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91.
A recent graphite-furnace atomic-absorption method for determining approximately 0.2 mug/g or more of arsenic in ores, concentrates, rocks, soils and sediments, after separation from matrix elements by cyclohexane extraction of arsenic(III) xanthate from approximately 8-10M hydrochloric acid, has been modified to include an alternative hydride-generation atomic-absorption finish. After the extract has been washed with 10M hydrochloric acid-2% thiourea solution to remove co-extracted copper and residual iron, arsenic(III) in the extract is oxidized to arsenic(V) with bromine solution in carbon tetrachloride and stripped into water. Following the removal of bromine by evaporation of the solution, arsenic is reduced to arsenic(III) with potassium iodide in approximately 4M hydrochloric acid and ultimately determined to hydride-generation atomic-absorption spectrometry at 193.7 nm, with sodium borohydride as reductant. Interference from gold, platinum and palladium, which are partly co-extracted as xanthates under the proposed conditions, is eliminated by complexing them with thiosemicarbazide before the iodide reduction step. The detection limits for ores and related materials is approximately 0.1 mug of arsenic per g. Results obtained by this method are compared with those obtained previously by the graphite-furnace method. 相似文献
92.
A synthesis of the C9-C16 segment of ambruticin is described which relies on organoiron methodology to establish the 1,2,3-trisubstituted cyclopropane ring. 相似文献
93.
Donaldson EM 《Talanta》1979,26(12):1119-1123
Two simple, reliable and moderately rapid atomic-absorption methods for determining trace and minor amounts of bismuth in copper, nickel, molybdenum, lead and zinc concentrates and ores, and in non-ferrous alloys, are described. These methods involve the separation of bismuth from matrix elements either by chloroform extraction of its diethyldithiocarbamate (DDTC) complex, at pH 11.5–12.0, from a sodium hydroxide medium containing citric acid, tartaric acid, EDTA and potassium cyanide as complexing agents, or by co-precipitation with hydrous ferric oxide from an ammoniacal medium. Bismuth is ultimately determined, at 223.1 nm after evaporation of the extract to dryness in the presence of nitric and petchloric acids and dissolution of the salts in 20% v/v hydrochloric acid, or by dissolution of the hydrous oxide precipitate with the same acid solution, respectively. Results obtained by both methods are compared with those obtained spectrophotometrically by the iodide method after the separation of bismuth by DDTC and xanthate extractions. 相似文献
94.
The performance of an approximate method for determining inventory replenishment quantities for the case of variable demand is examined using a method of exact analysis. Increasing and decreasing linear trends in demand are considered, the former yielding satisfactory—the latter questionable, performance. 相似文献
95.
96.
Nicolas Duguet Adele Donaldson Stuart M. Leckie Eddy A. Kallström Craig D. Campbell Peter Shapland Thomas B. Brown Alexandra M.Z. Slawin Andrew D. Smith 《Tetrahedron: Asymmetry》2010,21(5):601-616
The synthesis of a range of imidazolinium salts derived from acyclic 1,2-diamines, and an evaluation of the reactivity and asymmetric induction of the corresponding NHCs as catalysts for the asymmetric synthesis of β-lactams, is reported. An N-methyl-substituted NHC derived from (1R,2R)-1,2-diphenylethanediamine shows optimal reactivity and enantioselectivity in this series, in contrast to that observed with NHCs derived from (1R,2R)-cyclohexane-1,2-diamine. 相似文献
97.
In this work, a biomass processing facility is designed and simulated for the annual conversion of 77?ktons of sunflower residue into electricity and activated carbon. The residue is initially pyrolized to produce low hydrocarbon gases (35?wt%), bio-oils (30?wt%), and char (35?wt%). The gases and bio-oils are separated and combusted to generate high pressure steam, electricity, and steam for conversion of char into activated carbon. Assuming 35% of the char's mass is lost during activation, the proposed process produces 15.6?ktons activated carbon and 5.5?ktons ash annually, while generating 10.2?MW of electricity. Economic analysis of the proposed facility yielded capital costs of $31.64 million, annual operating costs of $31.58 million, and a yearly gross revenue of $38.9 million. A discounted payback period of 6.1?years was determined for the current design, extending to 10?years if the facility were operated at 75% capacity. While the proposed process appears to be economically viable, profitability is highly sensitive to the selling price of electricity and activated carbon, highlighting the need for additional research into the pyrolysis reactor design, char/ash separation techniques, and the quality of activated carbon obtained using char from sunflower residue pyrolysis. 相似文献
98.
El-Mansy MF Sar A Chaudhury S Wallock NJ Donaldson WA 《Organic & biomolecular chemistry》2012,10(25):4844-4846
Transformation of the simple hydrocarbon cyclooctatetraene into a variety of polycyclic skeletons was achieved by sequential coordination to iron, reaction with electrophiles followed by allylated nucleophiles, decomplexation and olefin metathesis. 相似文献
99.
In situ Synchrotron IR Microspectroscopy of CO2 Adsorption on Single Crystals of the Functionalized MOF Sc2(BDC‐NH2)3
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Dr. Alex Greenaway Berenice Gonzalez‐Santiago Dr. Paul M. Donaldson Dr. Mark D. Frogley Dr. Gianfelice Cinque Jorge Sotelo Dr. Stephen Moggach Elenica Shiko Prof. Stefano Brandani Prof. Russell F. Howe Prof. Paul A. Wright 《Angewandte Chemie (International ed. in English)》2014,53(49):13483-13487
Synchrotron radiation (SR) IR microspectroscopy has enabled determination of the thermodynamics, kinetics, and molecular orientation of CO2 adsorbed in single microcrystals of a functionalized metal–organic framework (MOF) under conditions relevant to carbon capture from flue gases. Single crystals of the small‐pore MOF, Sc2(BDC‐NH2)3, (BDC‐NH2=2‐amino‐1,4‐benzenedicarboxylate), with well‐defined crystal form have been investigated during CO2 uptake at partial pressures of 0.025‐0.2 bar at 298–373 K. The enthalpy and diffusivity of adsorption determined from individual single crystals are consistent with values obtained from measurements on bulk samples. The brilliant SR IR source permits rapid collection of polarized spectra. Strong variations in absorbance of the symmetric stretch of the NH2 groups of the MOF and the asymmetric stretch of the adsorbed CO2 at different orientations of the crystals relative to the polarized IR light show that CO2 molecules align along channels in the MOF. 相似文献
100.
Cyclopropenes possess very high strain energies1 and their organic and organometallic chemistry has been widely studied. They are reactive dienophiles in the Diels-Alder reaction,2 and they undergo ring opening reactions under vigorous photochemical3 and thermal4 conditions.5 Transition metal promoted ring opening reactions of cyclopropenes occur under very mild conditions,6 and have also been the subject of a theoretical study.7 相似文献