International Journal of Chemical Kinetics最新文献

In this work, the kinetic and stereochemical regularities of the kinetic resolution of the 1-phenylethylamine racemate in the acylation reaction under the action of optically active 4-nitrophenyl ester of N-protected phenylalanine in 2-propanol and 1,4-dioxane were studied. Kinetic measurements were carried out using UV spectroscopy. The studies of the reaction series made it possible to establish the reaction orders with respect to the reagents, as well as the kinetic regularities of the enantioselective acylation. It is shown that different kinetic schemes of the reaction take place in protic and aprotic solvents. Based on the experimental data on the reaction kinetics of both the individual enantiomers and the amine racemate, the enantioselectivity values of the acylation are calculated. It has been found that the nature of the solvent and the reagents ratio strongly affect the selectivity of kinetic resolution. Practical recommendations on the conditions of preparative kinetic resolution of amines by amino acid derivatives using the acylation reaction are proposed.

The Fe–Mn/Al₂O₃ nanocatalysts were manufactured via the sol-gel procedure and were evaluated for Fischer–Tropsch synthesis. The impact of different operational parameters of T, P, and H₂/CO ratio on the catalytic performance for light olefins production has been studied using response surface methodology (RSM). Furthermore, the optimization and modeling of selected responses were also carried out via RSM and historical data design type of DOE; and the best process conditions were found to be T = 365°C, H₂/CO = 1.50, and P = 1.50 bar. The mechanism of CO hydrogenation reaction over the Fe–Mn/Al₂O₃ nanocatalysts was also investigated using the non-linear regression method. It was found that the mechanism of the CO hydrogenation reaction is based on the Eley–Rideal type and the best-fitted equation for this mechanism was found to be −r_CO = KP_COP_H2/1+αP_CO. The obtained value of activation energy (85.20 kJ mol⁻¹) affirmed the absence of internal mass transfer limitations. The physico-chemical properties of the samples were investigated by various techniques of XRD, BET, TPR, TGA, and DSC.

The kinetics of the ligand exchange reaction between aquapentacyanoruthenate(II) [Ru(CN)₅OH₂]³⁻ ion and naphthalene substituted ligands [α-nitroso-β-naphthol (αNβN), and nitroso-R-salt (NRS)] has been studied in aqueous salt solutions of sodium chloride (NaCl) or tetrapropylammonium bromide (Pr₄NBr) salt. The kinetics was monitored spectrophotometrically at 525 nm corresponding to the λ_max of reddish-brown-colored substituted products, [Ru(CN)₅(αNβN)]³⁻ or [Ru(CN)₅(NRS)]³⁻. Increasing the ionic strength of the reaction mixture using NaCl, exerted a negative salt effect on the rate of formation of naphthalene-substituted products. At the same time, an increment in the concentration of Pr₄NBr imparted a positive salt effect on the reaction. The observed rate constant (k_obs) exhibits linear increment with respect to the concentration of NRS or αNβN while remaining invariant with variation in [Ru(CN)₅OH₂]³⁻. The computed activation parameters for NRS (∆H^# = 24.55 kJ mol⁻¹, E_a = 27.03 kJ mol⁻¹, ∆G^# = 87.83 kJ mol⁻¹, and ∆S^# = – 212.5 J K⁻¹ mol⁻¹) and αNβN ((∆H^# = 17.33 kJ mol⁻¹, E_a = 19.81 kJ mol⁻¹, ∆G^# = 87.87 kJ mol⁻¹, and ∆S^# = – 236.7 J K⁻¹ mol⁻¹) also support the proposed mechanism.

1,3-Butadiene is a carcinogenic and mutagenic air pollutant metabolized to butane epoxides, among which 1,2:3,4-diepoxybutane (DEB) exhibits the highest genotoxicity. DEB is also formed by 1,3-butadiene oxidation in the air, producing a direct environmental and occupational exposure. In this paper, we studied the kinetics of the nonenzymatic hydrolysis of DEB at a wide range of pH and temperature, including the catalytic effect of ionic species. The compound degradation involved a general and specific acid-base catalysis of the epoxide ring hydrolysis. DEB had the greatest stability at pH 5–9, when the rates of acid-catalyzed and base-catalyzed hydrolysis are negligible and the neutral hydrolysis predominates. The capability of the buffer anions to accelerate the DEB decay increased in the order H₂PO₄⁻ < HCO₃⁻ < CH₃COO⁻ < HPO₄²⁻ < and CO₃²⁻. The Arrhenius equation well described the influence of temperature on the acid-catalyzed, base-catalyzed, and neutral hydrolysis rate constants. According to the obtained hydrolysis model coupled with the found thermodynamic parameters, the half-life of DEB in natural fresh waters spans from 2 days at 30°C to 31 days at 0°C, but in the laboratory waste adjusted to pH 1or 13, the half-life shortens to 2–3 h at 20°C. Therefore, the results of the paper help to assess the risk of exposure to the genotoxic action of DEB.

The kinetic behavior of bis(2-methyl) butylene carbonate (BMBC) by the transesterification of dimethyl carbonate (DMC) with 1,4-butanediol (BDO) was investigated experimentally and theoretically. The Fourier transform infrared spectroscopy (FTIRs) test confirmed that the BMBC was successfully synthesized. The optimum preparation process of BMBC was investigated at atmospheric pressure, where Zn(Ac)₂∙2H₂O was the best catalyst for this transesterification reaction, and the optimal concentration was 0.3 wt%. The conversion was determined by measuring the amount of methanol produced during the reaction by refractometric method. A kinetic model was proposed according to the experimental results. The results showed that the transesterification reaction was a pseudo-first-order reaction. The apparent activation energy (E_a) significantly decreased with the increase of catalyst concentration from 0.1 wt% to 0.5 wt%. The E_a of the reaction was 102.13, 84.36, and 70.18 kJ mol⁻¹, respectively, when the catalyst concentration was 0.1 wt%, 0.3 wt%, and 0.5 wt%. Furthermore, the parameters of the optimal heating curve in the batch reactor was obtained according to the optimal model.

The oxidation of n-butane at elevated pressures has been investigated by experiments in a laminar flow reactor at 100 bar and temperatures of 450–900 K. The onset temperature for reaction increased from 550 K under oxidizing conditions (Φ = 0.02) to 625 K under reducing conditions (Φ = 13). NTC behavior was observed at 600–650 K (Φ = 0.02) and 625–675 K (Φ = 1.0). A detailed chemical kinetic model for the oxidation of n-butane was established. The present model and those suggested in literature were evaluated against the present experimental results and literature data at elevated pressures. None of the tested models could accurately reproduce the NTC behavior of n-butane under stoichiometric conditions of the present study, but all evaluated models could reproduce experimental data from literature with different levels of accuracy.

The shift in emphasis from fossil fuel-derived energy to waste-to-energy technologies has widened the possibility for environmentally sustainable methods such as pyrolysis. Algae collected from local sources that grow in wastewater using atmospheric CO₂ is a potential feedstock for pyrolysis. Thus, the work focuses on studying the pyrolysis reaction of macroalgae sourced from regional sources in the presence of Fe₂O₃ catalyst using the thermogravimetric analysis, followed by kinetic analysis using iso-conversional methods of Flynn–Wall–Ozawa (FWO), Kissinger–Akahira–Sunose (KAS), and Starink methods, and model free Kissinger method. The kinetic model was developed using master plot method. XRD analysis of the Fe₂O₃ catalyst confirms the presence of the maghemite and hematite phases in the sample. Based on the conversion profile, DTG trend, and kinetic parameter variation, the overall pyrolysis process can be divided into three different stages of dissociation reactions. The apparent activation energy calculated from different models varies in the range: stage I (∼268 kJ/mol), stage II (∼261 kJ/mol), and stage III (∼328 kJ/mol), respectively. Master plot analysis of the kinetic data confirms the best fit of the nucleation model (A2) to experimental data in stage II. Further, the thermodynamic properties of the reaction, such as change in enthalpy (ΔH), change in Gibbs free energy (ΔG), and change in entropy (ΔS) range between 206 and 405 kJ/mol, 189 and 651 kJ/mol, −450 and 27 J/mol/K, respectively, corroborates the complexity of the reaction. Kinetics and thermodynamic property analysis of complex reactions like pyrolysis is essential for pilot plant design.

The data on high hydrostatic pressure, temperature, and solvent influence on the Diels–Alder reaction rate of thiobenzophenone with cyclopentadiene have been obtained. Activation enthalpies, entropies, volumes, and reaction volumes in several solvents have been determined. The activation entropies and volumes of the Diels–Alder reaction of thiobenzophenone with cyclopentadiene are close to the corresponding activation parameters of Diels–Alder reactions involving dienophiles with C=C and N=N bonds. The rate of thiobenzophenone-cyclopentadiene reaction did not increase with increasing solvent polarity, which is also characteristic of other Diels–Alder reactions. The reaction of thiobenzophenone with cyclopentadiene is characterized by an “anomalous” ratio of the activation volume to the reaction volume ∆V^≠/∆V_r-n > 1. This can be explained by the less steric hindrances of transition-state molecules toward the solvent, compared with adduct molecules. The activities of a number of dienophiles with C=C, C=S, and N=N bonds have been compared, and the factors determining their reactivity in Diels–Alder reactions have been established.

With the advent of energy crisis and stringent emission regulations, natural gas (NG)/diesel dual-fuel engines have entered the popular view. In this paper, the accurate boundary conditions are determined by the Converge model and the transient parameters were introduced into the chemical kinetics model to make the operating conditions more closely match the actual engine operating conditions. The effects of different methane/n-heptane ratios, initial temperatures, initial pressures, and equivalence ratios on the IDT of methane/n-heptane fuel mixtures were analyzed using comprehensive chemical kinetic tools such as mole fraction analysis, ROP analysis, and sensitivity analysis. The IDT of methane/n-heptane mixture decreased significantly with increasing the equivalence ratio, initial pressure, and the proportion of n-heptane in the mixture, but the change of temperature was more complicated for the IDT. The NTC behavior of methane/n-heptane mixture was also affected by the NTC behavior of n-heptane. With the increase of initial temperature, the consumption of methane and n-heptane appeared to be significantly accelerated. The peak of radicals and intermediate groups appeared earliest and had the highest radical concentration when the n-heptane content was 30%. With the increase of initial pressure, the peak moments of the six radicals were further advanced, but the mole concentrations of O, OH, H radicals decreased significantly. This paper not only provides a reference for the design of NG/diesel dual-fuel engines, but also provides a theoretical basis and data support for improving the ignition and initial condition setting strategies of the engines.

The kinetics of the tautomerization of thio-imidic acids RC(SH)NH were determined at low (50–300 K) and high (500–1500 K) temperatures as R was varied to encompass mono- and diatomic species H, F, HO, NC, CN through H₂N, HC(O), HC(S), HC≡ C, H₃C, F₃C, HOCH₂, H₂C=CH, CH₃C(O), H₂NCH₂ and including ethyl, isopropyl and phenyl groups. The presence of a labile H-atom on the R-group can give rise to an alternative reaction, as in, H₃CC(SH)NH → CH₂=C(SH)NH₂ but these encounter much higher barriers. At the lowest temperatures there is over a million-fold difference in the rate constants for the fastest, R = H₂N, and slowest, R = F, reaction with quantum mechanical tunneling playing a dominant role which is dealt with by canonical transition state and small curvature tunneling theory. The tautomerization of similar imidic acids proceeds at much slower rates due to higher energy barriers to reaction. Additionally basic thermochemical data such as formation enthalpy, entropy, isobaric heat capacity and an enthalpy function are provided for all the species which may be useful training sets for machine-learning/AI purposes.