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Rapid Reaction (rapid + reaction)

Distribution by Scientific Domains

Chemistry	80%

Selected Abstracts

Kinetics and simulations of reaction between safranine- O and acidic bromate and role of bromide therein

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2002
S. B. Jonnalagadda
Safranine- O, a dye of the phenazinium class, was found to exhibit intricate kinetics during its reaction with bromate at low pH conditions. Under conditions of excess concentrations of acid and bromate, safranine- O (SA+) initially depleted very slowly (k = (3.9 ± 0.3) × 10,4 M,3 s,1) but after an induction time, the reaction occurred swiftly. Bromide exhibited a dual role in the reaction mechanism, both as an autocatalyst and as an inhibitor. The added bromide increased the initial rate of depletion of SA+, but delayed the transition to rapid reaction. The overall stiochiometric reaction was found to be 6SA+ + 4 BrO3, = 6SP + 3N2O + 3H2O + 6H+ + 4Br,, where SP is 3-amino-7-oxo-2,8-dimethyl-5-phenylphenazine. The fast kinetics of the reaction between aqueous bromine and safranine- O (k = (2.2 ± 0.1) × 103 M,1 s,1) are also reported in this paper A 17-step mechanism, consistent with the overall reaction dynamics and supported by simulations, is proposed and the role of various bromo and oxybromo species is also discussed. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 542,549, 2002 [source]

Effect of heating rate on kinetics of high-temperature reactions: Mo-Si system

AICHE JOURNAL, Issue 1 2005
Suren L. Kharatyan
Abstract By using the Computer Assisted Electrothermography (CAE) method and taking the molybdenum-silicon system as an example, the influence of preheating rate on the kinetics of gasless reactions at high temperatures (above Si melting point, 1683 K) is studied. It is shown that an increase of heating rate Vh in the range 10,105 K/s, leads to a substantial increase in the rate of chemical reaction. At high heating rates (>103 K/s), the first stage of interaction involves rapid reaction due to the direct dissolution of Mo in the Si melt. Furthermore, the formation of MoSi2 phase, owing both to crystallization from eutectic (MoSi2 -Si) melt and reaction-diffusion mechanism, is primarily responsible for the observed intensive heat release under these conditions. At lower Vh, a thin layer of Mo5Si3 phase formed at earlier stages (solid-solid interaction) significantly retards reaction at higher temperatures and changes the mechanism of interaction. Some methodological aspects of using the CAE technique for kinetic studies are also discussed. © 2004 American Institute of Chemical Engineers AIChE J, 51: 261,270, 2005 [source]

The quantification of carbon dioxide in humid air and exhaled breath by selected ion flow tube mass spectrometry

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 10 2009
David Smith
The reactions of carbon dioxide, CO2, with the precursor ions used for selected ion flow tube mass spectrometry, SIFT-MS, analyses, viz. H3O+, NO+ and O, are so slow that the presence of CO2 in exhaled breath has, until recently, not had to be accounted for in SIFT-MS analyses of breath. This has, however, to be accounted for in the analysis of acetaldehyde in breath, because an overlap occurs of the monohydrate of protonated acetaldehyde and the weakly bound adduct ion, H3O+CO2, formed by the slow association reaction of the precursor ion H3O+ with CO2 molecules. The understanding of the kinetics of formation and the loss rates of the relevant ions gained from experimentation using the new generation of more sensitive SIFT-MS instruments now allows accurate quantification of CO2 in breath using the level of the H3O+CO2 adduct ion. However, this is complicated by the rapid reaction of H3O+CO2 with water vapour molecules, H2O, that are in abundance in exhaled breath. Thus, a study has been carried out of the formation of this adduct ion by the slow three-body association reaction of H3O+ with CO2 and its rapid loss in the two-body reaction with H2O molecules. It is seen that the signal level of the H3O+CO2 adduct ion is sensitively dependent on the humidity (H2O concentration) of the sample to be analysed and a functional form of this dependence has been obtained. This has resulted in an appropriate extension of the SIFT-MS software and kinetics library that allows accurate measurement of CO2 levels in air samples, ranging from very low percentage levels (0.03% typical of tropospheric air) to the 6% level that is about the upper limit in exhaled breath. Thus, the level of CO2 can be traced through single time exhalation cycles along with that of water vapour, also close to the 6% level, and of trace gas metabolites that are present at only a few parts-per-billion. This has added a further dimension to the analysis of major and trace compounds in breath using SIFT-MS. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Intradaily Patterns in the Korean Index Futures Market

ASIAN ECONOMIC JOURNAL, Issue 2 2002
Laurence Copeland
This paper extends the research on intraday patterns in stock and futures exchanges into the Korean market. Similar patterns to those found previously in the heavily investigated Western markets are observed, despite the differing microstructures, institutional framework and time zones between East and West. In addition, we investigate the effect of the Asian financial crisis on intraday variables. In the Korean market, both volume and volatility were found to be consistently higher at the start of the trading day during the crisis, presumably due to a rapid reaction to overnight news. [source]

Very Fast Suzuki,Miyaura Reaction Catalyzed by Pd(OAc)2 under Aerobic Conditions at Room Temperature in EGME/H2O

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 1 2009
Alessandro Del Zotto
Abstract The results of a ligand-free Pd(OAc)2 -catalyzed Suzuki,Miyaura C,C coupling performed at room temperature under aerobic conditions are presented. It was found that the use of an ethylene glycol monomethyl ether/H2O mixture as the solvent resulted in very rapid reactions of aryl bromides with arylboronic acids. As a matter of fact, under optimized conditions, some substrates were converted quantitatively in less than 1 min with exceptionally high TOF values. For example, the reaction between 4-methoxyphenylboronic acid and bromobenzene afforded 4-methoxybiphenyl in 30 s with TOF = 180000 h,1. Furthermore, the reaction tolerates a wide range of functional groups and can be successfully applied to heteroaryl bromides such as 2-bromopyridine and 5-bromopyrimidine. Interestingly, also an activated aryl chloride such as 1-chloro-4-nitrobenzene reacted quantitatively with phenylboronic acid at 373 K. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]