Oxidative dehydrogenation of alkylheteroaromatic compounds 1. Catalysts containing vanadium and molybdenum for the oxidative dehydrogenation of alkylpyridines

The dehydrogenation of a series of alkylpyrïdines has been studied on vanadium and molybdenum oxide-containing catalysts in the presence of oxygen of the air and sulfur dioxide gas. A dependence was shown of the catalytic and physicochemical properties of the catalysts indicated on their composition and method of preparation. The optimum catalyst composition and the conditions of carrying out the reaction to provide high activity and selectivity when making vinylpyridines were determined. The relative reactivity of the alkylpyridines investigated on dehydrogenation and further oxidation was determined.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 802–811, June, 1994. Original article submitted April 19, 1994.     

New Data on the Crystal Structures of Colusites and Arsenosulvanites

The crystal structures of three minerals (arsenosulvanite, V,As-germanite, and colusite) of the general crystal chemical formula (As, Ge, Sn, Sb, V)₆S₃₂, where Cu^M, V^M are cations at interstitial positions, 0.2 x 2.0, 2.7 y 0, (space group , a = 10.527; 10.600; 10.653 ; R = 0.066; 0.046; 0.033) have been determined using single-crystal X-ray diffraction data. The minerals are the two structural modifications of the compound with the ideal formula V₂Cu₂₄As₆S₃₂; they differ from each other in the occupancy of the interstitial position 2a. In colusite, this position is occupied by the V⁵⁺ cations; in arsenosulvanite and V,As-germanite, by Cu²⁺. A characteristic feature of the structures is the presence of octahedral [ S₄]Cu₆ ( = V, Cu) complexes not directly interacting with each other and lying inside the Laves polyhedra. In the structures of arsenosulvanite and V,As-germanite, a sulvanite framework consisting of interpenetrating Laves polyhedra T₃S₄ ( = V, Cu; T = Cu, As, Ge) has been found. The sulvanite framework is statistically distributed over the sphalerite matrix. The variable composition of the minerals is due to heterovalent isomorphism in the sphalerite position 6c. Charge disbalance arising from substitution of the pentavalent arsenic cations by cations of lower valence is compensated by the appearance of additional Cu²⁺ cations. The nonstoichiometry of the compositions is explained by the presence of vacancies in the interstitial and sphalerite positions.     

Triclinic Structure of Birefringent Crystals of K(Al0.95Cr0.05)(SO4)2⋅12H2O

The crystal structure of alum K(Al_0.95Cr_0.05)(SO₄)₂12H₂O possessing anomalous birefringence was refined in space groups Pa3 and P1 (a = b = c = 12.165(2) , R = 0.0587). The distortions of cubic symmetry are attributed to the peculiarities of the orientational disorder in the distribution of SO₄ tetrahedra and to the different degrees of distortion of the aluminum octahedra.     

Structural aspect of the adduct formation mechanism of metal β-diketonate complexes with macrocyclic polyethers. The structure of the intermediate—The 1:1 guest-host complex of calcium nitrate with 18-crown-6

We compare the structures of intermediate and final products in adduct formation of metal β-diketonate complexes with macrocyclic polyethers using [Ca(NO₃)₂(18C6)] (I) and [Ca(HFA)₂(18C6)] (II), where 18C6 is 18-crown-6 and HFA is hexafluoroacetylacetone. Adduct formation occurs by replacement of nitrate groups in I by HFA ligands with preservation of the coordination number of calcium and the conformation of the macrocycle but with variation in the coordination polyhedron of calcium. Both structures have the same packing mode: the centers of the complexes (Ca atoms) are located in the nodes of planar nets (Shlafly symbol 4⁴) forming two stories parallel to the shortest translations of the monoclinic cell in the same space group C2/c. Because of great size and nonisometricity of HFA ligands as compared to the nitrate group, the planar nets in (II) are well separated, and the tetragons are substantially distorted as compared to those in (I). This structural mechanism of adduct formation is supposed to be true for other complex-forming metals and β-diketonate ligands. X-ray structural analysis and interpretation of results. Synthesis of single crystals. Instute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 3, pp. 56–66, May–June, 1994. Translated by T. Yudanova     

Interaction of sorbed Ni(II) ions with amorphous zirconium hydrogen phosphate

Samples of amorphous zirconium hydrogen phosphate with different zirconium and phosphorus concentrations in hydrogen and nickel-substituted forms are studied by means of electronic, ³¹P NMR, and impedance spectroscopy. It is shown that Ni(II) → H⁺ ion exchange is accompanied by the hydrolysis of sorbed cations and the formation of complexes with the dihydro- and hydrophosphate groups of the inorganic ionite. It is found that the coordination environment of Ni(II) in the sorbent phase includes 2–4 fragments of phosphate groups, along with OH groups and water molecules.     

Numerical study of the effects occurring near a circular cylinder in stratified fluid flows with short buoyancy periods

Flow around a two-dimensional circular cylinder of a stratified fluid with periods buoyancy T_b = 25.2 and 6.28 sec is studied numerically over a wide range of Reynolds and Froude numbers. It is found that in the presence of a perturbation ahead of a cylinder which moves downstream with increasing Reynolds number, the salinity isolines have the shape of a semi-circular comb with sharp teeth. The shape change of the attached waves and the occurrence of fluid layers of different densities in the cylinder wake are studied. In flows with a buoyancy period T_b = 6.28 sec at Reynolds numbers Re < 60, stagnant zones are found in the cylinder wake, and at Re > 60, these zones are absent.     

On the character of the ethoxyl groups introduced into lignin when it is niteated in alcohol

Conclusions The ethoxyl groups which enter into the lignin during alcoholic nitration are formed by the etherification of its arylcarbinol groups.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1366–1368, June, 1969.     

Absolute measurements of rayleigh factor in some pure organic liquids

An absolute light scattering determination method is described. Experimental results are presented for seven organic liquids at 23°C for two wavelengths 4416 Å and 6328 Å. The experimental data are compared with those calculated by theoretical formulas using experimental values of Landau-Placzek ratios and adiabatic compressibilities. A good agreement between experimental and calculated data confirms the validity of “low” values of light scattering factor.