Tuning the metal-adsorbate chemical bond through the ligand effect on platinum subsurface alloys

Scratching beneath the surface: Pt-M(3d)-Pt(111) (M(3d) = Co, Ni) bimetallic subsurface alloys have been designed to show the ligand effect tunes reactivity in oxygen and hydrogen adsorption systems. The platinum-oxygen bond order was investigated by oxygen atom projection in the occupied and unoccupied space using X-ray emission spectroscopy (XES) and X-ray absorption spectroscopy (XAS).     

CO2 Capture technologies: Current status and new directions using supported ionic liquid phase (SILP) absorbers

Current state-of-the-art techniques for CO2 capture are presented and discussed. Post-combustion capture of CO2 by absorption is the technology most easily retrofitted to existing installations, but at present this is not economically viable to install and run. Using ionic liquids instead of aqueous amine solutions overcomes the major thermodynamic issues. By applying SILP technology further advances, in terms of ease of handling and sorption dynamics, are obtained. Initial experimental studies showed that ionic liquids such as tetrahexylammonium prolinate, [N6666][Pro], provide a good candidate for CO2 absorption using SILP technology. Thus a solid SILP absorber comprised of 40 wt% [N6666][Pro] loaded on precalcined silica quantitatively takes up about 1.2 mole CO2 per mole of ionic liquid in consecutive absorption-desorption cycles in a flow-experiment performed with 0.09 bar of CO2 (9% CO2 in He).     

Heterocyclization of compounds containing diazo and cyano groups. 6. Theoretical and experimental investigations of cyclization of 2-cyano-2-diazoacetamides to 5-hydroxy-1,2,3-triazole-4-carbonitriles

A series of N-alkyl- and N-aryl-2-cyano-2-diazoacetamides was synthesized by the reaction of 2-amino-2-cyanoacetamides with sodium nitrite in hydrochloric acid. The mechanism of their heteroclectrocyclization to 5-hydroxy-1,2,3-triazoles was investigated kinetically and theoretically by the B3LYP/6-31+G^* method. The conclusion was made on the basis of the determined activation energy of the cyclization process. reaction parameters , and kinetic isotope effects, that there is a difference between the mechanisms of cyclization of the N-alkyl and N-aryl derivatives of 2-cyano-2-diazoacetamide; cyclization of the N-alkyl derivatives takes place by a monorotatory mechanism, while cyclization of the N-aryl derivatives takes place by a mechanism where one of the stages is heteroelectrocyclization of 2-diazoacetimidates.For Communication 5, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 26–41, January, 2000.     

Dimethylformamide as a carbon monoxide source in fast palladium-catalyzed aminocarbonylations of aryl bromides

Dimethylformamide (DMF) acts as an efficient source of carbon monoxide and dimethylamine in the palladium-catalyzed aminocarbonylation (Heck carbonylation) of p-tolyl bromide to provide the dimethylamide. Addition of amines to the reaction mixture in excess delivers the corresponding aryl amides in good yields. The amines employed, benzylamine, morpholine, and aniline, all constitute good reaction partners. The reaction proceeds smoothly with bromobenzene and more electron-rich aryl bromides, but electron-deficient aryl bromides fail to undergo aminocarbonylation. The reactions are conducted at 180-190 degrees C for 15-20 min with microwave heating in a reaction mixture containing imidazole and potassium tert-butoxide: the latter is required to promote decomposition of the DMF solvent at a suitable rate. The beneficial effects of controlled microwave irradiation as an energy source for the rapid heating of the carbonylation reaction mixture are demonstrated. The carbonylation procedure reported herein, which relies on the in situ generation of carbon monoxide, serves as a convenient alternative to other carbonylation methods and is particularly applicable to small-scale reactions where short reaction times are desired and the direct use of carbon monoxide gas is impractical.     

Dynamic microwave-assisted extraction coupled on-line with solid-phase extraction: determination of polycyclic aromatic hydrocarbons in sediment and soil

This paper describes a new extraction tool for the determination of polycyclic aromatic hydrocarbons (PAHs) in soil and sediment samples, using dynamic microwave-assisted extraction combined with solid-phase extraction (DMAE-SPE). The critical variables for DMAE-SPE are investigated and optimized in an experimental design. The technique proved to be fast, accurate and able to yield quantitative extraction of PAHs from naturally contaminated sediment and soil samples. The set-up is fully automated and features monitored extraction, which facilitates rapid optimization of the method. In addition, only small quantities of solvent and sample are required.     

Synthesis of a 56 component library of sugar beta-peptides

Many biological processes of vital importance are triggered by the molecular recognition of small carbohydrate units by proteins and receptors thus leading to the belief that carbohydrates could act as candidates for the design of new drugs. We have developed a new useful synthetic approach, which can be applied in a combinatorial manner, giving access to 1,1-di-substituted pyrans projecting amide side chains in both the alpha- and beta-directions. Thus, treatment of the readily accessible hemiketal (1) with TFA followed by trimethylsilyl trifluoromethanesulfonate (TMSOTf) in the presence of a nitrile gives dihydrooxazinones (2) via a new type of modified intramolecular Ritter reaction. The dihydrooxazinones (2) can either be isolated or used directly in reactions with a broad variety of amines. Final deprotection furnishes the 1,1-di-substituted sugar beta-peptides having the general structure (4).