How to Make 8,1,2‐closo‐MC2B9 Metallacarboranes

Three examples of the rare 8,1,2‐closo‐MC₂B₉ isomeric form of an icosahedral metallacarborane have been isolated as unexpected trace products in reactions. Seeking to understand how these were formed we considered both the nature of the reactions that were being undertaken and the nature of the coproducts. This led us to propose a mechanism for the formation of the 8,1,2‐closo‐MC₂B₉ species. The mechanism was then tested, leading to the first deliberate synthesis of an example of this isomer. Thus, deboronation of 4‐(η‐C₅H₅)‐4,1,8‐closo‐CoC₂B₁₀H₁₂ selectively removes the B5 vertex to yield the dianion [nido‐(η‐C₅H₅)CoC₂B₉H₁₁]^2?, oxidative closure of which affords 8‐(η‐C₅H₅)‐8,1,2‐closo‐CoC₂B₉H₁₁ in moderate yield.     

The Synthesis of Some Naphtho[2,3-b]pyran-5,10-Quinones as Preliminary Models for Biological Evaluations

Naphtho[2,3-b]pyran-5,10-quinones related to the known antibiotic, erythrostominone 5, have been synthesized and demonstrate that biological activity is a function of the pyran ring as well as substituents at C-2 and C-4.     

Model Route to 5-Bromo-3,4-dihydro-4-hydroxy-7,9,10-trimethoxy-1,3-dimethyl-1H-naphtho[2,3-c]pyran: A Potential Precursor to Extended Quinones

A protocol has been developed for the synthesis of the linear naphthopyran 16, by the TiCl₄-catalyzed isomerization of 2,5-dimethyl dioxolane 1, having a methoxy group at position 1′ and a bromine atom at position 4′ of the naphthyl precursor to favor isomerization at position 2′.

Use of wollastonite in a thermoplastic elastomer composition

Thermoplastic elastomer compositions (TPEs) based on wollastonite-filled SEBS/PP/oil blends were prepared and characterized. The development of new TPEs with improved mechanical strength may broaden their applications, especially for soft goods. Wollastonite is a natural filler that combines high thermal stability with low health hazard in comparison to other fibrous inorganic fillers. Morphological, thermal and mechanical properties of the composite materials were studied by transmission electron microscopy (TEM), thermogravimetry (TGA), tensile tests and dynamic mechanical analysis (DMA). The results indicate that the filler was mainly distributed as nanoparticles in the PS domains, improving the mechanical resistance of the materials even at low concentration (2 phr).     

The BIOREMA project—part 1: Towards international comparability for biofuel analysis

There is an increasing demand to accurately measure the quality of biofuel products (e.g. biodiesel and bio-ethanol). This demand is driven in Europe by directives promoting the use of renewable sources of energy and worldwide by national and international legislation setting out quality requirements for these fuels. Until now, there has been no international consensus on the minimum technical specifications to ensure biofuel quality. Furthermore, it is unclear which reference materials and measurement techniques are needed to provide the quality assurance and quality control framework to underpin these legislative requirements. As part of the European Commission’s 7th Framework Programme, the BIOREMA project (REference MAterials for BIOfuel specifications) demonstrated the feasibility of preparing biodiesel and bio-ethanol reference materials with reference values traceable to the international system of units for a range of parameters at levels relevant to technical specifications. However, the project concluded also that further research is needed to improve the current measurement capabilities for some parameters. Within the BIOREMA project, two global interlaboratory comparisons were carried out, using the biodiesel and bio-ethanol test materials prepared during the feasibility stage of the project, as well as two biodiesel standard reference materials from the National Institute of Standards and Technology (NIST, USA). The exercises showed that the measurement capabilities of the field laboratories were in many cases satisfactory, whereas for other laboratories the availability and regular use of certified reference materials would likely enhance the measurement capabilities for many of the parameters studied. A general overview of the BIOREMA project is presented in this paper. The details of the production of the two types of BIOREMA reference materials, and the results of the interlaboratory comparison for the bio-ethanol and biodiesel study materials, are discussed in parts 2 and 3 of this series of papers.     

Synthetic pathway for a new series of liquid crystal 2,6-disubstituted imidazo[2,1-b][1,3,4]thiadiazole

Herein, the synthesis of a novel series of liquid crystals 2,6-disubstituted imidazo[2,1-b]-1,3,4-thiadiazoles derivate is reported. These fused heterocyclic compounds were prepared through the cyclodehydration between 5-substituted-1,3,4-thiadiazole-2-amino derivatives and α-bromo aryl ketones. The derivates of 2-amino-thiadiazole were obtained from the condensation reaction between thiosemicarbazide and aryl/alkyl nitriles with good yields (60–83%). The α-bromination of aryl ketones was carried out using NBS as the source of electrophilic bromine, also with good yields (52–85%). For the final compounds, the liquid crystal behaviour was shown to be dependent on the number of chains. Mesomorphism was not observed for compounds without aliphatic chains, with more than two aliphatic chains or when the aliphatic chains are methoxy groups.     

Applying click chemistry to synthesis of chiral [1,2,3]‐triazole liquid crystals

1,3‐Dipolar cycloaddition of organic azides to triple bonds, or ‘click chemistry’ has been used in order to obtain chiral 1,4‐disubstituted [1,2,3]‐triazoles. Liquid crystalline compounds bearing such heterocycles were prepared and SmA and N* (cholesteric) phases identified. Contact experiments indicated a right‐handed helix (RH‐helix) for the cholesteric phase, and attempts to corroborate experimental and theoretical results are presented.     

Preparation and Crystal Structure of MnBiSe2I

Black single crystals of MnBiSe₂I were obtained by the reaction of stoichiometric amounts of Mn, Bi, BiI₃, and Se at 600 °C for 7 days. The compound crystallizes in the monoclinic system, space group C2/m, with a = 13.428(2), b = 4.112(1), c = 10.130(2) Å, β = 90.97(2)°, and Z = 4. The crystal structure refinement based on 849 reflections converged at R = 0.0380 and wR2 = 0.0916, respectively. MnBiSe₂I forms a layer structure consisting of MnSe₆ octahedra, MnSe₂I₄ octahedra, and BiSe₃₊₂ pyramids.     

Outer factorizations in one and several variables

A multivariate version of Rosenblum's Fejér-Riesz theorem on outer factorization of trigonometric polynomials with operator coefficients is considered. Due to a simplification of the proof of the single variable case, new necessary and sufficient conditions for the multivariable outer factorization problem are formulated and proved.

     

Particle Sizing by Photon Correlation Spectroscopy. Part IV: Resolution of bimodals and comparison with other particle sizing methods

The practical performances of single and multi-angle photon correlation spectroscopy (PCS) for resolving bimodal distributions of industrial poly (methyl methacrylate) samples was investigated in a comparative study by several users affiliated to academic and industrial groups and by two suppliers of commercial equipment. The results for the harmonic intensity averaged diameters obtained by cumulants analysis reported by the different laboratories are in agreement, in addition to the results for the normalized second cumulants. The uncertainty on the latter quantities is large, however. For the bimodal samples with two populations with average diameters in a ratio of about 2.5 : 1, not all users were able to resolve the distribution in its components by single-angle PCS. Some slight improvement was obtained by multi-angle PCS. Other indirect techniques (polarization intensity differential scattering, static light scattering data and disc photosedimentometer) appeared to be superior for resolving the bimodal distributions.