Zur Acylierbarkeit des Phosphorylsauerstoffs. I. Acyloxyphosphoniumsalze aus Hexamethylphosphorsäuretriamid und Carbonsäurederivaten

On the Acylation of the Phosphoryl Oxygen. I. Acyloxyphosphonium Salts from HMPT and Carboxylic Acid Derivates Acylation equilibria with participation of acyloxyphosphonium ions exist in solutions of HMPT and carboxylic chlorides, or anhydrides, respectively, as can be shown by ³¹P-n.m.r. after trapping the counter ion with SbCl₅. Moderately stable acyloxyphosphonium salts have been isolated for the first time by acylation of HMPT. In the alternative reaction of (Me₂N)₃P with CCl₄ and carboxylic acids, acyloxyphosphonium salts are formed only after prolonged reaction times, due to the stability of the intermediate chlorotris-(dimethylamino)-phosphonium ion.     

Ébullition par Convection Forcée des Mélanges Eau‐Ammoniac dans un Tube Vertical

An experimental study has been conducted on the forced convective boiling heat transfer of ammonia‐water mixtures flowing inside a 6 mm inner diameter vertical smooth tube. Using a water‐heated double pipe type generator, the local heat transfer coefficients are measured inside the inner tube for a range of heat flux density (29.93 — 99.79 kW/m²), mass flux density (35.36 — 99.04 kg/m²·s), mass flow rate (0.001 — 0.03 kg/s) and ammonia mass concentration (49%, 55% and 61%). The effect of the experimental parameters on the heat transfer coefficients is analysed. Three methods are used to predict the boiling heat transfer coefficients. Experimental data were compared with the available correlations. The obtained results confirm the good performance of the Mishra et al. (1981) and Bennett‐Chen's (1980) correlations in predicting the convective boiling heat transfer coefficient of NH₃‐H₂O mixtures. These methods are able to predict the boiling heat transfer data within an average accuracy of ± 20 %.     

Étude Théorique et Expérimentale de la Formation d'une Couche Limite par Convection Libre dans une Eau à Basse Température

A study, both analytical and experimental, has been made on the natural convection induced by an isothermal vertical plate immersed in a large volume of water at a temperature which was close to its freezing point. A particular attention has been paid to the effects resulting from the non-linearity existing between the density of water and its temperature. when the latter was close to 4°C. The plate temperature (T_w) was in the range from 8.0°C to 27.2°C, while the water temperature (T_i) varied between 0°C and 22.2°C. The Prandtl numbers for the flow were in the range from 6.4 to 13.7. An excellent agreement between the theoretical solution and the experimental data has been observed.     

Étude théorique et expérimentale de la formation d'une couche Limite par convection libre dans une eau à basse température

A study, both analytical and experimental, has been made on the natural convection induced by an isothermal vertical plate immersed in a large volume of water at a temperature which was close to its freezing point. A particular attention has been paid to the effects resulting from the non-linearity existing between the density of water and its temperature. when the latter was close to 4°C. The plate temperature (T_w) was in the range from 8.0°C to 27.2°C. while the water temperature (T_i) varied between 0°C and 22.2°C. The Prandtl numbers for the flow were in the range from 6.4 to 13.7. An excellent agreement between the theoretical solution and the experimental data has been observed.     

Neue ergebnisse bei der stabilisierung von ungesättigten polyesterharzen

The shelf-life at 50°C of unsaturated polyester resins which contain phenolic stabilizers can be increased by a factor of about three by addition of 0.1% hexamethylphosphoric triamide (HMPT) as costabilizer. The activity of the costabilizer is explained by an increase of the acidity (indicated by NMR-spectroscopy) of the phenolic protones of the inhibitor which accelerates the rate of inhibition. Suitable stabilizers are hydroquinone, toluhydroquinone, tert.-butylhydroquinone, p-tert.-butyl-o-dihydroxybenzene, 3.5-di-tert.-butyl-o-dihydroxybenzene or p-benzoquinone. Non suitable stabilizers for interaction with HMPT are 2.5-di-tert.-butyl-hydroquinone, 2.5-di-tert.-butyl-p-benzoquinone, tetrachloro-p-benzoquinone and p-hydroxymethoxybenzene. Their failure is assumed to be caused by steric effects or by their inability to regenerate hydroquinones by disproportionation during the inhibition reaction.     

Synthese von 1-(β-D-Arabinofuranosyl)-pyrimidinen

Syntheses of 1-(β-D-Arbinofuranosyl)-pyrimidines New synthetic methods of 1-(β-D-arabinofuranosyl)-pyrimidines are described. 1-(β-D-arabinofuranosyl)-uracil, 1-(β-D-arabinofuranosyl)-5-fluorouracil, 1-(β-D-arabinofuranosyl)-thymine, and 1-(β-D-arabinofuranosyl)-cytosine can be obtained in a high yield by the splitting of the anhydrobond in 2,2′-anhydropyrimidines in dipolar aprotic solvents, such as HMPT, DMF, and DMSO, respectively, in the presence of activated elemental copper. Unlike the formation of cyclopyrimidiens ribonucleosides are directly transformed to the corresponding arabinofuranosyl derivatives by the reaction with diphenylcarbonate and NaHCO₃ in the presence of copper. The reaction proceeds probably via an intermediate formation of the cycloproduct. Further aspects on the mechanism are described.     

Influence du molybdène sur la cinétique des réactions de conversion du méthane en présence de H2O et CO2

An experimental study of the catalytic action of molybdenum in the reactions of methane with water vapor and carbon dioxide was performed in a fluidized bed differential reactor. In the experiments, special care was taken to isolate the homogeneous reactions which could have interfered with the catalytic effect. The ratio O₂/CH₄ in the feed and the heterogeneous reactions of oxidation and carbide Mo₂C formation, were shown to have considerable influence on the obtained yields. From kinetic results obtained on carbide and pure metal, a reaction mechanism is proposed, and a rate equation is presented for the conversion of methane by water vapor on molybdenum.     

Influence de l'epaisseur de l'adhésif et du vieillissement sur les propriétés mécaniques dynamiques d'un assemblage: Adhésif structural/acier inoxydable

Dynamic mechanical properties of bounded joints—stainless steel/epoxy adhesive—are investigated as a function of the thickness of the adhesive and aging conditions. The viscoelastic properties of the bounded joints have been investigated by Dynamic Thermo Mechanical Analysis (DTMA). The glass transition temperature (T_g) showed a dependence on both the chemical/electrochemical pretreatments of the substrate and the thickness of the adhesive in the bounded joint. The crosslinking density in the adhesive thus seemed more important in the interfacial region than in adhesion bulk. The water uptake induces a plasticization of the adhesive and a decrease in T_g. The most stable bounded joints were obtained by carrying out sulfochromic acid anodization as a pretreatment step. The most important stability of the bounded joints was obtained with the sulfochromic anodization of the substrate.     

Etude par résonance magnétique nucléaire des polychlorures de vinyle polymérisés par les systémes titanate de butyle–alcoyles-aluminium

NMR analysis of the chain ends of samples of poly(vinyl chloride) prepared using a Ti(OBu)₄–alkylaluminum system in CCl₄ reveals that the mechanism of the formation of free radicals depends on whether the alkylaluminum used is chlorinated or not. In the first case, some of the radicals are reactive in the initiation step of the polymerization, while in the latter case theses radicals first undergo transfer to CCl₄, then the CCl₃· formed initiates the polymerization of vinyl chloride. The poly(vinyl chloride) radicals are chiefly stopped by transfer to CCl₄ (chlorine abstraction) or to alkylaluminum (hydrogen abstraction). In transfer reactions between growing radicals and alkylaluminum, the radicals formed have to react with CCl₄ before reinitiating the polymerization of vinyl chloride.     

Selective oxidation of H<Subscript>2</Subscript>S to ammonium thiosulfate and elemental sulfur using mixtures of V-Bi-O and Sb<Subscript>2</Subscript>O<Subscript>4</Subscript>

The selective oxidation of hydrogen sulfide in the presence of excess water and ammonia was investigated by using vanadium-bismuth based mixed oxide catalysts. Synergistic effect on catalytic activity was observed for the mechanical mixtures of V-Bi-O and Sb₂O₄. Temperature programmed oxidation (TPO), X-ray photoelectron spectroscopy (XPS), and two separated bed reactivity test results supported the role of Sb₂O₄ for reoxidizing the reduced V-Bi-O during the reaction. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

Modéalisation de la copolyméarisation éathylégne α-oléafine par catalyse ziegler—natta

A copolymerization model of ethylene and a α-olefin describing the monomer uptake and the quality of the polymer produced, namely M_n, M_w, M_z, the distribution of molecular weight, short branching index and double bonds, is presented. This model assumes the existence of several types of active sites (2 or 3) and do not involve any limiting diffusion. It is applied to ethylene and butene-1 bulk copolymerization at high pressure and high temperature. Parameters are identified with CSTR experiments.     

Selective oxidation of hydrogen sulfide over LaCoO<Subscript>3</Subscript> and LaSrCoO<Subscript>4</Subscript> mixed oxides

Perovskite LaCoO₃ and perovskite-like LaSrCoO₄ mixed oxides were prepared by polyglycol gel method, and their catalytic performance was compared for the selective oxidation of hydrogen sulfide in a stream containing excess amount of ammonia and water for the first time. These samples were investigated by using XRD, BET, O₂-TPD and XPS. The catalytic activity and the selectivity to solid products (ammonium thiosulfate and elemental sulfur) of LaCoO₃ were better than those of LaSrCoO₄, and this is explained in terms surface contents of oxygen and cobalt, oxidation state of cobalt, and BET surface area.     

Comparaison des méthodes de fractionnement par chromatographie de perméation et par gradient d'elution pour la détermination des répartitions moléculaires des polypropylénes

Molecular weight distributions for polypropylene samples have been determined by a permeation fractionation method (GPC). Porous silica beads were used as a packing material for the columns. The set of columns allows a good separation of the polypropylene macromolecular chains in a range of molecular weights from 5000 to 1.5 × 10⁶, and the thermal and mechanical stabilities of these beads are very good. The calibration has been carried out with fractions of polypropylene of narrow molecular weight distribution prepared by a large-scale column fractionation. The molecular weights M?_w and M?_n and the ratios M?_w/M?_n calculated from the GPC curves show, in general, good agreement with the ones calculated from the column fractionation curves. However, the M?_w/M?_n ratios are always highter in the case of GPC fractionation. This could be due to diffusion phenomena.     

On the thermodynamics of concentrated strong electrolytes aqueous solutions the system NaNO3—NaCl—H2O

A simple analytical function is proposed for the calculation of molar excess Gibbs energy of binary solutions of strong electrolytes in water. Empirical parameters can be easily determined from experimental data reported in the literature. The treatment is extended to ternary solutions and to solid liquid equilibria using an empirical equation. Absence of solid solutions is assumed. The correlations are applied to the common ion ternary system NaNO₃-NaCl-H₂O in the temperature range from 0 to 100°C. Predictions of activity coefficients of the binary systems and saturation curves of the ternary system are in good agreement with experimental data.     

Étude hydrodynamique des lits fluidisés sous vide et sous haute température

After having analyzed the few literature results concerning fluidized beds hydrodynamics under reduced pressure, new theoretical elements are proposed which provide an estimation of the beginning and finishing fluidization velocities. Numerous experimental results(U_mfapp, U_mb, U_mp, ?_mf, ?_mb, ?_mp), obtained at 20 and 500°C, are then presented for several sub-atmospheric pressures. Finally, f& the first time, at leastto our knowledge, by high frequency recording pressure drops through the bed, the influence of pressure decreases on the hydrodynamics is accurately analyzed.     

Ein nachhaltiges Konzept zur Bereitstellung von reinem CO2 als C‐Quelle für Solarfuels – Synergien zwischen Biokohle und Biogas

In times of the German energy transition (“Energiewende”) chemical storage technologies achieve an increasing interest because only with their help the energy of the excess electricity from wind‐ and solar plants can be stored in huge quantities in form of hydrocarbons. The hydrogen generated by water electrolysis can be converted with carbon dioxide to hydrocarbons. In addition, pure CO₂ must be available at a reasonable price. For this CO₂ supply a sustainable concept is presented.     

Conductance measurements of some electrolytes in N,N-dimethyformamide and its binary mixtures witth other organic solvents—II

Equivalent conductances of Bu₄NBPh₄, Bu₄NNO₃, Bu₄NI,KClO₄, Kl, NaI, NaBPh₄, Ph₄PCl, LiCl, AgNO₃ and CuClO₄. 4AN have been measured at 25°C in binary mixtures of N,N-dimethylformamide (DMF) containing 1 mol % of 1, 1, 3, 3-tetramethylurea (TMU), dimethylsulphoxide (DMSO) and hexamethylphosphotriamide (HMPT). Such measurements for LiCl, NaI, KClO₄ and CuClO₄. 4AN have also been carried out in DMF and in binary mixtures of DMF containing 1 mol % pyridine (Py), α-picoline (α-Pic), β-picoline (β-Pic), γ-picoline (γ-Pic) and acetonitrile (AN). The conductance data in all the cases have been analyzed by the Shedlovsky equation. Limiting ion conductances have been obtained by the method of Fuoss et al. The actual solvated radii of ions, evaluated using limiting ion conductances show that Ag⁺ and Cu₊ have strong preferential solvation by all solvents which have been used to prepare the binary mixtures with DMF and the preferential solvation for both Ag⁺ and Cu⁺ with HMPT, DMSO and TMU is relatively stronger than with AN and is practically of similar magnitude as with the organic bases.     

Une éequation d'éetat de clausius modifiée repréeasentant l'éeatat liquide

The three parameters of a modified Clausius state equation have been generalized with a view to calculating thermodynamic properties of saturated pure substances, from the normal boiling temperature to the critical one. The method described in the paper, which only requires the knowledge of the characteristic properties of the pure substances (T_c, P_c, Z_c, ω) has been tested on 28 different compounds (saturated and unsaturated hydrocarbons, simple and polar molecules). The results obtained show that the state equation proposed correctly describes the liquid-vapour equilibrium (saturation vapour pressure and vaporization enthalpy) and moreover provides a satisfactory representation of the saturated liquid condition.     

Synthèse et propriétés de polyuréthannes réticulés par des cycles isocyanurates

The reaction of α-ω-hydroxy-terminated polyethers or polybutadienes and diphenyl methane diisocyanate in presence of a basic catalyst, such as triethylene or dibutyl tin dilaurate gives polyurethane networks. IR spectroscopy shows that the networks contain isocyanurate rings. These rings are stable at high temperature showing a constant rubbery modulus from T_g up to 160°C. It is noted that the modulus varies with the formulation, the nature of the prepolymer and its molecular weight, the rate of diisocyanate and the catalyst as well as the possibility of introducing butanediol into the formulation.     

Anionic synthesis and characterization of ω-formyl-functionalized polystyrenes

ω-Formyl-functionalized polystyrenes can be synthesized in quantitative yield by reacting poly(styryl)lithium (M _n = 2 × 10³?8 × 10³ g/mol) in benzene with a 0.1?0.4 molar excess of 4-morpholinecarboxaldehyde followed by methanol termination and precipitation into methanol. Narrow molecular weight distribution ω-formyl-functionalized polystyrenes were characterized by hydroxylamine end-group titration, thin layer chromatography and both ¹H and ¹³C NMR spectroscopy. The mechanism of the functionalization was studied by trapping the tetrahedral α-amino alkoxide intermediate with diphenylphosphinic chloride.