Über sechsgliedrige Heterocyclen mit Phosphor-, Stickstoff- und Schwefelatomen im Ring

Cyclic sulphurylphosphazochloride (I: formula see ?Inhaltsübersicht”?) reacts with ammonia or methylamine forming the. tetramide(II) and (III), respectively, and with aniline or dimethylamine forming the diamide (IV) resp. (V). The synthesis of the diphenyl derivative (VI) is achieved starting from C₆H₅? PCl₄. (II) gives with PCl₅ the ionic compound (VII).     

Platinum(II) and palladium(II) complexes of bisphosphine ligands bearing o-N,N-dimethylanilinyl substituents: a hint of catalytic olefin hydration

Platinum(II) and palladium(II) complexes of the potentially hexadentate P,N-donor ligand family Ar2P-X-PAr2 (X = (CH2)2 [dmape], cyclic-C5H8 [dmapcp]; Ar = o-N,N-dimethylanilinyl) are described. In CH2Cl2, the dmape complexes exist as equilibrium mixtures of MCl2(P,P'-dmape) and [MCl(P,P',N-dmape)]Cl isomers (M = Pd, Pt), governed by deltaH(o) = -19 +/- 4 kJ mol(-1) and deltaS(o) = -100 +/- 30 J mol(-1) K(-1) for M = Pt, and deltaH(o) = -11 +/- 7 kJ mol(-1) and deltaS(o) = -60 +/- 20 J mol(-1) K(-1) for M = Pd. The water-soluble dmapcp complexes exist solely in the [MCl(P,P',N-dmapcp)]Cl form, but the free and coordinated anilinyl rings in these complexes are in slow diastereoselective exchange. X-ray crystal structures for MCl2(P,P'-dmape) (M = Pd, Pt), and the [PdCl(P,P',N-dmape)]+ and [PtCl(P,P',N-dmapcp)]+ cations, are presented. Some of the complexes show marginal activity in water for the catalyzed hydration of maleic to malic acid, giving about 6-7% conversion in 24 h at 100 degrees C and substrate:catalyst loadings of 100:1. Attempts to synthesize a PdCl(P,P',N-dmapm)+ species led instead to isolation of [Pd(mu-Cl)(P,P'-dmapm)]2[PF6]2 (dmapm = Ar2PCH2Ar2).     

Nets and generalized quadrangles

There is a new method of constructing generalized quadrangles (GQs) given by S. Löwe, which is based on covering of nets; all GQs with a regular point can be represented in this way. Here we give a method of constructing GQs with a regular point using the so-called content functions on nets. In the last part of the paper we lay the foundations for a research project aiming to use the more general notion of content to classify GQs and maybe to construct new ones.Both authors acknowledge the financial support by CRUI and DAAD in the frame of Programma Vigoni, which made this work possible.     

A cyclographic approach to the vertices of plane curves

For a closed plane curve the centers of distance functions are considered satisfying the condition that the function attains at least two absolute minima along. From the topology of the closure of this set some information on specific vertices of the curve can be obtained. If a simply closed curve has a finite number of vertices only, then the structure of this set is given by a tree, composed from regular arcs, such that the end points of this tree belong to minimal osculating circles of, which entirely are located in the interior of. Furthermore, the curve can be reconstructed from this set as the envelope of a suitable family of circles. These relations are used to give alternative proofs and extensions of several known vertex theorems for closed curves.Dedicated to N. Stephanidis on occasion of his 65. birthday     

Thermische Beständigkeit von linearen Polyisoprenen unterschiedlicher Kettenlänge

Zusammenfassung An einer polymerhomologen Reihe von linearen Polyisoprenen mit Molekulargewichten zwischen 40000 und > 10⁷ wurde im Festzustand und in L?sung die Abh?ngigkeit der thermischen Stabilit?t von der jeweiligen Kettenl?nge untersucht. Es zeigte sich, da? die zum Zerbrechen der Makromoleküle notwendigen Temperaturen mit steigendem Molekulargewicht deutlich abnehmen und für Polyisoprene mit Molekulargewichten > 10⁷ bei Raumtemperatur liegen.

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Summary The dependence of thermal stability from the molecular weight of linear macromolecules was tested using polyisoprenes with m. w. between 40000 and > 10⁷. We could demonstrate that the temperatures at which molecular fractures occur, decrease with increasing chain length and approach room temperature at molecular weights of about 10⁷.

     

Thermolysis of 1-(1-aryl-1-bromomethyl)cyclopropyl bromides: a reinvestigation

Two compounds, the (Z)- and (E)-isomers of 2,4-dibromo-1-p-tolyl-1-butene 2a and 3a, respectively, were isolated in 65% total yield when 1-(1-bromo-1-p-tolylmethyl)cyclopropyl bromide (1a) was heated at 150 degrees C for 1 h. 1,1-Dibromo-2-p-tolylcyclobutane (4a), previously reported to be the only product in this reaction, was not detected. The phenyl analogue of 1a reacted similarly and gave the (Z)- and (E)-isomers of 2,4-dibromo-1-phenyl-1-butene 2b and 3b, respectively, in 60% yield. A rationale for the reaction is presented.     

Electron-transfer polymers. XXXIV. Redox polyurethanes from p-benzoquinone-2,5-diols and diisocyanates

It is possible to prepare polyurethanes from p-benzoquinone-diols and diisocyanates by using dibutyltin diacetate catalyst at room temperature or below, since the benzoquinone group does not react with isocyanate under these conditions. This permits preparation of new redox polymers. In preparing the polyurethanes excess isocyanate groups must be destroyed at the end of the reaction time in order to prevent crosslinking during work-up. These polymers are readily reduced by aqueous hydrosulfite. Good viscosity numbers are obtained; and, in general, upon reduction the viscosity increases over that of the oxidized form. There is no evidence of crosslinking. When oxidized and reduced forms of these polymers are mixed there is no evidence of charge transfer.