Saturated heterocycles, 162 [1]. synthesis and steric structures of 3,4-disubstituted 1,6,7,11b-tetrahydropyrimido[6,1-a]isoquinolin-2-ones

The reaction of 1-(hydrazidomethyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline 3 with aromatic aldehydes yield hydrazones 4a,b or pyrimido[6,1-a]isoquinolines 5a-c depending upon the proportions of the reagents. With ketones, 3 gives only hydrazones 4a-d and 7 , which can be transformed to pyrimidoisoquinolines 10a-e and 11 with aldehydes. The ring closures are stereospecific; the relative configurations were determined by DNOE measurements.     

Novel electroanalytical techniques for pollution analysis

Summary Two new analytical techniques are described. The so-called injection technique operates on evaluating a dynamic concentration signal as a result of following the concentration change in a certain part of a flow-through channel after injecting a sample or reagent at a small volume into the current of an appropriate solution flowing at a constant rate.The second technique, the programmed coulometric titration technique, also uses the flow-through channel principle; that means this novel technique allows the more precise titrimetric way of analysis in flowing solutions. In the case of both techniques potentiometric and voltammetric detectors were involved. Several examples proved the multifold advantages of these techniques for environmental analysis.

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Neue elektroanalytische Verfahren für die Umweltanalyse

Zusammenfassung Zwei neue Methoden werden beschrieben. Die sog. Injektionstechnik wertet ein dynamisches Konzentrationssignal aus, das sich aus der Änderung in einem Durchflußkanal ergibt, wenn Probe oder Reagens in kleinen Volumina in einen konstant fließenden Flüssigstrom injiziert werden. Das zweite Verfahren, die programmierte coulometrische Titration, erlaubt die Anwendung der genaueren titrimetrischen Technik auf fließende Lösungen. Bei beiden Methoden werden potentiometrische und voltammetrische Detektoren verwendet. Mehrere Beispiele zeigen die vielfachen Vorteile dieser Verfahren bei der Anwendung auf die Analyse von Umweltmaterial.

Presented at the 6th Annual Symposium on Recent Advances in the Analytical Chemistry of Pollutants, April 21–23, 1976; Vienna, Austria     

über Katalysatoren- und Fermentmodelle (1)

Ohne Zusammenfassung Die Arbeit wurde aus Mitteln des Marshall-Planes (ERP-Mittel) und mit Spenden aus dem „Fonds Chemie“ ausgeführt. Wir sprechen den zust?ndigen Stellen für die Gew?hrung der Beihilfe unseren verbindlichsten Dank aus. Der Deutschen Forschungsgemeinschaft danken wir für die überlassung einer Ultrazentrifuge, den Behring-Werken für die uns zur Verfügung gestellten Serumalbumin- und -globulin-Pr?parate.     

Polarographic determination of pilocarpine using the catalysed pre-wave of nickel(II)

On the basis of a detailed study of the pilocarpine-induced nickel(II) pre-wave using various polarographic techniques, an electrode process mechanism is proposed in which the formation of a catalytic complex between aquo-nickel(II) and veronalate-nickel(II) on the one hand and unprotonated pilocarpine adsorbed on the electrode surface on the other is followed by the reduction of nickel(II) in the complex and the release of the catalytic ligand. The pre-peak recorded by differential-pulse polarography in the system 1 × 10^?3 M Ni(II)-1 × 10^?2 M sodium veronal, nitric acid (pH 8.5) (with ionic strength maintained at 0.2 with sodium nitrate) can be used for quantitative determination of pilocarpine at concentrations in the range 2.5 × 10^?7-8 × 10^?6 M.     

Beitr?ge zur titrimetrischen Bestimmung von dimeren Hydroxyaldehyden

Zusammenfassung Es wurden die Möglichkeiten für die titrimetrische Bestimmung von dimerem Glykolaldehyd (Fp: 94–96° C) und dl-Glycerinaldehyd (Fp: 138–141° C) untersucht. Die systematischen Fehler der auf Grund verschiedener funktioneller Gruppen durchführbaren Messungen sind von der Stabilität ihrer cyclischen Halbacetale sowie von den ihrer Depolymerisation folgenden weiteren Gleichgewichten bestimmt. Das aus dem dl-Glycerinaldehyd gebildete Halbacetal besitzt höhere Stabilität als dasjenige aus dem Glykolaldehyd.Mit der Hydrogensulfit-Methode werden 95–96%, mit der Hydroxylamin-Methode dagegen 98–99% vom wahren Wert gefunden.In Wasser gelöst zersetzt sich der Glykolaldehyd verhältnismäßig rasch, und das Gleichgewicht kann durch beide Aldehydreaktionen quantitativ gegen die Monomerenform verschoben werden.Unsere Untersuchungen ergaben, daß die Hydroxylamin-Methode zur Bestimmung der in Form cyclischer Halbacetale kristallisierenden, dimeren Hydroxyaldehyde Vorteile gegenüber der Hydrogensulfit-Methode bietet.Frau Dipl.-Ing. Eva Varsányi-Kiss danken wir für die derivatographischen Aufnahmen und deren Auswertung.     

Electroviscous Effect in Dilute Suspensions of Alumina

A study on the electroviscous effect of alumina suspensions has been made. At the low volume fraction of the particles studied here only a first-order effect was detected. Ubbelohde-type capillary viscometers have been used. A simple method to determine the hydrodynamic constant k(1) has been proposed. The experimental primary electroviscous coefficients corresponding to different electrolyte concentrations have been compared with two different theoretical approachs (I. G. Watterson, and L. R. White, J. Chem. Soc. Faraday Trans. 2 77, 1115 (1981); F. J. Rubio-Hernández, E. Ruiz-Reina, and A. I. Gómez-Merino, J. Colloid Interface Sci. 206, 334 (1998)) and the results suggest that the presence of a dynamic Stern layer plays a certain role in this effect. Copyright 2000 Academic Press.     

Influence of a silyl group on an allylic position. A theoretical approach

Allylsilanes show in certain cases a behaviour towards electrophiles which is opposite to that of its carbon homologues. Theoretical calculations using Dewar's MINDO/3 method performed on 3-methyl 3-butenyl trimethylsilane and 2-methyl 2-butene show that geometrical optimization leads to a silicon-allylic carbon bond nearly parallel to the double bond π cloud, and both net atomic charges and HOMO coefficients indicate an inversion between these two substrates.     

On the reactivity of benzidinesulfonic acids and their applications in analysis: Reaction of cupric salts with o-benzidinemonosulfonic acid in presence of alkali thiocyanate

In the present work a new method for the detection of coppcr(II) is described. It is based on the reaction of this ion with the alkali salts of o-benzidinemonosulfonic acid, alkali thiocyanate being present. The sensitivity of this test is $\text{1}\text{500,000}$ (l0^-5.7); it ia specific for the Cu⁺² ion and can also be used to distinguish quickly the above-mentioned acid from the benzidine o-o'-disulfonic and benzidine m-m' '-disulfonic acids. It is believed that the mechanism of the reaction can be explained by an oxidation process.     

HPLC-Electrochemical detection with graphite-poly (tetrafluoroethylene) electrode Determination of the fungicides thiram and disulfiram

The suitability of composite graphite-poly(tetrafluoroethylene) (Teflon) electrodes as amperometric indicator electrodes in HPLC detection is demonstrated. The determination of the fungicides thiram and disulfiram in the presence of ziram has been chosen as an analytical problem. The optimization of working conditions, such as the choice of the organic solvent used in the mobile phase as well as its percentage, the potential applied to the composite electrode, and the time elapsed between mixing the carbamates and the injection, has been accomplished by using the wall-jet flow-cell configuration. The effect of the acetonitrile percentage used in the mobile phase on the retention of thiram, disulfiram, ziram and phenol was evaluated. Resolution up to the baseline can be achieved with 45% acetonitrile. The sensitivity of the determination of thiram and disulfiram in the presence of a constant concentration of ziram is slightly better when using a wall-jet cell; however, the background current is higher, as well as the baseline noise and the time necessary to achieve stabilization of the baseline before the injection. Lower limits of detection for both fungicides, as well as a better repeatability, were obtained when using a thin-layer flow cell configuration. As an application, the determination of thiram in spiked apple samples, at a level of 0.5 mg thiram kg(-1) apple, has been carried out with a mean recovery of 97 +/- 3% for a significance level of 0.05.     

The cyclic fixation and reduction of molecular nitrogen with [WH4(Ph2PCH2CH2PPh2)2] in γ-irradiated solutions

Yields of NH₃ and N₂H₄ in radiation-catalytic reduction of N₂ by means of a hydride complex of W^IV with dppe in thf solution and in mixtures of thf with other solvents have been estimated. A mechanism proposed earlier of reduction of coordinated N₂ has been confirmed and the role of solvent in reduction of N₂ to NH₃ and amines has been explained.