Flow injection determination of oxalate in urine based on an inhibitory effect

Summary Two methods based on the use of the normal and stopped-flow injection modes were developed for the determination of oxalate based on its inhibitory effect on the catalytic action of Fe(III) on the 2,4-diaminophenol/hydrogen peroxide system. The linear determination ranges achieved were between 0.2 and 12.0 g ml^–1 and between 0.2 and 40.0 g ml^–1, the precision was ±5.4%, and ±3.5%, and the sampling rate was 30 and 20 samples h^–1 for the normal and stopped-flow method, respectively. Both methods have been applied to the determination of oxalate in urine with excellent results.     

Gravimetric determination of osmium with 1:2:3-benzotriazole

A method for the direct gravimetric determination of osmium with 1:2:3-benzotriazole in acetic acid-sodium acetate buffer is presented. The method is accurate and reproducible, and the conditions used in the determination are not critical. The precipitate is a stoichiometric compound which is stable from room temperature up to 200°. It appears that 1:2:3-benzotriazole is probably the first organic reagent to be used successfully in the direct gravimetric determination of osmium.     

Analytical diagnosis of soil pollution with heavy metals

Summary The diagnosis of soil pollution essentially depends on the adoption of a suitable procedure for sample treatment, rather than the choice of a purely analytical techniqueTotal soil analysis may give information about possible enrichment of the soil with heavy metals, but is generally and for most elements not a sufficient criterion for the estimation of the biological effect and has to be completed by additional chemical analyses, specifying the chemical forms and mobility of the contaminating compounds in the soil.The possibilities for the estimation of total and extractable elements are discussed as well as analytical speciation techniques in relation to the determination of their biological effects.

---

Analytische Bestimmung der Verunreinigung von Böden mit Schwermetallen

Zusammenfassung Die Bestimmung einer Bodenverunreinigung hängt wesentlich von der geeigneten Probenvorbehandlung ab und weniger von der rein analytischen Methode. Eine Gesamtanalyse gibt Auskunft über eine mögliche Anreicherung von Schwermetallen, ist aber im allgemeinen und für die meisten Elemente nicht ausreichend zur Erkennung der biologischen Wirkung und muß durch zusätzliche chemische Analysen zur Spezifizierung der chemischen Form und der Mobilität der Verunreinigungen ergänzt werden. Möglichkeiten zur Gesamtbestimmung der Elemente sowie des extrahierbaren Anteils werden diskutiert und Verfahren zur Spezifizierung in Beziehung zur biologischen Wirksamkeit aufgezeigt.

---

---

Dedicated to Prof. Dr. W. Fresenius on the occasion of his 70th birthday     

Dichrometric determination of mercury(I)

Summary A dichrometric procedure has been reported for the direct titration of mercury(I) to an iodine monochloride end point. The concentration of hydrochloric acid must be at least 7.5 N at the end point.     

Fluorocyclohexanes-III 1H:4H/2H- and 1H/2H:4H-nonafluorocyclohexane and derived compounds

Two nonafluorocyclohexanes of b.p. 92° and 101°, made by fluorination of benzene,¹ have each been dehydrofluorinated to give the same six unsaturated products. These were identified by oxidation and other studies as 3H:4H- and 4H:5H-octafluorocyclohexene, 1H-1:4-, 1H-1:3-, and 2H-1:3-heptafluorocyclohexadiene, and hexafluorobenzene,² thus indicating a 1H:2H:4H-structure for the saturated precursors. The stereochemistry of the adjacent> CHF groups was established by resolution, via the brucine salt, of the 3H:4H-hexafluoroadipic acid obtained by oxidation of the 4H:5H-mono-olefin, showing that the hydrogens were trans. The complete stereochemistry of the nonafluorides was suggested by the dehydrofluorinations and confirmed by further fluorination³ to give known decafluorocyclohexanes. Treatment of 4H/5H-octafluorocyclohexene with lithium aluminium hydride in diethyl ether gave 1H,4H/5H-heptafluorocyclohexene, a precursor of pentafluorobenzene.⁴     

Stoichiometric number molecularity and multiplicity

On the basis of the polynomial to which the system of pseudo-steady-state equations corresponding to the nonlinear single-route mechanism is reduced (kinetic polynomial), the known concepts of stoichiometric number and molecularity have been studied. A set of the minimal-integer stoichiometric coefficients is shown to correspond to the kinetic characteristics in the neighborhood of equilibrium.

---

, , ( ) — . , - .

     

The gas phase structure of tetrakis(trifluoromethylthio)ethene, CF3S)2C=C(SCF3)2

The geometric structure of (CF₃S)₂C=C(SCF₃)₂ in the vapour phase was determined by electron diffraction. The molecule possesses D₂ symmetry with the S---CF₃ bonds oriented perpendicular to the ethene plane, in alternating directions up-down-up-down. The following skeletal geometric parameters were obtained (r_a distances and angles, experimental uncertainties are 3σ values): C=C = 1.34Å (ass.), C(sp²---S = 1.761(5)Å, S---C(sp³) = 1.832(5)Å, S---C---C = 119.6(4)°, C---S---C = 100.6(13)°, and ø(C=C---S---C) = 90.9(11)°. The gas phase conformation differs considerably from the crystal structure, where the molecule possesses C_i symmetry and the CF₃ groups, which are bonded to cis-standing sulfur atoms, lie on the same side of the ethene plane with dihedral angles ø(C=C---S---C) of 117° and 127°.     

Alkaloids ofPetilium eduardi. Petine and petine N-oxide

Two new alkaloids — petine and petine N-oxide — have been isolated from the bulbs of Petilium eduardi. Their structures have been established on the basis of spectral characteristics and chemical transformations.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, FAX (3712) 89-14-75. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 524–528, July–August, 1994.     

Heterogenized rhodium complexes as hydrogen transfer catalysts

Cationic rhodium(I) norbornadiene complexes with polystyrene-immobilized imidazole, tetramethylbiimidazole or phosphine ligands in the presence of potassium hydroxide catalyze hydrogen transfer from isopropanol to acetophenone and 1-hexene. [Rh(NBD) (poly-PPh₂)₂] ClO₄ complexes are particularly efficient for the reduction of acetophenone, but slow decomposition to rhodium metal is observed.

---

(I) , , , 1-. [Rh(NBD) (-PPh₂)₂]ClO₄ , .

     

Effect of stirring on the Belousov-Zhabotinskii reaction: A problem of interpretation

It is probable that different phenomena attributed to mechanical stirring during the Belousov-Zhabotinskii (BZ) reaction are caused by atmospheric oxygen and, as far as our experiments show, they have nothing to do with dissipative structures or with the turbulence of the reacting mixture.

---

, , , -, .