Kinetics and mechanism of oxidation of aryl β-styryl ketones by osmium tetroxide in sulphuric acid-acetic acid medium. A structure-reactivity correlation study

Summary Oxidation of aryl -styryl ketones by osmium tetroxide has been studied in H₂SO₄-HOAc medium. The order with respect to osmium is unity in all the cases and the [substrate] order is unity for aryl -styryl ketone and fractional for substituted aryl -styryl ketone. Varying the concentration of [H⁺] at constant ionic strength had practically no effect on the rate; the salt effect is also negligible. Polymerisation did not occur when H₂C- CHCONH₂ was added to the reaction mixture. Increasing the percentage of AcOH decreased the rate. Direct attack at the 58-01 by Os^III in the slow step to give the oxidation product of aryl -styryl ketone, viz. 1-benzoyl-2-arylethane-1,2-diol is suggested and a possible mechanism for the reaction.     

Influence of the exchangeable cations on stability and rheological properties of montmorillonite suspensions

The effects of NaCl and CaCl₂ on the colloid stability and rheological properties of Na- and Ca-montmorillonite dispersions were studied. The distribution of cations between the surface and the bulk phase was determined. For both of monocationic montmorillonite, the critical coagulation concentration were 250 mmol NaCl/dm³ and 2 mmol CaCl₂/dm³. The changes in the Bingham yield stresses of Na- and Ca-montmorillonite dispersions as functions of the NaCl and CaCl₂ concentration could be explained in terms of the surface excess amount and equilibrium concentration of the cations, the second electroviscous effect and the formation of a gel structure.     

4,6‐Bis­(methyl­sulfanyl)‐1‐(4‐phenoxy­butyl)‐1H‐pyrazolo­[3,4‐d]­pyrimidine

The molecular structure of the title compound, C₁₇H₂₀N₄OS₂, does not show any intramolecular aromatic π–π interactions, but the crystal packing reveals the presence of intermolecular C—H...O and C—H...π interactions. The C—H...O interactions generate chains of mol­ecules that are linked into sheets by C—H...π interactions about inversion centres.     

Comparison of mild extraction procedures for determination of plant-available arsenic compounds in soil

In this work three mild extraction agents for determination of plant-available fractions of elements in soil were evaluated for arsenic speciation in soil samples. Pepper (Capsicum annum, L.) var. California Wonder was cultivated in pots, and aqueous solutions of arsenite, arsenate, methylarsonic acid, and dimethylarsinic acid, at a concentration of 15 mg As kg^–1 soil, were added at the beginning of the experiment. Control pots (untreated) were also included. Deionized water, 0.01 mol L^–1 CaCl₂, and 0.05 mol L^–1 (NH₄)₂SO₄ were used to extract the plant-available fraction of the arsenic compounds in soil samples collected during the vegetation period of the plants. Whereas in control samples the extractable arsenic fraction did not exceed 1% of total arsenic content, soil amendment by arsenic compounds resulted in extraction of larger amounts, which varied between 1.4 and 8.1% of total arsenic content, depending on soil treatment and on the extracting agent applied. Among arsenic compounds determined by HPLC–ICPMS arsenate was predominant, followed by small amounts of arsenite, methylarsonic acid, and dimethylarsinic acid, depending on the individual soil treatment. In all the experiments in which methylarsonic acid was added to the soil methylarsonous acid was detected in the extracts, suggesting that the soil bacteria are capable of reducing methylarsonic acid before a further methylation occurs. No significant differences were observed between analytical data obtained by using different extraction procedures.     

Symplectic Spaces And Ear-Decomposition Of Matroids

Matroids admitting an odd ear-decomposition can be viewed as natural generalizations of factor-critical graphs. We prove that a matroid representable over a field of characteristic 2 admits an odd ear-decomposition if and only if it can be represented by some space on which the induced scalar product is a non-degenerate symplectic form. We also show that, for a matroid representable over a field of characteristic 2, the independent sets whose contraction admits an odd ear-decomposition form the family of feasible sets of a representable Δ-matroid.     

Image feature extraction by dynamic neural filtering and phase-only joint transform correlation

Neural network-based image processing algorithms present numerous advantages due to their supervised adjustable properties. Among various neural network architectures, dynamic neural networks, Hopfield and Cellular networks, have been found inherently suitable for filtering applications. Combining supervised and filtering features of dynamic neural networks, this paper presents dynamic neural filtering technique based on Hopfield neural network architecture. The filtering technique has also been implemented by using phase-only joint transform correlation (POJTC) for optical image processing applications. Filtering structure is basically similar to the Hopfield neural network structure except for the adjustable filter mask and 2D convolution operation instead of weight matrix operations. The dynamic neural filtering architecture has learnable properties by back-propagation learning algorithm. POJTC presents significant advantages to achieve the operation of summing the cross-correlation of bipolar data by phase-encoding bipolar data in parallel. The image feature extraction performance of the proposed optical system is reported for various image processing applications using a simulation program.     

Theoretical evidence for a reentrant phase diagram in ortho-para mixtures of solid H2 at high pressure

We develop a multiorder parameter mean-field formalism for systems of coupled quantum rotors. The scheme is developed to account for systems where ortho-para distinction is valid. We apply our formalism to solid H2 and D2. We find an anomalous reentrant orientational phase transition for both systems at thermal equilibrium. The correlation functions of the order parameter indicate short-range order at low temperatures. As the temperature is increased the correlation increases along the phase boundary. We also find that even extremely small odd-J concentrations (1%) can trigger short-range orientational ordering.     

Interaction of dislocations with ordered cylindrical precipitates

The size and antiphase boundary effects of a cylindrical inclusion with zero axial misfit in f.c.c. alloys are calculated using the linear isotropic elasticity.The plane strain gives rise to nonzero elastic interaction even inside inclusions with zero misfit direction inclined to the Burgers vector. The extreme value of the total force on a straight dislocation cutting the inclusion axis is determined for different dislocation and inclusion orientations.     

Festphasensynthese von 2-l- und 3-d-Pipecolinsäurebradykinin

Zusammenfassung 2-l- und 3-d-Pipecolinsäure-Bradykinin wurden nach der üblichenMerrifield-Technik bzw. nach dem Adsorptions-kupplungs-Verfahren vonEsko undKarlsson dargestellt. Dabei wurde die Eignung von Essigsäureanhydrid, 3-Nitrophthalsäureanhydrid und N-Acetylimidazol für die Blockierung während der Synthese freigebliebener Aminogruppen verglichen. 2-l-Pipecolinsäure-bradykinin war biologisch aktiv.

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Solid phase synthesis of 2-l- and 3-d-Pipecolic acid-bradykinin

2-l- and 3-d-Pipecolic acid-bradykinin were synthesized using the general procedure ofMerrifield and the adsorption coupling method ofEsko andKarlsson. Acetic anhydride, 3-nitrophthalic anhydride, and N-acetylimidazole were compared with respect to their efficiency as blocking agents for unreacted amino groups. 2-l-pipecolic acid-bradykinin was biologically active.

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Abkürzungen entspr. IUPAC-IUB Commission on Biochemical Nomenclature. J. biol. Chem.241, 527, 2491 (1966);Pipec: Pipecolinsäure,DCCI: N,N-Dicyclohexylcarbodiimid,Boc: tert. Butyloxycarbonyl.