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Formation Step (formation + step)
Selected AbstractsA Coherent Mechanistic Rationale for Additive Effects and Autoinductive Behaviour in Proline-Mediated ReactionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 17 2009Natalia Zotova Abstract Differences in the kinetic behaviour of aldol reactions compared to aminoxylation and amination reactions are rationalized by consideration of the rate-determining step in each case. Both autoinductive behaviour and the rate-enhancing effect of additives are attributed to an effect on the enamine formation step. [source] A Highly Efficient Synthesis of a Naphthalenoid Histamine-3 AntagonistADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Yi-Yin Ku Abstract A highly efficient synthesis of the potent and selective histamine-3 receptor antagonist 1A was accomplished in four chemical steps and a salt formation step in 36% overall yield from 6-bromo-2-naphthalenol 9. The key features are a regioselective Suzuki coupling protocol for selective vinylation of 12 with potassium vinyltrifluoroborate in high yield (92%) with excellent regioselectivity (90:2) and a base-catalyzed hydroamination reaction of 11 in an anti-Markovnikov fashion under mild reaction conditions. An optimized copper-catalyzed cross coupling reaction is used to incorporate the pyridazinone 4. [source] Solid-solid reactions in series: A modeling and experimental studyAICHE JOURNAL, Issue 9 2009A. K. Suresh Abstract Reactions among particulate solid phases are important and abundant in many materials, chemical, and metallurgical process industries. Many of these are reaction networks, and not single-step reactions as normally assumed. There is no theoretical framework available for the analysis of such systems, and single-reaction models derived from the gas,solid literature continue to be used. Formation of cement clinker in the rotary cement kiln is a prime example of the genre, in which mechanistic aspects play an important role in determining energy efficiency and the composition and nature of the phases that form. In the present study, we formulate a model within the ambit of the "shrinking core" class of models, for reactions in series among solid phases. The model shows the presence of one or two moving fronts in the reacting particle, depending on the relative rates of the processes involved. A single Thiele-type parameter controls the model behavior, at once describing the relative rates of the intermediate formation and consumption processes, and the diffusion-reaction competition for the product formation step. The model has been shown to reduce to the well known single reaction models at the limits of low and high values of the Thiele parameter. Experimental data have been obtained on the calcia-alumina system, an important one in cement manufacture, in the temperature range 1150,1250°C. The model has been fitted to these data and the kinetic parameters determined. The comparison bears out the salient features of the theory, and shows that a degree of diffusion limitation exists for the intermediate conversion step under these conditions. The diffusivity values estimated are in the range of 10,19 to 10,18 m2/s and agree with values found in the literature for similar systems. The rate constant for the intermediate conversion step is of the order of 10,6 s,1. This being among the first such determinations, this value awaits confirmation from other studies. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Influence of the stacking order on structural features of the Cu-In-Ga-Se precursors for formation of Cu(In,Ga)Se2 thin films prepared by thermal reaction of InSe/Cu/GaSe alloys to elemental Se vapor and diethylselenide gasPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006F.B. Dejene Abstract A novel partway for the fabrication of copper-indium (gallium) diselenide has been developed. This two-stage process consists of the formation of Cu-In-(Ga)-Se precursors and subsequent selenization to form CuIn(Ga)Se2. In this work, we have investigated and compared the possible interactions in Cu-In-Ga-Se systems, using sequentially stacked precursors premixed with Se, in order to get a better understanding of the Cu(In,Ga)Se2 thin film formation. Comparison of these SEM micrographs clearly revealed that the surface morphologies and hence surface roughness of the resulting Cu(In,Ga)Se2 absorber films were significantly influenced by the structure of the precursor films prior to selenization. XRD analyses revealed the presence of a graded CuIn1-xGaxSe structure, irrespective of the stacking order during the precursor formation step for samples selenized using elemental Se vapor. It was established that distinct from the case of using Se vapor, a single-phase Cu(In,Ga)Se2 films were obtained by diethylselenide (DESe) selenization from Cu-In-Ga metal precursors premixed Se irrespective of the stacking order during the precursor formation step. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Resolution and absolute configuration assignment of a natural racemic chromane from Peperomia obtusifolia (Piperaceae)CHIRALITY, Issue 9 2009Joćo Marcos Batista Jr. Abstract The resolution of the natural racemic chromane 3,4-dihydro-5-hydroxy-2,7-dimethyl-8-(3,-methyl-2,-butenyl)-2-(4,-methyl-1,,3,-pentadienyl)-2H -1-benzopyran-6-carboxylic acid (1) isolated from the leaves of Peperomia obtusifolia has been accomplished using stereoselective HPLC. The absolute configuration of the resolved enantiomers was determined by the analysis of optical rotations and CD spectra. The finding of a racemic mixture instead of an enantiomerically pure metabolite raises questions about the final steps in the biosynthesis of this class of natural products, suggesting that the intramolecular chromane ring formation step may not be enzymatically controlled at all in P. obtusifolia. Chirality, 2009. © 2008 Wiley-Liss, Inc. [source] | ||||||||||