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Second-order Reaction (second-order + reaction)

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Chemistry100%

Selected Abstracts

Competing kinetic pathways in the bromine addition to allylic ethers in 1,2-dichloroethane: Opposite temperature effects

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2007
Alessandro Cecchi
The kinetics of the electrophilic bromination of three allylic ethers in a nonprotic solvent, 1,2-dichloroethane, has been investigated. Two of them followed a prevalent second-order pathway, while the third one exhibited a classical, clean third order. The second-order pathway in the first two olefins is attributed to electrophilic assistance of the ethereal oxygen to the attacking bromine molecule. In the molecular bromination of 2,4- cis -dimethyl-8-oxabicyclo[3.2.1]-6-octen-3- cis -ol, opposite temperature dependences were found for the two different kinetic pathways. An exoergonic process for the second-order reaction was explained by the lesser stability of the bromiranium,bromide ionic intermediate, compared to the bromiranium,tribromide in the third-order profile. © 2007 Wiley Periodicals, Inc. 39: 197,203, 2007 [source]

Monitoring of a second-order reaction by electronic absorption spectroscopy using combined chemometric and kinetic models

JOURNAL OF CHEMOMETRICS, Issue 6 2003
Tom J. Thurston
Abstract This paper reports the application of 11 methods for obtaining kinetic constants from a second-order reaction, that between phenylhydrazine and benzophenone. In this type of reaction the number of absorbing species is lower than the number of steps in the reaction minus one, resulting in a rank-deficient response matrix. The methods used include traditional univariate curve fitting, classical least squares using previously recorded pure spectra, alternating least squares methods with both kinetic and non-negativity constraints, and target-testing methods using principal component scores. An additional recently proposed method based on difference spectra is also examined, suitable for any single-step closed reaction. The methods that performed best were difference spectra, kinetically constrained alternating least squares, and target-testing approaches. Limitations of the traditional methods are described. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Thermochemical Properties and Decomposition Kinetics of Ammonium Magnesium Phosphate Monohydrate

CHINESE JOURNAL OF CHEMISTRY, Issue 1 2007
Jian Wu
Abstract Ammonium magnesium phosphate monohydrate NH4MgPO4·H2O was prepared via solid state reaction at room temperature and characterized by XRD, FT-IR and SEM. Thermochemical study was performed by an isoperibol solution calorimeter, non-isothermal measurement was used in a multivariate non-linear regression analysis to determine the kinetic reaction parameters. The results show that the molar enthalpy of reaction above is (28.795±0.182) kJ/mol (298.15 K), and the standard molar enthalpy of formation of the title complex is (,2185.43±13.80) kJ/mol (298.15 K). Kinetics analysis shows that the second decomposition of NH4MgPO4·H2O acts as a double-step reaction:an nth-order reaction (Fn) with n=4.28, E1=147.35 kJ/mol, A1=3.63×1013 s,1 is followed by a second-order reaction (F2) with E2=212.71 kJ/mol, A2=1.82×1018 s,1. [source]

A step-wise incremented Fourier series model for chemical reactivity prediction

JOURNAL OF CHEMOMETRICS, Issue 6-7 2006
Saloua Saidane
Abstract In this paper, chemical reactivity is modeled as a time series of events defined by a reactant's concentration decay measured at consecutive discrete time periods. Since traditional time series techniques such as ARIMA and current Artificial Neural Networks require large data sets that are typically not available for chemical reactions, we developed a Step Wise Incremented Fourier Series (SWIFS) algorithm to model and predict nonlinear short time series. The application of SWIFS to experimental data from first- and second-order reactions produced a significant improvement in prediction accuracy over traditional integrated rate laws. In forward-time prediction, SWIFS has achieved significantly higher prediction accuracy with first- and second-order chemical reactions data. SWIFS also proved more robust in terms of error propagation caused by the effect of the size of the estimation set. The proposed SWIFS model also outperformed rate law models in backwards-time prediction. The ability of SWIFS to provide high accuracy in predicting chemical reactions may have beneficial implications on the efficiency of industrial production of chemicals as well as on the effective control of hazardous materials degradation. Copyright © 2007 John Wiley & Sons, Ltd. [source]