Beiträge zur quantitativen Dünnschichtchromatographie. V

Zusammenfassung Eine dünnschichtchromatographische Trennung des Wismuts von einem Überschuß an Metallen der Schwefelwasserstoffgruppe wurde beschrieben. Als Laufmittel dient ein Gemisch von tert.-Butanol, Salzsäure und Wasser. Nach Absaugen der Sorptionsschicht wird das Wismut mit MDCM spektralphotometrisch bestimmt. Standardabweichung und Varianz des Verfahrens werden angegeben.

---

Summary A thin layer Chromatographic separation of the bismuth from an excess of metal ions of the hydrogen sulfide group is described. A mixture of tert. butanol, hydrochloric acid and water serves as mobile phase. After sucking off the sorption layer, the bismuth is determined spectrophotometrically with MDCM. The standard deviation and the variance of the procedure is given.

---

Résumé On décrit une séparation par Chromatographie en couche mince du bismuth de métaux en excès du groupe de l'hydrogène sulfuré. On utilise comme éluant un mélange de butanol tert., d'acide chlorhydrique et d'eau. Après aspiration de la couche de sorption, on dose par spectrophotométrie le bismuth par le MDCM. On communique l'écart-type et le coefficient de variation du procédé.

     

Influence of mobility of medium on dynamics of metallotropy in tin-containing 2-R-oxyphenoxyls

The rate of intramolecular migration of the triphenylstannyl group in 3,6-ditert-butyl-2(triphenylstannyl) oxyphenoxyl decreases with increasing viscosity of the medium. A linear relationship _ex=·_c is observed between the characteristic time of stannotropy _ex and the correlation time for reorientational motions of the radical _c within a range of temperature variation no greater than 30°C. The parameter depends on the medium; this is explained by the possibility of complexation of the radical with the solvent.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 781–786, April, 1990.     

Untersuchungen an oxidischen Katalysatoren. XXIX. Spektroskopische und katalytische Untersuchungen an Ni2+-, Co2+-, Cr3+- und Cu2+-ausgetauschten Mordeniten

Studies on Oxide Catalysts. XXIX. Spectroscopic and Catalytic Investigations on Ni²⁺-, Co²⁺-, Cr³⁺-, and Cu²⁺-exchanged Mordenites NiNaM, CoNaM, CrNaM und CuNaM (M = Mordenite) have been characterized by UV-VIS, EPR and i.r. spectroscopy and the results were compared with the catalytic activity and the activity-time-dependence in the cracking of n-octane and with the shape selectivity in the cracking of a n-octane and isooctane mixture. Water molecules acting as ligands of the exchanged cations are able to dissociate yielding Brönsted acidity. Brönsted sites may be regarded as catalytic active centers in the cracking reaction. Unreduced transition metal cations facilitate the “coking” of the mordenite. The unreduced chromium and cobalt cations for which a position within the main channel is expected, affect the diffusion of the branched paraffin molecule thus increasing shape selectivity.     

Gibberellin metabolites from ent-kaura-2,16-dien-19-ol and its succinate in Gibberella fujikuroi

Exposure of ent-kaura-2,16-dien-19-ol (1) or its succinate (2) to resuspended mycelia of G. fujikuroi has produced a complex mixture of acids which after methylation gave the esters of two C₁₉ (24) and (30) and five C₂₀ gibberellins (4, 11, 20, 32 and 33). The triester (32) and the lactone ester (24) have been prepared before from the esters of gibberellin A₁₃ (8) and gibberellin A₄ (26) respectively. The structures of the other metabolites were assigned on spectroscopic data and by chemical transformations. Thus the lactone diester (4) has been converted to the known keto triester (6). The epoxide (11) has been related to gibberellin A₁₄ (14) and the aldehyde (33) has been related to gibberellin A₁₃ trimethyl ester (8) by way of the triol (34). Selective de-epoxidation of the 16,17-epoxy function in diepoxides has provided a route from the dienes (20 and 24) to the epoxides (11 and 30) respectively, but not from the ester of gibberellin A₅ (23) to that of gibberellin A₆ (29). On the other hand the latter can be obtained by epoxidation of gibberellin A₅ methyl ester trifluoroacetate. Backfeeding experiments carried out with the epoxy diacid (12), the diene diacid (21) and the derived diol (39) indicate pathways connecting the various metabolites. The natural gibberellins A₅ and A₆ were shown to be formed in some of the backfeeding experiments.     

Zur Bestimmung von β-Aminocrotonsäureester nach Migration in Lebensmittel

β-Aminocrotonic esters are of great importance as stabilizers for the production of clearly transparent food packaging of PVC. For the purpose of studying the migration into foods a thin-layer Chromatographic and a polarographic method were elaborated. The TLC method consists of the visual comparison of the intensity of the spots after treatment with Fast Blue B salt. The polarographic determination is carried out after nitrosation of the stabilizer. By the TLC method 10^?7 g of ester per spot are still detectable; the concentration which is still determinable by cathode-ray polarography is 5×10^?7 g of ester and by conventional d.c. polarography 5×10^?6g of ester per ml of final solution. After extraction with acetonitrile traces of the stabilizer which are migrated into edible oil are still determinable down to 2 ppm by the methods described.     

Determination of the position of the acyl groups and the nature of some amino alcohols in native ester alkaloids of the genusVeratrum

Conclusions 1. On the basis of literature data on the structure of theVeratrum alkaloids, a definite law for the arrangement of the acyl radicals in these ester alkaloids and an interrelationship between the melting point and the structure of the substituent in the C₇ position, and between the melting point and the types of amino alcohols upon which the ester alkaloids are based, has been found.2. The features mentioned may be used in studying the structure of theVeratrum ester alkaloids according to a scheme which we propose.Khimiya Prirodnykh Soedinenii, Vol. 6, No. 4, pp. 440–443, 1970     

A hydrodynamic voltammetric study of the ferricyanide/ferrocyanide system with convective electrodes of platinum,gold, glassy carbon,carbon film,and boron carbide

Hydrodynamic voltammetry employing empirically determined mass transport coefficients is used to determine heterogeneous rate constants and transport coefficients for the ferricyanide/ferrocyanide system in 0.1 M phosphate buffer and other supporting electrolytes with turbulent tubular and rotated disk electrodes of platinum, gold, glassy carbon, carbon film, and boron carbide. Different kinetic parameters are obtained at the various electrode materials. For the platinum, gold, and boron carbide electrodes, the magnitudes of the rate parameters depend on scan direction. The nature of this hysteresis varies with the electrode material and is explained in terms of adsorbed oxide and ionic layers or other phenomena not described by simple double layer theory.     

Retention of85Sr and147Pm on insoluble hydroxides and phosphates prepared by the sol-gel procedure

Retention of strontium and promethium on hydroxides (hydrated oxides) and phosphates of iron and chromium prepared by the sol-gel method was studied. The sorption was determined under static conditions depending on the pH of the solution. The sorption isotherms and retention were investigated under dynamic conditions.