Solubility of Lithium Monoborate in High-Temperature Water

The solubility in water of anhydrous lithium monoborate has been determinedat 300 to 360°C. Equilibrium constants for the isocoulombic solubilityreactionLiBO₂ (s) + H⁺ (aq) + H₂O (1) = Li⁺ (aq) + H₃BO₃ (aq)have been calculated from measured concentrations of total B and total Li insolution. These high-temperature constants can be fitted by a three-term equationthat is consistent with thermodynamic data at 25°C. The heat capacity changefor the isocoulombic reaction is small and independent of temperature. Solubilityresults agree with unpublished measurements from early work on developmentof nuclear power. Solubilities reported by Bouaziz appear to be much too highand may apply to a hydrated phase.     

A kinetic study of the reactions of 2-propyl radicals in the liquid phase in the presence and absence of oxygen

2-Propyl radicals have been generated from the photolysis of solutions of 2,2-azopropane and 2,4-dimethyl-3-pentanone in decane in a glass and a metal cell. The time course of their reactions in the presence and absence of oxygen has been monitored between 323 and 373 K. The primary process involves the formation of solvent-caged radical pairs, two 2-propyl radicals and a 2-propyl and a 2-methylpropanoyl radical from the azo and ketone precursors, respectively. Subsequently these radicals are partitioned between cage escape and dimerization and disproportionation within the cage. In oxygenated solution the free 2-propyl radicals are effectively trapped as 2-propylperoxyl radicals. However, oxygen does not react with the solvent-caged radicals. This leads to a major difference in the hydrocarbon products from the two precursors. 2,2′-Azopropane gives propane, propene, and 2,3-dimethylbutane from the start of the reaction whereas the ketone only gives propene. Following the depletion of oxygen or in the absence of oxygen, both precursors behave analogously and give all three hydrocarbons. The 2-propylperoxyl radicals undergo self-reaction and hydrogen abstraction from the solvent to give 2-propanol, propanone, and 2-propyl hydroperoxide and, under conditions of low oxygen concentration, by reaction with 2-propyl radicals they give 2,2′-dipropylperoxide. Although the two cells lead to different overall rates of reaction, the relative rates and product distributions are unaffected by the cell design. A unified mechanism is described and the known and best estimates of rate constants for the individual steps are used to simulate the time dependence of the product yields from the photolysis of both precursors. © 1996 John Wiley & Sons, Inc.     

Enantioselective Synthesis of Cyclopropanone Equivalents and Application to the Formation of Chiral β-Lactams

Cyclopropanone derivatives have long been considered unsustainable synthetic intermediates because of their extreme strain and kinetic instability. Reported here is the enantioselective synthesis of 1-sulfonylcyclopropanols, as stable yet powerful equivalents of the corresponding cyclopropanone derivatives, by α-hydroxylation of sulfonylcyclopropanes using a bis(silyl) peroxide as the electrophilic oxygen source. This work constitutes the first general approach to enantioenriched cyclopropanone derivatives. Both the electronic and steric nature of the sulfonyl moiety, which serves as a base-labile protecting group and confers crystallinity to these cyclopropanone precursors, were found to have a crucial impact on the rate of equilibration to the corresponding cyclopropanone. The utility of these cyclopropanone surrogates is demonstrated in a mild and stereospecific formal [3+1] cycloaddition with simple hydroxylamines, leading to the efficient formation of chiral β-lactam derivatives.     

Probing local innate immune responses after mucosal immunisation

Background  

Intranasal immunisation is potentially a very effective route for inducing both mucosal and systemic immunity to an infectious agent.     

Hydrosilylation of Ketones,Imines and Nitriles Catalysed by Electrophilic Phosphonium Cations: Functional Group Selectivity and Mechanistic Considerations

The electrophilic phosphonium salt, [(C₆F₅)₃PF][B(C₆F₅)₄], catalyses the efficient hydrosilylation of ketones, imines and nitriles at room temperature. In the presence of this catalyst, adding one equivalent of hydrosilane to a nitrile yields a silylimine product, whereas adding a second equivalent produces the corresponding disilylamine. [(C₆F₅)₃PCl][B(C₆F₅)₄] and [(C₆F₅)₃PBr][B(C₆F₅)₄] are also synthesised and tested as catalysts. Competition experiments demonstrate that the reaction exhibits selectivity for the following functional groups in order of preference: ketone>nitrile>imine>olefin. Computational studies reveal the reaction mechanism to involve initial activation of the Si?H bond by its interaction with the phosphonium centre. The activated complex then acts cooperatively on the unsaturated substrate.     

Selective Binding of Imidazolium Cations in Building Multi‐Component Layers

Addition of 1‐alkyl‐3‐methylimidazolium (C_n‐mim) cations 3 – 5 to a mixture of bis‐phosphonium cation 2 and sodium p‐sulfonatocalix[4]arene ( 1 ) in the presence of lanthanide ions results in the selective binding of an imidazolium cation into the cavity of the calixarene. The result is a multi‐layered solid material with an inherently flexible interplay of the components. Incorporating ethyl‐, n‐butyl‐ or n‐hexyl‐mim cations into the multi‐layers results in significant perturbation of the structure, the most striking effect is the tilting of the plane of the bowl‐shaped calixarene relative to the plane of the multi‐layer, with tilt angles of 7.2, 28.9 and 65.5°, respectively. The lanthanide ions facilitate complexation, but are not incorporated into the structures and, in all cases, the calixarene takes on a 5? charge, with one of the lower‐rim phenolic groups deprotonated. ROESY NMR experiments and other ¹H NMR spectroscopy studies establish the formation of 1:1 supermolecules of C_n‐mim and calixarene, regardless of the ratio of the two components, and indicate that the supermolecules undergo rapid exchange on the NMR spectroscopy timescale.     

Investigation of the synergy in intumescent polyurethane by 3D computed tomography

The morphology of carbonized materials resulting from an intumescence phenomenon was studied. The investigated material is a polyurethane matrix filled either by 30 wt.-% of ammonium polyphosphate or by a combination of 28 wt.-% of ammonium polyphosphate and 2 wt.-% of nano-magnesium oxide. These fillers were incorporated in the polyurethane directly during the synthesis step. The carbonized materials or char, are obtained in a specific fire scenario. Characterization of their morphology is carried out using X-ray computed tomography. The heat conductivity of the systems is additionally measured as a function of temperature in order to correlate structure and properties of the intumescent residues. The formation of different char structures with incorporation of magnesium oxide (in particular formation of bubbles of different size) is first evidenced. These observations are consistent with the heat conductivity data. Tomography images demonstrate that the intumescence process is a dynamic process since non degraded polymer is left at the beginning of the fire test, which is not the case for longer time. The dispersion of fillers has finally been investigated in the chars and it is evidenced different steps of intumescence's development in the material.     

Mechanism and Chemoselectivity for HOCl-Mediated Oxidation of Zinc-Bound Thiolates

Quantum mechanical calculations reveal the preferred mechanism and origins of chemoselectivity for HOCl-mediated oxidation of zinc-bound thiolates implicated in bacterial redox sensing. Distortion/interaction models show that minimizing geometric distortion at the zinc complex during the rate-limiting nucleophilic substitution step controls the mechanistic preference for OH over Cl transfer with HOCl and the chemoselectivity for HOCl over H₂O₂.