Regioselective Nitration of 4′-R-Dibenzo-18-Crown-6 by Some Alkaline Metals Nitrates in Polyphosphoric Acid

We have studied the effect of the substituent nature on nitration of 4′-R-dibenzo-18-crown-6 (DB18C6, where R is NO₂, CH₃CO, or C₂H₅) in polyphosphoric acid (PPA). We also studied the influence of cations' nature on regioselectivity of nitration. It was found that electron withdrawing substituents direct the incoming NO₂-group mainly to the 4″-position of the unsubstituted benzene ring in the reactions with lithium nitrates. If there are two substituents: electron releasing and electron withdrawing in one benzene ring, then the orientation effect of the latest one is stronger. The obtained results once more confirmed the existence of ‘transannular transmission’, which we first of all observed during the acetylation of DB18C6. Based on these observations preparative methods leading to 4′,4″-dinitro-DB18C6, 4′,5″-dinitro-DB18C6, 4′-acetyl-4″-nitro-DB18C6, 4′-acetyl-5″-nitro-DB18C6, 4′-ethyl-5′,5″-dinitro-DB18C6, and 4′-ethyl-5′,4″-dinitro-DB18C6 have been developed.     

Synthesis of 4′4″(5″)-dibenzo-18-crown-6-disulfonic acid disalsolidinide,disalsolinide, and dianabasinide

New disulfamides of dibenzo-18-crown-6 with salsolidine, salsoline, and anabasine were prepared by condensation of the corresponding alkaloids with 4,4(5)-dibenzo-18-crown-6-disulfonyl chlorides.Presented at the 5th International Symposium on the Chemistry of Natural Compounds (Tashkent, Uzbekistan, May 20–23, 2003).Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 413–415, September–October, 2004.     

Synthetic magnetic opals

We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there exists no report in literature on any BiNi compound which is magnetic.     

Effect of heat treatment on α-ZnS and β-ZnS transformations

There remains no doubt today about the effect which the crystallographic structure of zinc sulfide, used for the preparation of electroluminophors, has on its optical and electrical-properties. A study of this effect is extraordinarily difficult, inasmuch as α-ZnS ? β-ZnS phase transitions are accompanied by the formation of intermediate phases, with a variety of disorder patterns and of polytypes, which in turn affects the distribution and the buildup of glow centers. Available test data pertaining to the relation between electroluminescence characteristics and the structure of zinc sulfide are far from exhaustive and often contradictory. Thus, while the authors of [1] find the intensity of electroluminescence to be minimum within the regions of structural distortions, these regions becoming luminescent at higher voltages than regions with cubic or hexagonal structures, the authors of [2, 3] emphasize that a higher intensity of electroluminescence is due to defects responsible for the formation of glow centers and that it is in these regions where the activator atoms are mainly concentrated. In this study the authors have set out to trace the changes in α-ZnS and β-ZnS concentration during heat treatment, inasmuch as such a treatment affects all electroluminescence characteristics.     

Symbatic Relationship between Proton Affinity and Ease of Dehydration and Dealkylation of Alcohol and Alkylbenzene Molecules on Acid Catalysts

We have used the temperature-programmed reaction method to study dehydration of C₂-C₄ alcohols and dealkylation of ethylbenzene and propylbenzene on zeolite H- and WO₃/ZrO₂. Based on analysis of the TPR spectra for olefin formation, we have found linear relationships between the temperatures at which the maximum rate occurs for these reactions and the proton affinity both in a series of alcohol molecules and in alkylbenzenes.     

Nitration of Benzo Crown Ethers with Potassium Nitrate in Polyphosphoric Acid

A general method for the nitration of benzo crown ethers with potassium nitrate in polyphosphoric acid has been developed. Mono- and dinitro derivatives of benzo-12-crown-4, benzo-15-crown-5, dibenzo-18-crown-6, and dibenzo-24-crown-8 have been prepared. The role of complex formation in the regioselective tendency for the nitration of dibenzo-18-crown-6 has been demonstrated.     

Formation of Iron Silicides Under Graphene Grown on the Silicon Carbide Surface

Physics of the Solid State - The formation of iron silicide thin films under graphene grown on the silicon carbide surface is investigated. The thin films are synthesized by consecutive...     

Formation of ultrathin iron magnetic films on the silicon vicinal surface

Physics of the Solid State - The phase composition, electronic structure, and magnetic properties of ultrathin layers of iron and iron silicides formed upon deposition of 1- to 25-Å-thick Fe...     

Molecular models for surfaces of solids with hypervalent coordination environment

A way to build molecular models for solids having crystal structures with coordination numbers of atoms exceeding their valences is proposed. The geometrical and thermodynamic characteristics of some models of stishovite and rutile have been studied.