Reactions of methyltris(triarylphosphine)cobalt : I. Formation of biaryls

Methyltris(triarylphosphine)cobalt (Ar₃P)₃CoCH₃, decomposes in solutions of THF, benzene or chlorobenzene to yield biaryls. Coupling to biaryls occurs at the ring carbon originally bonded to phosphorus. Mixed biaryls are obtained from crossover reactions of complexes bearing different triarylphosphine ligands and reactions of complexes with free triarylphosphines.     

Transesterification of fatty acid ethoxylates in supercritical methanol, then gas chromatography-mass spectrometric determination of the derived methyl esters, for identification of the initiators

Unknown fatty acid ethoxylate samples have been transesterified in supercritical methanol, using a loop made of a stainless-steel tubing as the reactor vessel. The initiator acids, now present as the corresponding methyl esters, were determined by gas chromatography-mass spectrometry (GC-MS). Quantitative transesterification is achieved by heating a solution of the ethoxylate sample in methanol at 280 degrees C for 10 min under pressure. The influence of reaction time, temperature, and presence of a Lewis acid catalyst has been investigated. The method of transesterification was optimized in respect of low cost, short reaction time, and availability to laboratories with standard analytical equipment.     

Alkaloids from marine organisms. Part 8: Isolation of bisdemethylaaptamine and bisdemethylaaptamine-9-O-sulfate from an Indonesian Aaptos sp. marine sponge

Bisdemethylaaptamine (6), a proposed biosynthetic precursor of the aaptamines has been isolated from an Aaptos sp. marine sponge harvested off the Indonesian coast, and its identity confirmed by comparison of its spectral data with that of synthetic material. Bisdemethylaaptamine-9-O-sulfate (7) was also isolated from the same source. This is the first report of a sulfated aaptamine.     

An asymptotic minimax risk bound for estimation of a linear functional relationship

We consider estimation of the parameter B in a multivariate linear functional relationship X_i=ξ_i+ξ_1i, Y_i=Bξ_i+ξ_2i, i=1,…,n, where the errors (ζ_1i^′, ζ_2i^′) are independent standard normal and (ξ_i, i ) is a sequence of unknown nonrandom vectors (incidental parameters). If there are no substantial a priori restrictions on the infinite sequence of incidental parameters then asymptotically the model is nonparametric but does not fit into common settings presupposing a parameter from a metric function space. A special result of the local asymptotic minimax type for the m.1.e. of B is proved. The accuracy of the normal approximation for the m.l.e. of order n^−1/2 is also established.     

Groupes de départ inhabituels lors de cyclisations dans la série des quinoxalines,II [1]

Quinoxaline-3-ketones substituted by different groups in position 2 (I) are easily cyclized by hydroxylamine and phenylhydrazine to form isoxazolo[4, 5-b] quinoxalines (II) and pyrazolo [3, 4-b] quinoxalines (III) respectively. The reactions proceed via the oximes resp. phenylhydrazones. Groups displaced are not only the customary leaving groups of aromatic S_N2 reactions (halogens, OH), but likewise H, COOH, CONH₂, CO-Ar, and, less easily, benzyl groups; methyl and phenyl groups were not displaced. The displacement of hydride ion in the presence of excess of hydroxylamine resp. phenylhydrazine is explained in terms of an extension of the theory of osazone formation.     

Periodic points of positive linear operators and Perron-Frobenius operators

LetC(S) denote the Banach space of continuous, real-valued mapsf:S and letA denote a positive linear map ofC(S) into itself. We give necessary conditions that the operatorA have a strictly positive periodic point of minimal periodm. Under mild compactness conditions on the operatorA, we prove that these necessary conditions are also sufficient to guarantee existence of a strictly positive periodic point of minimal periodm. We study a class of Perron-Frobenius operators defined by