Kinetics of the Formation of the Blue Complex CrO(O2)2 Formed by Dichromate and H2O2 in Acid Solutions. A Stopped-Flow Investigation Using Rapid-Scan UV-VIS Detection

Summary.  The kinetics of the CrO(O₂)₂ formation by H₂O₂ and Cr₂O₇ ²⁻ in aqueous acidic media was measured at 293 ± 2 K in a pH range between 2.5 and 3.3. Using the stopped-flow method with rapid scan UV-VIS detection, the rate law of the formation of CrO(O₂)₂ was determined. For the media HClO₄, HNO₃ and CH₃COOH, the reaction order in the Cr₂O₇ ²⁻ concentration was found to be 0.5. For [H₂O₂] as well as for [H⁺], the reaction was first order in all acids used. In HCl and H₂SO₄ media the reaction was first order in Cr₂O₇ ²⁻. At T = 293 ± 2 K the rate constant for the formation of Cr(O)(O₂)₂ was found to be (7.3 ± 1.9) · 10² M^−3/2 s⁻¹ in HClO₄. Corresponding author. E-mail: grampp@ptc.tu-graz.ac.at Received January 30, 2002; accepted (revised) June 5, 2002     

Crystal structure,conformation and vibrational characteristics of diethyl 4,4′-disulfanediylbis(6-methyl-2-phenylpyrimidine-5-carboxylate) – A new pharmaceutical cure

The crystal and molecular structures of diethyl 4,4′-disulfanediylbis(6-methyl-2-phenylpyrimidine-5-carboxylate) have been determined by X-ray diffraction and quantum chemical DFT analysis. The title compound crystallizes in orthorhombic Pbca (D_2h¹⁵) space group, with one molecule in the asymmetric unit. The molecular structure of the studied compound has been determined using the DFT B3LYP/6-311G(2d,2p) approach and compared to that derived from X-ray studies. The IR and Raman spectra have been measured and their wavenumbers have been compared to those calculated for the optimized geometry of the studied compound. The characteristic vibrations of the 4,4′-dithiobispyrimidine N₂C₄SSC₄N₂ skeleton have been identified and on this basis the correlation between the disulfide bridge conformation and vibrational data have been discussed.     

Optimization of the Sintering Process by DSC for the Preparation of High-Temperature Superconductors

The optimum calcination and sintering conditions for the preparation of the desired phases with the proper stoichiometry of the bulk high-temperature superconductors YBa₂Cu₃O_7-x (YBCO) and Bi₂Sr₂CaCu₂O_y> (BSCCO) were investigated by differential scanning calorimetry. DSC analysis on the corresponding superconducting coatings, electrophoretically deposited, indicated that the sintering and annealing procedure was suitable for the production of stable, strong and adherent coatings. X-ray diffraction analysis, Raman spectroscopy and magnetic measurements confirmed the improved properties of the superconducting powders and coatings obtained. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reaction of diketene with cyanothioacetamide: A convenient and regioselective method for the preparation of new 4(1H)-pyridone derivatives

The reaction of diketene with cyanothioacetamide in dry dioxane in the presence of triethylamine gives triethylammonium 3-cyano-6-methyl-4-oxo-1,4-dihydro-2-pyridinethiolate. The regioselective S-alkylation of this thiolate is a convenient method for the preparation of substituted 4(1H)-pyridones and also derivatives of thiazolo[3,2-a]pyridine and thieno[2,3-b]pyridine. The action of 2-amino-1,1,3-tricyanopropene on this thiolate leads to its transformation into a new heterocyclic system, namely, 5H-pyrido[2′,3′:4,5]thiopyrano[2,3-b]pyridine; treatment with iodine yields the oxidation product, namely, the corresponding bis(2-pyridyl) disulfide. The structure of isopropyl (3-cyano-6-methyl-4-oxo-1,4-dihydro-2-pyridinyl)thioacetate was confirmed by X-ray diffraction structural analysis. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 716–725, May, 2007.