Die potentiometrische Mikrobestimmung von Kupfer in organischen Verbindungen nach Verbrennung in einem modifizierten Schöniger-Kolben

Zusammenfassung Nach Verbrennung der Substanz in einem modifizierten Sauerstoffkolben werden die Verbrennungsprodukte in 2,5 ml 8M HNO₃ absorbiert; das gebildete CuO wird vom Pt-Netz durch eine spezielle Technik vollständig gelöst. Nach dem Erkalten wird die Lösung in die Titrationszelle übertragen, mit NaOH in Gegenwart von Phenolphthalein neutralisiert und das Cu(II) schließlich in gepufferter Lösung mit 0,01N Cyanoferrat(II) potentiometrisch titriert. Eine kupferselektive Elektrode und eine Single-Junction-Referenzelektrode dienen in Kombination mit einem pH-Meter mit gedehnter Skala zur Erkennung des Titrationsendpunktes. Die Resultate sind innerhalb ±0,10% genau: die Wiederfindungsrate von Kupfer liegt zwischen 99,65 und 100,10%; die Standardabweichung beträgt 0,04%. Die Bedingungen und die Charakteristiken der Titration von Cu(II) mit Cyanoferrat(II) ebenso wie die Störung einiger Anionen werden diskutiert. Der beschriebene modifizierte Verbrennungskolben eignet sich zur Mikrobestimmung auch anderer Elemente in metallorganischen Verbindungen.

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Potentiometric microdetermination of copper in organic compounds after combustion in a modified schöniger's flask

Summary After combustion of the sample in a modified oxygen flask, the combustion products are absorbed in 2,5 ml 8M HNO₃ and the CuO formed is completely dissolved from the Pt-basket by a special technique. After cooling, the solution is transferred to the titration cell and neutralized with NaOH in the presence of phenolphthalein; the copper(II) is finally titrated potentiometrically in a buffered medium with 0,01N hexacyanoferrate (II). A copper-selective electrode and a single junction reference electrode are used in combination with an expanded-scale pH-meter to detect the endpoint. The results obtained are very accurate and reproducible: the max. error does not exceed 0.10% (abs.), the recoveries of copper range from 99.65 to 100.10% and the standard deviation is 0.04%. Conditions and features of the titration of copper(II) with hexacyanoferrate(II) as well as the effect of some interfering anions are discussed. The modified oxygen flask described is also useful for the microdetermination of other elements in organometallic compounds.

     

Molecular imprinting technology in capillary electrochromatography

Molecularly imprinted polymers (MIPs) are tailor-made synthetic polymers with a predetermined selectivity for a given analyte, or group of structurally related compounds, that make them ideal materials for use as stationary phases in affinity chromatography. However, extensive peak broadening and tailing, especially of the more retained compound (normally the template) are often observed. Thus, huge efforts have been made during recent years to use MIPs in capillary electrochromatography, which is inherently a more efficient chromatographic technique than conventional HPLC. Accordingly, this paper gives an overview of the attempts carried out in the recent past to improve the chromatographic performance of MIPs in capillary electrochromatography as well as more recent applications. It is concluded that MIPs are very promising materials for use as selective stationary phases in CEC.     

Quantum chemical predictions concerning two unknown “mesoionic” compounds

The Pariser-Parr-Pople approximation was used to predict the properties of compounds I, 3-oxo-2H-1,2,3-triazolo[3,4-a]pyridine, and II, 3-oxoisoxazolo[2,3-a]pyridine, originated by joining a pyridine ring to two sydnone-like heterocyclic systems not yet reported in the literature. A parallel computation was carried out for two known compounds of similar structure, to give the predictions a better reliability through the comparison with observed spectral data and chemical behaviour. Compound I is expected to be stable, with an absorption spectrum similar to III, 2-oxo-1,3,4-oxadiazolo[4,5-a]pyridine, and chemical properties analogous to IV, 1-methyl-3-oxo-1,2,4-triazolo-[4,3-a]pyridine. A reaction path is suggested for obtaining from I the unknown isomeric structure V, 3-oxo-1H-1,2,3-triazolo[3,4-a]pyridine. Compound II is predicted as an unstable orange-red substance which should be handled and kept at low temperatures.     

Asymmetric synthesis of fluorinated amino macrolactones through ring-closing metathesis

The synthesis of new chiral fluorinated amino and azamacrolactones of types 1 and 2 is described. A ring-closing metathesis (RCM) reaction constitutes the key step in this methodology, which uses fluorinated amino alcohols 7 as starting materials. The influence of the CF2 group, which is located in the alpha-position relative to the carbon bearing the amino group, on the efficiency of the RCM reaction is noteworthy. This method allows for the preparation of the desired fluorinated macrolactones in excellent yields.     

Physicochemical aspects of novel surfactantless, self-templated mesoporous SnO2 thin films

A novel method of synthesis consisting of the production of ordered arrangements of tubular pores distributed inside SnO2 annealed thin films, which are prepared from a rotating disk process carried out at 2000-3500 rpm, is herein described. The main novelty is that no surfactant molecules are required in order to create these ordered pore structures; the templating entities are supramolecular assemblies of oligomeric chains formed during the extra-long aging allowed to the sol-gel processing of tin(IV) tetra-tert-amiloxide, Sn(OAm(t))4, chelated with acetylacetone molecules. Low angle X-ray diffraction peaks of SnO2 thin films calcined at 500 degrees C clearly certify the existence of ordered mesostructures when employing the right H2O/Sn(OAm(t))4 molar ratio during the SnO2 sol-gel synthesis. The final SnO2 ordered mesostructures are reminiscent of those linked to MCM-41 and SBA-15 substrates. Pore-size distribution analyses proceeding from N2 sorption isotherms at 76 K on the SnO2 thin films calcined at 500 degrees C unequivocally confirm the presence of tubular mesopores (mode pore sizes ranging from 5 to 7 nm). The thicknesses of the SnO2 films range from 80 to 150 nm after performing a drying process at 100 degrees C and from 70 to 125 nm after calcining in air at 500 degrees C; these film thicknesses show, in general, decreasing trends when either the spinning rate or the H2O/(Sn(OAm(t))4 ratio is increased.     

Characterization of the chloranilate(*3-) pi radical as a strong spin-coupling bridging ligand

Dinuclear [(TPA)Co(II)(CA2-)Co(II)(TPA)](BF4)2.2MeOH (1) [TPA = tris(2-pyridylmethyl)amine] and [(TPA)CoII(CA*3-)CoII(TPA)](BF4).2Et2O (2) with a bridging chloranilate radical ligand formed by reduction of 1 are crystallographically and magnetically characterized. 1 has shown a weak antiferromagnetic coupling within the Co(II) dimer [J/kB = -0.65 K (-0.45 cm(-1))], while 2 has a 2 orders of magnitude stronger antiferromagnetic interaction between the Co(II) ion and a radical [J/kB = -75 K (52 cm(-1))].     

Thermal- and pressure-induced cooperative spin transition in the 2D and 3D coordination polymers {Fe(5-Br-pmd)z[M(CN)x]y} (M=AgI, AuI, NiII, PdII, PtII)

A new family of cyanide-based spin-crossover polymers with the general formula {Fe(5-Br-pmd)z[M(CN)x]y} [M=AgI (1), AuI (2), NiII (3), PdII (4), PtII (5); 5-Br-pmd=5-bromopyrimidine; z=1 or 2, x=2 or 4, and y=2 or 1] have been synthesized and characterized using single-crystal X-ray diffraction (XRD), X-ray powder diffraction (XRPD), magnetic susceptibility measurements, and differential scanning calorimetry (DSC). At 293 K, compound 1 presents the monoclinic space group C2/c, whereas at 120 K, it changes to the monoclinic space group P21/c. At 293 K, the crystal structure of 1 displays an uninodal three-dimensional network whose nodes, constituted of FeII, lie at the inversion center of an elongated octahedron. The equatorial bond lengths are defined by the N atoms of four [AgI(CN)2]- groups belonging to two crystallographically nonequivalent AgI atoms, Ag(1) and Ag(2). They are shorter than those of the axial positions occupied by the N atoms of the 5-Br-pmd ligands. The Fe-N average bond length of 2.1657(7) A is consistent with a high-spin (HS) state for the FeII ions. At 120 K, the crystal structure changes refer mainly to the FeII environment. There are two crystallographically independent FeII ions at this temperature, Fe(1) and Fe(2), which adopt the HS and low-spin (LS) states, respectively. The average Fe-N bond length for Fe(1) [2.174(5) A] and Fe(2) [1.955(5) A] agrees well with the reported magnetic data at this temperature. The spin transition of the FeII ions labeled as Fe(1) is found to be centered at Tc downward arrow=149 K and Tc upward arrow=167 K and accompanied by a drastic change of color from orange (HS) to red (LS). Magnetic susceptibility measurements under applied hydrostatic pressure performed on 1 have shown a linear displacement of the transition to higher temperatures while the hysteresis width remains unaltered in the interval of pressures of 105 Pa to 0.34 GPa. A further increase of the pressure induces the spin transition in the Fe(2) ions, which is completely accomplished at 1.12 GPa (T1/2=162 K). Compounds 1 and 2 are isostructural, but 2 does not exhibit spin-transition properties; the FeII centers remain in the HS state in the temperature range investigated, 5-300 K. Compounds 3-5 are not similar or isostructural with 1. A two-dimensional structure for 3-5 has been proposed on the basis of analytical data and the XRPD patterns. Compounds 3-5 undergo first-order spin transition where the critical temperatures for the cooling (Tc downward arrow) and warming (Tc upward arrow) modes are 170 and 180 K (3), 204 and 214 K (4), and 197 and 223 K (5), respectively. It is worth mentioning the color change from yellow to orange observed in 3-5 upon spin transition. The thermodynamic parameters associated with the spin transition estimated from DSC measurements are DeltaH=6 kJ mol(-1) (1), 11 kJ mol(-1) (3), 16 kJ mol(-1) (4), and 16 kJ mol(-1) (5) and DeltaS=38 J K(-1) mol(-1) (1), 62 J K(-1) mol(-1) (3), 76 J K-1 mol(-1) (4), and 81 J K(-1) mol(-1) (5).     

Characterizing projective bundles by means of ample divisors

Let X be a complex projective manifold and AX a non-singular hypersurface which is an ample divisor having characteristic cycles A_i non-singular in every dimension i0. The pairs (X,A) such that g(A₁)=h^1,0 (X) are characterized.     

Comparison of the effectiveness of solid-phase and ultrasound-mediated liquid-liquid extractions to determine the volatile compounds of wine

Two ultrasound-assisted liquid–liquid extraction (LLE-I, LLE-II) methods were compared to a solid-phase extraction (SPE) protocol to assess their effectiveness for the analysis of up to 44 volatile compounds in a synthetic and several commercial white, red and “cream” wines produced in the southwest of Spain. Regardless of the extraction protocol used the highest recoveries corresponded to acids and terpene alcohols and the lowest to lactones and alcohols. In any case, it was concluded that one of the liquid–liquid extraction protocols evaluated led to higher recoveries for a greater number of odorants that could be implicated in the aroma of the wines than the solid-phase extraction. However, the SPE method also presented some advantages that should not be overlooked, like higher repeatability and throughput and lower solvent consumption.