyl (propan‐2‐yl), sec‐butyl (butan‐2‐yl), and tert‐butyl (2‐methylpropan‐2‐yl) radicals with molecular chlorine as a function of temperature (190–480 K). The experiments were done in a tubular laminar flow reactor coupled to a photoionization quadrupole mass spectrometer employing a gas‐discharge lamp for ionization. The radicals were homogeneously produced in the reactor by photolyzing suitable precursor molecules with 193‐nm pulsed exciplex laser radiation. The bimolecular rate coefficients were obtained by monitoring the radical decay signals in real time under pseudo–first‐order conditions. The rate coefficients of all three reactions showed negative temperature dependence. The bath gas used in the experiments was helium, and the rate coefficients appeared to be independent of the helium concentrations employed ([2.4–14] × 10¹⁶ cm^?3) for all three reactions. The rate coefficients of the reactions can be approximated in the studied temperature range by the following parameterizations: We estimate that the overall uncertainties of the measured rate coefficients are ±20%. We were able to observe 2‐chloropropane (i‐C₃H₇Cl) product for the i‐C₃H₇^● + Cl₂ reaction. No products were observed for the other two reactions, and the reasons for this are briefly discussed in the text.     

Pressure Dependence and Kinetic Isotope Effects in the Absolute Rate Constant for Methoxy Radical Reacting with NO2

We have investigated the kinetics for the reaction CH₃O? + NO₂ in N₂ bath gas. The rate constants are well‐fit by the Troe expression over the temperature (250–335 K) and pressure range (30–700 Torr) investigated. The termolecular rate constant is given by cm⁶ molecule^?2 s^?1, and the rate constant at the high‐pressure limit is given by cm³ molecule^?1 s^?1. We also studied the kinetics of the reaction of CD₃O? + NO₂ as a function of temperature and pressure under similar conditions as those for CH₃O? + NO₂. The resulting low‐ and high‐pressure limiting rate constants are cm⁶ molecule^?2 s^?1 and cm³ molecule^?1 s^?1, respectively. The rate constants for the two isotopologues track each other closely as the high‐pressure limit is approached. The present results agree with most previous results at 295 K over a range of pressures, but there is substantial disagreement about the temperature dependence.     

Electrochemical corrosion kinetics of cold spray copper composite coatings in a high potential region

In this paper, copper composite anticorrosion and antifouling coatings were prepared by a cold spray technique. Polarization experiments of the coatings were performed by rotating ring‐disk electrode technology at high potential. The electrochemical reaction mechanisms were proposed, and corresponding polarization kinetics models were built. Experimental results show that the copper and cuprous oxide formed corrosion microcells in the coatings, and the cuprous oxide did not alter the electrochemical reaction process of copper. In the high potential region (about 0.2–0.8 V), a CuCl film formed on the surface of the coatings was not damaged or broken down. The film played a role in corrosion protection. The currents in the high potential region increased relative to the limiting current 1. Because in the high potential region, was produced by the dissolution of the CuCl film and was oxidized to Cu²⁺. In addition to being oxidized to Cu²⁺, has the other two destinations, which were deposition as a CuCl film and diffusion to the solution bulk. The three processes were in parallel competition relations. In the limiting current 2 region, oxidation of was dominant. A rate‐controlling step of electrochemical dissolution of the coatings in the high potential region was the diffusion processes of and Cu²⁺. The electrochemical polarization kinetic models based on the reaction mechanisms established in this research accorded well to the experimental results. It demonstrated the rationality of polarization kinetics models and reaction mechanisms.     

Catalytic Activity of Cobalt Nanoparticles for Dye and 4‐Nitro Phenol Degradation: A Kinetic and Mechanistic Study

Cetyltrimethylammonium bromide (CTAB) capped nanosized α‐cobalt hydroxides (CoNPs) were prepared to the removal of Congo red at room temperature in the absence and presence of sunlight. UV/visible spectra reveal that the CoNPs and NaBH₄ have no catalytic effects toward Congo red and 4‐nitrophenol (4‐NP) degradation, whereas CoNPs act as an efficient catalyst with a small amount of NaBH₄. The catalytic reaction has an induction period followed by an autoacceleration, which depends on the [NaBH₄]. The reaction follows fractional‐order kinetics with respect to [NaBH₄] for Congo red degradation. The activation energies were found to be 24 and 74 kJ mol⁻¹, respectively, for Congo red and 4‐NP catalyzed reactions. The AgNPs has no catalytic activity toward Congo red. The degradation pathway mechanism with observed kinetics has been proposed and discussed, which follows the following rate law:      

The Kinetics and Mechanism of the Reaction between Barbituric Acid and Glycidol,Part I: The Products Analysis

The hydroxyalkyl derivatives of barbituric acid (BA) were formed in the reaction between BA and glycidol (GL). The reaction was performed at BA:GL 1:1, 1:2, and 1:4 molar ratios in DMF or without solvent. The progress of reaction was monitored by determination of the epoxide number and IR and NMR spectroscopy. It was found that primary reactive site of BA was C5 and further nitrogen ring atoms. BA was always involved in keto‐enol equilibrium, the latter form being less reactive. The isolated hydroxyalkyl derivatives are useful precursors of oligoetherols with the pyrimidine ring.     

Experimental Study of the Reaction of Isopropyl Nitrate with OH Radicals: Kinetics and Products

The kinetics of the reaction of isopropyl nitrate (IPN) with OH radicals has been studied using a low‐pressure flow tube reactor coupled with a quadrupole mass spectrometer: OH + (CH₃)₂CHONO₂ → products (2). The rate constant of the title reaction was determined using both the absolute method, monitoring the kinetics of OH radicals consumption in excess of IPN, and the relative rate method using the reaction of OH with Br₂ as reference one and following HOBr formation. As a result of the absolute and relative measurements, the overall rate coefficients, k₂ = (6.6 ± 1.2) × 10^?13 exp(–(233 ± 56)/) was determined at a pressure of 1 Torr of helium over the temperature range 268–355 K. Acetone, resulting from H‐atom abstraction from the tertiary C–H bond of IPN followed by 2‐nitroxy‐2‐propyl radical decomposition, was found to be a major reaction product with the yield of 0.82 ± 0.13, independent of temperature in the range 277–355 K.