Untersuchungen an reagenzien für niob und tantal—I

On examination of a wide range of hydroxylic organic compounds it has been found that two hydroxyl groups in the ortho position to each other in an aromatic system act as a functional analytical group for niobium and tantalum. peri-Dihydroxynaphthalene derivatives react similarly. After a systematic examination, tribromopyrogallol is proposed as a new selective and sensitive reagent for niobium.

Résumé

Au cours de l'étude d'un grand nombre de composés organiques oxhydrilés, il a été constaté qu'en présence d'acide tartrique, les composés possédant deux groupements oxhydriles en ortho sur un noyau aromatique présentaient des propriétés analytiques spécifiques pour le niobium et le tantale. Les dérivés du péri-dihydroxynaphtalène réagissent d'une manière analogue. Après une étude systématique, le tribromopyrogallol est proposé comme un nouveau réactif spécifique et sensible du niobium.     

New Results on the Stereoselective Alkylations of Malic Acid Derivatives Supported by Molecular Modeling

The stereoselectivity of the alkylation of dialkyl malates is dependent on steric hindrance of both ester alkyl groups. It was found that the two alkyl groups have opposite effects on diastereoselectivity. Increased steric hindrance at the C(1) carboxy group increases the anti‐selectivity, whereas increased steric hindrance at the C(4) carboxy group decreases it. The results are explained by comparing the structures of the enolates, which were obtained by molecular modeling. Alkylation at C(4′) of dioxolanones, derived from benzyl‐substituted malic acids, with an additional stereogenic center on the side chain is dependent on the stereogenic centers of the ring acetal and of the side chain. Alkylation at low temperatures occurs only with cis‐dioxolanones having an (R)‐configured side‐chain stereogenic center. The corresponding trans‐dioxolanone and the cis‐dioxolanone with a (S)‐configured side‐chain stereogenic center were recovered unchanged. A rationale is presented with models of monolithiated dioxolanones obtained by ab initio calculations.     

Investigation of the Nature of Iron Oxide Species Present in Ruby Glasses Prepared by the Sol-Gel Method

Mössbauer spectroscopy in an external magnetic field, electron diffraction microscopy and electron spin resonance (ESR) measurements were used in an attempt to characterize the iron oxide particles present in ruby glasses prepared by the sol-gel method. The obtained results lead to the conclusion that particles are present as a ferromagnetic phase that shows superparamagnetic behaviour.     

Analytische Anwendungen der Methode der abgeschw?chten Totalreflexion

Zusammenfassung Einige Anwendungen der ATR-Technik auf unterschiedliche Analysenprobleme, die Besonderheiten der Probenaufbereitung und ein Vergleich zwischen ATR und Durchlichtspektren werden beschrieben. Die besonderen Vorteile der ATR-Technik wie etwa eine Analyse optisch undurchlässiger Medien, dünner Schichten auf Oberflächen, der Möglichkeit zur Verwendung wäßriger Lösungen und des Erhalts analytischer Daten aus Probemengen im g-Bereich führten trotz prinzipieller Nachteile und der schwierigen Theorie der Messung der Totalreflexion zu einem steilen Anstieg der Entwicklungsarbeiten auf diesem Gebiet. Die ATR-Technik wird hier beispielsweise zur Identifikation von geringsten Schmierstoffmengen und von Spurengehalten an Bornitrid im Rückstand nach der Stahlprobenisolierung angewendet. Zahlreiche Spektren sollen die Anpassungsfähigkeit und hohe Aussagekraft dieser Methode dokumentieren. Sämtliche ATRSpektren wurden auf dem Beckman IR-20-Spektrometer unter Verwendung eines ATR-Zusatzes mit Neunfachreflexion aufgenommen, der Kristall besteht aus TlBr/TlJ (KRS-5) und der Einfallswinkel beträgt in allen Fällen 45°.Teilweise vorgetragen auf der Tagung der GDCh-Fachgruppe Analytische Chemie in Düsseldorf am 4.Juni 1971.     

Stereoelectronic effects in ring-chain tautomerism of 1,3-diarylnaphth[1,2-e][1,3]oxazines and 3-alkyl-1-arylnaphth[1,2-e][1,3]oxazines

The disubstitution effects of X and Y in 1-(Y-phenyl)-3-(X-phenyl)-2,3-dihydro-1H-naphth[1,2-e][1,3]oxazines on the ring-chain tautomerism, the delocalization of the nitrogen lone pair (anomeric effect), and the (13)C NMR chemical shifts were analyzed by using multiple linear regression analysis. Study of the three-component equilibrium B<==>A<==>C revealed that the chain<==>trans (A<==>B) equilibrium constants are significantly influenced by the inductive effect (sigma(F)) of substituent Y on the 1-phenyl ring. In contrast, no significant substituent dependence on Y was observed for the chain<==>cis (A<==>C) equilibrium. There was an analogous dependence for the epimerization (C<==>B) constants of 1-(Y-phenyl)-3-alkyl-2,3-dihydro-1H-naphth[1,2-e][1,3]oxazines. With these model compounds, significant overlapping energies of the nitrogen lone pair was observed by NBO analysis in the trans forms B (to sigma*(C1-C1'), sigma*(C1-C10b), and sigma*(C3-O4)) and in the cis forms C (to sigma*(C1-H), sigma*(C1-C10b), and sigma*(C3-O4)). The effects of disubstitution revealed some characteristic differences between the cis and trans isomers. However, the results do not suggest that the anomeric effect predominates in the preponderance of the trans over the cis isomer. When the (13)C chemical shift changes induced by substituents X and Y (SCS) were subjected to multiple linear regression analysis, negative rho(F)(Y) and rho(F)(X) values were observed at C-1 and C-3 for both the cis and trans isomers. In contrast, the positive rho(R)(Y) values at C-1 and the negative rho(R)(X) values at C-3 observed indicated the contribution of resonance structures f (rho(R) > 0) and g (rho(R) < 0), respectively. The classical double bond-no-bond resonance structures proved useful in explaining the substituent sensitivities of the donation energies and the behavior of the SCS values.     

Reaction kinetics at linearly increased temperature. IV. Relationships between dta curves,rate curves and adiabatic calorimetry

A general concept is presented for the kinetic interpretation of DTA curves. This is based on the limiting conditions of a DTA measurement: either the kinetic cell constant is zero (adiabatic conditions), or infinite (rate curve). On the other hand, the self-heating effect (thermal feedback), based on the product of the reaction enthalpy with the reactant feed, may be absent (“ideal” kinetic DTA curve) or infinite (impulse reaction). Our recent formulae for the correction of the kinetic classification parameters, shape index and reaction type index, as well as other relationships and their utility, are successfully tested by application to ca. 2000 experimental DTA curves obtained in stirred solutions.The expressions reveal the influence of the activation parameters, heating rate, maximum signal height and cell constant and, therefore, allow a general discussion of the kinetics, independent of the experimental conditions.     

Röntgenspektrometrische bestimmung von blei in automatenstahl : Teil II. Sulfat-verfahren

A method is described for the x-ray spectrometric determination of 0.02–0.5% Pb in free-cutting steels. Lead in the sample solution is precipitated as sulphate with barium sulphate as collector, and the dried fixed precipitate is used for the X-ray Spectrometric measurement. The method shows a reproducibility (s) of ±0.002 % Pb. The time required is ca. 32 min for one determination and ca. 120 min for a series of 20 samples.     

Neue Ergebnisse bei der Bestimmung von Stickstoff und Sauerstoff in Stahl durch Schmelzextraktion im Graphittiegel unter Inertgas

Zusammenfassung Vergleichende Stickstoffuntersuchungen mit dem naßchemischen Aufschlußverfahren, dem oxydierenden Aufschmelzverfahren und dem Trägergasverfahren zeigten, daß das Trägergasverfahren auch für die Untersuchung vieler legierter Stähle anwendbar ist. Die Ergebnisse von Stickstoffbestimmungen 81 legierter und 100 bereits früher untersuchter unlegierter Stähle werden miteinander verglichen. Eine Korrelationsrechnung ergab, daß die Untersuchungsergebnisse des Trägergasverfahrens und des oxydierenden Aufschmelzverfahrens gleichwertig sind. Sie sind etwas höher als die des naßchemischen Aufschlußverfahrens. Die Differenzen sind gering.Ferner wurde festgestellt, daß die Reduktion aluminiumoxidhaltiger Stähle bei der Sauerstoffbestimmung in Stahl innerhalb weniger Minuten durchgeführt werden kann, wenn man, wie bei der Stickstoffbestimmung nach dem Schmelzextraktionsverfahren, für jede Untersuchung einen neuen kleinen Graphittiegel benutzt. Die Ergebnisse der alten und neuen Arbeitsweise werden in einer Gegenüberstellung gezeigt.

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Summary Comparative nitrogen determinations using the wet-chemical digestion, the oxidizing fusion, and the carrier-gas techniques showed that the latter one may also be applied for analysing a great number of alloy steels. A comparison was made of the results of nitrogen determinations of 81 alloy and 100 non-alloy steels analysed previously. A correlation calculation proved that the carrier-gas and the oxidizing fusion techniques are equivalent when considering the results. Their values were slightly higher than those obtained by the wet-chemical digestion. There were minor differences only.In addition, it has been found that the reduction of alumina-bearing steels during the determination of oxygen can be effected within a few minutes, provided a new small graphite crucible is used for each new determination as in nitrogen determination by the fusion-extraction technique. A comparison was made of the results of the old and the new methods.

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Herrn E. Voss danken wir für seine stets sorgfältige und wertvolle Mitarbeit.

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Herrn Prof. Dr. C. Mahr zum 65. Geburtstag gewidmet.     

Further developments in the high-precision coulometric titration of uranium

An experimental study of the current efficiency in the coulometric generation of Ti(III), as a function of electrolyte composition, current density and electrode material, has been performed. The cathodes investigated include platinum, mercury and graphite. The first two are suitable for high-precision determination of uranium. The graphite surface is readily poisoned, rendering it useless for high-accuracy work. The use of mercury requires thorough removal of chloride from the system. The precision and error obtained are comparable for both the mercury and platinum cathodes, and are of the order of 50 ppm.