Parallel Reaction Mechanism Research Articles

Synthesis of palm oil-based trimethylolpropane ester as potential biolubricant: Chemical kinetics modeling

The environmental impact of large amounts of lubricants from mineral oils has become an increasingly important issue. The use of rapidly biodegradable lubricants, vegetable products as well as modified vegetable oil esters, could significantly reduce the environmental pollution compared to mineral oils. A kinetic/mathematical model describing chemical transesterification of palm oil-based methyl esters (POMEs) with trimethylolpropane (TMP) to polyol esters has been developed. The kinetics of the transesterification reaction was modeled as three distinct elementary reversible series–parallel reaction mechanisms. The model considers the transesterification reaction to take place in both forward and reverse directions. The resulting kinetics equations were solved using ode45 solver function in MATLAB, where the rate constants of the proposed kinetic model were determined by minimization of errors based on the optimum criteria of statistical analysis and by comparing the component concentrations at maximum and at equilibrium. The forward and reverse rate constants of all three steps involved in the transesterification reaction were reported. The validity of the model was tested by comparing the observed experimental values with the theoretical calculated data. A good correlation between simulated results and experimental data was observed, confirming that the model was able to predict the rate constants with plausible accuracy. The new proposed kinetic model would facilitate the design of a pilot-scale chemical reactor for the transesterification of POME with TMP to obtain palm oil-based polyol esters as a potential biolubricant.

The DFT study on C [sbnd]C activation of butanone by Ni + in gas phase: Two parallel decomposition reaction mechanisms

The different potential energy surfaces (PESs) of Ni + ( 2D, 3d 9) with butanone in gas phase have been systematically explored by density functional theory (DFT). Two parallel decomposition reaction mechanisms have been identified. The course that the Ni + inserts into the σ-bond of the C C 2H 5 or C CH 3 leading to the C C bond activation has been analyzed using the natural bond orbital (NBO). Finally, the conclusion of the theory calculation was consistent with the experimental results which provided by the Darrin J. Bellert group in 2011 that three neutral organic molecule products (ethylene, acetaldehyde and methane) were obtained.

Influence of alkali carbonates on benzyl phenyl ether cleavage pathways in superheated water

Benzyl phenyl ether conversion in superheated water yields a broad product distribution. In addition to the hydrolysis products, phenol and benzyl alcohol, a large amount of consecutive products are formed depending on the operating conditions. The influence of Li2CO3, Na2CO3, and K2CO3 on these reactions is explored between 270 and 370°C. It is shown that high selectivity towards hydrolysis can be achieved at low temperatures and short reaction times. At higher severities the yields of phenol and especially benzyl alcohol decrease and higher molecular weight compounds are formed by consecutive reactions. Alkali carbonates effect this distribution by decreasing the concentration of protons in the system and by providing and enhancing parallel and secondary reaction mechanisms. The yields of toluene, 2 and 4-benzyl phenol are strongly enhanced in the presence of an alkali carbonate, by formation of a cation–BPE adduct in which the ether bond is strongly polarized.

No.43 無触媒・触媒並列反応機構に基づくチャー水蒸気ガス化の速度解析(ガス化・燃焼・液化(5))

No.43 無触媒・触媒並列反応機構に基づくチャー水蒸気ガス化の速度解析(ガス化・燃焼・液化(5))

Chemical Mechanisms for Skin Sensitization by Aromatic Compounds with Hydroxy and Amino Groups

It is well-known that aromatic diamino-, dihydroxy-, and amino-hydroxy compounds, with NH(2) and OH groups in ortho- or para-positions relative to each other, are strong skin sensitizers. In this paper, we analyze published potency and cross-reactivity data, whereby animals sensitized to one of these compounds are challenged with other compounds. The data are consistent with two parallel chemical reaction mechanisms: oxidation to electrophilic (protein reactive) quinones or quinone imines or formation of protein-reactive free radicals such as the Wurster salt, which can be formed by para-phenylene diamine. Compounds with NH(2) and OH groups meta to each other have also been found to be skin sensitizers, in some cases quite strong sensitizers. For these compounds, direct formation of quinones or quinone imines is not possible, and free radicals of the Wurster salt type are not favored. Here, we present a molecular mechanism to rationalize the sensitization potential of such compounds and, using the results of quantum mechanics calculations, show how this mechanism can explain observed structure-potency trends.

Diagenetic smectite-to-illite transition in clay-rich sediments: A reappraisal of X-ray diffraction results using the multi-specimen method

Smectite illitization is a common mineralogical reaction occurring during the burial diagenesis of clay-rich sediments and shales, and has thus attracted sustained interest over the last fifty years. Prior studies have concluded that smectite illitization proceeds through a steady set of homogeneous reactions involving intermediate mixed layers of varying compositions. In these intermediate structures, illite and smectite or, more generally, expandable layers (I and Exp layers, respectively) coexist among the same crystallites giving rise to non-periodic structures (I-Exp) characterized by specific diffraction effects. Consistent with this model, reaction progress was characterized by the simultaneous increase in the illite content in I-Exp and in their stacking order leading to the following mineralogical sequence: smectite → randomly interstratified I-Exp with high smectite contents (\> 50% Exp layers) → ordered I-Exp with high illite contents (\> 50% I layers) → illite. Although reaction mechanisms have been extensively debated, this structural characterization has not been challenged, possibly due to a methodological bias. In the present study, X-ray diffraction patterns typical of the diagenetic illitization of smectite are interpreted using modern approaches involving profile fitting (multi-specimen method). Novel insights into the structure of intermediate reaction products are thus obtained. In particular, original clay parageneses are described that include the systematic presence of illite, kaolinite, chlorite and a mixed layer containing kaolinite and expandable layers (K-Exp). In contrast to previous descriptions, the early stages of smectite illitization are characterized by the coexistence of discrete smectite and of a randomly interstratified I-Exp with a high content of illite layers (\>50% I layers). Both the smectite and the I-Exp are authigenic and form under shallow burial, that is at low temperature conditions. With increasing burial depth, the relative proportion of I-Exp increases, essentially at the expense of discrete smectite, and the composition of I-Exp becomes slightly more illitic. In the second stage of smectite illitization, two illite-containing mixed layers are observed. They result from two parallel reaction mechanisms affecting the randomly interstratified I-Exp present in the shallow section of the series. The first reaction implies the dissolution of this randomly interstratified I-Exp and leads to the crystallization of an ordered I-Exp without significant illitization, possibly because of the low K-availability. The second reaction affecting the randomly interstratified I-Exp implies the growth of trioctahedral (Mg, Al) hydroxide sheets in Exp interlayers, thus developing di-trioctahedral chlorite layers (Ch layers) in the initial I-Exp to form an I-Exp-Ch. A layer-by-layer mechanism is hypothesized for this reaction. In this scheme, Mg cations released by the dissolution-recrystallization reaction of I-Exp likely represent the source of Mg for the formation of brucite-like sheets in expandable interlayers, and thus of the I-Exp-Ch. The reported structural characterization of smectite illitization intermediate products contradicts the conventional wisdom of a homogeneous reaction through a series of pure mixed layers of variable composition. In contrast, the coexistence of different phases implies a heterogeneous reaction via a sequence of intermediate phases and requires reassessing the reaction mechanisms proposed in the literature. The compositional range (relative proportion of the different layer types) of these phases is limited and smectite illitization proceeds essentially as relative proportions of the different phases vary. In addition, reaction kinetics and stability of the different intermediate products also need to be reconsidered.

First-order parallel and consecutive reaction mechanisms — Isosbestic points criterium

A criterium for the selection of reaction mechanism derived from a condition for isosbestic points occurrence is presented. Analytical relationships involving the molar absorption coefficients of the species, which participate in a mechanism of parallel first-order reactions and the corresponding rate coefficients, are also reported. A model system of four species that present overlapping absorption spectra may correspond to the reactant and products of a system of parallel or consecutive first-order reactions. In the first case, under experimental conditions in which the absorbances are additive, the presence of an isosbestic point in the spectrum of the reaction mixture at a given wavelength leads to a time-independent ratio of the degree of advancement of reaction variables. From this, relevant kinetic information may be extracted, namely, the ratio of the reaction rate coefficients. Moreover, the occurrence of isosbestic points allows discarding the second mechanism. This conclusion is independent of the number of absorbing species. Model calculated examples show the application of the equations here derived. The resolution for the general case of mechanisms of N first-order reactions is provided.Key words: chemical kinetics, time-resolved absorption spectra, reaction mechanism.

DFT Study on the Structure and Racemization Mechanism of 1,1-Binaphthalene-8,8-diol

Density functional theory (DFT) was applied to study the ground state geometries and isomerization processes of 1,1-binaphthalene-8,8-diol. Three isomers, denoted as ISO1, ISO2, and ISO3, were found, distinguished by different orientations of the OH groups, and each OH-orientational isomer has R- and S-enantiomer. The conformational stabilities of these isomers were investigated by tracking the energy change with respect to the ring-to-ring torsion. The inter-conversions between the three OH-orientational S-isomers were found to have quite low barriers owing to the nearly free rotation of OH groups around the O-C single bonds. The S-R enantiomerization of ISO1 and ISO2 can take place through the ring-ring torsion around the C1C1 single bond, either in the anti-rotation manner or in the syn-rotation manner. The barriers of the anti routes are lower than those of the corresponding syn routes by 87.95 and 75.04 kJ/mol. For the S-R enantiomerization of ISO3, only the anti route was found. The barriers for the anti route enantiomerizations of ISO1, ISO2, and ISO3 are 119.61, 120.43, and 121.59 kJ/mol, respectively. A parallel reaction mechanism via three anti enantiomerization routes was proposed for the racemization of 1,1-binaphthalene-8,8-diol.

Engineering Variants of the I-SceI Homing Endonuclease with Strand-specific and Site-specific DNA-nicking Activity

The number of strand-specific nicking endonucleases that are currently available for laboratory procedures and applications in vivo is limited, and none is sufficiently specific to nick single target sites within complex genomes. The extreme target specificity of homing endonucleases makes them attractive candidates for engineering high-specificity nicking endonucleases. I-SceI is a monomeric homing enzyme that recognizes an 18 bp asymmetric target sequence, and cleaves both DNA strands to leave 3′-overhangs of 4 bp. In single turnover experiments using plasmid substrates, I-SceI generates transient open circle intermediates during the conversion of supercoiled to linear DNA, indicating that the enzyme cleaves the two DNA strands sequentially. A novel hairpin substrate was used to demonstrate that although wild-type I-SceI cleaves either the top or bottom DNA strand first to generate two nicked DNA intermediates, the enzyme has a preference for cleaving the bottom strand. The kinetics data are consistent with a parallel sequential reaction mechanism. Substitution of two pseudo-symmetric residues, Lys122 and Lys223, markedly reduces top and bottom-strand cleavage, respectively, to generate enzymes with significant strand- and sequence-specific nicking activity. The two active sites are partially interdependent, since alterations to one site affect the second. The kinetics analysis is consistent with X-ray crystal structures of I-SceI/DNA complexes that reveal a role for the lysines in establishing important solvent networks that include nucleophilic water molecules thought to attack the scissile phosphodiester bonds.

Thermal simulation experiment on the hydrocarbon regeneration of marine carbonate source rock

Hydrocarbon regeneration of marine carbonate source rock was simulated with thermal experiments in a laboratory. The results reveal that hydrocarbon regeneration does not simply continue the primary hydrocarbon generation process, and that, for marine carbonate source rock, discontinuous hydrocarbon generation differs greatly from the continuous generation. Several different features of hydrocarbon regeneration were observed in the experiments. First, the liquid hydrocarbon generation peak was always observed no matter what the initial maturity of the sample was. Moreover, the maturity and the liquid hydrocarbon yield corresponding to the peak varied with the sample’s initial maturity. Second, the hydrocarbon regeneration started earlier than the continuous one. In the experiments, the hydrocarbon could be re-generated when the sample maturity did not rise to any great extent. Third, the accumulative hydrocarbon-generating quantity during discontinuous generation was always more than that during continuous generation. And the hydrocarbon-generating quantity varied with the discontinuous generation history. Chemical kinetic analysis suggests that discontinuous hydrocarbon generation should not only be explained by the parallel reaction mechanism but also by the consecutive reaction mechanism which has been ignored in the traditional chemical kinetic model for continuous hydrocarbon generation.

Thermal decomposition of azobisisobutyronitrile dissolved in xylene in the presence of tin(IV) chloride

The rate of thermal decomposition of azobisisobutyronitrile (AIBN) dissolved in xylene was investigated alone and in the presence of tin(IV) chloride over the temperature range of 90–107°C. It was found that the decomposition rate of AIBN increases linearly with increasing concentration of tin(IV) chloride, which suggests the formation of an activated complex between AIBN and tin(IV) chloride. A parallel reaction mechanism is proposed to describe the kinetic behavior. The Arrhenius relationships of rate constants were also obtained.

In-situ Surface-enhanced Raman Spectroscopic Investigation on Ethanol Electrooxidation in Different Media

Electrochemical voltametric methods and in-situ electrochemical surface-enhanced Raman spectroscopy (SERS)were used to investigate the electrooxidation behavior of ethanol in different media on a roughened platinum electrode.It was found that ethanol could dissociate spontaneously to produce strongly adsorbed intermediate,CO,in acidic,neutral,and alkaline media on the roughened platinum electrode.The complete oxidation potential of CO_(ad) on the roughened platinum electrode was negatively shifted about 0.300 V in the alkaline medium(0.20 V)compared with that in the acidic and neutral media(0.50 V).The positive oxidation peak potential of ethanol was negatively shifted about 0.85 V in the alkaline medium(-0.20 V)than that in the acidic medium(0.65 V).By comparing the oxidation current and the peak potential,it was found that the electrocatalytic activity of roughened platinum electrode for ethanol and CO oxidation in the alkaline medium was higher than in acidic and neutral media.The results suggested that ethanol was oxidized to CO_2 on the roughened platinum electrode via parallel reaction mechanism in acidic, neutral or alkaline media.

Electrooxidation of acetaldehyde on carbon-supported Pt, PtRu and Pt3Sn and unsupported PtRu0.2 catalysts: A quantitative DEMS study

The oxidation of acetaldehyde on carbon supported Pt/Vulcan, PtRu/Vulcan and Pt3Sn/Vulcan nanoparticle catalysts and, for comparison, on polycrystalline Pt and on an unsupported PtRu0.2 catalyst, was investigated under continuous reaction and continuous electrolyte flow conditions, employing electrochemical and quantitative differential electrochemical mass spectroscopy (DEMS) measurements. Product distribution and the effects of reaction potential and reactant concentration were investigated by potentiodynamic and potentiostatic measurements. Reaction transients, following both the Faradaic current as well as the CO2 related mass spectrometric intensity, revealed a very small current efficiency for CO2 formation of a few percent for 0.1 m acetaldehyde bulk oxidation under steady-state conditions on all three catalysts, the dominant oxidation product being acetic acid. Pt alloy catalysts showed a higher activity than Pt/Vulcan at lower potential (0.51 V), but do not lead to a better selectivity for complete oxidation to CO2. C–C bond breaking is rate limiting for complete oxidation at potentials with significant oxidation rates for all three catalysts. The data agree with a parallel pathway reaction mechanism, with formation and subsequent oxidation of COad and CHx, ad species in the one pathway and partial oxidation to acetic acid in the other pathway, with the latter pathway being, by far, dominant under present reaction conditions.

Liquid phase alkylation of phenol with 1-octene over large pore zeolites

A comparative study is presented of the liquid phase alkylation of phenol with 1-octene over different zeolite catalysts: H-beta (BEA(15)), H-mordenite (MOR(11)) and H-USY (FAU(15)). A wide spectrum of monoalkylated products, identified as isomers of phenyl octyl ether ( O-alkylate) and octyl phenol ( C-alkylate), was formed in the reaction. The reaction was studied in detail over BEA(15), such studies included the influence of process variables such as temperature, reactant mole ratio, catalyst amount and alkali metal (K) poisoning on its performance in the alkylation reaction. A kinetic analysis of the reaction over BEA(15) was also carried out assuming a second order parallel reaction mechanism. The activity of the different catalysts for the reaction followed the order: BEA(15) > FAU(15) > MOR(11). The poisoning of BEA(15) with potassium resulted in a decrease in the catalyst activity concomitant with a decrease in the number of strong acid centres in the catalyst.

Ethylene glycol electrooxidation on carbon supported Pt, PtRu and Pt 3Sn catalysts—A comparative DEMS study

We present results of a comparative study on the interaction of ethylene glycol (EG) with carbon supported Pt, PtRu and Pt 3Sn nanoparticle catalysts, employing electrochemical and quantitative differential electrochemical mass spectroscopy (DEMS) measurements under continuous reaction and continuous electrolyte flow conditions. For all three catalysts EG adsorption is inhibited at very cathodic adsorption potentials, dissociative adsorption starts above 0.06 V and increases with increasing potential. Based on the electron yield per formed CO 2 molecule and on the similarity with the CO ad stripping characteristics CO ad is identified as the main stable adsorbate; the relative coverage in terms of adsorbed C1 species, relative to that of a saturated CO adlayer on the respective catalyst, reaches a maximum of ca. 0.6 at around 0.4 V on Pt/Vulcan, ca. 0.2 at around 0.2 V on PtRu/Vulcan and ca. 0.4 at around 0.35 V on Pt 3Sn/Vulcan. Bulk EG electrooxidation under steady-state conditions shows a very small current efficiency for CO 2 formation of below 6% for 0.1 M EG on all three catalysts, the oxidation of EG mainly generates partly oxidized C2 by-products. Catalyst modification by Ru or Sn improves the activity for EG oxidation at low potentials (≤0.56 V), but does not lead to better selectivities for complete EG oxidation to CO 2 at potentials with significant oxidation rates. Hence, C–C bond breaking is rate limiting for complete oxidation under present reaction conditions for all three catalysts. The data are consistent with a parallel pathway reaction mechanism, with formation and subsequent oxidation of CO ad in the one pathway and partial oxidation, via a sequence of reaction steps, to increasingly oxidized C2 species in the other pathway.

Kinetic and reaction mechanisms of calcium bisulfite catalytic oxidation

In this paper, the oxidation of calcium bisulfite in the presence of ferrous ions as a catalyst is studied in a laboratory scale apparatus at a fixed oxygen partial pressure (21.3 kPa) and at a temperature of 45 °C. The analysis of the experimental results, carried out by using the theory of mass transfer with chemical reaction, indicates that the slow reaction regime has been explored, and the transition from the kinetic to the diffusional subregime identified. A kinetic analysis allows to develop a reaction rate equation, assuming that the bisulfite oxidation in the presence of ferrous ions follows a parallel reaction mechanism; the resulting overall reaction rate has been found to be of first order with respect to ferrous ion concentration and of three halves with respect to bisulfite concentration. Moreover, the catalytic effect of ferrous ions has been compared with that of manganese ions previously studied, showing that ferrous is a catalyst more active than manganese.

DBT derivatives adsorption over molybdenum sulfide catalysts: a theoretical study

We report density-functional calculations of dibenzothiophene and dimethyldibenzothiophene over different molybdenum sulfide surfaces representing the active sites of the simplest hydrodesulfurization catalysts. Using the adsorption energies and geometries of the molecules on the different sites, we propose an interpretation of the catalytic activities and selectivities published in the literature, which demonstrated the existence of two parallel reaction mechanisms. Among the various possible configurations, η 1(S) adsorption on the sulfur edge of the active phase seems to be at the origin of the direct desulfurization of the molecules whereas benzene ring adsorption on the molybdenum edge is at the origin of the hydrogenation pathway. Although a combination of aromatic and steric effects strongly inhibits its adsorption, we show that the presence of stacking defects on the molybdenum sulfides would allow the adsorption and the activation of DMDBT.

Kinetics of reduction of ferric iron in Fe2O3-CaO-SiO2-Al2O3 slags under argon, CO-CO2, or H2-H2O

The rates of reduction of ferric iron in Fe2O3-CaO-SiO2-Al2O3 slags containing 3 to 21 wt pct Fe2O3 under impinging argon, CO-CO2, or H2-H2O have been studied at 1370 °C under conditions of enhanced mass transfer in the slag using a rotating alumina disc just in contact with the slag surface. For a 6 wt pct Fe slag at a stirring speed of 900 rpm the observed reduction rates by 50 pct H2-H2O were a factor of 2 to 3 times higher than those by 50 pct CO-CO2 and more than one order of magnitude higher than those under pure argon. The observed rates were analyzed to determine the rate-controlling mechanisms for the present conditions. Analysis of the rate data suggests that the rates under 50 pct H2-H2O are predominantly controlled by the slag mass transfer. The derived values of the mass-transfer coefficient followed a square-root dependence on the stirring speed for a given slag and, at a given stirring speed, a linear function of the total iron content of the slags. The rates of oxygen evolution during reduction under pure argon were shown to be consistent with a rate-controlling mechanism involving a fast chemical reaction at the interface and relatively slow mass transfer in the gaseous and the slag phases. The rates of reduction by CO-CO2 (pCO=0.02 to 0.82 atm) were found to be likely of a mixed control by the slag mass transfer and the interfacial reaction. A significant contribution of oxygen evolution to the overall rates was observed for more-oxidized slags and for experiments with relatively low values of pCO. Assuming a parallel reaction mechanism, the estimated net reduction rates due to CO were found to be of the first order in pCO, with the first-order rate constants being approximately a linear function of the ferric concentration.

Decomposition Products of 50 Mass% Hydroxylamine/Water Under Runaway Reaction Conditions

I n the present work, the gaseous and liquid decomposition products of 50 mass% hydroxylamine/water solution were measured for samples subsequent to a thermally induced runaway reaction. The noncondensablegas phase composition was approximately 70 mol% N2, 24 mol% N2O, 4mol% NO, and 2 mol% H2, and ammonia was detected in the liquid residue. Based on analysis of the gas phase decomposition products, the following overall decomposition reaction (summation of several series and parallel reaction mechanisms taking place during the experiment) was determined: 157NH2OHliq → 61NH3gas + 35N2gas + 12N2Ogas + 2NOgas + 143H2Ogas + H2gas This reaction has an associated theoretical standard heat of reaction of −124 kJ mol−1(−29.6 kcal mol−1), which is consistent with −117 kJ mol−1 (−28 kcal mol−1) estimated for the hydroxylamine overall heat of decomposition reported previously.

Photoinduced diradical formation and decay in uncomplexed and metal-bound benzotriazine systems: mechanistic implications to chemically and biologically relevant photochemistry

The photochemical reactivities of 3-hydroxy-1,2,3-benzotriazine-4(3H)-one (1a) and tris[3-hydroxy-1,2,3-benzotriazine-4(3H)-one]iron(III) (1b) have been studied in solution and low temperature (5–77 K) glasses. Photoexcitation (λ345 nm) of 1a and 1b ultimately results in population of a ligand-centered excited state that releases N2. Electron paramagnetic resonance reveals the presence of S = 1 and S = 0 diradical intermediates upon photolysis of 1a and 1b, respectively, at 4 K. These species convert to an S = 1/2, nitrogen-centered monoradical species (aN = 23 G) upon warming to 77 K ia H-atom abstraction from the matrix. In solution, the first intermediates observed upon photolyses (λ = 355 nm) of 1a and 1b are oxime ketenes (5: λ = 385, 440 nm; 9: λ = 390, 430, 740 nm) that are formed from collapse of the diradical to generate a 4-membered β-lactam ring. The decay kinetics for the oxime ketene 5 decay can be fitted to a biexponential expression representing a parallel reaction mechanism with an element of reversibility. Thus, the data proposes the existence of an equilibrium between the oxime ketene and the spectroscopically silent β-lactam intermediate, as well as a first or pseudo first-order solvent-dependent pathway for the oxime ketene. The kinetics for formation and decay of the ketene are strongly influenced by the presence of the Fe(III) center, which leads to an increase in the lifetime of the diradical in solution, and a retarded rate of formation for the oxime ketene 9. The solution lifetimes suggest that the diradical intermediates only persist sufficiently long to react with bound solution substrates, whereas the ketene intermediates have suitable kinetic viabilities to react bimolecularly in solution.