Reactions of 1,5-diketones with hydrogen selenide in the presence of trifluoroacetic acid

Two competing pathways were found in the transformations of 1,5-diketones and the 4H-selenopyrans formed from these diketones upon reaction with CF₃CO₂H in the presence of hydrogen selenide entailing disproportionation and the electrophilic addition of hydrogen selenide.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1634–1637, December, 1984.     

Adsorption of Eu(III) ions on silicas with noncovalently immobilized thiacalix[4]arene derivatives

Using the noncovalent immobilization of some thiacalix[4]arene derivatives on the surface of silanized silica, we obtained efficient adsorption materials for the extraction of Eu(III) ions from aqueous solutions of medium mineralization. The specific surface area of the adsorbents is 200–370 m²/g. It is shown that adsorbents containing thiacalix[4]arenes with phosphoryl groups selectively extract up to 99% of europium ions from aqueous solutions at pH 5.5–6; they are characterized by adsorption capacity of 7.5–14.5 mg/g and high distribution coefficients. The studied adsorbents exhibit high selectivity with respect to Eu(III) ions, wherein the distribution coefficients for Cs, Sr, Tb(III), Sm(III), Gd(III), La(III), and UO₂²⁺ are five times or more smaller.     

Effect of Bismuth(III) Complexes M3Bi(Nta)2·nH2O and KBi(Edta)·nTu on Sea Bacteria,Ulva Fenestrata Seaweed,and Macrobiofouling

The effect of bismuth(III) nitrilotriacetate M₃Bi(Nta)₂·nH₂O (M = Na, K, Rb, Cs, NH₄, CN₃H₆) and mixed-ligand bismuth(III) complex with ethylenediaminetetraacetate and thiourea KBi(Edta)·2tu on an association of sea bacteria, seaweed (Ulva fenestrata), and biofouling was studied. The minimal concentrations of some of these complexes suppressing bacterial growth were determined.     

Statistical aspects of the failure of organic-fiber-reinforced plastics

Conclusions Dispersion of the strength of filaments and of the Weibull coefficient leads to a drop in strength of a strand compared with the strength of the components when the adhesion by gluing together does not amount to 2–5%. The drop in strength is determined by the dispersion of strength which depends on the length of the tested specimens.Gluing together of the fibers in filaments changes the nature of the load diagrams - of a filament when its length exceeds ₀. A consequence is that the mechanism of rupture of the strand changes, and this leads to an additional drop of its strength. When specimens are 500 mm long, the drop in strength of the strand compared with the mean strength of the filaments amounts to 10%.Because of the dispersion of the Weibull coefficient, the strength of filaments does not correspond exactly to the strength of the microplastic obtained from these filaments. When there is dispersion of the strength of the filaments, failure of the plastic proceeds by failure of the microplastics as a whole.Gluing together of fibers has a double effect on the strength of the material: increased degree of gluing together of the fibers reduces the noneffective length from ₀ to 0.4–0.5 mm, and this leads to an increase of approximately 50% of the strength of the microplastic; increased gluing together leads to a change in the mechanism of failure of the strand and of the organic-fiber-plastic made from it if there is dispersion of the strength of the component filaments, and this reduces the strength of the material in accordance with (3) (by 12–14% in our case). The longitudinal instability of the properties of the filament leads to an additional drop in strength of the material by 4.5%.Translated from Mekhanika Kompozitnykh Materialov, No. 6, pp. 1011–1017, November, 1984.     

Reactions of 2(3′-oxoalkyl)-1,3-cyclohexanediones with nitrogenous reagents

Condensed 1,4-dihydropyridines, which do not contain a substituent in position 4 and which are formed in the reaction of 2-(3-oxoalkyl)-1,3-cycohexanediones with ammonium acetate in acetic acid, undergo disproportionation. Pyridine bases are formed as the result of two competing reactions: disproportionation and oxidation of 1,4-dihydropyridines, intermediates in the heterocyclization of oxo-1,3-diketones with participation of the nitrogen atom, by air oxygen.N. G. Chernyshevskii Saratov State University Saratov 410026. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 647–651, May, 1994. Original article submitted April 22, 1994.     

Isolobal analogy between trivalent boron and divalent silicon

Singlet organosilylenes with a lone pair and an emptyp orbital are isolobal to trivalent borane if a B-H is equated to the lone pair on Si. Using this analogy, a particular isomer of CSi₂H₂ (24) is predicted to be a stable structure. MNDO calculations on24 and many of its possible isomers suggest that24 is at global minimum on the potential energy surface of CSi₂H₂.Ab initio calculations using a, minimal STO-3G basis set, on some selected structures also support these results.     

Oxidation reactions of 4H-chalcogenopyrans

We have studied the oxidation of 4H-chalcogenopyrans and chalcogenopyrylium salts by lead tetraacetate. We have established that the major reaction products on oxidation of 2,6-diphenyl-4H-thiopyran and selenopyran are 2,6-diphenyl-4H-thio(seleno)pyran-4-ones, while 2-benzoyl-5-phenyl(seleno)thiophenes are formed as impurities. The major product on oxidation of 2,6-diphenyl-4H-pyran is 2-benzoyl-5-phenylfuran. We have shown that 2,4,6-triphenyl-4H-pyran does not undergo oxidation by hydrogen peroxide in neutral medium, in contrast to its S and Se analogs. This supports the hypothesis that the heteroatom participates in the oxidation process.N. G. Cherynshevskii Saratov State University, Saratov 410071. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 913–916, July, 1996. Original article submitted March 6, 1996.     

Furan and its derivatives in the synthesis of other heterocycles (review)

Data on methods of transforming furans into heterocycles containing oxygen, nitrogen, sulfur, and selenium are discussed and summarized.Scientific-Research Institute, N. G. Chernyshevskii Saratov State University. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1034–1052, August, 1995. Original article submitted November 24, 1994, revision submitted February 20, 1995.