Crystal structure oftrans-ethyl(1,5,6-trimethylbenzimidazole)-bis(dimethylglyoximato)cobalt(III). Relationships between structural and spectroscopic properties in compounds of the general formulae [Co(dmgH)2(R)(1,5,6-Me3Bzm)]

Summary The synthesis and x-ray crystal structure oftrans-[Co(dmgH)₂(Et)(1,5,6-Me₃Bzm)] where dmgH=dimethylglyoximate(–1), and 1,5,6-Me₃Bzm=1,5,6-trimethylbenzimidazole, is reported. The compound C₁₉H₂₆N₆O₄Co is monoclinic, space group P2₁/n;a=11.700(4);b=24.205(6);c=8.500(3) Å and =101.63(3)°. D(calcd) 1.299 g cm^–3; Z=4 and R=0.066 for 2359 independent reflections. Comparison of Co-N(axial ligand) bond lengths for compounds of general formulaetrans-[Co(dmgH)₂(R)(L)], with L=pyridine or 1,5,6-trimethylbenzimidazole and R=CH(CN)Cl, CH₂NO₂, Me, Et,i-Pr, cyclo-hexyl or adamantyl is made. The Co–N(1,5,6-Me₃Bzm) bond lengths of the trimethylbenzimidazole derivatives show a fairly linear relationship with the electronic parameter of the axial R group, derived from the¹³C-n.m.r. spectra of their pyridine analogues. The influence of steric effects on the properties of these Co^III compounds is discussed.     

Comparison of the retention behaviour of phenol derivatives on porous graphitized and octadecylsilica columns

Summary The retention of 22 ring-substituted phenol derivatives on porous graphitized carbon (PGC) (eluents: acetonitrile — water and methanol — water mixtures) and on octadecylsilica (ODS) (eluents: methanol — 0.025 M KH₂PO₄ mixtures) was determined, and the relationship between retention and physicochemical parameters were evaluated by principal component analysis followed by two-dimensional nonlinear mapping and by cluster analysis as well as by canonical correlation analysis. Calculations proved that marked differences can be detected between the retention characteristics of PGC and ODS columns, and the electronic parameters of phenol derivatives have the highest impact on their retention. The comparison of various multivariate mathematical-statistical methods indicated that principal component analysis followed by two dimensional non-linear mapping is the most appropriate method for the evaluation of large data matrices in RP-HPLC.     

Oscillating autoxidation reaction of p-xylene in the liquid phase, catalyzed by metal oxides

Oscillatory reaction was observed during liquid-phase oxidation of p-xylene in the presence of certain transition metal oxides as catalysts. Experimental conditions under which oscillations occur and parameters influencing this behavior are described.

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The additivity principle in pyrolysis—gas chromatography of brown coal

Pyrolysis—gas chromatography of brown coal exhibits additive properties and it is therefore possible to construct the pyrogram of the original coal from the individual pyrograms of the bitumen, humic acids, lignin and humin fractions. The contents of phenols in the pyrograms are typical for all of the above classes except bitumen and are in agreement with the contents of the individual groups in the original coal. The results suggest that the separation does not bring about significant chemical changes in individual brown coal fractions.     

Synchronization of signal sampling with liquid pulsation in systems with peristaltic pumps

Method and electronic circuitry are described for synchronization of analytical signal sampling with pulsation of liquid flow in systems with a peristaltic pump. The technique is illustrated for cathodic stripping voltammetry of manganese.     

Acidity and activity of H-mordenite in m-xylene isomerization

The dependence of the activity of H-mordenites prepared from a natural mordenite on the nature and strength of the acid groups present was studied. The superior catalytic activity and stability of the H(Ag)–MOR zeolite compared with other H-forms is explained on the basis of NH₃ adsorption and IR measurements.

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H-, . H(Ag)–MOP H- NH₃ .

     

Maßanalytische Bestimmung von Merkapto-Benzthiazol im Wärmeaustauscher eines Reaktors

Zusammenfassung Eine volumetrische Methode zur Bestimmung geringer Mengen Merkapto-Benzthiazol in der Kühlflüssigkeit von Reaktoren wurde ausgearbeitet. Es wird in ammoniakalischem Medium mit ammoniakalisehem Silbernitrat titriert. Das Merkapto-Benzthiazol bildet mit Silberionen einen weißen, flockigen Niederschlag. Der Endpunkt der Titration wird mit Hilfe der Dead-stop-Indikation bestimmt. Er wird durch eine sprunghafte Stromstärkeerhöhung (Pt-Pt-Elektrode, 500 mV und 10^–7 A Empfindlichkeit des Galvanometers) angezeigt. Die Methode wird durch Triäthanolamin, Glykol, geringe Mengen von Chlorid und Phosphat nicht gestört.

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Summary A volumetric method has been developed for determining slight amounts of mercapto-benzthiazol in the cooling liquid of reactors. It is titrated in ammoniacal medium with ammoniacal silver nitrate. The mercapto-benzthiazol yields a colorless flocculent precipitate with silver ions. The endpoint of the titration is found by the dead stop indication. It is signalled by a sudden jump in the current strength (Pt-Pt-electrode, 500 mV and 10^–7 amp sensitivity of the galvanometer). The method is not impaired by triethanolamine, glycol, slight amounts of chloride, nor by phosphate.

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Résumé On a mis au point une méthode volumétrique pour le dosage de faibles quantités de mercaptobenzothiazole dans le liquide de refroidissement des réacteurs. On titre en milieu ammoniacal par le nitrate d'argent ammoniacal. Le mercaptobenzothiazole forme un précipité blanc, floconneux avec les ions argent. On détermine le point d'équivalence du titrage par la méthode du «dead stop end point». Il se trouve signalé par une augmentation brusque de l'intensité (électrodes Pt-Pt, 500 mv et 10^–7 A de sensibilité du galvanomètre). La triéthanolamine, le glycol, de petites quantités de chlorures et de phosphates, ne gênent pas.

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Vorgetragen beim Symposium für analytische Chemie in Graz, 29. September bis 1. Oktober 1965.     

Pattern of separatrices and intrinsic reaction coordinates for degenerate thermal rearrangements

A structurally stable model of the standard adiabatic gradient field of the potential energy surface for certain pericyclic reactions is derived.These reactions are not subjected to the principles of orbital isomerism or to the Woodward-Hoffmann rules.Use is made of a principle established by Ariel Fernández and Oktay Sinanolu which precludes direct meta-IRC connections between transition states.It is shown that Jahn-Teller isomers of the singlet biradicals involved in the process are not interconvertible since the biradical configuration is not a transition state but a critical point with Hessian matrix with two negative eigenvalues.The topological features of the PES obtained by combinatorial methods are in full agreement with earlier results obtained from MINDO calculations.     

Derivatives of carbohydrazide,thiocarbohydrazide and diaminoguanidine as photometric analytical reagents. III

Summary An absorption method for the collection of acid and condensable volcanic gases is described. A Cd(OH)₂ suspension allows the simultaneous sampling of sulfide and sulfur dioxide. A complete scheme for chemical analysis of H₂O, CO₂, H₂S, SO₂, HCl and HF is presented.The method is relatively simple and accurate and requires only simple equipment. Moreover, separate samples of the condensable part of the volcanic gas may be used for analysis of trace elements.

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Probenahme und Analyse vulkanischer Gase

Zusammenfassung Eine Absorptionsmethode zur Probenahme saurer und kondensierbarer Vulkangase wurde beschrieben. Eine Cd(OH)₂-Suspension ermöglicht die gleichzeitige Probenahme von H₂S und SO₂. Ein Analysenschema für die chemische Analyse von H₂O, CO₂, H₂S, SO₂, HCl und HF wurde angegeben. Das Verfahren ist relativ einfach und genau; es erfordert nur eine einfache Ausrüstung. Proben des kondensierbaren Anteils der Gase dienen zur Bestimmung der Spurenanteile.

     

On-line coupling of supercritical fluid extraction with high-performance liquid chromatography for the determination of explosives in vapour phases

An investigation into the selectivity of an iminodiacetic acid (IDA) modified silica gel column for transition and heavy metal ions using non-chelating inorganic eluents has been carried out. A number of eluent parameters were investigated to determine the exact retention mechanism taking place and to control selectivity. The parameters studied were eluent ionic strength and the nature of the inorganic salt used, eluent pH and eluent temperature. The results obtained showed how despite certain metal ions exhibiting similar stability constants with the bonded IDA groups, careful control of each of the above parameters, in particular eluent chloride ion concentration and eluent temperature, could result in large changes in selectivity. Optimal conditions for the isocratic and gradient separation of Mg(II), Ca(II), Mn(II), Cd(II), Co(II), Zn(II) and Pb(II) were determined. An isocratic method using a 0.035 M KCl, 0.065 M KNO3 (pH 2.5) eluent was successfully applied to the determination of Mn(II), Cd(II), Co(II) and Zn(II) at concentrations between 20 and 121 microg/l in a freshwater certified reference material (NIST 1640).