Odile Babot

A new practical synthesis of silyl enol ethers : Part.I. From simple aldehydes and ketones

Abstract A new, practical route to enoxysilanes is described from simple enolizable aldehydes or ketones, using the trimethylchlorosilane-sodium iodide—tertiary amine reagent in acetonitrile. From certain aldehydes, an onium intermediate has been isolated. A conformational study of this onium intermediate and a thermal unimolecular syn-elimination process may explain the stereoselectivity of the reaction. Such an interpretation can be extended to all the aldehydes and ketones considered, Steric factors related to the nature both of the carbonyl derivative and of the amine play a capital role for the regio- as well as for the stereo-control of the reaction

Near- and Supercritical Alcohols as Solvents and Surface Modifiers for the Continuous Synthesis of Cerium Oxide Nanoparticles

Supercritical fluids offer fast and facile routes toward well-crystallized tailor-made cerium oxide nanoparticles. However, the use of surfactants to control morphology and surface properties remains essential. Therefore, although water, near-critical (nc) or supercritical (sc), is a solvent of choice, the poor water solubility of some surfactants could require other solvent systems such as alcohols, which could themselves behave as surface modifiers. In here, the influence of seven different alcohols, MeOH, EtOH, PrOH, iPrOH, ButOH, PentOH, and HexOH, in alcothermal conditions (300 °C, 24.5 MPa) over CeO(2) nanocrystals (NCs) size, morphology, and surface properties was investigated. The crystallite size of the CeO(2) nanocrystals can be tuned in the range 3-7 nm depending on the considered alcohol, and their surface has been modified by these solvents without the use of surfactants. Mechanisms are proposed for the interaction of primary and secondary alcohols with CeO(2) surface and its functionalization during the synthesis based on FTIR and TGA-MS studies. This study allows apprehending the role of alcohols during the synthesis and may lead to an informed choice of solvent as a function of the required size and surface properties of CeO(2) NCs. It also opens new route to CeO(2) functionalization using supercritical alcohol derivatives.

A new practical synthesis of silyl enol ethers : II. From α,β-unsaturated aldehydes and ketones

Abstract In acetonitrile as the solvent and in the presence of a tertiary amine the trimethylchlorosilane/sodium iodide (trimethyliodosilane “in situ”) reagent provides the corresponding siloxy dienes when reacted with α,β-unsaturated series. These reactions occurs via the formation of 1,2 or -1,4 onium salt intermediates.

Syntheses and characterization of highly mesoporous crystalline TiO2 macrocellular foams

Titanium dioxide open-cell macro-cellular foams have been generated with emphasis toward controlling macro-, meso- and microstructures thus reaching hierarchically organized inorganic architectures. At the macroscopic length scale a non-static air–liquid foam strategy allows strong control over the open-cell morphologies. At the meso- and/or nanoscopic length scales various mesogenic templates or latex colloids have been used to promote mesoporosity. Among the strategies in use, a Pluronic copolymer P-123 combined with tetradecyltrimethylammonium bromide induce vermicular-like mesoporosity associated with a specific surface area around 400 m2 g−1. At the microscopic length scale, upon the use of specific thermal treatment, either monophasic anatase, biphasic anatase–rutile or monophasic rutile allotropic forms are obtained.

CeO2 Nanocrystals from Supercritical Alcohols: New Opportunities for Versatile Functionalizations?

The fast and controlled synthesis of surface-modified cerium oxide nanoparticles was carried out in supercritical {ethanol + alcohol derivative} mixtures. The newly found ability of supercritical alcohols to graft onto cerium oxide nanocrystals (CeO2 NCs) during their synthesis was exploited to control their surface chemistry via the addition of three aminoalcohols: ethanolamine, 3-amino-1-propanol and 6-amino-1-hexanol. Although the ethanol to aminoalcohol ratio was consistent (285:1), the successful grafting of these alcohol derivatives onto CeO2 NCs was identified based on Fourier transform infrared (FTIR) and thermogravimetric analysis-mass spectrometry (TGA-MS) measurements. Smaller crystallite size of CeO2 NCs synthesized in the presence of aminoalcohols, compared to those synthesized in supercritical ethanol alone, were also noticed and attributed to a possible intervention of amine groups helping the grafting of the alcohols, allowing one to stop the growth of the CeO2 NCs faster. The use of supercritical alcohol mixture-ethanol with hexanol, dodecanol, or octadecanol, with a 285:1 ratio-was also investigated. Such mixtures allow accessing a finer control in CeO2 NCs crystallite size compared to pure alcohols, according to calculation made from X-ray diffraction measurements. Finally, fluorescent molecules (fluorescein isothiocyanate) were grafted onto amine-modified CeO2 NCs. The powders displayed a fluorescent behavior under UV light, confirming the suitability and interest of CeO2 NCs surface modification by such technique.

Shaping zirconium phosphate α-Zr(HPO4)2·H2O: from exfoliation to first α-ZrP 3D open-cell macrocellular foams

Using a two-step synthetic route that first takes benefit of an α-Zr(HPO4)2·H2O (α-ZrP) exfoliation process followed by an air–liquid foam shaping method we have designed for the first time 3D macrocellular foams made of α-ZrP lamellae. Apart from this high scale texturation we were able to tune the macroscopic void space shapes (polygonal-type or spherical-type) as well as cell wall thickness by varying the starting foam’s water volume fraction (ρ). Also, by adjusting the size of the porous disk employed during the bubbling process we can define the macroscopic cell diameters with a strong degree of control.

Tough silicon carbide macro/mesocellular crack-free monolithic foams

Taking the benefit of Si(HIPE) as a hard monolithic template to shape macro-mesoporous foams by using polycarbosilane as pre-ceramic precursor β-SiC, macro/mesocellular foams have been synthesized. Both macroscopic Plateau border morphology and final mechanical properties can be tuned through varying the starting amount of polycarbosilane precursor. Resulting silicon carbide foams, labeled SiC(HIPE), are composed of β-SiC at the microscopic length scale, while bearing 110 m2 g−1 as specific area at the mesoscopic length scale, and up to 92% of macroporosity. The as-synthesized crack-free SiC(HIPE) monolithic foams are associated with outstanding mechanical properties as, for instance, 50–58 MPa of compression Young modulus. The thermal behaviors of these foams are assessed with bulk heat capacities comprising between 0.15 J g−1 K−1 to 0.55 J g−1 K−1 that decrease when the foam porosity increases, while their heat conductivities are following the same rules ranging from 2.6 to 4.6 W m−1 K−1.

Effect of Thermal Treatment on the Textural Properties of CeO2 Powders Synthesized in Near‐ and Supercritical Alcohols

CeO2 nanocrystals (NCs) have attracted increasing interest over the past few years, in particular for their use in catalytic reactions. Syntheses mediated by near- and supercritical alcohols have proven to be innovative ways to obtain CeO2 NCs with controlled crystallite sizes (from 3 to 8 nm depending on the alcohol) and surface functionalities, with alcohol moieties. When submitted to a thermal treatment at 500 °C, required to desorb/degrade surface organic species, these powders displayed different behaviors depending on the alcohol used during the synthesis. Cerium oxide powders synthesized in sc-MeOH, sc-EtOH and sc-iPrOH undergo sintering during treatment at 500 °C, with a decrease of their specific surface area. Conversely, those synthesized in sc-BuOH, nc-PentOH and nc-HexOH keep their initial crystallite sizes and morphology, but show a great enhancement of their specific surface area (up to 200 m(2) g(-1)), which is unprecedented after such a thermal treatment.

Catalyseurs pour la transformation de polydiméthylsilanes en polycarbosilanes

Abstract The conversion of polydimethylsilanes into the corresponding polycarbosilanes has been studied using liquid monomeric catalysts such as B(OR)3 (R = Me, Pr, SiMe3) or the BN bonded compounds: Me2BN(SiMe3)2 and B(NEt2)3. Using this route it is possible to obtain polycarbosilanes which are more stable than the “Mark III” synthesized by the Yajima route and have a smaller polydispersity. These precursors obtained at 380–400°C do not require the use of an autoclave.

Utilisation en synthèse organique de MeSi(CN)3 préparé in situ

Abstract We report the first synthesis of tricyanohydrines by using MeSi(CN) 3 prepared “in situ” as reagent, and their potential use as acyl anion or as intermediates in the preparation of β-aminoethyl alcohols.