Polarographic reduction of pyridinium ion in pyridine tetraethylammonium perchlorate as background electrolyte

Tetraethylammonium perchlorate, compared to lithium perchlorate as background electrolyte for the reduction of pyridinium ion in pyridine, is effective over a wider potential range, but is more difficult to obtain in a pure state; slight amounts of impurities do not, however, affect the pyridinium wave. The pyridinium wave produced in 0.1 M Et₄NClO₄ may occur at a more negative potential than the main pyridinium wave in 0.1 M LiClO₄, depending on the source of the pyridinium ion, but still appears to be due to a diffusion-controlled reduction, whose limiting current is linearly proportional to concentration; the prewave observed in LiCl0₄ background generally does not appear in Et₄NClO₄ background. Specific differences in the effect of Li(I), Na(I) and Et₄N(I) background cation appear to be due to electrocapillary phenomena and perhaps to the extent of solvation of the ions. The constancy of current for solutions containing acetic acid with added acetate, pyridinium nitrate with added nitrate, and benzoic acid with added benzoate indicate that the pyridinium reduction is independent of anion concentration.     

A semi-quantitative method for the determination of microgram amounts of manganese on millipore filters

A method is described in which the intensity of coloration of brown manganese dioxide on white Millipore filters is taken as the measure of the manganese content. A solution of manganese(II) is made strongly basic, whereupon manganese dioxide precipitates via its auto-oxidation. Optimum conditions for the precipitation are studied. Less than 0.5 μg of manganese can be determined.     

Zum Verlaufe der Antoxydation von Ferroion

Zusammenfassung Don Geschwindigkeitsbeziehungen, die unter zeitlicher Verfolgung der Autoxydation von Ferroion erhalten worden sind, werden Rektionsmechanismen zugeordnet: der charakteristische Aciditätseinfluß sei durch einen Primärschritt bedingt, der in electron transfer zwischen O₂ und OH-Ion besteht, unter gleichzeitiger Anlagerung von OH; eine entsprechende Struktur wird auch jenem Mechanismus zuzuordnen versucht, der zu quadratischer Abhängigkeit der Autoxydationsgeschwindigkeit von der Ferroionkonzentration führt.     

Kinetics of solid-state synthesis and properties of lead-containing niobate pyrochlores

The main features of the synthesis of (Pb_1-x Sr_x)₂Nb₂O₇ and (Pb_1-x Ba_x)₂Nb₂O₇ pyrochlore solid solutions were determined using isothermal thermogravimetry in tandem with formal-kinetic analysis. The stability and electron-transport properties of the triple niobates were studied, which allowed us to test them as electrode-active materials for membranes in ion-selective electrodes (ISEs).     

Computational study on the ring-opening reaction of protonated oxirane and methylpropene

A computational study on the intermolecular reaction of protonated oxirane with methylpropene, as a model for initiation of oxidosqualene cyclisation, shows that the S_N2-like ring opening is strongly exothermic with a low barrier to reaction and establishes the geometry of the intermolecular reaction.     

Hydrogenation of ethyl esters of 4-phenyl-and (2-furyl)-substituted 2,4-dioxobutyric acids at palladium black

The hydrogenation of ethyl 4-R-2,4-dioxobutyrates (R = phenyl, 2-furyl) at 5% Pt/Al₂O₃ catalyst, modified with cinchonidine, and at palladium black was investigated. The former had low activity under the conditions we tested. The main products during the hydrogenation of these compounds at palladium black are ethyl 4-R-2-hydroxy-4-oxobutyrates. The yield of the phenyl derivative amounts to 68.5%, while the yield of the corresponding 2-furyl derivative amounts to 97%. In the last case ethyl 2-hydroxy-4-oxo-4-(2-tetrahydrofuryl)butyrate was detected as impurity. The optimum conditions for the formation of ethyl 2-hydroxy-4-phenylbutyrate (yield 88.2%) were determined. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 655–659, May, 2006.     

A simple optical device for measuring free surface deformations of nontransparent liquids

In this paper, a novel optical device for measuring the deformation of liquid free surfaces is presented. The device employs a laser beam, which can be focused on any chosen location on the free surface. The key measurement is of the intensity of the beam reflected from a location on the free surface where the deformation exhibits a local extremum. The optics of the device is so designed as to measure a maximum intensity when the distance between the focusing lens and the selected point on the free surface is equal to the focal length, thus enabling a height measurement. The device is tested in ferrofluid pools where the height of the spikes of the normal field instability is measured. The simplicity of the suggested technique enables the fabrication of a quite cheap device for measuring surface deformation of nontransparent liquids, which provides good accuracy and reproducibility.     

Curve crossing in two excited states of IBr studied by photofragmentation

Curve crossing in two excited states of IBr was studied by means of photodissociation with a pulse dye laser. The ratios of the formed ground state Br(²P_{$\text{3}\text{2}$} and excited Br(²P_{$\text{1}\text{2}$}) were measured at various wavelengths. They are compared with ratios calculated with the Landau-Zener formula, using parameters given by Child. The agreement between the measurements and the calculations is very good.     

Optimization of a wet chemical continuous flow analysis method exemplified by the determinations of kjeldahl nitrogen and total phosphorus

The optimization of a rather complex wet chemical analysis method, such as the measurement of Kjeldahl nitrogen or total phosphorus with the Technicon AutoAnalyzer, is extremely tedious when purely empirical approaches are used. A mathematical model of the different stages of the measuring method (digestion, neutralization and color reaction) is described. The system can then be optimized for maximum measuring sensitivity. Optimization is done by solving numerically the non-linear optimization problem with constraints. The starting values for the optimization algorithm were found by varying these values systematically within the tolerated range, with checks that none of the constraints were violated. The theoretical results predict an increase in sensitivity by a factor of 15 compared to the method used previously. In practice, the sensitivity was increased by a factor of 10 for the total phosphorus method. For the simultaneous low-level determinations of Kjeldahl nitrogen and total phosphorus some problems of stability remain.