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111.
Summary Borax forms peroxy species when dissolved in 30% hydrogen peroxide which can be transferred into the organic phase when biphase mixtures are agitated. The addition of a catalytic amount ofBTEAC promotes the transfer. This biphase system was used for theBaeyer-Villiger oxidation of several ketones insoluble in water. Effects of changing various parameters,e.g. temperature, time, amount of H2O2 etc. were investigated. At higher temperature (ca. 80°C), 100% conversion could be achieved in 2–4h. The results show that under appropriate conditions this reaction is of synthetic value for the oxidation of acid-sensitive ketones using inexpensive and easily available reagents.
Oxidation von Ketonen mit Borax-H2O2 unter Phasentransferkatalyse
Zusammenfassung In Wasserstoffperoxid (30%) gelöstes Borax bildet Peroxyverbindungen, die durch Schütteln in die organische Phase zweiphasiger Systeme übergeführt werden können. Der Transferprozeß wird durch die Zugabe von katalytischen MengenBTEAC gefördert. Die zweiphasigen Systeme wurden zurBaeyer-Villiger — Oxidation einiger in Wasser unlöslicher Ketone eingesetzt und die Auswirkung der Variation verschiedener Parameter (z.B. Temperatur, Zeit, Menge an H2O2 etc.) untersucht. Unter dem Einfluß höherer Temperature (ca. 80°C) wurde vollständige Umsetzung innerhalb von 2–4 h erreicht. Die Ergebnisse zeigen, daß die genannte Reaktion unter geeigneten Bedingungen von synthetischem Wert zur Oxidation säureempfindlicher Ketone unter Verwendung billiger und leicht verfügbarer Reagenzien ist.相似文献
112.
Asheesh Kumar Jain Pradeep Kumar Gupta Kumaran Ganesan Ambuja Pande Deepak Pardasani Ramesh Chandra Malhotra 《Journal of heterocyclic chemistry》2005,42(5):985-989
4‐Benzyloxyindole‐2‐carboxylic acid hydrazide reacts with aromatic and heterocyclic aldehydes in alcoholic medium in refluxing conditions to give 4‐benzyloxy‐1H‐indole‐2‐carboxylic acid (arylidene)‐hydrazides, important synthetic intermediates for the synthesis of a newer class of pharmacologically active compounds. We describe here the synthesis of various 4‐benzyloxy‐1H‐indole‐2‐carboxylic acid (arylidene)‐hydrazides by conventional as well as microwave irradiation techniques. The structures of these compounds have been confirmed by spectroscopic techniques (FTIR, NMR and MS). Some of the interesting features of the electron impact mass spectral fragmentation pattern of these compounds are also discussed. 相似文献
113.
Using over 75 mus of molecular dynamics simulation, we have generated several thousand folding simulations of the 20-residue Trp cage at experimental temperature and solvent viscosity. A total of 116 independent folding simulations reach RMSDcalpha values below 3 A RMSDcalpha, some as close as 1.4 A RMSDcalpha. We estimate a folding time of 5.5+/-3.5 mus, a rate that is in reasonable agreement with experimental kinetics. Finally, we characterize both the folded and unfolded ensemble under native conditions and note that the average topology of the unfolded ensemble is very similar to the topology of the native state. 相似文献
114.
Anurag Noonikara-Poyil Alvaro Muoz-Castro H. V. Rasika Dias 《Molecules (Basel, Switzerland)》2022,27(1)
Copper plays an important role in alkyne coordination chemistry and transformations. This report describes the isolation and full characterization of a thermally stable, copper(I) acetylene complex using a highly fluorinated bis(pyrazolyl)borate ligand support. Details of the related copper(I) complex of HC≡CSiMe3 are also reported. They are three-coordinate copper complexes featuring η2-bound alkynes. Raman data show significant red-shifts in C≡C stretch of [H2B(3,5-(CF3)2Pz)2]Cu(HC≡CH) and [H2B(3,5-(CF3)2Pz)2]Cu(HC≡CSiMe3) relative to those of the corresponding alkynes. Computational analysis using DFT indicates that the Cu(I) alkyne interaction in these molecules is primarily of the electrostatic character. The π-backbonding is the larger component of the orbital contribution to the interaction. The dinuclear complexes such as Cu2(μ-[3,5-(CF3)2Pz])2(HC≡CH)2 display similar Cu-alkyne bonding features. The mononuclear [H2B(3,5-(CF3)2Pz)2]Cu(NCMe) complex catalyzes [3 + 2] cycloadditions between tolyl azide and a variety of alkynes including acetylene. It is comparatively less effective than the related trinuclear copper catalyst {μ-[3,5-(CF3)2Pz]Cu}3 involving bridging pyrazolates. 相似文献
115.
116.
We present a maximum likelihood argument for the Bennett acceptance ratio method, and derive a simple formula for the variance of free energy estimates generated using this method. This derivation of the acceptance ratio method, using a form of logistic regression, a common statistical technique, allows us to shed additional light on the underlying physical and statistical properties of the method. For example, we demonstrate that the acceptance ratio method yields the lowest variance for any estimator of the free energy which is unbiased in the limit of large numbers of measurements. 相似文献
117.
Along with the normally produced pulses of dI/dt, x-ray, optical emission, neutrons and ions by a Mather type plasma focus gun, one more set of pulses were observed to be
generated by a low energy device at Trombay, a few 100 ns after the first set of pulses, in majority of the discharges. In
a small number of discharges even three or more sets of pulses were observed. Signals from pick-up probes placed in the run
down region of the device suggest formation of more than one sheath which subsequently may form more than one focus which
in turn is responsible for the second and subsequent sets of pulses. 相似文献
118.
Enakshi Khular Arun Kumar Anurag Sharma I. C. Goyal A. K. Ghatak 《Optical and Quantum Electronics》1981,13(2):109-115
The refractive index profile of buried graded-index planar optical waveguides fabricated by ion migration can be described by a buried secant hyperbolic function. Using such a profile, we have obtained the exact propagation characteristics for such buried optical waveguides. We have also shown that profiles which deviate slightly from the above profile can be treated as perturbations and a first-order perturbation correction gives very accurate results. 相似文献
119.
120.