Kinetics of radical telomerization of vinylidene fluoride in the presence of CCl3Z chain transfer agents

The kinetics of radical telomerization of VDF at 141 °C, initiated by ditertbutylperoxide, in the presence of three chain transfer agents (CTAs), HCCl₃, CCl₄ and CCl₃Br, are presented. The values of the chain transfer constants were assessed as 35, 0.25 and 0.06 at 141 °C for CCl₃Br, CCl₄ and HCCl₃, respectively. The values of the degree of polymerization (DP_n) were obtained for each CTA and were compared for the same CTA concentration. Hence, CCl₃Br behaved as an efficient CTA towards VDF and usually afforded the monoadduct selectively, but in certain conditions the VDF diadduct can also be produced. In contrast, HCCl₃ was not so efficient since a polymeric structure was identified as the major product.     

Synthesis and X-ray structural characterisation of the tetramethylene oxonium derivative of the hydrodecaborate anion. A versatile route for derivative chemistry of [B10H10]

The oxonium derivative P(C₆H₅)₄[2-B₁₀H₉O(CH₂)₄] (1) has been prepared from [B₁₀H₁₀]²⁻ by a solvent-addition reaction route, promoted by Et₂O · BF₃. Its structure has been confirmed by single crystal X-ray analysis. 1 is assumed to be a useful synthon for the derivative chemistry of [B₁₀H₁₀]²⁻. As an illustration, ring-opening reaction occurred in presence of the strong nucleophilic agent OH⁻, giving the monoanionic derivative [P(C₆H₅)₄]₂[2-B₁₀H₉O(CH₂)₄OH] (2).     

Stereoselective synthesis of functionalised triol units by SnCl4 promoted allylation of α-benzyloxyaldehydes: crucial role of the stoichiometry of the Lewis acid

Enantiomerically pure syn-anti and syn-syn configured triol units are efficiently synthesized by the SnCl₄ mediated allylation of chiral α-benzyloxyaldehydes with the uniquely functionalised allylstannane 9. Remarkably, the stereochemistry of the adducts is solely governed by the amount of Lewis acid employed.     

Preparation d'esters par deshydrogenation d'alcools primaires en phase liquide catalysee par l'oxyde de cuivre - observations preliminaires

Linear primary alcohols with at least 7 carbon atoms are quite quantitatively transformed in esters, by CuO, at temperatures > 170°, without air in liquid phase. Preponderant influence of carbon in position 2 is evidenced. In the same conditions lactones are obtained from diols, and benzylic alcohols undergoes, by hydride transfer, a disproportionation into toluene, benzaldehyde and water.     

Novel RPLC stationary phases for lipophilicity measurement: solvatochromic analysis of retention mechanisms for neutral and basic compounds

An RPLC was developed to rapidly determine lipophilicity of neutral and basic compounds using three base deactivated RPLC stationary phases particularly designed for the analysis of basic compounds, namely, Supelcosil ABZ(+)Plus, Discovery RP Amide C16, and Zorbax Extend C18. The work consisted of three sets of experiments. In the first log kw values of neutral compounds were extrapolated using hydroorganic mobile phases at different compositions. Good correlation between log kw and log Poct indicated that the method was appropriate for these supports, without adding a silanol masking agent. In the second set of experiments, isocratic log k values of neutral and basic compounds were measured with three different mobile phases. The best estimation of lipophilicity was obtained for neutral and basic compounds when the secondary interactions were strongly reduced (i. e., when basic compounds were under their neutral form). In the third set of experiments, isocratic retention factors of basic compounds (in their neutral form) were measured with a high-pH mobile phase, on a chemically stable support (Zorbax Extend C18). Under these chromatographic conditions, correlation between the isocratic retention factors and log Poct (log D10.5) for basic compounds was similar to that for neutral compounds.     

The acidity functions of trifluoroethanol and hexafluoroisopropanol,and their mixtures with water

Acidity measurements in trifluoroethanol and hexafluoroisopropanol as solvents, and in their mixtures with water, are reported. The hydrogen electrode and the glass electrode were used for pH measurements. The “experimental” autoprotolysis constants were determined from measurements in strongly acidic (trifluoromethanesulfonic) media and in strongly basic (alcoholate) media: for trifluoroethanol, pK = -log K/mol² l^-2 = 15 and for hexafluoroisopropanol, pK = 14.8. Evaluation of the pH-indicator potential systems with reference to the ferrocene/ferricinium couple gives the acidity function R₀(H). The values obtained are compared to the H₀ values evaluated in the same conditions.     

Synthesis of 4H-3,1-benzoxazin-4-ones and 4-(3H)quinazolinones from anthranilic acids and their derivatives by the use of triphenyl phosphite and pyridine

A series of 2-substituted 4H-3,1-benzoxazinones and 2,3-disubstituted 4-(3H)quinazolinones have been synthesized in mild conditions by the use of triphenyl phosphite and pyridine as cyclising medium. Benzox-azinones are produced either by ring closure of 2-(acylamino)benzoic acids or in the reaction of benzoic acid with anthranilic acids. In the presence of aniline, the reaction leads to quinazolinones.     

On the mechanism of conformational interconversion in cyclohexene derivatives

The free energy barriers to ring inversion for 3,3-dimethylcyclohexene, 4,4-dimethylcyclohexene and 3,3,6,6-tetramethylcyclohexene were determined by low temperature PMR studies. The results were interpreted in terms of a mechanism whereby the boat conformation is of highest energy on the energy profile for conformational interconversion. The very high ΔG^≠ value for 3,3,6,6-tetramethylcyclohexane (8·4 kcal/mole) is considered a reflection of the serious non bonded interaction that exists between methyl groups at the “prow” positions of the boat form.     

Photoinduced morphism of gemini surfactant aggregates

The photochemical behaviour of an azobenzene chromophore inserted in a gemini surfactant imparts photocontrol to the resulting amphiphile assemblies, including the collapse, upon irradiation, of the multi lamellar vesicles formed in aqueous solution.     

An optimal two-step quadratic spline collocation method for the Dirichlet biharmonic problem

Numerical Algorithms - A two-step quadratic spline collocation method is formulated for the solution of the Dirichlet biharmonic problem on the unit square rewritten as a coupled system of two...