Results 1 - 10 of 1906
Results 1 - 10 of 1906. Search took: 0.028 seconds
|Sort by: date | relevance|
[en] Rearrangements of 1,3-oxathiolane sulfoxides 8 and 9 in the presence of base are described from a mechanistic viewpoint of sigmatropic and elimination reactions. In the presence of triethylamine the (Z)- sulfoxide 8 gave the corresponding thiolsulfinate 10 by way of dimerization of the sulfenic acid intermediate 2 at room temperature while the (E)-sulfoxide 9 was recovered even after refluxing in ethyl acetate by the reversal of the [2,3]-sigmatropic rearrangement of the sulfenic acid 4. Triethylamine promoted the developing charge separation in the transition state of the sigmatropic rearrangement of the (Z)-sulfoxide 8 to facilitate the ring opening to the sulfenic acid 2. The reason for more facile ring opening of the (Z)-sulfoxide 8 in comparison with the corresponding (E)-sulfoxide 9 is attributable to the differences in the reactivity of the hydrogen adjacent to the carbonyl group. Triethylamine was not strong base to deprotonate the carbonyl-activated methylene hydrogen of the (E)-sulfoxide 9 but enough to catalyze the sigmatropic process of the sulfoxides. The sulfenic acid 2 dimerized to the thiolsulfinate 10 while the sulfenic acid 4 proceeded the sigmatropic ring closure. In the presence of strong base such as potassium hydroxide, the elimination reaction was predominant over the sigmatropic rearrangement. In this reaction condition, both sulfoxides 8a and 9a gave a mixture of the disulfide 12, the isomeric disulfide 14, and the sulfinic acid 13. Under the strong alkaline condition an elimination of activated hydrogen from the carbon adjacent to the carbonyl group to furnish the sulfenic acid 2a and the isomeric sulfenic acid 18. The formation of the transient intermediate in the reaction was proven by isolation of the isomeric disulfide 14. The reactive entity was regarded as the sulfenic acid rather than sulfenate anion under these reaction conditions
[en] Due to pharmacological importance of 1,3,4-Oxadiazoles, a new series of S-substituted derivatives of 5-(1-(phenylsulfonyl)piperidin-4-yl)-1,3,4-Oxadiazol-2-thiol (4a-v) was synthesized. The reaction of benzenesulfonyl chloride with ethyl isonipecotate yielded ethyl 1-(phenylsulfonyl)piperidine-4-carboxylate (1), which was further converted into 1-(Phenylsulfonyl) piperidine-4-carbohydrazide (2) and 5-(1-(phenylsulfonyl)piperidin-4-yl)-1,3,4-Oxadiazol-2-thiol (3) in the presence of hydrazine hydrate and CS2 along with KOH respectively. The target compounds (4a-v) were synthesized by the reaction of compound 3 with different electrophiles in the presence of DMF and sodium hydride. The structures of all the synthesized compounds were confirmed via IR, 1H-NMR and EI-MS spectral data and were evaluated for antibacterial activity against Gram-positive and Gram-negative bacteria. It was observed that the electrophilic substitution influenced significantly for the variation of antibacterial activity from moderate to excellent level. (author)
[en] The development of highly efficient electrocatalysts for water splitting is critical for various renewable-energy technologies. In this letter, we demonstrate a cobalt phosphide nanowire array grown on a Ti mesh (CoP/TM) behaving as a bifunctional electrocatalyst for water splitting. The CoP/TM electrode delivers 10 mA cm−2 at an overpotential of 72 mV for the hydrogen evolution reaction (HER) and 310 mV for the oxygen evolution reaction (OER) in 1.0 M KOH. Furthermore, its corresponding two-electrode alkaline electrolyzer displays 10 mA cm−2 at 1.64 V. (letter)
[en] Fibrous TiO2 layer was formed on a metal Ti plate by soaking it in a KOH solution and subsequently firing it in air at 600 °C for 2 h. Hydrophobic solid–liquid bulk composite (SLBC) was prepared by impregnation of a commercial silicone-based oil into the fibrous TiO2 layer after coating with fluoroalkylsilane. Based on the spreading coefficients from interface energies, the topmost solid surface of the SLBC was covered by the oil film when a water–glycerin mixture droplet was placed on the surface. The mixture droplets slid down the SLBC with acceleration. Particle image velocimetry (PIV) analysis revealed rolling and slipping modes in the sliding of the mixture droplets on the SLBC surface. During sliding, the coefficient of the viscous drag force was correlated with the velocity ratio (Utotal/Uslip). Results suggest that the estimation of the internal fluidity of the liquid droplet was feasible to some degree by evaluating the coefficient during droplet sliding with constant acceleration on the SLBC surface.
[en] A comparative study of niobium electrochemical behaviour in NaOH and KOH solution, with concentrations between 0,5 and 6,1M is presented. The studies were done through electrochemicals assays, consisting in the corrosion potential and anodic and cathodic polarization curves, complemented by loss of mass experiments. The niobium anodic behaviour in alkaline medium is characterized by passivation occurrence, with a stable film formation. The Na oH solution in alkaline medium are more corrosible to niobium than the KOH solution. The loss of mass assays showed that the corrosion velocit is more dependente of hydroxide concentration in KOH medium than the NaOH medium. (C.G.C.)
[pt]Estudos anodicos efetuados e forca ionica constante mostraram que em meio de NaOH as densidades de corrente critica e de passivacao crescem com o aumento da concentracao de OH-, enquanto que em meio de KOH independe da [OH-]. Os ensaios de perda de massa revelaram que a velocidade de corrosao e mais dependente da concentracao do hidroxido em meio de KOH do que em meio de NaOH. (autor)
[en] An isotropic wet chemical etching of silicon plays an important role in the realization of three dimensional micro electromechanical system structures (MEMS) like membranes and cantilevers. Many factors such crystal orientation, etchant composition, temperature, and doping influence the etching rates. Therefore the prediction of the etching result can be sometimes very difficult. In this work a new approach to simulate negative sloped planes, which often appear underneath convex mask cornets in wet chemical etching of semiconductors, is represented. Additionally the two-sided wet chemical etching of silicon wafers is simulated. In order to investigate the quality of the simulation method we presented simulated and experimental results of the etching system Si in KOH. Good agreement between both results can be observed. (author)
[en] Introduction of the alternative materials for complete replacement of cement in ordinary concrete will play an important role to control greenhouse gas and its effect. The 100% replacement of binder with fly ash (in integration with potassium hydroxide (koh) and potassium silicate (k2sio3) solutions) in concrete gives a significant alternative to conventional cement concrete. This paper focuses on the effect of alkaline solutions koh and k2sio3 on strength properties of fly ash based geo polymer concrete (fgpc); compared the strength at different molarities of alkaline activator koh at different curing temperature. Fly ash based geo polymer concrete was produced from low calcium fly ash, triggered by addition of koh and k2sio3 solution and by assimilation of superplasticizer for suitable workability. The molarities of potassium hydroxide as 8m, 10m and 12m molarities were used at various curing temperatures such as 60°c, 70 °c and 80°c. Results showed that for given proportion to get maximum compressive strength the optimum molarity of alkaline solution is 12m and optimum curing temperature is 70 °c. (paper)
[en] An efficient method for the synthesis of pyrazolopyrimidines by the tandem reactions of dienones with pyrazole-3-amine through an aza-Michael addition/nucleophilic addition/1,3-hydrogen transfer process in the presence of potassium hydroxide is described. This protocol offers access to 7-arylethyl-5-arylpyrazolopyrimidines in good to excellent yield. Meanwhile for 4-substituted dienones, different products, 7-arylethylene-5-arylpyrazolopyrimidines, are given through an aza-Michael addition/nucleophilic addition/oxidation process. A gram-scale reaction has been performed to demonstrate the potency of optimized procedure for the scale-up process.
Graphical AbstractSYNOPSIS7-Arylethyl-5-arylpyrazolopyrimidines were efficiently synthesized by the reactions of 4-unsubstituted dienones with pyrazole-3-amine. In contrast, 7-arylethylene-5-arylpyrazolopyrimidines could be afforded by the reactions of 4-substituted dienones with pyrazole-3-amine. .
[en] Investigation of redox reactions on silver, and bismuth doped silver electrodes in aqueous KOH solutions, by using potentiostatic steady-state polarization technique, has been carried out. The redox wave potential and current displacements along with multiplicity of the latter have been examined. These electrodes were employed for the oxidation of organic molecules such as ethylamine in alkaline media. Subsequently, these electrodes were ranked with respect to their activity for the redox reactions. (author)
[en] In clause the new method of synthesis of new connections 1,3 dihlopropan-2 with the rests is dipeptides given, at which the group is protected amines. The physics is determined by chemical methods structure of the received connection