Dosage direct de traces de bore dans l'acier par la methode fluorimetrique a l'Hydroxy-2-Methoxy-4-Chloro- 4'-Benzophenone (HMCB)

A simple and rapid method for the direct determination of traces of boron in mild steels, using 2-hydroxy-4-methoxy-4'-chlorobenzophenone (HMCB) as the fluorimetric reagent for boron is proposed     

Dosage de l'oxygene dans l'uranium et ses composes par la methode au monochlorure de soufre

A sulfur monochloride method is proposed for the determination of oxygen in uranium compounds. Sulfur monochloride reacts with oxygenated compounds at temperatures depending upon their nature; the sulfur dioxide produced is titrated by iodometry, after the excess reagent has been eliminated by a selective adsorption-desorption process using activated charcoal. This method has been successfully applied to uranium oxides (UO₂, U₃O₈), to mixtures of uranium dioxide with uranium, uranium nitride, and uranium carbide, and to substituted carbides (UC_1-xO_x). The results are generally satisfactory for oxygen contents higher than 500 p.p.m. However, in the presence of free or combined carbon, this limit is considerably higher. A loss of oxygen as carbon monoxide is also possible, and a simultaneous determination of carbon monoxide must be carried out. The relative error is of the order of a few per cent.     

Dosage colorimetrique de traces de zinc dans la bauxite,l'alumine et l'aluminium raffine

A method for the colorimetric determination of traces of zinc in bauxite, alumina, and refined aluminium by means of dithizone is proposed. Ga, Fe, Si, Ti, Ni, Pb, Ca, Mg, Na, etc. do not interfere; Co interferes but can be masked with cyanide. The limit of sensitivity of the method is 2 p.p.m. for bauxite and alumina and 0.4 p.p.m. for aluminium.     

Dosage de l'azote dans le vanadium par fusion reductrice sous vide

A study of the conditions for the determination of nitrogen in vanadium by vacuum fusion in a platinum bath has shown that (a) the amount of nitrogen extracted depends on the ratio (R) of the weights of platinum and vanadium, and (b) the amount extracted passes through a maximum value for a particular R value depending on the temperature. With R values of ca. 2 and extraction temperatures above 1900°, results were in reasonable agreement with those obtained by the Kjeldahl method, the reproducibility being 2–3%.     

Dosage de l'americium par coulometrie a potentiel impose

A coulometric determination of americium by reduction of Am(VI) to Am(V) at a potential of + 1.3 V is proposed. The accuracy of the method was evaluated by analyzing ²⁴¹Am solutions prepared by weighing and dissolving AmO₂ of known purity. The results must be corrected by a factor of 1.017, in order to eliminate the systematic error due to autoreduction. After this correction, the relative standard deviation of the method ranged from 0.44% for américium concentrations of 3.125·l0^-3M to 0.96% for those of 1.25·10^-4M.     

Programme de minimisation de l'energie empirique d'une molecule par une methode simpliciale

A method of assessing the minimum energy of a molecule in a given conformation is discussed. This method can easily be adapted to impose constraints (symmetry, for example) to the molecules studied. The results are compared with recent experimental values and analogous calculations. We show, with butane, cyclopentane and cyclohexane, methods of recognising false minimum values.     

Greffage de l'acide methacrylique sur des films de poly(chlorure de vinyle) par la methode radiochimique directe

Since PVC films do not swell in pure methacrylic acid (MAA) the films were subjected to gamma-rays while dipped in various mixtures MAACHCl₂. Under such conditions, the grafting proceeds smoothly and its rate exhibits a flat maximum for the mixture containing ca. 50% (molar) monomer. The rate satisfies the relationship Rate = KI^0.6 and the over-all activation energy of the process is 4 kcal/mole. MAA grafted PVC films do not swell in solvents for PMAA (such as water or methanol) even for high grafting ratios. This result is unexpected since PTFE films grafted with either acrylic or methacrylic acid swell to a large extent in water and are excellent membranes. The swelling of the grafted PVC films was investigated in mixtures 1,2-dichloroethylene -methanol. It was found that the extent of swelling was highest in the mixture containing 35% methanol. The unusual swelling properties of these grafted films are attributed to strong polar interactions between PVC and PMAA chains.     

Effet de longueur d'onde et controle par la geometrie de l'etat fondamental de la photoisomerisation de derives de l'hexatriene-1,3,5

Irradiations at different wavelengths (313, 254, 229 and 214 nm) of the 4 geometric isomers of 5-phenyl-1,3,5-heptatriene show that the photochemical behaviour of these trienes is mainly controlled by their ground state equilibrium.     

Etude calorimetrique et analytique de l'adsorption du cyanogene sur la silice

The adsoprtion of C₂N₂ on well outgassed specimens of SiO₂ at temperatures from 35 to 913°C has been studied by heat flow calorimetry, volumetry, and mass spectrometry.Small amounts of cyanogen are adsorbed at low temperature: reversibly by hydrogen bonding with the silanol groups, and irreversibly on strained siloxane bridges or Lewis acid sites. Above 200°C cyanogen reacts, with silanol groups, leading to the formation of HCN (partly reversibly adsorbed on non-reacted silanol groups) and silyl isocyanate:

. The process is complete at 418°C and the measured enthalpy for the reaction

is ΔH = ?12.2 ± 0.3 kcal mole^?.Above 500°C, HCN and C₂N₂ react with ordinary siloxane bridges. At higher temperature, the pyrolysis of

produces CO₂ with CO and N₂ (in smaller quantities), showing that a large proportion of N-atoms are bonded on the surface.     

Selectivite de la reduction de l'androsten-4 dione-3,17 et de la progesterone par divers borohydrures: role de l'assistance electrophile par le cation ou un solvant hydroxyle

The reduction of Δ⁴-androsten-3, 17 dione 1 and of progesterone 2 by nBu₄NBH₄ is highly chemioselective: in THF only the a-enone moiety is reduced, the saturated C₁₇ or C₂₀ keto group being kept unchanged. When TMEDA is added, saturated alcohols are obtained, without any allylic alcohol when the reaction goes to completion. However this reduction is poorly stereoselective as 70:30 mixtures of A/B cis and trans ring junction compounds are obtained. In MeOH, the saturated keto group is more than 90% selectively reduced. However, the reduction of 1 and 2 by LiBH₄ and Zn(BH₄)₂ is poorly chemioselective. These results are interpreted in terms of competition between electrophilic assistance and steric effects.     

Transposition des oxirannes-ethanols par l'intermediaire d'alcoxyetains. Influence de la configuration de l'oxiranne

The transposition of oxirane-ethanols, through alkoxytin compounds, into oxetane-2-methanols and/or oxolan-3-ols (tetrahydrofuran-3-ols) is dependent upon the oxirane configuration. Cis configuration is more suitable for the formation of the smallest ring. Steric hindrance is not sufficient enough to explain the results.     

Etude de l'aromaticite par la theorie de hückel

Dewar theory and Breslow theory of aromaticity in contrast to Kruszewski-Krygowski theory, do not regard aromaticity as a chemical property, resulting in numerous contradictions between experimental behaviour of hydrocarbons and theoretical expectations are observed. Two new indexes can be introduced into the Kruszewski-Krygowski's theory,² one concerned with hydrocarbon stability, the other with its aromatic character.     

Greffage radiochimique de l'acrylonitrile dans la masse de films de PTFE

Acrylonitrole can be grafted in the bulk of PTFE films provided the monomer is allowed to diffuse into the grafted zones. For a given radiation dose, the amount of grafting is higher the lower the dose-rate. Even higher grafting efficiencies are reached under conditions of discontinuous irradiations, the reacting mixture being stored in the dark in a thermostat between successive irradiations. The grafting yield is higher the higher the storage temperature. The bulk grafting involves a progressive swelling of the grafted polyacrylonitrile branches by acrylonitrile monomer via a dipole-dipole association of the -CN groups of the monomer with the -CN groups in the polymer.     

Influence de la temperature sur les manifestations de l' “effet de matrice” dans la polymerisation de l'acide acrylique en solution

This study is concerned with the influence of temperature on the kinetics of the polymerization of acrylic acid dissolved in dioxane or toluene and on the type of molecular association complexes present in these solutions. In dioxane solutions, an increase in temperature destroys the oligomeric auto-associations of acrylic acid and gives rise to monomer-solvent associations. Simultaneously, the consequences of the “matrix effect” (auto-acceleration and stéréospecificity) become less pronounced. In contrast, in toluene solutions, an increase in temperature converts the cyclodimeric auto-associations of the monomer into linear oligomers and the consequences of the matrix effect appear (or become more pronounced). The Arrhenius plots exhibit anomalies which conform with the above interpretation. The results obtained in dioxane and in toluene solutions are similar to earlier findings in methanol and n-hexane solutions respectively. This makes it possible to generalize the conclusions reached here to acrylic acid solutions in other solvents which may or may not associate with the monomer.