Influence of halogen substituents on the catalytic oxidation of 2,4,6-halogenated phenols by Fe(III)-tetrakis(p-hydroxyphenyl) porphyrins and potassium monopersulfate

The influence of halogen substituents on the catalytic oxidation of 2,4,6-trihalogenated phenols (TrXPs) by iron(III)-porphyrin/KHSO? catalytic systems was investigated. Iron(III)-5,10,15,20-tetrakis(p-hydroxyphenyl)porphyrin (FeTHP) and its supported variants were employed, where the supported catalysts were synthesized by introducing FeTHP into hydroquinone-derived humic acids via formaldehyde poly-condensation. F (TrFP), Cl (TrCP), Br (TrBP) and I (TrIP) were examined as halogen substituents for TrXPs. Although the supported catalysts significantly enhanced the degradation and dehalogenation of TrFP and TrCP, the oxidation of TrBP and TrIP was not enhanced, compared to the FeTHP catalytic system. These results indicate that the degree of oxidation of TrXPs is strongly dependent on the types of halogen substituent. The order of dehalogenation levels for halogen substituents in TrXPs was F > Cl > Br > I, consistent with their order of electronegativity. The electronegativity of a halogen substituent affects the nucleophilicity of the carbon to which it is attached. The levels of oxidation products in the reaction mixtures were analyzed by GC/MS after extraction with n-hexane. The most abundant dimer product from TrFP via 2,6-difluoroquinone is consistent with a scenario where TrXP, with a more electronegative halogen substituent, is readily oxidized, while less electronegative halogen substituents are oxidized less readily by iron(III)-porphyrin/KHSO? catalytic systems.     

A new class of chiral calix[4]arenes as receptors with planar chirality

The modification of title compounds to chiral receptors and their characterization are reported. The two synthetic methods were developed. The racemates obtained could be resolved to each stable enantiomer by a chiral HPLC column. Chiral calixarenes were designed as the receptors with planar chirality. The (−)-receptor strongly forms 1:1 complex with (R)-(+)--phenylethylammonium picrate.     

Zirconia based oxide ion conductors for solid oxide fuel cells

The electrical conductivity in the ZrO₂-Ln₂O₃ and ZrO₂-MO₂-Ln₂O₃(M = Hf, Ce, Ln = lanthanides) systems has been examined.The highest conductivity of 0.3 S/cm at 1000 °C was found in the ZrO₂-Sc₂O₃ system. The addition of MO₂ into the ZrO₂-Ln₂O₃(Ln = Sc, Y, Yb) systems showed the conductivity decreasing. The conduction mechanism in the zirconia based oxide ion conductors was discussed in view of the dopant ionic radius. The aging effect of the conductivity in the ZrO₂-Ln₂O₃ systems has been measured in a temperature rang 800–1000 °C. ZrO₂ with a high content of Ln₂O₃ showed no significant conductivity degradation. Paper presented at the 97th Xiangshan Science Conference on New Solid State Fuel Cells, Xiangshan, Beijing, China, June 14–17, 1998.     

13C nmr study of α- and β-anomeric pairs of d-mannopyranosides and l-rhamnopyranosides

¹³C NMR spectra for a variety of α and β-anomeric series of d-mannopyranosides and l-rhamnopyranosides are presented and analyzed in comparison with those of D-glucopyranosides. The results obtained in the present study are valuable for the structure studies of plant-glycosides as well as carbohydrates, especially for determination of anomeric configurations of mannosides and rhamnosides which has been extremely difficult by other classical techniques.     

Modifizierung von anionischen Austauschmembranen mit Polystyrolsulfonsliure

Ohne Zusammenfassung     

Synthesis, modification, and optical properties of C3-ethynylated chlorophyll derivatives

3-Ethynyl-chlorin was prepared from methyl pyropheophorbide-d using Bestmann-Ohira reagent. The mono-substituted acetylene was subjected to copper-free, Pd-mediated coupling to form chlorin derivatives possessing a series of substituted ethynyl groups at the C3-position. Its 1,3-dipolar cycloadditions with azido compounds were also demonstrated.     

One-pot synthesis of 3-fluoro-4-(trifluoromethyl)quinolines from pentafluoropropen-2-ol and their molecular modification

Pentafluoropropen-2-ol (PFP) was prepared by the reaction of hexafluoroacetone (HFA) with Mg/TMSCl. The one-pot tandem sequential reactions of PFP via Mannich addition with aldimines followed by Friedel-Crafts cyclization and aromatization afforded the title quinolines. A variety of corresponding 3-substituted quinolines were derived from the title quinoline by nucleophilic substitution of 3-fluorine with nucleophiles. A defluorinative transformation of the 4-trifluoromethyl group of the title quinoline with hydrazine afforded pyrazoloquinoline.