Spektrophotometrische Bestimmung von L-Askorbinsäure mit 2,2',5,5'-Tetra-(4-nitrophenyl)-3,3'-(3,3'-dimethoxy-4, 4'-biphenyl)-ditetrazoliumchlorid (TNBT)

Zusammenfassung Die Optimalbedingungen für die spektrophotometrische Bestimmung der L-Askorbinsäure mit TNBT wurden ermittelt. Die L-As-korbinsäure wurde in Anwesenheit eines 100fachen Überschusses folgender Stoffe bestimmt: Glukose, Fruktose, Saccharose, Wein-, Zitronen-, Oxal-, Äpfel- und Bernsteinsäure. 0,5g/ml ist die minimale Askorbinsäurekonzentration, die sich bestimmen läßt. Die rel. Standardabweichung beträgt 2,1%, der rel. Fehler 0,875%.

---

Spectrophotometric assay of L. ascorbic acid with 2,2,5,5-tetra-(4-nitro-phenyl)-3, 3-(3,3-dimethoxy-4,4-biphenyl)-ditetrazolium chloride (TNBT)

Summary The optimal conditions for spectrophotometric assay of L-ascorbic acid with TNBT were determined. L-ascorbic acid was assayed in the presence of a 100 fold excess of the following substances: glucose, fructose, sucrose, tartaric acid, citric acid, oxalic acid, malic acid and succinic acid. 0.5g/ml is the minimum concentration of ascorbic acid which can be assayed. The relative standard deviation is 2.1%, the relative error 0.875%.

     

Tetrakis (methylidene)cyclobutane (‘[4]Radialene’): Electronic states of the molecular ion

The photoelectron spectrum of tetrakis (methylidene)cyclobutane ( 1 , ‘[4]radialene’) is reported. The electronic states of 1 ⁺ are assigned on the basis of model calculations and with reference to related systems. Jahn-Teller activity in the degenerate states is discussed. A failure of the simple LCBO-model for the π(e_g)-orbital of 1 is noted and traced to the fact that this orbital, though having a symmetry-equivalent π*-counterpart, does not interact with it. This feature is confined to [4n]radialenes; their total π-energies are therefore higher than those of the other members. It is shown that radialenes, in principle, do not constitute a class analogous to that of the linear polyenes as inferred earlier.     

Anwendung mikroanalytischer Methoden zur Lösung kunst- und kulturgeschichtlicher Probleme

Zusammenfassung Mit bekannten mikroanalytischen Arbeitsmethoden — Oberflächenreaktionen, Abstrichuntersuchungen mit dem Korundstäbchen, Schutzschichtreaktionen sowie dem Abdruckverfahren — lassen sich archaeometrische Probleme einer Lösung näherbringen. Die Art der Korrosion kupferhaltiger Oberflächen wurde diskutiert.

---

Application of microanalytical methods to the solution of artistic- and cultural historical problems

Summary Archeometrical problems are brought closer to a solution by means of known microanalytical procedures-surface reactions, surface scraping studies with the corundum rod, protective layer reactions as well as the imprint method. A discussion of the corrosion of copper-bearing surfaces is included.

---

---

Vortrag anläßlich der Tagung Chemische Analysen — Kunst- und Kulturwissenschaften im Reiß-Museum in Mannheim, 19.–21. September 1974.     

The surface activity of the lower homologues of n-alkylammonium chlorides in aqueous solutions. Effect of hydrophobic hydration

Summary The surface tensions of aqueous solutions ofn-alkylammonium chlorides (methyl to hexyl) have been measured at 25 °C. With methylammonium chloride the surface tension increased with concentration, whereas with ethylammonium chloride and higher homologues, the surface tension decreased with concentration. The results suggest that this transition is attributed to the effect of hydrophobic hydration. For propylammonium chloride and higher homologues, the relation between the surface tension lowering da and the concentrationC in the range of 0–10 dyne/cm, can be expressed by the equation; = AC + BC, whereA andB are constants. The surface tension coefficientB has been found to increase approximately twofold for each additional CH₂ group of alkyl chain.

---

Zusammenfassung Es wurden die Oberflächenspannungen wäßriger Lösungen vonn-Alkylammoniumchloriden (Methyl- bis Hexylammoniumchloride) bei 25 °C gemessen. Für Methylammoniumchlorid nimmt die Oberflächenspannung mit der Konzentration zu, aber bei allen höheren Homologen mit der Konzentration ab. Die Ergebnisse deuten darauf hin, daß dieser Übergang durch die hydrophobe Hydration bedingt wird. Für Propylammonium-chlorid und die höheren Homologen wird die Beziehung zwischen der Erniedrigung der Oberflächenspannung und der KonzentrationC in dem Bereich von 1 bis 10 dyn/cm durch die folgende Gleichung ausgedrückt: = AC + BC (A undB sind Konstanten). Es wurde gefunden, daß B für jede zusätzliche CH₂-Gruppe etwa um den Faktor 2 größer wird.

     

Fluoroalkyl-s-triazines

A series of symmetrically and asymmetrically substituted s-triazines was synthesized by condensation of fluorocarbon nitriles (Scheme II, compounds 1a-c ) and by cyclodehydration of a fluorocarbon imidoylamidine utilizing a fluorocarbon anhydride (Scheme III, compounds 2a-e ). Among the new nitriles prepared for incorporation in these reaction paths were 11-H-4,9-dioxahexadecylfluoroundecanenitrile ( 3 ) and 6-chloro-6-H-4-oxaheptafluorohexanenitrile ( 4 ), prepared by Scheme 1.     

Mechanosynthesis of zinc ferrite in hardened steel vials: Influence of ZnO on the appearance of Fe(II)

Nanocrystalline ZnFe₂O₄ spinel powders are synthesized by high-energy ball milling, starting from a powder mixture of hematite (α-Fe₂O₃) and zincite (ZnO). The millings are performed under air using hardened steel vials and balls. X-ray diffraction and Mössbauer spectrometry are used to characterize the powders. A spinel phase begins to appear after 3 h of milling and the synthesis is achieved after 9 h. Phase transformation is accompanied by a contamination due to iron coming from the milling tools. A redox reaction is also observed between Fe(III) and metallic iron during milling, leading to a spinel phase containing some Fe(II). The mechanism for the appearance of this phase is studied: ZnO seems to have a non-negligeable influence on the synthesis, by creating an intermediate wüstite-type phase solid solution with FeO.     

Darstellung und Reaktionen des 3-Ethinyl-2,4-diformyl-pentandials

Preparation and physical and chemical properties of 3-ethinyl-2,4-diformyl-pentandial (3 a) and its salts are described.3 a contains 2 malonaldehyde groups. Starting from3 a, 4H-pyranes, 4H-dihydropyridines, dipyrazoles, diisoxazoles, bisdiazepines and vinamidine derivates are obtained.

---

---

Mit 1 Abbildung     

Zur Umsetzung des 3,4,5,6-Tetrahydro-6-hydroxy-4,4,6-trimethyl-1,3-thiazin-2-thions mit sekundären Aminen

Tetrahydro-6-hydroxy-trimethyl-1,3-thiazine-2-thione (1) reacts with secondary amines via the dialkylammonium-3-oxoalkyldithiocarbamate3, either via isothiocyanates6 to 4-dialkylaminodihydro-2(1H)-pyridinethiones7 or to dialkylammonium dithiocarbamates (13), depending on the amine used and the reaction conditions. Subsequently, 6-dialkylaminotetrahydro-1,3-thiazine-2-thiones11 or tetrahydro-6-mercapto-1,3-thiazine-2-thione10 are formed. On being heated to reflux,11 reacts to pyridinethione7 and 4-dialkylaminodihydrothiopyranthione19. With secondary amines only13 is formed from tetrahydro-6-hydroxytetramethyl-1,3-thiazine-2-thione20. The reaction of dihydrotrimethyl-1,3-thiazine-2-thione21 with secondary amines leads to N,N-dialkylthioureas16 or dialkylammonium thiocyanates17 and with dialkylformamides 4-dialkylaminodihydropyridinethiones7 are formed. Dihydrotetramethyl-1,3-thiazine-2-thione24 reacts neither with secondary amines nor with dialkylformamides.     

Koordinationschemie von Dinitroresorcin mit Kupfer-, Kobalt-, Nickel-, Eisen- und Zinksalzen

The reactions of the bidentate dinitrosoresorcinol (DNR) with copper, cobalt, nickel, iron and zinc salts were investigated. This ligand was found to react with these metal salts in aqueous media where hydrogen ion was confirmed to be liberated except in case of iron. The solid complexes were prepared in alcoholic media. Chemical analyses, magnetic and spectral data were compatible to determine the structure of these complexes and their mode of chelation.

---

---

Mit 2 Abbildungen     

Beiträge zur Chemie der Pyrrolpigmente, 19. Mitt.: Die elektrochemische Oxidation von Pyrromethenonen und Pyrromethenen (Gallenpigment-Partialstrukturen)

The electrochemical oxidation of arylmethylene-pyrrolinones, pyrromethenones and pyrromethenes as representative bile pigment partial structure models was investigated by means of a rotating disc platinum electrode using acetonitrile as the solvent. Two different oxidation reactions were found. The first reaction being a reversible one-electron oxidation with compounds of the arylmethylene-pyrrolinone series and pyrromethenones which are unsubstituted in position 5 of the pyrrole ring. A two step reaction (the first one reversible, the second irreversible) on the other hand was found to be typical for pyrromethenones bearing a methyl group in this position.Through protonation the first step is at a higher potential, whereas the second one is lowered and becomes reversible. The resulting oxidation pattern can be interpreted analogous to the oxidation of hydroquinones in aprotic solvents.The geometrical isomers of a pyrromethenone were oxidized at appr. the same potential, but there is a strong dependence of the potential of the first oxidation step on the substitution: a higher degree of alkylation favours oxidation by lowering the oxidation potential.

---

---

Mit 1 Abbildung