Materials and Methods

Materials and Methods Synthesis of thionyl chloride-activated succinamidopropyl-glass beads     

The effect of thermal processing on PVC—III. Photo-oxidation of unstabilized PVC

The rate of photo-oxidation of unstabilized PVC is markedly dependent on the severity of the processing operation. In mildly processed PVC, peroxy gel appears to be a very effective photo-initiator whereas in more severely processed polymer, solvent soluble polymer containing polyconjugation, hydroperoxides and carbonyl groups is primarily responsible for photo-initiation. The auto-retardation of photo-oxidation which occurs in all samples is believed to be due to the build-up of a highly absorbing surface layer of degraded polymer.     

Reductive spiroannulation of nitriles with secondary electrophiles

The scope of reductive decyanation and spiroannulation reactions has been expanded to include secondary electrophiles for potentially useful transformations. Secondary phosphates and chlorides, as well as terminal epoxides, cyclize in a stereospecific fashion. Both endo and exo modes of cyclization were observed with terminal epoxides.     

A kinetic and spectroscopic study of the interaction between a M(CO)5 (M=Cr, W) fragment and ethyl diazoacetate

The reaction between Cr(CO)₅[C₆H₆] and ethyl diazoacetate (EDA) has been studied using the technique of laser flash photolysis. Results indicate that the Cr(CO)₅ fragment reacts very rapidly with the EDA ligand. Low temperature spectroscopic studies suggest that in the case of W(CO)₅, and by analogy also in the case of Cr(CO)₅, the initial adduct between the pentacarbonyl fragment and EDA is one where the oxygen atom of the diazocarbonyl ligand is bound to the metal center. This kinetic product is then converted to a thermodynamically favored complex which is tentatively assigned as the nitrogen bound W(CO)₅-EDA complex that appears to be stable at r.t.     

Maximum hardness in P6 isomers

Parr and Chattaraj proposed a principle of maximum hardness for stable molecular structures. Pearson and Palke used ab initio SCF MO calculations for ammonia and ethane to demonstrate the operation of the principle. In this paper, we present ab initio SCF MO results for five isomeric forms of the homoatomic P⁶ cluster as further support for the principle of maximum hardness. © 1994 John Wiley & Sons, Inc.     

Bimetallic palladium-platinum dendrimer-encapsulated catalysts

We report the synthesis, characterization, and catalytic activity of bimetallic palladium-platinum dendrimer-encapsulated catalysts (DECs). These materials are prepared by co-complexation of different ratios of palladium and platinum salts to the interior tertiary amines of fourth-generation, hydroxyl-terminated poly(amidoamine) (PAMAM) dendrimers. Chemical reduction of these composites yields stable, fairly monodisperse, water-soluble bimetallic DECs having sizes on the order of 1.9 +/- 0.4 nm. Evidence that these nanoparticles are bimetallic comes from single-particle X-ray energy dispersive spectroscopy (EDS) and catalysis experiments. The latter indicate that the hydrogenation rate of allyl alcohol is enhanced in the presence of the bimetallic nanoparticles compared to DECs containing only platinum or only palladium nanoparticles. EDS results indicate that the percentage composition of the bimetallics is reflected by the percentage of metal salts initially complexed with the dendrimer.     

Enantioselective synthesis of an aziridinomitosane and selective functionalizations of a key intermediate

An enantioselective synthesis of mitosane core (-)-1 has been achieved. Key steps include a rapid assembly of a key eight-membered-ring intermediate employing ring-closing metathesis. Kinetic resolution of an advanced secondary alcohol was then accomplished by using a peptide-based asymmetric acyl transfer catalyst that was discovered from a parallel screen of catalyst candidates. Optically pure material was then converted to the mitosane core, which was the subject of additional studies on the selective modification to produce several substituted compounds containing a mitosane ring system.     

The effect of fiber coating on the tensile properties of ionomer-based composites

Asbestos fibers, of the chrysotile variety, were coated with a thin polyamide film by an in situ polycondensation technique. Ionomer-based composites were prepared containing the so-modified asbestos fibers in a random in-plane orientation; results of testing the tensile properties of these asbestos/polyamide/ionomer composites are presented. Parameters investigated comprise the asbestos content in the composite and the polyamide content deposited on asbestos. A significant improvement in the tensile performance was established, especially at the intermediate polyamide content of 3.4 phr. The behavior is discussed in terms of possible interactions between the phases present in the composite material.     

Mechanism of meerwein-pondorf-verley type reductions

The reduction of benzophenone by lithium and chloromagnesium alkoxides has been studied as well as the transformation of certain lithium alkoxides to the corresponding ketones by electron transfer. Fluorenone was reduced by lithium sec-butoxide to the corresponding lithium ketyl to the extent of 65%. Lithium 9-fluoroenolate underwent in tetrahydrofuran a spontaneous transformation to lithium fluorenone ketyl. This process was interpreted as involving 1,2-hydrogen shift in an oxygen-centred radical. A mechanism for the Meerwein-Pondorf-Verley-type reductions is proposed, invoking single electron as well as 1,2-hydrogen shift steps.