Hydrogenation asymetrique en presence de diphosphines chirales

Chiral diphosphines analogues of 2,3-isopropylidene dihydroxy-1,4-bis(diphenylphosphino) butane (DIOP), where the acetonide ring has been substituted by a hydrocarbon chain, were prepared. The hydrogenation of prochiral compounds with a rhodium complex of these diphosphines shows that there is a relation between the optical yield and a structural property of the diacid precursor. The best optical yields were obtained with the diphosphine prepared from the trans-1,2-cyclobutane dicarboxylic diacid.     

Mecanisme d'inhibition de la corrosion d'un acier ferritique ecroui par l'alcool propargylique,en milieu sulfurique dilue

A ferritic steel (RCA 44) pulverized with corindon microbreaker in a dilute sulphuric solution is corroded very quickly: the percussion hammerhardening makes a very great number of dislocations and the emerging atomes are immediately attacked.When it is pulverized in the presence of propargylic alcool, the powdered metal remains unaffected at room temperature and during several months. The complex formation by π-bonding between metallic atom and triple bond may explain the inhibitor effect. The long-breaking increases considerably the number of active site and it becomes possible to point out by electronic spectrography the formation of aromatic or linear oligomers from propargylic alcool. A parallel may be drawn between this formation and known catalytic properties of some transition metal π-complexes in cyclisation or linear polymerisation reactions of alkynes.     

Systemes eau/surfactant ionique/alcool/hydrocarbure Influence de la nature de l'alcool sur la configuration du domaine de microémulsion et les propriétés de transport des microémulsions

The realms-of existence of water/sodium dodecylsulfate/C₄ to C₇ n-alkanols/n- dodecane monophasic, stable, fluid, transparent and isotropic media, (so-called microemulsions), were determined, atT=25 C, for different values of the surfactant/ alcohol mass ratiok _m. It was found that the configuration of the microemulsion domain in the system phase tetrahedron depends tightly upon that of the mutual solubility area of water, surfactant and alcohol. It has been possible to establish a general correlation between microemulsion domain configuration and microemulsion transport properties such as viscosity and electrical conductivity.

     

Polymerisation radiochimique de l'acide acrylique en solution dans l'alcool isopropylique et le dimethylformamide

The radiation-induced polymerization of acrylic acid in isopropyl alcohol and dimethylformamide solutions was investigated between?196°and40°. Mixtures which form glasses at low temperatures exhibit a maximum in the rate of polymerization at 30° and 50° above the glass transition temperature (T_g). The difference between the most favourable temperature for polymerization and T_g is larger than in systems studied previously. This fact could be due to the presence of H-bonded aggregates.The study of the polymerization of acrylic acid in dimethylformamide solution at 20° led to a correlation between this reaction and the presence of plurimolecular aggregates. The very high polymerization rate and the syndiotacticity of the resulting poly(acrylic acid) confirm the earlier assumption of a favourable orientation for propagation of the molecules of acrylic acid in these aggregates.     

Etude rheologique de gels mixtes de poly(alcool vinylique) et d'alginate de sodium

Snake-cage hydrogels were prepared by the association of poly(vinyl alcohol) (PVA) and sodium alginate. The aim of this work is to study the viscoelastic properties of PVA networks having different molecular weights and trapping alginates of various mannuronate/guluronate ratios, molecular weights and aqueous concentration. The elastic and viscous moduli, G′ and G″, were found to depend on alginate concentration. With the sodium alginate (mannuronate/guluronate =1.78, M̄w=380 000), the elasticity was observed to be independent of the PVA molecular weight in the 7.5% to 10% (w/w) concentration range. Hydrogels elasticity was found to be sodium alginate nature-dependent only in the case of PVA with M̄w =22 000. Moreover, it seems that the viscoelastic parameters G′ and G″ become increasingly insensitive to the nature of sodium alginate as the molecular weight of PVA increases.     

Une voie originale et selective de fonctionnalisation en position meta du fluoro- et de l''ethylbenzene

An original and regioselective method for the meta functionalisation of fluoro- and ethylbenzene is reported. This process involves a 2,5- disilylation of these substrates using trimethylchlorosilane in the presence of lithium in THF as the solvent. After aromatisation, monodesilylation in position 2- and electrophilic substitution of the trimethylsilyl group in position 5-, meta acetyl-, senecioyl-, benzoyl-, and iodo-fluorobenzenes and ethylbenzenes as well as the sodium salts of meta fluoro or meta ethylbenzenesulfonic acid and 3- aminosulfonylfluorobenzene were obtained in good yields.     

Etude de la cristallinite de derives n-octadecyliques de l'alcool polyvinylique obtenus par greffage chimique

Differential scanning calorimetry has been used to study the heats of fusion and melting transitions of n-octadecyl derivatives of polyvinyl alcohol. These derivatives were obtained by grafting paraffinic chains on polyvinyl alcohol, at various proportions. The melting transitions are independent of the degree of substitution; the heats of fusion are proportional to the fraction of crystallizable units. Using Flory's equilibrium crystallization theory, it is possible to interpret these results assuming, as demonstrated previously, that the chemical grafting is sequential with two unreacted hydroxyl groups between two adjacent paraffinic side-chains.     

Preparation de membranes echangeuses de cations par photogreffage d'ethers allyliques du poly (alcool vinylique). Etude de certaines de leurs proprietes—I: Preparation et etude de poly (alcool vinyliques) allyles

A new preparation of poly(vinyl alcohol) partially allylated (PAOV) is reported. The possible existence of crosslinking is explained but, under suitable conditions, it can be avoided. A detailed analysis of the infra red spectrum of PAOV shows that during allylation the structure of the original poly(vinyl alcohol) (PAV) is not changed. The compatibility of various monomers is studied.     

Obtention selective de synthons nucleosidiques utilisables en synthese oligoribonucleotidique : differenciation 2′,3′ en serie nucleosidique

A practical regio- and stereoselective synthesis of asymmetrically substituted ribonucleosides is described in which glycosylation of ribofuranoid 2-O-esters (alkyl or silyl) with either pyrimidines or purines is the key step.     

Preparation de membranes echangeuses de cations par photogreffage d'ethers allyliques du poly (alcool vinylique). Etude de certaines de leurs proprietes—III: Caracteristiques physicochimiques des membranes poly (alcool vinylique-g-sulfonique)

The membranes of poly(vinyl alcohol-g-vinyl sulphonic acid) have been studied. The swelling can be controlled: the exchange capacity, the conductivity, the flux of diffusion, the critical current density have been determined and analysed with respect to the experimental parameters of the preparation.     

Etudes en series bicycliques: Cetalisation selective de dicetones octalinique et tetrahydroindanique et stereochimie de leurs analogues satures

The 1-oxo functions of 8a-methyl 1,6-dioxo 1,2,3,4,6,7,8,8a-octahydronaphthalene1 and 7a-methyl 1,5-dioxo 5,6,7,7a-tetrahydroindane11 were ketalized selectively with 2-ethyl 2-methyl 1,3-dioxolane at room temperature. This reaction was extended to the corresponding saturated decalindiones4,5 and hydrindan-diones16,18, which give the 6- and 5-monoketals respectively. The double bond of the monoketals from1 and11 was reduced and four corresponding saturated cis- and trans-fused monoketals obtained, A new method, based on the differences of solvent effect on the chemical shift of angular methyl groups, is described for unambiguous determination of the nature of the ring junction of these compounds.     

Synthese de polyalcadienes monochloroformiates. Modification chimique par des alcool,amine et thiol

Some monofunctional polydienes with various extremities are obtained by chemical modification of ω-monochloroformate polymers. The chosen products are an alcohol, an amine and a thiol. The organic compounds are attached to the end of a macromolecular chain by a carbonate, a urethane or a thiolcarbonate link. The resulting polymers are characterized by i.r. and NMR analysis. These modification reactions of end groups may be used as model reactions for polymers having specific properties.     

Hydrodimerisation electrochimique de cetones aromatiques encombrees en milieu aprotique et en presence de chlorure de chrome

The electrochemical reduction of hindered aromatic ketones which are difficult to reduce alone, can be achieved in an aprotic medium (DMF) on a mercury pool cathode, in presence of Cr(III) chloride, at the reduction potential or the Cr(II)/Cr(0) system, but at a less negative potential than that of the ketone itself. There is selective hydrodimerisation into an α-glycol, with total lack of polymerisation. With dissymetric ketones, the dl-diastereoisomers of the diols are produced. The effect of chromium is due either to the reduction of a Cr-ketone complex or to the reduction of the ketone by a film of colloidal chromium on the electrode surface.     

Analyse en Spectrometrie de Masse de Derives Fluores en Serie Pyrimidine et Triazine

We have synthesised all the fluorinated derivatives of perchloropyrimidine, trichloro-2,4,6-pyrimidine and perchloro-s-triazine. Fluorine n.m.r. analysis, associated with gas chromatography coupled with mass spectrometry, allowed separation and identification of the products. The behaviour of these compounds under electron-impact is presented and discussed here.     

Migration d'acides aromatiques en chromatographie sur couche mince de gel de silice en fonction de la teneur en eau ou en acide formique de solutions créant l'atmosphère de la cuve à chromatographie

Résumé Les auteurs étudient la mobilité de divers acides aromatiques sur couche mince de gel de silice en fonction, soit de la teneur en eau de mélanges acide sulfurique-eau, soit de la teneur en acide formique de solutions (eau ou diéthylèneglycolmonoéthyléther) créant l'atmosphère de la cuve à chromatographie. Ils tentent de mettre en évidence les phénomènes de compétition au niveau des sites actifs de la silice entre les acides aromatiques et les agents de conditionnement de la couche mince (eau, acide formique). Ces recherches ont permis la mise au point d'une méthode efficace de séparation d'un certain nombre d'acides aromatiques.

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Mobility of aromatic acids during TLC on silica gel. Dependence on water or formic acid content of liquid phase in the chromatographic tank

Summary The authors study the mobility of some aromatic acids on thin layers of silica gel as a function either of water content of sulphuric acid-water mixtures or of formic acid solutions (water or diethyleneglycolmonoethylether) creating the chromatographic tank atmosphere. They try to demonstrate the competition for active sites on the silica gel between aromatic acids and the conditioning agents of thin layer (water, formic acid). These researches helped to find an efficient method for the separation of some aromatic acids.

     

Reconocimiento de nicotina en una hebrita de tabaco

Summary Adaption of theLuís method for the detection of nicotine to microscale, usingEmich's capillary technic proved successful, attaining identification limit of 0,03g.Applying a sub-micro steam distillation effect, the nicotine in a speck of tobacco (1 mm² and less) could still be detected by using the above reaction.Extension of the above procedure to mixtures of nicotine with substances not volatile with steam, inorganic (halides) as well as organic compounds (other alkaloids, acids, etc.) proved to be successful, even when the nicotine is present in proportions of only 1 part in 1000.

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Zusammenfassung Die Anwendung der Kapillartechnik vonEmich zum Nachweis von Nikotin nachLuís war erfolgreich und zeigte eine Erfassungsgrenze von 0,03g.Bei Anwendung einer Ultramikrodampfdestillation kann das Nikotin nach obiger Methode noch in Spuren von Tabak (1 mm² und weniger) nachgewiesen werden.Die Reaktion ist auch positiv bei Gemischen von Nikotin mit anderen, mit Wasserdampf nicht flüchtigen sowohl anorganischen (Halogenide) als auch organischen Substanzen (andere Alkaloide, Säuren etc.), selbst dann noch, wenn das Nikotin bloß im Verhältnis von 11000 vorhanden ist.

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Résumé La technique capillaire d'Emich a été utilisée avec succès pour identifier la nicotine suivant le procédé deLuís; la limite de sensibilité est alors de 0,03g. La mise en oeuvre d'un ultramicroentraînement à la vapeur permet en outre, par application de la précédente méthode, d'identifier la nicotine dans des traces de tabac (moins de 1 mm²). La réaction est également positive en présence d'autres substances non entraînables par la vapeur d'eau, qu'elles soient minérales (halogénures) ou organiques (autres alcaloïdes, acides, etc. ...) même si la proportion de nicotine n'est que de l'ordre de grandeur de 1/1000.