A. Cambon

Highly fluorinated thermotropic liquid crystals: an update

Abstract Fluorine is used in liquid crystal materials in order to give them particular properties as compared to their hydrocarbon homologues. This leads to use of the new compounds as materials mainly in display devices such as Twisted Nematic Liquid Crystals Display (TNLCD) or for the development of Surface Stabilized Ferroelectric smectic C* display (SSFLCDs). In this paper, we describe recent studies and research effort concerning the liquid crystalline behavior of compounds incorporating a highly fluorinated part with more than one fluoromethylene units. We examine some of their mesophase properties and the impact of molecular shape on the resulting liquid crystal behavior.

Fonctionnalisation des iodures de F-alkyl-2 ethane par catalyse transfert de phase : importance de cette technique en serie F-alkylee

Abstract F-alkyl-2 ethane iodides are very important starting materials in the field of organic fluorine chemistry. Their reactivity in homogeneous medium shows some drawbacks : reactions are uncomplete and resulting compounds are not pure. We resolved these problems using phase transfer catalysis and obtained outstanding results. F-alkyl-2 ethane iodides are strongly hydrophobic; so organic solvents are not necessary (water was used) and moreover the emulsions promoted during the reaction are not stable.

SYNTHESIS OF F-ALKYL N-SULFONYL CARBAMATES AND THIOCARBAMATES

Abstract The syntheses of F -alkyl (alkoxy) and aroxysulfonyl carbamates and thiocarbamates result by addition of F -alkyl alcohols and thiols to alkoxy and aroxysulfonyl isocyanates. At room temperature the reaction occurs rapidly with very good yields.

LIQUID CRYSTALLINE PHASES OF PERFLUORINATED COMPOUNDS WITH SEGREGATED SUBLAYERS

Abstract The liquid crystalline polymorphism (SA, SB, CrE) and the structures of the phases of N-n-perfluoralkylethyl-(4-phenylbenzylidene)imines are described. It is shown that the smectic layer consists of two sublayers in to which the incompatible moieties of the compounds segregate. It is proved that the perfluoralkyl chains remain disordered until crystallization occurs, whereas with decreasing temperature, the aromatic parts are ordered in types of SB and CrE structure.

Influence of different spacers on the mesomorphic properties of 4-biphenyl derivatives within the F-alkylated series

In order to determine the influence of modification of the shape of the connector, within the fluorinated series, on the formation of mesophases in low molecular mass compounds, we decided to examine the mesomorphic behaviour of molecules which consist of a 4-biphenyl unit linked to a fluorinated tail via different spacers. The synthesis and the physical properties of these new materials are reported. The mesomorphic properties were characterized by polarized light microscopy and by differential thermal analysis, thereby showing the peculiar contribution of each of the spacers. The data collected from the 4-biphenyl derivatives synthesized allow us not only to confirm the enhancement of the smectic properties owing to the fluorinated alkyl chains, but also to display the impact of the spacer on these properties. Actually, some spacers like the amide or thioether type, as well as that of the hemithioacetal derivatives give suppression of the smectic character. Some others like that in the esters with an OC...

Synthèse des isocyanates de 2-F-alkyléthyle

Abstract Isocyanates are extremely important compounds in organic synthesis but their preparation is not always easy. One of the most convenient methods uses the acids as intermediates. In the F-alkyl series it it sometimes difficult to obtain them. We have optimized an efficient synthetic route to 2-F-alkylethyl isocyanates.

Eudesmane sesquiterpenes from laggera alata

Two new eudesmane-type sesquiterpenoids (7-epi-γ-eudesmol and 7-epi-β-eudesmol) were isolated and characterized along with five other sesquiterpene compounds (β-selinene, 7-epi-α-eudesmol, isointermedeol, juniper camphor and β-dihydroagarofuran) from the essential oil of Laggera alata var. alata grown in Madagascar. The assigned structures were based on their spectral data.

Nouvelles methodes de preparation des F-alkyl oxiranes a partir des acetates de bromo-2 F-alkyl-2 ethyle et des bromo-2 F-alkyl-2 ethanol

Abstract F-alkyl oxiranes provide many interesting intermediates. Their synthesis from 2-bromo-2-F-alkylethyl acetates and from 2-bromo-2-F-alkylethanols was improved by two different methods which are very easy to apply. One requires the use of concentrated caustic soda and a phase transfer catalysts; the other one, potassium fluoride in triethylene glycol.

Synthèse de F-alkyl oxirannes

Abstract The perfluoroalkyloxirans were obtained with good yields from the long chain perfluoroalkyl ethylenes R F CHCH 2 . All the reaction intermediates were isolated and described. Their structure was determinated by the usual spectroscopy methods : N.M.R., infra-red, mass spectrometry and by microanalysis.

Municipal Tropical Compost: Effects on Crops And Soil Properties

Three kinds of tropical soils (inceptisol, mollisol and oxisol: USDA) were amended with increasing quantities of municipal refuse compost. Prepared mixtures: 0, 1.2, 2.5, 5, 10 and 25.6 percent (by volume) of compost were utilized as growing substract (without mineral fertilizer) in pot vegetation trials including three successive plantations taking corn as the test plant. Plant yields and heavy metal concentrations were determined. Urban compost effects on soil chemical parameters were evaluated. Corn growth had been significantly enhanced by the presence of urban compost showing no toxic effects. However, this fertilizing effect decreases after successive harvestings. Cadmium and lead concentrations in the plants were found to be under detection concentration limits (0.5 and 5.2 ppm respectively). Concentrations of copper and zinc in the plants increased relative to the amounts of urban compost but never reached toxic concentrations.