Substituted 1,3,2,4‐benzodithiadiazines and related compounds

Despite some limitations, the 1:1 condensation of n‐RC₆H₄‐N=S=N‐SiMe₃ (n = 2, 3, 4; R = CH₃, OCH₃, F, Cl, CF₃) with SCl₂, followed by intramolecular electrophilic ortho‐cyclization, was found to be a general synthetic approach to the corresponding 5‐R, 6‐R, and 7‐R–substituted 1,3,2,4‐benzodithiadiazines, formally antiaromatic 12π‐electron compounds. For precursors with n = 3, the high regioselectivity of the cyclization resulted in exclusive (R = OCH₃, F) or predominant (R = CH₃, Cl) formation of 6‐R isomers; the ratio of the major 6‐R isomer to the minor 8‐R one was found to be 72:28 (R = CH₃) or 78:22 (R = Cl). The preferred direction of cyclization is consistent with thermodynamics of the corresponding intermediate σ‐complexes as well as factors of kinetic control for an orbital‐controlled El‐Nu reaction. According to the X‐ray diffraction data, the molecules of 5‐CF₃ (15) and 6‐F (12) derivatives are nearly planar, while the molecules of 5‐OCH₃ (7) and 6‐CH₃ (4) derivatives are bent along the S¹ … N⁴ line by ∼11° (7) or 7° (4). An attempt to adopt CsF‐induced intramolecular nucleophilic ortho‐cyclization of Ar_F‐S‐N=S=N‐SiMe₃ into polyfluorinated 1,3,2,4‐benzodithiadiazines for polyfluoropyridine derivatives resulted in formation of polyfluorinated aminopyridines. Data obtained are consistent with a previously suggested scheme of sulfur–nitrogen chain shortening during cyclization. Mild acid hydrolysis of the title compounds was shown to be a convenient synthetic route to substituted 2,2′‐diaminodiphenyl disulfides (including polyfluorinated ones) via the corresponding 2‐aminobenzenethiols. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 113–124, 1999     

Ionic liquid matrices for MALDI mass spectrometry of lignin

Analytical and Bioanalytical Chemistry - The use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the study of lignin is still extremely limited due to its low...     

Transformations of 5-(2-arylethynyl)-2-methyl-2H-tetrazoles under superelectrophilic activation

Reaction of 5-arylethynyl-2-methyl-2H-tetrazoles (acetylene tetrazoles) with arenes under the action of Brønsted superacid CF₃SO₃H or acidic zeolite HUSY CBV-720 gives rise to E-/Z-5-(2,2-diarylethenyl)-2-methyl-2H-tetrazoles, as products of hydroarylation of acetylene bond, in yields up to 98% with predominant formation of E-isomers. Cationic intermediates of these reactions have been studied theoretically by DFT calculations. Addition of CF₃SO₃H to the triple bond of acetylene tetrazoles leads to the corresponding E-/Z-vinyl triflates in high yields. Hydration of triple bond in these tetrazoles in H₂SO₄ results in the formation of 5-(2-aryl-2-oxoethyl)-2-methyl-2H-tetrazoles. Tandem hydroarylation-ionic hydrogenation of acetylene tetrazoles in the systems acid(CF₃SO₃H or AlCl₃)-arene-cyclohexane affords 5-(2,2-diarylethyl)-2-methyl-2H-tetrazoles.     

Room temperature MgI2-catalyzed Friedel–Crafts reaction between electron-rich (het)arenes and ethyl glyoxylate

Magnesium iodide-catalyzed addition of electron-rich (het)arenes to ethyl glyoxylate proceeds at room temperature with high chemoselectivity to afford ethyl 2-(het)aryl- 2-hydroxyacetates in yields up to 95%.     

Fluorescent ternary complexes of some biogenic amines and their metabolites with europium and oxytetracycline for applications in the chemical analysis

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In Situ Investigations of Mechanochemical One‐Pot Syntheses

We present an in situ triple coupling of synchrotron X‐ray diffraction with Raman spectroscopy, and thermography to study milling reactions in real time. This combination of methods allows a correlation of the structural evolution with temperature information. The temperature information is crucial for understanding both the thermodynamics and reaction kinetics. The reaction mechanisms of three prototypical mechanochemical syntheses, a cocrystal formation, a C?C bond formation (Knoevenagel condensation), and the formation of a manganese‐phosphonate, were elucidated. Trends in the temperature development during milling are identified. The heat of reaction and latent heat of crystallization of the product contribute to the overall temperature increase. A decrease in temperature occurs via release of, for example, water as a by‐product. Solid and liquid intermediates are detected. The influence of the mechanical impact could be separated from temperature effects caused by the reaction.     

CsF–Si(OEt)4 catalyzed addition of (hetero)aromatic amides to ethyl acrylate

The conjugate addition of some (hetero)aromatic amides to an α,β‐unsaturated ester (ethyl acrylate) proceeds efficiently in the presence of an equimolar amount of the CsF–Si(OEt)₄ system to afford the corresponding ethyl esters of N‐substituted β‐amino acids. Copyright © 2001 John Wiley & Sons, Ltd.     

Influence of pH of solution on phase composition of samarium-strontium cobaltite powders synthesized by wet chemical technique

Powders of Sm_0.6Sr_0.4CoO_3-δ and La_0.6Sr_0.4CoO_3-δ were synthesized using wet chemical technique. Structural and surface properties of synthesized materials were studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), IR spectroscopy, and scanning electron microscopy (SEM). The influence of pH on the phase state, chemical composition, morphology, and fractal dimension of the synthesized powders were investigated. It was found that the change of pH has the influence on phase composition of synthesized powders. The increase of solution pH allows one to obtain homogeneous samples at lower temperatures down to 900–950?°C.

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Methyl methacrylate particles with amino groups on the surface: Colloid stability and sorption of biologically active substances

The present article investigates the influence of dispersion medium on the aggregate stability of cross-linked poly-(methyl methacrylate) particles on the surface layer of which aliphatic amino groups are localized. It is shown that particle size depends on the ionic strength of dispersion medium. The research determines the optimal content of cross-linked agent, ethylene glycol dimetharylate that results in the formation of cationic particles being stable in saline. Particle modification is performed by bovine serum albumin and luminophore fluorescein 5(6)-isothiocyanate. Protein sorption is observed not to influence luminescent properties of the particles. It is also determined that due to the aggregate stability of particles obtained from 5?wt% of ethylene glycol dimethacrylate in saline, the monodispersity and the absence of inversion of zeta potential in wide pH range is retained, such particles may be considered as perspective carriers of biologically active substances.