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Acid-base Reaction (acid-base + reaction)
Selected AbstractsSynthesis, Coordination and Catalytic Utility of Novel Phosphanyl,ferrocenecarboxylic Ligands Combining Planar and Central ChiralityEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2007Martin Lama Abstract The chiral ferrocene derivative (R,Rp)-2-[1-(diphenylphosphanyl)ethyl]ferrocenecarboxylic acid (1) is prepared together with selected derivatives resulting from modification at the phosphane moiety [P -oxide (5) and P -sulfide (4)] and the carboxyl group {amides bearing benzyl (6) and (R)- or (S)-1-phenylethyl substituents [(R)- 7 and (S)- 7] at the amide nitrogen atom}. Acid 1 and amide 6 are studied as ligands in rhodium and palladium complexes. Bridge cleavage of the dimer [{Rh(,-Cl)Cl(,5 -C5Me5)}2] with 1 gives [RhCl2(,5 -C5Me5)(1 -,P)] (9) containing P-monodentate 1, which undergoes smooth conversion to the (phosphanylalkyl)ferrocenecarboxylato complex [RhCl(,5 -C5Me5){Fe(,5 -C5H5)(,5 -C5H3 -1-CH(Me)PPh2 -2-COO-,2O,P}] (10) upon treatment with silica gel or alumina. Yet another O,P -chelate complex,[Rh{Fe(,5 -C5H5)(,5 -C5H3 -1-CH(Me)PPh2 -2-COO-,2O,P}(CO)(PCy3)] (11; Cy = cyclohexyl) is obtained directly by an acid-base reaction between the acetylacetonato complex [Rh(acac)(CO)(PCy3)] and 1. Amide 6 reacts with [{Pd(,-Cl)(,3 -C3H5)}2] to give the expected phosphane complex [PdCl(,3 -C3H5)(6 -,P)] (12), while the replacement of the cyclooctadiene (cod) ligand in [PdCl(Me)(cod)] affords the chelate complex [PdCl(Me)(6 -,2O,P)] (13). All compounds are characterised by spectroscopic methods and the solid-state structures of 5, 9, 11, 13, (R,Sp)-2-[1-(diphenylphosphoryl)ethyl]-1-[N -(R)-(1-phenylethyl)carbamoyl]ferrocene [(R)- 8; phosphane oxide from (R)- 7], and the synthetic precursors (R,Sp)-1-bromo-2-[1-(diphenylphosphanyl)ethyl]ferrocene (2) and (R,Sp)-1-bromo-2-[1-(diphenylthiophosphoryl)ethyl]ferrocene (3) determined by single-crystal X-ray diffraction. The catalytic properties of 1 and the amides are probed in enanatioselective rhodium-catalysed hydrogenation and palladium-catalysed asymmetric allylic alkylation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Acid-Base Interactions in Energetic Materials: I. The Hard and Soft Acids and Bases (HSAB) Principle,Insights to Reactivity and Sensitivity of Energetic MaterialsPROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 1 2005Ernst-Christian Koch Abstract The chemistry of energetic materials can be described applying acid-base reaction formalism. Addressing the HSAB concept, the number of electrons transferred, ,N, in an acid-base reaction, allows for description and prediction of properties of composite and homogeneous materials. At first ,N helps in estimating the rate of reaction of binary systems with either given fuel or oxidizer. Nevertheless ,N is only a relative number thus the range of comparability remains narrow. At second ,N can be used as a measure for the sensitivity of homogeneous explosives. The increased reactivity of hypothetical fragments to recombine in a reaction such as R3C.+.NO2=R3C,NO2 given by ,N correlates very well with experimentally determined reduced impact sensitivity of 1,3,5-trinitrobenzene compounds. On the contrary the rising impact sensitivity of metal azides correlates with rising values of ,N of Mn+/N3, reaction because increased reactivity, that is increased electron transfer from the azide anion to the metal cation triggers formation of the azide radical (.N3). The latter then decomposes rapidly to give dinitrogen. This increased reactivity/sensitivity of metral azides coincides with covalent bonding whereas ionic azides are relatively insensitive. [source] Enhanced mixing of Newtonian fluids in a stirred vessel using impeller speed modulationTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2009Wei M. Yek Abstract This paper reports on an experimental study of mixing intensification using speed modulation of a six-blade Rushton turbine in a stirred vessel. Mixing times were measured using a non-intrusive technique based on direct visualisation of an acid-base reaction in a Newtonian fluid. The impeller speed modulation was achieved by using two waveforms: a square wave and a sine wave. The amplitude was fixed between a maximum Reynolds number of Remax,=,60 and minimum Reynolds numbers of Remin,=,40 or 30. The wave periods were varied (10, 20, or 40,s) in order to compare the effects of unsteady stirring on mixing performance. It was observed that a square wave protocol with the shortest wave period and the larger amplitude resulted in the shortest time to destroy the observed isolated mixing regions (IMRs), which are known to exist in stirred vessels operating at low Reynolds number. However, the sine wave protocol led to a slow diffusive mechanism in which IMR structures reached an asymptotic volume and remained visible even after several hours. The results are presented and discussed using digital photographs taken at different time intervals during experimentation. Ce papier présente une étude experimentale concernant l'intensification du mélange en modulant la vitesse d'une turbine de type Rushton a six palettes dans une cuve agitée. Les temps de mélanges sont mesurés avec une technique non-intrusive basée sur la visualisation directe d'une réaction acide-base au sein d'un fluide Newtonien. La modulation de la vitesse de la turbine a été realisée en utilisant deux formes d'ondes: une onde carrée et une onde sinusoidale. L'amplitude de chaque onde a été fixée entre un nombre de Reynolds maximal de Remax,=,60 et un nombre de Reynolds minimal de Remin,=,40 ou 30. Les périodes des ondes étaient variées (10, 20 ou 40,s) dans le but de comparer les effets du mélange non-stationnaire sur les performances du systeme. Il a été observé que le protocole suivant l'onde carrée avec la periode la plus courte et l'amplitude la plus large produisait le temps le plus court necessaire pour la destruction des zones de mélanges isolées (IMRs), dont l'éxistense est connue dans les cuves a mélange opérant aux nombres de Reynolds bas. Toutefois, le protocol suivant une onde sinusoidale a conduit a un mechanisme de diffusion lent dans lequel les IMRs atteignies un volume symptotique et sont restées visibles après plusieurs heures. Les résultats sont présentés and discutés en utilisant des photographes digitales prises à des intervales de temps differents durant les éxperiences. [source] Determination of Transverse Dispersion Coefficients from Reactive Plume LengthsGROUND WATER, Issue 2 2006Olaf A. Cirpka With most existing methods, transverse dispersion coefficients are difficult to determine. We present a new, simple, and robust approach based on steady-state transport of a reacting agent, introduced over a certain height into the porous medium of interest. The agent reacts with compounds in the ambient water. In our application, we use an alkaline solution injected into acidic ambient water. Threshold values of pH are visualized by adding standard pH indicators. Since aqueous-phase acid-base reactions can be considered practically instantaneous and the only process leading to mixing of the reactants is transverse dispersion, the length of the plume is controlled by the ratio of transverse dispersion to advection. We use existing closed-form expressions for multidimensional steady-state transport of conservative compounds in order to evaluate the concentration distributions of the reacting compounds. Based on these results, we derive an easy-to-use expression for the length of the reactive plume; it is proportional to the injection height squared, times the velocity, and inversely proportional to the transverse dispersion coefficient. Solving this expression for the transverse dispersion coefficient, we can estimate its value from the length of the alkaline plume. We apply the method to two experimental setups of different dimension. The computed transverse dispersion coefficients are rather small. We conclude that at slow but realistic ground water velocities, the contribution of effective molecular diffusion to transverse dispersion cannot be neglected. This results in plume lengths that increase with increasing velocity. [source] On the applicability of the HSAB principle through the use of improved computational schemes for chemical hardness evaluationJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 7 2004Mihai V. Putz Abstract Finite difference schemes, named Compact Finite Difference Schemes with Spectral-like Resolution, have been used for a less crude approximation of the analytical hardness definition as the second-order derivative of the energy with respect to the electron number. The improved computational schemes, at different levels of theory, have been used to calculate global hardness values of some probe bases, traditionally classified as hard and soft on the basis of their chemical behavior, and to investigate the quantitative applicability of the HSAB principle. Exchange acid-base reactions have been used to test the HSAB principle assuming the reaction energies as a measure of the stabilization of product adducts. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 994,1003, 2004 [source] | ||||||||||