Complexometric titration of phosphorus in organic compounds

Summary A new complexometric method for the determination of phosphorus in organic compounds is described. After combustion in an oxygen-flask, phosphorus is precipitated as cerous phosphate. The excess cerous ion is back-titrated at pH 6–7 with EDTA in the presence of methylthymol blue or xylenol orange indicators. Alkaline hypobromite is used as an absorbent. Tight clamping of the paper carrier in the platinum holder insures complete combustion.

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Komplexometrische Titration von Phosphor in organischen Verbindungen

Zusammenfassung Die Probe wird im Sauerstoffkolben nach Schöniger verbrannt und der Phosphor als Cer(III)-phosphat ausgefällt. Der Überschuß an Cer(III) wird bei pH 6–7 mit ÄDTA zurücktitriert, wobei Methylthymolblau oder Xylenolorange als Indicator dient. Als Absorptionsmittel wird alkalische Hypobromitlösung verwendet. Um eine vollständige Verbrennung zu gewährleisten, ist es wichtig, daß das Papier mit der Probe fest am Platinhalter angeklammert wird.

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This work was performed under the auspices of the U.S. Atomic Energy Commission.     

Orthogonal Algebraic Polynomial Schauder Bases of Optimal Degree

For any fixed we construct an orthonormal Schauder basis for C[-1,1] consisting of algebraic polynomials with The orthogonality is with respect to the Chebyshev weight.     

Microdetermination of aliphatic amines and polyamines with cupric ion: Relationship between pK1 and half-complexation potential

The first equilibrium constant for the combination of ligand with cupric ion, K₁, is related to the half-complexation potential, E_HC, by log K₁ = a + b[E_HC]. The coefficients differ for n ? 2 and n ? 2, where n is the number of nitrogen atoms in the molecule. The correlation coefficients, r, based on data available from the literature were ?0.98. The equations can be used for estimating log K₁ of aliphatic amines. Successful titration of aliphatic amines vs cupric ion requires log K₁ ? 4 and an initial pH of a 10^?3M solution of ?9.     

New titrants for perchlorate and fluoroborate

Three new titrants have been evaluated for the precipitation titration of perchlorate: cetylpyridinum chloride (CPC), cetyltrimethylammonium chloride (CETAC), and benzyldimethyltetradecylammonium chloride (BDTAC). CETAC yielded the highest precision and largest potentiometric break, closely followed by CPC. BDTAC produced considerably lower precision and smaller breaks. Fluoroborate was similarly determined with CPC and CETAC. Again CETAC yielded the highest precision and largest potentiometric break. Titrations were monitored with a fluoroborate ion-selective indicator electrode and a double-junction reference electrode. The perchlorate and nitrate ISEs may also be used for monitoring the emf. Both titrants are considerably less expensive than equivalent amounts of the commonly used tetraphenylarsonium chloride titrant.     

Crystallographic evidence for different modes of interaction of BF3/BF4 species with water molecules and 18-crown-6

We report the crystal and molecular structures of the complex of 18-C-6 with H₃O⁺BF₄⁻ (I) and the complex of 18-C-6 with BF₃OH₂·H₂O (II). The different modes of appearance of the “BF₃” species as BF₃, BF₃OH₂, BF₃OH₂·H₂O and BF₄⁻, as well as their structurally significant intermolecular and intramolecular interactions, are discussed. In complex I the oxonium ion is bound at the centre of the 18-C-6 macrocycle. The oxonium oxygen is located practically equidistant (2.68–2.73 Å) from the six macrocyclic ethereal oxygens. The BF₄⁻ counter-ion is positioned 7.3 Å away from the oxonium ion in the same general plane of the crown ether. This anion is not involved in any direct intermolecular contacts, a fact that may explain why it is spherically disordered. In complex II there is no guest molecule (or ion) present in the “cavity” of the macrocycle, but there are two hydrogen-bonded systems of BF₃OH₂·H₂O that are interacting with the crown ether on either side of the general macrocyclic plane. Complex II features three types of hydrogen bonds—the O(water)-HO(crown) bonds (2.83 and 2.85 Å), the O(water)H-O(BF₃) bond (2.49 Å) and the O(BF₃)-HO(crown) bond (2.65 Å). The strong intermolecular O(crown)O(water)O(BF₃) and O(crown)O(BF₃) interactions stabilize the normally unstable BF₃OH₂·H₂O species.     

Intercalation of halogen fluorides into graphite

IF₇ intercalates into graphite accompanied by the partial fluorination of the graphite host. The intercalated species was identified as IF₅ by IR and ¹⁹F nmr spectroscopies. Mass spectrometric analyses of the gases evolved from the intercalate showed only IF₅ and fluorocarbons. Iodine pentafluoride intercalates only in the presence of HF, yielding a compound with the stoichiometry C₈IF₅ and no fluorination of the graphite host. Careful elimination of even traces of HF resulted in no intercalation. Evolved gas analysis showed that the only species recovered from the intercalation was IF₅. The remaining interhalogens, ClF₅, ClF₃, BrF₅ and BrF₃ all intercalate into graphite with extensive fluorination of the lattice. In the case of these four compounds, the intercalate proved to be more difficult to characterize, e.g. stoichiometry was often variable, and ¹⁹F nmr yielded resonances that did not agree with any known halogen fluorides. Thermal decomposition of these intercalates showed little or no gas evolution until relatively high temperatures were reached, whereupon Cl₂ or Br₂ was evolved, followed by fluorocarbons.     

Microdetermination of phosphate with cetylpyridinium chloride by constant-current potentiometry

Summary Eightg to 8 mg of phosphorus as orthophosphate were determined by titration with cetylpyridinium chloride after conversion to the 12-molybdophosphate. Solutions were acidified with hydrochloric acid to pH 1.1–1.3. A constant current of 1.1A in the cathodic direction was applied. A log-log relationship exists between the amount of phosphate present and the optimum MoP ratio. The molybdate blanks are relatively small. Silicate can be determined by a similar method.

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Potentiometrische Mikrobestimmung von Phosphat mit Cetylpyridiniumchlorid

Zusammenfassung 8g bis 8 mg Phosphor in der Form von Orthophosphat wurden nach Umsetzung zu 12-Molybdophosphat mit Cetylpyridiniumchlorid titriert. Die Lösungen werden mit HCl auf pH 1,1–1,3 eingestellt. Ein konstanter Strom von 1,1 A in der Richtung zur Kathode wurde angewendet. Zwischen der Menge anwesenden Phosphats und dem optimalen Mo: P-Verhaltnis besteht ein Log-log-Verhaltnis. Die Molybdat-Blindwerte sind verhaltnismaig gering.Silikat last sich in ahnlicher Art bestimmen.

     

The determination of microgram amounts of orthophosphate using ion-selective electrodes

Summary The potentiometric titration ofg amounts of orthophosphate with lead perchlorate using a lead ISE, and with silver nitrate using a silver sulfide ISE, was investigated. With 0.001N lead perchlorate the practical limit of the determination is approximately 10g (0.3mol) of phosphorus. Microgram amounts of phosphate require the application of a small polarizing current to the lead ISE to enhance the potential breaks near the endpoint.Previously reported titrimetric methods for orthophosphate with silver nitrate were reinvestigated using a silver sulfide ISE. The borate-buffered system proved superior to the sodium acetate-methanol system when a partially non-aqueous medium of 60–70% methanol was used. With the borate-buffered system, 0.005N silver nitrate can be used, while it cannot be used in the sodium acetate-methanol system. Also, considerably larger amounts of sulfate and fluoride can be tolerated in the borate-buffered system. The sequential determination of halides and phosphate is feasible in this system.

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Zusammenfassung Die potentiometrische Titration von Mikrogrammengen Orthophosphat mit Bleiperchlorat und einer bleispezifischen Elektrode bzw. mit Silbernitrat und einer silberspezifischen Elektrode wurde untersucht. Mit 0,001-n Bleiperchlorat liegt die praktische Grenze der Bestimmbarkeit bei etwa 10g (0,3Mol) Phosphor. Bei Mikrogrammengen Phosphat muß man an die bleispezifische Elektrode einen schwachen Polarisationsstrom anlegen, um den Potential-Knick nahe dem Endpunkt zu verstärken.Früher veröffentlichte Titrationsmethoden für Orthophosphat mit Hilfe von Silbernitrat wurden neuerlich mit einer Silbersulfidelektrode bearbeitet. Ein Boratpuffersystem erwies sich der Pufferung mit Natriumacetat-Methanol überlegen, wenn in 60–70%igem Methanol gearbeitet wird. In boratgepufferter Lösung kann man mit 0,005-n Silbernitrat titrieren im Gegensatz zu acetat-methanolischer Lösung. Auch können wesentlich größere Mengen Sulfat und Fluorid im boratgepufferten System toleriert werden. Halogenide und Phosphat können in diesem Milieu nacheinander bestimmt werden.

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This work was performed under the auspices of the U. S. Atomic Energy Commission.     

The application of Stille cross-coupling reactions with multiple nitrogen containing heterocycles

Substituted imidazoles and purine bioisosteres have been widely studied in the literature. We endeavored to combine these heterocyclic core structures into precursors, especially 7-azaindoles, of previously unknown pharmacologically relevant lead structures. A highly flexible synthetic procedure was developed, derived from investigations of the influence of the substrates, solvents, ligand systems, and side reactions.