Synthesis of diisocyanides with phenolic groups and their polymerization to helically chiral poly(quinoxaline‐2,3‐diyl)s

The development of synthetic routes which lead to five new diisocyanide monomers with one or two phenolic groups is described. Their polymerization behavior is studied with Pd‐ and Ni‐based initiators, as well as under microwave irradiation. The polymerizability is mainly dominated by steric effects as is concluded from experiments using different protecting groups. Chiroptical properties of these new polymers are studied by CD‐spectroscopy. After deprotection, helically chiral poly(quinoxalin‐2,3‐diyl)s are obtained which display a Brønsted function attached to a stereolabile biaryl axis whose configuration should be influenced by the chiral polymer backbone. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1320–1329     

Versuche zur Totalsynthese von Brefeldin A

Preliminary results leading towards the total synthesis of Brefeldin A are presented.     

Beiträge zur Chemie des Phosphors. 203 [1].(t- BuSi)4P3Cl3, das erste Silaphosphan mit Norcuban-Struktur

Contributions to the Chemistry of Phosphorus. 203. (t-BuSi)₄P₃Cl₃ – The First Silaphosphane with a Structure Analogous to Norcubane The reaction of t-BuSiCl₃ with LiAl(PH₂)₄ yields the compound (t-BuSi)₄P₃Cl₃ ( 1 ), which has been isolated in pure form. According to NMR spectroscopic investigations and an X-ray single-crystal analysis, 1 is 2,4,6,7-tetra-tert-butyl-2,4,7-trichloro-1,3,5-triphospha-2,4,6,7-tetrasilatricyclo[3.1.1.0^3,6]heptane and thus the first silaphosphane with a structure analogous to norcubane. The compound crystallizes monoclinically in the space group P2₁/n with a = 1102.1 pm, b = 1609.2 pm, c = 1612.8 pm, β = 90.90° and Z = 4. The main structural feature is a cube alternately composed of Si and P, from which one phosphorus atom has been removed. The Si atoms are each substituted by t-Bu groups, the three adjacent to the missing corner additionally by Cl atoms.     

Der Gaskomplex MnAlF5 und sein Einfluß auf die sublimative Reinigung von AlF3

The Gas Complex MnAlF₅ and its Influence on the Purification of AlF₃ by Sublimation The gas complex MnAlF₅ has been determined mass spectroscopically by the ions MnAlF₅⁺ and MnAlF₄⁺. The gas complex MnAlF₅ is formed above 973 K by heating up mixtures of AlF₃/MnF₂ or AlF₃ · 3 H₂O endowed with Mn²⁺ or by heating up solid MnAlF₅ too. At 1 008 K the enthalpie of dissociation is 197 kJ/mole. The equilibrium structures of the high spin molecule MnAlF₅ (S = 5/2) were examined with ab initio calculations at the HF-level by comlete gradient optimizing. Two minimum structures were found on the potential energy surface. A bidentate fluorine bridged structure was found to be the most stable at the HF-level. Vibrational frequencies and thermodynamic functions of complex formation were estimated for both minimum structures. The importance of the formation of the gas complex for the separation of MnF₂ and AlF₃ by sublimation is discussed.     

Chronocoulometric study of the electrochemistry of Prussian blue

During the electrochemical oxidation of Prussian blue (PB) to Prussian yellow (PY), an electrocatalytic oxygen production proceeds at the electrode when aqueous electrolyte solutions are used. The formed oxygen is scavenged by the PY, probably by absorption, and it is consumed during the electrochemical reduction of PY to PB by a heterogeneous chemical reaction of PB with oxygen to PY and hydrogen peroxide. Because of this catalytic regeneration of PY, it is impossible to determine the amount of low-spin iron by chronocoulometry using a potential program in which PB is first oxidized to PY and then the charge is measured to reduce PY to PB. The latter charge is biased by the electrocatalytic PY regeneration.     

Sulfide ion electrooxidation catalysed by cobalt phthalocyanine microcrystals

Electrooxidation of sulfide ion catalysed by microcrystals of cobalt phthalocyanine was investigated by cyclic voltammetry in 0.5M KNO₃ at pH 9.22. Traces of catalyst were immobilized at the surface of a paraffin-impregnated graphite electrode by the mechanical transfer of its powder. The electro-oxidation of HS^– proceeds in two irreversible steps, with the first peak between 0 V and –0.12 V and the second at 0.17 V. The first step is second order in HS^– and its product is the adsorbed disulfide, which may further dissociate to give adsorbed sulfur atoms. The reduction of sulfur occurs at –0.1 V.