Effect of the mobile phase composition on the retention behaviour of diphenylsilica pre-coated plates

The retention of some rifamycins and steroids on diphenyl bonded pre-coated silica gel plates, in relation to the mobile phase used, was examined by thin-layer chromatography. Neat organic solvents, non-aqueous and aqueous binary mixtures were tested as eluents. By comparison of retention data for rifamycins and steroids, respectively, under non-aqueous and aqueous conditions, a dual retention mechanism on this diphenyl phase was found. Interactions with the residual silanol groups seemed to prevail when employing as mobile phase the more lipophilic solvents tested, such as chloroform or dichloromethane, whereas interactions with the aryl groups of the bonded phase prevailed when using high polarity alcohols or aqueous mixtures. As a consequence, by changing the mobile phase, a large variation in selectivity with a concomitant change in retention order of the test compounds was observed.     

Fragmentation of the unsubstituted carbohydrate units of cardenolide monosides

In the mass spectra of unsubstituted monosides of cardenolide nature are observed the M⁺ peaks, and also, in each case, three characteristic processes of the fragmentation of the carbohydrate unit. The formation of the ions AglOCH=OH⁺ is the most universal property of these compounds. The stability of ions of the type under consideration depends on the nature and position of attachment of the sugar residue and on the number of polar groups in the aglycone. The laws of the fragmentation of the carbohydrate unit are extended to the spectra of glycosides of other classes.Deceased.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodynykh Soedinenii, No. 3, pp. 345–354, 1983.     

Synthesis and transformations of 4-hydroxy-5-methyl-2-trifluoromethylpyridine

4-Hydroxy-5-methyl-2-trifluoromethylpyridine was synthesized from 3-hydroxy-3-methyl-6-trifluoromethyl-2,3-dihydro-4H-pyran-4-one. Its methylation leads to the formation of a mixture of N- and O-alkylation products, which were isolated chromatographically in the pure state. Convenient methods of their preparation are proposed.Belorussian State University, Minsk 220050. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 780–784, June, 1998.     

Synthesis and structure of complex compound Rh(III) of (NH4)2[Rh(NO2)3(NH3)(µ-OH)]2 composition

The crystalline structure of a new compound Rh(III) of (NH₄)₂[Rh(NO₂)₃(NH₃)(μ-OH)]₂ composition has been determined. The crystallographic characteristics are H₁₆N₁₀O₁₄Rh₂: a = 6.3963(2) Å, b = 9.3701(4) Å, c = 13.6646(5) Å, β = 102.266(1)°, V = 800.28(5) ų, Z = 2, d _calc = 2.432 g/cm³. The distance Rh...Rh in the dimer is 3.200 Å. Original Russian Text Copyright ? 2006 by S. P. Khranenko, I. A. Baidina, and S. A. Gromilov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 47, No. 2, pp. 380–384, March–April, 2006.     

Sodium aluminum hydride reduction of organic compounds in hydrocarbon media

Summary The reduction of complex esters and carbonyl compounds in hydrocarbon media by aluminum hydrides of the alkali metals results in the formation of the corresponding alcohol in high yield. The reduction of nitriles proceeds with the formation of primary amines.     

Liquid-phase oxidation of tert-butyldimethylsilane

Kinetics and mechanism of liquid-phase oxidation of tert-butyldimethylsilane t-BuMe₂SiH with molecular oxygen in the temperature range 297–350K were studied. Reaction orders in silane, initiator, and oxygen were evaluated. The major product of the oxidation of t-BuMe₂SiH is tert-butyldimethylsilyl hydroperoxide t-BuMe₂SiOOH. It was shown for the first time that the major reaction product is a silyl hydroperoxide. A kinetic scheme of the oxidation of t-BuMe₂SiH is offered and discussed.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 10, 2004, pp. 1625–1630.Original Russian Text Copyright © 2004 by Lutsik-Maksim, Timokhin, Zaborovskii, Pristanskii, Turovskii, Chatgilialoglu.This revised version was published online in April 2005 with a corrected cover date.     

Configurational bias Monte Carlo simulation of phase segregation in block copolymer networks

Cross-linked block copolymers are used as adhesives in fiber-reinforced composite material manufactures for automotive applications. Good adhesion between the polymer matrix and fibers in the interphase region is required for the structural integrity of these materials. Experimental evidence indicates that superior adhesion is obtained when phase segregation occurs between the two matrix phase block copolymers. It is therefore desirable to predict the conditions under which phase segregation is expected to occur. Configurational bias Monte Carlo simulations of two-component, trifunctional block copolymer networks were carried out to investigate phase segregation in these materials. The effects of four principal parameters on phase segregation were examined: the weight fractions of the two components, the cross-link length, the connectivity of the network, and the ratio of the square-well interactions. The molecular simulation results confirmed trends observed in laboratory measurements.     

Reactions of O2 --Containing Supramolecules with Alkyl Halides

Formation of O₂ ^--containing supramolecules generated from the system 18-crown-6-KO₂ and electrochemically (tetraethylammonium superoxide) and the kinetics of the reactions of the generated O₂ ^- with alkyl halides in acetonitrile were studied conductometrically and UV-spectrophotometrically; the kinetic parameters of the processes were determined. The E2 mechanism was suggested for the reaction.     

New method of preparing β-lactams

Summary A method has been devised for the synthesis of -lacrams from amides of -ha!ocarboxylic acids. Some new azetidinones with residues containing carboxyl groups on the nitrogen have been piepated. The method permits the conversion of $-amino acids trio difficulty accessible mixed (secondary) amino acids.This paper is publised under the regulations governing Brief Communications.     

Synthesis and modification of 4-hydroxy-2-methyl-3-(2-chloro-2-propenyl)quinoline

4-Hydroxy-2-methyl-3-(2-chloro-2-propenyl)quinoline was prepared by O-allylation of 4-hydroxy-2-methylquinoline followed by the Claisen rearrangement of the 2-methyl-4-(2-chloro-2-propenyloxy)quinoline obtained. Chemical modifications of 4-hydroxy-2-methyl-3-(2-chloro-2-propenyl)quinoline resulted in the synthesis of 4-amino-2-methyl-3-(2-methyl-3-indolyl)quinoline.