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Observed Rate Constant (observed + rate_constant)
Selected AbstractsMedium Effect on the Reaction of N -Butyl-2,4,6-trinitroaniline with NaOH,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 13 2007Marķa Laura Salum Abstract The kinetics of the reaction of N -butyl-2,4,6-trinitroaniline (3) with NaOH have been studied in 10 and 60,% 1,4-dioxane/H2O at 25 °C. In both cases, several processes were observed. In 10,% 1,4-dioxane/H2O the only product formed was 2,4,6-trinitrophenol (4), whereas in 60,% 1,4-dioxane/H2O a mixture of 4 and 5,7-dinitro-2-propyl-1H -benzimidazole 3-oxide (5) was observed in ratios that depend on the HO, concentration. A mechanism involving the formation of , complexes through the addition of one or two HO, anions to unsubstituted ring positions is proposed for 2,4,6-trinitrophenol formation. The presence of these complexes was confirmed by NMR studies in 60,% [D8]1,4-dioxane/D2O. The mechanism suggested for the formation of the N -oxide includes the cyclization of an N -alkylidene-2-nitrosoaniline-type intermediate as the rate-determining step. The decrease in solvent polarity produces a decrease in the observed rate constant for the formation of 4 of about one order of magnitude making the cyclization reaction a competitive pathway. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Micellar Effects on the Reaction between an Arenediazonium Ion and the Antioxidants Gallic Acid and Octyl GallateHELVETICA CHIMICA ACTA, Issue 1 2008Losada Barreiro, Sonia Abstract The effect of sodium dodecyl sulfate (SDS) micelles on the reaction between the 3-methylbenzenediazonium (3MBD) ion and either the hydrophilic antioxidant gallic acid (GA) or the hydrophobic analogue octyl gallate (OG) have been investigated as a function of pH. Titration of GA in the absence and presence of SDS micelles showed that the micelles do not alter the first ionization equilibrium of GA. Analysis of the dependence of the observed rate constant (kobs) with pH shows that the reactive species are GA2, and OG,. Kinetics results in the absence and presence of SDS micelles suggest that SDS aggregates do not alter the expected reaction pathway. SDS Micelles inhibit the spontaneous decomposition of 3MBD as well as the reaction between 3MBD and either GA or OG, and upon increasing the SDS concentration, with kobs approaching the value for the thermal decomposition of 3MBD in the presence of SDS. Our results are consistent with the prediction of the pseudophase model and show that the origin of the inhibition for the reaction with GA is different to that for the reaction with OG; in the former case, the observed inhibition can be rationalized in terms of the micelle-induced electrostatic separation of reactants in the micellar Stern layer, whereas the observed inhibition in the reaction with OG is a consequence of the dilution effect caused by increasing SDS concentration, decreasing the local OG, concentration in the Stern layer. [source] Spectrophotometric variable-concentration kinetic experiments applied to inorganic reactionsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2003Giuseppe Alibrandi The dependence of the observed rate constant of inorganic substitution reactions on the concentration of nucleophilic reagents was obtained by single variable-parameter kinetic runs. The experiments were carried out spectrophotometrically, varying the concentration of the nucleophile inside the reaction vessel. Software and apparatus were developed for an easy and rapid performance. The method gives accurate results and a saving in time by a factor of up to 100 compared to conventional methods. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 497,502, 2003 [source] Dediazoniation of 1-naphthalenediazonium tetrafluoroborate in aqueous acid and in micellar solutionsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2008Carlos Bravo-Diaz We have measured the rates and product yields of dediazoniation of 1-naphthalenediazonium (1ND) tetrafluoroborate in the presence and absence of sodium dodecyl sulfate (SDS) micellar aggregates by employing a combination of UV,vis spectroscopy and high-performance liquid chromatography (HPLC) measurements. Kinetic data were obtained by a derivatization procedure with product yields were determined by HPLC. HPLC chromatograms show that in aqueous acid and in micellar solutions only one dediazoniation product is formed in significant quantities, 1-naphthol (NOH), and the observed rate constants (kobs) are the same when 1ND loss is monitored spectrometrically and when NOH formation is monitored by HPLC. Activation parameters were obtained both in the presence and absence of SDS micellar aggregates. In both the systems, the enthalpies of activation are high and the entropies of activation are positive. The enthalpy of activation in the absence of SDS is very similar to that in the presence of SDS micelles, but the entropy of activation is lower by a factor of 4. As a consequence, SDS micelles speed up the thermal decomposition of 1ND and increase kobs by a factor of 1.5 when [SDS] = 0.02 M. In contrast, results obtained in the presence of complexing systems such as crown ethers and polyethers show significant stabilization of the parent arenediazonium ions. Kinetic and HPLC data are consistent with the heterolytic DN + AN mechanism that involves the rate-determining fragmentation of the arenediazonium ion into a very reactive phenyl cation that reacts competitively with available nucleophiles. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 301,309, 2008 [source] | ||||||||||