Some physical properties of polyorganosiloxanes. I. Linear polyorganosiloxanes

Some physical properties of linear polydimethylsiloxanes have been studied. The states and transitions in polydimethylsiloxanes have been investigated by using the method of dynamic heat capacity and a thermomechanic method in the temperature range from ?150 to +200°C. The temperature dependence of primary and secondary crystallization has been studied by optical, calorimetric, and x-ray methods.     

Isotopic splitting in matrix isolated BF3

Small isotopic frequency shift information, if precisely determined, provides an effective constraint on intramolecular force fields. The most precise data for these frequency shift parameters Δν are derived from high resolution, gas-phase infrared spectral analyses. In the present study, we compare for BF₃ the isotopic frequency shift Δν₄ from a recently published gas-phase study with the value for Δν₄ that we obtain from the spectrum of matrix isolated BF₃. The excellent agreement between the two methods suggests further applications of the matrix technique for obtaining precise frequency shift data.     

The effect of the sintering atmosphere on the densification of B4C ceramics

Densification of boron carbide during sintering may be improved by a two-stage process, namely heating to 2000°C under vacuum and sintering at 2190°C under argon. This sintering regime allows achieving a relative density of the ceramic bodies fabricated from a fine powder higher than 95%. The nitrogen treatment of the boron carbide phase at 1900°C leads to the formation of the BN phase and precipitation of graphite. Vacuum treatment of these samples at 2000°C leads to decomposition of the boron nitride phase. The liberated free boron may again react with graphite to form in situ boron carbide particles. The experimental investigations of the sintering behavior of the boron carbide phase under various atmospheres supported the thermodynamic predictions regarding the phase transformation. No evidence, however, was found for enhanced sintering under a nitrogen atmosphere.     

Structural Study of an Unusual Cubic Pyrochlore Bi1.5Zn0.92Nb1.5O6.92

Single-phase pyrochlore-type specimens of Bi_1.5Zn_0.92Nb_1.5O_6.92 were studied using combined electron, X-ray and neutron powder diffraction techniques. Rietveld refinements using neutron powder diffraction data confirmed an average pyrochlore structure A₂B₂O₆O′ (Fd&3macr;m, a=10.5616(1) Å) with both Bi and Zn mixed on the A-sites. However, refinements revealed significant local deviations from the ideal pyrochlore arrangement which were caused by apparent displacive disorder on both the A and O′ sites. The best fit was obtained with a disordered model in which the A-cations were randomly displaced by ∼0.39 Å from the ideal eight-fold coordinated positions. The displacements occur along the six 〈112〉 directions perpendicular to the O′-A-O′ links. In addition, the O′ ions were randomly displaced by ∼0.46 Å along all 12 〈110〉 directions. Crystal-chemical considerations suggest the existence of short-range correlations between the O′ displacements and both the occupancy of the A-sites (i.e., Bi or Zn) and the directions of the A-cation displacements. The combined A-cation and O′ displacements change the coordination sphere of the A-cations from 8 to (5+3); the resulting coordination environment of the A-cations bears similarities to that of the (5+1)coordinated Zn in zirconolite-like Bi₂Zn_2/3Nb_4/3O₇. The observed displacive disorder in the A₂O′ network of the Bi_1.5Zn_0.92Nb_1.5O_6.92 structure involves atoms associated with the lowest-frequency vibrational bending mode, and is likely responsible for both the high dielectric constant and the dielectric relaxation reported for this compound.     

Analysis of uniform binary subdivision schemes for curve design

The paper analyses the convergence of sequences of control polygons produced by a binary subdivision scheme of the form

Absolute infrared intensities of hydrocarbons

Dipole-moment derivatives, calculated by both the CNDO/2 method with different parameterizations and the INDO method, are compared to the experimental values determined from absolute infrared intensity measurements for the IR active modes of methane, ethane, ethylene and acetylene. A parameter refinement procedure is introduced in which the CNDO/2 molecular orbital parameters are adjusted through a damped least-squares treatment to give best agreement with the observed dipole-moment derivatives. It is found that the refinement does not substantially improve the agreement obtained with the original CNDO/2 parameterization. The INDO method gives somewhat poorer agreement than the CNDO/2 calculations. As an example of the applicability of the molecular orbital methods toward reproducing relative infrared intensities, the spectrum of cyclopropane in the gasphase is examined.

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Zusammenfassung Die Ableitungen des Dipol-Moments, die nach der CNDO/2-Methode mit verschiedenen Parametrisierungen sowie der INDO-Methode berechnet wurden, werden mit den experimentellen Ergebnissen aus Messungen der absoluten Infrarot-Intensitäten für die IR-aktiven Schwingungen von Methan, Äthan, Äthylen und Azetylen verglichen. Die CNDO/2-Parameter werden mit einer Methode der kleinsten Quadrate den beobachteten Dipol-Moment-Ableitungen angepaßt. Die Ergebnisse sind jedoch nicht wesentlich von denen der ursprünglichen CNDO/2-Methode verschieden. Die INDO-Ergebnisse sind nicht so gut wie die CNDO/2-Ergebnisse. Als Beispiel der Anwendbarkeit der MO-Methoden zur Berechnung von relativen IR-Intensitäten wird das Spektrum des Cyclopropans in der Gasphase untersucht.

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Résumé Les dérivées du moment dipolaire, calculées par la méthode CNDO/2 avec différentes paramétrisations et par la méthode INDO, sont comparées aux valeurs expérimentales déterminées à partir de mesures d'intensité absolue pour les modes actifs dans l'infra-rouge dans le méthane, l'éthane, l'éthylène et l'acétylène. Les paramètres sont ajustés de manière à donner le meilleur accord avec les dérivées du moment dipolaire. Cet ajustement n'améliore pas sensiblement l'accord obtenu avec la paramétrisation CNDO/2 originale. La méthode INDO donne des résultats moins bons que les calculs CNDO/2. Le spectre du cyclopropane en phase gazeuse est étudié comme exemple de l'applicabilité de la méthode des orbitales moléculaires au calcul des intensités relatives infra-rouge.

     

Fused polycyclic nitrogen-containing heterocycles

The condensation of methyl phenylchloropyruvate with 1-phenyl-3-(2-pyridyl)thiourea and its 3-and 4-picolyl homologs affords the corresponding 4-hydroxythiazolidines, which react with o-phenylenediamine to give one of two possible thiazolo[3,4-a]quinoxalines containing the pyridyl-or picolylimine substituents at position 1. 3a-Hydroxy-3-phenylimino-1-(2-pyridyl)thiazolo[3,4-a]quinoxalin-4-(3H,5H)-one, which is a covalent hydrate of the final product, was isolated as an intermediate in this reaction.     

Liquid chromatographic analysis of vitamin B6 in reconstituted infant formula: collaborative study

A liquid chromatographic (LC) method was validated for the determination of total vitamin B6 in infant formula. Total vitamin B6 was quantified by converting the phosphorylated and free vitamers into pyridoxine. Pyridoxine was determined by ion pair reversed-phase LC with fluorescence detection. The method was subjected to an AOAC collaborative study involving a factory-manufactured, milk- and soy-based infant formula. Each was spiked at 3 concentrations in the range of 0-1 microg/g and sent as blind duplicate to participant laboratories. Nine laboratories returned valid data which were statistically analyzed for outliers and precision parameters. The repeatability relative standard deviation (RSD(r)) ranges were 2.0-4.0 and 3.5-5.9% for fortified milk- and soy-based formulas, respectively. The reproducibility relative standard deviation (RSD(R)) ranges were 8.2-8.4 and 6.7-11.2% for fortified milk- and soy-based formulas, respectively. HORRAT values ranged from 0.42 to 0.53, indicating that the precision of the method is acceptable. The mean RSD(r):RSD(R) values were 0.60 and 0.55 for milk- and soy-based formulas, respectively. As expected, RSDs for the unfortified samples were higher, but their HORRAT values (0.81 and 2.06) helped define a realistic limit of quantitation as 0.05 microg/g. Recovery data were quantitative and varied between 81.4 and 98.0% (mean = 89.8%) for each of 6 spiked materials.     

Synthesis of dihydro-1,3-thiazine derivatives. II

1-Oxo-3-thioxo-5-hydroxy-2-acyl-2,3-dihydro-1H-1,3-thiazino[6,5-c]quinolines were obtained for the first time by condensation of 2-hydroxy-3-mercaptoquinoline-4-carboxylic acid with acyl isothiocyanates. Alkyl and acyl isothiocyanates react with 1-methyl-2-oxo-3-mercapto-1, 2-dihydroquinoline-4-carboxylic acid to give 1,5-dioxo-3-thioxo-2-alkyl (acyl)6-methyl-2, 3,5,6-tetrahydro-1H-1,3-thiazino [6,5-c] quinolines.See [1] for communication I.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 641–643, May, 1973.