Trimethylsilylverbindungen der Vb-Elemente. VI. Synthese,Molekül- und Kristallstruktur des Tetrakis(trimethylsilyl)distibans im Vergleich mit Tetraphenyldistiban

Trimethylsilyl Derivatives of Vb-Elements. VI. Synthesis, Molecular and Crystal Structure of Tetrakis(trimethylsilyl)distibine Compared with Tetraphenyldistibine Tetrakis(trimethylsilyl)distibine already isolated by Breunig et al. [9] from cleavage reactions of tris(trimethylsilyl)stibine may also be obtained in high yields from lithium bis(trimethylsilyl)antimonide · 2THF and 1,2-dibromoethane in n-pentane. This compound intensely red in the solid state, but only slightly yellow in solution or in the melt crystallizes in the monoclinic space group P2₁/c with a = 680.6(1); b = 1672.8(2); c = 1190.0(1) pm; β = 119.01(5)°; Z = 2 at +20°C. An X-ray structure determination (R = 0.017) shows the bis(trimethylsilyl)-stibino groups to be arranged in a transoid position. Characteristic bond lengths and angles are: Sb? Sb 286.7(1); Sb? Si 259.4 pm; Si? Sb? Si 94.46(3); Sb? Sb? Si 98.68(3) and 94.43(3)°. As in similiar 2,2′,5,5′-tetramethyldistibolyl published recently by Ashe III et al. [8] this crystal structure, too, is characterized by a nearly linear sequence of Sb? Sb groups. Compared with the sum of van-der-Waals radii the intermolecular Sb-Sb contact in such a chain is shortened from 440 to 399 pm. This probably allows electronic interactions of unknown type responsible for the colour of the crystals. In keeping with this assumption an analogous formation of chains is not found in solid, only yellow tetraphenyldistibine 5 the structure of which has already been studied by Rehder et al. [44].     

Neutron activation analysis of high purity Selenium: Determination of Bromine

Neutron activation analysis for 2–0.8 p.p.m. bromine in selenium was performed by irradiating i-g samples for 2 h at a neutron flux of 4.10¹¹ n/cm²/sec. The bromine was separated by a double precipitation technique as silver bromide to obtain adequate decontamination and the isotope ⁸²Br (T_{$\text{1}\text{2}$}=35.87 h) measured. Errors due to self-shielding in the standards and flux-depression in the selenium were calculated. Measurements on 2 different photopeaks were made to avoid errors from interfering isotopes.     

Liquid chromatographic and mass spectral analysis of 1-(3,4-methylenedioxyphenyl)-3-butanamines, homologues of 3,4-methylenedioxyamphetamines

The 1-(3,4-methylenedioxyphenyl)-3-butanamines (HMDAs) are prepared via reductive amination of the corresponding ketone with a series of low molecular weight alkylamines. These amines are homologues of the N-substituted 3,4-methylenedioxyamphetamines (MDAs). Compounds of the HMDA series have UV absorption properties similar to the MDAs because both series contain the same 3,4-methylenedioxyphenyl chromophore. The HMDAs are separated via reversed-phase liquid chromatographic methods using a C18 stationary phase and an acidic aqueous acetonitrile mobile phase. The mass spectra of these potential designer drugs are very similar to the spectra of the MDA homologues having the same N-substituent.     

Radiochemical studies of some separation methods for phosphorus

Various methods of radiochemical separation were tested for the determination of phosphorus in metals and alloys by neutron activation analysis. Classical methods of separation revealed some defects when they were applied to this problem. Methods using liquid extraction gave low yields and were not reproducible. Methods based on precipitation gave better results, but were not selective enough in most of the cases. Retention on alumina was not possible without preliminary separations We studied a new radiochemical separation based on the extraction of elemental phosphorus in the gaseous phase after reduction at high temperature with carbon. Measurements with radioactive phosphorus showed that the extraction yield is better than 99%.     

The stereochemistry of bicyclo[3.2.1]-octane—XII The photohalogenation of bicyclo[3.2.1]octene-2 derivatives

The light-initiated halogenation of bicyclo[3.2.1]octene-2, its 3-phenyl and 3-bromo derivatives with N-bromosuccinimide and t-butyl hypochlorite resulted in the exclusive formation of the exo-4-halobicyclo[3.2.1]octene-2-derivatives.     

Biomimetic chemistry of xylomollin

Kingiside aglucon ($\text{2}$$\text{b}$) undergoes stereoselective addition of CH₃OH to its C(3,4) enol ether double bond to give a C(1,3,9) diastereomer of xylomollin ($\text{1}$), a secoiridoid aglucon that has insect antifeedant properties.     

Instrumental neutron activation analysis of Elbe river suspended particulate matter separated according to the settling velocities

Suspended particulate matter in Elbe river water near Hamburg has been separated into different fractions by pouring the samples into special sedimentation tubes called Atterberg cylinders. The fractions are obtained by decanting the water after different settling periods, and by filtrating the decanted part. The analysis is done by neutron activation in the absolute mode, after irradiation periods of 5 min and 3 days. Mean settling velocities of the SPM-mass and the elements determined have been calculated.