A general method for synthesis of folic acid, its conjugates and analogues (author's transl)]

A general method for synthesis of folic acid, its conjugates and analogues . A new and general method for the synthesis of folic acid, folic acid conjugates and folic acid analogues is described. The key step, i.e. the condensation of N(2′)-acetyl-6-formyl-pterine (I: R¹ ? COCH₃) with aminoaryl derivatives II, is achieved by refluxing in absolute ethanol to afford the azomethines III. NaBH₄-reduction followed by basic hydrolysis gives pure V products in high yield, free from 7-isomers.     

A new potentiometric method for the estimation of vanadium

Summary A new potentiometric method is given for the accurate determination of small amounts of vanadium after reduction to the 4-valent state, involving back-titration of an added excess of EDTA by mercuric solution. The fact that 5-valent, but not 4-valent, vanadium has no influence on the course of the back-titration of excess EDTA with mercuric ions was used in the analysis of various binary, ternary and quaternary mixtures with requisite accuracy by two, three or four potentiometric titrations of identical mixtures at different pH-values. The method, slightly modified, may be applied to the analysis of cobalto-and nickelo-vanadium alloys.

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Zusammenfassung Zur genauen Bestimmung kleiner Mengen Vanadium nach, der Reduktion zur 4 wertigen Stufe wird ein potentiometrisches Verfahren beschrieben, bei dem ein zugesetzter überschu\ an ÄDTA mit Quecksilber(II)-Lösung zurücktitriert wird. Die Tatsache, da\ 5 wertiges (jedoch nicht 4wertiges) Vanadium die Rücktitration von ÄDTA mit Hg²⁺-Ionen nicht stört, wurde zur Analyse von binÄren, ternÄren und quaternÄren Gemischen ausgenutzt, wobei 2, 3 oder 4 potentiometrische Titrationen identischer Proben bei verschiedenen pH-Werten durchgeführt wurden. Kobalt- und Nickel-Vanadiumlegierungen können nach geringer Modifizierung des Verfahrens ebenfalls analysiert werden.

     

Oxidation with manganate solutions

Summary Manganate solutions prepared by the reduction of permanganate with formic acid in 1 M NaOH are fairly stable in a concentration of 0.015 M in presence of 1 M NaOH. They can be titrated successfuly with arsenite in the presence of telluric acid but not in its absence owing to the sluggishness of the reaction. Titration of arsenite with manganate yields always lower results deviating by 0.77% from the theoretical values in presence of telluric acid and 0.1–0.2 M NaOH. Much earlier end points with errors amounting to – 17 or – 38% are obtained in the absence of telluric acid.This work was started during 1957. Since that time the reactions of manganate with arsenite, tellurite, bivalent manganese and hydrogen peroxide were studied in our laboratory. While this work was prepared for publication den Boef et al. published their first investigation in the same line in 1959.     

Rapid potentiometric methods for vanadium and for analysis of ferrovanadium and some vanadium steels

Rapid and reliable potentiometric methods are given for determination of vanadium based on titrating unreacted KBr or KI in H₂SO₄ acid medium with Hg(I) or Hg(II), using silver amalgam as the indicator electrode. The methods are successfully applied to the analysis of ferrovanadium, three varieties of vanadium steels and synthetic mixtures of about identical constitution. In all cases the potential breaks were sharp enough for the accurate determination of the end points.     

Fast grey as a new indicator in titrations with EDTA

An acqueous solution of the Solochromate Fast Grey RA dye has proved a suitable indicator for the direct determination of thorium, ferric iron, bismuth and zinc, or the analysis of binary mixtures, thorium-iron, zinc-calcium, zinc-magnesium or zinc-thorium, with EDTA. Thorium can be determined in present of U, Fe, Zn, Ba, Be, Mg, and comparatively large amounts of rare carths. Ferric iron and zinc can be estimated in presence of U, Mg, Ca, Ba and Be. Cations of the rare and the alkaline carths can do not interfere with the determination of bismuth.     

Study of thermal behaviour of some derivatives of triphenylamine,with a view to obtaining new stationary phases for gas chromatography

A study was carried out upon the thermal behaviour of eight derivatives of triphen-y l amine, i. e. trinitrotriphenylamine; triaminotriphenylamine; triaminotriphenylamine chlorhydrate, tetraphenylborate and picrate; and a trisazo derivative and its compound with Be(II) and U(VI). The aim of this study was to find compounds with satisfactory thermal stability for use as stationary phases in gas chromatography.

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Zusammenfassung Eine umfassende Untersuchung zum thermischen Verhalten von acht Triphenylaminderivaten, d. h. Trinitrotriphenylamin, Triaminotriphenylamin, Triaminotriphenylamin Chlorhydrat, Tetraphenylborat und Pikrat, sowie ein Trisazoderivat und seine Verbindungen mit Be(II) und U(VI) wurde durchgeführt. Der Zweck dieser Studie war Verbindungen befriedigender Thermostabilität zum Einsatz als stationäre Phasen in der Gaschromatographie zu finden.

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: , , -, , () U(VI). .

     

Solochrome violet R.S. as a new colorimetric reagent

Summary Solochrome violet R.S. has proved to be a sensitive colorimetric reagent for the microdetermination of vanadium in the limits of 0.05 to 6 ppm with a sensitive filter photometer or a spectrophotometer, at 580 nm. A large number of cations up to 100 fold the vanadium amount do not interfere with its determination. The present work comprises a comparative study on the behaviour of solochrome violet and Fast Grey, based upon the great similarity in the molecular structure of the two dyes and the influence of the orthonitrophenolic group in the molecule of Fast Grey.Part I: See Z. analyt. Chem. 178, 184 (1960).     

Applications involving oxidation with KBrO3: Potentiometric determination of some inorganic white and yellow pigments

Rapid potentiometric methods were given for determination of some sulfide and chromate pigments in pure as well as adulterated samples. The methods are based on oxidation of S^2? or Cr³⁺ with known excess of KBrOs³ to the corresponding (S ↓) or Cr^6?. Oxidation of trivalent chromium proceeds only toward completion in presence of a catalyst such as Co²⁺. Sulfide oxidation needs gradual liberation of H₂S—which can be achieved by dropwise additions of the acid—together with the presence of excessive amount of water, in order to obtain accurate results excess oxidant was subsequently reduced with SO₂ to produce Br^? that can be titrated against Hg(I). The potential breaks are quite sharp for accurate determination of the equivalent points.     

Characterization of the photoisomers from cis- and trans-chlordanes, trans-nonachlor and heptachlor epoxide

Irradiation of acetone solutions of trans-chlordane (4a) and trans-nonachlor (4b) with UV light produces new half-cage photoisomers (5a or 6a and 5b or 6b, respectively) with bridging that differs from that of the photoisomers (2 and 8a) obtained from cis-chlordane (1b) and heptachlor epoxide (7). A new photoisomer (10) obtained from heptachlor epoxide is transformed into photoisomer 8a on further irradiation. Detailed PMR and ¹³C-NMR studies establish the structures of the new photoisomers and permit a decision between alternative formulations for the structures of the half-cage photoisomers of heptachlor epoxide and cis-chlordane,