Sur la thermogravimétrie des précipités analytiques: Dosage du thallium

With the help of the chevenard thermobalance the authors have established the following limits for drying or ashing, of thallium derivatives before weighing. Trioxide prepared chemically: 126° to 230°; trioxide prepared electrolytically: 156° to 283°; chloride: 56° to 425°; iodide. 70° to473°; sulphate : 92° to 355°; luteocobaltic thalliumchloride :50° to 210°; chromate : 97° to 745°; hexachloroplatinate: 65° to 155°; thionalide complex: 69° to 156°; mercaptobenzothiazole complex: 52° to 217°.The two trioxides which have been prepared show signs of a transitory formation of 3Tl₂O₃.Tl₂O on heating, but above 600° they behave differently. The chemically prepared trioxide shows two ranges of thermal stability.     

Propriétés themodynamiques des mélanges binaires. Chaleurs de mélange des n-alcanes ainsi que de leurs isomères

The following heats of mixing have been measured: the five isomers of hexane with n-dodecane at 10°, 20° and 30°C, and with n-hexadecane at 20°C, as well as the systems dodecane-hexene-1 at 20°C, and dodecane-methyl-2-pentene-1 at 10° 20° and 30°C.     

Thermal decomposition of some rare earth metal cupferrates and neocupferrates

The thermal decomposition of the eupferrates and neocupferrates of europium, terbium, dysprosium, holmium, erbium, and ytterbium was studied on the thermobalance. The metal chelates possessed poor thermal stability as well as a pronounced tendency to Coprecipitate reagent. The minimum oxide level temperatures for the metal cupferrates were : Eu, 570°; Tb, 540°; Dy, 550°; Ho, 610°; Er, 550° and Yb, 520°. The minimum oxide level temperatures for the metal neocupferrates were: Eu, 560°; Tb 565°; Dy, 540°; Ho,445°; Er, 530°; and Yb, 485°.     

Estimation of the conformation of 2-hydroxy-4,6-dimethylbenzophenone and 2,4,6-trimethoxybenzophenone from electronic absorption spectra and PPP LCI ca

The twisting effect of benzene rings on the electronic spectra of derivatives of benzophenone (BPh), 2-hydroxy-4,6-dimethylbenzophenone (2-OH-4,6-diCH₃BPh) and 2,4,6-trimethoxybenzophenone (2,4,6-triOCH₃BPh) has been interpreted by the PPP method. The effect of structure, protonation, ionization and interaction with proton-acceptor solvent on the twisting of aromatic rings is discussed. The following twist angles of substituted ring (θ_I) and unsubstituted ring (θ_II) in 2-OH-4,6-diCH₃BPh were found: neutral form in cyclohexane θ_I = 39°–48°, θ_II = ?30°–(?45°); neutral form in ethanol θ_I = 66°–72°, θ_II = ?30°–0°; protonized form θ_I = 64°–6°, θ_II = ?30°–0°; ionized form θ_I = 66°–74°, θ_II = ?30°–0°. In the neutral form of 2,4,6-triOCH₃PBh the substituted ring is twisted by angle θ_I ~ 70° while in the protonated form the unsubstituted ring is twisted by angle θ_II ~ 60° and the substituted one is coplanar with the CO group.     

Creation of low hysteresis superhydrophobic paper by deposition of hydrophilic diamond-like carbon films

The creation of low hysteresis superhydrophobic paper is reported using a combination of oxygen plasma etching and plasma deposition of an 80 nm non-fluorinated, hydrophilic diamond-like carbon (DLC) coating. The DLC has an equilibrium (flat surface) contact angle (θ _e ) of 68.2° ± 1.5°, which is well below the 90° contact angle that is typically believed to be a prerequisite for superhydrophobicity. Coating of paper substrates with the DLC film yields an advancing contact angle of 124.3° ± 4.1°, but the surface remains highly adhesive, with a receding contact angle <10°. After 60 min of plasma etching and DLC coating, a low hysteresis, superhydrophobic surface is formed with an advancing contact angle of 162.0° ± 6.3° and hysteresis of 8.7° ± 1.9°. To understand the increase in contact angle and decrease in hysteresis, atomic force microscopy and optical profilometry studies were performed. The data demonstrates that while little additional nanoscale roughness is imparted beyond the first 5 min of etching, the roughness at the microscale continually increases. The hierarchical structure provides the appropriate roughness to create low hysteresis superhydrophobic paper from a hydrophilic coating.     

Thermal analysis of eugenol,isoeugenol and their benzoic acid esters

Eugenol and isoeugenol were investigated by means of thermal analysis. It was observed that eugenol and isoeugenol have one characteristic endothermic effect at 260° and 290°C, respectively, and two exothermic effects in the temperature intervals 270°–590°C. The DTA curves of the benzoyl esters of eugenol and isoeugenol begin with endothermic effects at 70° and 95°C, respectively, which coincide with the melting points of these compounds.     

Thermal transitions of DODAB vesicular dispersions

Two endothermic transitions, at 36°C and 44°C, were observed with differential scanning calorimetry (DSC) upon heating dioctadecyldimethylammonium bromide vesicle dispersions that were equilibrated below 15°C while in samples kept at 25°C there was only the transition at 44°C, which was shown to be the gel to liquid–crystalline transition by ¹H-NMR measurements. The transition at 36°C was reversed in an exothermic transition around 13°C upon cooling. The slowness of this transition at ambient temperatures suggests that the presence of the transition at 36°C in a DSC upscan depends strongly on the sample history.     

Morphological studies on polybutylene terephthalate

The morphology of poly(butylene terephthalate) (PBT) crystallized from the melt at various temperatures was studied by small-angle light scattering, polarizing microscopy, and wide-angle x-ray diffraction. Spherulites with a maltese cross at 45° to the polars formed at lower temperatures while spherulites having an apparently higher melting point with a maltese cross along the polars (0°–90°) formed at higher temperatures. The spherulite size and crystallinity increased with increasing crystallization temperature. The H_v scattering patterns arising from the spherulites formed at lower temperature showed intensity maxima at azimuthal angles of 0° and 90°, while those obtained at higher temperatures showed the more common 45° intensity maxima. Microtomed samples from molded PBT bars showed spherulites with a 45° maltese cross which changed to a 0°–90° maltese cross upon heating just prior to melting. The skin-core effect due to varying thermal histories in these molded bars was clearly observed. Solvent crystallized films contained positive 0°–90° spherulites. Some changes occurring upon uniaxial stretching of PBT films are also discussed.     

Molecular distillation

Molecular distillation was studied for the separation of tocopherols from soya sludge, both experimentally and by simulation, under different operating conditions, with good agreement. Evaporator temperatures varied from 100°C to 160°C and feed flow rates ranged from 0.1 to 0.8 kg/h. The process pressure was maintained at 10⁻⁶ bar, the feed temperature at 50°C, the condenser temperature at 60°C, and the stirring at 350 rpm. For each process condition, samples of both streams (distillate and residue) were collected and stored at −18°C before tocopherols analyses. Owing to the differences between molecular weights and vapor pressures of free fatty acids and tocopherols, tocopherols preferentially remained in the residue at evaporator temperatures of 100°C and 120°C, whereas for higher temperatures (140°C and 160°C) and lower feed flow rate, tocopherols tended to migrate to the distillate stream.     

Synthesis and properties of amine‐containing poly(arylene ether sulfone) as an anion‐exchange matrix

Poly(arylene ether sulfone) (PSF), showing good thermal stability and excellent mechanical properties, was synthesized as an anion‐exchange matrix. It was synthesized by the condensation polymerization between bisphenol A and 4,4′‐dichlorodiphenylsulfone. 1°‐Amine‐containing poly(arylene ether sulfone) (1°‐APSF) was synthesized by the reduction reaction of a nitrated PSF. Then, it was transferred to 3°‐amine‐containing poly(arylene ether sulfone) (3°‐APSF) by the alkylation of the amine of 1°‐APSF. The properties of PSF, 1°‐APSF, and 3°‐APSF were investigated by Fourier transform infrared, ¹H NMR spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. The introduction of the 3°‐amine group into PSF increased the glass‐transition temperature but decreased thermooxidative stability. The ion‐exchange capacities of 1°‐APSF and 3°‐APSF were shown to be 2.24 and 2.86 mequiv/g, respectively. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4281–4287, 2002     

C−X Bond Activation by Palladium: Steric Shielding versus Steric Attraction

The C−X bond activation (X = H, C) of a series of substituted C(n°)−H and C(n°)−C(m°) bonds with C(n°) and C(m°) = H₃C− (methyl, 0°), CH₃H₂C− (primary, 1°), (CH₃)₂HC− (secondary, 2°), (CH₃)₃C− (tertiary, 3°) by palladium were investigated using relativistic dispersion-corrected density functional theory at ZORA-BLYP-D3(BJ)/TZ2P. The effect of the stepwise introduction of substituents was pinpointed at the C−X bond on the bond activation process. The C(n°)−X bonds become substantially weaker going from C(0°)−X, to C(1°)−X, to C(2°)−X, to C(3°)−X because of the increasing steric repulsion between the C(n°)- and X-group. Interestingly, this often does not lead to a lower barrier for the C(n°)−X bond activation. The C−H activation barrier, for example, decreases from C(0°)−X, to C(1°)−X, to C(2°)−X and then increases again for the very crowded C(3°)−X bond. For the more congested C−C bond, in contrast, the activation barrier always increases as the degree of substitution is increased. Our activation strain and matching energy decomposition analyses reveal that these differences in C−H and C−C bond activation can be traced back to the opposing interplay between steric repulsion across the C−X bond versus that between the catalyst and substrate.     

Thermal analyses of polymers. XIII. Crystalline character of the 70°c transition of poly(ethylene terephthalate)

The abrupt changes in the linear expansion and dilatometric measurements of poly-(ethylene terephthalate) near 70°C indicate that the transition may be first order. DTA and DSC data show the normal heat capacity change at 70°C, while annealing for for 30 min. at 110°C induces further molecular order. Rapid quenching of PET after heating to 120°C yields an amorphous sample and measurement by depolarized light transmission as the sample is reheated shows rapid crystallization occurring near 80°C. With the occurrence of shrinkage near 68°C and apparent recrystallization at slow heating rates by depolarized light analyses, further support is added to the first-order character of this phase transition. Isothermal annealing for short times at temperatures between 50°C and 80°C produces further increases in molecular order. Cyclic and linear PET oligomers do not contribute to the occurrence of the 70°C transition.     

Newtonian behavior of a styrene–butadiene–styrene block copolymer

The melt rheological behavior of an anionically polymerized styrene–butadiene–styrene (SBS) block copolymer sample (S: 7 × 10³ and B: 43 × 10³) was studied using a Weissenberg rheogoniometer. Highly non-Newtonian behavior, high viscosity and high elasticity, which are characteristics of ABA type block copolymers, were observed at 125°C, 140°C, and 150°C. The data at these temperatures superimposed well onto a master curve giving a constant flow activation energy. However, the data at 175°C indicated a marked change in the flow mechanism between 150°C and 175°C. At 175°C, the sample showed Newtonian behavior, negligible elasticity, and deviation from the master curve. These findings may be considered as an indication that the SBS block copolymer sample undergoes a structural change from a multiphase structure at low temperatures into a homogeneous structure at some temperature between 150°C and 175°C.     

Polymorphism and stability of norfloxacin, (1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinil)-3-quinolinocarboxylic acid

Norfloxacin was studied by thermal methods (TG and DSC), X-ray powder diffraction, and by FT-IR, UV-VIS and NMR spectroscopy. The drug substance can be prepared in two different crystalline forms and in amorphous state, depending on the experimental conditions of preparation. DSC examinations were carried out at various heating rates and by cycling the samples in the temperature range 50°–250°C. The unstable crystalline form undergoes two irreversible solid-solid phase transitions at 176.5° and 197.6°C. The polymorph melts in the temperature range 218.5°–220.0°C.

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Zusammenfassung Norfloxacin wurde mittels thermischer Methoden (TG und DSC), weiterhin mittels der Debye-Scherrer-Methode und FTIR-, UV-VIS-und NMR-Spektroskopie untersucht. Je nach den experimentellen Bedingungen bei der Herstellung kann die Wirkstoffsubstanz in zwei verschiedenen kristallinen und in einer amorphen Form hergestellt werden. Die DSC-Untersuchungen wurden bei zahlreichen Aufheizgeschwindigkeiten und durch abwechselnden Temperaturwechsel zwischen Raum- und Schmelztemperatur durchgeführt. Die unstabile kristalline Form unterliegt zwei irreversiblen Feststoff-Feststoff-Umwandlungen bei 176.5° und bei 195.6°C. Das polymorphe Material schmilzt im Temperaturbereich 218.5°–220.0°C.

     

Synthesis and properties of mesogenic laterally fluorinated compounds containing benzoxazole unit

Series of mesogenic laterally fluorinated compounds, 2-(2′,3′-difluoro-4′-alkoxybiphenyl-4-yl)-benzoxazole derivatives (nB-Fx) bearing different substituents (H, CH₃, Cl, NO₂, coded as nB-FH, nB-FM, nB-FC and nB-FN, respectively) at 5-position, were prepared and characterised. Their phase transition behaviour was investigated by differential scanning calorimetry and polarising optical microscopy. nB-Fx with alkoxy chain lengths of 2 to 10 carbons exhibited enantiotropic mesophases, for which the mesophase ranges were 0°C–58°C and 0°C–71°C on heating and cooling for nB-FH, 41°C–93°C and 66°C–140°C for nB-FM, 44°C–133°C and 87°C–155°C for nB-FC, and 0°C–76°C and 0°C–95°C for nB-FN, respectively. Compared to non-fluorinated analogues, with the exception of nB-FC, fluorinated nB-Fx mainly exhibited nematic mesophase both in heating and cooling, which were attributed to the disruption of the side-to-side intermolecular packing caused by the two ortho-lateral fluoro substituents. For nB-Fx series, nB-FM, nB-FC and nB-FN exhibited a much wider mesophase range than the corresponding nB-FH series, which indicated that the substituent at benzoxazole moiety was helpful in increasing the mesophase stability. With the exception of nB-FN, the nB-Fx series displayed intense photoluminescence emission at 379–383 nm in methylene chloride solution, when it was excited at its absorption maxima.     

Transition metal—Chalcogen systems,V.

The iron—tellurium phase diagram was investigated by thermal, X-ray, and isopiestic measurements up to 1,100°C. Tetragonal β(≈FeTe_0.9) with a homogeneity range from 45.9 to 48.1 at % Te at 715°C is stable from room temperature to 844°C where it decomposes peritectoidally into Fe and rhombohedral high-temperature β′(≈FeTe_0.9). β′ decomposes at 914°C peritectically into Fe and liquid, and at 800°C by a eutectoid reaction into β and γ(≈FeTe_1.2). γ exists between 809° (γ→β′+δ) and 636°C (γ→β+δ). The monoclinically distorted NiAs-phase δ decomposes peritectically at 55.2 at % Te and 812°C into β′ and liquid and is stable down to the eutectoid δ?β+δ′ at 565±15°C and 58.8 at % Te. δ is separated from hexagonal NiAs-type δ′ by a narrow two-phase region. δ′ has a maximum range of homogeneity at 650°C from 59.2 to 65.1 at % Te and exists between the eutectoid δ′?β+ε at 519°C and the peritectic δ+L?δ′ at 766°C. Orthorhombic ε(≈FeTe_2.0) is stable from room temperature to the peritectic δ′+L=ε at 649°C. ε and Te form a degenerate eutectic at 446°C.     

Relative reactivities of 1,2-cyclohexadiene with conjugated dienes and styrene

Generation of 1,2-cyclohexadiene in the presence of conjugated dienes leads to (2 + 2) and/or (2 + 4) cycloaddition products. Methods used to generate 1,2-cyclohexadiene were: (1) treatment of 6,6-dibromobicyclo[3.1.0]hexane with methyllithium in tetrahydrofuran-ether at 0° and 60°; (2) treatment of 1,6-dichlorocyclohexene with magnesium in tetrahydrofuran at 60°; and (3) treatment of 1-bromocyclohexene with t-BuOK in THF at 60° or dimethyl sulfoxide at 40°. Comparison of relative reactivities with various dienes and styrene in ether solvents at 60° confirmed that the same intermediate, uncomplexed 1,2-cyclohexadiene, was involved in these reactions. Relative reactivities at 0° and 60° were found to be: 2-methylfuran (0·12, 0·14); furan (0·17, 0·16); 2,4-hexadiene (0·17,—); cis-pentadiene (0·53, 0·53); 2,3-dimethylbutadiene (2·35, 1·9); 1,3-cyclohexadiene (1·85,—); styrene (2·35, 1·9); and 1,3-cyclopentadiene (47, 14).     

Sur la thermogravimétrie des précipités analytiques : Dosage du Lithium

The four salts normally used for the gravimetric determination of lithium have been submitted to pyrolysis with the aid of the chevenard thermobalance. To obtain correct results it is necessary to heat the chloride between 175° C, and 606° C, the sulphate above 160°, the phosphate above 450° C, and the aluminate above 471°.     

Cryochemistry. Large acceleration of the oxidation of hydroxylamine by iodate in frozen solution

A large rate increase of the oxidation of hydroxylamine by iodate has been shown in frozen aqueous solution as compared to the supercooled one. The experiments were conducted under frozen conditions at ?5°, ?10°, ?15°, and ?20°C and in liquid solution at 0°, ?5°, and ?10°C, as well. At given time intervals the progress of the reaction was traced by the pH decrease of the unbuffered samples. The around 500-fold enhanced reaction rate of the frozen samples (at ?5° and ?10°C) points to an important role of the ice itself beside the increased solute concentration in the compartmentalized heterogeneous system. The contribution of ice to this pH-regulated oxidation is discussed as a consequence of the high mobility and transfer rate of proton on the ice surface. © 1993 John Wiley & Sons, Inc.     

Thermal decomposition of poly(α,α,α′,α′-tetrafluoro-p-xylylene) in nitrogen and oxygen

The thermal decomposition of poly(α,α,α′,α′-tetrafluoro-p-xylylene) (parylene AF-4) films with thicknesses of ca. 7.5 and 10 μm has been studied by both dynamic (10°C min^?1) and isothermal TG in either nitrogen or oxygen atmospheres. In dynamic studies with nitrogen, gross decomposition occurs between 546.7±1.4 and 589.0±2.6°C, with 26.8±4.4% of the initial mass remaining at 700°C. With oxygen as the purge gas, the onset of decomposition shifts slightly to 530.8±4.2°C. The end of the transition at 587.4±2.6°C is within experimental error of the nitrogen value, but no polymer remains above 600°C. Isothermal data were obtained at 10°C intervals from 420 to 490°C in nitrogen, and from 390 to 450°C in oxygen. Plots of log(Δ%wt/Δt)vs. T^?1 are linear throughout the specified range for oxygen and from 420 to 470°C for nitrogen. The calculated activation energies of (147±16) kJ mol^?1 and (150±12) kJ mol^?1 in N₂ and O₂, respectively, are equal within experimental error.