Une généralisation de la théorie de brönsted en chimie analytique

The proposal is made that all reactions be considered as corresponding to the exchange of particles (particules).1. Exchange of electrons between an oxidising agent and a reducing agent. This is the classical conception of oxidation-reduction reactions.2. Exchange of ions (or of polar molecules) between an “acceptor” of the ion and a “donor” of the same ion. In the case of exchange of protons the reaction is one between acids and bases, according to Brönsted.The majority of reactions concern the exchange of different ions. It is proposed to apply to these reactions, and that for each type of particle exchanged, the type of reasoning which Brönsted has used for the exchange of protons.The analogy thus created between the different types of reactions leads to a considerable simplification. It allows identical reasoning and the use of similar formulations for all reactions.Further, the distinction between reactions in terms of the nature of the particle exchanged permits recognition of the respective influence of the factors which are available for controlling the reactions.It is suggested that the use of this conception is advantageous in teaching analytical chemistry.     

Premières applications du thiocarbohydrazide en chimie minérale

Résumé Les auteurs proposent l'emploi du thiocarbohydrazide en chimie minérale. Ils donnent une première liste d'ions réagissants. Ce réactif apparaît déjà intéressant pour le dosage gravimétrique ou colorimétrique du molybdène en présence de tungstène et d'uranium.

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Summary The authors propose the use of thiocarbohydrazide in inorganic chemistry. They give a preliminary list of reacting ions. This reagent appears to have some interest for the gravimetric or colorimetric determination of molybdenum in the presence of tungsten and uranium.

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Zusammenfassung Die Anwendung von Thiocarbohydrazid in der anorganischen Chemie wird vorgeschlagen und eine Liste der mit dieser Verbindung reagierenden Ionen angeführt. Für die gravimetrische oder kolorimetrische Bestimmung von Molybdän in Gegenwart von Wolfram und Uran scheint das Reagens von Interesse zu sein.

     

Les réactifs de l'analyse minérale moderne dans la chimie de l'azote organique

Résumé L'auteur introduit les réactifs de l'analyse minérale moderne dans la chimie de l'azote organique par substitution des cations organiques aux cations minéraux. L'exemple proposé applique un réactif de Cu á l'isolement de l'éphédrine; la limite de sensibilité de cet isolement á froid passe ainsi de 5000g á 20g/ml sans que les pertes dépassent 2%.Seconde originalité de ce travail: l'emploi, pour le contrôle de cet isolement, d'une réaction d'addition á intensité compensée: dans le milieu oú apparaît le composé d'additionA (B) n, n augmente systématiquement par diminution de [A].

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Summary The reagents employed in modern inorganic analysis have been now introduced into the chemistry of organic nitrogen compounds by substitution of organic cations for the inorganic cations. For example a reagent for copper is applied for the isolation of ephedrine. The sensitivity limit of this isolation in the cold exceeds 5000g at a concentration of 20g/ml and the loss does not exceed 2%.

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Zusammenfassung Reagenzien der modernen anorganischen Analyse lassen sich für organische Stickstoffbasen heranziehen, die als Kationen an die Stelle anorganischer Kationen treten. So eignet sich zum Beispiel ein Reagens für Kupfer zur Abscheidung von Ephedrin; die Nachweisempfindlichkeit wird so in der Kälte von 5000 auf 20g/ml verbessert, ohne daß der Verlust 2% übersteigt. Eine weitere Eigentümlichkeit dieses Nachweisverfahrens ist darin zu sehen, daß mit zunehmender Bildung des AdditionsproduktesA(B) n der Wertn durch Minderung der Konzentration vonA erhöht wird.

     

Emploi du,cadion en chimie analytique : Un microdosage spectrophotométrique du mercure

A new method is described for spectrophotometric microdetermination of the mercury ion by means of a triazine dye, the “Cadion”. If the well-defined experimental conditions are maintained, the method is very sensitive and accurate. The influence of foreign ions is described.     

Emploi du ,′cadion″ en chimie analytique : Un microdosage spectrophotométrique du cadmium

A new method is presented for spectrophotometric micro-determinations of cadmium by means of a triazine dye, called “Cadion”The method is a highly sensitive one, permitting the determination of 0.05 p.p.m. cadmium in the final solution, with satisfactory accuracy and reproducibility.The interference of the main foreign anions and cations is studied, and a way of eliminating the interfering ions is suggestedSome examples are given for the application of the proposed method     

Synthesis of polyoxovanadates via “chimie douce”

A large variety of new polyoxovanadates have been synthesized during the past few years by sol–gel chemistry or hydrothermal methods. These wet chemistry methods offer many advantages compared to the usual solid state syntheses. New open structures have been obtained from aqueous precursors. They result from the self-assembling of ionic species in the solution.Vanadium oxide gels and sols, V₂O₅·nH₂O, are formed around the point of zero charge (pH≈2). They have a ribbon-like structure and exhibit a liquid crystal behavior. These mesophases are similar to those currently observed with nematic polymers. Xerogel layers deposited from V₂O₅·nH₂O gels exhibit some preferred orientation and behave as versatile host structures for intercalation giving new hybrid organic–inorganic nanocomposites.Layered structures are formed around pH≈7 in the presence of large organic cations. They are built of mixed valence polyoxovanadate planes made of [VO₅] pyramids and [VO₄] tetrahedra. Organic cations lie between the oxide layers where they interact with the negative oxygen of the VO double bonds.Anions can behave as templating agents. Hollow cluster shells are formed around anions that remain encapsulated within the negatively charged polyvanadate cage. Large cations only behave as counter ions for the formation of a neutral crystalline network.It appears that the molecular structure of V^V precursors depends mainly on pH, but the way they self-assemble may be governed by other ionic species in the solution.     

Synthèse par chimie douce et caractérisation d'oxynitrate de hafnium HfO(NO3)2, xH2O

Synthesis by soft chemistry and characterization of hafnyle (IV) nitrate hydrate HfO(NO₃)₂, xH₂O. This paper deals with the synthesis and characterization of hafnyle (IV) nitrate hydrate from HfCl₄. The elaboration method is a soft chemistry one which allows to obtain a pure product. The nitrate was characterized by FTIR spectra, X ray diffraction and thermal analysis data (TDA-TGA). The degree of hydration was determined to be 2.     

Coal from carbohydrates: The “chimie douce” of carbon

The production of porous materials together with their associated applications using cheap precursors demonstrates the potential of a “chimie douce” based on carbohydrates and their hydrothermal decomposition products to replace same of the standard organic monomers, fulfilling the today's requirements towards greener chemistry processes and the sustainability of the starting products.     

Les origines de la chimie organique au-delà du mythe fondateur

According to a legend, organic chemistry emerged in 1828 with the synthesis of urea performed by the German chemist Friedrich Wöhler from mineral reagents and “without the help of the kidneys”, thus ending the mysterious “vital force”. This article aims to show that this myth, invented in the nineteenth century by chemists and widely spread until today, is actually something that is certainly important, but is not enough to account for the emergence of a specialty as complex as organic chemistry. Synthesis is a fundamental component of this discipline, but its foundations lay in chemical analysis.     

Activation mécanique d'oxydes de fer et de vanadium en vue d'une synthèse de ferrite de vanadium nanométrique similaire au composé issu de la chimie douce

Co-milling of iron and vanadium oxides allows us to obtain an intimate oxide mixture at a nanoscale, similar to a coprecipitate elaborated by soft chemistry. Reduction of such a mixture in the same temperature and oxygen partial pressure conditions (500 °C and 10⁵ Pa) as the Pa) as the soft chemistry products leads to a nanometric vanadium ferrite with only a spinel phase. Homogeneity of grain size and chemical composition is reached if the initial oxides have similar grain sizes.     

Linéarisation et homogénéisation en viscoélasticité

Constitutive equations for non-linear viscoelastic materials are expressed first using a causal operator which relates a response function to any loading history. The corresponding tangent linear equations are then defined through the Fréchet derivative of this operator. This definition is used to propose a step-by-step treatment in view of the derivation of the overall behaviour of non-linear non-ageing viscoelastic heterogeneous materials.     

Géométrie de l'intermittence en turbulence développée

A geometrical interpretation of intermittency in fully developed turbulence is realized through an hierarchy of fractal structures Ω_p of dimensions Δ_p linked each other by the relations Ω_{p + 1} − Ω_p (i.e. Δ_{p + 1} < Δ_p) and γ = (Δ_{p + 1} − Δ_∞)/(Δ_p − Δ_∞) with γ = ((1 + 3/√8)^1/3 + (1 − 3/√8)^1/3)³ and Δ_∞ = 1 and Δ_∞ = 1. This is obtained by the introduction of an entropy jump, defined at the scale r, ΔS_p(r) = (Δ_{p + 1} − Δ_p) ln (r/r₀) characterizing the order level of each sub-structure Ω_p and verifying a linear relation ΔS_p(r) = γ ΔS_{p − 1}(r).     

Étude immunologique comparative de la glycéraldéhyde-3-phosphate-déshydrogénase chez les entérobactéries: Apports d'un sérum anti-glycéraldéhyde-3-phosphate-déshydrogénase de Enterobacter intermedium

A comparative immunological study of glyceraldehyde-3-phosphate dehydrogenase among Enterobacteriaceae was carried out with an antiserum against Enterobacter intermedium G-3-PDH. Results of immunodiffusion experiments and microcomplement fixation studies showed E. intermedium to be a homogeneous species. The genera Enterobacter and Escherichia were found to be quite heterogeneous.     

Etude polarographique du méthyl-phényl-dodécyl-triméthylammonium (désogène)

Rèsumè Le méthyl-phényl-dodécyl-triméthylammonium (désogène), donne une vague polarographique caractéristique, en utilisant comme électrolyte de support l'hydroxyde de tétraméthylammonium, le CILi ou le ClK.Les propriétés de cette vague ont été étudiées en fonction de la concentration du saponium. La loi d'Ilkovi est vérifiée.Deux électrons interviennent dans la réduction du saponium.

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Summary The cationic detergent désogène (methyl-phenyl-dodecyl-trimethylammonium) gives a characteristic polarographic wave in LiCl or in tetramethylammonium solution. The wave seems to correspond to a 2 electronprocess, following Ilkovi's law at low concentrations. A typical adsorption maximum, proceeded by a prewave wich does not follow the Ilkovi' law is found at higher concentrations. At high ionic strength this maximum disappears.

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Zusammenfassung Das kationische Detergens Désogène (Methylphenyl-Dodeeyl-Trimethylammonium) gibt in Lithiumchlorid- oder in Tetramethylammoniumhydroxydlösung eine charakteristische polarographische Welle. Diese scheint einem 2-Elektronen-Prozeß zu entsprechen und folgt bei niederen Konzentrationen dem Gesetz von Ilkovi. Ein typisches Adsorptionsmaximum, dem eine dem Ilkovi-Gesetz nicht folgende Welle vorangeht, findet sich bei höheren Konzentrationen. Dieses Maximum verschwindet bei hoher Ionenkonzentration.

     

Étude des propriétés des mélanges pebd régénéré / pebd vierge

This study is a contribution to the valorization of recycled low-density polyéthyléne (LDPE). First the characterization of five recycled LDPE produced from wastes coming from different sources was performed. The physical properties (density, melt flow index), chemical structure (Fourier transform infra-red spectroscopy) and mechanical properties (tensile strength and hardness) were investigated. The effect of the ratio of virgin LDPE on these physical and mechanical properties was studied in the case of the blends of recycled LDPE / virgin LDPE.