Thermogravimetric and EPR study of the solid-state reactions between zinc chromate and zinc oxalate

The formation of some catalytically active Cr(V) and Cr(III) species is studied when the progressive thermal reduction of zinc chromate is enhanced by the addition of solid zinc oxalate, the reducing agent CO being formed in situ, during thermal analysis.When compared with the decomposition of pure ZnCrO₄, Cr(VI) reduction, as followed by EPR, is similar concerning the nature of the intermediate Cr species formed: Cr(V), Cr(III) in a Cr₂O₃-like bulk phase and Cr(III) dispersed in ZnO. However, the temperature range of Cr₂O₃ formation, as well as the magnitude of the Cr(III)-Cr(III) interaction in such a phase is found to be strongly dependent on the amount of ZnO formed. On the other hand, after the Cr(V) species resulting from progressive oxygen release have disappeared, some other stable Cr(V) species are formed again at higher temperatures. Their formation may be related to a further reduction of the remaining Cr(VI) species by CO stemming from the oxalate.

---

Zusammenfassung Die Bildung einiger katalytisch aktiver Cr(V) und Cr(III) Species wird für den Fall untersucht, bei dem die progressive thermische Reduktion von Zinkchromat durch Zugabe von festem Zinkoxalat gefördert wird, wobei das Reduktionsmittel CO in situ, während der Thermoanalyse gebildet wird.Ein Vergleich mit der Zersetzung der reinen ZnCrO₄ ergibt die ÄhnIichkeit der durch EPR verfolgten Cr(VI)-Reduktion hinsichtlich der Beschaffenheit der gebildeten Cr Intermediärspecies: Cr(V), Cr(III) in einer Cr₂O₃-artigen Hauptphase und Cr(III) in ZnO dispergiert. Jedoch sind Temperaturbereich der »Cr₂O₃«-Bildung sowie der Umfang der Cr(III)-Cr(III) Wechselwirkung in einer solchen Phase stark von der Menge des gebildeten ZnO abhängig. Andererseits werden nach dem Verschwinden der durch die progressive Sauerstoff-Freisetzung entstandenen Cr(V)-Species wider einige andere stabile Cr(V)-Species bei höheren Temperaturen gebildet. Ihre Bildung mag mit einer weiteren Reduktion der noch vorhandenen Cr(VI)-Species durch aus dem Oxalat stammendes CO verbunden sein.

---

Cr(V) Cr(III) , , , , . , Cr(VI), ZnCrO₄ . , Cr : Cr(V) Cr(III) , Cr₂₃, Cr(III) ZnO. , «Cr₂₃», Cr(III)-Cr(III) . , , Cr(V) , Cr(V) . Cr(VI) , .

     

A study of the alkaloids of Kirghiz opium

Summary Morphine, codeine, narcotine, thebaine, papaverine, protopine, xanthaline, prophyroxine, bases with mp 267 and 263°C,l-canadine, and cryptopine have been isolated from Kirghiz opium.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 711–713, November–December, 1970.     

New method for the synthesis of macrocyclic compounds

The intramolecular acylation of acid chlorides of ω-thienylalkanoic acids of various structures in the presence and absence of silica gel was investigated. The reaction of aluminum chloride etherate and the indicated acid chlorides with the surface groups of silica gel was studied by IR spectroscopy, and the role of the compounds formed on the surface in the reaction under consideration was discussed. A sequence of processes and a mechanism involving participation of the solid phase in the intramolecular acylation of acid chlorides of ω-thienylalkanoic acids are formulated.     

An application of perturbation theory ideas in configuration interaction calculations

Configuration interaction calculations of electronic wave functions for atoms and molecules have generally been limited to relatively small basis sets because of the exponential increase in the number of configurations as basis functions are added. While higher than quadruply excited configurations are of negligible importance in CI wave functions, it is shown that the effect of triple and quadruple excitation configurations can be substantially included even when the matrix elements between such configurations are neglected, leaving only their diagonal elements and the elements connecting them with the single and double excitations. This approximation is seen to be formally practically equivalent to a first-order perturbation expression for the wave function (second-order for the energy) based on an optimum linear combination of the zero, single, and double excitation configurations as the zero-order function. If suitable procedures are used, the amount of computational effort involved in such a calculation is roughly proportional to the fourth power of the number of basis functions employed, thus preventing the CI stage of the calculation from increasing in magnitude much faster than the stages involving the calculation and manipulation of the elementary integrals.     

Simultaneous determination of neodymium, erbium and holmium in rare earth mixtures with 2-phenyltrifluoroacetone and octylphenol poly(ethyleneglycol) ether by third-derivative spectrophotometry

The complexes of the rare earth metals with 2-phenyltrifluoroacetone in the presence of TX-100 are reported. The characteristic absorbances of neodymium, holmium and erbium complexes can be increased by factors of 8.5, 31 and 15 respectively, compared to those of the cholrides. The third-derivative spectra have been used to eliminate the interference of cerium, and the sensitivities are increased again by factors of 7.4, 5.5 and 6.5. A method for the direct determination of neodymium, erbium and holmium in rare earth mixtures is proposed.     

Transport properties of alkanes through ceramic thin zeolite MFI membranes

Polycrystalline randomly oriented defect free zeolite layers on porous α-Al₂O₃ supports are prepared with a thickness of less than 5 μm by in situ crystallisation of silicalite-1. The flux of alkanes is a function of the sorption and intracrystalline diffusion. In mixtures of strongly and weakly adsorbing gases and a high loadings of the strongly adsorbing molecule in the zeolite poze, the flux of the weakly adsorbing molecule is suppressed by the sorption and the mobility of the strongly adsorbing molecule resulting in pore-blocking effects. The separation of these mixtures is mainly based on the sorption and completely different from the permselectivity. At low loadings of the strongly adsorbing molecules the separation is based on the sorption and the diffusion and is the same as the permselectivity. Separation factors for the isomers of butane (n-butane/isobutane) and hexane (hexane/2,2-dimethylbutane) are respectively high (10) and very high (> 2000) at 200°C. These high separation factors are a strong evidence that the membrane shows selectivity by size-exclusion and that transport in pores larger than the zeolite MFI pores (possible defects, etc) can be neglected.     

EPR study of free radicals in a main chain thermotropic polymer

Free radicals were generated in a rigid rod-like copolymer via mechanical route and by gamma radiation. The (EPR) method was used for studying free radicals formed at 123 K. The spectra of free radicals observed and the influence of molecular motions on the transport of radical centers in the fracture surface layer are discussed.     

The determination of trace amounts of tin by flow-injection hydride generation atomic-absorption spectrometry with on-line ion-exchange separation and preconcentration

A hydride generation atomic-absorption spectrometric (AAS) method with flow-injection (FI), aimed at developing a practical routine assay for the determination of tin in food digests, is described. In order to modify the sample matrix and to achieve optimized and reproducible conditions for the hydride generation reaction, the analyte is initially converted into its chlorostannate-complex thereby allowing it to be separated and preconcentrated on-line on an incorporated micro-column packed with a strongly basic anion exchanger and subsequently to be eluted by diluted nitric acid under strictly controlled conditions. Optimum acidic conditions for the FI hydride generation AAS system was found to be 0.01-0.05M nitric acid. At a consumption of 2.7-ml sample volume, aspirated by time-based injection, the procedure resulted in an enrichment factor of 3.5 and yielded a detection limit of 0.08 microg/l. (3sigma) at a sampling frequency of 72/hr. The precision was 2.5% rsd at the 10 microg/l. level. Potential interferents, such as Ni(II), Co(II), Zn(II) and Fe(III) could, at a Sn level of 10 microg/l., be tolerated at an excess of 1000 times without impairing the assay, while a 100-1000-fold excess of Cu(II) decreased the signal by 10-15%. Recoveries in the range 94-102% were obtained for canned food sample digests spiked with 10 microg/l. Sn.     

Organometallic complex compounds,part 6(1). Property-specific ligand control of stability and reactivity of (1,3-dimethyl-η3-allyl)methylnickel-ligand complexes. Separation of electronic and steric effects

Summary The property-specific ligand control of 28 ligands on the decomposition temperatures in solution, measured by d.t.a. of a four-coordinate nickel(II)-complex is reported. A quantitative separation of electronic and steric effects by a multilinear regression analysis (75% electronic and 25% steric influence for the chosen ligands) is presented. The controlling effect of the selectivity on the decomposition (fraction of the C-C-linked product) (25 P-ligands) leads to an electronic: steric ratio of the property-specific ligand control of 5545 for the chosen ligands. An increase in the relative acceptor character of the P-ligands relatively destabilizes the complexes and thereby favours formation of a C-C-bond. An increase in steric hindrance also favours C-C-bond formation. A method for revising the steric parameter of P-ligands is presented and is used to correct the -value of (PhCH₂)₃P is corrected to 135°. SCCC-MO-calculations for testing the chemical reasoning of the separated electronic and steric ligand property control are shown.     

Quasi-column chromatography of barbituric acid derivatives II. Separation on Non-polar adsorbents using binary water-organic solvent mixtures as the mobile phase

Summary Twenty barbituric acid derivatives having four different types of substitution were separated in TLC-S chambers. Using non-polar adsorbents (silanized silica gel or silica gel coated with paraffin oil) and binary water-organic solvent mixtures as the mobile phase. Linear relationships between R_M and the concentration of the organic solvent were observed for the majority of the investigated compounds. The non-polar absorbents ensure a better separation than untreated silica gel especially for the therapeutically useful C₅ disubstituted barbiturates. The results can be used for the optimization of the systems for the chromatography of barbiturates. The R_f values were correlated with the number of carbon atoms of the substitutions, molecular connectivity and a parameter associated with the molecular volume. The best correlations were obtained for this last parameter.