Abtrennung durch Diasolyse mit Hilfe gequollener Silicongummimembranen

Zusammenfassung Ein Gerät zur Diasolyse (Flüssig-flüssig Extraktion mit phasentrennender Membran) wird beschrieben, bei dem ein Silicongummischlauch als Membranmaterial dient. Der Einfluß einer Reihe von Parametern wurde untersucht (Pumpgeschwindigkeit, Schlauchlänge, Temperatur, pH, Volumen der wäßrigen Phase, Konzentration der zu bestimmenden Substanz, Quell- und Lösungsmittel, Fremdsubstanzen, kontinuierliche und diskontinuierliche Ausführung). Als Testsubstanzen wurden Barbiturate verwendet. Die Methode eignet sich zur Trennung von lipophilen und lipophoben Stoffen sowie zur Spurenanreicherung.

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Separation by diasolysis by means of swollen silicone rubber membranes

An apparatus for diasolysis (liquid-liquid extraction with phase separation by membranes) is described, which employs silicone rubber tubes as membrane material. The effect of various parameters has been investigated (pumping rate, tube length, temperature, pH, volume of aqueous phase, concentration of substance to be determined, swelling agent, solvent, foreign substances, continuous and discontinuous mode of operation). Barbiturates served as testing substances. The method is suitable for the separation of lipophilic from lipophobic substances and also for the enrichment of traces.

     

Investigations of aromatic polyesters with polynaphthalene systems in the main chain—VI: NMR studies of the structure of the aromatic copolyesters

Nuclear magnetic resonance spectra of several kinds of terephthalic copolyesters of 4,4′dihydroxydinaphthyl 1,1′ and 2,2 bis(4-hydroxyphenyl) propane were recorded. Proton signals of the terephthalic acid unit corresponding to heterolinkages and homolinkages could be observed in the range from 8.23 to 8.53 ppm. The average sequence lengths and the degrees of randomness in the copolyesters were calculated from the intensities of these signals.     

Rates of base-catalysed cleavage of pyridyl-, quinolyl-, picolyl- and (quinolylmethyl)-trimethylsilanes

Rates of cleavage of some picoyl- and (quinolylmethyl)-trimethylsilanes (RSiMe₃, where R = PyCH₂ or QnCH₂SiMe₃) have been measured in “90%” aqueous methanolic sodium methoxide at 50°C. Relative reactivities are: 2-PyCH₂, 1.0; 3-PyCH₂, 0.030; 4-PyCH₂, 8.9; 2-QnCH₂, 41; 3-QnCH₂, 0.161; 4-QnCH₂, 37. The rates correlate well with those for base-catalysed hydrogen-exchange in the parent carbon acids RH. Approximate pK_a's (based on the scale of ion-pair acidities in CsNHC₆H₁₁H₂NC₆H₁₁, with pK_a of 9-phenylfluorene = 18.6) for the carbon acids, RH, can be derived as follows: 2-PyCH₃, 29.5; 3-PyCH₃, 34; 4-PyCH₃, 27; 2-QnCH₃, 25; 3-QnCH₃, 32; 4-QnCH₃, 25.Rates of cleavage of pyridyl- and quinolyl-trimethylsilanes (PySiMe₃ and QnSiMe₃) by sodium hydroxide in 4 : 1 v/v Me₂SO/H₂O at 50°C have also been measured; and the relative reactivities are: 2-Py, 1.0; 3-Py, 2.9; 4-Py, 8.4; 2-Qn, 15.9; 3-Qn, 12.7; 4-Qn, 184. The sequence of reactivity differes from that for base-catalysed hydrogen-exchange at the relevant positions of pyridine and quinoline, indicating that the reactivities are not determined in both cases (if in either) solely by the stabilities of the corresponding carbanions.     

Conformational effects in 3-halotetrahydropyrans

The conformational equilibria of 3-chloro- and 3-bromotetrahydropyran were measured by NMR and IR spectroscopy using model 2-alkyl-5-halotetrahydropyrans. The 3-chloro compound was 76·2% equatorial in carbon tetrachloride and 58·5% in acetonitrile and the 3-bromo compound 85% equatorial in carbon tetrachloride. The conformational equilibrium is discussed in terms of dipole, electronic and van der Waals effects.     

Delocalization resonance energy of the allylic radical from the geometrical isomerization of hexa-1,3,5-trienes

Thermal cis, trans geometrical isomerization theoretically involves a 90° twisted, singlet diradical-like transition state which may serve as a base for the examination of structural perturbations. Although thermal rearrangement of hexa-1, trans-3,5-triene (and all-trans octa-2,4,6-triene) to the cis isomer cannot be followed directly owing to subsequent cyclization and 1,5 hydrogen shifts, activation parameters for disappearance have been determined. Experimental complications and mechanistic uncertainties which make interpretation difficult are removed in the bicyclic hexatriene, cyclopentenylidenecyclopentene. These geometrical isomers undergo uncomplicated thermal cis, trans isomerization in vessels of lead-potash glass: log k₁ = 12·03±0·32?41·7±0·8/(0·004575T_abs). Extraction of a value for allylic delocalization energy from the behavior of hexa-1, trans-3,5-triene [log k₁ = 12·91 ± 0·47?44·3±1·2/(0·004575 T_abs)] requires corrections of the Dewar-Schmeising type for changes in hybridization of the σ bonds. Depending on whether ethylene or trans-butene is taken as standard, values of 12·2 and 13·1 kcal/mol are obtained (estimated uncertainty ± 2 kcal/mol).     

Esr spectra and magnetic constants of α-Al2O3:Co,H

ESR spectra of the defect α-Al₂O₃:Co²⁺, H⁺ are reported and used to derive the magnetic tensors g and A. This defect is shown to exist in several types, and models in the framework of the α-Al₂O₃ structures are proposed.     

Friedel-crafts copolymerization of thiophene and p-di(chloromethyl)benzene. II. Products of the later stages of the reaction

Products of the copolymerization of thiophene and p-di(coloromethyl)benzene in presence of stannic chloride have been separated by using gel-permeation chromatography (GPC) and identified by using principally mass, infrared, and nuclear magnetic resonance spectroscopy. The GPC separation is not nearly as efficient as the separation of the products of the corresponding benzene–DCMB and diphenylmethane–DCMB reactions which have previously been described. A further complication which makes a kinetic analysis of this reaction more difficult is the occurrence of intramolecular condensation of certain of the earlier products leading to cyclic structures incorporating four aromatic rings. These investigations have made it possible to deduce some of the principal structural differences between the thiophene–DCMB and benzene–DCMB polymers which may have some bearing on the differences which have been found in their thermal stabilities.     

Über die Michael-Reaktion mit Chinolacetaten, 3. Mitt.

Zusammenfassung Versuche, von o-Benzochinolacetaten ausgehend die hydroaromatischen (primären) Additionsprodukte derMichael-Reaktion zu erhalten, hatten bisher nur bei Ia und Ib mit Malonsäuredinitril Erfolg. Mit p-Benzochinolacetat VI gelingt die Darstellung der primären Additionsprodukte auch mit anderen Reaktionskomponenten, wie z. B. Malonsäurediäthylester. *** DIRECT SUPPORT *** A3615076 00007     

Theoretical study of the effect of frit quality on chromatography using computational fluid dynamics

Summary Frits at both ends of a chromatographic column, especially for a preparative column, have significant influence on the flow distribution within the column and thus the column efficiency. However, frits have received little attention from chromatographers in the past. Here a theoretical study was conducted with the aid of CFD software FLUENT to investigate the effect of frits on the performance of homogeneous and heterogeneous chromatographic columns. A dimensionless number,FQ, was applied to characterize frit quality. This study visualized how frit quality affects the flow distribution and the concentration band, the shape of eluted pulse at the colum exit and column efficiency. Simulation results show that the development length of the flow distribution is related toFQ but has nothing to do with the packing heterogeneity. The curvature of the concentration band in a column depends onFQ and packing quality. This study shows column efficiency can be improved significantly by increasingFQ and/or frit permeability.     

Viscosity effects on the thermal decomposition of bis(perfluoro-2-N-propoxypropionyl) peroxide in dense carbon dioxide and fluorinated solvents

The thermal decomposition of the free-radical initiator bis(perfluoro-2-N-propoxyprionyl) peroxide (BPPP) was studied in dense carbon dioxide and a series of fluorinated solvents. For the fluorinated solvents, the observed first-order decomposition rate constants, k(obs), increased with decreasing solvent viscosity, suggesting a single-bond decomposition mechanism. The k(obs) values are comparatively larger in dense carbon dioxide and similar to the "zero-viscosity" rate constants extrapolated from the decomposition kinetics in the fluorinated solvents. The decomposition activation parameters demonstrate a compensation behavior of the activation enthalpy with the activation entropy upon change in solvent viscosity. Comparison of the change in activation parameter values upon change in solvent viscosity for BPPP with two additional initiators, acetyl peroxide (AP) and trifluoroacetyl peroxide (TFAP), further suggests that carbon dioxide exerts a very minimal influence on the decomposition mechanism of these initiators through solvent-cage effects.