Mitteilungen aus dem Institut für Radiumforschung

Zusammenfassung Es wurde mit Hilfe des schon früher beschriebenen Quarzapparates Thoriumbromid aus reinem Thoroxyd dargestellt, das nach zwei verschiedenen Methoden gereinigt war und auf Grund spektroskopischer Untersuchung als absolut rein und frei von seltenen Erden angesehen werden mu\te.Das geschmolzene Thorbromid wurde nach zwei Methoden analysiert und dabei die beiden VerhÄltnisse ThBr₄4 Ag und ThBr₄4 AgBr bestimmt.Zwei unabhÄngige Serien von 12, respektive 15 Analysen gaben die folgenden Resultate:Serie I. 54·45867g Thorbromid verbrauchten 42·58666g Silber und gaben 74·13448g Silberbromid, entsprechend einem Atomgewicht des Thoriums Th=232·15±0·016.Serie II. 74·30630g Thorbromid verbrauchten 58·11096g Silber und gaben 101·15848g Silberbromid, woraus sich das Atomgewicht Th=232·12±0·014 berechnet.Als Mittel dieser beiden Werte ergibt sich Th=232·135.Da aber die Analysenserie aus den oben besprochenen, uns triftig erscheinenden Gründen als die zuverlÄssigere angesehen werden mu\, glauben wir, da\ der aus ihr resultierende WertTh=232·12 als das derzeit wahrscheinlichste Atomgewicht des Thoriums anzusehen ist, wenn Ag=107·880 angenommen wird. Aus dem in 27 Bestimmungen gefundenen VerhÄltnis von angewandtem Silber zu gefundenem Silberbromid, AgAgBr= 0·574453, ergibt sich dann das Atomgewicht des Broms zu Br=79·916 in vollster übereinstimmung mit der von Baxter seinerzeit gefundenen Zahl.     

Über einige neue Bispirane

We have obtained four new bispirane systems in which both spiroatoms are vicinal atoms in cyclopropane or cyclobutane rings and in which the heterocyclic component has the basic structure of 1,4-dioxep-2-ene. We have shown that from two possibilities (bispiran, propellan) the general reaction leads only to a bispiran system. To the bispiran2 exhibiting the highest hyperchromism we ascribed the bispirocoplanar conformation (Fig. 1).

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Identification of amber and imitations by near infrared reflection spectroscopy

Imitations of amber have been prepared since a long time, but the number of imitations is increasing since modern polymers are available. At present, many imitations are based on a few synthetic polymers and even experts have some problems in distinguishing between real and falsed amber without destruction of the material. IR-Spectroscopy or pyrolysis combined with gas chromatography/mass spectrometry are very efficient methods in identifying amber and imitations but these methods need a sample preparation. By means of near infrared reflection spectroscopy it is possible to identify amber and imitations without any sample preparation in a short time. Optimization of the method and the application are discussed.     

Classification of Poincaré duality algebras over the rationals

The Poincaré duality algebras over Q play a key role in the rational homotopy classification of closed manifolds [3]. In this paper we give a way of classifying general Poincaré duality algebras and then specialize to the case of algebras which are generated by some homogeneous component and show how the classification reduces to the linear classification of certain homogeneous polynomials and exterior forms.     

IBX-mediated alpha-hydroxylation of alpha-alkynyl carbonyl systems. A convenient method for the synthesis of tertiary alcohols

[reaction: see text] IBX (o-iodoxybenzoic acid) is an excellent reagent for the alpha-hydroxylation of alpha-alkynyl carbonyl compounds without giving dehydrogenation products. The convenient procedure proves to be useful for the construction of a variety of tertiary alcohols (55-91%) under mildly acidic conditions.     

A Short Synthesis of (−)-Carbovir

(–)-Carbovir ((–)- 1 ) was synthesized via the cyclic carbonate 2 in four steps starting from enantiomerically enriched (–)-(S)-(cyclopent-2-enyl)methanol ((–)- 3 ).     

A novel MCR of isocyanates, aldehydes, and dienophiles

[reaction: see text] A novel one-pot procedure for the three-component coupling reaction of isocyanates, aldehydes, and dienophiles (IAD reaction) has been developed. Condensation of isocyanates and aldehydes and subsequent Diels-Alder reactions with electron-deficient dienophiles furnishes endo-selective amino-substituted cyclohexenes in good yield.     

The intermediacy of metathiophosphonate PhPSO in the reaction of N-tert-butyl-P-phenylphosphonamidothioic acid with alcohols

Kinetic studies of the reaction of N-tert-butyl-P-phenylphosphonamidothioic acid (1) with alcohols were carried out in CH2Cl2 by means of 31P NMR spectrometry. The reaction is of the first order with respect to thio acid 1. The first-order rate constant at 30 degrees C increases with increasing methanol concentration below 0.25 M, but otherwise the rate constants are either independent of alcohol concentration (MeOH above 0.25 M, BuOH) or decrease with increasing alcohol concentration (i-PrOH, t-BuOH). The effect of alcohols on the order of the reaction and parameters of activation, as well as results of competition experiments, lead us to the conclusion that reaction of 1 with alcohols occurs by an elimination-addition mechanism involving the association of the thio acid 1 and the alcohol and then formation in the rate-determining step of an encounter complex 2' ' involving metathiophosphonate 4, amine, and alcohol. Metathiophosphonate 4 reacts preferentially with the alcohol as the encounter complex (primary alcohols) or after diffusion apart as a "free" intermediate (hindered alcohols).     

Syntheses of macrocyclic bisbibenzyls on solid support

We describe a route for the polymer supported total synthesis of the cyclic bisbibenzyls of the isoplagiochin type found in liverworts. TentaGel^® resins were used as solid support for a sequence involving Suzuki, Wittig and hydrogenation protocols. The polymer linked intermediates could be characterized by HR-MAS NMR. This route is to be extended to the synthesis of small libraries of differently halogenated derivatives.