Use of Ferric Chloride in Carbohydrate Reactions.1 Iv. Acetolysis of Benzyl Ethers of Sugars

Acetolysis of benzyl ethers of sugars has been carried out with anhydrous ferric chloride in acetic anhydride. By employing this reagent, benzyl ether groups variously placed in sugars or in their glycosides could be removed with ease and replaced by acetyl groups. By controlled acetolysis, preferential removal of certain benzyl groups was possible. The results show that in D-glucose the relative ease of removal of benzyl ether groups by acetolysis follows the order C-6 > C-4 > C-3 > C-2 and that the rate of acetolysis is 6-O-Bn : 3-O-Bn : 2-O-Bn = 125 : 24 : 1. The corresponding methyl ethers were very sluggish towards acetolysis.     

Synthetic Studies Toward Gangliosides and Their Analogs: Synthesis of Appropriately Protected Core Oligosaccharides as Construction Blocks

Abstract

2-(Trimethylsilyl)ethyl 2, 3, 6, 2′-tetra-O-acetyl-3′-O-benzyl-6′-O-benzyloxymethyl-β-d-lactoside (9) was synthesized starting from acetobromolactose (1) via 2-(trimethylsilyl)ethyl β-d-lactoside (3). Compound 9 was converted to the trisaccharide derivative 17 after coupling with 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-α-d-galacto-pyranosyl bromide (11). Coupling of 17 with acetobromogalactose (19) gave the tetrasaccharide 20.     

Slow and Fast Transport in Heap Leaching of Precious Metals

Heap leaching of precious metals from low-grade ores is modeled using the slow and fast zone concept of liquid movement in porous media (Kartha and Srivastava Transport in Porous Media 75, 227?C247, 2008). The heap is conceptualized as a porous medium with the pores filled by liquid and/or air. The liquid phase is further divided into three zones??immobile, slow moving, and fast moving, with only the immobile and slow-moving liquids interacting with the solid particles. The conceptual model is applied to simulate two- dimensional leaching of a shallow gold ore heap. Temporal evolution of gold concentration in the solid and the liquid phases are analyzed to ascertain the effect of several parameters on the leaching process. Sensitivity analyses are performed with respect to the irrigation rate, the equilibrium sorption coefficient, and the fractional volume of the slow-moving liquid. For a constant volume of the leaching solution and for the same duration of leaching, the metal extraction is higher when a larger number of irrigation cycles are used. The metal extraction is found to be smaller for higher values of the sorption coefficient.     

Crystal and molecular structure of α,α′-azobis[4-bromobenzaldehyde]bis (O-carboxyoxime)diethyl ester

Journal of Chemical Crystallography - The title compound is a dimer of chemical formula (C10H9BrN2O3)2 and yielded crystals of two forms, one monoclinic with space groupP21/a and the other...     

Chemical separation and electrothermal atomic-absorption spectrophotometric determination of Cd, Co, Cu and Ni in high-purity uranium

Summary An electrothermal atomic-absorption spectrophotometric method has been developed for the estimation of trace concentrations of Cd, Co, Cu and Ni in high-purity uranium after their chemical separation. The trace constituents from 100 mg of uranium sample in 3 M nitric acid solution were separated using 0.2 M di-n-octyl sulphoxide in xylene. The concentration of the analytes in the aqueous phase was determined by graphite furnace AAS. The detection limits were 0.001, 0.01, 0.025 and 0.05 ng for Cd, Co, Cu and Ni, respectively. The precision of the determinations was 7–14%. The effect on absorbances of the analytes due to the presence of Al, Ca, Fe, Mg, Pb, W and uranium was examined.

---

Chemische Abtrennung und elektrothermische AAS-Bestimmung von Cd, Co, Cu und Ni in hochreinem Uran

Zusammenfassung Die Spuren werden aus einer 100 mg Uranprobe in 3 M salpetersaurer Lösung durch Extraktion des U mit Hilfe von 0.2 M Di-n-octylsulfoxid im Xylol abgetrennt und werden anschließend in der wäßrigen Phase durch Graphitofen-AAS bestimmt. Die Nachweisgrenzen betragen 0,001 ng (Cd), 0,01 ng (Co), 0,025 ng (Cu) und 0,05 ng (Ni). Die Reproduzierbarkeit beträgt 7–14%. Der Einfluß von Al, Ca, Fe, Mg, Pb, W sowie Resturan auf die Absorption der analysierten Elemente wurde untersucht.

     

The vibrational and electronic spectra of 5-methyl pyrimidine and 4-methyl pyrimidine

The infrared and Raman spectra of 5-methyl pyrimidine and the infrared spectrum of 4-methyl pyrimidine have been examined and vibrational assignments are given for the ground electronic states. The ultra-violet absorption spectra of these molecules corresponding to π* ←n electronic excitation have been studied and vibrational assignments are given for most of the observed bands.     

N.M.R. and I.R. studies of 1, 1, 1 trifluoroacetone in proton donor solvents

Interactions of 1, 1, 1 trifluoroacetone with proton donor solvents of the type RH [where R=HO, CH₃S, CH₃CH₂CH₂CH₂S, CH₃O, (CH₃)₂N, (C₂H₅)₂N] have been investigated using NMR and infra-red techniques. Evidence of the formation of addition products of the type CF₃.C(OH)R.CH₃ where OH group is hydrogen-bonded with the fluorine of the CF₃ group has been obtained.