Bestimmung geringer Uranmengen nach Konzentrierung durch Extraktion und Anionenaustausch in einem tri-n-octylphoshinoxidhaltigen Lösungsmittelsystem

Zusammenfassung Auf Grund systematischer Untersuchungen des Verhaltens von Uran in verschiedenen wäßrig-organischen, Tri-n-octylphosphinoxid (TOPO) enthaltenden Lösungsmittelsystemen gegenüber verschiedenen Anionenformen des stark basischen Anionenaustauschers Dowex 1, X 8 wurde eine Methode zur Abtrennung des Urans entwickelt. Bei diesem Verfahren wird das Uran aus einer ascorbin-säurehaltigen, 1-n salzsauren Lösung mit 0,1-m TOPO in Diäthyläther extrahiert und aus einem Gemisch aus 50 Vol. % Äther (0,1-m an TOPO), 45 Vol. % Methylglykol und 5 Vol. % 12-n Salzsäure am Ionenaustauscher (Chloridform) adsorbiert. Nach Elution mit 1-n Salzsäure wird das Uran entweder fluorimetrisch oder spektrophotometrisch nach der Thiocyanatmethode bestimmt. Mit diesem Anionenaustauschverfahren ist eine Abtrennung des Urans von allen, seine fluorimetrische oder spektrophotometrische Bestimmung störenden Ionen und auch vom TOPO selbst möglich. Besonders wurde auf die spektrophotometrische Bestimmung des Urans bei Anwesenheit großer Molybdänmengen eingegangen und eine Methode zur Abtrennung dieses Elementes entwickelt.

---

Determination of small amounts of uranium after concentrating through extraction and anionic exchange in a solvent agent system containing tri-n-octylphosphine oxide

Summary A method has been developed for the separation of uranium that is based on systematic studies of the behavior of uranium in various water-organic solvent systems containing tri-n-octylphosphine oxide (TOPO) towards various anion forms of the strongly basic anion exchanger Dowex 1, X 8. In this procedure, the uranium is extracted from a 1N hydrochlorid acid solution containing ascorbic acid into diethyl ether and adsorbed from a mixture consisting of 50 vol.% ether (0.1N in TOPO), 45 vol.% methylglycol and5 vol.% 12N hydrochloric acid on the ion exchanger (chlorid form). Following elution with 1M hydrochloric acid, the uranium is determined either fluorimetrically or spectrophotometrically by the thiocyanate method. By means of this anion exchange procedure, it is possible above all to separate the uranium from all ions interfering with its fluorimetric or spectrophotometric determination and also from TOPO itself. In particular, consideration is given to the spectrophotometric determination of the uranium in the presence of larger amounts of molybdenum, and a method was worked out for the removal of this element.

     

In situ NMR observation of mono- and binuclear rhodium dihydride complexes using parahydrogen-induced polarization

Starting from the binuclear complex [RhCl(NBD)]2 (NBD = 2,5-norbornadiene) in the presence of the phosphines L = PMe3, PMe2Ph, PMePh2, PEt3, PEt2Ph, PEtPh2, or P(n-butyl)3, various mononuclear dihydrides of the type Rh(H)2CIL3, i.e., those of the homogeneous hydrogenation catalysts RhCIL3, have been obtained upon addition of parahydrogen, and their 1H NMR spectra have been investigated using parahydrogen-induced polarization (PHIP). Furthermore, the two binuclear complexes (H)(Cl)Rh(PMe3)2(mu-Cl)(mu-H)Rh(PMe3) and (H)(Cl)Rh(PMe2Ph)2(mu-Cl)(mu-H)Rh(PMe2Ph) have been detected and characterized by means of this in situ NMR method. Analogous complexes with trifluoroacetate instead of chloride, i.e., Rh(H)2(CF3COO)L3, have been generated in situ starting from Rh(NBD)(acac) in the presence of trifluoroacetic acid in combination with the phosphines L = PPh3, PEt2Ph, PEt3, and P(n-butyl)3, and their 1H NMR parameters have been determined.     

Mechanistic insights into the photochromism of trans-10b,10c-dimethyl-10b,10c-dihydropyrene derivatives

A series of dimethyldihydropyrene derivatives was studied to elucidate the photochemical mechanism associated with the switching between the dimethyldihydropyrene (DHP, closed) and metacyclophanediene (CPD, open) forms of the molecule. Quantum yields of ring opening and closure, fluorescence quantum yields and lifetimes, as well as laser flash photolysis studies were performed to establish the effect of substituents on the switching efficiency. Ring opening of the DHPs occurs from the first singlet excited state. The low quantum yields for the ring opening reaction observed (< or =0.042) are a consequence of the low rate constant (< or =1.7 x 10(7) s(-1)) for this process. The quantum yields for ring closure of the CPD were determined for select compounds and were of the order of 0.1-0.4. These results show that the efficiency for ring opening of this class of compounds is intrinsically low, but can be modulated to some extent by the introduction of substituents. These properties should be taken into account when considering what type of photoswitching devices DHPs might be useful for.     

Photometrische Bestimmung von Antimon in Eisen und Stahl

Zusammenfassung Zur Bestimmung von 2,5–100 ppm Sb in Eisen, unlegierten und niedrig legierten Stählen sowie in Automatenstählen wird das Antimon zuerst in 2 Stufen vorisoliert mit Hilfe der Spurenfällung mit Mangan(IV)-oxidhydrat als Spurenfänger und anschließender Jodidextraktion. Nach der Rückextraktion erfolgt die photometrische Bestimmung mit Methylfluoron in der wäßrigen Phase. Der relative Fehler beträgt ±5%, der Zeitbedarf für eine Einzelbestimmung 1,5 h.Herrn H. Sifirin danke ich für die sorgfältige Durchführung der Versuche.     

Photometrische Bestimmung von Antimon mit Methylfluoron

Zusammenfassung Es wird eine Arbeitsvorschrift zur photometrischen Bestimmung kleiner Mengen Antimon mit Methylfluoron beschrieben. Die günstigsten Arbeitsbedingungen und die Störung durch Fremdionen werden untersucht. Das Extinktionsmaximum liegt bei 530 nm. Die photometrische Bestimmung wird bei 495 nm durchgeführt. Das Beersche Gesetz ist im Bereich von 0,2– 4 g Sb/ml erfüllt, die Bestimmungsgrenze liegt bei 0,21 g Sb/ml · cm. Der Zeitbedarf einer Einzelbestimmung beträgt 15–20 min.Für die sorgfältige Durchführung der zahlreichen Versuche sprechen wir Herrn H. Siffrin unseren Dank aus.     

Restricted rotation about partial C,N double bonds

The restricted rotation about the partial C,N double bond in 2-chloro-6-NR₂-pyran-4-ones is discussed in the light of NMR spectroscopic data and theoretical calculations.Ab initio calculations at the HF/6-31G^* level were carried out using a continuum model to take solvent effects into account. The delocalization of-electron density [described by natural bond orbital analysis (NBO)] was applied to determine the degree of conjugation in the ground state (GS) and in the transition state (TS) for the restricted rotation of the compounds studied. The reason for the different barriers to rotation of the NR₂ substituents (pyrrolidino > dimethylamino > morpholidino > piperidino) at the 2-chloro-pyran-4-one ring appears to be the different steric hindrance of the NR₂ substituents in the GS for the restricted rotation.     

Probing the surface polarity of native celluloses using genuine solvatochromic dyes

The surface polarity of native celluloses has been investigated by the following solvatochromic dyes: dicyano-bis (1,10)-phenanthroline iron (II) Fe(phen)2 (CN)2 (1), bis(4-N,N-dimethylamino)-benzophenone (2), and cou-marine 153 (3). Linear Solvation Energy (LSE) relationships and the UV/Vis data have been used to characterize the surface polarity of different native cellulose batches in terms of the empirical Kamlet–Taft polarity parameters (hydrogen bond acidity), (hydrogen bond basicity), and * (dipolarity/polarizability). , , *and calculated Reichardt's E T (30) values are reported for various native and regenerated cellulose samples with different degrees of crystallinity. The degree of crystallinity of the cellulose samples has been determined by X-ray. The microcrystalline environment of cellulose can be exactly parameterized in terms of the , and *values. It shows a fairly strong acidity and a low dipolarity/polarizability. For the amorphous sections smaller and larger * values are observed. The correspondence of the empirical polarity parameters determined has been discussed in relation to results from pyrene fluorescence and zetapotential measurements.