Zur Reaktion von 1,3-Oxazolidinen mit Dicarbonsäureanhydriden

Reaction of 3-methyl-1,3-oxazolidine with phthalic anhydride in chloroform leads to ring opening and higher oligomers2 are formed. These are cleaved by addition of protic solvents and 2-methylaminoethyl hydrogenphthalate3 a is obtained. Other 1,3-oxazolidines and succinic anhydride behave similarly.

Herrn Prof. Dr. Dr. h. c.Karl Kratzl mit den besten Wünschen zum 70. Geburtstag gewidmet.     

Semiempirical calculation of photoionization cross sections for the first excited levels of F I

Radial matrix elements and photoionization cross sections have been calculated for all levels of the first excited configuration 2p ⁴(³ P) 3s of neutral fluorine as an example for the application of the Scaled Thomas-Fermi method. The extrapolation of empirical data on energy levels to positive electron energies and the reliability of the method are discussed.     

Spectrophotometric determination of organic nitrogen by a modified Lassaigne method and its application to meat products and baby food

A modified Lassaigne method was developed for N determination based on fusion of the organic substance with metallic Na, conversion of the cyanide in the aqueous leachate to thiocyanate by ammonium polysulfide treatment, and colorimetric measurement of the thiocyanate formed by the addition of excessive ferric ions in acidic medium. The mean molar absorptivity of the Fe(NCS)2+ complex at 480 nm is 2.96 x 10(3) L/mol x cm, enabling quantitation of 0.25-7.72 ppm N (linear range) in the final solution. The relative amounts of Na, (NH4)2S2, and Fe(III) with respect to nitrogen in the analyte were optimized. The developed method was successfully applied to the determination of N in various brands of baby food, and it was compared statistically with the conventional Kjeldahl and elemental analysis methods. Protein nitrogen in a number of meat products was also precisely determined by the developed method. Thus, the total digestion time of the conventional Kjeldahl method was reduced considerably (e.g., to approximately 15 min for a dried sample) with a relatively simple spectrophotometric method requiring no sophisticated instrumentation.     

Deprotonation of chloropyridines using lithium magnesates

4-Chloropyridine was deprotonated on treatment with 1/3 equiv of the highly coordinated magnesate Bu₃(TMP)MgLi₂ in THF at −10 °C, as evidenced by trapping with I₂. The use of Bu(TMP)₂MgLi in Et₂O allowed the reaction of 2-chloropyridine, giving the 3-functionalized derivative as the main product. Mixtures of 3- and 4-functionalized derivatives were obtained when 2,6-dichloropyridine was involved in the reaction. Performing the reaction on 3-chloropyridine with lithium magnesates in THF, either the 4,4′-dimer or the 4-iodo derivative was formed after quenching by I₂, the former using 1/3 equiv of Bu₂(TMP)MgLi and the latter using 1 equiv of (TMP)₃MgLi. Similar results were observed with 3,5-dichloropyridine, 2,5-dichloropyridine and 3-chloro-2-fluoropyridine. 1,2-Migration of the lithium arylmagnesate formed by deprotonation was proposed to justify the dimers formation.     

Model prediction of batch emulsion copolymerization as a function of conversion: A sensitivity analysis

Recently a model has been developed capable of predicting absolute monomer concentrations and their ratios in the polymer, aqueous, and monomer droplet phases as a function of conversion in batch emulsion copolymerizations without using any adjustable parameters. In this article the sensitivity of model predictions of composition drift toward deviations of 10% in all model parameters (maximum swellabilities of monomer in the polymer phase, water solubilities, reactivity ratios, and monomer and polymer densities) was estimated using the monomer combination methyl methacrylate-styrene as an example. From the sensitivity analysis it can be concluded that the reactivity ratios are the most important parameters affecting composition drift. The effects of deviations in maximum swellabilities and monomer and polymer densities on composition drift can be neglected, while the water solubility is important only in those cases where the amount of monomer in the aqueous phase cannot be neglected as compared with the total monomer amount. © 1994 John Wiley & Sons, Inc.     

Calculation of current densities using gauge-including atomic orbitals

A method for calculating the various components of the magnetically induced current-density tensor using gauge-including atomic orbitals is described. The method is formulated in the framework of analytical derivative theory, thus enabling implementation at the Hartree-Fock self-consistent-field (HF-SCF) as well as at electron-correlated levels. First-order induced current densities have been computed up to the coupled-cluster singles and doubles level (CCSD) augmented by a perturbative treatment of triple excitations [CCSD(T)] for carbon dioxide and benzene and up to the full coupled-cluster singles, doubles, and triples (CCSDT) level in the case of ozone. The applicability of the gauge including magnetically induced current method to larger molecules is demonstrated by computing first-order current densities for porphin and hexabenzocoronene at the HF-SCF and density-functional theory level. Furthermore, a scheme for obtaining quantitative values for the induced currents in a molecule via numerical integration over the current flow is presented. For benzene, a perpendicular magnetic field induces a (field dependent) ring current of 12.8 nA T(-1) at the HF-SCF level using a triple-zeta basis set augmented with polarization functions (TZP). At the CCSD(T)/TZP level the induced current was found to be 11.4 nA T(-1). Gauge invariance and its relation to charge-current conservation is discussed.     

A parallel implementation of the COLUMBUS multireference configuration interaction program

Summary In this work a parallel implementation of the COLUMBUS MRSDCI program system is presented. A coarse grain parallelization approach using message passing via the portable toolkit TCGMSG is used. The program is very well portable and runs on shared memory machines like the Cray Y-MP, Alliant FX/2800 or Convex C2 and on distributed memory machines like the iPSC/860. Further implementations on a network of workstations and on the Intel Touchstone Delta are in progress. Overall, results are quite satisfactory considering the complexity and the prodigious requirements, especially the I/O bandwidth, of MRCI programs in general. For our largest test case we obtain a speedup of a factor of 7.2 on an eight processor Cray Y-MP for that section of the program (hamiltonian matrix times trial vector product) which has been parallelized. The speedup for one complete diagonalization iteration amounts to 5.9. An absolute speed close to 1 GFLOPS is found. Results for the iPSC/860 show that ordinary disk I/O is certainly not sufficient in order to guarantee a satisfactory performance. As a solution for that problem, the implementation of a fully asynchronous distributed-memory model for certain data files is in preparation. On leave from: Bereich Informatik, Universität Leipzig, Augustusplatz 10/11, O-7010 Leipzig, Germany     

Development of solid phase reactors for continuous detection systems

Summary The methodical development of a solid phase reactor (SPR) as an integrated part of a chemical reaction detector is described for manganese. The preparation of a suitable reactor packing material byin situ precipitation of lead-dioxide on silica gel permits running the SPR in low pressure ranges. Divalent manganese and also higher oxidation states of the metal are oxidized to permanganate in the reactor. Thus, an isoformation of all manganese species originally present in the sample takes place. As the direct photometrical detection of permanganate is not sensitive enough for trace analyses, the heterogeneous oxidation system is followed by a homogeneous chemical reaction system, in which permanganate reacts with leucomalachite green. The resulting blue-green dye is detected photometrically at 620 nm.The application of a column switching technique allows the continuous enrichment, separation, and determination of manganese down to the nanogram level with high precision and also a differentiation between divalent manganese and three- to seven- valent manganese.This chemical reaction detector can be used also for continuous detection in chromatography, especially HPLC. The detection limit is 10 ng/ml.

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Entwicklung eines Festbettreaktors für kontinuierliche Nachweissysteme. Teil I

Zusammenfassung Die methodische Entwicklung eines Festbettreaktors als integrierter Bestandteil eines chemischen Reaktionsdetektors wird beschrieben. Die Herstellung einer geeigneten Reaktorpackung durch Ausfällen von Bleidioxid auf Kieselgel erlaubt den Betrieb des Festbettreaktors im Niederdruckbereich. Zweiwertiges Mangan sowie höhere Oxydationszustände des Metalls werden im Reaktor zum Permanganat-Ion oxydiert, so daß eine Isoformierung aller in der Probe vorhandenen Mangan-Spezies stattfindet. Da die photometrische Detektion des Permanganat-Ions für spurenanalytische Messungen nicht ausreichend empfindlich ist, wird im Anschluß an den heterogenen Bleidioxid-Reaktor ein homogenes chemisches Reaktions-system betrieben, in dem das Permanganat-Ion mit Leukomalachitgrün umgesetzt wird. Dabei entsteht der blaugrüne Farbstoff Malachitgrün, der bei 620 nm photometrisch gemessen wird.Die Verwendung einer Säulenschalttechnik ermöglicht eine kontinuierliche Anreicherung, Abtrennung und Bestimmung von Manganspuren bis in den Nanogramm-Bereich mit hoher Genauigkeit, sowie eine Differenzierung zwischen zweiwertigen Mangan-Spezies einerseits und dreibis siebenwertigen Oxydationsstufen andererseits.Der vorgestellte chemische Reaktionsdetektor kann auch zur kontinuierlichen Chromatographie-Detektion benutzt werden. Die Nachweisgrenze beträgt 10 ng/ml.

     

Paleoenvironmental organic indicators in Eocene paleosols from Arctic Canada

Summary The analytical potential of the combination of solid state NMR and soft ionization mass spectrometry for direct investigations of complex organic matter in soils without chemical pretreatment is demonstrated. The results show that the Oh horizon of a Gleysolic paleosol (±45 Ma) from the Canadian Arctic consists mainly of components of cuticular waxes which include 10-nonacosanol, C₁₅–C₃₆ n-fatty acids, C₄₄–C₇₅ n-alkyl monoesters and C₆₀–C₇₆ diesters. It is likely that these waxes originated from the coniferous and deciduous vegetation which dominated this area when these soils were formed and that the climate was warm and moist.     

Vergleichende Untersuchungen an polarographischen Analysenverfahren

The universal voltammetric instrument, described in part I of this series, is used for comparative studies on the most important polarographic methods, direct current, derivative pulse, simple and phase-sensitive alternating current, double-tone, and harmonic-wave polarography. In general the peak-heights of these methods are influenced in the same measure by the composition of base electrolyte. In single cases characteristic differences are observed.